The Not-So-Fast Tachycardia: A Paradoxical Rhythm Leading to Cardiomyopathy.

CASE SUMMARY: An 88-year-old man with baseline sinus bradycardia and bifascicular block developed an incessant rhythm at 97 to 98 beats/min without discernible P waves and QRS morphology identical to baseline. Holter monitoring confirmed marked rate invariance. Echocardiography revealed new left ventricular systolic dysfunction (left ventricular ejection fraction 35%-40%; previously normal). Electrophysiology study demonstrated very slow typical (slow-fast) atrioventricular nodal re-entry tachycardia; slow-pathway ablation restored sinus rhythm, and left ventricular ejection fraction normalized within 3 months.

TAKE-HOME MESSAGES: A near-100 beats/min junctional-appearing rhythm may represent atrioventricular nodal-dependent reentry. When incessant and associated with new cardiomyopathy, electrophysiology study can diagnose the mechanism and enable curative ablation.