Survival After Implantable Cardioverter-Defibrillator Shocks.

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.