The phase characterization of ventricular pre-excitation via Mahaim Pathways

The authors evaluate the functional scintigraphic pattern during pre-excitation by electrophysiologically confirmed Mahaim (M) pathways (P). Six patients (pts), 5 nodo-ventricular (NV) and 1 fasciculo-ventricular (FV) P were studied while pre-excited, 3 during rapid atrial pacing. In NVP, the site of earliest phase angle (phi) was seen in a septal or right paraseptal location, progressing in 4 pts through the right ventricle (RV) then through the left ventricle (LV) and mean RV(RVphi) was smaller than LVphi(-6.5 +- 32.4 vs. 12.7 +- 15.8, rho=0.05). The FVP revealed earliest phi in septal and LV lateral walls, progressing through the LV(LVphi=41.5 +- 11.0) and later through the RV(RVphi=71.8 +- 14.3). These phase patterns resemble those of L bundle branch block (BBB) and RBB in the absence of pre-excitation but can be differentiated from pre-excitation via a septal Kent (K) P, with symmetric RV and LV phase variation, or via lateral RV or LV KP, where earliest phi localized to the atrio-ventricular groove of the affected ventricle. In pts with MP serial changes in phi paralleled known activation and presumed contraction, sequence. During known pre-excitation the presence and configuration of a MP could be suggested from scintigraphic phi patterns.