Discussion
Several previous reports have suggested that these potentials indicate the preferential pathway conduction connecting the origin of an arrhythmia and the myocardial breakout site, and a preferential pathway potential guided ablation can be an effective strategy for PVC ablation.1, 3, 7 We reported that presystolic potentials during PVCs and late potentials during SR were seen at the successful ablation site, and the configuration of the vertically and horizontally-flipped presystolic potentials during PVCs nearly matched that of the late potentials during SR.8 In this case series, we also found that the M-shaped presystolic potentials during PVCs and the W-shaped late potentials during SR were reversely matched. These reversed potentials might indicate bidirectional conduction of the preferential pathway in opposite directions.8 To demonstrate the hypothesis, we created an activation vector mapping with the annotation of the onset of the presystolic potentials and offset of the late potentials. At several points around the successful ablation site, both the presystolic potentials during PVCs and late potentials during SR were observed. At the PVC origin, the presystolic potentials during PVCs were earliest and the offset of the ventricular electrogram during SR was latest. Coherent maps visualizing the vector of this preferential conduction indicated that the propagation direction of the presystolic potentials was opposite to that of the late potentials, which was supportive of our hypothesis.
These potentials are commonly seen in the periaortic area, but rare in the RVOT³. In our case series, however, those potentials were also seen in the peri-pulmonary-artery (PA) area. Based on our findings, those M-shaped and W-shaped potentials may reflect the slow conduction due to the smaller amount of myocardium adjacent to the valve annulus such as the aortic valve and pulmonary valve.
The flipped M-shaped presystolic potentials matched the W-shaped late potentials in the majority of our cases, but not in some cases. Those observations might be explained by the difference in the direction between the propagation of the preferential pathway to the ventricular myocardium during the PVC and the propagation of the ventricular myocardium to the preferential pathway during SR. Regarding the association of the catheter position with the direction of the preferential pathway conduction, if the catheter position is not parallel to the direction of the preferential pathway conduction, those potentials might not be reversely matched. To assess the configuration of those potentials, we should consider the catheter position.