Altered Interatrial Conduction Detected in MADIT II Patients Bound to Develop Atrial Fibrillation

BACKGROUND: Changes in P-wave morphology have recently been shown to be associated with interatrial conduction route used, without noticeable changes of P-wave duration. This study aimed at exploring the association between P-wave morphology and future atrial fibrillation (AF) development in the Multicenter Automatic Defibrillator Trial II (MADIT II) population. METHODS: Patients included in MADIT-II without a history of AF with sinus rhythm at baseline who developed AF during the study ("Pre-AF") were compared to matched controls without AF development ("No-AF"). Patients were followed for a mean of 20 months. A 10-minute high-resolution bipolar ECG recording was obtained at baseline. Signal-averaged P waves were analyzed to determine orthogonal P-wave morphology, P-wave duration, and RMS20. The P-wave morphology was subsequently classified into one of three predefined types using an automated algorithm. RESULTS: Thirty patients (age 68 +/- 7 years) who developed AF during MADIT-II were compared with 60 patients (age 68 +/- 8 years) who did not. P-wave duration and RMS20 in the Pre-AF group was not significantly different from the No-AF group (143 +/- 21 vs 139 +/- 30 ms, P=0.26, and 2.0 +/- 1.3 vs 2.1 +/- 1.0 muV, P=0.90). The distribution of P-wave morphologies was shifted away from Type 1 in the Pre-AF group when compared to the No-AF group (Type 1/2/3/atypical; 25/60/0/15% vs 10/63/10/17%, P=0.04). CONCLUSIONS: This study is the first to describe changes in P-wave morphology in patients prior to AF development. The results indicate that abnormal interatrial conduction may play a role in AF development in patients with prior myocardial infarction and congestive heart failure.