Blocked Atrial Bigeminy as an Unusual Cause of Bradycardia: A Case Report

The diagnosis of blocked atrial bigeminy may be challenging. It can easily be misinterpreted as sinus bradycardia or sinus exit block leading to unnecessary pacemaker implantation. We report a case of frequent blocked premature atrial contractions leading to episodes of marked bradycardia. A 66-year-old man disturbed with low pulse (42 bpm) measured by an automated blood pressure monitor sought medical attention. The patient also had untreated grade I arterial hypertension. Ambulatory ECG monitoring was performed and very frequent blocked premature atrial contractions were seen. The P wave of the atrial premature atrial contractions was always superimposed on the ST segment or T wave simulating a bifid T wave. Blocked atrial quadrigeminy, blocked atrial trigeminy, and blocked atrial bigeminy were observed. The minimum heart rate associated with blocked atrial bigeminy was 37 bpm. There were multiple episodes of regular ventricular rhythm during blocked atrial bigeminy. NT-proBNP concentration was within normal limits. Echocardiography showed only mild left ventricular hypertrophy, mild left atrial dilation and type I diastolic dysfunction. Therapy with flecainide and amiodarone separately was not effective. Option of radiofrequency catheter ablation was discussed with the patient, but was not accepted due to procedural risks and absence of severe symptoms related to blocked PACs. The patient was reassured and regular follow-up was recommended. The target values of blood pressure were achieved with candesartan at a dose of 32 mg. Thus, blocked atrial bigeminy is a rare cause of bradycardia with a regular ventricular rhythm. Recognition of the P wave superimposed on the ST segment or the T wave may be a clue for a correct diagnosis. Physicians should be aware of this condition to avoid unnecessary pacemaker implantation.