Estimates may overstate toll of sudden cardiac death

Researchers trying to get a precise picture of sudden cardiac death in Portland, Ore. found that checking with ambulance services, medical examiners and hospitals revealed the actual number of cases was only about one-third the total estimated by a commonly used method that involves reviews of death certificates, according to a new study in the Sept. 15, 2004 issue of the Journal of the American College of Cardiology.

“It has been said that half of overall mortality is due to coronary heart disease and half of that is sudden cardiac death. But those numbers don’t add up with ours. It turns out that sudden cardiac death may make up a smaller chunk of mortality than we thought it did. That’s a slight surprise. We thought it would be more,” said Sumeet S. Chugh, M.B.B.S., F.A.C.C. from the Oregon Health and Science University in Portland.

The OHSU researchers, along with colleagues at the Centers for Disease Control and Prevention in Atlanta, identified 353 sudden cardiac arrests in Multnomah County, Ore. between Feb. 1, 2002, and Jan. 31, 2003 by working with emergency medical responders, the medical examiner’s office and 16 hospitals. Resuscitation was attempted in about two-thirds of the cases and 28 patients (8 percent) survived to hospital discharge. These cases accounted for 5.6 percent of all deaths in the county during the study period.

By contrast, a retrospective review of death certificates for the same one-year period yielded 1,007 cases of sudden cardiac death. Since there is no specific code for sudden cardiac death, this type of review identifies cardiac-related causes of death in cases that occurred outside of hospitals or in an emergency room. Only 193 of the death certificate cases matched those found through the prospective study method, which indicates that the death certificate review mislabeled four out of five cases.

The scientific definition of sudden cardiac death includes all patients who suffer a sudden cardiac arrest, whether or not they are resuscitated. The abrupt loss of heart function usually occurs when the heart’s rhythm is disturbed, becoming too fast, too chaotic or too slow to pump blood effectively. Most patients have coronary artery disease, although by definition the cases of sudden cardiac death are unexpected.

Dr. Chugh noted that these results come from just one county during a single year, but he said the study paves the way for similar efforts to study sudden cardiac death in other communities by demonstrating a practical method of identifying cases as they occur. He said researchers don’t need to settle for reviewing death certificate reviews, which are often imprecise and incomplete and typically lead to overestimates of sudden cardiac deaths.

“It is important to assess the burden of sudden cardiac death on a community-wide basis, and it can be done. Secondly, if it is done is a systematic manner, you can actually get a fair amount of detail about each person who had sudden cardiac death, and that’s the only way you’ll be able to figure out risk factors for such a sudden and unexpected event,” Dr. Chugh said.

Sudden cardiac death is generally thought to kill three times as many men as women, so Dr. Chugh said the researchers were surprised to find there were almost as many women (151 cases, 43 percent) as men (202 cases, 57 percent) who suffered sudden cardiac death during this study.

“This burden of sudden cardiac death may be shared more equally between the genders than we previously expected,” he said.

The study results did confirm that most victims had coronary artery disease and most deaths occurred at home. Dr. Chugh said that with a survival rate of only 8 percent, sudden cardiac arrest remains a difficult and devastating public health problem. He said the study methods his team used will help develop a more accurate picture of sudden cardiac death.

“The first thing you have to know if you want to solve a problem is to figure out how big the problem is,” Dr. Chugh said.

Kelley P. Anderson, M.D., F.A.C.C. at the Marshfield Clinic in Wisconsin, who was not part of this research effort, said that sudden cardiac death remains a threat worthy of intense national and individual concern even if the number of cases is not as high as previously estimated. He said he is concerned by the apparently poor performance of the death certificate review in this study.

“This suggests that the CDC’s and similar estimates are missing the boat in terms of the identification of populations and individuals at risk. This could have a significant impact on how a physician should manage his or her patients and how health care resources should be used,” he said.

Dr. Anderson added that this study needs to be replicated in other communities.

“The Chugh study was rigorously performed but the analysis addresses one community over a limited period of time. Thus, there is potential for substantial statistical variability. For instance, the CDC reports that Oregon has an age-adjusted sudden cardiac death rate of 146 cases per 100,000 people, which is well below the national average of 175 cases per 100,000 people. There is, therefore, an urgent need for accurate assessments of sudden cardiac death incidence and risk factors in other communities,” he said.

Douglas P. Zipes, M.D., M.A.C.C. at the Indiana School of Medicine noted that the prospective method used by the researchers is an improvement over most previous efforts.

“Virtually all of the other studies estimating the incidence or prevalence of sudden cardiac death are retrospective and are based on medical examiner reports, which may be inaccurate. The authors of this study claim a high degree of verification of each death, which is important. If their results are accurate, past studies significantly overestimate the incidence of sudden cardiac death. This finding has major implications for the use of automatic external defibrillators, implantable cardioverter-defibrillators, public education and more,” Dr. Zipes said.