Identification of patients most likely to benefit from implantable cardioverter-defibrillator therapy - The Canadian implantable defibrillator study

Background-Patients with resuscitated ventricular tachyarrhythmias (ventric ular tachycardia/ventricular fibrillation) benefit from implantable cardiov erter-defibrillators (ICDs) compared with medical therapy. We hypothesized that the patients who benefit most from an ICD are those at greatest risk o f death. Methods and Results-In the Canadian Implantable Defibrillator Study (CIDS), 659 patients with resuscitated ventricular tachyarrhythmias were randomly assigned to receive an ICD or amiodarone and were then followed for a mean of 3 years. There were 98 and 83 deaths in the amiodarone and ICD groups, r espectively. We used multivariate Cox analysis to assess the impact of base line parameters on the mortality in the amiodarone group. Reduced left vent ricular ejection fraction, advanced age, and poor NYHA status identified hi gh-risk patients (P=0.0001 to 0.0009). Quartiles of risk were constructed, and the mortality reduction associated with ICD treatment in each quartile was assessed. There was a significant interaction between risk quartile and the ICD treatment effect (P=0.011). In the highest risk quartile, there wa s a 50% relative risk reduction (95% CI 21% to 68%) of death in the ICD gro up, whereas in the 3 lower quartiles, there was no benefit. Patients who ar e most likely to benefit from an ICD can be identified with a simple risk s core (greater than or equal to 2 of the following factors: age greater than or equal to 70 years, left ventricular ejection fraction less than or equa l to 35%, and NYHA class III or IV). Thirteen of 15 deaths that were preven ted by the ICD occurred in patients with greater than or equal to 2 risk fa ctors. Conclusions-In CIDS, patients at highest risk of death benefited most from ICD therapy. These can be identified easily on the basis of age, poor ventr icular function, and poor functional status.