Abstract and Introduction
Abstract
GFR, Mortality and ICD Therapy After ICD Generator Replacement. Background: Impaired renal function is associated with increased mortality among patients with implantable cardioverter-defibrillators (ICDs). The relationship between renal function at time of ICD generator replacement and subsequent appropriate ICD therapies is not known.
Methods and Results: We identified 441 patients who underwent first ICD generator replacement between 2000 and 2011 and had serum creatinine measured within 30 days of their procedure. Patients were divided into tertiles based on estimated glomerular filtration rate (eGFR). Adjusted Cox proportional hazard and competing risk models were used to assess relationships between eGFR and subsequent mortality and appropriate ICD therapy. Median eGFR was 37.6, 59.3, and 84.8 mL/min/1.73 m for tertiles 1–3, respectively. Five-year Kaplan–Meier survival probability was 34.8%, 61.4%, and 84.5% for tertiles 1–3, respectively (P < 0.001). After multivariable adjustment, compared to tertile 3, worse eGFR tertile was associated with increased mortality (HR 2.84, 95% CI [1.36–5.94] for tertile 2; HR 3.84, 95% CI [1.81–8.12] for tertile 1). At 5 years, 57.0%, 58.1%, and 60.2% of patients remained free of appropriate ICD therapy in tertiles 1–3, respectively (P = 0.82). After adjustment, eGFR tertile was not associated with future appropriate ICD therapy. Results were unchanged in an adjusted competing risk model accounting for death.
Conclusions: At time of first ICD generator replacement, lower eGFR is associated with higher mortality, but not with appropriate ICD therapies. The poorer survival of ICD patients with reduced eGFR does not appear to be influenced by arrhythmia status, and there is no clear proarrhythmic effect of renal dysfunction, even after accounting for the competing risk of death.
Introduction
Despite significant advances in medicine and technology, sudden cardiac death remains a significant cause of morbidity and mortality, resulting in approximately 300,000 deaths annually in the United States. In properly selected patients with both primary and secondary prevention indications, implantable cardioverter-defibrillators (ICDs) significantly reduce both sudden death and total mortality. However, given the cost of ICD implantation, the risk of adverse side effects including inappropriate shocks, lead malfunction, and device-related infections, and the fact that many patients who get ICDs die from causes unrelated to sudden cardiac death without ever receiving any appropriate ICD therapy, great effort is being made to evaluate the most appropriate and cost effective ways of selecting patients who are most likely to benefit from initial ICD implantation.
The reported median ICD battery lifespan is 4.6 years, and many patients will require at least 1 ICD generator replacement in their lifetime. ICD generator replacement is costly and can be associated with significant procedural complications, including bleeding and infection. Patients undergoing ICD generator replacement are older, often with progressive or new comorbidities that can limit their functional status, quality of life, and expected longevity compared to their status when their initial ICD was implanted. Despite the significant effort that has been made to select those patients who are the most appropriate candidates for initial ICD implantation, ICD generator replacement often occurs without reconsidering the ongoing appropriateness for ICD therapy.
Impaired renal function at the time of initial ICD implantation has been shown to predict increased procedural complications and increased mortality. Small studies that have evaluated the association between renal function and appropriate ICD therapies after initial ICD implantation have also suggested that impaired renal function is independently associated with a higher incidence of ventricular arrhythmias requiring ICD therapy, although not all reports have confirmed this relationship. The correlations between renal function, mortality, and appropriate ICD therapies after ICD generator replacement are not well defined. Because patients at the time of initial ICD implantation are inherently different than patients at the time of ICD generator replacement, the risk factors that are associated with mortality and ventricular arrhythmias at the time of initial ICD implantation may not be valid at the time of ICD generator replacement. We therefore evaluated the association between renal function at the time of first ICD generator replacement and subsequent mortality and ventricular arrhythmias.