ECG in LMCA Stenosis

ECG in a person with persistent anginal pain for the past several hours showing significant ST segment depression anterolateral leads along with sinus tachycardia. ST segment elevation is noted in aVR. Such a pattern is consistent with significant left main coronary artery stenosis.
Clinical evaluation and X-Ray chest showed features of pulmonary edema. Angiography done after initial stabilization showed severe stenosis of distal left main coronary artery. In addition, there were multiple lesions in all three vessels, making a standard indication for an urgent coronary artery bypass grafting.
A similar ECG pattern can also occur in severe proximal triple vessel disease. The previous ECG is shown here for comparison, which shows minimal changes. There is minimal ST segment elevation in aVR as well. This highlights the need for serial ECGs in acute coronary syndrome as initial ECGs may be near normal even in those with severe disease.
Classical electrocardiographic pattern in left main coronary artery disease is ST elevation in aVR with extensive ST depression in other leads, most prominent in I, II and V4-V6. ST elevation may be noted in V1, but ST elevation in aVR is more than or equal to that in V1.
ST elevation in aVR greater than or equal to that in V1 distinguished left main stenosis from left anterior descending coronary artery stenosis with 81% sensitivity and 80% specificity. ST segment elevation in aVR in proximal LAD occlusion before first septal is thought to be due to transmural ischemia of the basal part of the septum.
Injury current of basal part of septum is directed towards right shoulder and aVR. ST elevation in aVR noted in left main disease is also likely due to the same mechanism as flow to first septal is blocked in this case as well. Mortality was more frequently observed in left main obstruction patients with higher degree of ST elevation in aVR.
Another ECG showing ST elevation in aVR and diffuse ST segment depression in inferior and lateral leads suggesting left main coronary artery disease. ST elevation in aVR more than that in V1 is also suggestive of left main disease.
In a study comparing acute obstruction of left main, left anterior descending and right coronary occlusions, aVR ST elevation of more than 0.05 mV was noted in 88% of left main obstruction, 43% of LAD obstruction and 8% of RCA obstruction. One limitation of the study was lack of comparison with left circumflex obstruction.
In addition to ST elevation in aVR, this ECG also shows Q in V1 followed by a tall, slurred R called QRBBB, indicative of anterior wall infarction with right bundle branch block. The initial R of the RSR’ pattern expected in right bundle branch block is knocked off by the infarction. Multiple supraventricular ectopics are also seen in the ECG.
In a case reported by Shinde RS et al, coronary angiography documented total occlusion of left coronary artery and the patient underwent emergency coronary artery bypass surgery. In that case there was ST depression in I, aVL, II, aVF and V2-V6. ST elevation was 2 mm in aVR and 1 mm in V1. This patient had reported with recent onset angina.
Usually, patients with LMCA occlusion deteriorate hemodynamically and electrically very rapidly. They can present with anterior wall infarction. On other extreme, total left main coronary artery occlusion with normal ECG and left ventricular function has also been reported. In that patient, collaterals from right coronary artery supplied both left anterior descending and left circumflex territories.
Significant left coronary artery narrowing of more than 50% luminal narrowing is noted in about 5% of patients undergoing coronary angiography. But total occlusion being documented on coronary angiography is extremely rare as many of them do not survive. One series documented only 6 patients in around twelve thousand cases.

References

1. Sen F et al. Classical electrocardiographic clues for left main coronary artery disease. Indian Heart J. 2016 Sep;68 Suppl 2(Suppl 2):S226-S227.
2. Yamaji H et al. Prediction of acute left main coronary artery obstruction by 12-lead electrocardiography. ST segment elevation in lead aVR with less ST segment elevation in lead V(1). J Am Coll Cardiol. 2001 Nov 1;38(5):1348-54.
3. Engelen DJ et al. Value of the electrocardiogram in localizing the occlusion site in the left anterior descending coronary artery in acute anterior myocardial infarction. J Am Coll Cardiol. 1999 Aug;34(2):389-95.
4. Shinde RS et al. Images in cardiology. ECG showing features of total left main coronary artery occlusion. Heart. 2006 May;92(5):670.
5. Bhatia V et al. 12 lead ECG in the detection of left main coronary artery occlusion during acute coronary syndromes. Int J Cardiol. 2007 Apr 4;116(3):e83-4.
6. Singhal G et al. Total left main coronary artery occlusion with normal ECG and normal LV function: A rare case. Journal of Indian College of Cardiology. 2016; 6:49-51.
7. Ward DE et al. Occluded left main stem coronary artery report of five patients and review of published reports. Br Heart J. 1983;49:276–279.