J. David Burkhardt, MD, FACC and Andrea Natale, MD, FACC, FHRS, Executive Medical Director
Texas Cardiac Arrhythmia Institute
Austin, Texas

In this special feature, J. David Burkhardt, MD, FACC and Andrea Natale, MD, FACC, FHRS discuss electrophysiology advancements from the past year.

The year 2009 has yielded some interesting developments in the field of cardiac electrophysiology. Many of the advances reported in the last decade in atrial fibrillation have focused on ablative therapy. This year is no exception; however, new treatment options are also available in both stroke prevention and rhythm control. Left atrial appendage occlusion devices and direct thrombin inhibitors have reported promising results, and the first new anti-arrhythmic medication for atrial fibrillation in nearly a decade is available. Device-based therapy for congestive heart failure continues to evolve, with a trial showing benefit of cardiac resynchronization therapy in patients with relatively asymptomatic left ventricular dysfunction and cardiac dyssynchrony. Ablative therapy for cardiac arrhythmias also continues to expand. This year reported improved success rates in atrial fibrillation ablation with repeat ablation procedures, success with endoscopic laser balloon based ablation systems, successful reduction of ventricular tachycardia with ablation in patients with prior myocardial infarction, and new methods for improving the success and reducing the complications associated with epicardial ablation.

Options for Stroke Prevention and Rhythm Control
The options for stroke prevention associated with atrial fibrillation have been limited to aspirin and warfarin for many years. Devices that occlude the left atrial appendage may soon be added to the treatment options. In a study of 707 patients with atrial fibrillation and stroke risk factors, the left atrial occlusion device was not inferior to warfarin for stroke prevention. The device was associated with a higher rate of complications, most of which were peri-procedural complications such as bleeding or pericardial effusion.1 This device is currently being evaluated by the Food and Drug Administration for possible approval to prevent stroke in such a population.

Warfarin is the only drug option currently available for patients with atrial fibrillation who are at high risk for stroke; however, a new direct thrombin inhibitor may be an option in the near future. Dabigatran was studied in over 18,000 patients with atrial fibrillation and stroke risk factors. The lower dose studied showed similar stroke prevention to warfarin with lower bleeding complications, while the higher dose showed superior stroke prevention with similar bleeding complications.2 Obviously, one of the major benefits is the lack of dose adjustment and monitoring that is necessary with warfarin.

The first new anti-arrhythmic medication in nearly a decade was approved this year. Dronederone is an amiodarone analog that is approved for atrial fibrillation. It does not appear to have many of the side effects of amiodarone, but may not be as effective.3 Its major contraindication is advanced heart failure, but it can be used in the presence of coronary artery disease and left ventricular dysfunction. In the ATHENA trial, dronedarone reduced hospitalization due to cardiac events or death compared to placebo.2 In a post hoc analysis, dronedarone also appeared to reduce the risk of stroke, but this will need further investigation.4

Cardiac Resynchronization Therapy
Cardiac resynchronization therapy continues to be a powerful tool in combating congestive heart failure. The MADIT-CRT trial published this year showed that this therapy reduced the risk of heart failure events as well as improved the left ventricular ejection fraction and reduced left ventricular volumes in patients with NYHA Class 1-2 congestive heart failure, left ventricular dysfunction and a wide QRS on EKG.5 We may soon see the expansion of cardiac resynchronization therapy to any patient with left ventricular dysfunction and a wide QRS complex.

Ablative Therapy for Cardiac Arrhythmias
Regarding the ablation of cardiac arrhythmias, many advancements were reported in 2009. Atrial fibrillation ablation can result in remarkably high success rates in patients with non-paroxysmal atrial fibrillation. Additional procedures may be required, but 84% of patients with persistent and long-standing persistent atrial fibrillation were free from atrial fibrillation after ablation across a group of operators using the pulmonary vein antrum isolation technique.6

New technology continues to be developed to make atrial fibrillation ablation easier to perform. An endoscopic laser balloon was studied in patients with paroxysmal atrial fibrillation. Using this technology alone, 91 percent of veins were isolated and 60 percent of patients were free from atrial fibrillation with a year of follow up.7 These types of large area lesion technology may make atrial fibrillation ablation faster and easier to perform. These types of technological advances may allow more patients to receive this therapy.

Ablation therapy for ventricular tachycardia is also becoming more commonplace. Irrigated ablation catheter technology has improved the results that can be obtained with these ablations. Stevenson et al reported that in patients with prior myocardial infarction, episodes of ventricular tachycardia can be significantly reduced with ablation. Even if multiple or unmappable ventricular tachycardias were present, most patients were improved after the procedure.8 Patients who suffer from ventricular arrhythmias are no longer limited to only antiarrhythmic therapies and their potential toxicities.

Minimally invasive epicardial ablation is increasingly used to treat cardiac arrhythmias.9 Some of the limitations include the tools used and the potential complications. A couple of publications have addressed these limitations. Cryoablation has been used endocardially for arrhythmias in dangerous locations such as the coronary sinus or near the AV node. The same energy source can be used successfully in the pericardial space after radiofrequency ablation is unsuccessful.10 Also, since the phrenic nerve lies on the epicardial surface, this structure can be damaged by epicardial ablation in the area of its course. One study compared strategies for separating the nerve from the epicardial surface, making ablation near this structure safer. Using a combination of air and saline infused into the pericardial space was more successful in preventing phrenic nerve stimulation with high output pacing than using saline alone or a large peripheral angioplasty balloon.11 These studies may help to lead to further technology to assist in minimally invasive epicardial ablation.

The year 2009 has renewed old treatments for atrial fibrillation. Many of the last few years have focused on ablation therapy for atrial fibrillation, but 2009 offers a new anti-arrhythmic medication and a potentially new drug and mechanical device for stroke prevention. Cardiac resynchronization therapy may now expand to include minimally or asymptomatic patients with left ventricular dysfunction and a wide QRS complex. Irrigated ablation catheters have allowed ventricular tachycardia ablation to show promising results in patients with prior myocardial infarction, and epicardial ablation continues to evolve and expand. Hopefully 2010 will allow electrophysiologists to continue to advance the art and science of treating arrhythmias.

References
1. Holmes DR, Reddy VY, Turi ZG, et al. Percutaneous closure of the left atrial appendage versus warfarin therapy for prevention of stroke in patients with atrial fibrillation: A randomised non-inferiority trial. Lancet 2009;374:534-542.
2. Connolly SJ, Ezekowitz MD, Yusuf S, et al. Dabigatran versus warfarin in patients with atrial fibrillation. N Engl J Med 2009;361:1139-1151.
3. Piccini JP, Hasselblad V, Peterson ED, et al. Comparative efficacy of dronedarone and amiodarone for the maintenance of sinus rhythm in patients with atrial fibrillation. J Am Coll Cardiol 2009;54:1089-1095.
4. Connolly SJ, Crijns HJ, Torp-Pedersen C, et al. Analysis of stroke in ATHENA: A placebo-controlled, double-blind, parallel-arm trial to assess the efficacy of dronedarone 400 mg BID for the prevention of cardiovascular hospitalization or death from any cause in patients with atrial fibrillation/atrial flutter. Circulation 2009;120:1174-1180.
5. Moss AJ, Hall WJ, Cannom DS, et al. Cardiac-resynchronization therapy for the prevention of heart-failure events. N Engl J Med 2009;361:1329-1338.
6. Bhargava M, Di Biase L, Mohanty P, et al. Impact of type of atrial fibrillation and repeat catheter ablation on long-term freedom from atrial fibrillation: Results from a multicenter study. Heart Rhythm 2009;6:1403-1412.
7. Reddy VY, Neuzil P, Themistoclakis S, et al. Visually-guided balloon catheter ablation of atrial fibrillation: Experimental feasibility and first-in-human multicenter clinical outcome. Circulation 2009;120:12-20.
8. Stevenson WG, Wilber DJ, Natale A, et al. Irrigated radiofrequency catheter ablation guided by electroanatomic mapping for recurrent ventricular tachycardia after myocardial infarction: The multicenter thermocool ventricular tachycardia ablation trial. Circulation 2008;118:2773-2782.
9. Cano O, Hutchinson M, Lin D, et al. Electroanatomic substrate and ablation outcome for suspected epicardial ventricular tachycardia in left ventricular nonischemic cardiomyopathy. J Am Coll Cardiol 2009;54:799-808.
10. Di Biase L, Saliba WI, Natale A. Successful ablation of epicardial arrhythmias with cryoenergy after failed attempts with radiofrequency energy. Heart Rhythm 2009;6:109-112.
11. Di Biase L, Burkhardt JD, Pelargonio G, et al. Prevention of phrenic nerve injury during epicardial ablation: Comparison of methods for separating the phrenic nerve from the epicardial surface. Heart Rhythm 2009;6:957-961.

Disclosures: Dr. J. David Burkhardt is a Chief Medical Advisor to Stereotaxis, and consultant to Medtronic, Biosense Webster, and St. Jude Medical. Dr. Andrea Natale is a consultant to Stereotaxis, Biosense Webster, St. Jude Medical, Medtronic, Atritech, and CardioFocus.