Unstable angina

Unstable angina is considered an extremely dangerous stage of exacerbation of ischemic heart disease, threatening the development of myocardial infarction or sudden death. In terms of clinical manifestations and prognostic value, unstable angina occupies an intermediate place between stable angina and acute myocardial infarction, but, unlike infarction, in unstable angina the degree and duration of ischemia are insufficient for the development of myocardial necrosis.

What causes unstable angina?

It happens that myocardial infarction develops suddenly, without any precursors. But more often, several days or even weeks before, patients experience symptoms that can be regarded as signs of the onset or exacerbation of coronary insufficiency. This may be a change in the nature of existing angina, that is, attacks may become more frequent, intensify, change or expand the area of irradiation, and occur with less stress. Night attacks or episodes of arrhythmia may join in.

The development of unstable angina is usually associated with the rupture of an atherosclerotic plaque and subsequent intracoronary thrombus formation. In some cases, the cause is an increase in the tone of the coronary arteries or their spasm.

Sometimes the pre-infarction period is characterized by symptoms that are relatively non-specific for coronary insufficiency, such as increased fatigue or general weakness. Interpreting such signs is more than difficult unless they are accompanied by electrocardiographic changes in myocardial ischemia.

How does unstable angina manifest itself?

Unstable angina includes:

• newly developed angina pectoris (within 28-30 days from the moment of the first pain attack);
• progressive angina (conditionally - during the first 4 weeks). Pain attacks occur more frequently, become more severe, tolerance to stress decreases, angina attacks occur at rest, the effectiveness of previously used antianginal drugs decreases, the daily need for nitroglycerin increases;
• early post-infarction angina (within 2 weeks from the development of myocardial infarction);
• spontaneous angina (the appearance of severe pain attacks at rest, often lasting more than 15-20 minutes and accompanied by sweating, a feeling of shortness of breath, rhythm and conduction disturbances, and a decrease in blood pressure).

Newly developed angina does not require additional definition. Progressive angina is a sudden worsening of the clinical course of angina: occurrence of attacks of angina of effort with a lighter load, an increase in their duration, the appearance of angina at rest, the appearance of ECG changes that persist after the cessation of angina. With progressive angina, attacks often last more than 20 minutes, occur at night, additional symptoms appear: fear, sweat, nausea, palpitations).

A separate variant is angina pectoris that appears in the early period after myocardial infarction (within 2 weeks to 1 month from the onset of myocardial infarction) or after coronary artery bypass grafting.

The guidelines for the diagnosis and treatment of unstable angina developed in the USA (1994) propose to differentiate the following clinical variants of unstable angina:

1. Rest angina (usually attacks lasting more than 20 minutes;
2. Newly developed angina pectoris (at least functional class III);
3. Progressive angina pectoris - an increase in the severity of angina from class 1 to FC III or IV.

The classification of unstable angina proposed by J. Braunwald (1989) is widely known:

Risk level	Option
I - severe angina pectoris (newly developed or progressive)	A - secondary
II - subacute angina at rest (remission within the last 48 hours)	B - primary
III - Acute angina at rest (attacks within the last 48 hours)	C - after myocardial infarction

Secondary unstable angina includes cases where the cause of instability is extracardiac factors (anemia, infection, stress, tachycardia, etc.)

With unstable angina, the risk of myocardial infarction increases sharply. The maximum probability of myocardial infarction is in the first 48 hours of unstable angina (class III - acute unstable angina at rest).

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How is unstable angina recognized?

Usually, with unstable angina, there are no persistent ST segment elevations on the electrocardiogram, and there is no release of myocardial necrosis biomarkers (cardiac-specific enzymes) into the bloodstream. In some cases, with unstable angina, there are no changes at all indicating ischemia and myocardial damage. Unfavorable prognostic signs in unstable angina:

• ST segment depression;
• transient ST segment elevation;
• T wave inversion (polarity reversal).

Echocardiographic examination of patients with unstable angina may reveal impaired mobility of ischemic areas of the myocardium. The degree of these changes is directly dependent on the severity of the clinical manifestations of the disease.

It is very important to record ECG during attacks and in the interictal period. Although the absence of changes on the ECG does not allow us to exclude the presence of ischemia, the risk of myocardial infarction in such patients is usually relatively low. On the other hand, recording any changes on the ECG and the persistence of ECG changes after the cessation of attacks indicates a high risk of myocardial infarction and complications. Most often, patients with unstable angina have ST segment depression or negative T waves. In some patients, unstable angina manifests itself in the form of attacks of spontaneous angina with ST segment elevation. It should be noted that newly occurring angina may be stable (or "conditionally stable") in its clinical course, for example, newly occurring angina of FC II effort.

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