AV Node Reentry
This rhythm problem is due to an abnormality of the AV node itself which results in a "short circuit" to develop in the area around the AV node. An electrical signal can get trapped into a small loop in this area, causing the heart to race. The tachycardia may feel very similar to that experienced by those with WPW syndrome simply because a racing heart still feels like a racing heart regardless of the cause.
Catheter ablation is directed at destroying the tissue near the AV node causing the heart racing without causing serious damage to the AV node. To minimize this risk, your doctor will start by burning a safe distance from the AV node and gradually burn tissue progressively closer until he/she sees signs that enough burning has been done or if signs of danger appear. The technique is similar to whittling away at a piece of wood where you shave away part of the wood without weakening it and causing it to break.
Unfortunately, the abnormal tissue can be very, very close to the AV node and damage to the AV node occurs in 2-3% of cases depsite all measures taken to avoid it. If this should happen, a pacemaker will be necessary but does not need to be put in immediately (it can be implanted several days later if desired). The success rate for a first attempt is nearly 95% because of the desire to avoid damaging the AV node. If the first catheter ablation procedure does fail to get rid of all the tachycardia, it is possible to undergo a second or even third attempt. Your doctor will speak to you about the merits of trying again and make you aware of any additional risks.
Acknowledgements: Contributors to this information were: Dr. R. Yee M.D., Arrhythmia Service, LHSC (UC), Dr. A. Krahn MD, Arrhythmia Service, LHSC (UC), and various staff members.