The effect of induction method on defibrillation threshold and ventricular fibrillation cycle length.
BACKGROUND
Since no clinical data are available on the comparison of the "shock on T-wave" and "high frequency burst" ventricular fibrillation (VF) induction modes during defibrillation threshold (DFT) testing, we aimed to compare these two methods during implantable cardioverter defibrillator implantation.


METHODS
The DFT was determined with a step-down protocol using biphasic, anodal polarity (100%, 40%, 20% voltage control) shocks. Patients were randomized: VF was induced by 50 Hz burst in group B (n = 45) and T-wave shock in group T (n = 41). The DFT was defined as the lowest energy level that terminated VF; confirmed DFT (DFTc) was defined as the minimal energy level that consecutively terminated VF twice. Success rate of DFTc was calculated during an intraindividual test for the alternate induction method.


RESULTS
A total of 546 episodes of VF were induced: n = 278 (B) vs n = 268 (T). Incidence of VT during inductions was 9.9% (B) vs 2.7% (T), P < 0.05. Neither the DFT, 8.8 +/- 4.0 J (B) vs 9.7 +/- 4.2 J (T), nor the DFTc, 10.6 +/- 5.1 J (B) vs 10.8 +/- 4.2 J (T), proved to be significantly different. A significant correlation was found between VF cycle length (CL) and the concomitant DFT (r = 0.298, P < 0.05) in group T only. Subgroup analysis of patients under chronic class III antiarrhythmic treatment showed no increase of the DFT in either group and significantly lower incidence of VT induction in group T regardless of antiarrhythmic treatment.


CONCLUSIONS
The DFT and the VFCL proved to be independent of the VF induction method. The T-wave shock was more unlikely to induce VT during DFT testing. These results suggest that both methods are reliable in DFT determination, though T-wave shock application is a more reliable method for DFT testing.
Zima
Endre
E
Cardiovascular Center, Department of Cardiovascular Surgery, Semmelweis University, 68 Városmajor Str., H-1122 Budapest, Hungary.
Gergely
Mihály
M
Soós
Pál
P
Gellér
László Alajos
LA
Nemes
Attila
A
Acsády
György
G
Merkely
Béla
B
D000368:Aged; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000379:methods*; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*