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Exercise testing is an accessible, relatively inexpensive non-invasive method for assessing the nature of pain in chest and signs of myocardial ischemia.
Among the stress tests, bicycle ergometry and the treadmill test are the main methods for clarifying the diagnosis of IHD (standard methods for determining exercise tolerance in patients with an established or suspected diagnosis of IHD). They can be used to assess the prognosis of the disease, action medicines and efficiency rehabilitation activities.
During exercise testing, two types of signs of myocardial ischemia can be recorded: clinical and electrocardiographic. When conducting a test, it is advisable to evaluate not only the presence of angina, but also its severity in points, using a special scale. The patient must be familiarized with this scale before the procedure.
The only reliable ECG sign of myocardial ischemia is a decrease in the horizontal or oblique ST segment by 1 mm or more. Changes in the amplitude of the Q, R and especially T waves are nonspecific for myocardial ischemia and should not be considered as reliable sign positive test. It should be noted that a horizontal decrease in the ST segment during an exercise test in some cases may not reflect myocardial ischemia (so-called false-positive changes in the ST segment). That is why the most reliable sign of myocardial ischemia during exercise testing is a combination of electrocardiographic (horizontal decrease in the ST segment) and clinical (angina attack) manifestations.
Asymptomatic decrease in the ST segment (more than 3 mm) during an exercise test in patients with typical angina or previous myocardial infarction is considered a manifestation of the so-called silent ischemia myocardium. However, if such changes are recorded for the first time, the patient is advised to undergo additional examination methods. Asymptomatic decrease in the ST segment (even horizontal type) in a patient with unconfirmed coronary artery disease does not give the right to consider this decrease as a manifestation of myocardial ischemia.
The sensitivity of the exercise test is not the same in patients with varying severity IHD (in particular, it depends on the degree of damage to the coronary arteries). It has been shown that when only one coronary artery is affected, the results of an exercise test are often (in 40-50% of patients) negative, and this gives the right to exclude the diagnosis of angina pectoris, but in no case is ischemic heart disease as such. In patients with damage to two or more major coronary arteries, a significantly closer correlation is observed between exercise test data and CAG results. The agreement in these cases reaches 90% or more.
The sensitivity of the exercise test is 70-75%, the specificity is 60-80%.
The results of a test with physical activity depend to a certain extent on the scheme of its implementation and the equipment used. The sensitivity of exercise testing for detecting myocardial ischemia is significantly higher when performed on a treadmill than on a bicycle ergometer. This applies primarily to patients with high exercise tolerance.
Diagnostic value Exercise testing differs significantly between men and women. Changes in the ECG associated with a stress test in the absence of coronary pathology, are observed in women much more often than in men. False-positive results of a stress test, as a rule, are noted in women with not quite typical pain syndrome. In women, to increase the specificity of the diagnostic test, the depth of ST segment depression can be increased to 2 mm, at which the test can be regarded as positive. Pronounced changes ST segment, as well as recording these changes in several leads at once with high probability indicate positive result samples.
This circumstance should not cause a negative attitude towards performing exercise tests in women. The results obtained should be considered in connection with the clinical manifestations, the nature of angina attacks, a history of myocardial infarction, age, and the presence of risk factors for coronary artery disease (the level of cholesterol in the blood, smoking, glucose tolerance, etc.).
Currently, two main types of physical activity are used: on a bicycle ergometer and on a treadmill. When conducting a test on a bicycle ergometer, you can directly measure the amount of work performed by the patient; when doing a load on a treadmill, you can only estimate the load indirectly. When conducting tests on a bicycle ergometer, it is easier to ensure good quality recording an ECG, when using a treadmill, you have to use special electrodes to obtain a high-quality ECG. However, the treadmill stress test is more physiological.
When conducting exercise testing, precautions should be taken. First of all, this is an assessment of the patient’s condition before exercise and identification possible contraindications to carry out the test. The premises where samples are carried out must be equipped with the necessary equipment to carry out resuscitation measures. Contraindications to stress testing can vary significantly depending on where the test is performed (in a specialized center or in district clinic), as well as the qualifications of the personnel conducting them.
The main indications for performing stress tests (recommendations of the All-Russian Scientific and Cultural Organization, 2004):
Absolute contraindications to stress testing (recommendations of VNOK. 2004):
Pozdnyakov Yu.M., Martsevich S.Yu., Koltunov I.E., Urinsky A.M.
Stable angina
Functional stress tests are used in the diagnosis of IHD. They are divided into tests that improve metabolism in the myocardium (test with potassium, obzidan, rauwolfia preparations, ambosex), improve coronary circulation (tests with nitroglycerin), and increase the load on the myocardium and the myocardial oxygen demand (test with physical activity).
Medication tests Drug tests are prescribed to patients with suspected ischemic heart disease and with an altered terminal part of the ventricular complex. Before administering the drug, a baseline ECG is recorded, and after administration, a control ECG is recorded.
Test with potassium P When potassium is given to patients with metabolic disorders in the myocardium, there is an improvement metabolic processes and normalization of the terminal part of the ventricular complex. Therefore, the test is positive in case of functional disorders in the myocardium. The potassium test is contraindicated in persons over 60 years of age and in patients with impaired atrioventricular and intraventricular conduction. After a light breakfast, the patient is given 5–6 g of potassium chloride dissolved in 100 ml of water. The control ECG is examined after 30, 60, 90 minutes.
Nitroglycerin test
When nitroglycerin is given to patients with coronary artery disease, an improvement in the terminal part of the ventricular complex is observed. Therefore, a positive test indicates the presence of ischemic heart disease. The patient is given 2-3 drops of a 1% solution of nitroglycerin under the tongue or 1 tablet of nitroglycerin. A control ECG is taken after 5 and 10 minutes. To prevent collaptoid reactions, the test is performed in a horizontal position.
Test with obsidan
The test is positive for functional disorders of the heart and is associated with blockade of β 1 - β 2 adrenergic receptors.
The test is carried out in the morning on an empty stomach, the patient is given 40–60 mg of ob-zidan or anaprilin. A control ECG is taken 30, 60, 90 minutes after taking the drug.
Isoprenaline test
The drug stimulates β 1 - and β 2 -adrenergic receptors, increases heart rate and myocardial oxygen demand. Isoprenaline (isadrin) 0.5 mg (1 ampoule) is diluted in 250 ml of saline or 5% glucose solution. The drug is administered intravenously dropwise until the pulse rate reaches 130–140 beats (more correctly, up to a submaximal rate of 200 - age in years). After reaching the required heart rate, hold it for 3 minutes. After the end of the test and after 5 and 10 minutes, a control ECG is taken. The test is assessed in the same way as for a test with physical activity. During the test, arterial hypertension and ventricular extrasystole may be observed. The test is carried out in a specialized department.
Ergometrine test
Ergometrine increases tone smooth muscle, including coronary vessels, reveals variant Prinzmetal angina. Ergometrine is administered intravenously as a bolus of 0.15 and 0.3 mg, with a 5-minute break between administrations. The test is carried out under constant ECG control during the test and 15 minutes after its completion.
The test assessment is the same as for bicycle ergometry. The test is carried out in a specialized department.
Test with chimes (dipyridamole) The drug is a powerful vasodilator, dilates the
coronary arteries affected by atherosclerosis and does not expand those narrowed by atherosclerosis. As a result of this, there is an even greater decrease in blood flow in the ischemic areas of the myocardium, which is known as the steal phenomenon and is manifested by an attack of angina or a change in ECG ischemic type.
Dipyridamole (chirantil) is administered intravenously at the rate of 0.75 mg per 1 kg of body weight. The calculated dose is divided into 3 parts. The first third of the dose is administered over 3 minutes, the second third over 7 minutes. If an attack of angina or ECG changes occurs ischemic type, further administration of the drug should be stopped; if there are none, a third of the dose is administered over 5 minutes. When an attack of angina occurs, a nitroglycerin tablet is given under the tongue and 5–10 ml of a 0.24% aminophylline solution is injected intravenously. Eufillin is a physiological antagonist of dipyridamole. Tests are carried out in cases where it is impossible to perform a VEP.
Breath-holding tests, orthostatic and sugar tests are less informative for identifying coronary artery disease.
Breath-hold test The test is performed in a supine position. The initial ECG is taken. The subject takes a deep breath and holds his breath. The duration of the breath hold is determined and a control ECG is taken at the end of the hold. In the presence of IHD, negative T readings appear. Normally, the minimum breath-holding time is 30 seconds.
Orthostatic test
Causes an increase in the tone of the sympathetic nervous system and reflex tachycardia. Increased heart rate increases the myocardial oxygen demand and the appearance of coronary disorders.
The initial ECG is recorded in a horizontal position, then the patient is asked to stand and the ECG is recorded in a vertical position after 30 seconds, 3, 5 and 10 seconds.
Sugar test The sugar test is performed on an empty stomach. The subject is taken with an initial ECG and 40 ml of a 40% glucose solution is administered intravenously. Control ECGs are taken immediately after glucose administration and at 10-minute intervals for an hour. In patients with coronary artery disease, negative T waves are recorded on the ECG; the mechanism of changes in T waves is unclear; apparently, it is associated with an increase in oxygen consumption of the heart muscle, which is necessary for the utilization of glucose in the heart muscle.
Frequency positive samples increases with increasing severity of atherosclerotic cardiosclerosis.
Bicycle ergometer test
VEP is one of the options for exercise testing to detect coronary artery disease. The diagnostic value of VEP is 85% with high specificity. In addition to VEP, physical activity on the treadmill, Master's test, step test, abnormal physical activity in the form of climbing stairs, squats, running, walking, etc. are used to identify IHD.
The diagnostic value of treadmill load for identifying ischemic heart disease is approaching that of VEP, but medical institutions do not have treadmills. The Master's test and the step test are of little use for the early diagnosis of IHD due to the low power of physical activity. Therefore, VEP is widely used in cardiology.
Indications:
1) detection of coronary artery disease (early and clinically pronounced forms);
2) determination of exercise tolerance in patients with coronary artery disease and the functional class of exertional angina;
3) monitoring the effectiveness of treatment for patients with coronary artery disease;
4) determination of the effectiveness of coronary agents;
5) identification of transient arrhythmias. In addition to diagnosing coronary heart disease, VEP is widely used for the rehabilitation of patients with cardiovascular pathology.
Most often, VEP is used to diagnose coronary artery disease. Contraindications to VEP in the diagnosis of coronary artery disease:
1) progressive angina, suspicion of myo
card;
2) rhythm disturbance ( frequent extrasystole, atrial fibrillation, paroxysmal tachycardia);
3) conduction disorders (atrioventricular blockade, complete blockades left or right leg His bundle).
VEP should not be prescribed if the initial blood pressure is 170/100 mm Hg. Art. and higher as the temperature rises.
Currently, a continuously stepwise increase in VEP is generally accepted until the end points - submaximal pulse rate or positive test criteria.
180 kg/m/min, every 3 minutes the load power increases by 25–30 W (150–180 kg/m/min). The load is performed on an empty stomach or no earlier than 2 hours after eating. Smoking is prohibited during this period. Patients with coronary artery disease do not take nitrates, β-blockers, tranquilizers, cardiac glycosides, or diuretics on the day of the test.
Positive criteria VEP for identifying IHD:
1) angina attack during the test;
2) ST depression more than 1 mm horizontal;
3) oblique ST depression more than 1.5 mm through 0.08 from the junction point or QX more than 50;% QT;
4) frequent extrasystole (4:40 or more), transient atrioventricular and ventricular block;
5) deepening or broadening of previously existing Q.
Other criteria (decrease and inversion of T, increase in am
amplitudes R) have low specificity for identifying ischemic heart disease.
The test is considered negative when the subject reaches a submaximal pulse rate without signs of coronary insufficiency.
VEP stops when blood pressure decreases by 25–30% from the initial level, blood pressure increases to more than 220/120 mm Hg. Art., a feeling of lack of air, the appearance of general weakness, dizziness, and the patient’s refusal to carry out the test.
VEP should be performed in a stress test room equipped with a bicycle ergometer, a multichannel electrocardiograph with an oscilloscope, and equipment for studying oxygen consumption. It is necessary to have a defibrillator and a set of medications to provide emergency care(nitroglycerin, cardamine, mezaton, analgin, promedol, fentanyl, ammonia, etc.). There should be a syringe in the bag with alcohol. Medical staff(doctor and technician conducting the study) must have resuscitation skills. Before the start of the study, an ECG is recorded in 12 leads, every 3 minutes it is advisable to monitor the ECG III, avF, V 2, V 4 - V 6 leads, or chest V 1 - V 6, using an oscilloscope, observation is carried out in lead V 5. After the end of the load, the ECG is recorded in 12 leads, the ECG is monitored during the recovery period after 5 and 10 minutes.
In cardiology, the most frequently used functional tests are tests with physical activity (bicycle ergometer, treadmill). They are usually performed on patients for the purpose of diagnosis, determining prognosis and functional assessment. Continuous step-increasing load is given until the appearance of symptoms indicating its poor tolerance, or until the subject reaches a certain heart rate (submaximal, maximum). The amount of load performed is usually expressed in watts (W). The maximum oxygen consumption may also be indicated in MET units (metabolic equivalent) - in ml of oxygen used per 1 kg of body weight per minute. During exercise, ECG, blood pressure, and sometimes ventilation parameters are recorded. There are physiological and pathological reactions to stress. The pathological reaction that has the greatest clinical and diagnostic significance in CAD is the appearance of angina and ECG changes in the form of a horizontal or oblique decrease in the ST segment by 1 mm or more. Pathological changes in blood pressure include its insufficient increase or decrease during exercise, which indicates the development of severe left ventricular dysfunction, or an excessive increase in blood pressure (with arterial hypertension).
Key words: diagnostics, coronary disease heart, tests with dosed physical activity, bicycle ergometry, dobutamine test, test with dipyridamole.
GENERAL CHARACTERISTICS
Functional or stress testing in cardiology is used to determine response cardiovascular system with increased demands on it (physical, psycho-emotional stress) or in artificial conditions (changes in body position in space, after the administration of pharmaceuticals) for diagnosis, determination of prognosis and functional assessment (Table 5.1).
Tests with physical activity, as the most physiological and informative, are used more often than others.
A psycho-emotional test consists of performing a logical, mathematical or mechanical task under unfavorable external conditions (limited time, noise, temperature, lighting, etc.).
Pharmacological tests are usually performed with drugs that cause hemodynamic reactions, for example, dobutamine, which has a rapid and pronounced inotropic effect, or dipyridamole, which causes coronary dilation and coronary steal syndrome.
For the first time, ECG changes in the occurrence of pain during physical activity in patients with angina pectoris were described by N. Feil and M. Segal in 1928 in the USA.
A year later, A. Master and F. Oppenheimer developed a standardized exercise protocol.
In 1993, D. Sherif and S. Goldhammer in Germany proposed a technique for conducting a stress test with simultaneous recording of an ECG.
In 1950, A. Master in the USA introduced a two-stage load test.
Table 5.1
Types of Load Tests
With physical activity:
Dynamic (bicycle ergometer, treadmill)
Isometric (wrist press) Psycho-emotional
Pharmacological (dobutamine, dipyridamole)
With changes in body position in space and during accelerations
Transesophageal pacing
Tests involving changes in body position in space and acceleration are used in aerospace medicine for the purpose of selecting and monitoring the training of pilots and astronauts.
Transesophageal pacing is used to assess function sinus node or provocation of myocardial ischemia caused by increased heart rate.
During exercise, hemodynamic (heart rate, blood pressure) and ventilation parameters (oxygen consumption, carbon dioxide emissions, respiratory rate, minute ventilation) can be measured. In special cases, stress tests are often combined with other studies: with echocardiography - for the purpose, for example, of identifying areas of myocardial asynergy or with myocardial scintigraphy with thallium-201 to assess its perfusion. Instrumental monitoring can be carried out in automatic mode (ECG, blood pressure). To evaluate the ECG, a computer is used, which, based on the average ECG complex, analyzes the position of the ST segment, the steepness of ST elevation or depression and other parameters. At the same time, oxygen consumption and carbon dioxide release can be determined, which makes it possible to calculate energy expenditure and aerobic capacity (the amount of oxygen absorbed in 1 minute per 1 kg of body weight).
PHYSIOLOGICAL AND PATHOLOGICAL RESPONSES TO LOAD
During exercise, heart rate increases rapidly, which depends on the intensity of the load and the involved muscle mass. As a result of this, as well as the Frank-Starling mechanism, cardiac output and oxygen uptake increases. Maximum oxygen consumption or maximum aerobic capacity is determined by the arteriovenous oxygen difference and cardiac output. With increasing age, this ability decreases. With cardiovascular disease or detraining, aerobic capacity also decreases due to limited cardiac output.
Maximum aerobic capacity can be determined with reasonable accuracy using empirical formulas that take into account gender, age, weight and height. With sufficient load power, achievable
reaching approximately 50-60% of maximum aerobic capacity, muscles switch to anaerobic metabolism. The lactate level in the blood begins to rise. Due to the interaction of lactate with buffered bicarbonate in the blood, the release of carbon dioxide increases, which becomes disproportionately large in relation to oxygen consumption. The respiratory coefficient reflects the ratio between the volume of carbon dioxide released and the amount of oxygen absorbed and usually at rest ranges from 0.7-0.85 depending on the substrate that is used for oxidation (1.0 - with the predominant use of carbohydrates and 0.7 - with the predominant use of fatty acids). If during exercise the subject reaches the anaerobic threshold, then the respiratory coefficient exceeds 1.1.
The term metabolic equivalent (MET) describes the resting oxygen consumption of a 40-year-old man weighing 70 kg. One MET unit is equal to the consumption of 3.5 ml of oxygen per 1 kg of body weight per minute. Therefore, work intensity can be expressed in MET units.
At maximum heart rate, the body uses 100% of its aerobic capacity, i.e. ability to capture and use oxygen.
Maximum heart rate is calculated using the formula:
Heart rate max = 220 - age.
The approximate values of heart rate max are as follows: 20 years - 200; 30 years - 190; 40 years - 180; 50 years - 170; 60 years - 160. In addition, there is the concept of submaximal heart rate, which occurs during submaximal exercise, when not 100% aerobic capacity is achieved, but a smaller, predetermined one, for example, 70 or 80% of aerobic capacity. This predetermined target load corresponds to experimentally determined heart rate values, and the load continues until the subject has reached submaximal heart rate values. This will be the submaximal load.
Submaximal heart rate is determined by the equation:
Heart rate submax = 220 - (age? 0.65).
In some people, heart rate increases slightly in response to exercise, indicating dysfunction of the sinus node (sick sinus syndrome, hypothyroidism) or the influence of drugs (beta-blockers, ivabradine). Excessive acceleration of heart rate occurs with detraining, unusual anxiety, LV dysfunction, anemia, and hyperfunction of the thyroid gland.
With increasing load, systolic blood pressure increases, reaching 200 mm Hg. and more. A more significant increase in blood pressure is typical for hypertensive patients. Diastolic blood pressure does not change significantly in healthy people (with fluctuations of ±10 mmHg), but increases in hypertensive patients.
If SBP does not increase or decreases during exercise, this may be due to insufficient cardiac output (myocardial dysfunction) or excessive systemic vasodilation. Insufficient increase in blood pressure during exercise or even its decrease occurs not only in cardiovascular diseases in which myocardial dysfunction develops during exercise (with the development of angina, myocardial disease, taking antihypertensive drugs, arrhythmias), but also in people with pronounced vasovagal reactions. A decrease in blood pressure during the onset of angina during exercise is typical of severe stenotic coronary lesions and asynergy in ischemic areas of the LV myocardium.
At a constant submaximal level of load, after 2-3 minutes a steady state is established, in which heart rate, blood pressure, cardiac output and pulmonary ventilation remain at a relatively stable level.
People with impaired cardiorespiratory function may not have a steady state, and the oxygen debt increases with exercise. After stopping the load, their oxygen consumption exceeds their normal consumption at rest by the amount of oxygen debt.
The product of heart rate and systolic blood pressure (double product) increases with increasing load and correlates with myocardial oxygen consumption. The calculation of this product is used
as an indirect index of myocardial oxygen consumption.
With detraining and with increasing age, the maximum oxygen consumption by the myocardium during exercise decreases due to an age-related decrease in maximum heart rate and systolic ejection.
The uptake of oxygen from the coronary bloodstream by the myocardium, even at rest, is maximum, and its increase during exercise is achieved due to coronary dilatation. With CAD, this dilatation is impossible in areas of stenosis. In addition, patients with variant Prinzmetal angina, which is rare, may experience coronary vasospasm during exercise. Therefore, in patients with angina pectoris during physical activity, there comes a period when, due to stenosis of the coronary vessels, an increase in oxygen delivery to the myocardium becomes impossible and cannot be higher than a certain level (internal angina threshold).
Therefore, myocardial oxygen consumption during the development of angina pectoris is maximum, which can be expressed by a double product, the value of which during the period of pain onset is also maximum for a given patient and characterizes his internal angina threshold.
Subendocardial areas of the myocardium are more susceptible to ischemia due to higher systolic tension. With the development of ischemia, the so-called ischemic cascade begins (Table 5.2).
Table 5.2
Ischemic cascade
Increased lactate production
Diastolic dysfunction:
Impaired diastolic filling;
Increased diastolic pressure Systolic dysfunction:
Impaired contractility of ischemic areas of the heart;
Decreased ejection fraction (EF) and systolic ejection ECG changes
Angina pectoris
The double product (heart rate and systolic blood pressure) is an index of myocardial oxygen consumption, and during the development of angina pectoris it is maximum for a given patient.
ECG CHANGES DURING LOAD
Under load, as the heart rate increases, the P-Q, QRS and QT intervals shorten, the P voltage increases, the J point and the ST segment decrease, the ST segment takes on an oblique-ascending appearance (functional decrease) (Fig. 5.1).
From top left to bottom: normal ECG, J-point of connection (“junction”, English) of the S wave and the ST segment; rapidly ascending ST segment depression, normal variant; deep horizontal ST depression indicating subendocardial myocardial ischemia.
From top right to bottom: downward-sloping ST depression, characteristic of subendocardial myocardial ischemia; ST segment elevation, indicating transmural myocardial ischemia; elevation of the ST segment in the scar area after Q-infarction, associated with asynergy of the left ventricular myocardium.
In patients with angina pectoris, when subendocardial myocardial ischemia occurs, a decrease in the ST segment of a slowly ascending, horizontal or oblique type occurs (Fig. 5.1-5.4). The depth of depression increases with increasing ischemia.
As ischemia increases, slowly ascending depression can turn into horizontal and then downward. After stopping the load, these changes disappear within a few minutes and the ECG becomes normal, but immediately after stopping the load, the horizontal depression of the ST segment can turn into a downward depression. If changes in the position of the ST segment are already present at rest, this should be taken into account during subsequent assessment. With a large decrease in this segment at rest, the value of a stress test to assess changes in the position of the ST segment is significantly reduced.
To measure ST segment depression, the PQ segment is used as an isoline. It is advisable to have three consecutive
Rice. 5.1. Changes in the ST segment during exercise. Explanations in the text
Rice. 5.2. ECG in chest leads at rest (left) and at threshold load (right) in a patient with CAD. During exercise, slowly ascending ST segment depression (2 mm at ST60 in lead V5), indicating myocardial ischemia
Rice. 5.3. ECG in chest leads at rest (left) and at threshold load (right) in a patient with CAD. On the right, horizontal ST depression (1.8 mm in lead V5), indicating myocardial ischemia
Rice. 5.4. ECG in chest leads at rest (left) and at threshold load (right) in a patient with CAD. On the right - depression of the ST segment of an oblique type (by 1.6 mm in lead V5), indicating myocardial ischemia
ECG complex with a good isoline. Depression of the ST segment of a horizontal or oblique type by more than 1 mm at a distance of 80 milliseconds from the J point (ST 80) is considered nonphysiological and occurs with myocardial ischemia. When the heart rate exceeds 130 bpm, the ST 60 point is sometimes used to determine ST segment depression (some ECG machines always use the ST 60 point).
Points ST 60 and ST 80 are sometimes designated by the letter "i" (ischemia), and its offset from the isoline by the letter “h” (height, vertical dimension).
Rapidly rising ST depression (less than 1.5 mm at ST 80) during maximal exercise is considered a normal response. Slowly rising depression of 1.5 mm or more at ST 80 is considered an abnormal response and occurs in patients with stenotic atherosclerotic coronary artery disease and in people with a high pretest probability of CAD. In people with a low pretest probability of CAD, a definite assessment of such changes is difficult.
Sometimes in leads with a pathological Q wave (after a MI) or without such a Q, ST segment elevation is observed. In the first case, it is interpreted as an indicator of myocardial dysfunction (akinesia, dyskinesia) in the area of former MI, usually in patients with reduced EF and poor prognosis. ST elevation in leads without pathological Q is regarded as an indicator of severe transmural myocardial ischemia (Fig. 5.5).
Changes in the ST segment during exercise in patients with CAD cannot be used to localize ischemia and coronary lesions.
In addition to coronary causes, there are also non-coronary causes of ST segment depression:
LV hypertrophy (aortic stenosis, arterial hypertension);
Hypokalemia;
Treatment with cardiac glycosides;
Hyperventilation;
Mitral valve prolapse;
WPW syndrome;
Intraventricular conduction disorders;
Severe volume overload (aortic, mitral insufficiency);
Supraventricular tachycardia.
Rice. 5.5. ECG in precordial leads V1-5 at rest (left) and at threshold load (right) in a patient with early post-infarction angina. A stress test was performed 3 weeks after the development of MI without a Q wave. With a low load (25 W), grade 3 angina developed with ST segment elevation of 2.5-3.0 mm in the precordial leads, indicating severe transmural myocardial ischemia
Changes in the T wave during exercise are nonspecific. Its form, even at rest and in healthy people, is very variable and depends on many factors (body position, breathing). With hyperventilation, flattening of the T waves or the appearance of negative ones are often observed. If T waves are negative before exercise, they often become positive during exercise, and this is not considered a sign of disease.
Ventricular extrasystoles, including group ones, or ventricular “jogs” occur during exercise in healthy people. On the other hand, both in healthy people and in patients with CAD, ventricular extrasystole can disappear with exercise. Therefore, it does not have significant diagnostic value. In patients who have had an MI, group ventricular extrasystoles or periods of ventricular paroxysmal tachycardia during exercise are more typical for patients with high risk sudden death.
Supraventricular extrasystole during exercise is observed both in healthy people and in patients with heart disease. For the diagnosis of CAD, its appearance during the test is not significant.
During exercise, a blockade of the left or right bundle branch may occur, although rarely, which does not have an independent diagnostic or prognostic value.
With myocardial ischemia, the ECG shows depression of the ST segment (deep oblique ascending, horizontal, oblique descending) or elevation (rarely) of the ST segment (in leads without a post-infarction Q wave)
CARRYING OUT A TEST WITH DOSED PHYSICAL ACTIVITY
When studying cardiac patients, the most physiological and informative tests are exercise tests on a bicycle ergometer or treadmill, but a 6-minute walking test can also be used. The name "treadmill" comes from the English verb "to thread"- step, put your foot down and noun "mill"- mill. In the Middle Ages, prisoners were forced to set the mill mechanism in motion by stepping on the steps of a large wheel.
The disadvantages of bicycle ergometry include learning difficulties for older women, as well as a large increase in blood pressure compared to walking on a treadmill. But a bicycle ergometer takes less space, produces less noise and costs less. A device like a bicycle ergometer can also be adapted to work with your hands.
Before exercise, a 12-lead ECG is recorded in the supine and sitting position, and blood pressure is measured. Most loading tests are carried out in the form of a continuous step-increasing load. The duration of each load level is 1-5 minutes. It is advisable that the total examination time does not exceed 15 minutes, since otherwise most patients will not be able to continue working due to general fatigue and weakness in the legs.
The test begins with a warm-up for 1-2 minutes, followed by a loading period, during which the load gradually or intermittently (stepwise) increases.
At the end of each load stage, an ECG is recorded and blood pressure is measured.
The load is dosed either in watts (W) or in kilopond meters per minute, 1W = 6 kilopond meters/min.
Here are several bicycle ergometry protocols (Fig. 5.6), which may differ from those used in other countries and centers:
Rice. 5.6. Exercise protocols
1. The load starts at 10 watts for 1 minute and increases by 10 watts every minute.
2. The load starts at 20 watts for 2 minutes and increases by 20 watts every 2 minutes.
3. The load starts at 30 watts for 3 minutes and increases by 30 watts every 3 minutes.
4. The load starts at 25 or 50 watts for 5 minutes and increases by 25-50 watts every 5 minutes (“Scandinavian” protocol).
The threshold power of the performed load is calculated by the formula:
Power = A + [(V - A)/T]g,
where A is the power of the last fully completed load stage; B is the power of the load stage at which the test was stopped; T is the duration of each load step (min) according to the protocol; t is the duration of the load (min) at the last stage.
If the subject has completely completed the next stage of the load, but has not progressed further, this will be his threshold power. For example, if the subject completely completed the load stages of 50 and 100 watts for 5 minutes each stage and the test was stopped, then his threshold power is 100 watts.
If, after performing a load with a power of 100 watts, the subject performed the next load with a power of 150 watts for 1 minute, his threshold power is 110 watts, 2 minutes - 120 watts, 3 minutes - 130 watts, 4 minutes - 140 watts and 5 min - 150 watts, etc.
Or with a different protocol. For example, the subject performed sequential 3-minute load stages with a power of 60 and 90 watts, i.e. his threshold power is 90 watts, if there was the next load step with a power of 120 watts and he completed it within 1 minute, then his threshold power is 100 watts, 2 minutes - 110 watts, 3 minutes - 120 watts, etc.
The load on the bicycle ergometer is performed until subjective or objective signs of the inappropriateness or impossibility of continuing it appear, which are called the criteria for stopping the load (Table 5.3).
After stopping, the samples are recorded/or observed on an ECG monitor for 5 minutes or until it is completely normalized.
Evaluation of research results Test positive
This conclusion is based only on ischemic changes in the ST segment, which include:
Horizontal or downward ST segment depression (ST 80) of 1 mm or more;
Slowly rising ST segment depression (ST 80) of 1.5 mm or more;
ST segment elevation (ST 60) of 1 mm or more in leads without a post-infarction Q wave.
Table 5.3
Load termination criteria*
Subjective Angina pectoris, grade 3 on a 5-point scale:
1 - very light
2 - light
3 - quite strong
4 - strong
5 - intolerable fatigue
Severe shortness of breath ( relative reading) Pain in legs, joints Dizziness
Pallor or cyanosis
Reluctance of the subject to continue the load Objective ECG changes
ST segment depression of 2 mm or more from baseline through 80 milliseconds from the J point (ST 80) of a horizontal or downward type (relative reading)
ST segment elevation of more than 2 mm in leads with a Q wave or more than 1 mm in leads without a pathological Q wave (ST 60)
The appearance of paroxysmal cardiac arrhythmias
Increasing frequency of ventricular extrasystoles, especially polymorphic, group ones (relative indication)
Supraventricular tachycardia (relative indication)
The appearance of new conduction disorders, bradyarrhythmias (relative indication)
Submaximal heart rate (approximately 85% of maximum, approximately equal to 200 - age):
20 years - 180
30 years - 170
40 years - 160
50 years - 150
60 years and older - 140-130 Changes in blood pressure
Increase in systolic blood pressure more than 220 mm Hg. or diastolic more than 115 mm Hg. (relative reading)
A decrease in systolic blood pressure by more than 10 mm Hg, despite an increase in load or no increase in two or more load levels (relative reading)
Note:*may vary different countries and centers.
Test negative
This conclusion is possible when the patient reaches a submaximal heart rate without ischemic changes on the ECG. In a number of clinics, a negative test with peculiarities is identified - when rhythm and conduction disturbances appear during the study or when blood pressure increases above normal values for the corresponding level of load, etc.
The test is questionable
This conclusion is justified when it appears on ECG depression ST 80 less than 1 mm and (or) pain in the chest.
If the test is stopped for other reasons, this is reflected in the conclusion. For example, the test is stopped because the systolic blood pressure reaches 230 mm Hg. or general fatigue, etc.
The second part of the conclusion characterizes exercise tolerance. To do this, it is necessary to calculate the threshold load power (see above).
When performing treadmill testing, special tables are used, where power and aerobic capacity (in MET units) are determined based on the level of load, or these parameters are issued automatically by a computer, as is the conclusion of the test.
The normal threshold load for untrained men 40-50 years old is 2 W/kg body weight, for women - 1.5 W/kg body weight.
It is believed that in men with angina pectoris of functional class 1, the threshold load is about 1.5 W/kg, with class 2 1-1.5 W/kg, with class 3 0.5-1 W/kg and class 4 0.5 W /kg body weight. These are average values.
Teddylometry
Multi-stage protocols are used (Naughton, Bruce, etc.), the duration of each load stage is 1-3 minutes. To increase the load power, the speed of the track and its elevation angle are increased. While walking along the path, subjects can hold onto handrails.
Wrist press
A form of static exercise that causes a greater increase in blood pressure and a smaller increase in heart rate compared to exercise
bicycle ergometer or treadmill. The increase in heart rate is often insufficient to provoke myocardial ischemia. First, the maximum compression force is recorded on a hand-held dynamometer, then the subject squeezes the dynamometer to 1/4-1/3 of the maximum force and holds the press for 3-5 minutes.
Indications and contraindications for stress tests
Load tests are of greatest importance in diagnostics, functional and prognostic assessment in patients with CAD (Table 5.4).
Table 5.4
Indications for stress testing
Diagnosis of CHD
Establishing the functional class of angina pectoris, assessing the effectiveness of various interventions (medicines, surgeries, etc.)
Assessment of prognosis in cardiac patients
Selection of training load for physical rehabilitation
Determination of the cardiovascular system's response to stress
Since complications may develop during stress tests, the patient’s condition should be monitored during exercise (visually, ECG, blood pressure) and patients with a high risk of complications should not be tested (Table 5.5).
The physician recommending exercise testing should explain the purpose of the test and the possible response to exercise. It is advisable to obtain the patient's informed consent for the test. The study is carried out by a doctor trained in cardiac intensive care. The room for stress tests is equipped with a defibrillator and other resuscitation equipment.
Before the diagnostic test, antianginal drugs are discontinued (nitrates 24 hours before, calcium antagonists and β-blockers 48 hours before the test). Changes in the ST segment at rest and during exercise can be affected by cardiac glucosides (it is advisable to discontinue them 7 days before the test), saluretics, tricyclic antidepressants, and lithium salts. Latest drugs if possible, cancel 3-4 days before the test. Antianginal drugs are not discontinued when determining their effect on exercise tolerance in patients with angina pectoris.
Table 5.5
Contraindications for exercise testing*
Unstable angina
Acute MI (during the first days)
Dangerous arrhythmias
Decompensated heart failure
High degrees of sinoauricular or atrioventricular block
Acute myocarditis, pericarditis
Uncontrolled hypertension
Aortic aneurysm
Severe aortic or subaortic stenosis
Acute systemic disease
Acute thrombophlebitis
Acute cerebrovascular accident Note:* may vary by country and center.
THE IMPORTANCE OF EXERCISE TESTS
Use of exercise testing to diagnose CAD
When explaining the results of stress tests, you should consider the possible limitations inherent in these methods and learn a number of new concepts that are relevant to any research method (Table 5.6).
A 1998 European meta-analysis of bicycle ergometry compared with coronary angiography in 24,074 patients showed a sensitivity of 68% (23-100%) and a specificity of 77% (17-100%) in middle age.
The sensitivity of the test increases with the number of affected vessels: from 25-71% with damage to a single vessel to 81-86% (40-100%) with multi-vessel disease. Changes in the ST segment during exercise are more often detected with atherosclerotic changes in the anterior branch of the left coronary artery.
A positive stress test may occur in people with angiographically normal coronary vessels, e.g.
measures due to a violation of the mechanism of coronary vasodilation (coronary X syndrome), with LV hypertrophy, cardiomyopathies. In addition, the appearance of “ischemic” changes in the ST segment during physical activity is possible during treatment with cardiac glycosides, with hypokalemia, anemia, and mitral valve prolapse.
Table 5.6
Basic terminology when assessing physical test results
load
True positive | Abnormal response to exercise in illness |
False positive (FP) | Abnormal response in the absence of disease |
True negative | Normal response in the absence of disease |
False negative | Normal response in the presence of disease |
Sensitivity | Percentage of CAD patients with abnormal response to exercise = PI/(PI+LP) |
Specificity | Percentage of those examined without CAD with a normal response to physical activity = TI/(IO+LP) |
Predicted significance (test positive) | Percentage of patients with abnormal response who have CAD = PI/(PI + LP) |
Predicted significance (test negative | The percentage of those examined with a normal response who do not have CAD, IO/(IO + LO) |
Ischemic ECG changes during exercise become more pronounced as multivessel coronary lesions develop in patients with coronary artery disease and with increasing load levels, with the most informative leads V4 - 6 (Table 5.7).
Table 5.7
Signs of severe coronary lesions during stress testing
Early onset of angina
No increase in systolic blood pressure as the level of exercise increases or its decrease
Deep depression of the ST segment of the oblique type,
persisting for more than 5 minutes after exercise
ST segment elevation during exercise
(in leads without pathological Q)
Prognostic value of exercise tests
The prognostic value of stress tests has been studied in healthy people and in patients with cardiovascular diseases (Table 5.8).
Table 5.8
Groups of subjects and features of the exercise test, characterizing an increased risk of developing cardiovascular diseases and complications
Use of graded physical exercise tests for functional assessment of cardiovascular patients
First of all, these are patients with coronary artery disease, chronic heart failure and heart defects.
Along with other research methods, stress tests are used to functionally assess patients with cardiac arrhythmias and test the effect of antiarrhythmic drugs. Thus, in patients with paroxysmal ventricular tachycardia, physical activity usually provokes ventricular arrhythmias, incl. and paroxysms of ventricular tachycardia. In patients with sick sinus syndrome, a stress test demonstrates that the heart rate does not increase sufficiently during exercise, although this is not the rule.
In patients with a tendency to hypertension, a more significant increase in blood pressure is detected during exercise.
Patients with heart defects undergo functional assessment before and after surgery.
PHARMACOLOGICAL TESTS
Dipyridamole
Used to provoke myocardial ischemia and mainly during myocardial perfusion studies with thallium-201. Dipyridamole blocks the metabolism of adenosine. Adenosine is formed from ATP and has short period half-life (10 s) and has a pronounced local arteriolodilating effect. Intravenous administration of dipyridamole increases the concentration of adenosine in the myocardium, increases coronary blood flow, slightly reduces systolic blood pressure and accelerates heart rate. In areas of the myocardium that are supplied with blood through stenotic arteries (85-90% stenosis), the coronary bed distal to the stenosis is maximally expanded already at rest. There is no coronary reserve in these areas. The administration of dipyridamole can lead to a redistribution of coronary blood flow towards less stenotic or healthy arteries and “intercoronary steal”, i.e. ischemia of myocardial areas distal to the stenosis. The appearance of ischemia is indicated by the development of angina pectoris and changes in the ECG.
Indications: impossibility of carrying out tests with physical activity (in persons with joint diseases, vessels lower limbs etc.) or stopping the exercise test before reaching the criteria for its evaluation, provoking myocardial ischemia during radionuclide studies.
Contraindications the same as for testing with physical activity.
Dipyridamole is administered intravenously at the rate of 0.75 mg/kg body weight (sometimes a dose of 0.84 mg/kg body weight is used), in a physiological solution of 20 ml for 5 minutes (4 ml/min). The endpoints and evaluation criteria of the dipyridamole test are similar to the exercise test.
Dipyridamole, causing coronary vasodilation, increases blood flow in unchanged vessels and reduces it (stealing) in stenotic ones, which creates ischemia in the area of their blood supply.
Side effects when taking dipyridamole: headache, nausea, weakness.
The dipyridamole test provokes myocardial ischemia mainly in cases of severe stenosis of the coronary arteries and has low sensitivity (20-30%).
Dipyridamole infusion is often given before radiotracer insertion for myocardial scintigraphy.
Sometimes a dipyridamole test is combined with a low-power stress test.
Dobutamine
Dobutamine is a short-acting synthetic catecholamine, the intravenous administration of which increases heart rate, blood pressure, myocardial contractility and, as a result, myocardial oxygen demand. The occurrence of ischemia is recognized using myocardial scintigraphy with thallium-201 or stress echocardiography. During the latter, changes in local contractility are observed, which is disrupted with the development of myocardial ischemia.
The dobutamine test is used with diagnostic purpose in patients who cannot perform a test with dosed physical activity or if such a test is not informative.
WPW syndrome or ventricular preexcitation syndrome is known to be associated with the presence of accessory conduction pathways between the atria and ventricles, which causes characteristic changes Resting ECG. The prevalence of WPW syndrome in the population is relatively low - from 0.01-0.3%, however, it can be combined with other cardiovascular pathologies, including coronary heart disease (CHD). Load tests, in particular bicycle ergometry and treadmill tests, are widely used in the diagnosis of coronary artery disease. From the literature we know about the possibility false positive results ECG tests for WPW syndrome. However, in practice, these tests are often used in this group of patients. The choice of the type of stress test and the correct interpretation of its results in WPW syndrome for this reason remain an important task.
We present clinical case diagnosing ischemic heart disease using various types stress testing in an asymptomatic woman with ventricular preexcitation syndrome.
Patient K., 43 years old, was hospitalized for examination with a diagnosis of coronary artery disease and post-infarction cardiosclerosis. Upon admission she did not present any specific complaints. From the anamnesis it is known that the diagnosis was made retrospectively based on ECG changes. Indications for protracted anginal attack not noted in the anamnesis. The patient did not describe the symptoms of angina pectoris, did not note increases in blood pressure and heart rhythm disturbances. Earlier with repeated biochemical analyzes The patient's blood showed an increase in total cholesterol levels from 6.0-6.5 mmol/l. The woman had been smoking for several years, but had stopped smoking shortly before hospitalization and had maintained menstrual function. Changes in the resting ECG were first discovered accidentally during an examination in a sanatorium. As can be seen from the presented ECG (Fig. 1), in the right precordial leads the ventricular complex had a QS-shape, which persisted when recording the ECG during inspiration, which at the prehospital stage was interpreted as cicatricial changes in the anteroseptal region. In addition, there was a shortening P-Q interval up to 0.10 s. and changes in the initial part of the QRS complex in the form of a weakly expressed “delta” wave.
At the outpatient stage, in order to identify episodes of myocardial ischemia, the patient underwent daily monitoring ECG, according to the results of which no ischemic changes or significant rhythm disturbances were registered. During an objective examination, no peculiarities of the cardiovascular system were noted; blood pressure was 130/80 mm Hg. Art., heart rate - 70 beats/min.
Rice. 1. Resting ECG of patient K., 43 years old.
At the clinic, the patient underwent echocardiography (EchoCG) and a test with dosed physical activity according to the R. Bruce protocol (treadmill test with ECG and EchoCG assessment). According to echocardiography, there was no rest pathological changes the size of the heart chambers, wall thickness, systolic and diastolic function. No areas of local contractility impairment were identified. When performing stress echocardiography, no changes in the ST segment were noted on the resting ECG. Against the background of maximum load in the 4th minute (heart rate 164 beats/min, blood pressure 140/90 mm Hg, exercise performed - 4.8 METS), the appearance of ST segment depression was noted (Fig. 2). Maximum horizontal ST segment depression of more than 2 mm was observed in leads II, III, aVF, and up to 2 mm in leads V4-V6. According to echocardiography, no zones of local contractility disturbance were detected in the first 2 minutes after the end of the load. There were no clinical manifestations of angina pectoris in the form of pain or discomfort in the chest, and no rhythm disturbances were recorded.
Rice. 2. ECG dynamics during a stress test of patient K., 43 years old.
Considering the risk factors for coronary artery disease and the ambiguous results of the stress test, the patient underwent single-photon emission computed tomography of the myocardium with assessment of perfusion at rest and against the background of an exercise test (Fig. 3 - see page 1 of the cover). 99mTc-technetrile was used as a radiopharmaceutical; VEM was performed according to the standard R. Bruce protocol. During the test, a heart rate of 170 beats/min was achieved, clinical signs acute myocardial ischemia was not established. On perfusion tomoscintigrams, when examined at rest and during a stress test, no regional perfusion defects were detected, and no disturbances in local contractility of the left ventricle were detected. Thus, despite the existing risk factors, good tolerance to physical activity, as well as the absence of perfusion defects and disturbances in local myocardial contractility both at rest and under load conditions allowed us to evaluate ECG results stress test as false positive, and the patient as having a low risk of coronary heart disease. Changes in the QRS complex were interpreted as characteristic of WPW syndrome, type B (shortening of the P-Q interval to 0.10”, negative “delta” wave in leads V1-V3, positive in leads V5-V6), which caused a specific “pseudo-infarction” resting ECG picture. During 5 years of observation, the patient continues to remain asymptomatic; while following dietary recommendations, normalization of blood lipid levels is noted (total cholesterol - 4.0-4.5 mmol/l, low-density lipoproteins - less than 2.5 mmol/l).
Rice. 3. Results of single-photon emission computed tomography at rest and under load
DISCUSSION
The high frequency of false-positive results of a stress test with an ECG in the syndrome of premature excitation of the ventricles has been repeatedly described in the literature. Thus, according to M.R. Jezior et al. , who analyzed 8 studies of stress testing in WPW syndrome, with a total of 176 patients, false-positive results were recorded in 49% of patients (Table 1). In this series of cases, against the background of load, the “delta” wave disappeared with simultaneous normalization of the ST segment. At the same time, changes in the ST segment in some cases persisted despite the disappearance of the “delta” wave, which the authors explain by the “cardiac memory” phenomenon, which causes the persistence of repolarization disorders, for example, after cessation of stimulation or after tachycardia. In some cases, ST segment depression was very severe (more than 4 mm) with angiographically normal coronary arteries.
Table 1. False-positive results of the stress ECG test in patients with WPW syndrome according to M.R. Jezior et al.
| Study | Type ST | Patients with ST segment depression, n | Patients with performed AI, n | Patients with abnormal AI results, n |
| Gazes (n=23) | T | 20 | ||
| Poyatos et al. (n=58) | T | 31 | 18 | 9 |
| Strasberg et al. (n=54) | T | 19 | ||
| Paquet and others (n=1) | T | 1 | 1 | 1 |
| Archer et al (n=8) | B | 7 | 8 | 2 |
| Tawarahara et al. (n=20) | WITH | 20 | 2 | |
| Pattoneri et al. (n=11) | B | 7 | ||
| Greenland and others (n=1) | T | 1 | ||
| Total (n=176) | 86 (49%) | 47 | 14 (30%) |
where, ST - stress test, II - isotope study, T - treadmill; B - bicycle ergometry; C - myocardial scintigraphy (thallium) with load.
This case also demonstrates possible difficulties in assessing the results of a stress test in the presence of premature ventricular excitation syndrome. According to ACC recommendations, the stress test with ECG for WPW syndrome is a class III indication. Therefore, first of all, the correct diagnosis of WPW syndrome is important, since the choice of functional diagnostic method depends on this. As is known, in WPW syndrome, excitation from the atria to the ventricles is transmitted both through the atrioventricular node and through an additional conduction pathway (bundle of Kent), which causes a shortening of the P-Q interval and expansion of the QRS complex with the appearance of a “delta” wave.
In the presented case, despite the shortening of the P-Q interval, the weak severity of the “delta” wave can lead to the problem of recognizing the syndrome of premature excitation of the ventricles and the erroneous interpretation of ECG changes as scar post-infarction. This conclusion may also be supported by myocardial scintigraphy data, where attenuation by breast tissue may simulate hypoperfusion in the anterior apical region (Fig. 3). At the same time, the absence of zones of local contractility disorders according to both echocardiography and scintigraphy allows us to exclude cicatricial damage to the myocardium.
Disturbances in repolarization processes in the form of ST segment depression during a stress test could be regarded as evidence of ischemia in the inferolateral wall of the LV. However, the absence of zones of hypokinesia during exercise according to scintigraphy and echocardiography, as well as stress-induced perfusion disturbances, allows us to exclude transient myocardial ischemia. Thus, the diagnosis of CHD in persons with WPW syndrome should be carried out on the same principles as for other patients, and be based on an assessment of risk, pre-test probability of CHD and clinical data, but with mandatory consideration of the presence of initial ECG changes. The correct choice of functional diagnostic method allows you to avoid false positive results, which, in turn, can lead to unreasonable prescription invasive methods diagnostics
LITERATURE
