Prognosis of patients with ventricular tachycardia or fibrillation and a normal electrophysiologic study

Primary ventricular fibrillation is associated with increased paced right ventricular electrogram fractionation

BACKGROUND

The mechanisms of spontaneous ventricular fibrillation (primary VF) in patients without structural heart disease are obscure. A new technique has shown that in patients with hypertrophic cardiomyopathy conduction of fractionated ventricular paced beats, recorded at several right ventricular sites, is prolonged in individuals who have suffered a VF arrest, and this may reveal one component of a reentrant substrate. Patients with primary VF were studied with the same methods to determine whether similar abnormalities are present in this group.

METHODS AND RESULTS

Nine patients with primary VF were studied by pacing one right ventricular (RV) site by use of a constant drive train with an extrastimulus inserted every third beat and reducing the extrastimulus coupling interval (S1S2 interval) by 1 ms on each occasion while recording at three other sites. The delay of each fractionated potential in the high-pass-filtered electrograms in response to the extrastimulus was determined and used to form conduction curves of delay versus the S1S2 interval. These curves were repeated by pacing each RV site in turn and recording from the other three sites. The curves were characterized by determining the S1S2 interval at which electrogram components increased in delay by 0.75 ms/20 ms reduction in S1S2 interval and the increase in electrogram duration between a coupling interval of 350 ms and 1 ms above refractoriness. Seven control patients were studied 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 coupling 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 potentials in VF patients and control patients.

CONCLUSIONS

In primary VF patients, the individual potentials within fractionated electrograms have increased delays when compared with control patients. This may identify one component of a reentrant arrhythmic substrate.

Comparison of epicardial and endocardial programmed stimulation in patients at risk for ventricular arrhythmias after cardiac surgery

Programmed ventricular stimulation was performed on 36 patients after recent cardiac surgery using implanted right ventricular epicardial temporary wires and with catheters positioned percutaneously at two right ventricular endocardial sites. Patients were followed for a mean of 18.5 months (range 3 to 36 months). Epicardial wires were nonfunctional in 10 patients (28%) due to excessively high pacing thresholds. Overall, 22 patients (61%) had inducible sustained ventricular tachycardia; epicardial wires were functional in 15 (68%) of these patients. Six patients without inducible ventricular tachycardia with epicardial stimulation were inducible using endocardial stimulation. Of the 24 patients in whom epicardial and endocardial ventricular stimulation could be performed, concordant results were obtained in only 17 (71%), despite similar epicardial and endocardial ventricular effective and functional refractory periods. A total of 14 arrhythmic events occurred during the follow-up period. Of the 22 patients with an inducible sustained ventricular tachycardia, 12 (64%) had subsequent arrhythmic events. Only 2 of the 14 noninducible patients had follow-up arrhythmic events, one of which was caused by medication proarrhythmia. Endocardial ventricular stimulation had a superior sensitivity (83% versus 30%, P < 0.0001) and an improved negative predictive value (86% versus 61%, P < 0.05) compared with epicardial ventricular stimulation. These results indicate that noninducibility using epicardial programmed ventricular stimulation does not reliably portend a low risk for recurrent ventricular tachyarrhythmias. Epicardial programmed stimulation, used alone, may be inadequate for postoperative electrophysiological evaluation of patients at risk for ventricular arrhythmias.

Prognosis after syncope: impact of left ventricular function

A cardiac cause of syncope has been associated with increased sudden death risk, whereas unexplained syncope has a benign prognosis. However, in patients who have depressed left ventricular function, the accuracy of diagnostic tests and the efficacy of therapy, such as antiarrhythmic drugs, are reduced. Previous studies of patients with syncope have not evaluated the contribution of left ventricular performance in risk stratification for sudden death. The purpose of our study of a large population of patients with syncope was to determine the impact of left ventricular dysfunction on sudden death risk if syncope is caused by a cardiac cause or remains unexplained after electrophysiologic testing. We retrospectively evaluated the relationship of left ventricular ejection fraction to sudden death prognosis in 88 consecutive patients referred for electrophysiologic testing to determine a cause of syncope. The mean age was 57 +/- 18 years, left ventricular ejection fraction was 0.41 +/- 0.20, and 66 patients (75%) had structural heart disease. In 49 patients (56%) a cardiac cause of syncope was diagnosed, and in 39 patients (44%) the cause of syncope remained unexplained after evaluation. Cardiac syncope was attributed to ventricular tachycardia in 27 patients, bradyarrhythmia in 11 patients, and supraventricular tachyarrhythmia in 11 patients. By logistic regression only structural heart disease was independently associated with cardiac cause of syncope (p = 0.003). After a mean follow-up of 790 +/- 688 days, nine patients had died suddenly, eight (89%) of whom had left ventricular ejection fraction less than 0.30.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognosis of patients with sustained ventricular tachycardia and of survivors of cardiac arrest not inducible by programmed stimulation

The aim of this study was to analyze the long-term clinical outcome of 60 prospectively studied patients with documented sustained ventricular tachyarrhythmia that was not inducible during baseline programmed ventricular stimulation: 39 with cardiac arrest due to noninfarction ventricular fibrillation (VF) and 21 with mild hemodynamically compromising sustained ventricular tachycardia (VT). Left ventricular ejection fraction was 55 +/- 14% in the VF group and 50 +/- 13% in the VT group (difference not significant). Patients were discharged without conventional antiarrhythmic drugs and received only empirical beta-blocker therapy. During a mean follow-up period of 21 +/- 16 months (mean +/- SD), 10 of 60 patients (17%) died suddenly. The actuarial incidence of sudden death at 1 and 4 years was similar in both groups (VF group, 10 and 20%; VT group, 16 and 16%) (p = 0.48). The actuarial incidence of sudden cardiac death was significantly higher in patients with left ventricular ejection fraction < or = 40% than in those with > 40% (1-year incidence in VF group, 40 vs 0%; VT group, 50 vs 0%) (p = 0.005 and p = 0.01, respectively). Multivariate regression analysis identified left ventricular ejection fraction < or = 40% and previous myocardial infarction as the only independent predictor of sudden cardiac death. The occurrence of frequent ventricular pairs during Holter monitoring was the only independent predictor of sustained VT recurrences. It is concluded that patients with sustained ventricular tachyarrhythmia in whom arrhythmia was non-inducible during baseline ventricular stimulation and not treated with antiarrhythmic therapy have a favorable outcome if left ventricular ejection fraction is high.(ABSTRACT TRUNCATED AT 250 WORDS)