Scar Voltage Mapping in Fast Ventricular Tachycardia for Identifying Functional Substrates of Tachycardia Isthmuses: A Proof-of-Concept Study.

Abstract

Background: Identification of fast ventricular tachycardia (FVT; cycle length <320 ms) isthmuses is often hindered by hemodynamic instability during sustained FVT and by rate-dependent (functional) scar properties. Comparing ultra-high-density voltage heterogeneity maps (0.1-1.5 mV) of the scar area during sinus rhythm (SR) and FVT may delineate the rate-dependent components of the FVT isthmus (FVTI) and improve substrate identification during SR.

Methods: Thirty Large White swine with anterior myocardial infarction underwent cardiac magnetic resonance imaging for signal intensity mapping, followed by electrophysiological studies at 4 and 16 weeks post-infarction. FVTIs were defined as corridors of high-frequency electrograms spanning electric diastole and completing reentrant circuits in activation maps. Voltage heterogeneity mapping during FVT and SR was performed to identify voltage channels and delineate functional substrate. Statistical comparisons were performed using the Student t test, with data presented as mean±SD.

Results: Sixty ventricular tachycardias were induced, including 27 monomorphic episodes with a cycle length < 320 ms. Of these, 25 exhibited reentrant activation with identifiable FVTI. All FVTIs were housed within channels identified in voltage heterogeneity maps during FVT and signal intensity maps; 22 of 25 (88%) colocalized with a channel visible in SR voltage maps. Comparing FVT and SR voltage maps revealed that (1) dense scar area (<0.1 mV) was larger in FVT than in SR maps (1.5±0.3 versus 0.1±0.2 cm², P<0.001), (2) voltage channels sustaining FVTI in FVT were longer than in SR (18.7±7.1 versus 14.6±6.1 mm, P=0.047), and (3) while all channels in FVT maps were bordered by dense scar (<0.1 mV), only 4 in SR exhibited this feature, indicating a functional substrate in 84% of FVTIs.

Conclusions: FVTIs are located within channels identified in voltage heterogeneity maps during SR and FVT. These channels colocalize with heterogeneous tissue channels in signal intensity maps. Comparative analysis of SR and FVT voltage maps enables delineation of functional borders.