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Nervous system’s role in fatal heart rhythm studied

23.12.2005

Finding out why seemingly healthy people experience ventricular fibrillation, a fatal irregular heart rhythm, could eventually lead to better methods of early detection, according to a Medical College of Georgia researcher.

“We don’t know what starts ventricular fibrillation or why defibrillation – electrically shocking the heart back into beating normally – works to correct it,” says Dr. Autumn Schumacher, a new faculty member in the MCG School of Nursing who recently won the American Heart Association’s Martha N. Hill New Investigator Award for her research. “We do, however, need a better understanding of this abnormal rhythm and its subtle warning signals so that we can develop smarter bedside monitors.”

While the condition is more common in people with undiagnosed heart problems, those who’ve had a previous heart attack and those with coronary artery disease, it also happens to seemingly healthy people when the body is under stress and secreting adrenaline, says Dr. Schumacher, a physiological and technological nursing professor.

Her current research focuses on what effect adrenaline has on the electrical patterns in the heart.

“The autonomic nervous system controls the heart rate by signaling our body to secrete adrenaline and increase our heart rate based on what we need – the fight or flight reflex,” she says.

Researchers already know that ventricular fibrillation occurs when the heart’s electrical system malfunctions, the electrical signals that control the pumping of the heart become rapid and chaotic causing the lower chambers of the heart to quiver instead of contract. Those chambers can no longer pump blood to the rest of the body, which leads to sudden cardiac death without defibrillation – a successful emergency shock to jump start the heart back into a regular beat.

Studying those electrical signals is what will lead to better medical equipment, Dr. Schumacher says.

Traditional cardiac tests such as electrocardiograms, which record the electrical activity of the heart and identify abnormal rhythms, and echocardiograms, which use sound waves to create a moving picture of the heart, haven’t been able to pinpoint minute changes that are a precursor to ventricular fibrillation; they only provide a picture of large scale electrical activity.

But, by using voltage-sensitive fluorescent dye, injecting it into an isolated animal model and photographing the images at 1,000 frames per second, researchers have been able to see the small picture. These minute images of ventricular fibrillation have recently led to the discovery that the electrical activity during ventricular fibrillation forms distinct patterns.

“The patterns aren’t random as we previously thought,” Dr. Schumacher says. “They actually form spiral waves that often collide with each other and spin off more spiral waves.”

Better bedside monitors will be able to detect the precursors to those spiral wave patterns so that doctors and nurses will have a two-to-three minute warning and can prevent ventricular fibrillation before it happens, she says.

To find out what role adrenaline plays in the whole process, Dr. Schumacher uses various drugs to simulate autonomic nervous system imbalance in an isolated animal heart. Then she photographs fluorescent images of the electrical activity while recording the heart’s rhythm with an electrocardiogram.

“We know that autonomic imbalance and too much adrenaline can contribute to the conditions promoting ventricular fibrillation,” she says. “This research aims to find out why.”