In this study, we noted that the contribution of out-of-hospital cardiac deaths to the overall survival was small, especially among patients living independently. The overall mortality among patients with repeated hospital admissions related to heart failure would have remained high even if all out-of-hospital cardiac deaths were prevented with the use of implantable defibrillators. This lack of benefit would be more pronounced among patients of advanced age who have comorbid illnesses that decrease overall survival and who have had multiple hospital admissions because of heart failure. As a corollary, patients less than 65 years of age, and older patients without kidney disease, dementia or cancer would be most likely to benefit from the use of an implantable defibrillator to prevent sudden death.
In contrast to our observations, information from the US National Cardiovascular Data Registry for 2006–2007 indicates that implantable defibrillators are frequently implanted in older patients with heart failure: 61% of patients were 65 years or older, and 15% were 80 years or older.15
Prior hospital admission because of heart failure was reported in 58% of patients, and noncardiac comorbidities were common.15
Compared with patients in clinical trials of heart failure,16–18
our study population had a substantially lower incidence of cardiac deaths overall and out-of-hospital cardiac deaths in particular. However, patients enrolled in clinical trials tend to be younger and to have fewer comorbidities than the general population of patients with heart failure encountered in the community. Increasing age has previously been associated with a decreased risk of sudden cardiac death,19
and having more comorbidities increases the risk of death from noncardiac causes.
In a study population similar to ours, Khand and colleagues20
identified 12 640 patients in Scotland who had a first admission to hospital because of heart failure and a mean age of 74 years. They found that 50% of the patients who survived after the first admission died over a 3-year follow-up period and that 43% of these deaths occurred out of hospital. These findings are similar to our results. The impact of age on the potential cost-effectiveness of preventing sudden death was also modelled by Yao and colleagues.21
Although they based their analysis on data from the Cardiac Resynchronization in Heart Failure (CARE-HF) trial, in which patients received resynchronization therapy, similar conclusions can be derived regarding the diminishing impact of the prevention of sudden death among older patients.
Our study has several limitations. First, our definition of out-of-hospital cardiac deaths included causes of death in addition to sudden cardiac death. Using this definition we may have overestimated the survival benefit with implantable defibrillators. Second, there are obvious competing risks, especially in older patients, that we did not account for in our analysis. Third, studies have shown that, among patients with symptomatic heart failure, implantable defibrillators prevent only about half of all sudden cardiac deaths.22
Fourth, we relied on nosologist-coded causes of death to identify out-of-hospital cardiac deaths. Although such coding has good agreement with physician-adjudicated causes in major categories (e.g., cardiac v. noncardiac),23
this method of identifying cardiac deaths could be by exclusion of other obvious causes such as motor vehicle crashes and bleeding and tend to include more than cardiac causes, which may have led to further overestimation of the benefit. Finally, our data did not allow distinction between heart failure due to systolic dysfunction and heart failure with preserved left ventricular function. It has been estimated that the incidence of sudden cardiac death is almost 3 times higher among patients with systolic dysfunction than among patients with heart failure who have a preserved ejection fraction.24
Therefore, an optimistic upper boundary of the estimated benefit among patients with systolic dysfunction would be 1.5 times that observed in the overall population of patients with heart failure, half of whom have systolic dysfunction.25–27
However, the maximum potential benefit of preventing sudden death would still be less than 6 months after 2 hospital admissions and 5 months after 3 hospital admissions.
Given the multiple limitations in any such analysis of a large population outside of a clinical trial, our study provides a liberal estimate of the limited potential benefit of preventing sudden death among patients with heart failure in the general community.
Our analysis indicates that the maximum potential benefit of preventing sudden death is limited in patients with repeated hospital admissions related to heart failure. This is particularly true among older patients and among patients with comorbidities. However, patients less than 65 years old as well as older patients without kidney disease, dementia or cancer are most likely to benefit from the prevention of sudden death with the use of implantable defibrillators.
@@ See related commentary by Dorian, page 599