Malplacement of endocardial pacemaker electrodes in the middle cardiac vein.

Endocardial transvenous pacemaker electrodes have been implanted in 246 patients owing to symptomatic bradycardia. The electrode was malplaced in the middle cardiac vein in 12 patients. All the patients were on stable ventricular pacing at the time of implantation. The electrodes were still in function in six patients after 5-96 months (average 55). The electrode was replaced in three patients owing to the occurrence of exit block. Three patients died during the period under study. Right-sided bundle branch block (RBBB) configuration of paced QRS complexes was observed on the ECG when the electrode was malplaced in the middle cardiac vein. As RBBB only occurs with malplacement, the ECG can be employed to ensure correct positioning of the electrode.