Ann Thorac Surg 2006;81:406-407
© 2006 The Society of Thoracic Surgeons
Correspondence
The Signal-Averaged P-Wave to Predict Atrial Fibrillation After Cardiac Surgery
R. Andrew Archbold, MD
Department of Cardiology, London Chest Hospital, Bonner Rd, London, E2 9JX United Kingdom
(Email: andrew.archbold{at}bartsandthelondon.nhs.uk).
To the Editor:
Hayashida and colleagues' [1] article adds to the considerable body of evidence that has identified advanced age and prolonged signal-averaged P-wave duration (SAPWD) as the only consistent markers of increased risk for the development of atrial fibrillation (AF) after cardiac surgery [2–7]. However, an important issue concerning the clinical utility of SAPWD in predicting this arrhythmia needs to be highlighted.
The cutoff identified in this study as best predicting AF was 135 ms, whereas previous studies of SAPWD have reported values ranging from 122 ms to 155 ms as having the greatest predictive accuracy for postoperative AF [3–7]. One explanation for these divergent values is that a variety of filtering techniques were applied in these studies including least-squares fit, unidirectional, bi-directional and finite impulse response filtering. The effects of each of these filtering techniques on SAPWD and the strength of the association between SAPWD and AF were examined in a study of 15 patients with paroxysmal AF and 15 controls [8]. A least-squares fit filter resulted in the longest P waves and also produced the strongest association with AF. Personal experience has demonstrated that P wave characteristics are altered in an unpredictable way, some P waves having almost identical durations when filtered by two different methods, whereas others have significantly different durations. In some cases, the SAPWD is shortened or prolonged beyond the chosen cutoff, such that the resulting prediction for the development of postoperative AF is changed. Therefore the methodology of P-wave filtering is critical to the derivation of the best predictive SAPWD cut-off. Ideally, each center should prospectively validate its own SAPWD cut-off for the prediction of AF after cardiac surgery before introducing its use into clinical practice [3].
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