Unshielded 36-channel Magnetocardiographic Mapping of the P-Wave in Patients with Paroxysmal Atrial Tachyarrhythmias

Atrial fibrillation (AF) predictors, such as clinical and echocardiographic parameters, as well as P-wave (Pw) signal-averaged (SA) electrocardiographic (ECG) analysis, have been widely studied [1,2], but the role of multichannel magnetocardiographic mapping (MMCG) in predicting recurrences of paroxysmal (Par) AF and/or Atrial Flutter (AFL) has not been fully investigated yet [3]. Aim of this study was to evaluate if high-resolution (HR) P-wave MMCG could predict AF and/or AFL recurrences in comparison to age, sex, and 15 other clinical and echocardiographic parameters. Methods: the study was a retrospective collection of 21 patients with different cardiac substrates (M/F 17/4, mean age 55.4 ± 14.3) in which clinical, echocardiographic and magnetocardiographic parameters and arrhythmic events were prospectively noted during e mean clinical follow-up of 63.8 ± 61.5 months. As inclusion criterion at least one recurrence of ParAF and/or ParAFL preceding the MMCG session was required. A 36-channels DC-SQUID system (sensitivity 20 fT/Hz½) was used to map, under sinus rhythm, the cardiac magnetic field component perpendicular to the anterior chest wall (Bz) from 36 points simultaneously (measuring grid 20 x 20 cm). 17 variables, among clinical non-cardiac, cardiac and echocardiographic parameters predictors of AF were considered, according to the Framingham Heart Study and the Cardiovascular Health Study. From signal averaged HR MMCG, magnetic P wave duration (PwD) and atrial magnetic field due P wave depolarisation (Pwd) and repolarization (Pwr) components were measured in ms. Then Pwd/PwD, Pwr/PwD and (Pwd/Pwr)/PWD ratios were calculated. HR SA ECG PwD was also measured. Following univariate analysis ANOVA (UVA), the factors with an associated p value < 0.1 were tested in a multivariate model. Cox regression analysis was performed to predict independent factors of ParAF and/or ParAFL relapse. A p value < 0.05 was considered significant. Results: Among 11 factors with an associated p value < 0.1 at UVA, the multivariate Cox regression analysis found that the only independent predictors of ParAF and/or ParAFL were the MMCG Pwr/PwD (p<0.045) and (Pwd/Pwr)/PWD (p<0.044) indexes. Conclusion: SA HR MMCG is a novel method, which provides differentiation between atrial depolarisation and repolarization phenomena during the P wave. Interestingly our preliminary results show that the HR MMCG Pwr/PwD and (Pwd/Pwr)/PWD indexes are independent predictors of ParAF and/or ParAFL recurrences. However a larger patients population is needed to define the clinical value of this diagnostic approach.