Spatial resolution of defibrillator electrograms to detect distinct exit sites of scar-related ventricular tachycardia.

Abstract

Analysis of implantable cardioverter-defibrillator electrograms (IEGMs) with pacing along the scar edge is often used to approximate distinct exit sites of scar-related ventricular tachycardia (VT). We evaluated the spatial resolution of IEGMs in identifying distinct exit sites of scar-related VT. Seventeen patients with scar-related VT were included. Threshold pacing (500-ms cycle length) was performed at sites spaced 10 mm apart along the scar border, as defined by high-density bipolar voltage mapping. Twelve-lead electrocardiogram and near-field and far-field IEGMs were recorded at each pacing site and assessed for morphology. The average scar size was 60 ± 30 cm(2) and the scar border perimeter measured 28 ± 9 cm. A median of 18 pacing sites per patient were collected, spaced 14 ± 11 mm apart. The mean spatial resolution for the near-field, far-field, and combination of both was 82.7 ± 76 mm, 62.7 ± 53.6 mm, and 56.7 ± 50 mm (P for trend < 0.001). In all cases, IEGM analysis failed to identify distinct VT exit sites spaced <2 cm apart. Analysis of IEGM morphology with pacing around the edge of the scar is unable to distinguish distinct VT exit sites spaced <2 cm apart, with an average spatial resolution of 5 cm. Given the wide range of values observed, detailed pace mapping over a perimeter of 10-15 cm along the scar edge appears crucial to define the boundaries of a linear ablation strategy to target the VT exit site based on IEGM pace match alone.