In recent years, the incidence and mortality rate of coronary heart disease in China has been increasing year by year. An epidemiological data from the Ministry of Health shows that the mortality rate of coronary heart disease in some cities and towns in China was 41.88/100,000 in 1988, and rose to 64.25/100,000 in 1996, an increase of 53.4% in 8 years; in rural areas, it rose from 19.17/100,000 to 26.92/100,000, an increase of 40.4% in 8 years (Coronary Cardiology 80-86). Clinical trials have proven that coronary revascularization therapy (PCI and CABG procedures) is the most effective way to prevent or reduce the occurrence of coronary heart disease deaths. Therefore, only early detection of coronary heart disease can lead to early treatment and early treatment can prevent cardiac events. Hu Fenghuan, Department of Cardiovascular Medicine, Fu Wai Hospital, Beijing
At present, the main clinical methods used for early diagnosis of coronary heart disease are: 1) conventional electrocardiogram; 2) electrocardiogram stress test; 3) drug stress echocardiogram; 4) exercise and resting nuclear myocardial perfusion imaging; 5) multi-row CT examination.
I. Electrocardiogram
ECG is the earliest examination method used to diagnose myocardial infarction and coronary artery supply deficiency in coronary heart disease, which is convenient, fast and economical. However, the sensitivity of ECG for the diagnosis of coronary heart disease is low, only 23%, and the specificity is 87% (1.). Therefore, in most patients with coronary artery disease, the ECG can be completely normal if there is no angina attack. If a patient has an angina attack, the ECG ST-segment depression, which returns to its original level after remission, has definite significance for the diagnosis of coronary artery disease.
II. Electrocardiographic load test
In 1932, Golhammer et al. first proposed that ECG exercise testing could help in the diagnosis of insufficient coronary artery blood supply, and then Master developed the criteria of second-step exercise test and post-exercise ECG to diagnose insufficient coronary artery blood supply. In view of the low sensitivity of the second-step exercise test, Wood et al. proposed in 1950 that increasing the amount of exercise could improve the positive diagnostic rate. 1971 Bruce et al. conducted a study on the extreme exercise test and gained further insight into the diagnostic value and limits of the exercise test in ischemic heart disease, which led to the choice of increasing the load and specifying the duration of exercise at each level by varying the speed and incline, and The endpoints of the exercise test were selected in advance according to symptoms or heart rate limits. In the 1970s, the understanding of exercise testing was further updated due to the widespread development of coronary angiography and comparative studies on the correlation between exercise testing and imaging, and its application became more widespread in the 1980s. After half a century of research, the ECG exercise test is a simple, practical and reliable diagnostic test, which is also safe if a well-developed protocol is followed and contraindications to exercise are strictly mastered (3).
The currently used ladder, bicycle and moving plate exercise tests are all dynamic stress, also known as isotonic exercise. During isotonic exercise, the extensor and flexor muscles alternately contract rhythmically, thus increasing peripheral arterial perfusion and promoting venous return, making the circulatory response proportional to the corresponding increase in oxygen demand, which can more comprehensively reflect the work of the heart and oxygen uptake capacity, in line with the characteristics of physiological exercise, and is widely used in clinical practice.
ECG load test methods
(A) Second-step exercise test
1, method: according to age, sex and body weight to specify the amount of exercise, to stopwatch timing, with a metronome to adjust the speed of the stirrup, so that the test subject in each level of high 9 traces of castor 8-10 traces of 1-27 cynical mu zhi dioscorex Xi draping Shaiminai Mamata tough file plate 3 minutes. Before exercise, lying down, trace the resting 12-lead ECG, after 3 minutes of exercise, immediately lying down, trace the ECG immediately after exercise, 2, 4 and 6 minutes. If angina occurs during exercise, the exercise should be stopped immediately and the ECG should be recorded lying down. The exercise test should be performed on an empty stomach or after 2 hours after a meal.
2. Positive criteria: (1) Angina pectoris or ECG change during exercise is positive if it is one of the following: (1) Horizontal or downward-sloping ST-segment drop (intersection angle between ST-segment and R-wave vertex drape R90 degrees) >0.05mv after exercise in the lead dominated by R-wave, lasting for 2 minutes. If the original ST-segment decrease, it should be further decreased >0.05mv on the basis of the original, lasting for 2 minutes; 2), in the R wave dominant leads, the ST-segment arch-back-up type elevation >0.2mv after exercise. (2) Post-exercise ECG changes are considered suspicious if one of the following conditions is met: 1) horizontal or downward-sloping ST-segment drop <0.05mv or close to 0.05mv for 2 minutes after exercise in R wave-dominant leads; 2) T-wave change from upright to inverted for 2 minutes after exercise in R wave-dominant leads; 3) U-wave inversion; 4) any One kind of arrhythmia: multi-source premature ventricular wave, paroxysmal ventricular tachycardia, atrial fibrillation or park, sinus atrial block (degree I, II, III), bundle branch block or left bundle branch block, complete right bundle branch block, or intraventricular conduction block.
3. Evaluation: (1) According to the early reports of double exercise test and coronary angiography control, its sensitivity for the diagnosis of coronary artery disease is 48%-63% and specificity is about 83%. In asymptomatic patients with positive double exercise test, the incidence of coronary heart disease during the follow-up period of 2-11 years was 4-6.8 times higher than that of those with negative exercise test. It suggests that he has some value for both diagnosis and prognosis of coronary artery disease. (2) The two-step exercise test is the longest used exercise test. The initial Master standard exercise test, which specifies an exercise time of 1.5 minutes, is of little diagnostic value due to the small amount of exercise, and has been changed to a double two-step test with 3 minutes of exercise in the last 50 years. Despite the doubling of exercise time, but for some people still can not reach enough exercise, sensitivity and specificity is low; and exercise can not be heart rate, blood pressure monitoring, with a certain degree of blindness, there are potential risks; repeated test when the positive results are not constant, the current domestic has largely abandoned this test method. However, because of the simplicity of the equipment required, it is still of some value as a preliminary diagnostic test in primary clinics.
(B) Graded exercise test
The graded exercise test is an exercise method that gradually increases the load starting from a low load under continuous ECG monitoring. The former is based on reaching the maximum heart rate expected for age or a certain percentage of it as the end point of exercise; the latter is based on the maximum heart rate as the standard, and is determined by the restrictive symptoms, i.e. reaching the physiological limit as the end point. The graded exercise test includes two types of exercise tests: bicycle exercise test and flat exercise test.
1.Bicycle exercise test
(1) Method: The subject was asked to pedal on a special bicycle metric meter with equal incremental load, starting from level one to level eight, with 2-3 minutes of exercise per level. The starting load was 25-30 Watts (W), i.e., 1W = 6.13 kgm/min, while those under 40 years of age could start at 50-60 W and increase by 25-30 W at each level. the cycling rate was kept at 35-100 revolutions per minute (35-100 rpm), with the ideal rate being 60 rpm (5).
2.Active plate exercise test
(1) method: let the subject walk on the movable plate instrument with automatic adjustment of slope and speed, according to the pre-designed exercise program, and stipulate to increase a certain slope and speed at a certain time.
(2) Bruce classification criteria: There are a variety of foreign exercise programs, and after domestic clinical trials, it is believed that the Bruce program, which calculates the maximum heart rate according to age, is more suitable for our subjects, so the Bruce program is now commonly used in China (4).
(3) Heart rate calculation standard: the graded exercise test heart rate calculation standard is calculated according to age, and the sub-polar exercise test is based on 85% of the maximum heart rate (approximately equivalent to: 195 – age).
3.The positive assessment criteria of graded exercise test: (1) typical angina pectoris occurs during exercise; (2) ST level or downward sloping type decrease R0.1mv appears on ECG during or after exercise, or if the original ST decreases, it should decrease 0.1mv on top of the original one after exercise; (3) if blood pressure decreases during exercise.
4.Exercise endpoints of graded exercise test: (1) heart rate reaches the expected standard; (2) typical angina pectoris appears; (3) positive ECG result appears; (4) serious heart rate arrhythmia appears (frequent premature ventricular beats, ventricular tachycardia, etc.); (5) blood pressure drops R10mmHg or rises R20mmHg compared with that before exercise; (6) dizziness, pale face and unsteady gait appear.
5, Precautions: When conducting the graded exercise test, resuscitation drugs and equipment (defibrillator and intracardiac injector, etc.) should be prepared for cardiopulmonary resuscitation, as well as medical technicians skilled in cardiopulmonary resuscitation techniques.
Factors affecting the determination of exercise test results
(A) false positive reaction: the incidence of false positive exercise test detection is about 10% to 20% (6 ). The factors affecting the following: (1) female; (2) drugs: the most common is digitalis, quinidine or other antiarrhythmic drugs, thiazides and methyldopa, etc., the impact of such drugs can be eliminated after a few weeks of discontinuation. (3) Electrolyte disorders, such as hypokalemia, etc. (4) After a full meal or glucose injection. (5) Transitional ventilation. (6) Thoracic deformity, such as funnel chest. (7) Anemia. (8) Postural changes, generally deeper ST-segment decrease in the prone position than in the standing position, involving a wide range of leads. (9) Atrial repolarization wave effects. The reasons for the high false positive rate in women include abnormal hemoglobin metabolism; low erythrocyte pressure volume and total red blood cells in circulation; high pulmonary and body circulatory resistance; high SBP×HR; low plasma ß-endorphin level; easy transitional ventilation and relatively low blood potassium.
(b) False-negative reactions: The overall incidence of false negatives is about 12% to 37%, with more men than women (6). Influencing factors are: (1) drugs: anti-anginal drugs (ß-blockers, calcium antagonists and nitrates); (2) those with old myocardial infarction or only a single coronary artery lesion (mostly in the right coronary artery single lesion); (3) insufficient exercise, about 1/5 of the subjects exercise with paradoxical increase in heart rate, while the end point of exercise is to reach the set expected heart rate as the limit, paradoxical increase in heart rate is not due to ischemia.
Therefore, the patient’s gender, medications and other systemic diseases should be fully considered when judging the test results to facilitate a correct diagnosis.
Contraindications to exercise testing
(1) unstable angina pectoris or early acute myocardial infarction; (2) severe arrhythmias and high atrioventricular block; (3) left heart insufficiency and decompensated heart failure; (4) known coronary left main artery disease; (5) uncontrolled severe hypertension; (6) other cardiovascular disorders such as severe aortic stenosis and severe hypertrophic obstructive cardiomyopathy; (7) after installation of a fixed frequency pacemakers; (8) the presence of drug effects or electrolyte disturbances; (9) other serious illnesses or physical failure.
Safety and risks of exercise testing
Exercise testing has an excellent safety record. The risks depend on the clinical characteristics of the patient being examined. Large series of data suggest that life-threatening complications can occur with exercise testing, including, among others, myocardial infarction, acute pulmonary edema, and dangerous arrhythmias. In the non-selected patient population, the overall incidence of exercise test complications is 1.2 to 2.4/10,000, with ventricular fibrillation predominating, accounting for approximately 50% or more; the incidence leading to death is approximately 0.24 to 1.0/10,000 (7). The risk increases if the exercise test is performed shortly after the onset of acute ischemia. A statistic of 151,941 patients with AMI who underwent an exercise test over a four-week period showed a mortality rate of 0.03% (8). Clinical and coronary angiography in survivors of sudden death due to exercise testing showed that sudden death is thought to be associated with a reduction in coronary blood flow or acute occlusion of the coronary arteries caused by excitation of enhanced transient platelet aggregation during exercise, coronary artery spasm during exercise, atheromatous plaque rupture and bleeding, and thrombosis. Severe arrhythmias sometimes occur after the endpoint of the exercise test and may be related to the continued release of catecholamines even up to 10 times as high after exercise as at rest, which in turn leads to myocardial ischemia. Therefore, it is important to monitor continuously for several minutes after exercise until the heart rate and blood pressure return to pre-exercise levels. It can be seen that exercise test has certain risks, so it is necessary to strictly grasp the indications, contraindications and termination indications of exercise test examination, correctly estimate the condition, closely monitor, and have the equipment and skills for rapid and effective cardiopulmonary resuscitation in order to reduce the occurrence of complications and avoid death.
Evaluation of exercise test for diagnosis of coronary artery disease
According to a comprehensive analysis of the results of exercise testing in 5046 patients with coronary artery disease confirmed by imaging, it had a sensitivity of 70% and a specificity of 79% for the diagnosis of coronary artery disease. gianrossi et al. performed a retrospective analysis of data from 24474 patients reported in 1147 publications, who had both coronary angiography and exercise testing. The results showed that the average sensitivity of the exercise test was 68% (23%-100%) and the average specificity was 77% (17%-100%) (9); for multiple lesions, the average sensitivity and specificity were 81% (40%-100%) and 66% (17%-100%), respectively (10); for left main or 3-branch lesions, the weighted average sensitivity and specificity were 86% ±11% and 53% ±24%, respectively (11). It can be seen that the plate motion test is a more sensitive and specific method for the diagnosis of coronary artery disease, especially in patients with multi-branch lesions. Therefore, it is an accurate method for early diagnosis of coronary artery disease. However, its diagnostic value is still different for patients with different types of coronary artery disease.
(1) Typical angina, confirmed by coronary angiography, a history of typical angina in men with both ischemic ST changes on ECG during angina attack, the predictive accuracy of the plate exercise test for coronary artery disease can be as high as 95% or more, while for women with similar conditions, the predictive accuracy is only about 70%. In men, the false-positive rate of the exercise test is low (about 8%) and the false-negative rate is as high as 37%. Therefore, in men with a history of typical angina pectoris, the value of the exercise test is limited and it is not a necessary diagnostic tool. In women, the false-negative rate of exercise test is low (about 12%) and the false-positive rate is high (about 67%), so in women with a history of typical angina, a positive exercise test does not necessarily increase the reliability of the diagnosis.
(2) Atypical angina. Men with a history of atypical angina are 2.5 times more likely to have coronary artery disease than women with a similar history, although they are less likely to have coronary artery disease. A positive test at this point would help in the diagnosis of coronary artery disease in men, and a negative test would not help much in negating the diagnosis. In women with an atypical history, the accuracy of the exercise test for predicting coronary artery disease is only 40%, and a positive diagnostic value is not limited, while a negative result is helpful for a negative diagnosis.
(3) Complete bundle branch conduction block or preexcitation syndrome, such patients have abnormal ventricular depolarization sequence, producing corresponding abnormal repolarization process, then the ECG appears secondary S-T changes, which may mask myocardial ischemia or produce similar ischemic response, and the results of exercise test detection are not easy to distinguish, thus not helpful for etiologic diagnosis.
(4) The extent of vascular lesions The abnormal ST changes caused by exercise are proportional to the number of coronary artery branches involved in R75% of coronary artery stenosis. If the percentage reduction in vessel diameter measured by coronary angiography is used as the basis, the exercise test has a predictive sensitivity of 61% and specificity of 73% for a coronary lesion with a diameter stenosis of R60%. The positive rate of the exercise test was 40% to 84%, 63% to 91% and 76% to 100% in single, double, triple or left main coronary lesions, respectively (12). False-negative rates were 57%, 34%, and 8%, respectively. The false-negative rate for left main stem lesions was only 1%. If the load exercise time is 5 during the exercise test, SBP×HR peak Q23000 or blood pressure decrease are highly suggestive of multibranch or left main stem lesions (13). In conclusion, the more abnormal variables measured in the exercise test, the greater the likelihood of severe or multibranch lesions.
Prognostic evaluation of exercise test
1. Asymptomatic population: the incidence of abnormal ECG on exercise in asymptomatic middle-aged men is 5% to 12% (14 ). The risk of cardiac events such as angina pectoris, myocardial infarction and death was more than 9 times higher in men with abnormal tests than in those with normal tests; however, only 1/4 of them will suffer a cardiac event during the 5-year follow-up, and most often it is angina pectoris. In the Baltimore Longitudinal Study of Aging, Fleg et al. performed extreme-activity flat-panel exercise ECG and 201TL myocardial perfusion imaging in 407 asymptomatic volunteers with a mean age of 60 years; 6% of those with positive results on both tests had a 48% incidence of cardiac events during a mean 4-year follow-up (15). Therefore, only the combination of the two tests can accurately predict the occurrence of their subsequent cardiac events.
2. Symptomatic individuals Patients with excellent exercise tolerance (e.g., >100 MET) usually have an excellent prognosis regardless of the anatomical extent of the coronary lesion. In the CASS study, Weiner et al. studied the role of exercise testing in 4083 patients with confirmed or suspected coronary artery disease who were treated with medication and found that the subgroup of high-risk patients (12% of the patients) whose exercise load Bruce class III and whose exercise ECG remained normal had an annual mortality rate during the 4-year follow-up period
3. asymptomatic myocardial ischemia The presence of exercise-induced ischemic ST depression in patients with diagnosed coronary artery disease, regardless of the presence or absence of angina attacks during exercise, suggests an increased risk of future cardiac events. information from the CASS database shows that the 7-year survival rates of patients with asymptomatic and symptomatic exercise-induced myocardial ischemia are the same when stratified by coronary anatomy and left ventricular function (17).
This shows that the active plate exercise test examination can more accurately predict the prognosis of various populations and provide guidance for the early diagnosis of coronary heart disease.
III. Drug loading echocardiography test
The basic principle of diagnosing coronary artery disease by loading echocardiography is that myocardial ischemia is induced by intravenous drug injection, and the abnormal motion of the left ventricular wall segments (16-segment division of the left ventricle of the American Society of Echocardiography) of the heart before and after comparing drug administration is directly observed by echocardiography, and if there is abnormal motion of the ventricular wall segments, it is considered that there is myocardial ischemia and coronary artery disease is diagnosed. The commonly used drugs are pansentin, adenosine and dobutamine.
(i) Bipyridamole (Pansentine) stress echocardiography test
Dipyridamole (Pansentin), when injected intravenously, inhibits the uptake and blocks the cell membrane transport of endogenous adenosine by cardiac muscle and vascular smooth muscle cells, and reduces adenosine fire extinguishment by inhibiting plasma adenosine deaminate, resulting in a 2-fold increase in intraplasma adenosine concentration. Adenosine has a strong vasodilating effect, but its dilating effect is limited to the resistance vessels in the non-ischemic area, which causes a significant decrease in vascular resistance in the non-ischemic area compared with the ischemic area, resulting in an increase in blood flow in the non-ischemic area and a decrease in blood flow in the ischemic area, causing the phenomenon of “blood theft” and thus causing an ischemic response. Echocardiography directly observes the abnormal motion of ventricular wall segments to determine the site and extent of ischemia. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of this test were 61%, 91%, 74%, 90%, and 64%, respectively, for the diagnosis of coronary artery disease (18). It can be seen that the test has low sensitivity and negative predictive value, and even if the test is negative, coronary artery disease cannot be excluded.
(ii) Dobutamine loading echocardiography test
Dobutamine is a ß-agonist that acts selectively on ß1-receptors and weakly on ß2 and α-receptors, causing a dose-related increase in heart rate and increased myocardial contractility. When the dose is greater than 20 mg/kg/min heart rate increases, blood pressure increases, myocardial contractility is excessively enhanced, myocardial oxygen consumption increases, causing myocardial ischemia in the lesioned vascular area and abnormal systolic function, and at this time, echocardiography is used to directly observe ventricular wall segmental motion and determine the site and extent of ischemia. Clinical trials have confirmed its sensitivity, specificity, accuracy, positive predictive value and negative predictive value of 88%, 80%, 84%, 85% and 83%, respectively, for the diagnosis of coronary artery disease (18). This method can be seen to be superior to the pansentine echocardiography test. However, the side effects are increased at high doses of dobutamine and may be unsafe in some patients with coronary artery disease. Therefore, from the clinical point of view, the most simple ECG exercise test should still be preferred for the diagnosis of myocardial ischemia, except for patients who cannot undergo exercise testing.
(C) Adenosine loading echocardiography test
Exogenous adenosine acts directly on vascular endothelial cells and smooth muscle cells to cause vasodilation, and its strength of vasodilation to increase blood flow is positively correlated with the dose, and the same dose has a stronger effect compared with that of pansentin, with a short half-life (10 seconds) and fast action. The accuracy was similar to that of the Pansentine test.
IV. Nuclear myocardial perfusion imaging
Nuclear myocardial perfusion imaging can be divided into 201TL myocardial perfusion imaging, 99mTC-labeled compound myocardial perfusion imaging, etc. according to the different imaging agents, and into exercise load myocardial perfusion imaging, drug load myocardial perfusion imaging, and resting myocardial perfusion imaging according to whether the patient is exercising or drug-loaded.
(A) Pathophysiology of myocardial perfusion imaging
Human coronary arteries have a strong reserve function of blood perfusion. The degree of myocardial perfusion is reduced due to coronary artery stenosis, which mainly depends on the degree of stenosis and the demand of myocardial metabolism at that time, and is generally divided into the following cases.
1.Coronary artery stenosis
2.Coronary artery stenosis >50%.
3.Coronary artery stenosis >80%.
4.Coronary artery stenosis >95%, where the perfusion is severely impaired at rest.
The above situation shows that myocardial perfusion imaging has different manifestations depending on the degree of coronary artery stenosis, and myocardial perfusion imaging may be positive at rest for 50% and 80% of coronary artery stenosis, and the positive rate of exercise test is higher.
(B) Ideal conditions for myocardial perfusion imaging agent
The uptake of myocardial perfusion imaging agent by myocardial tissue is proportional to the local myocardial blood perfusion, with more myocardial blood flow, more myocardial uptake of imaging agent, and less myocardial blood flow, less uptake. Characteristics of the ideal myocardial perfusion developer.
1, the uptake of the developer must be proportional to the coronary blood flow, that is, the uptake of the developer by the myocardial tissue and the local myocardial blood supply are consistent, and the amount of local myocardial uptake of the developer responds to normal myocardial perfusion or ischemia.
2. The uptake rate of the myocardium for the first time through the coronary artery should be as high as possible. Ideally, 100% of the myocardial contrast agent should be taken up by the myocardium when it passes through the coronary capillary bed for the first time, so that it can truly reflect the distribution of myocardial blood flow when the contrast agent is injected intravenously.
3, The mechanism of contrast uptake should be independent of myocardial cell metabolism.
4.The concentration and distribution of the developer taken up by the myocardium should be stable within a certain period of time. Because it takes 15-30 minutes to perform an image acquisition, if the radioactive activity changes during this time, there will be errors and it will not reflect the real situation of the patient.
5. The uptake of the imaging agent by the heart should be specific. This is difficult to do, so far, no imaging agent has been found that will only be specifically concentrated in the heart and not taken up by other tissues.
6, reasonable price, convenient supply, safe application, no toxic side effects on human body.
(C) Myocardial perfusion contrast agent
At present, the domestic imaging agents used for SPECT myocardial perfusion imaging are 201TL and 99mTC-MIBI.
1.201TL
201TL is an accelerator-generated radionuclide with a physical half-life of 73 hours. The contrast agent is injected intravenously for 5-10 minutes to reach equilibrium in the whole body, at which time the initial distribution in the myocardium is the initial distribution, and after 3-4 hours it shows redistribution.
(1) Initial distribution The initial distribution of 201TL in myocardial cells depends on coronary blood flow and cell membrane Na-K ATPase activity. In the resting state, normal myocardium showed 201TL
uptake is 85%, and during exercise test, myocardial blood flow increases, and if there is no stenotic lesion in coronary arteries and cardiomyocytes survive, the 201TL entering cardiomyocytes increases, and when there is stenotic lesion in coronary arteries and cardiomyocytes survive, the blood flow in diseased coronary arteries does not increase, resulting in no or little increase in 201TL uptake in ischemic myocardium. In this way, the difference in 201TL uptake reflects the perfusion of normal and ischemic myocardium.
(2) 201TL redistribution Redistribution is an important characteristic of 201TL myocardial perfusion imaging. 201TL is distributed in the myocardium in a dynamic process; after the peak of 201TL uptake, the myocardium continuously elutes 201TL into the blood, and the radioactive activity gradually decreases, generally reaching a new equilibrium after 3 to 4 hours. The elution rate of 201TL from ischemic myocardium is lower than that of normal myocardium, therefore, the difference in 201TL concentration between ischemic and normal myocardium is reduced, forming a relative refill phenomenon, i.e., 201TL redistribution occurs on myocardium, which is a characteristic manifestation of myocardial ischemia.
Features of 201TL: 1), easy to use, no need for temporary labeling process, 2) patient receives one injection, load test and delayed visualization examination can be completed on the same day. 3) expensive; 4) long half-life, small recommended application dose, image quality is not as good as 99mTc-MIBI, which is still widely used abroad.
2.99mTc-labeled myocardial perfusion imaging agent
Compared with 201TL, 99mTc physical half-life is short (6 hours), radiation is small, larger doses can be given, and image quality is good; the first uptake rate of 99mTc-MIBI by myocardial cells is 60%-70%, and its distribution is proportional to coronary blood flow under certain conditions. Under ischemic conditions, the uptake of 99mTc-MIBI by myocardium was reduced. Whether injected under exercise or at rest, the distribution of 99mTc-MIBI in the myocardium can remain fairly stable for several hours, and imaging is generally appropriate at 1-2 hours of administration.
(D) Imaging methods
1, resting imaging Resting 201TL myocardial perfusion imaging can be performed 10-30 minutes after intravenous injection of 201TL. If 99mTc-MIBI is used, 1.5~2 hours after injection is appropriate.
2, load test imaging Coronary arteries have a strong reserve function, even if there is a stenotic lesion in the coronary artery anatomy, due to the coronary artery’s own regulation function, the resting state can still maintain normal blood flow, and myocardial contraction function is not abnormal, only when exercise or drug load, the lesion will show insufficient coronary artery blood flow reserve. If a certain amount of exercise load is given to the patient, the normal coronary arteries will automatically dilate to adapt to the increase of myocardial oxygen consumption and increase the blood flow by more than three times, while the blood flow in the narrowed coronary arteries cannot increase, resulting in insufficient local myocardial perfusion and imbalance of myocardial oxygen supply and demand, causing myocardial ischemia, and the nuclear myocardial perfusion imaging shows a sparse distribution or defect of local myocardial radioactivity, which can be restored to normal during resting imaging. The myocardial perfusion imaging shows a localized sparse or defective distribution of myocardial radiation, which can be restored to normal on resting imaging. Thus, exercise or pharmacological stress tests reflect the relative reserve function of the coronary arteries and provide a more accurate indication of pathophysiological significance than anatomical stenosis.
Stress tests include two categories: physiological stress tests such as exercise tests and drug stress tests. Exercise tests are currently the most commonly used method for myocardial perfusion imaging, accounting for about 60% to 70% of the total. Drug tests (about 30%) are used only when the patient cannot perform exercise tests for some reason. Drugs commonly used for drug loading tests include pansentin, adenosine, and dobutamine.
(E) Diagnostic value of coronary artery disease
Nuclear myocardial perfusion imaging mainly shows the consequences of myocardial ischemia caused by coronary artery stenosis, i.e., whether the local myocardium is ischemic, rather than directly evaluating the anatomical stenosis of the coronary artery itself. It has been routinely used for early diagnosis of coronary artery disease and to determine the site, extent and degree of myocardial ischemia.
In patients with a clinical history of chest pain or ST-T changes in the ECG that are suspected of having coronary artery disease, coronary angiography is required, and myocardial perfusion tomography has a “gatekeeper” effect (20). Patients with normal myocardial perfusion imaging under appropriate exercise or drug load can basically exclude significant myocardial ischemia, and the prognosis is good, so coronary angiography is not needed. Otherwise, coronary angiography is required.
1, Generally speaking, if 201TL or 99mTc-MIBI exercise load myocardial perfusion imaging, myocardial segments distributed along the coronary artery branch blood flow, there is obvious radioactive sparing or defect, and in 201TL delayed imaging or 99mTc-MIBI resting imaging shows radioactive filling in the original defect area, it shows myocardial ischemia, which can be diagnosed as coronary artery disease, and its positive predictive value is 90% to The positive predictive value is more than 90% to 95% (21). Massachusetts General Hospital in the United States summarized a total of 1897 cases of 201TL planar imaging with a sensitivity of 83% and specificity of 91% for the diagnosis of coronary artery disease, while the sensitivity of exercise ECG was 60% and specificity was 80%. Fu Wai Hospital reported a comparative study of 50 cases of 201TL with myocardial perfusion planar imaging, ECG and coronary angiography, and the compliance rate of 201TL with coronary angiography was 94%, while the compliance rate of ECG with coronary angiography was 80% (22. Liu, X. J., et al. Evaluation of the specificity of nuclear myocardial perfusion imaging for the diagnosis of coronary heart disease. (Chinese Journal of Nuclear Medicine; 1992, 12: 135). In addition, the overall agreement between the extent of lesions detected by 201TL myocardial imaging and the extent of coronary angiographic lesions was 93.5%, compared with 87.1% for ECG. 99mTc-MIBI myocardial perfusion imaging showed similar results to 201TL, and the sensitivity and specificity of 505 exercise-rest 99mTc-MIBI myocardial tomography images for the diagnosis of coronary artery disease were 92.5% and 71.1 %, respectively. In 115 cases of 99mTc-MIBI myocardial SPECT imaging with coronary angiography control analyzed at Fu Wai Hospital, the sensitivity was 96%, specificity 87.9%, positive predictive value was 95%, and negative predictive value was 90.6% (23).
Drug-loaded myocardial perfusion imaging
Drug tests are used when the patient is unable to perform an exercise test for one reason or another (approximately 30% of cases). Drugs commonly used for drug loading tests include pansentin, adenosine, and dobutamine. The mechanism of drug action is described in the drug-loaded echocardiogram, and the contrast agents are 201TL and 99mTc-MIBI. clinical trials have shown that
2, prognostic evaluation A large amount of information proves that some parameters in myocardial perfusion imaging are important for determining the relative risk of coronary artery disease and for prognostic evaluation.
(1) Prognostic significance of normal imaging. normal 201TL myocardial perfusion imaging is an important indicator of good patient prognosis. brown et al. conducted a 46-month follow-up of 100 patients and showed that the annual incidence of cardiac events (cardiogenic death, myocardial infarction) with normal 201TL myocardial perfusion imaging was only 0.8%, even though the coronary arteries proved the presence of significant coronary stenosis. The good prognosis of normal 201TL myocardial perfusion imaging is also certain, with an annual cardiac event rate of only 0.7% to 1.1% (24).99 Similar findings have been reported for 99mTc-MIBI myocardial tomography imaging, where Stratmann et al. followed 534 patients for 132 months, and the incidence of future cardiac events in 179 patients with normal motion imaging Berman et al. followed 1178 patients with normal exercise myocardial perfusion imaging for 20 months, and there were only 2 cardiac deaths, 5 nonfatal myocardial infarctions, and 11 revascularizations, with an overall incidence of 1.5%.
In conclusion, the incidence of future cardiac events was about 1% in those with normal loading myocardial perfusion imaging, and the patients had a good prognosis; therefore, normal myocardial perfusion imaging has an important predictive value for the occurrence of future cardiac events.
(2) Prognostic significance of reversible defects: Ladenhein et al. performed a 12-month follow-up of 1689 patients, and the number and severity of reversible defects in 201TL myocardial perfusion imaging were the best predictors of future cardiac events (26). machecourt equals 1926 cases with up to 33 months of follow-up and found that the 201TL myocardial perfusion imaging defects The number was strongly associated with the occurrence of cardiac death and fatal myocardial infarction, and the size of the defect was the most important predictor of the occurrence of future cardiac events.
(3) Prognostic significance of fixation defects: The presence of fixation defects on exercise or drug-loaded imaging and resting imaging indicates that the local myocardium may be necrotic or in hibernation, a condition that may have similar prognostic value to reversible defects and needs to be further investigated.
3. Selection of loading nuclide myocardial perfusion imaging When performing loading tests for the diagnosis of coronary artery disease, the baseline level of the ECG should be considered. Extreme exercise induced ST-T changes in patients with normal ECG baseline have diagnostic added value. It has been observed that those with normal ST-T segments after extreme exercise almost invariably have normal exercise myocardial perfusion images. Therefore, it is true that myocardial perfusion imaging does not provide additional new information. However, a significant number of patients with positive or suspected positive exercise ECGs have normal exercise myocardial perfusion images. Therefore, the best cost/benefit ratio can be achieved by using exercise ECG as the test of choice in certain patient groups with a normal baseline ECG and doing exercise myocardial perfusion imaging only in patients with abnormal exercise ECG. However, Nallamothu et al. found that SPECT imaging was superior to exercise ECG for the detection of coronary artery disease in patients with moderate to high likelihood of coronary artery disease and a normal ECG baseline.
V. Multi-row CT for the diagnosis of coronary artery disease
New advances in imaging have shown that multi-row CT and electron beam CT can clearly show the coronary artery lumen and even know the density of atheromatous plaque. It can show the site and degree of coronary stenosis, and the sensitivity and specificity for the diagnosis of luminal stenosis are 87.5% and 97.2%, respectively, and the positive predictive value and negative predictive value are 82.4% and 98.1%, respectively. A comparative study between 64-row CT and 99mTc- tetrofosmin-SPECT showed that the sensitivity, specificity, accuracy, positive predictive value and negative prognostic value of 64-row CT in the diagnosis of coronary lesions were 76%, 95%, 94%, 50% and 99%, respectively (27). It can be seen that the negative exclusion value of multi-row CT is greater and can avoid unnecessary invasive coronary angiography, but is more expensive than exercise testing.
In clinical patients with coronary artery disease with left bundle branch, ECG and exercise ECG tests cannot make a correct diagnosis, while a clinical trial confirmed that the sensitivity, specificity, accuracy, positive predictive value and negative predictive value of multislice CT for the diagnosis of coronary artery disease were 97%, 95%, 95%, 93% and 97%, respectively (28). Therefore, multislice CT is an accurate method for diagnosing patients with coronary artery disease with left bundle branch. If no coronary abnormalities are seen on multi-row CT, coronary angiography can be completely omitted.
Multi-row CT is not only an accurate diagnosis of coronary artery disease, but also an accurate prognosis. A pilot study of 100 patients who underwent multi-row CT found that 80 (80%) had plaque in the coronary arteries, and at 16 months of follow-up, the incidence of cardiac events (including cardiac death, nonfatal myocardial infarction, unstable angina requiring hospitalization, and revascularization) at one year was 30 times higher than in patients without plaque (30% vs. 0%); the incidence of cardiac events in patients with coronary stenosis was The incidence of cardiac events was significantly higher in patients with coronary stenosis than in those without (63% versus 8%). Multiple regression analysis showed that the number of obstructive coronary plaque segments, obstructive coronary artery disease, stenosis in LAD/LM and the number of segments with mixed plaque were strong predictors of cardiac events (29).
Multi-row CT examination is safe except for individuals who are allergic to contrast agents, especially in some patients with recent atypical chest pain, when it is difficult to exclude unstable angina, exercise test examination has certain risks and may induce myocardial infarction or even death, when CT examination is the safest choice to clarify coronary lesions and avoid the occurrence of exercise test-induced cardiac events; if CT examination reveals coronary artery stenosis, further coronary angiography will be performed; otherwise, the diagnosis of coronary artery disease can be basically excluded.
In conclusion, there are many methods for early diagnosis of coronary artery disease, and the accuracy of exercise nuclear myocardial perfusion imaging is the best, followed by exercise plate test, and the accuracy of general electrocardiography is low. Multi-row CT examination is used to evaluate coronary artery lumen plaque and stenosis, and the accuracy of negative exclusion is high. If combined with exercise test and myocardial perfusion imaging, the diagnostic accuracy of coronary artery disease can be improved and unnecessary coronary angiography can be avoided.