High-resolution analysis of the surface P wave as a measure of atrial electrophysiological substrate

At present atrial electrophysiology can only be assessed by invasive study. This limits available data in humans concerning atrial electrophysiologic changes in disease and in response to intervention. Indirect evidence suggests that the signal-averaged P wave (SAPW) may provide noninvasive markers of atrial electrophysiology but no direct evaluations that measure both refractoriness and conduction time have been reported.

We investigated 9 patients attending for diagnostic electrophysiological studies (4 male; mean age 35.7 years). A 20-pole catheter was positioned in the right atrium; a decapole catheter was placed in the coronary sinus. Atrial effective refractory period (AERP) and conduction times were measured at the lateral and septal right atrium and the left atrium during sinus rhythm (SR) and at pacing cycle lengths of 600, 500, and 400 ms. Simultaneous SAPW recordings were taken during SR and pacing at 600 ms. Intravenous flecainide (2 mg/kg) was given after which the protocol was repeated.

Flecainide slowed conduction significantly at all sites (P < 0.05). During baseline measurements, rate adaptation of AERP was observed (P < 0.02 at the septum). Flecainide increased filtered P wave duration (P < 0.05) and reduced P wave energies (P < 0.05). Negative correlation was observed between P wave energies and conduction time with an inverse relationship between high-frequency energy and left atrial AERP.

The SAPW provides a noninvasive marker of atrial electrophysiology.