DALLAS, Jan. 29 – Smart bombs are touted for their ability to precisely target and destroy an enemy. Now equally “smart” technology is being used by heart experts to target and destroy cells that trigger the irregular heart rhythm called atrial fibrillation, according to a report in today’s rapid access publication of Circulation: Journal of the American Heart Association.
In atrial fibrillation (AF) the two upper chambers of the heart, the atria, beat erratically, causing blood to pool inside the chamber and become stagnant. When this occurs, blood clots may form and cause strokes.
In a study of 70 people with AF, Hakan Oral, M.D., assistant professor of medicine at the University of Michigan, Ann Arbor, used radio frequency energy delivered from a catheter tip to locate and destroy cells that cause the extra heartbeats leading to AF. All abnormal beats were eliminated and a normal rhythm was restored in more than 80 percent of the people in the study who had intermittent, or paroxysmal, AF. The treatment, called radio frequency ablation, was less effective for those with persistent AF.
“By zapping the cells this way, we disconnect cells with abnormal electrical activity from the rest of the heart,” says Oral. “When those misfired electrical impulses reach the atrium, they can trigger atrial fibrillation.”
Palpitations and rapid heart beat are symptoms of AF. Devices called defibrillators are used to shock the heart back into a normal rhythm, or medicines called antiarrhythmics are used, says Oral. These antiarrhythmic medicines are also used to prevent recurrences of AF. However, drug therapy may not be effective in all patients and may be associated with side effects. In addition to antiarrhythmic treatment, medicines that thin the blood are used to prevent blood clots, which are common in people with AF.
Oral says the only way to “cure” AF is to eliminate the source of the problem: those cells that trigger the extra beats. “Earlier studies show that most of these signals appear to originate in the pulmonary veins that carry clean, oxygenated blood from the lungs to the left atrium. These cells, located within a few centimeters of the opening into the left atrium, can spontaneously fire and cause the extra beats,” he explains.
“The best strategy for ablation is to electrically disconnect the muscle of the vein from the rest of the heart by precisely identifying the sites around the circumference of the pulmonary veins where there is ‘communication’ between the vein and the atrium,” he says.
In the new study, Oral and his colleagues attempted to ablate at least three of the four pulmonary veins in a series of 70 patients with either paroxysmal or persistent AF who had not responded to drug therapy.
Fifty-seven men and 13 women participated. Their average age was 53. Fifty-eight patients had paroxysmal AF and 12 had persistent AF.
Researchers threaded a catheter into the pulmonary veins. The catheter had a ring-shaped tip that could detect electrical impulses sent by cells inside the veins. “We used this catheter to map the exact location of the electrical connection between the pulmonary vein and the left atrium,” says Oral. Once the targets were mapped, the researchers used an ablation catheter to deliver 30-35 watts of radiofrequency energy at these sites. This technique used for segmental isolation was adapted from techniques first introduced by Dr. Haissaguerre and coworkers in Bordeaux.
Five months after treatment, 70 percent of patients with paroxysmal AF were free from AF and did not need an antiarrhythmic drug. An additional 13 percent had a more than 90 percent improvement in the frequency of spells either without an antiarrhythmic drug or with a drug that had been ineffective previously.
Overall, 83 percent of the patients with paroxysmal AF were either cured or had substantial improvement after the procedure. However, only 30 percent of patients with persistent AF were free of recurrent episodes at five months follow-up. Persistent AF is AF that has been continuously present for months or years.
“Novel therapeutic strategies will be necessary in those with persistent AF to improve their outcomes since long-lasting AF leads to electrical and structural changes in the heart. Also, the lower success rates in patients with persistent AF underscores the importance of early intervention in paroxysmal AF before it progresses to persistent AF,” says Oral.
The procedure can take as long as four hours but usually can be done in about two to three hours, he says. In the study, patients were admitted to the hospital in the morning, had the procedure, and were released the next morning after overnight observation.
The American Heart Association estimates that about 2 million Americans have either paroxysmal or persistent AF. About 70 percent of these people are aged 65 or older. About 15 percent of stroke victims have a history of AF.
Co-authors in the study were Bradley P. Knight, M.D.; Hiroshi Tada, M.D.; Mehmet Ozaydin, M.D.; Aman Chugh, M.D.; Sohail Hassan, M.D.; Christoph Scharf, M.D.; Steve WK, Lai, M.D.; Radmira Greenstein, M.D.; Frank Pelosi Jr., M.D.; S. Adam Strickberger, M.D.; and Fred Morady, M.D.
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