Objective: The aim was to determine the beat to beat variability in local activation time during sustained monomorphic ventricular tachycardia in a canine model of experimental myocardial infarction.
Methods: A digital template matching algorithm was developed for detecting subtle beat to beat variability in local activation timing at each of multiple ventricular sites. Ten electrically induced sustained ventricular tachycardia episodes, mean cycle length 211 (SD 40) ms, were endocardially and epicardially mapped in mongrel dogs weighing 15-20 kg. Digitised data were analysed for beat to beat local activation time variability. Similar data recorded during ventricular pacing at comparable rates and during sinus rhythm served as controls.
Results: The overall mean variability of local activation time for all 10 ventricular tachycardias was 3.2(1.6) ms, range 1.8(1.1) ms to 4.7(2.8) ms, in contrast to the overall mean variability of 0.2(0.4) ms (p = 0.0001) for ventricular pacing and 0.7(0.6) ms (p = 0.0001) for sinus rhythm. Oscillations in local activation time manifested alternans type periodicity during seven of 10 ventricular tachycardias independent of any alternans in local electrogram morphology.
Conclusions: During sustained, monomorphic ventricular tachycardia, beat to beat variability and alternans type oscillations in local activation time are common and may be an intrinsic property of re-entry since they are negligibly small during ventricular pacing.