Induction of ventricular fibrillation by T wave shocks: observations from monophasic action potential recordings.
BACKGROUND
Shocks given during the vulnerable period of cardiac repolarization may induce ventricular fibrillation (VF). However, the relationship of the vulnerable period and the monophasic action potential (MAP) has not yet been reported in humans. The purpose of this study was, therefore, to determine how the monophasic action potential recorded from the right ventricle correlates with inducibility of VF using T wave shocks during ventricular pacing.


METHODS
Eleven patients undergoing implantable cardioverter defibrillator (ICD) implantation had a MAP catheter positioned in the right ventricle (RV). The local monophasic action potential duration at 90% repolarization (MAP90) duration was measured during pacing at 400 ms. VF induction was attempted by pacing at 400 ms for 10 cycles and then giving a 1.0 joule monophasic T wave shock at varying coupling intervals (CI) to the last paced stimulus. The maximum and minimum CI that induced VF were determined and mapped in relation to the MAP90 recording.


RESULTS
The average paced MAP duration was 275 +/- 20 ms. The minimum and maximum CI to induce VF were 255 +/- 24 ms and 325 +/- 36 ms respectively. This ranged from 93% to 118% of the MAP90 duration but because of delay in conduction time to the MAP catheter, shocks that induced ventricular fibrillation occurred between 74% and 99% of local repolarization time.


CONCLUSIONS
VF is inducible with low energy T wave shocks falling during the last 25% of the right ventricular MAP90 recording. This corresponds with VF initiation during phase III repolarization.
Shepard
R K
RK
The Department of Medicine, Division of Cardiology, Virginia Commonwealth University/Medical College of Virginia and McGuire VA Medical Center, Richmond, VA 23298-0053, USA. Keck.S@ATT.net
Wood
M A
MA
Dan
D
D
Clemo
H F
HF
Gilligan
D M
DM
Ellenbogen
K A
KA
D000200:Action Potentials; D000368:Aged; D002304:Cardiac Pacing, Artificial; D004198:Disease Susceptibility; D004562:Electrocardiography; D006801:Humans; D008875:Middle Aged; D011930:Reaction Time; D014693:Ventricular Fibrillation / Q000209:etiology* / Q000503:physiopathology; D016278:Ventricular Function, Right