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Cohort study
Primary prevention implantable cardioverter defibrillators are effective in preventing overall mortality in older patients
  1. Sana M Al-Khatib
  1. Duke University Medical Center, Durham, USA
  1. Correspondence to : Dr Sana M Al-Khatib, Duke Clinical Research Institute, P.O. Box 17969, Durham, NC 27715, USA; alkha001{at}mc.duke.edu

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Context

The implantable cardioverter defibrillator (ICD) is a life-saving therapy in patients with systolic heart failure. This benefit was first demonstrated by randomised clinical trials that enrolled outpatients who had well-controlled heart failure. Therefore, when those trials were published, it was not clear whether the results would apply to patients seen in clinical practice who might be older and sicker. Consequently, several studies reported on the outcomes of the ICD in clinical practice with one study showing no significant difference in survival between clinical trial ICD patients and a similar group of clinical practice ICD patients.1 The analysis by Chen and colleagues examined the effectiveness of primary prevention ICDs specifically in older patients who received the ICD during hospitalisation for heart failure or other acute comorbidities.

Methods

This was a retrospective cohort study of 23 111 patients (≥66 years old) that linked data from the Centers for Medicare and Medicaid Services and the American College of Cardiology-National Cardiovascular Data Registry ICD registry with a nationwide heart failure registry and Medicare claims data from 2004 to 2009. Outcomes of interest were all-cause mortality and sudden cardiac death. Latency analyses with Cox regression were performed to determine crude HRs. High dimension propensity scores were used to adjust the HRs for potential confounders at baseline while analysing outcomes 180 days from index ICD implantation or discharge.

Findings

Patients who received an ICD during a hospital admission had lower mortality rate than patients who did not receive an ICD (40% vs 60% at 3 years); however, when a latency period of 180 days was applied and adjustment for high-dimension propensity score was performed, the apparent superior survival with an ICD was not evident for sudden cardiac death (adjusted HR 0.95, 95% CI 0.78 to 1.17) and was only slightly evident for total mortality (0.91, 0.82 to 1.00).

Commentary

Although this study addresses a clinically important group of patients, it suffers from several weaknesses. The latency analyses are flawed. Deaths in the first 6 and 12 months that might have been prevented by the ICD were not counted and patients saved by the ICD remained in the population whereas those who died because they did not have an ICD did not remain in the population. This likely resulted in a mix of high risk and low risk patients in the ICD group and lower risk survivors in the non-ICD group. Although the authors adjusted patient outcomes for potential confounders, their approach was statistically incorrect because they did not adjust for patient characteristics at 6 or 12 months after the latency period. Instead, they adjusted for baseline characteristics. This adjustment was inappropriate as risk factors at 6 and 12 months are different from those at baseline. Furthermore, clinically it is not plausible to assume that ICDs cannot treat ventricular arrhythmias and as a result prevent sudden death in the first 6 and 12 months after implantation. Although two randomised clinical trials of ICDs showed no significant difference in outcomes between the ICD group and the non-ICD group in the first year this likely resulted from the small number of events in the first 6–12 months.

A major concern is how the authors classified sudden cardiac death. They justify their approach by using a previously validated algorithm for defining sudden cardiac death.2 A careful review of that reference shows that the methodology is questionable. The authors’ assertion that a prior study by our group did not include elderly patients who underwent device implantation during an acute hospital admission is incorrect.3 All of the patients in that study received their ICD during a hospitalisation for heart failure.3 Finally, in a similar analysis that our group conducted using the ICD Registry and Get With the Guidelines-Heart Failure databases, we found that ICDs implanted in patients during a heart failure hospitalisation are associated with a lower risk of mortality even when the comorbidity burden and prior heart failure hospitalisation were considered.4

Implications for practice

This study does not provide evidence for a change in practice; however, it highlights the need for further research on ICDs in patients with extensive comorbid medical illnesses. Therefore, primary prevention ICDs should be considered in patients hospitalised for heart failure once their heart failure status is optimised.

References

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Footnotes

  • Competing interests None declared.

  • Provenance and peer review Commissioned; internally peer reviewed.