Characterization of the Effects of Single Ventricular Extrastimuli on Endocardial Activation in Human Infarct-Related Ventricular Tachycardia Original Research Article

Objectives The purpose of this study was to examine the resetting response in human ventricular tachycardia (VT) circuits with 3-dimensional mapping. Background In characterizing re-entry with the resetting response, inferences are made about interaction of single ventricular extrastimuli (SVE) with VT. Methods Non-contact mapping was used to examine the effects of SVE from 25 sites on 10 infarct-related VT circuits. Results The local temporal excitable gap (EGap) was 113.8 ± 64.3 ms, 25.8 ± 11.2% of VT cycle length. In 7 VT circuits there was a clear difference in the EGap at different points in the circuit. All circuits could be pre-excited over a range of SVEs, resulting in either: 1) premature activation throughout the circuit resulting in reset; 2) premature activation at entry, but subsequent interval dependent conduction slowing (IDCS) resulting in a fully compensatory return cycle; or 3) change to functional lines of block and return cycle QRS morphology. The principal determinant of whether SVE resulted in reset was the degree of IDCS within the diastolic pathway (DP) of the circuit. Resetting occurred from 9 sites (7 VT) but was absent from 15 sites despite pre-excitation of a sizeable EGap in the circuit in all cases. Conclusions In infarct-related VT, all circuits can be pre-excited over a range of SVEs, the effect of which is dependent on the degree of IDCS within the DP or modification of functional block defining the circuit. Failure to reset does not therefore indicate the absence of an EGap or failure of entry to the circuit. The temporal and spatial properties of the EGap vary at different sites of entry to the circuit.