Case: “Shark-fin” — a life-threatening ECG sign

Sep 28
2 min read

Background

A man in his early sixties with a history of atrial fibrillation and a mechanical aortic valve developed acute chest pain while cycling and collapsed.

Prehospital

The prehospital ECG (attached) was machine-interpreted as showing very wide QRS complexes.

On hospital arrival

He was hypotensive, confused, clammy, and diaphoretic. Echocardiography showed markedly reduced left-ventricular function. He was accepted for emergent coronary angiography.

Course in the cath lab

He suffered cardiac arrest in the lab. Mechanical chest compressions were initiated, and during ongoing compressions angiography demonstrated a thrombotic occlusion of the left main coronary artery, which was stented. He achieved return of spontaneous circulation, was intubated, and started on vasopressors. Despite treatment he developed both respiratory and circulatory failure, progressed to pulseless electrical activity, and could not be resuscitated.

ECG interpretation

The machine reported an extremely wide QRS duration (around 255 ms), but this was incorrect. The apparent widening was due to massive ST-segment elevation in the anterolateral leads with reciprocal ST depression inferiorly. Comparing with a prior ECG in which V1 and V2 share essentially the same QRS configuration as in the index tracing helps distinguish the QRS from the ST segment. This pattern is known as the “shark-fin sign” and is often associated with proximal LAD or left main occlusion.

Key observations

The pattern occurs in approximately 1–2 percent of such infarctions.
Nearly all patients with this pattern develop cardiogenic shock or cardiac arrest, often ventricular fibrillation (reported by Cipriani and Schrieber, among others).
P waves may be absent. The rhythm can be junctional or idioventricular, which is also seen with reperfusion.

Learning points

The shark-fin sign is a high-risk ECG pattern that demands immediate recognition and action.
Do not rely blindly on automated ECG interpretation. Assess ST-segment changes carefully.
With chest pain plus this pattern, an occluded left main or proximal LAD is very likely present.