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Survival After ICD Shocks
Quick Takes
- An analysis of five ICD trials showed that appropriate shocks and therapies for rapid VT or VF are associated with higher subsequent mortality than inappropriate ICD shocks and therapies delivered for slower VT.
- It is unknown what impact ablation therapy may have on survival in patients who experience their first ICD shock for fast VT/VF.
Study Questions:
Does the underlying arrhythmic substrate or the shocks themselves increase mortality following implantable cardioverter-defibrillator (ICD) shocks?
Methods:
The study included 5,516 ICD recipients in five ICD trials (MADIT-II, MADIT-RISK, MADIT-CRT, MADIT-RIT, and RAID). The authors evaluated the association of ICD therapy with subsequent mortality in four separate models.
Results:
When analyzed by the type of ICD therapy, a first appropriate ICD shock was associated with increased risk of mortality with or without concomitant occurrence of inappropriate shock during follow-up (hazard ratios [HRs], 2.78 and 2.31; p < 0.001 and p = 0.12), whereas inappropriate shock alone was not associated with mortality risk. ICD therapy for ventricular tachycardia (VT) ≥200 beats/min or ventricular fibrillation (VF) 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 did not reach statistical significance. Combined assessment of all therapy and arrhythmia types during follow-up 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 ICD appropriate shocks were not associated with incremental risk to the first appropriate ICD shock.
Conclusions:
The combined data from five ICD trials suggest that the underlying arrhythmic substrate rather than the ICD therapy is the more important determinant of mortality in ICD recipients.
Perspective:
The impact of ICD shock on subsequent mortality risk has been uncertain. In the MADIT-II and SCD-HeFT trials, patients experiencing both appropriate and inappropriate shocks had an increased risk of mortality, but this was not observed in other trials. The present analysis of five studies showed that: 1) only appropriate ICD shocks were associated with an increased risk for subsequent mortality, 2) only ventricular arrhythmias (mainly fast VT) were associated with a significant risk for subsequent death, 3) death is primarily influenced by the underlying arrhythmic substrate rather than the type of ICD therapy, and 4) repeated appropriate ICD shocks do not confer incremental risk to a first appropriate ICD shock (when excluding repeated therapies for VT storm). In the present study, appropriate ICD shocks for fast VT or VF were associated with a significantly increased risk for the subsequent composite endpoint of HF hospitalization or death. It is unknown what impact ablation therapy may have on survival in patients who experience their first ICD shock for fast VT/VF.
Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure
Keywords: Arrhythmias, Cardiac, Defibrillators, Implantable, Heart Failure, Pacemaker, Artificial, Secondary Prevention, Shock, Survival, Tachycardia, Ventricular, Ventricular Fibrillation
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