Left atrial electrograms recorded through the patent foramen ovale

The presence of a patent foramen ovale allows direct recording of a left atrial (LA) electrogram. Three patients are reported in whom simultaneous high right atrial (HRA), coronary sinus (CS), and direct LA electrograms were obtained. In two patients with normal surface ECG P waves the direct LA lead depolarized before the CS or low RA. The HRA to LRA and HRA to CS conduction times were similar to those reported previously. In a patient with a prolonged surface ECG P wave, the direct LA electrogram occurred late and after low RA depolarization. Recording LA electrograms through a patent foramen ovale is a useful technique, and these defects should be sought in all patients undergoing electrophysiological study.