Inappropriate shocks in implantable cardioverter defibrillator (ICD)

Inappropriate defibrillator shocks are one of the commonest problems faced by a patient implanted with an ICD. It produces psychological problems and affects quality of life in many ICD recepients. Inappropriate shocks are shocks delivered for rhtyhms other than ventricular fibrillation and sustained ventricular tachycardia. Most common cause of inappropriate shocks are supra ventricular arrhythmias including supraventricular tachycardia, atrial fibrillation and sinus tachycardia. Myopotential oversensing and T wave oversensing are other two important causes. Lead fracture and device malfunction can also cause inappropriate shocks. Electromagnetic interferences from sources within and outside the hospital are also an important cause of inappropriate shocks. The actual cause in a given case can often be ascertained by ICD interrogation and retreival of the rhythm prior to the shock which has culminated in the delivery of a shock. Myopotentials can be reproduced by various manoeuvre like isometric hand grip, Valsalva manoeuvre and pushing against a wall with the outstretched hands. Reprogramming the sensitivity and detection algorithms are often helpful in removing interferences due to myopotential oversensing and T wave oversensing. Radiofrequency catheter ablation is an option in paroxysmal supraventricular tachycardia. Lead fracture can be detected by image intensifier fluroscopy and also indicated by an increase in lead impedance on interrogation. Fractured lead needs replacement to prevent inappropriate therapy due to noise detected at the fracture site as well as to deliver effective appropriate therapy when needed. Most of the electromagnetic interferences can be prevented by proper precautions in and out of the hospital.