The signal-averaged P wave duration: A rapid and noninvasive marker of risk of atrial fibrillation

Abstract

Objectives. This study was undertaken to determine the ability of the signal-averaged electrocardiogram (ECG) to identify evidence of delayed atrial activation in patients with a history of atrial fibrillation.Background. Atrial fibrillation is a reentrant rhythm and depends on atrial conduction delay for its development. The signal-averaging technique is useful for accurately measuring total cardiac activation times, including delayed low amplitude signals, and thus can help identify the substrate for reentrant arrhythmias.Methods. Standard 12-lead and signal-averaged ECGs were recorded from 15 patients with a documented history of prior paroxysmal or chronic atrial fibrillation and 15 age- and disease-matched control subjects without a history of atrial fibrillation. Signal averaging was performed using an orthogonal lead system with the QRS complex as a trigger and the P wave as a template for the signal-averaging process. Total P wave duration was measured before and after filtering with a least squares fit filter. The P wave complexes on the three bipolar leads were combined into a vector combination of orthogonal leads. The total P wave duration of the individual unfiltered and filtered leads and the vector combination of filtered leads were calculated and used for analysis.Results. The P wave duration by standard ECG was not significantly different in patients with a history of atrial fibrillation and control subjects. Signal-averaged P wave durations were measured from orthogonal leads before and after digital filtering. Mean unfiltered P wave duration was significantly longer in patients with a history of atrial fibrillation than in control subjects (132 ± 22 vs. 114 ± 14 ms [p < 0.03] is the X lead, 135 ± 21 vs. 115 ± 15 ms [p < 0.03] in the Y lead and 133 ± 23 vs. 114 ± 14 ms [p < 0.03] in the Z lead). Mean filtered P wave duration was also longer ia patients with atrial fibrillation than in control subjects (151 ± 23 vs. 130 ± 19 ms [p < 0.01] in the X lead, 157 ± 22 vs. 136 ± 17 ms [p < 0.01] in the Y lead and 154 ± 23 vs. 135 ± 15 ms [p < 0.01] in the Z lead). After filtering, a vector composite of orthogonal leads was determined. Again, P wave duration in patients with a history of atrial fibrillation exceeded that in the control subjects (162 ± 15 vs, 149 ± 12 ms [p < 0.01]). Using the vector composite of filtered orthogonal leads, a P wave duration ≥ 155 ms was associated with a sensitivity of 80%, a specificity of 93% and a positive predictive value of 92% for identifying patients with history of atrial fibrillation.Conclusions. A prolonged signal-averaged P wave duration may be a simple noninvasive marker of the risk for development of atrial fibrillation.