Relation of Magnetocardiographic Arrhythmia Risk Parameters to Delayed Ventricular Conduction in Postinfarction Ventricular Tachycardia

Time-domain late field and intra-QRS fragmentation parameters in magnetocardiography (MCG) identify patients prone to VT after myocardial infarction. This study investigated if they are related to slow ventricular conduction and affected by arrhythmia surgery. Twenty-two patients with old myocardial infarction undergoing map-guided subendocardial resection to treat sustained VT were included. Bipolar electrograms were recorded during operation using an epicardial jacket and endocardial balloon electrode array. The time from the QRS onset to the end of local ventricular excitation in each electrogram was measured during sinus rhythm. Multi-channel MCG was recorded before and after operation and filtered QRS duration (QRSd), root mean square amplitude of the magnetic field strength during the last 40 ms of the QRS complex (RMS40), duration of the low amplitude signal < 300 fT (LAS300), fragmentation index M (M), and fragmentation score S (S) were determined. All patients had one or two VT foci localized and resected. MCG parameters correlated with time to the latest end of ventricular excitation; r = 0.45 for QRSd (P = 0.035), r = 0.64 for M (P = 0.001), and r = 0.73 for S (P < 0.001). The correlations were even better in patients with anterior infarction (e.g., r = 0.87 for QRSd, P < 0.001; r = 0.91 for M, P < 0.001). The operation reduced the abnormalities in MCG parameters and 20 of the 21 patients tested postoperatively became noninducible. MCG parameters indicating postinfarction arrhythmia propensity are related to delayed ventricular conduction. Abolition of the arrhythmia substrate reverses the abnormality of these parameters.