• Similarly to paced rhythm, electrical stimuli released by ICDs appear as prominent vertical lines on ECG.
• ICDs use 2 mechanisms to terminate ventricular tachyarrhythmias: antitachycardia pacing and direct current shock.
• If successful, a normal sinus rhythm will appear on ECG after either a shock stimulus or antitachycardia pacing spikes.
• Inappropriate shocks (to SVT rather than ventricular arrhythmia) are common problems of ICDs.
• Antitachycardia pacing (ATP) delivers runs of ventricular-paced beats at a higher rate than that of the detected ventricular tachycardia to outcompete hence terminate it, particularly good at breaking reentrant ventricular tachycardia.
• ECG shows antitachycardia pacing spikes running along ventricular tachycardic beats which are followed by the restoration of normal sinus rhythm.
• If ATP fails (which is more tolerable for patients), direct current shock kicks in.
• Direct current shocks are strong electrical impulses used to terminate tachyarrhythmias.
• There are 2 types of shocks:
Synchronized: used for organized rhythm such as ventricular tachycardia
Unsynchronized: used for unorganized rhythm such as ventricular fibrillation
