THE MEAN VENTRICULAR-FIBRILLATION CYCLE LENGTH - A POTENTIALLY USEFULPARAMETER FOR PROGRAMMING IMPLANTABLE CARDIOVERTER-DEFIBRILLATORS

In programming the implantable cardioverter defibrillator (ICD), the v entricular tachycardia (VT) detection cycle length (CL) is based on th e CL of the documented tachycardia but the ventricular fibrillation (V F) detection CL is set arbitrarily. Appropriate programming of VF dete ction may not only reduce the incidence of inappropriate ICD shocks fo r non-VF rhythms but can also avoid the fatal underdetection of VF. Th e mean VFCL may provide a useful parameter for optimal ICD programming for VF detection if it is reproducible. This study examined the intra patient reproducibility and interpatient variation of the mean VFCL in 30 ICD patients (25 men and 5 women, mean age 63 +/- 13 years). A tot al of 210 VF episodes (7 +/- 4 per patient, range 3-17) induced by T-w ave shocks (166) or AC (44) at the ICD implant (30 patients) and the p redischarge test (12 of 30 patients) were analyzed. The mean VFCL was calculated from the stored V-V intervals in the ICDs. Although the mea n VFCL varied significantly from 171 +/- 6 to 263 +/- 11 ms (P < 0.01) among different patients, if was reproducible among different VF epis odes in an individual patient (maximal variation 4-50 ms, P > 0.05). T he mean VFCL was not significantly different between patients with and without antiarrhythmic drugs (210 +/- 32 vs 220 +/- 23 ms, P > 0.05) and was correlated with the ventricular effective refractory period (r = 0.5, P < 0.05). The mean VFCL varies greatly among different patien ts but remains reproducible in an individual patient, suggesting that the mean VFCL may serve as a reference for ICD programming of VF detec tion.