BACKGROUND: Left bundle branch block (LBBB) is associated with atrial fibrillation (AF) and systolic heart failure, which can be treated with cardiac resynchronization therapy (CRT) that includes an implantable cardiac device (ICD). However, in some patients, LBBB may vary with heart rate, and during episodes of AF in LBBB, aberrant ventricular conduction, or wide QRS complex tachycardia (Ashman beats) can occur. This report is a case of LBBB treated with pharmacologic CRT, without the use of an ICD.

CASE REPORT: A 68-year-old man presented with persistent AF and systolic heart failure. Serial electrocardiograms (ECGs) showed AF and mixed narrow (116 ms) and wide (152 ms) QRS duration of LBBB. Echocardiography showed a left ventricular ejection fraction (LVEF) of 30%. Catheter ablation for AF resulted in the restoration of sinus rhythm. The patient was treated with step-wise decreasing doses of amiodarone, from 200 mg to 75 mg daily, and step-wise increasing doses of bisoprolol, from 3.75 mg to 5.0 mg daily, which effectively slowed heart rate, inhibited aberrant cardiac conduction due to LBBB, reduced the symptoms of heart failure, and improved LVEF to 60%, despite persistent sinus bradycardia and the inability of the heart rate to increase during activity (chronotropic incompetence).

CONCLUSIONS: This report of a case of AF associated with LBBB shows that pharmacologic CRT can restore sinus rhythm following catheter ablation and can reduce heart rate and treat heart failure without the use of an ICD.

Keywords: Atrial Fibrillation, cardiac resynchronization therapy