Magnetocardiographic study of patients with right and left bundle branch blocks

Intraventricular conduction disturbances can be usually registered as complete bundle branch blocks (cBBB): right (RBBB) or left (LBBB), as hemiblocks: anterior-left (LAH) or posterior-left (LPH), isolated or in combination with RBBB. LBBB often creates problems in ECG diagnosis of ischemic heart disease (IHD). It has been recently proposed that magnetocardiographic (MCG) mapping can be useful for early diagnosis of IHD also in patients with LBBB; however MCG patterns of cBBB in the absence of IHD have not been described. This study was aimed to define typical magnetic field (MF) distribution (MFD) patterns, during ventricular depolarization (QRS) and repolarization (VR), in patients with cBBB. Methods 36 patients (pts) with ECG diagnosis of cBBB [14 RBBB, 18 LBBB (2 with IHD), 4 RBBB+LAH] and 33 healthy subjects (HS) were consecutively investigated with an unshielded 36-channels DC SQUID MMCG system (sensitivity is 20 fT/Hz½, at 1 Hz) recording the z component of cardiac MF from a 36-point grid (20 x 20 cm). MFD maps and MF gradient orientation (MFGO) were analyzed with a time resolution of 2 ms. Quantitative analysis of VR was performed utilizing automated MCG analysis program according to preset T-wave parameters. Results In RBBB pts, the direction of septal depolarization was normal (avg. MFGO: 67.2°±17.4). A significant (p<0.001) difference of Rpeak MFGO was observed between RBBB pts with (52.8°±15) and without (-50.8± 28.5) cardiac abnormalities (CaAb), or associated with LAH (-148°±17.3). In pts with RBBB + LAH, average ST and Tpeak MFGO values were different (p<0.01 and p<0.05, respectively) from those of pts with RBBB only. All pts with LBBB had cardiac abnormalities, mostly dilated cardiomyopathy (DCM). As compared to HS, LBBB was characterized by an inversion (from right-to-left) of the direction of septal activation (-49.9°±20.9), a counterclockwise rotation of Rpeak MFGO (-113.4°±7.6) and an inversion of ST and Tpeak MFGO (61.4°±14.1 and 57.9°±14.1, respectively). In the 2 IHD pts, no difference of T-wave parameters was found. In one post-myocarditis DCM, ST and Tpeak MFGO rotated clockwise, toward more positive values. Discussion MCG differentiates RBBB associated with CaAb. MCG detection of ischemia in LBBB remains questionable.