Do baseline characteristics accurately discriminate between patients likely versus unlikely to benefit from implantable defibrillator therapy? Evaluation of the Canadian Implantable Defibrillator Study implantable cardioverter defibrillatory efficacy score in the Antiarrhythmics Versus Implantable Defibrillators Trial

Objective Our purpose was to evaluate whether baseline characteristics pred ictive of implantable cardioverter defibrillator ([CD) efficacy in the Cana dian Implantable Defibrillator Study (CIDS) are predictive in the Antiarrhy thmics Versus Implantable Defibrillators [AVID) Trial. Background ICD therapy is superior to antiarrhythmic drug use in patients w ith life-threatening arrhythmias. However, identification of subgroups most likely to benefit from ICD therapy may be useful. Data from CIDS suggest t hat 3 characteristics (age greater than or equal to 70 years, ejection Frac tion [EF] less than or equal to0.35, and New York Heart Association class > II) can be combined to reliably categorize patients as likely (22 character istics) versus unlikely to benefit (<2 characteristics) from ICD therapy. Methods The utility of the CIDS categorization of ICD efficacy was assessed by Kaplan-Meier analysis and Cox hazards modeling. The accuracy of the CID S score was formally tested by evaluating for interaction between categoriz ation of benefit and treatment in a Cox model. Results ICD therapy was associated with a significantly lower risk of death in the 320 patients categorized as likely to benefit (relative risk [RR] 0 .57, 95% confidence interval [CI] 0.37-0.88, P = .01) and a trend toward a lower risk of death in the 689 patients categorized as unlikely to benefit (RR 0.70, 95% CI 0.48-1.03, P = .07). Categorization of benefit was imperfe ct, as evidenced by a lack of statistical interaction (P = .5). Although 32 of the 42 deaths prevented by ICD therapy in AVID were in patients categor ized as likely to benefit, all 42 of these patients had EF values <less tha n or equal to>0.35. Neither advanced age nor poorer functional class predic ted ICD efficacy in AVID. Conclusion of the 3 characteristics identified to predict ICD efficacy in C IDS, only depressed EF predicted ICD efficacy in AVID. Thus physicians face d with limited resources might elect to consider ICD therapy over antiarrhy thmic drug use in patients with severely depressed EF values.