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CLINICAL RESEARCH: HEART RHYTHM DISORDER

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

Department of Cardiac Electrophysiology, St. Mary’s Hospital and Imperial College, London, United Kingdom.

Manuscript received May 26, 2006; revised manuscript received October 30, 2006, accepted November 16, 2006.

^_* Reprint requests and correspondence: Prof. Nicholas S. Peters, Waller Cardiac Department, St. Mary’s Hospital, Praed Street, London W2 1NY, United Kingdom. (Email: n.peters{at}imperial.ac.uk).

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.

Abbreviations and Acronyms   CI = coupling interval   CL = cycle length   DP = diastolic pathway   ECG = electrocardiogram   EGap = excitable gap   IDCS = interval dependent conduction slowing   LV = left ventricle   SVE = single ventricular extrastimuli   VT = ventricular tachycardia