Abstract
Case Summary
The shark-fin morphology on electrocardiogram (ECG) represents a malignant ST-segment elevation myocardial infarction pattern associated with profound transmural ischemia. A 49-year-old man with episodic chest pain had an initially nondiagnostic ECG. With recurrent symptoms and rising troponins, repeat ECG showed ventricular bigeminy and a giant triangular QRS-ST-T waveform in the anterolateral leads. Angiography revealed subtotal proximal left anterior descending artery occlusion, which was managed urgently with percutaneous coronary intervention.
Take-Home Messages
The shark-fin morphology is a rare but malignant ST-segment elevation myocardial infarction pattern that may mimic wide-complex ECG abnormalities. Prompt recognition should trigger immediate reperfusion and vigilance for cardiogenic shock and ventricular fibrillation.
Key words: acute coronary syndrome, electrocardiogram, percutaneous coronary intervention
Graphical Abstract
Case Description
A 49-year-old man with a history of hypertension presented with chest tightness radiating to the left arm which began at 06:00. He reported intermittent episodes of similar symptoms over the preceding 5 weeks, with progressive worsening in intensity. An initial 12-lead electrocardiogram (ECG) obtained on presentation at 08:00 demonstrated no significant ischemic changes (Figure 1A). However, with worsening chest pain 1 hour later, repeat ECG revealed ventricular bigeminy and a giant triangular QRS-ST-T waveform involving leads I, aVL, and V1-V6 (Figure 1B), accompanied by a rise in high-sensitivity troponin from 545 to 1,647 ng/L (reference range: <14 ng/L). Creatine kinase–MB was not measured at the referring hospital. This prompted activation of the ST-segment elevation myocardial infarction (STEMI) pathway. Emergency coronary angiography demonstrated subtotal occlusion of the proximal left anterior descending artery, with flow-limiting disease in the mid left anterior descending artery (Figure 1C). Lesion preparation was performed using a 3.5 × 20 mm noncompliant balloon, followed by implantation of a 3.5 × 40 mm Orsiro drug-eluting stent (BIOTRONIK). Intravascular ultrasound–guided postdilatation was subsequently performed with a 4.5 × 12 mm noncompliant balloon. Final angiographic and intravascular ultrasound results were satisfactory (Figure 1D). Transthoracic echocardiography demonstrated a left ventricular ejection fraction of 45% to 50% with apical, anterolateral, and inferoseptal hypokinesis. There was prompt resolution of ST-segment elevation and ischemic symptoms after percutaneous coronary intervention.
Take-Home Messages
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The shark-fin morphology is a rare but malignant STEMI pattern that may mimic wide-complex ECG abnormalities.
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Prompt recognition should trigger immediate reperfusion and vigilance for cardiogenic shock and ventricular fibrillation.
Figure 1.
Serial ECGs and Coronary Angiography in Dynamic Anterolateral STEMI
(A) Initial ECG without diagnostic ST-segment elevation. (B) Repeat ECG 1 hour later demonstrates ventricular bigeminy and a giant triangular QRS-ST-T waveform (“shark fin”) in leads I, aVL, and V1-V6 (C) Coronary angiogram in the left anterior oblique–cranial view demonstrates subtotal proximal LAD occlusion (red arrow) (D) Final angiogram in the right anterior oblique–cranial view after IVUS-guided PCI with drug-eluting stent implantation demonstrates a satisfactory result. ECG = electrocardiogram; IVUS = intravascular ultrasound; LAD = left anterior descending artery; PCI = percutaneous coronary intervention; STEMI = ST-segment elevation myocardial infarction.
Question
Which is the best interpretation of the ECG in Figure 1B?
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A.
Monomorphic ventricular tachycardia
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B.
Severe hyperkalemia
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C.
Acute anterior STEMI with a triangular QRS-ST-T (“shark fin”) pattern
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D.
Acute pericarditis/myopericarditis
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E.
Brugada pattern
Answer
C: Acute anterolateral occlusive myocardial infarction with a triangular QRS-ST-T (“shark fin”) pattern.
Discussion
Figure 1B demonstrates ventricular bigeminy with a giant triangular QRS-ST-T waveform, also known as the “shark-fin” pattern in the anterolateral leads. This distinctive ECG morphology reflects fusion of the QRS complex, ST-segment, and T wave due to extreme ST-segment deviation, signifying a substantial burden of transmural myocardial ischemia. Although the precise electrophysiological mechanism remains poorly understood, several hypotheses have been proposed, most involving heterogeneous endocardial and epicardial repolarization that generates a marked transmural voltage gradient. This ultimately produces the characteristic large R wave and downsloping ST-segment.1, 2, 3
The differential diagnosis includes monomorphic ventricular tachycardia, severe hyperkalemia, acute pericarditis, and Brugada pattern. In contrast to ventricular tachycardia, which typically demonstrates a consistent wide QRS morphology with atrioventricular dissociation, shark-fin ECGs often retain sinus activation with a territorial injury pattern. Hyperkalemia is characterized by diffuse, symmetric peaked T waves with progressive QRS widening and PR interval prolongation. Acute pericarditis typically produces diffuse concave ST-segment elevation with PR depression, while Brugada syndrome is confined to the right precordial leads.
In a STEMI cohort study, the triangular QRS-ST-T waveform was observed in approximately 1.4% of cases and associated with an increased risk of cardiogenic shock and higher in-hospital mortality.3 The key clinical implication is urgency, as identification of this ECG pattern in the appropriate clinical context should prompt management as an occlusive myocardial infarction until proven otherwise, with immediate reperfusion and intensive monitoring given the high risk of malignant ventricular arrhythmias and hemodynamic collapse.1, 2, 3
Funding Support and Author Disclosures
The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
Footnotes
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References
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