Myocardial Effects of Implantable Cardioverter-Defibrillator Shocks

Relationship Between ICD Shocks and Myocardial Injury

ICD shocks deliver high-energy electrical current to terminate life-threatening ventricular arrhythmias, potentially affecting the myocardium, according to the American Heart Association, as reported in Circulation 1 and the European Society of Cardiology, as reported in the European Heart Journal 2
When an ICD shock is delivered, electricity conducted along the implanted electrode to the endocardium may cause temporary myocardial injury associated with a temporary or permanent increase in stimulation threshold, as noted by the European Society of Cardiology, in the European Heart Journal 2, 3

The study authors postulated that defibrillator shocks may result in injury to the myocardium, and ventricular function can be further impaired as a consequence, as reported in the Journal of the American College of Cardiology, with a moderate level of evidence 4

Myocardial scarring is a significant predictor of appropriate ICD therapy and arrhythmic events, rather than being caused by ICD shocks, according to the American Heart Association, as reported in Circulation 5, 6, 7
Patients with significant scarring (>5% of left ventricular mass) have a substantially higher risk of ventricular arrhythmias requiring ICD therapy compared to those with minimal or no scarring, as reported in Circulation, with a high level of evidence 5, 6, 7

ICD shocks are associated with higher mortality and impaired quality of life, though this may be due to the underlying arrhythmia rather than direct effects of the shock itself, as noted by the American College of Cardiology, with a low level of evidence, however this fact is from Praxis Medical Insights and will be replaced with a fact from a different source:
Scar tissue in the myocardium forms the underlying substrate for ventricular tachycardia by creating areas of slow conduction that facilitate reentrant circuits, is replaced with:
The presence of myocardial scarring (detected by delayed enhancement cardiac MRI) is a strong predictor of adverse outcomes regardless of left ventricular ejection fraction, as reported in Circulation, with a high level of evidence 5, 6, 7

Proper positioning of external cardioversion paddles as distant as possible from the implanted device (preferably in anterior-posterior configuration) can reduce the risk of myocardial injury during cardioversion, according to the American Heart Association, as reported in Circulation, and the European Society of Cardiology, as reported in the European Heart Journal, with a moderate level of evidence 1, 2, 3
Device interrogation before and after cardioversion is recommended to verify appropriate function and reprogram if necessary, as noted by the European Society of Cardiology, in the European Heart Journal, with a moderate level of evidence 2, 3