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Patients with implantable defibrillators (ICDs) or resynchronization devices with defibrillator (CRT-Ds) were most likely to die of heart failure or noncardiac causes, not sudden death, a single-center study found.

Of the 2,859 patients included in the analysis, the 8-year cumulative incidence for heart failure death was 8.6% among patients with an ICD for primary prevention and 9.6% among secondary prevention ICD patients, and 22.6% for those with a CRT-D (log rank P<0.001), reported Martin J. Schalij, MD, PhD, and colleagues from Leiden University Medical Center in Leiden, The Netherlands.

Conversely, the 8-year cumulative incidence of sudden death was 2.1% and 3.2% in the primary and secondary prevention ICD patients, and 3.6% in those with a CRT-D (log rank P=0.026), according to the study published online in the journal HeartRhythm.

Defibrillator devices have been shown in large randomized trials to decrease mortality among primary prevention ICD patients, including those with ischemic and nonischemic heart disease at risk of sudden arrhythmic death.

They also have been shown to have a mortality benefit in secondary prevention, including those who have survived life-threatening ventricular arrhythmias.

Currently, many heart failure patients receive CRT-D devices because the addition of defibrillation has been shown to confer a mortality benefit, researchers said.

With the drop in deaths from sudden arrhythmias, Schalij and colleagues theorized that the mode of death would be shifting, particularly outside the setting of clinical trials.

They decided to examine this phenomenon in patients with ICDs and CRT-D devices to "provide reasonable expectations and prognosis for patients and physicians."

They included patients with such devices implanted at their center between 1996 and 2010.

They classified deaths as cardiac, noncardiac, and sudden death. They further divided the cardiac group into tachyarrhythmic, bradyarrhythmic, heart failure, nonarrhythmic nonheart failure, and in cardiac but unable to classify further.

Of the 2,859 patients who received devices in this analysis, 26% received an ICD for primary prevention and 32% for secondary prevention; 42% received a CRT-D.

Patient age increased slightly moving from primary to secondary prevention with ICD, and increased further with CRT-D. Most of the patients in the three groups were men and being male was associated with a higher odds of receiving a device.

The cumulative incidence of all-cause mortality increased over time, going from 2% at 2 years to 40% after 8 years. It was highest in the CRT-D group (P<0.001).

Heart failure was the most common mode of cardiac death across the three groups:

• 35 out of 44 deaths among patients with an ICD for primary prevention
• 71 out of 91 deaths in the secondary prevention ICD group
• 131 out of 159 CRT-D deaths

The most common causes of noncardiac death among the three groups were malignant neoplasm (15, 35, and 32, respectively), followed by infection (8, 28, and 29, respectively).

There were six sudden cardiac deaths in the primary prevention ICD group, 11 in the secondary prevention group, and 15 in the CRT-D group.

However, there was a large number deaths for which the cause could not be determined (22, 56, and 36, respectively).

The researchers noted the overall low number of cases of sudden death among the ICD patients (7%) compared with death rates seen in clinical trials, which can range from 15% to 36%.

They suggested that the 17% of cases of unknown cause of death "probably contain a relatively high number of patients who died suddenly."

Schalij and colleagues also found it "remarkable" that all three groups of patients had comparable rates of sudden death: 7%, 8%, and 7%, respectively. However, they said, this should be interpreted with caution because of "wide confidence intervals making accurate comparison difficult between the three groups."

The study was limited because of the high number of patients whose cause of death could not be determined, the authors wrote.

Also, although the patients in this study represent routine practice, such practice could differ in other countries. Results should therefore be extrapolated cautiously, they added.

From the American Heart Association

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