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Published on: February 28, 2012
Survival After Implantable Cardioverter-Defibrillator Shocks
Mehmet K Aktaş1, Arwa Younis2, Wojciech Zareba1
1Clinical Cardiovascular Research Center, University of Rochester, Rochester, New York, USA.
Insights
Implantable cardioverter-defibrillator (ICD) shocks indicate a higher risk of death, but the underlying heart rhythm problem, not the shock itself, is the primary driver of mortality in ICD recipients.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Devices
Background:
- Conflicting data exist regarding the impact of implantable cardioverter-defibrillator (ICD) shocks on patient mortality.
- The role of the arrhythmic substrate versus ICD therapy in determining mortality requires clarification.
Purpose of the Study:
- To investigate whether the arrhythmic substrate leading to ICD therapy or the therapy itself is the primary determinant of mortality in ICD recipients.
- To analyze the association between different types of ICD therapies and arrhythmias with subsequent mortality.
Main Methods:
- Analysis of a cohort of 5,516 ICD recipients from 5 landmark trials (MADIT-II, MADIT-RISK, MADIT-CRT, MADIT-RIT, RAID).
- Evaluation using 4 time-dependent models assessing ICD therapy type, arrhythmia type, combined factors, and incremental risk from repeated shocks.
- Hazard ratios (HR) and p-values were calculated to determine statistical significance.
Main Results:
- Appropriate ICD shocks, particularly for ventricular fibrillation (VF) and fast ventricular tachycardia (VT ≥200 beats/min), significantly increased mortality risk (HR > 2.8, p < 0.001).
- Inappropriate shocks alone were not significantly associated with increased mortality (HR: 1.23, p = 0.42).
- Repeated appropriate ICD shocks did not show an incremental mortality risk beyond the first shock.
Conclusions:
- The findings suggest that the underlying severity of the arrhythmic substrate is a more critical predictor of mortality in ICD recipients than the ICD therapy itself.
- Understanding the arrhythmic substrate is crucial for risk stratification and management of patients with ICDs.
Background:
There are conflicting data on the impact of implantable cardioverter-defibrillator (ICD) shocks on subsequent mortality.
Objectives:
The aim of this study was to determine whether the arrhythmic substrate leading to ICD therapy or the therapy itself increases mortality.
Methods:
The study cohort included 5,516 ICD recipients who were enrolled in 5 landmark ICD trials (MADIT-II, MADIT-RISK, MADIT-CRT, MADIT-RIT, RAID). The authors evaluated the association of device therapy with subsequent mortality in 4 separate time-dependent models: model I, type of ICD therapy; model II, type of arrhythmia for which ICD therapy was delivered; model III, combined assessment of all arrhythmia and therapy types during follow-up; and model IV, incremental risk associated with repeated ICD shocks.
Results:
When analyzed by the type of ICD therapy (model I), a first appropriate ICD shock was associated with increased risk of subsequent mortality with or without concomitant occurrence of inappropriate shock during follow-up (hazard ratio [HR]: 2.78 and 2.31; p < 0.001 and p = 0.12), whereas inappropriate shock alone was not associated with mortality risk (HR: 1.23; p = 0.42). Similarly, ICD therapy for ventricular tachycardia (VT) ≥200 beats/min or ventricular fibrillation (VF) (model II) was associated with increased risk of death with or without concomitant therapy for VT <200 beats/min (HRs: 2.25 and 2.62; both p < 0.001), whereas appropriate therapy for VT <200 beats/min or inappropriate therapy (regardless of etiology) did not reach statistical significance (all p > 0.10). Combined assessment of all therapy and arrhythmia types during follow-up (model III) showed that appropriate ICD shocks for VF, shocks for fast VT (≥200 beats/min) without prior antitachycardia pacing (ATP), as well as shocks for fast VT delivered after failed ATP, were associated with the highest risk of subsequent death (HR: all >2.8; p < 0.001). Finally, 2 or more ICD appropriate shocks were not associated with incremental risk to the first appropriate ICD shock (model IV).
Conclusion:
The combined data from 5 landmark ICD trials suggest that the underlying arrhythmic substrate rather than the ICD therapy is the more important determinant of mortality in ICD recipients.
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