PRIMARY VENTRICULAR-FIBRILLATION IS ASSOCIATED WITH INCREASED PACED RIGHT-VENTRICULAR ELECTROGRAM FRACTIONATION

Background The mechanisms of spontaneous ventricular fibrillation (pri mary VF) in patients without structural heart disease are obscure. A n ew technique has shown that in patients with hypertrophic cardiomyopat hy conduction of fractionated ventricular paced beats, recorded at sev eral right ventricular sites, is prolonged in individuals who have suf fered a VF arrest, and this may reveal one component of a reentrant su bstrate. Patients with primary VF were studied with the same methods t o determine whether similar abnormalities are present in this group. M ethods and Results Nine patients with primary VF were studied by pacin g one right ventricular (RV) site by use of a constant drive train wit h an extrastimulus inserted every third beat and reducing the extrasti mulus coupling interval (S1S2 interval) by 1 ms on each occasion while recording at three other sites. The delay of each fractionated potent ial in the high-pass-filtered electrograms in response to the extrasti mulus was determined and used to form conduction curves of delay versu s the S1S2 interval. These curves were repeated by pacing each RV site in turn and recording from the other three sites. The curves were cha racterized by determining the S1S2 interval at which electrogram compo nents increased in delay by 0.75 ms/20 ms reduction in S1S2 interval a nd the increase in electrogram duration between a coupling interval of 350 ms and 1 ms above refractoriness. Seven control patients were stu died using the same method. The mean increase in electrogram duration in VF patients was 13 ms (range, 3 to 23 ms) compared with 4 ms (range , -2 to 14 ms) in unaffected control patients. The extrastimulus coupl ing interval at which delay increased was 318 ms (range, 293 to 334 ms ) in VF patients and 274 ms (range, 265 to 284 ms) in control patients (P<.01). There was no difference between the number of fractionated p otentials in VF patients and control patients. Conclusions In primary VF patients, the individual potentials within fractionated electrogram s have increased delays when compared with control patients. This may identify one component of a reentrant arrhythmic substrate.