Association of P-wave duration, dispersion, and terminal force in relation to P-wave axis among outpatients

Background: While P-wave duration (P-dur) and dispersion (P-disp) could both reflect fractionated and inhomogeneous propagation of sinus cardiac impulses, and may therefore be associated with each other, a clear relationship has not been extensively studied. We studied these markers as well as the significance of P-wave terminal force in lead V1 (PTFV1) in relation to the P-wave axis (P-axis). Methods: We appraised our previously studied sample of 500 consecutively numbered, otherwise unselected, electrocardiograms (ECGs) of outpatients from the University of Massachusetts, Worcester, Massachusetts, for the foregoing P-wave characteristics. P-disp, defined as the difference of the duration between the widest and narrowest P wave, and the greatest P-dur after a 12-lead ECG search, was measured manually to the nearest 10 ms. PTFV1 was considered positive when ≥40 mm² terminal deflection was present on biphasic P waves on lead V₁. Normal P-axis was considered 0° to +75° by manually constructing the mean frontal plane electrical P-axis from standard limb leads. Results: After excluding those with atrial arrhythmias, paced rhythms, errors in lead placement, P waves with low amplitude or overall technically poor tracing, 428 ECGs formed our final sample. P-dur was strongly associated with P-disp (P < 0.0001), but the correlation remained weak (r = 0.42). Overall, P-dur was not significantly associated with P-axis but when divided into tertiles and quintiles, the significance was evident within the range of the normal P-axis, particularly 0° to +60° (P < 0.0001). In a subanalysis of 380 ECGs that had appreciable biphasic P waves on lead V₁, PTFV1 was noted on 178 (47%) ECGs and was significantly associated with P-dur (P < 0.0001), P-disp (P < 0.0001), and P-axis (P = 002). When considering P-axis in tertiles and quintiles, P-dur was greater in patients with a positive PTFV1 and significant within the normal range of the P-axis, especially from 0°to +60°. Conclusion: P-dur, P-disp, and PTFV1 appear to share a significant tripartite association in relation to the normal P-axis, particularly when P-axis ranges 0°to +60°. Therefore, for optimal clinical assessment, these markers should be evaluated in relation to the normal P-axis.