title: Mechanistic enquiry into the effect of increased pacing rate on the upper limit of vulnerability.
abstract: The goal of this study is to investigate the mechanisms responsible for the increase in the upper limit of vulnerability (ULV; highest shock strength that induces arrhythmia) following the increase in pacing rate. To accomplish this goal, the study employs a three-dimensional bidomain finite element model of a slice through the canine ventricles. The preparation was paced eight times at a basic cycle length (BCL) of either 80 or 150ms followed by delivery of shocks of various strengths and timings. Our results demonstrate that the shock strength, which induced an arrhythmia 50% of the time, increased 20% for the faster pacing compared to the slower pacing. Analysis of the mechanisms underlying the increased vulnerability revealed that delayed post-shock activations originating in the tissue depths appear as breakthrough activations on the surfaces of the preparation following an isoelectric window (IW). However, the IW duration was consistently shorter in the faster-paced preparation. Consequently, breakthrough activations appeared on the surfaces of this preparation earlier, when the tissue was less recovered, resulting in higher probability of unidirectional block and reentry. This explains why shocks of the same strength were more likely to result in arrhythmia induction when delivered to a preparation that was rapidly paced.
authors.affiliation: Tulane University, Department of Biomedical Engineering 7001 Freret Street, New Orleans, LA 70118, USA. dbourn@tulane.edu
authors.forename: David W
authors.initials: DW
authors.lastname: Bourn
authors.forename: Mary M
authors.initials: MM
authors.lastname: Maleckar
authors.forename: Blanca
authors.initials: B
authors.lastname: Rodriguez
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Trayanova
mesh_terms: D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology* / Q000503:physiopathology*; D001683:Biological Clocks; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects*; D003198:Computer Simulation; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D008955:Models, Cardiovascular; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors