Asymptomatic myocardial ischemia in the elderly

Introduction to asymptomatic myocardial ischemia in the elderly Asymptomatic myocardial ischemia (SMI) in the elderly refers to objective evidence of myocardial ischemia without angina and related symptoms. The incidence of SMI in the elderly is higher than that of young and middle-aged people, some with advanced age, myocardial infarction, diabetes, etc. Related to the pain warning system, millions of people in the United States suffer from SMI, which causes hundreds of thousands of people each year to have myocardial infarction and sudden death from coronary heart disease. Therefore, mastering the basic knowledge of this disease has important clinical significance. basic knowledge Sickness ratio: 0.1% Susceptible people: the elderly Mode of infection: non-infectious Complications: acute myocardial infarction

The cause of asymptomatic myocardial ischemia in the elderly

Ischemia (35%):

Angina pectoris is a subjective sensation of myocardial ischemia caused by myocardial oxygen supply and aerobic imbalance. Similarly, SMI is also the result of myocardial oxygen supply and aerobic imbalance. In SMI, 52% of patients occur in daily life. 33.5% occurred in sleep, and 14.5% occurred in strenuous exercise. Therefore, it is difficult to explain the reduction of coronary blood supply alone or the increase of myocardial oxygen consumption. At rest, only coronary artery stenosis more than 90% will cause coronary artery disease. Reduced blood supply, plus exercise and tension, coronary stenosis more than 50% have coronary blood flow reduction, and the length of stenosis has a very important role in coronary blood flow reduction, SMI and symptomatic myocardial ischemia The heart rate increased by 13 times/min and 22 times/min, respectively, which was less than the heart rate level of the submaximal exercise test, suggesting slight physical activity in daily life and myocardial ischemia and exercise induced during rest. There are some differences in the mechanism of myocardial ischemia. Exercise-induced myocardial ischemia is a significant increase in myocardial oxygen consumption. Coronary fixed stenosis can not increase the myocardial blood supply, and myocardial deficiency occurs in daily life. In addition to a slight increase in myocardial oxygen consumption, blood is mainly reduced by coronary blood supply, and SMI has a time rhythm. The heart rate and blood pressure increase before the onset of noon, which may play an important role in the increase of myocardial oxygen consumption, and evening to night. Onset, coronary vasospasm is more important than myocardial oxygen consumption.

Painless (20%):

(1) elevated plasma endorphin: endorphin is a strong analgesic substance, mainly secreted by salivary glands. It has been found that plasma -endorphin concentration in patients with SMI is higher than that in symptomatic myocardial ischemia. If the endorphin antagonist (Maloxone) can cause ischemic symptoms in SMI patients, this indicates that an increase in plasma endorphin concentration leads to an increase in pain threshold, which is one of the causes of myocardial ischemia and painlessness.

(2) milder degree of ischemia: biochemical (potassium loss, lactic acid accumulation), mechanical (first diastolic dysfunction, post-systolic function decline), electrocardiogram (reduced ST segment) and clinical (angina), etc. A series of changes, angina is the latest manifestation of cardiac ischemia. If the range of myocardial ischemia is small, mild and short-lived, the bradykinin released by ischemic myocardium, prostaglandin and serotonin cause pain. The substance did not reach the pain threshold and showed no symptoms.

(3) Pain alarm system damage: There is a protective pain alarm system in the body, which causes pain when myocardial ischemia, reminds the patient to reduce or stop the activity, and takes medication in time to protect the heart from further ischemic damage. Large-area myocardial infarction, extensive coronary lesions, diabetes, etc., easily cause damage to the pain alert system, reduce sensitivity to pain-causing substances, and cause myocardial ischemic lesions to develop unconsciously until a fatal episode.

Compensatory regulation of myocardial ischemia (15%):

(1) Myocardial contusion: Myocardial contusion refers to short-term ischemia of the myocardium without necrosis, but the structural, metabolic and functional changes caused by recovery can be recovered from hours to days after reperfusion. Myocardial contusion can be myocardium. The result of ischemia may also be a compensatory protection mechanism, which is mainly related to oxygen free radicals and excessive calcium overload.

(2) Hibernating myocardium: This is a myocardial protection or compensatory mechanism. The blood flow reduction of chronic myocardial ischemia is not serious, but the oxygen supply for a long time is reduced, and the myocardial oxygen consumption is also reduced accordingly. Maintaining myocardial metabolic balance, followed by slow myocardial dysfunction, but complete recovery after coronary reperfusion.

Through the above-mentioned compensatory regulation of myocardial ischemia, the metabolism and function of the myocardium are significantly reduced, and as a result, the frequency and degree of ischemia are reduced, and angina is reduced, and the expression is mainly SMI. The study shows that angina ischemic attack. Myocardial blood supply decreased, cardiac work (heart rate × systolic blood pressure) increased significantly; while SMI attack, only showed local myocardial perfusion decreased, heart rate and blood pressure product did not increase significantly, in short, the compensatory regulation of myocardial ischemia may also be SMI One of the reasons for this.

Asymptomatic myocardial ischemia prevention in the elderly

1. Prevention First, we must stop a variety of risk factors for coronary heart disease, such as high blood lipids, high blood pressure, diabetes, smoking and so on.

2. Reasonable diet, avoid high sugar, high fat, high salt diet, eat more fruits, vegetables and so on.

3. Work and rest, properly exercise and improve heart function.

Asymptomatic myocardial ischemia complications in the elderly Complications, acute myocardial infarction, sudden death

Asymptomatic myocardial ischemia can also cause acute myocardial infarction and sudden death.

Asymptomatic myocardial ischemia in the elderly Symptoms Arrhythmia conduction block angina When the heart beats during sleep, heart rate increases, myocardial infarction, sudden death, platelet aggregation enhances blood oxycorticosteroids

1. Clinical Type Cohn (1981) classifies SMI into 3 types:

(1) Type I: 3% to 5%, with SMI attack, but completely asymptomatic, and no history of myocardial infarction or angina pectoris, including normal people and people with coronary heart disease susceptibility factors.

(2) Type II: 1/3, refers to the SMI that occurs during the recovery period of uncomplicated myocardial infarction.

(3) Type III: The most common, refers to the occurrence of SMI in patients with angina. Recently, Braunwald divided SMI into 2 types: type I is a coronary artery disease caused by pain alarm system damage (no angina); type II is symptomatic in the same patient. (angina) coexists with SMI (equivalent to CohnIII type).

2. Clinical features

(1) There are similarities and differences in the rhythm of the attack: SMI is generally considered to be frequent in the morning and less in the middle of the night. The elderly are the same as the young and middle-aged. The high-risk time is still between 6 and 10 in the morning, and may be sympathetically excited after morning, catecholamine. It is associated with increased corticosteroids, increased platelet aggregation, and low fibrinolytic activity, as heart rate increases and blood pressure rises before SMI, and beta blockers reduce the frequency of SMI episodes in this time zone, suggesting an increase in myocardial oxygen consumption. At this time, SMI has a certain effect, but the frequency of SMI at 2 to 6 o'clock in the night, the elderly (18.1%) is significantly higher than the young and middle-aged (8.1%), which may be poor with the elderly, and when lying down Increased blood flow, increased ventricular filling pressure and left ventricular dilatation, therefore, the treatment of elderly SMI should consider the concentration of drugs at night.

(2) ST segment has the same degree of low pressure and long duration, and the number of episodes is many: the degree of ST segment depression in elderly SMI is not significantly different from that of young and middle-aged people, 1.8±0.6mm and 1.7±0.6mm, respectively. The duration (10.3±8.4min) was significantly longer than that of young and middle-aged people (7.5±6.1min), and the per capita group was also significantly higher than that of young and middle-aged people. This may be related to the severity of coronary lesions in the elderly, increased pain threshold and myocardial degeneration. With the increase of ST segment, the duration of prolongation and the frequency of seizures increase, the detection rate of SMI decreases, and the detection rate of symptomatic myocardial ischemia increases. (3) Serious arrhythmia complicated: elderly At the onset of SMI, ventricular arrhythmias with Lang grade III or higher, atrial fibrillation, and atrioventricular block above II degree were significantly higher than those of young and middle-aged people (52.4% and 32.7%, respectively), myocardial ischemia Can induce arrhythmia, heavier arrhythmia can also induce or aggravate myocardial ischemia, about half of patients with arrhythmia caused by myocardial ischemia, severe arrhythmia and sudden death, SMI and acute myocardial infarction, so SMI with Severe arrhythmia Treatment.

(4) Increased serum CPK-MB and CPK-MB/CPK ratios: Studies have shown that elderly patients with SMI have elevated serum CPK-MB, normal CPK, and a significant increase in CPK-MB/CPK ratio, which can be caused by ischemia and hypoxia. The physicochemical properties and permeability of the myocardial cell membrane are altered, making it unique in the myocardium (CPK-MB is released into the blood, resulting in an increase in serum CPK-MB, which accounts for only 15% of CPK, if CPK-MB is mildly moderately elevated There is little effect on the CPK value (normal), but the CPK-MB/CPK ratio is significantly increased.

Examination of asymptomatic myocardial ischemia in the elderly

Early blood routine is basically normal.

1. Dynamic electrocardiogram can not only detect SMI, but also observe the frequency, severity and duration of SMI. It can be used as the total myocardial ischemic load (the sum of millimeters of each ST segment within 24 hours × the sum of duration) The quantitative index of blood is used to observe the curative effect. The diagnostic criteria are ST-segment level or down-slope type 1mm and extend to Jms 80ms, and the duration is 1min. The interval between the two episodes is at least 1min, and the SMI occurs in daily life. For self-generated SMI, the SMI that occurs during larger movements is called induced SMI.

2. Echocardiographic load test In the elderly, due to age, osteoarthrosis and cardiopulmonary dysfunction, it is often difficult to perform ECG exercise test, especially suitable for echocardiographic load test, and the latter is more sensitive and reliable than the former.

3. Radionuclide examination 201Ti myocardial perfusion imaging has a high sensitivity and specificity for the diagnosis of this disease.

Diagnosis and diagnosis of asymptomatic myocardial ischemia in the elderly

Diagnostic criteria

Although the disease is asymptomatic, it may have a predisposing factor for coronary heart disease. Type II and III patients have a history of myocardial infarction and angina, respectively. The diagnosis depends mainly on the following tests:

1 dynamic electrocardiogram: not only can detect SMI, but also can observe the frequency, severity and duration of SMI, as the total myocardial ischemic load (the sum of millimeters of each ST segment within 24 hours × the sum of duration) The quantitative index of blood is used to observe the curative effect. The diagnostic criteria are ST-segment level or down-slope type 1mm and extend to Jms 80ms, and the duration is 1min. The interval between the two episodes is at least 1min, and the SMI occurs in daily life. For self-generated SMI, the SMI that occurs during larger movements is called induced SMI.

2 Echocardiographic load test: Because of age, osteoarthrosis and cardiopulmonary insufficiency, it is often difficult to perform ECG exercise test, especially suitable for echocardiographic load test, and the latter is more sensitive and reliable than the former.

3 radionuclide examination: 201Ti myocardial perfusion imaging method has a higher sensitivity and specificity for the diagnosis of this disease.

Differential diagnosis

Clinically, it must be differentiated from painless myocardial infarction and occult coronary heart disease.

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