Irregularly Irregular Wide Complex Tachycardia: Look Beyond the Atrium.

CASE SUMMARY: A 69-year-old gentleman, a patient with ischemic cardiomyopathy with a single-chamber implantable cardioverter-defibrillator, presented with palpitations. Electrocardiogram revealed a wide QRS, irregularly irregular rhythm (>50 ms variability), mimicking atrial fibrillation but favoring ventricular tachycardia (VT) via the Basel algorithm, superior axis, morphology criteria, and evidence of atrioventricular dissociation. Electrophysiology study confirmed inducible irregular VTs; successful substrate-based catheter ablation was performed.

TAKE-HOME MESSAGES: Irregularly irregular wide complex tachycardia in structural heart disease warrants consideration of VT despite irregularity, using integrated algorithms like the Basel algorithm and morphology criteria. In patients with documented irregularly irregular VT, it is prudent to disable the stability criterion and rely on onset and morphology criteria for supraventricular tachycardia discrimination in a single-chamber implantable cardioverter-defibrillator.