A drug that is used to treat atrial fibrillation, the most common heart rhythm disturbance in the United States, may have wider applications than previously thought, according to researchers at the University of California San Francisco.
In two recent studies, UCSF cardiologists have shown that Ibutilide, a class III drug approved by the FDA two years ago to treat atrial fibrillation, may be an important tool for treating adults and children who have a congenital heart defect, Wolff-Parkinson-White Syndrome (WPW), as well. Their most recent findings will be presented at the North American Society of Pacing and Electrophysiology (NASPE) meeting on May 14 in Toronto.
"We've shown that Ibutilide is an effective and safe drug to use in patients with WPW, atrial fibrillation, and otherwise normal hearts," says Kathy Glatter, MD, a UCSF cardiology fellow and principle investigator of the study. "This finding is important because it could give WPW patients a better chance to either slow their heart rate during atrial fibrillation or restore the normal rhythm."
Wolff-Parkinson-White Syndrome is a congenital birth defect in which extra electrical connections, or accessory pathways, are present in the heart. Although people with WPW are otherwise healthy, the extra connection can cause an electrical "short circuit" and a very fast heartbeat. Additionally, 30 to 40 percent of WPW patients will develop atrial fibrillation at some point during their lives.
The combination of having WPW plus atrial fibrillation can be deadly. Some of the drugs that are routinely used in emergency rooms to treat atrial fibrillation can also impair the heart's normal electrical pathways. For someone with WPW, this can allow electrical impulses to travel down the shorter accessory pathway and cause the heart to beat even faster, rather than slowing it down, said Glatter.
"Ibutilide seems to be as safe and more effective than Procainamide and other drugs currently used for the treatment of atrial fibrillation with WPW," says Melvin Scheinman, MD, UCSF professor of electrophysiology and senior author of the study. "It will likely be used more frequently in emergency rooms for these patients and thus help a lot of people who aren't adequately treated right now."
In a study presented at the 1998 American Heart Association meetings in November, the UCSF researchers showed for the first time that Ibutilide can safely and effectively stop atrial fibrillation in patients with WPW. Atrial fibrillation was induced in the controlled environment of UCSF Stanford Health Care's electrophysiology (EP) labs during EP study in 14 patients with WPW. Intravenous Ibutilide stopped the atrial fibrillation within twenty minutes of the infusion in 13 of the 14 patients.
In a second ongoing prospective study, the researchers are examining the mechanisms of how Ibutilide works. To date, eighteen WPW patients ranging in age from 4 to 75 years old have been given Ibutilide during EP study. The researchers have identified Ibutilide's effects on conduction over the abnormal accessory pathway.
Ibutilide has previously been shown to effectively stop atrial fibrillation in adults only. The UCSF studies have included children as well, including Shannon Koehler, a boy with WPW. Koehler was given Ibutilide when he was nine years old and developed atrial fibrillation during an EP study. The Ibutilide allowed the electrophysiologists to continue their work and safely eliminate Koehler's two accessory connections.
Normally, electrical impulses flow in a controlled rhythm from the upper chambers of the heart (atria) to the lower chambers (ventricles), causing the heart to contract and pump blood at a steady pace. The accessory pathway found in WPW patients allows electrical impulses to return back to atria rapidly and acts as a "short circuit," which can lead to tachycardia or atrial fibrillation.
If left untreated, the rapid rhythm can lead to ventricular fibrillation and death.
In addition to Glatter and Scheinman, co-authors of the NASPE abstract include Parvin Dorostkar, MD, chief of pediatric EP at Case Western Reserve University; Yanfei Yang, MD, visiting scientist from Beijing, China; Nancy Chiesa, RN, UCSF pediatric EP nurse; George Van Hare, MD, director of the pediatric arrhythmia centers at Lucile Packard Children's Health Services at UCSF Stanford Health Care; and Edmund Keung, MD, director of the Pacemaker and Arrhythmia Service at the San Francisco Veterans Affairs Medical Center.