Heart Drug Used for Wolff-Parkinson-White Syndrome

May 13, 1999
News Office: Rebecca Sladek Nowlis (415) 502-6397

A drug 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 UCSF Medical Center.

In two recent studies, UCSF cardiologists have shown that Ibutilide, a class III drug approved by the Federal Drug Administration 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). Their findings were presented at the North American Society of Pacing and Electrophysiology (NASPE) 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," said Dr. Kathy Glatter, 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 the condition are otherwise healthy, the extra connection can cause an electrical "short circuit" and a very fast heartbeat. Additionally, 30 percent to 40 percent of patients with the condition will develop atrial fibrillation at some point during their lives.

The combination of having WPW and atrial fibrillation can be deadly. Some of the drugs routinely used in emergency rooms to treat atrial fibrillation also can 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, Glatter said.

"Ibutilide seems to be as safe and more effective than Procainamide and other drugs currently used for the treatment of atrial fibrillation with WPW," said Dr. Melvin Scheinman, 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 electrophysiology (EP) labs during a study in 14 patients with WPW. Intravenous Ibutilide stopped the atrial fibrillation within 20 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, 18 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 included children.

In addition to Glatter and Scheinman, co-authors of the abstract include Dr. Parvin Dorostkar, chief of pediatric EP at Case Western Reserve University; Dr. Yanfei Yang, visiting scientist from Beijing, China; Nancy Chiesa, UCSF pediatric EP nurse; Dr. George Van Hare, director of the pediatric arrhythmia centers at Lucile Packard Children's Hospitals, a part of Stanford Health Care; and Dr. Edmund Keung, director of the Pacemaker and Arrhythmia Service at the San Francisco Veterans Affairs Medical Center.