Sudden cardiac death still a mystery - Heart Disease

USA Today (Society for the Advancement of Education), Feb, 2004

Sudden cardiac death (SCD) is a catastrophic disruption of the heart rhythm that can cause a seemingly healthy human to drop dead without warning. More people die from SCD each year than from AIDS, breast cancer, and lung cancer combined. The condition accounts for nearly 60% of all cardiovascular-related deaths, claiming the lives of approximately 300,000 people per year in the U.S.

Yet, because there are few warning signs or symptoms to identify people at risk, and since SCD is, by definition, fatal, leaving no survivors to study, scientists know little about the underlying mechanisms that cause the condition. The Center for Research in Cardiovascular Medicine at the University at Buffalo (N.Y.) is poised to change that scenario. The university has assembled a cadre of specialists in several fields who are investigating SCD from the single-cell level up, with the goal of developing strategies for treatment and prevention.

"Great strides have been made in treating ischemic heart disease, heart attack, and heart failure," points out John M. Canty, Jr., director of the center. "However, the impact of these developments on sudden cardiac death is disappointing. The percentage of sudden deaths is increasing, while mortality from other cardiovascular causes continues to decline. As a result, sudden death has become one of the nation's major public health problems."

A multidisciplinary team encompassing specialists in cardiology, physiology, biophysics, biochemistry, genetics, pharmacology and toxicology, positron emission tomography (PET) scanning, and electrophysiology is interested particularly in studying a phenomenon called "hibernating myocardium," in which hear cells receiving a depleted blood supply due to arterial narrowing adapt to the life-threatening situation by reducing their function and oxygen needs. The cells remain viable and are able to result normal activity if and when surgery restores full blood flow.

Nevertheless, since areas of hibernating myocardium exist side-by-side with normal heart muscle, the disparity in electrical activity can result in rhythmic chaos, making the heart vulnerable to fatal arrhythmias. "Although much previous research has focused on the role of scarring following a heart attack as the underlying factor leading to the arrhythmias responsible for sudden death, we think that the areas that are viable and hibernating may actually be a greater risk factor," explains Canty.

The researchers cleverly circumvented the problem of having no human survivors to study by creating the hibernating myocardium phenomenon in the first animal model--a pig--for the disease, and implanting a defibrillator similar to that used in patients with advanced heart disease. When an irregular heartbeat that ordinarily would be fatal occurs, the defibrillator activates, saving the animal and providing a living model of the sudden cardiac death syndrome to study. By monitoring what transpires in the heart cells leading up to a potentially fatal ventricular fibrillation, and analyzing the physical and biological effects in the heart post-SCD, the researchers can gain information never before available.

In another major project, patients will undergo PET scanning before and after coronary bypass surgery to determine whether electrical activity to the heart can return to normal, which could explain favorable effects of surgery on reducing sudden death in some patients. PET scanning allows researchers to trace biological processes noninvasively in real-time. Using this technology, physicians hope to identify changes early on that could lead to identifying patients at high risk of sudden cardiac death and develop routine diagnostic procedures to detect these anomalies and correct them.