Seattle Risk Models to Predict ICD Benefit
Does the combination of the Seattle Heart Failure Model (SHFM) for overall survival and the Seattle Proportional Risk Model (SPRM) for proportional risk of sudden death from ventricular arrhythmia predict the survival benefit with an implantable cardioverter-defibrillator (ICD)?
Patients with primary prevention ICDs from the National Cardiovascular Data Registry (NCDR) were compared with control patients with heart failure (HF) without ICDs with respect to 5-year survival using multivariable Cox proportional hazards regression.
There were 87,914 patients with ICDs and 10,932 without ICDs. The SHFM was strongly associated with all-cause mortality (p < 0.0001). The ICD-SPRM interaction was significant (p < 0.0001), such that SPRM quintile 5 patients had approximately twice the reduction in mortality with the ICD versus SPRM quintile 1 patients (adjusted hazard ratio [HR], 0.602 [95% CI, 0.537-0.675] vs. 0.793 [95% CI, 0.736-0.855] for patients with and without an ICD, respectively). Among patients with SHFM-predicted annual mortality ≤5.7%, those with a SPRM-predicted risk of ventricular arrhythmias below the median had no reduction in mortality with the ICD (adjusted ICD HR, 0.921; 95% CI, 0.787-1.08; p = 0.31), while those with SPRM above the median derived the greatest benefit (adjusted HR, 0.599; 95% CI, 0.530-0.677; p < 0.0001).
The SHFM predicted all-cause mortality in a large cohort with and without ICDs, and the SPRM discriminated and calibrated the potential ICD benefit. Together, the models identified patients less likely to derive a mortality benefit from primary prevention ICDs.
Despite the highly significant reductions in death rates in patients with severely reduced left ventricular function who undergo primary prevention ICD, the majority of these patients do not receive appropriate shocks. Additionally, data for patients with nonischemic cardiomyopathy are mixed, as the recent DANISH-ICD trial demonstrated. It is clear that risk stratification tools beyond left ventricular function are needed. The presence and extent of late gadolinium enhancement on cardiac magnetic resonance imaging has been shown to offer additional risk stratification information in both ischemic and nonischemic cardiomyopathies.
The authors of the present study examined the potential role that functional heart failure assessment may play. The SHFM has been shown to predict the risk of all-cause mortality; the SPRM predicts the mode of death (sudden vs. nonsudden). Using a combination of the two, the authors were able to identify a large group of patients with good overall survival that was not altered by ICD implantation, and a quartile of patients who had a 40% reduction in mortality with the ICD.
One limitation of the present study is that it was not randomized and the control group was derived from historical patient cohorts prior to widespread use of ICD for primary prevention. Additionally, not all data needed in the models were available in the NCDR registry. Future studies would need to examine these risk models prospectively. Ultimately, the challenge to widespread adoption of such models may be their relative complexity compared with ejection fraction ≤35% versus >35%.
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