Atrial fibrillation (often called "A Fib") is most commonly seen in people who have other heart disease (such as heart valve problems, heart attacks, long-standing high blood pressure) or thyroid disease but can be seen in otherwise healthy people without any medical problems. The atria become scarred and irritable and are not able to pass the electrical impulse smoothly like a ripple traveling across a calm water pond. Instead, the electrical impulse breaks up into many smaller ripples that travel around the atria in a very fast, irregular and disorganized manner much like a stormy ocean surface. This makes the atria beat at between 300-600 beats/minute. A proportion of these impulses travel down the AV node and cause the ventricles to beat quite fast (120-190 beats/min) and very irregularly. The atria beat so fast that blood does not get pumped normally and blood clots tend to form in the atria. Therefore, blood thinners are often prescribed. Atrial fibrillation is often very difficult to control with drugs.
A number of different drugs are used to treat atrial fibrillation. Some drugs are prescribed to try and prevent atrial fibrillation attacks from recurring. Other drugs (beta blockers, calcium blockers, digoxin) are used slow the heart when atriual fibrillation occurs and makes the attacks more tolerable or less uncomfortable but do not prevent attack from recurring. When a person cannot tolerate medications or when drugs are not effective at preventing attacks or reducing symptoms from attacks, catheter ablation may be necessary.
There are several types of ablation that can be performed for atrial fibrillation and each has a slightly different purpose and approach.
1) AV node-His bundle ablation: This type of ablation was the first type ever to be performed and was introduced in 1983. This treatment does not cure someone of AF attacks. Rather, it eliminates symptoms by destroying the AV node-His bundle so that the atrial fibrillation signals cannot cause the ventricles to beat rapidly and irregularly. After the ablation, AF is still present BUT people no longer have any symptoms from the fibrillation. AV node ablation is 99% successful on the first attempt and the risks are very low (<1%). Remember however, that before your AV node ablation, a permanent pacemaker will be required. This may be done on the same day or some weeks in advance of your AV node ablation.
2) AV node modification: This form of ablation procedure is a variant of AV node-His bundle ablation. Rather than completely destroy the AV node-His bundle, AV node modification attempts to burn only part of the AV node- His bundle so that the number of atrial fibrillation impulses getting through is reduced and the resulting heart rate is reduced by 25-50%. Because signals still get through, there is no need for a pacemaker after a modification procedure. However, a good result is only obtained in 50% of patients in whom this is tried while 25% have only a temporary improvement and the other 25% end up with complete AV node-His bundle ablation and a permanent pacemaker. This procedure is no longer offered at London Health Sciences Center.
3) AF ablation: In recent years, new research has found that some patients have atrial fibrillation that is triggered by one or more spots in the atrial chambers. Heart cells in these areas send out rapid electrical pulses and start the atrial fibrillation just like a malfunctioning ignition on a gas barbeque or oven. The most common sites for these abnormal rapidly firing cells is in the pulmonary veins that connect to the left atrium. Pulmonary veins are veins that carry blood back from the lungs to the heart. Every person usually has four pulmonary veins but the most common veins causing atrial fibrillation are the left and right upper veins. In focal atrial fibrillation, these spots are either destroyed by burning them or burning completely around the spots so they are trapped and the impulses coming from these cells are prevented from getting out to the rest of the heart and causing atrial fibrillation. The procedure can be very long (6 hours or more) and the success rate is about 70%. Another 10-20% of people having AF ablation are improved by having much fewer or shorter attacks and may be better controlled by antiarrhythmic drugs that previously were not effective. Some of these patients may require a second procedure.
This procedure is relatively new and is still being improved. We do not yet know which persons with atrial fibrillation have the best chance of success but, at our London Health Sciences Center, good candidates for this procedure are people who: 1) have otherwise normal hearts free of any scarring or damage from other heart disease, 2) have atrial fibrillation attacks that stop on their own (have periods where the heart beat returns to normal in between attacks and 3) few other medical problems. While age is not strictly speaking a criterion, we generally recommend focal ablation only for younger patients because of the increased risk in the elderly. For people of advanced age or who have other medical problems, AV node ablation and permanent pacemaker insertion may be a easier and safer choice.
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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.