Off tempo

Understanding the genetics of disturbed heart rhythms and sudden cardiac death

Leigh MacMillan, Ph.D.
Published: October, 2007

Davis Nwankwo
Photo by Dean Dixon
Hank Gathers. Reggie Lewis. Sergei Grinkov. Young athletes. Unexpected collapse. Sudden death.

In March 2006, Davis Nwankwo nearly joined the list.

It was a routine Monday morning practice. The Vanderbilt Commodores were heading to the Southeastern Conference Men’s Basketball tournament later in the week. Nwankwo arrived for practice about an hour early, as usual, to visit the trainer and have his ankles iced and taped.

He felt fine.

About 20 minutes into the practice, “my mind went blank and I started to walk away from the drill,” recalls Nwankwo, 21, a 6-foot, 10-inch tall senior from College Park, Md. He learned later that he collapsed, stopped breathing, and had no pulse. His heart’s normal rhythmic contraction was gone, replaced by rapid, uncoordinated twitching: ventricular fibrillation.

Nwankwo was lucky. Athletic trainer Mike Meyer sent someone racing to get the automated external defibrillator (AED) from the training room. A jolt from the AED and two breaths from Meyer saved Nwankwo’s life.

Without these measures, “he would have died on the spot,” says Dan Roden, M.D., director of the John A. Oates Institute for Experimental Therapeutics at Vanderbilt University Medical Center and one of the cardiologists who cared for Nwankwo during his hospital stay.

All in the family

Though the unexpected collapse and death of a young athlete in prime physical condition garners national attention, it is a rare event. But sudden cardiac death in the general population is all too common.

“About 15 percent of all deaths in adults in the United States—almost one death every minute—are sudden cardiac deaths, most due to ventricular fibrillation,” Roden says. “That’s a major public health problem.”

For patients with known heart disease, the “cardiovascular world has gotten very good at projecting risk of sudden cardiac death,” Roden says. Patients who are considered high risk generally undergo surgery to place an implantable cardioverter defibrillator, an electronic watchdog that monitors heart rhythm and delivers a shock in the event of cardiac arrest. Nwankwo had a defibrillator implanted two days after his collapse.

“But very good (at determining risk) is not perfect,” Roden adds. To complicate matters further, fewer than half of all sudden cardiac deaths occur in patients with known heart disease or conventional markers. That means that for a majority of those who suffer sudden cardiac death, it is the first symptom they experience.

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