The Effects of Pulmonary Vein Isolation on the Morphology of P Waves: The Contribution of Pulmonary Vein Muscle Excitation to the Formation of P Waves

Background: Although the pulmonary veins have been demonstrated to play an important role in initiating and perpetuating atrial fibrillation, the role that cardiac muscle tissue in the pulmonary veins plays regarding the formation of P wave remains to be elucidated. We sought to clarify the contribution of pulmonary vein cardiac muscles to the formation of P waves by analyzing the P loops/waves in patients with atrial fibrillation. Methods: The subjects in this study consisted of 21 patients (mean age, 57 ± 10 years) with drug‐refractory, paroxysmal atrial fibrillation who had undergone a segmental ostial isolation of all four pulmonary veins from the left atrium. Vectorcardiograms, intracardiac electrograms, and electrocardiograms (ECGs) were recorded before and after pulmonary vein isolation. Results: The morphology of P waves changed after pulmonary vein isolation procedures with a significant increase in the maximal amplitude of both the leftward force in lead x and the anterior force in lead z (P < 0.05). The middle part (second one of three parts) of P loop on the horizontal plane shifted anteriorly and leftward after pulmonary vein isolation. Intracardiac electrograms in the pulmonary veins demonstrated the averaged activation times of all four pulmonary veins to range from 40% to 84% of the P duration. Conclusions: The excitation of cardiac muscle tissue, which has migrated to the pulmonary veins, was thus found to play an important role in the formation of the middle part of the P wave/loop.