Subepicardial ischemia

ECG 1A: Sinus rhythm, normal PR interval; presence of a relatively wide Q-wave in lead III and QS pattern in aVF; isoelectric ST-segment; negative T-waves in the inferior territory from V4 to V6 (posterolateral subepicardial ischemia); peaked and symmetrical T-waves of “ischemic” appearance in V4-V5;

ECG 1B: ECG performed just after administration of 2 nitroglycerine puffs; resolution of pain and normalization of T-waves (positive in leads II, aVF, V4-V6);

Comments: The coronary angiography performed in this patient showed the presence of a severe stenosis of the right coronary artery.

In the absence of ischemia, repolarization begins in the epicardium followed by the endocardium with positive T-waves with the exception of the aVR lead. In the presence of subepicardial ischemia, a local prolongation of the repolarization time of the two layers of the myocardium is observed, although predominant in the subepicardial layer. Repolarization is therefore achieved in the reverse direction, from the subendocardial layers to the delayed subepicardial layers leading to the detection of negative T-waves in the leads facing the ischemic wall.

The electrocardiogram of a subepicardial ischemia is characterized by the presence of negative, symmetrical and peaked T-waves of «ischemic» appearance in several leads corresponding to a given myocardial territory. The symmetrical and peaked pattern is more frequently observed when the T-waves are deep. The pattern is all the more indicative of ischemia in the presence of a pronounced inversion (> 5 mm), a biphasic T-wave, the presence of a necrosis Q-wave, a modification of the ST-segment (elevation or depression, linear ST), an elongated QT interval or a pathological U wave, and in the absence of electrical signs pointing to a heart disease of other origin (hypertrophic cardiomyopathy). The T-wave inversion may be dynamic, appearing only during pain and regressing spontaneously or after administration of nitroglycerine puffs.

Take-home message: Ischemic T-waves can be positive (symmetrical and peaked, subendocardial ischemia), negative (symmetrical and peaked, subepicardial ischemia), flattened, biphasic (particular pattern of Wellens’ syndrome) or normalized (negative T-waves temporarily positive).