Effect of transthoracic shocks on left ventricular function

Causes and Prevention of Inappropriate Implantable Cardioverter-Defibrillator Shocks

Use of implantable cardioverter-defibrillators as a primary prevention therapy has been shown to reduce mortality in patients after cardiac arrest and also with left ventricular systolic dysfunction. Yet, inappropriate shocks are variably reported and associated with a reduction in quality of life. Inappropriate shocks are the result of environmental causes leading to electromagnetic interference and inappropriate sensing of external noise, device-related causes from inappropriate sensing of physiologic or pathologic signals, and supraventricular arrhythmias. Strategies to reduce inappropriate shocks include aggressive treatment of supraventricular tachycardia, changes in device programming including prolonged detection time, programming antitachycardic pacing and using discriminator algorithms, and cardiac rehabilitation.

Survival after shock therapy in implantable cardioverter-defibrillator and cardiac resynchronization therapy-defibrillator recipients according to rhythm shocked. The ALTITUDE survival by rhythm study

OBJECTIVES

This study sought to determine if the risk of mortality associated with inappropriate implantable cardioverter-defibrillator (ICD) shocks is due to the underlying arrhythmia or the shock itself.

BACKGROUND

Shocks delivered from ICDs are associated with an increased risk of mortality. It is unknown if all patients who experience inappropriate ICD shocks have an increased risk of death.

METHODS

We evaluated survival outcomes in patients with an ICD and a cardiac resynchronization therapy defibrillator enrolled in the LATITUDE remote monitoring system (Boston Scientific Corp., Natick, Massachusetts) through January 1, 2010. First shock episode rhythms from 3,809 patients who acutely survived the initial shock were adjudicated by 7 electrophysiologists. Patients with a shock were matched to patients without a shock (n = 3,630) by age at implant, implant year, sex, and device type.

RESULTS

The mean age of the study group was 64 ± 13 years, and 78% were male. Compared with no shock, there was an increased rate of mortality in those who received their first shock for monomorphic ventricular tachycardia (hazard ratio [HR]: 1.65, p < 0.0001), ventricular fibrillation/polymorphic ventricular tachycardia (HR: 2.10, p < 0.0001), and atrial fibrillation/flutter (HR: 1.61, p = 0.003). In contrast, mortality after first shocks due to sinus tachycardia and supraventricular tachycardia (HR: 0.97, p = 0.86) and noise/artifact/oversensing (HR: 0.91, p = 0.76) was comparable to that in patients without a shock.

CONCLUSIONS

Compared with no shock, those who received their first shock for ventricular rhythms and atrial fibrillation had an increased risk of death. There was no significant difference in survival after inappropriate shocks for sinus tachycardia or noise/artifact/oversensing. In this study, the adverse prognosis after first shock appears to be more related to the underlying arrhythmia than to an adverse effect from the shock itself.

Near-fatal incident on routine induction of ventricular fibrillation at the replacement of an implantable cardioverter defibrillator

The case of a 54-year-old patient with severe coronary artery disease and storms of ventricular tachyarrhythmias is presented. On the replacement of an implantable cardioverter defibrillator due to battery depletion, he suffered life-threatening complications associated with arrhythmia induction. Performing a routine induction of ventricular arrhythmias on the occasion of pulse generator replacement may be reconsidered in selected patients.