What Is an Inferior Myocardial Infarction?

Subendocardial myocardial infarction refers to the infarction that affects only one third of the myocardium on the inner side of the ventricular wall, and affects the muscle column and papillary muscles. The electrocardiogram generally does not have pathological Q waves. On the ECG, ST segment depression is> = 0.1mv, but the ST segment of lead aVR (and sometimes V1 lead) is elevated and tall T waves appear. Subendocardial myocardial infarction, also known as non-Q-wave myocardial infarction, non-transmural myocardial infarction.

Subendocardial infarction

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Subendocardial myocardial infarction

The diagnostic criteria for acute subendocardial myocardial infarction have not been unified. Some people believe that the following criteria can be used as diagnostic criteria:

(1) Myocardial ischemic chest pain lasts for more than 30 minutes;

(2) Electrocardiogram shows ST segment decline and / or T wave inversion, lasting for more than 48 hours, without pathological Q wave;

(3) The serum myocardial enzymes and their isoenzymes are elevated, which is consistent with the dynamic changes of the enzyme spectrum of acute myocardial infarction, and can increase serum enzyme levels caused by other reasons.

Intravenous thrombolysis (not applicable with cardiogenic shock), emergency percutaneous coronary intervention (PCI) to prevent heart failure.

ECG features are classified as follows:

1, ST segment myocardial infarction,

A, ST segment depression is mainly characterized by: Except for avR, ST segment is widely depressed, ST segment depression is greater than or equal to 0.1mv, and ST segment time is greater than or equal to 0.08 seconds, with or without T wave changes.

B, ST segment elevation mainly, ST segment is a one-way curve, elevation above 0.1-0.2mv, lasting for more than 24-48 hours, and dynamic evolution, but can return to normal.

2. T wave type myocardial infarction. Except for avR, most leads show a deep and symmetrical inverted T wave with a depth greater than 1mm, which gradually deepens.

3. Myocardial infarction with normal ECG.

Non-ST-elevated myocardial infarction is more severe and lasts longer than incomplete blockage of diseased arteries in patients with unstable angina pectoris, resulting in temporary reduction in myocardial blood flow and MI. Non-ST-elevated MI is compared with ST-elevated MI. The blood flow in the ischemic area of the former is usually rebuilt within minutes to hours after the onset of the disease. This is due to: early dissolution of completely blocked thrombus; Some plaques are healed faster; vasospasm is relieved; there is extensive collateral circulation when completely blocked; the total thrombus load is low and the forward blood flow never disappears. These mechanisms all stop myocardial necrosis earlier and limit the development of infarction. It can be considered that myocardial infarction with non-ST elevation is an intermediate state between myocardial infarction with ST elevation and unstable angina pectoris. Myocardial necrosis of non-ST-elevated myocardial infarction is often characterized by less fusion of myocardial necrosis sites, and is more concentrated in the inner third of the myocardial wall, because blood flow is restored and / or the formed side Branch circulation prevents the necrotic area from spanning the entire ventricular wall thickness.