Background: The presence of dynamic conduction and repolarisation changes facilitate functional block and re-entry in ventricular tachycardia (VT).
Objectives: We aimed to study the dynamic delay in late potentials and late repolarisation in creating functional substrate changes that facilitate re-entry.
Methods: Thirty patients (age 61 ± 5 yrs, 26 Male) underwent ablation. High-density multipolar mapping was performed with the AdvisorTM HD Grid catheter (Abbott). The HD Grid is a unique mapping catheter containing 16 equally spaced electrodes in a 4 x 4 grid with 3 mm spacing. This equal spline spacing allows the HD-wave bipolar mapping solution to be applied whereby the signal with the highest amplitude along and across splines is accepted removing the bias created by wavefront directionality.
A bipolar scar substrate map was performed during sinus rhythm and right ventricular (RV) sensed extra pacing (Bart’s Sense Protocol) to invoke conduction and repolarisation delay. The Bart’s Sense Protocol involves delivering single-sensed extra beats from the RV apex at an interval 20 ms above ERP in the RV. These single extra beats were templated within the system and a substrate map of voltage, late potentials (LP) and repolarisation time (RT) was made accepting only these templated beats. This was compared to sinus rhythm. A bipolar voltage of <0.5 mv was defined as dense scar, a voltage of 0.5–1.5 mv as scar border zone and voltages of >1.5 mv were defined as healthy tissue. Ventricular RT was calculated from unipolar contact electrogram T-waves using the Wyatt method, as the dv/dtmax of the T-wave. Entrainment or pace mapping confirmed critical sites for ablation and these were compared to sites of late potentials and late repolarisation before ablation.
Results: At a mean follow up of 9 months, freedom from ICD shocks and ATP was 90%. The mean dense scar area was 38.2 mm2 during intrinsic rhythm and 37.4 mm2 during the sense protocol map (p=0.25). The mean area of late potentials during sinus rhythm was 6.4 mm2 during sinus rhythm mapping and 19.3 mm2 during sense protocol pacing (p=0.001), suggesting that the sense protocol increases the ability to find regions of late potentials. Dynamic late repolarisation and/or late potentials were located within 7 mm of critical ablation sites in all patients. In 22 patients (p=0.04) dynamic late potentials were located at critical ablation sites. In 24 patients (p=0.02) dynamic late repolarisation was located at the sites critical for ablation. During intrinsic rhythm, the global ventricular repolarisation pattern within each patient was largely homogenous, with a narrow repolarisation range compared to the sense protocol. The median repolarisation range (mix-min RT per patient) was 166 ms versus 208 ms during the sense protocol (p=0.0003 versus intrinsic rhythm). Figure 1A demonstrates the paced voltage map of an example patient, where the VT diastolic pathway was mapped and entrained Figure 1B. Dynamic functional late potentials (Figure 1C) and late repolarisation surrounded by a corridor of early repolarisation either side of the diastolic pathway were identified (Figure 1D).
Conclusion: Ablation of functional LP via the sense protocol results in excellent outcomes in VT ablation. Regions of LP and late repolarisation were part of critical areas of the VT circuit in a significant number of patients. This demonstrates the potential for functional substrate mapping of LP and late repolarisation to safely ablate VT without mapping ventricular tachycardia.
