Implantable devices for treating tachyarrhythmiasBMJ 2003; 327 doi: https://doi.org/10.1136/bmj.327.7410.333 (Published 07 August 2003) Cite this as: BMJ 2003;327:333
- Timothy Houghton, specialist registrar in cardiology,
- Gerry C Kaye, consultant cardiologist at Hull and East Yorkshire Trust
- Castle Hill Hospital, Hull
Pacing treatment for tachycardia control has achieved success, notably in supraventricular tachycardia. Pacing termination for ventricular tachycardia has been more challenging, but an understanding of arrhythmia mechanisms, combined with increasingly sophisticated pacemakers and the ability to deliver intracardiac pacing and shocks, have led to success with implantable cardioverter defibrillators.
Mechanisms of pacing termination
There are two methods of pace termination.
Underdrive pacing was used by early pacemakers to treat supraventricular and ventricular tachycardias. Extrastimuli are introduced at a constant interval, but at a slower rate than the tachycardia, until one arrives during a critical period, terminating the tachycardia. Because of the lack of sensing of the underlying tachycardia, there is a risk of a paced beat falling on the T wave, producing ventricular fibrillation or ventricular tachycardia, or degenerating supraventricular tachycardias to atrial fibrillation. It is also not particularly successful at terminating supraventricular tachycardia or ventricular tachycardia and is no longer used routinely.
Overdrive pacing is more effective for terminating both supraventricular and ventricular tachycardias. It is painless, quick, effective, and associated with low battery drain of the pacemaker. Implantation of devices for terminating supraventricular tachycardias is now rarely required because of the high success rate of radiofrequency ablative procedures (see previous article). Overdrive pacing for ventricular tachycardia is often successful but may cause acceleration or induce ventricular fibrillation. Therefore, any device capable of pace termination of ventricular tachycardia must also have defibrillatory capability.
Implantable cardioverter defibrillators
Initially, cardioverter defibrillator implantation was a major operation requiring thoracotomy and was associated with 3-5% mortality. …