Severe stenosis of the left main coronary artery

ECG 1A: This electrocardiogram shows sinus rhythm of 95 bpm, with an ST-segment elevation of 3 mm in aVR, 2 mm in V1 and a diffuse and relatively large ST-segment depression (inferior leads, V3-V6);

ECG 1B: Emergency coronary angioplasty identified a severe sub-occlusive stenosis of the left main coronary artery; an angioplasty with stent placement was successfully performed; the electrocardiogram upon the return to the ward showed a normalization of the ST-segment;

Comments: The electrocardiographic aspect of this patient was highly evocative of an occlusive or sub-occlusive disease of the left main coronary artery which was confirmed by coronary angiography. This clinical situation represents a critical emergency since the risk of occurrence of severe ventricular rhythm disorders and rapid hemodynamic deterioration is maximal, the left main coronary artery supplying approximately 75% of the entire left ventricular myocardial mass. These patients have a significantly increased mortality in the absence of emergency revascularization. It is not possible to define a uniform electrical pattern in patients with steno-thrombosis of the left main coronary artery although certain signs observed in this patient are highly evocative: ST-segment elevation in aVR associated with a diffuse ST-segment depression In the anterior and inferior leads, the vector of the ischemic attack pointing to the right and upward, in the direction of aVR.

• The ST-segment elevation in aVR is secondary to the transmural ischemia observed in the basal portion of the interventricular septum;
• The diffuse reciprocal depression is mainly observed from V3 to V5 and in the inferior leads;
• A number of ischemia-induced conduction disorders have been described: right bundle branch block, left anterior fascicular block, parietal blocks;

The aVR lead is an augmented unipolar frontal lead, allowing direct exploration of the upper and right aspects of the heart, a region which includes the basal wall of the interventricular septum, underneath the aortic and pulmonary valves, and the pulmonary infundibulum. This lead has long been neglected during the analysis of the electrocardiogram (« I only use the aVR lead to define the sinus origin of the atrial activity »). Indeed, it is not adjacent to any other lead, and was initially intended to provide only reciprocal information on an anterior, inferior or lateral lesion in the context of an acute coronary syndrome. However, several relatively recent studies have suggested that the presence of a ST-segment elevation in aVR is strongly suggestive of a left main coronary artery disease or of severe three-vessel disease and is associated with a high mortality risk. Indeed, the left main coronary artery and the first septal branches supply the basal region of the interventricular septum, the region directly explored by aVR, which explains the electrical signs during an occlusion. This very proximal involvement reflects a severe impairment, is associated with an altered prognosis and therefore justifies emergency myocardial revascularization preferentially by angioplasty or surgery (aorto-coronary bypass surgery).

The aVR elevation can be observed in patients with three-vessel disease, left main coronary artery or very proximal LAD disease. An elevation in aVR >1 mm with an elevation amplitude greater in aVR than in V1 is typically indicative of a left main coronary artery disease or a three-vessel disease patient; in patients with ostial stenosis of the LAD, the elevation is often modest and less than 0.1 mm in aVR and can be higher in the anteroseptal leads (V1, V2) with an occasional right bundle branch block pattern. The reciprocal depression is generally larger (> 2-3 mm) and followed by a negative T-wave in patients with a left main coronary artery stenosis compared to a tritroncular patient or a patient with ostial stenosis (less prominent depression and more positive T-waves).

The aVR lead (-150° in the frontal plane) also allows objectifying the reciprocal information stemming from the lateral and inferior left ventricular regions (+30°, between lead I and lead II for the reciprocal images), which explains the frequent presence of a depression for certain anterior as well as inferior infarctions.

Take-home message: The presence of a ST-segment elevation in aVR during chest pain is a sign of severe and proximal disease, is a factor of poor prognosis and should warrant an emergency revascularization procedure.