Check out new and important updates in Arrhythmia:
The Effect of Cardiac Resynchronization Therapy (CRT) in Heart Failure
Update on Atrial Fibrillation Ablation: Cryo Energy
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Update on Atrial Fibrillation Ablation: Cryo Energy
Atrial fibrillation (AF) ablation has been performed for several years and has become an important intervention to eliminate atrial fibrillation and the need for medical therapy. Carefully done, the procedure is highly successful and has a low complication rate. The procedure should be done in high volume centers by experienced operators with a well-defined track record.
The Arrhythmia Service at St. Luke's-Roosevelt Hospital Center has published its results for AF ablation (see newsletter Vol.10/Issue 7, 2005 (in PDF format)). In a large series of patients, the complete response rate was approximately 80% during follow-up, indicating a large proportion of patients had become completely free of atrial fibrillation and no longer required chronic or intermittent medical treatment. Overall, 95% of the patients responded to the procedure, either by complete elimination of symptoms, or a substantial improvement in symptoms or response to medications that were previously ineffective.
The underlying basis for AF ablation was the seminal new understanding that reproducible trigger sites are important, and these typically arise from within the pulmonary veins in the back of the left atrium. By eliminating these trigger sites, AF would not initiate. Initially, procedures were designed to isolate all pulmonary veins by segmental ablation guided by sophisticated mapping. A number of alternative techniques were subsequently introduced over the years in an effort to perform adjunctive ablation, i.e. by altering atrial tissue substrate or antonomic modulators, and to make the procedure quicker and easier. However, most recently, a number of investigators examining and comparing alternative techniques have concluded that the key to a successful procedure is pulmonary vein electrical isolation. Since this is most readily achieved by directly targeting the left atrial-pulmonary vein junction, it seems logical that a segmental procedure specifically designed to achieve this end point would be successful. The Arrhythmia Service results are consistent with this strategy.
Although the procedure is overwhelmingly safe, there is a small risk of complication including rare pulmonary vein stenosis. Alternative energy modalities, rather than the conventional radio-frequency energy have been introduced for further investigation. Radio-frequency energy is similar to electro-cautery used in surgical procedures and is the conventional approach for most or all ablation procedures. Radio-frequency energy heats and desiccates cardiac tissue making it electrically non-functional, and ultimately turning it into scar tissue.
An alternative form of energy for ablation is cryo energy, which works by freezing heart tissue to the point where it is no longer functional and viable. For many years, surgeons have used this technique to ablate heart tissue during cardiac surgery, but more recently, the technique has been modified for use with intravenous catheters.
The cryo technique is currently approved for ablation of supraventricular tachycardia, and the Arrhythmia Service at St. Luke's-Roosevelt Hospital Center participated in the seminal clinical trials that led to product approval.
This technique is now being tested in patients with atrial fibrillation to accomplish pulmonary vein isolation. The concept is the same as described above except that tissue is frozen rather than heated. A potential advantage of cryo energy is the fact that the tissue may undergo less scarring after the procedure and thus may have a lower incidence of pulmonary vein stenosis and may be less prone to clot formation on catheter tips. This will be tested in an FDA approved trial now underway (for more information, visit www.cryocor.com).
