Cardiology / Экг ИБС

ECG in ischemic heart disease (IHD)

Acute ischemia of myocardium causes a current of injury of myocardium.

Subendocardial ischemia - the resultant ST vector directs toward the inner layer of the affected ventricle. Overlying leads therefore will record ST depression. Transmural or epicardial ischemia - the ST vector is usually shifted in the direction of the outer (epicardial) layers, producing ST elevations and sometimes, in the earliest stages of ischemia, tall, positive so-called hyperacute T waves over the ischemic zone.

ECG in myocardial infarction

Electrocardiographic examination is especially important. It establishes the presence of myocardial infarction and also some important details of the process such as localization, depth of the process, and the size of the affected area.

Three zones of myocardial damage in acute myocardial infarction can be detected by ECG: necrotic zone, ischemic myocardium injury zone, and zone of ischemia.

Myocardial necrosis is detected by pathological Q-wave:

Pathological Q-wave is characterized by width≥0.04 s (in V mm or>1/4 R-wave (in V4-6 >15%R) (Fig. Suppl. 8).

Ischemic myocardium injury is detected by ST-interval:

-Transmural or epicardial injury - convexing elevation ST with transmission in T- wave;

-Subendocardial injury – horizontal or concaving depression ST.

Ischemia of myocardium is detected by T-wave:

-Subendocardial ischemia – symmetrical acute high T-wave in overlying leads (>6 mm in standard and augmented leads, >8-10 mm in chest leads) (Fig. Suppl. 10);

-Transmural or epicardial ischemia - symmetrical acute deep T-wave.

The S-T segment and T wave change during the first hours of the disease (Table 9). The descending limb of the R wave transforms into the S-T segment without reaching the isoelectric line. The S-T segment rises above the isoelectric line to form a convexing arch and to coincide with the T wave. A monophase curve is thus formed. These changes usually persist for 3—5 days. Then the S-T segment gradually lowers to the isoelectric line while the T wave becomes negative and deep.

A deep Q wave appears, the R wave becomes low or disappears at all. The QS wave is then formed, whose appearance is characteristic of transmural infarction. Depending on localization of infarction, changes in the ventricular complex are observed in the corresponding leads (Table 10, Fig. Suppl. 11-12). The initial shape of ECG can be restored during cicatrization, or the changes may remain for the rest of life.

Table 10

Localization of myocardial infarction Pathological changes of ventricular complex (Q-wave) V1-4, I, aVL

V1-2

I, aVL, V5-6

II, III , aVF

High R V1-2

Variability of ECG patterns with acute myocardial ischemia:

-Non–infarction subendocardial ischemia – transient ST depressions;

-Non–infarction transmural ischemia - transient ST elevation or paradoxical T- wave normalization, some times followed by T-waves inversions;

-Non–Q-wave (non-ST elevation) infarction - ST depressions or T-inversions without Q-wave;

-Q-wave – infarction - Q-wave with hyperacute T-waves/ST-elevations followed by T-waves inversions.

Exercise stress ECG testing:

Because the diagnosis of angina pectoris is usually primarily based on the patient's history, exercise testing in a patient with typical symptoms is generally used to determine functional and ECG response to graded stress (for exercise stress testing using radionuclide imaging; for exercise testing in asymptomatic persons to determine fitness for exercise programs, see below).

The patient exercises to a predetermined goal (e.g., 80 to 90% of maximal heart rate, which can be approximated as 220 less the age in years), unless distressing cardiovascular symptoms (dyspnea, reduced endurance, fatigue, hypotension, or chest pain) supervene. The ischemic ECG response during or after exercise is characterized by a flat or downward-sloping ST segment depression>0.1 millivolts (1 mm on the ECG when properly calibrated) lasting > 0.08 sec.

Acute ischemia causes a current of injury of myocardium.

Subendocardial injury (A) - the resultant ST vector directs toward the inner layer of the affected ventricle, overlying leads therefore will record ST depression. Transmural or epicardial injury (B) - ST elevations and sometimes tall, positive, hyperacute T waves over the ischemic zone.

Fig. Suppl. 8. Myocardial necrosis is detected by the pathological Q-wave - - width≥0.04 s (in V4-6 >0.025 s), depth>2 mm or>1/4 R-wave (in V4-6 >15%R).

Fig. Suppl. 9a. Ischemic myocardium injury is detected by ST-interval. Transmural or epicardial injury - convexing elevation ST with transmission in T-wave.

Fig. Suppl. 11. Acute anterior left ventricular myocardial infarction

(A) Superacute period (1-2 hours), (B) acute period (24 hours), (C) subacute period (>1 week).

Fig. Suppl. 12. (A) Superacute period (1-2 hours), (B) acute period (24 hours),

(C) subacute period (>1 week).