Subendocardial ischemia and LAD stenosis

ECG 1A: This tracing was recorded during a consultation in an asymptomatic patient; left anterior fascicular block with no significant abnormality of the ST-segment or T-wave; Three months after this consultation, appearance of typical chest pain; recording of a tracing at his cardiologist’s office in the absence of pain;

ECG 1B: Relative to the previous tracing, modification of the electrocardiogram with signs of subendocardial ischemia (significant increase in T-wave amplitude in V2-V4, symmetrical and peaked T-waves); ST-segment remaining more or less isoelectric;

 Comments: The second tracing of this patient is suggestive of an anterior endocardial ischemia and severe LAD stenosis was demonstrated at coronary angiography. In a healthy left ventricular myocardium, depolarization begins in the endocardium; given that the action potential is shorter in the epicardium, repolarization in the opposite direction begins at the level of the epicardium (the repolarization of the epicardium thus physiologically precedes that of the endocardium). A subendocardial ischemia (isolated ischemia or first sign of coronary occlusion) induces a delayed subendocardial repolarization; this repolarization delay does not alter the general direction of the repolarization (epicardial repolarization always precedes endocardial repolarization), but alters its progression by adding an ischemic disease vector directed from the ischemic zone to the healthy zone explaining the increase in T-wave voltage. The demonstration of reciprocal images is rare, the pathological dipole of the ischemic wall being close to the normal dipole and the repolarization dipole of the wall opposite the dipole of the diseased wall most often canceling its effects.

The normal T-wave is asymmetrical, of low voltage and positive in all leads except aVR and occasionally V1. There is, in some patients with no significant abnormalities, a negative T-wave in leads III, aVF and very rarely in lead II or aVL, when the axis of the heart is vertical. The appearance of negative and symmetrical T-waves or of positive, symmetrical and tall T-waves is therefore abnormal and suspicious.

The typical pattern of endocardial ischemia corresponds to the highlighting of tall (> 5 mm), positive, symmetrical and peaked T-waves. This pattern is poorly specific and can be observed in other situations including variants of the norm (vagotonia, athletic patients): acute alcoholism, hyperkalemia, stroke, reciprocal image of a posterior subepicardial ischemia, aortic insufficiency (diastolic-type hypertrophy), acute pericarditis, etc.

Take-home message: The subendocardial ischemia pattern (positive, tall, symmetrical and pointed T-waves) may diminish (spontaneously or after administration of nitroglycerine puffs) in the presence of stenosis of a coronary artery or, conversely, evolve toward a Pardee wave pattern with elevation in the presence of a coronary occlusion.