Diagnostic Value of the Modified Limb Lead System in Localizing the Origin of Outflow PVCs

The most common subgroup of premature ventricular contractions (PVCs) is the idiopathic outflow tract premature ventricular contraction (IOT-PVC). The radiofrequency catheter ablation of PVCs is the choice of treatment in drug-resistant or intolerant patients. There are many different ways to localize PVC origins, some of which pose a challenge. We hypothesized that changing limb electrode locations can help us localize IOT-PVCs.
 
This cross-sectional study was done in Rajaie Cardiovascular Medical and Research Center, Tehran, Iran, from 2019 through 2020. In all patients, in addition to surface electrography, 3 limb electrodes were placed at 3 spaces: right parasternal at the second intercostal space, left parasternal at the second intercostal space, and the tip of the left scapula. Three new vectors were achieved, which were then compared with the same-named limb vectors.
 
The study population consisted of 102 patients. The voltage of the R and S waves of PVCs were compared in modified and conventional leads. All the formulas used had a statistically significant relationship (P<0.007) with the origin of PVCs other than IMR/ICR and IMR-S/ICR-S.
 
Comparison of the R and S waves of PVCs in modified lead II and III with the same-named conventional leads can yield the best results to estimate the origin of PVCs. The most useful formulas concerning sensitivity and specificity are IIMR/IICR and IIIMR/IIICR. The absence of notching at modified lead II can be a predictor of successful PVC ablation. (Iranian Heart Journal 2022; 23(4): 29-37)