ECG Prediction of Culprit Lesion in STEMI can Be a Real Challenge,at Times!

In the setting of ST-elevation myocardial infarction (STEMI), predicting the culprit vessel/lesion based on surface electrocardiogram (ECG) is a routine practice in most of the cardiac-emergency units. Precordial leads (V1-V3) showing ST elevation with reciprocal ST depression in inferior leads suggest left anterior descending artery (LAD) occlusion. Inferior ST-segment elevation is caused by right coronary artery (RCA) or less commonly left circumflex (LCx) (Table 1). The usefulness and limitations of ECG in localizing the culprit vessel have been well reviewed in literature.^{1, 2}

Table 1.

Quick Reference for Identifying Occluded Vessel (Valid for Single Vessel Involvement).

Leads Showing ST-Segment Elevation	Culprit Vessel
V1, V2 (septal MI)	Proximal LAD
V3, V4 (anterior MI)	LAD
V5, V6 (apical MI)	Distal LAD
I, aVL (lateral MI)	LCx
II, III, aVF (inferior MI)	90% RCA; 10% LCx

Source: Rafla (2020). ¹

Abbreviations. LAD, left anterior descending; LCx, left circumflex; MI, myocardial infarction; RCA, right coronary artery.

The complexity and confusion are compounded in a less common situation-simultaneous ST-segment elevation (SST-SE) in two different coronary artery territories. An acute occlusion of LAD when wraps around the apex can result in significant changes in the inferior leads of ECG either as an isolated finding or in addition to STEMI in LAD territory. At times after coronary angiography in acute coronary syndrome (ACS), pin-pointing the culprit lesion may be challenging if 2 or more lesions are present. In this issue, Pankaj et al ³ have described an interesting case of SST-SE in both anterior and inferior leads and explained this phenomenon in presence of wraparound LAD. Their patient had thrombotic lesion in mid-LAD and a critical lesion in RCA. The distal LAD was diffusely diseased. The authors discussed the various situations of SST-SE and explained the genesis of such confusing ECG changes.

It is interesting to relearn about abnormally long LAD vessels one may come across on rare occasions.

Wraparound LAD (Type-III) is defined as LAD that perfuses at least one-fourth of the inferior wall of left ventricle (when assessed on RAO projection). ⁴

Superdominant LAD/Hyperdominant (type-IV) where the vessel continues as posterior descending artery (PDA) can cause inferior wall myocardial infarction (IWMI) or isolated right ventricular myocardial infarction (RVMI). ⁵

Jariwala and Padma Kumar described the later, rare coronary anomaly and stated that there are only 19 cases reported till their publication in 2018. This excellent review also emphasizes the therapeutic implication of such a coronary anomaly. Early appropriate intervention can be lifesaving. ⁶

The take-home message from this interesting article is that in ACS, when there are STE changes in 2 coronary territories, along with conspicuous absence of reciprocal ST depression, one should analyze the angiograms carefully for the presence of a wraparound or superdominant LAD.