Long-Term Benefit of Implantable Cardioverter/Defibrillator Therapy After Elective Device Replacement: Results of the Incidence Free Survival After ICD Replacement (INSURE) Trial—A Prospective Multicentre Study
Do patients who have never received an appropriate implantable cardioverter-defibrillator (ICD) shock warrant ICD replacement?
INSURE was a multicenter observational study of 510 patients undergoing their first ICD replacement due to either battery depletion or other reasons at least 3 years after initial ICD implant. At the time of device replacement, patients were grouped according to presence (group A) or absence (group B) of prior appropriate ICD therapy. Patients were then followed prospectively every 3-6 months after ICD replacement. The primary endpoint was time to first occurrence of appropriate ICD therapy (antitachycardia pacing [ATP], shock, or death) after device replacement in those with and without a prior history of appropriate ICD discharge.
Patients underwent ICD replacement a mean of 62 ± 18 months after their initial generator implant. Over 75% of patients had had an ICD implanted for secondary prevention. There were 245 (48%) patients who experienced appropriate ICD therapy prior to generator change (group A). Compared to those patients without prior arrhythmias (group B, n = 265), patients with appropriate ICD discharges were more likely to have had an ICD placed for secondary prevention, had lower left ventricular ejection fraction, and worse New York Heart Association (NYHA) class at time of initial ICD implant. Patients in group A were also more likely to be on amiodarone and diuretics, and were less likely to be on beta-blockers. Patients were followed for a mean of 22 ± 16 months after generator change. Appropriate ICD therapies occurred in 158 patients after generator change, of whom 107 (68%) were from group A and 51 (32%) from group B. Compared with group B patients, patients in group A had a 3.1 [2.2-4.4] higher adjusted hazard of having an appropriate ICD therapy following device exchange. However, at 2 and 3 years after device exchange, 18% and 21% of group B patients, respectively, had suffered an appropriate ICD discharge. Aside from worse NYHA class, no clear predictor of ICD discharge was found in group B patients.
The authors concluded that patients without prior ICD therapies still have a high risk of arrhythmic events after device replacement.
This was an interesting evaluation of patients with pre-existing ICDs (implanted per current guidelines), examining risk of appropriate ICD discharge upon device replacement. While there were clear limitations to this observational study (10% dropout and questionable appropriateness of including ATP in ‘ICD therapy’ outcome), it is a ‘true to life’ examination of arrhythmias and ICD utility in patients with congestive heart failure. Rates of appropriate ICD therapies continued to be high in those with prior events, with a trend toward increased mortality. However, discerning appropriateness of ICD implant/replacement in those without a history of arrhythmic events continues to be a challenge. Given that group B patients were overall ‘lower risk’ heart failure patients with a presumably better heart failure survival, an 18% cumulative incidence of ICD discharge at 2 years after replacement suggests that ICD replacement is warranted regardless of prior arrhythmia history. A larger study with longer follow-up and more detailed monitoring of adverse device-related events (inappropriate discharge, infection) is needed. Further, a larger population of patients initially implanted for primary prevention indication is needed (>80% were secondary prevention implants).
Keywords: Defibrillators, Heart Failure
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