Asymptomatic myocardial ischemia

Introduction to asymptomatic myocardial ischemia Asymptomatic myocardial ischemia, also known as painless myocardial ischemia or occult myocardial ischemia (SMI), is an objective evidence of myocardial ischemia (ECG activity, left ventricular function, myocardial perfusion, and myocardial metabolism, etc.) Abnormal), but lack of chest pain or subjective symptoms associated with myocardial ischemia. Asymptomatic myocardial ischemia is very common in coronary heart disease, and myocardial ischemia can cause reversible or permanent damage to the heart muscle, and cause angina, arrhythmia, pump failure, acute myocardial infarction or sudden death. Therefore, it is a coronary heart disease. Independent types have attracted more and more attention. basic knowledge Sickness ratio: 0.05% Susceptible people: no special people Mode of infection: non-infectious Complications: myocardial infarction

Asymptomatic causes of myocardial ischemia

(1) Causes of the disease

A large number of epidemiological studies of coronary atherosclerotic heart disease have shown that the following factors are closely related to the onset of coronary heart disease, which are known as coronary heart disease susceptibility factors (also known as risk factors):

1. Age: This disease is more common in people over 40 years of age. The occurrence of atherosclerosis can begin in children, and the incidence of coronary heart disease increases with age.

2. Gender: Men are more common, the ratio of male to female incidence is about 2:1, because estrogen has anti-atherosclerosis, so women's incidence after menopause increases rapidly.

3. Family history: Patients with coronary heart disease, diabetes, hypertension, and family history of hyperlipidemia have an increased incidence of coronary heart disease.

4. Individual type: Type A personality (strong competition, competitive) There is a high prevalence of coronary heart disease, and people with excessive mental stress are also susceptible to disease, which may be related to the long-term high concentration of catecholamines in the body.

5. Smoking: It is an important risk factor for coronary heart disease. The prevalence of coronary heart disease in smokers is 5 times higher than that of non-smokers, and it is proportional to the amount of smoking. The blood carbon monoxide hemoglobin is increased in smokers, and nicotine in blood vessels shrinks blood vessels. Arterial wall damage due to lack of oxygen in the arterial wall.

6. Hypertension: an important risk factor for coronary heart disease. Hypertensive patients with coronary heart disease are four times more likely to have normal blood pressure. 60% to 70% of patients with coronary heart disease have hypertension, and the shear stress is increased when arterial pressure is increased. Changes in sidewall pressure cause damage to the intima of the blood vessels, and elevated blood pressure causes plasma lipids to penetrate into the endovascular cells, thereby causing platelet accumulation and smooth muscle cell proliferation, and atherosclerosis occurs.

7. Hyperlipidemia: Hypercholesterolemia is an important risk factor for coronary heart disease. Hypercholesterolemia (total cholesterol >6.76mmol/L, low-density lipoprotein cholesterol >4.42mmol/L) is higher than normal (total cholesterol) <5.2mmol/L) The risk of coronary heart disease increased by 5 times. Recent studies have shown that hypertriglyceridemia is also an independent risk factor for coronary heart disease. High-density lipoprotein has a protective effect on coronary heart disease, and its value is reduced. Coronary heart disease, high-density lipoprotein cholesterol and total cholesterol ratio <0.15, is a valuable predictor of coronary atherosclerosis, recent studies have found that serum -lipoprotein [Lp ()] concentration increased (> 0.3g/L) is also an independent risk factor for coronary heart disease.

8. Diabetes: It is an important risk factor for coronary heart disease. The risk of coronary heart disease is 2 times higher than that of normal people. The risk of coronary heart disease in women with diabetes is 3 times higher than that of male patients, and heart failure is prone to occur. And death, high blood sugar, the increase of glycosylated low-density lipoprotein in the blood, the degradation metabolism of the low-density lipoprotein receptor pathway is inhibited; at the same time, hyperglycemia also damages the intima, combined with diabetes often associated with lipids Abnormal metabolism, so diabetics are prone to coronary heart disease.

9. Obesity and exercise are too small: 1 standard body weight (kg) = height (cm) - 105 (or 110), 2 body mass index = body weight (kg) / (height m) 2, over 20% of standard body weight or body mass index > 24 people are called obesity. Although obesity is not as important as hypertension, hyperlipidemia, and diabetes, obesity can indirectly affect coronary heart disease by promoting the development of these three factors. Exercise can regulate and improve vascular endothelial function. In patients with coronary heart disease, the establishment of coronary collateral circulation, the amount of exercise is less likely to cause obesity, so the importance of treating obesity and increasing the amount of exercise should be fully recognized.

10. Other:

(1) drinking: long-term high-drinking high-alcohol liquor has damage to the function of heart, blood vessels, liver and other organs, which can cause alcoholic cardiomyopathy, cirrhosis, and hypertension; and moderately drink low-quality colored wine (for example) Wine) can reduce the risk of coronary heart disease, because drinking alcohol can increase the concentration of high-density lipoprotein.

(2) Oral contraceptives: long-term oral contraceptives can increase blood pressure, increase blood lipids, abnormal glucose tolerance, and at the same time change the coagulation mechanism and increase the chance of thrombosis.

(3) Eating habits: eating high calorie, high animal fat, high cholesterol, high sugar diet is prone to coronary heart disease, and other changes in the intake of trace elements.

(two) pathogenesis

It is unclear why some patients with evidence of significant myocardial ischemia do not show chest pain, while others have chest pain.

Maseri believes that the reason for SMI is that the patient's sensitivity to pain is reduced, and there are coronary microvascular dysfunction. There is a protective pain warning system in the body. When the myocardium is damaged by ischemia, the patient is reminded to stop the ischemia by the pain. Activities to avoid further aggravation of myocardial damage and reduce potential fatal arrhythmias; and when the patient's alarm system is fully or incompletely defective, patients with coronary heart disease may be completely asymptomatic or partially asymptomatic during myocardial ischemic attacks, The specific mechanism involves the following three links:

1. Autonomic nervous system damage sensory peripheral nerves: such as diabetes complicated with neuropathy, cardiac denervation and so on.

2. Increased pain threshold: By measuring endorphin in plasma and cerebrospinal fluid, it was found that in patients with SMI, plasma leucine and -endorphin were higher in patients with myocardial ischemic attack, suggesting that A large number of endogenous substances (endorphins) can be produced to increase the pain threshold.

3. Ischemic injury: Mild type II SMI patients may have seizures due to milder myocardial ischemia, smaller ischemic range, and shorter duration. Some SMI patients have continuous ECG tracing in 24 hours. Myocardial ischemia in a short period of time is asymptomatic; while myocardial ischemia for a long time has angina pectoris, but it has also been found that there is no significant difference in ST segment changes between painful and painless. Therefore, it is not clear that the above three species The point of possibility, or the combination of the three possibilities, plays a major role in the onset of SMI, and may also be the result of multi-factor participation, but the exact mechanism remains to be elucidated.

In patients with asymptomatic coronary heart disease, pathological examination showed no obvious histomorphological changes in the myocardium. At this time, the endothelial cells showed mild damage to the endothelial cells, platelet adhesion, connective tissue hyperplasia, smooth proliferation or displacement of smooth muscle cells, and lipid deposition. The coronary lumen presents with mild stenosis and myocardial ischemia.

Asymptomatic myocardial ischemia prevention

Primary prevention

For people who do not have coronary heart disease, intervention of coronary heart disease susceptibility factors to prevent the occurrence of coronary heart disease, this work is a very difficult task, starting from the child, adolescents should start the prevention of coronary heart disease.

Recognized risk factors for coronary heart disease include men, family history of premature coronary heart disease (parents, brothers with defined myocardial infarction or sudden death before age 55), smoking (current cigarette smoke 10 / d), hypertension , diabetes, HDL-C concentration was determined by repeated determination <0.9mmol / L (35mg / dl), a clear history of cerebrovascular or peripheral vascular occlusion, severe obesity (overweight 30%), in many coronary heart disease Some of the factors are immutable factors: age, gender, family history of cardiovascular and cerebrovascular diseases; others are modifiable factors: high blood pressure, high blood fat, high blood sugar, smoking, eating habits, obesity, etc. In order to prevent coronary heart disease, we should actively control changeable factors, control weight, moderate exercise, quit smoking, low-fat and low-salt diets are important health measures, effective control of hypertension, hyperlipidemia and diabetes are more urgent. Tasks, taking positive preventive measures, the incidence of coronary heart disease can be significantly reduced.

2. Secondary prevention

For those who have coronary heart disease, prevent the development of the disease and sudden death, for those who have not had myocardial infarction, should actively prevent the occurrence of myocardial infarction.

For the secondary prevention of patients with myocardial infarction, the following aspects should be included: health education for patients and their families; targeted measures for risk factors for coronary heart disease to prevent the progression of coronary artery disease; drug or surgery for prevention and treatment of myocardium Ischemia, left ventricular dysfunction or severe arrhythmia; those who are at high risk for re-infarction or sudden death should minimize the risk factors.

In recent years, the meaning of the ABC program in the prevention and treatment of coronary heart disease can be summarized as follows: AAspirine (aspirin), meaning that anticoagulant and antiplatelet drugs should be used in the prevention and treatment of coronary heart disease. Clinicians believe that it also contains the use of angiotensin-converting enzyme inhibitor (ACEI); B - Blocker (beta blocker); C - Cholesterol, which means lowering cholesterol.

Asymptomatic myocardial ischemia complications Complications, myocardial infarction, sudden death

Asymptomatic myocardial ischemia increases the risk of myocardial infarction and sudden death.

Asymptomatic myocardial ischemia symptoms Common symptoms Heartbeat during sleep accelerate myocardial infarction Myocardial cells edema angina and sudden coronary artery spasm

Spontaneous asymptomatic myocardial ischemia

SMI occurs in daily activities. Dynamic electrocardiogram monitoring found that about 3/4 of these spontaneous SMIs are characterized by transient ST-segment depression and clinical asymptomatic, usually occurring during non-physical activities or mental activities in daily life. The rate of myocardial ischemia is much slower than that of the active plate test, which is about 20 times slower, about 50% slower than the basal heart rate, suggesting that SMI is a decrease in coronary blood supply rather than myocardium. Increased demand, in addition, the frequency of SMI attacks, like symptomatic myocardial ischemia, has a typical circadian cycle change, which is most common in the morning. This rhythm change is consistent with various biological processes such as catecholamine secretion. Spontaneous SMI patients seem to be healthy, but often with sudden death, myocardial infarction as the first clinical manifestation.

2. Induced asymptomatic myocardial ischemia

SMI occurs in the cardiac load test. In exercise-induced myocardial ischemia, about 1/3 of this type of asymptomatic myocardial ischemia, induced SMI is characterized by exercise ST-segment depression, and the usual ECG can be completely normal, suggesting Such patients are the result of increased myocardial oxygen consumption based on fixed coronary stenosis.

3. Asymptomatic myocardial ischemia in patients with symptoms of coronary heart disease

Can be seen in the following situations: 1 about 40% of patients with angina pectoris have painless myocardial ischemia in exercise test; 2 patients with angina pectoris have persistent ST-segment depression during pain episodes; 3 patients with angina pectoris under drug treatment Asymptomatic ST-segment depression; 4 asymptomatic ST-segment depression after acute myocardial infarction.

Pepine divides patients with this disease into two categories:

1. Completely asymptomatic: These patients usually have no clinical symptoms at all, and may have transient myocardial ischemia during accidental examination. Sometimes, no evidence of ischemia can be found before birth. Only after death, severe coronary artery is found. The lesions and focal fibrosis areas were identified as having myocardial ischemia before birth.

2. Patients with coronary artery disease or coronary artery spasm symptoms and signs: divided into: 1 old myocardial infarction, asymptomatic; 2 sometimes angina; 3 sudden death or near death, these patients have the above symptoms , electrocardiogram, nuclides, or other tests show temporary myocardial ischemia without symptoms. These ischemic episodes are more common than angina pectoris, making them a more common form of myocardial ischemia in patients with coronary heart disease.

Asymptomatic myocardial ischemia

1. There may be elevated blood lipids: typical total cholesterol, triacylglycerol, low density lipoprotein increased; high density lipoprotein decreased.

2. Some patients may have elevated blood sugar.

After myocardial ischemia, a series of metabolic and functional changes occur in cardiomyocytes. These pathophysiological changes can be detected by a variety of non-invasive and invasive methods to reflect the occurrence of myocardial ischemia. Currently, the commonly used methods in clinical practice are:

1. Electrocardiogram: The basis of ordinary electrocardiogram diagnosis SMI is: ST segment level or down-slope type depression 1mm with or without T wave inversion, but asymptomatic, persistent ST-T wave abnormalities often have severe coronary artery disease.

2. Dynamic ECG monitoring:

Its clinical application is the most common. It is the best way to study painless ischemia in daily life. It has the advantages of non-invasive, simple, accurate, real-time, reproducible and quantifiable, which can accurately reflect the onset of myocardial ischemia. Frequency, duration, severity and dynamic changes, about 30% of myocardial ischemic attacks are asymptomatic in dynamic electrocardiogram, and about 68% to 84% of ischemic ST-segment depression in patients with coronary heart disease It is asymptomatic. The standard of transient myocardial ischemia is: 80 ms after j point, ST segment level or hypotensive depression 1 mm, lasting more than 1 min, seizure interval is more than 1 min, and ST segment is obliquely elevated and T wave changes can occur frequently in normal people, not as a temporary ischemic index. Dynamic electrocardiogram has few false positives and can provide the frequency and duration of myocardial ischemia, which is helpful for estimating prognosis and guiding treatment.

3. Exercise load test ECG:

It has been widely used in the screening and preliminary diagnosis of coronary heart disease ischemic patients. Because of the lack of subjective symptoms during ischemic attack in patients with painless myocardial ischemia, ischemic challenge test is a very important auxiliary means in diagnosis; it is also screening high-risk patients. Further coronary angiography, coronary intervention, coronary artery bypass surgery and evaluation of drugs, surgical efficacy, and an important method to predict patient prognosis.

It is used to detect people with normal SEG and normal SMI risk factors, but it has the disadvantages of high false positive and low specificity. The following changes in exercise test indicate severe coronary lesions: 1 exercise time <10min, ST segment pressure 1mm , and lasting 6min; 2 female patients exercise time 3min; 3 male patients > 40 years, exercise time < 5min, ST segment depression 1mm or R wave amplitude increased; 4 systolic blood pressure decreased 1.33kPa (10mmHg); 5 exercise ECG The u wave inversion occurred; 8 the heart rate at the beginning of the ST segment depression was <140 times/min.

4. Radionuclide inspection:

Radionuclide 99mTc-MIBI myocardial perfusion imaging showed asymptomatic myocardial perfusion reduction, radionuclide blood pool scan showed asymptomatic wall motion abnormalities, all contribute to the diagnosis of myocardial SMI.

5. Echocardiography:

Resting or exercise echocardiography showed that localized wall motion abnormalities contribute to the diagnosis of SMI. The specificity and sensitivity of two-dimensional echocardiography and 201 (201Tl) myocardial imaging are similar, but exercise ultrasound is over-replaced by patients. Gas and other effects, although better observation of the apex and anterior wall, but poor observation of the inferior wall, the use of esophageal atrial pacing load ultrasound examination, can eliminate the adverse effects caused by exercise, but the sensitivity is low.

6. Coronary angiography:

Coronary angiography can show the location, extent and extent of coronary lesions, and has a diagnostic value for the diagnosis of asymptomatic myocardial ischemia. Patients with suspected coronary artery spasm can be used for ergometrine challenge test.

Diagnosis of asymptomatic myocardial ischemia

diagnosis method:

1) Electrocardiogram and exercise test: For those suspected of having SMI, ECG should be routinely performed at rest. If it is negative, exercise test can be done. Some people think that in the exercise test, if the ST segment depression is accompanied by hypotension and R wave abnormalities, it is a sign of serious lesions. Some authors also believe that exercise test causes ST segment deviation accompanied by tachycardia, suggesting myocardial ischemia with or without symptoms. The sensitivity and specificity of the exercise test can reach 70% to 90%.

2) Dynamic ECG monitoring: It is recognized as the most effective means of detecting SMI in daily life. The frequency and elapsed time of myocardial ischemia can be observed, and the relationship between SMI and daily life and activities can be understood. It has been reported that its accuracy rate is 72%, sensitivity is 71.4%, and specificity is 83.3%.

3) 201 development and 82 neutron emission tomography: evidence of myocardial ischemia when ST-segment depression is obtained. The 82neutron emission tomography scan can better reflect the ischemic condition of the heart.

4) Cold pressurization test: The patient's limb is placed in cold water to induce blood vessels, including coronary vasoconstriction, and then an electrocardiogram is performed.

5) X-ray chest X-ray examination of coronary artery atherosclerosis can be found in coronary artery calcification.

6) Coronary angiography can directly understand the extent of coronary artery disease, but after all, because of its traumatic nature, it can not be used to detect asymptomatic patients.

Diagnostic points:

1. Objective evidence of myocardial ischemia: Patients with asymptomatic myocardial ischemia often have objective evidence of myocardial ischemia when undergoing electrocardiogram (including ECG load test and dynamic electrocardiogram), radionuclide, echocardiography, etc. .

2. Clinical manifestations without myocardial ischemia: Although such patients have objective evidence of myocardial ischemia, there are no signs and symptoms associated with myocardial ischemia, such as angina, during ischemic attack.

3. Often associated with a variety of risk factors for ischemic heart disease.

4. Patients with asymptomatic myocardial ischemia often have multiple risk factors for ischemic heart disease, such as hyperlipidemia, hypertension, diabetes, smoking and overweight or obesity, etc. can be regarded as asymptomatic myocardial deficiency Auxiliary diagnostic criteria for blood.

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