Heavy Hearts And The Risk Of Sudden Death

Science Daily — Those with heavy hearts -- in the literal not figurative sense -- long have been known to be prone to cardiac arrest and sudden death. But many are not, and who among them is subject to serious risk is a mystery. To find clues to the puzzle, the National Heart Lung and Blood Institute (NHLBI) of the National Institutes of Health has just awarded $2 million to Sumeet Chugh, M.D., director of Oregon Health & Science University's cardiac arrhythmia center in the division of cardiovascular medicine.

he condition known as left ventricular hypertrophy (LVH), or a thickening and swelling of the heart wall, can be found, by some estimates, in up to 20 percent of the middle-aged population with heart disease in the United States. Some $3 billion to $5 billion worth of pocket defibrillators are being implanted under Medicare guidelines annually to jump start hearts at risk of a cardiac arrest. Yet research studies show that only one out of 15 of the devices ever will be needed to save a life, which is why pinpointing who among those with LVH is at greatest risk of cardiac arrest is a multibillion dollar priority.

The five-year NHLBI grant will provide funds for Chugh, the principal investigator and an associate professor in the cardiovascular division of the OHSU School of Medicine, along with his team of clinicians, scientists and researchers, to continue the landmark Oregon Sudden Unexpected Death Study (Ore-SUDS), which Chugh initiated five years ago. The Ore-SUDS study is a community-based effort that includes a partnership with the emergency medical response system (Jonathan Jui, M.D., professor of emergency medicine, OHSU School of Medicine) the state medical examiner network (Karen Gunson, M.D.) and 16 area hospitals, thus enabling a systematic study of all sudden cardiac arrests that occur in the Portland metropolitan area.

Several findings have been published earlier including the only U.S. data on the current burden of cardiac arrest obtained in a prospective manner. A separate collaborative effort with the Donald W. Reynolds Cardiovascular Clinical Research Center at Johns Hopkins University Reynolds Cardiovascular Center (Eduardo Marban, M.D., Ph.D., director) focusing on the link between cardiac arrest and the human genome is also ongoing.

"We found in analyzing the Ore-SUDS data," said Chugh, "that if you have left ventricular hypertrophy in Multnomah County your risk of cardiac arrest is increased at least twofold and, in combination with specific other conditions such as a weakened pumping ability of the heart muscle, the risk can be much higher. But that doesn't mean everybody with the condition is at risk. Left ventricular hypertrophy is associated with high blood pressure, and lots of people have high blood pressure but not all of them are prone to cardiac arrest.

Chugh reported in the Journal of the American College of Cardiology in March that less than a third of the sudden cardiac deaths where left ventricular dysfunction had previously been evaluated in the Ore-SUDS data had dysfunction that was severe enough to warrant implantation of a cardioverter-defibrillator. "These findings support the aggressive development of alternative screening methods to enhance identification of patients at risk," Chugh wrote.

Speaking about his team's plans going forward, Chugh said: "We want to figure out what will significantly improve our ability to predict cardiac arrest," Chugh continued. "Our ultimate aim is to nip it in the bud, which for patients that will suffer cardiac arrest means averting disaster before it happens. The evaluation of information that we have gathered in Ore-SUDS combined with what we learn at the bedside from patients together with bench research we are doing on the molecular mechanisms involved represent a comprehensive approach that we think hold great promise of solving the puzzle. If we can predict who the high risk patient with left ventricular hypertrophy is, that is likely to have huge significance for our patients."

According to the American Heart Association, about 250,000 Americans succumb each year to sudden cardiac death, which is defined as death within one hour of the time a person displays symptoms such as chest pain or difficult breathing. About half have shown no prior evidence of heart disease and about 40 percent are under age 65. In most cases, cardiac arrest results from arrhythmia, or abnormal heart rhythm. The survival rate ranges between 5 percent and 10 percent despite improvement in emergency medical services and widespread training in application of CPR.