Can we predict which patients with implantable cardioverter defibrillators receive appropriate shock therapy? A study of 155 patients

Background: Appropriate shock therapy (AST) occurs in the minority of patients with implantable cardioverter defibrillators (ICDs). We assessed which patients received AST and whether there were any predictive factors. Methods: We retrospectively analysed data from 155 patients implanted with ICDs at our institution from a period from February 1984 to February 2001. Stored electrogram data were analysed. We sub-divided patients on the basis of underlying cardiac disease. Various clinical echocardiographic and electrophysiological variables were studied. Results: AST occurred in 53 (34%) of patients (Group 1) and no AST in 102 (64%) of patients (Group 2). Impaired LV function was significantly associated with AST. Group 1 patients had a lower ejection fraction (EF) compared to Group 2 (37.5±13% vs. 47.8±14%, P<0.0001). Seventy-two percent of patients with AST had an EF <40% vs. 35% of patients in Group 2 (P<0.0001). NYHA Class was also associated with AST, 42% of Group 1 were in NYHA Class III/IV vs. 12% in Group 2 (P<0.001). Programmed electrical stimulation (PES) was a predictor of AST. PES was positive in a greater proportion of patients in Group 1 vs. 2 (88% vs. 64%, P<0.0006). Sub-group analysis showed that patients with dilated cardiomyopathy (DCM) had a high incidence of AST (80%). In these patients PES was a poor predictor of AST being positive in only 25%. Conclusion: AST occurs in the minority of our patients. Certain pre-procedural variables predict AST. PES does not appear useful in predicting shock therapy in DCM patients and a negative PES should not preclude ICD implantation in this group.