New challenge to cardiac death data

“What are the mechanisms that cause somebody to collapse and die suddenly?” Cardiologist Zian Tseng, lead researcher in study

Many San Francisco fatalities attributed to sudden cardiac arrest were actually from other causes, according to a study that reviewed nearly every death in the city over a three-year period.

And of those that were correctly classified, nearly half were not arrhythmic — involving an irregular heartbeat — meaning that defibrillators or CPR would not have saved the person, the study found. The research was a collaboration between UCSF and the San Francisco medical examiner’s office.

“The whole reason to do this was to understand: What are the mechanisms that cause somebody to collapse and die suddenly?” said lead researcher Dr. Zian Tseng, a UCSF cardiologist who specializes in heart arrhythmias. “The point of our paper is we can’t assume these deaths are cardiac.”

From February 2011 to March 2014, the researchers looked at more than 20,000 deaths in San Francisco. Each morning, Tseng and his colleagues reviewed all deaths reported to the medical examiner’s office the prior day, then read through paramedic logs.

In total, they identified 912 deaths initially attributed to out-of-hospital cardiac arrest. In all but 16 of those cases — where family members objected for religious reasons — Dr. Ellen Moffatt of the medical examiner’s office conducted a full autopsy, including a battery of tests.

A panel composed of the assistant medical examiner, a cardiac pathologist, a neurologist and two cardiologists then determined a final cause of death. The researchers used medical records from all adult hospitals in San Francisco, three emergency medical service agencies, death certificates and more.

It turned out that 40 percent of the cases were not sudden or unexpected, and did not meet the criteria to actually be considered sudden cardiac deaths.

For those that were deemed sudden cardiac deaths, just over half were arrhythmic — where devices like an automated external defibrillator can save someone’s life. Sudden death was the first manifestation of cardiac disease for more than half the arrhythmic cases, the study found, meaning the individuals had no prior warning sign to their condition.

The autopsies uncovered the fact that the leading causes of the presumed sudden cardiac deaths were such conditions as coronary disease or an overdose that wasn’t initially obvious.

According to UCSF, it was the most comprehensive study to date on sudden cardiac death. The research is valuable because coroners typically do not perform full autopsies for people presumed to have died from cardiac arrest, Tseng said.

“They’re busy with possible criminal deaths or unnatural deaths,” he said. “This kind of thing would be very impractical anywhere else.”

The study did not include deaths of people younger than 18 or older than 90.

The mean age in the group that was found to have died from sudden cardiac death was 63, and 69 percent were men. African Americans had the highest rate of sudden cardiac death, and Hispanics had the lowest, the study found.

The idea for the study came after Tseng was researching the genetics of sudden death and found that the medical literature seemed to have an imprecise definition of sudden cardiac death.

The finding that cardiac arrest deaths are overestimated calls into question the reliability of aggregate mortality data that form the basis for some clinical trials and research studies.

“Many of our big overall health care interventions — the baseline of this denominator — is really inaccurate,” Tseng said.

Tseng said the research, funded by the National Institutes of Health, will continue in a number of directions.

“Can we uncover new genes, proteins, expression patterns, biomarkers that might make someone more susceptible to sudden death?” Tseng said. “This is just the beginning.”

He said the research team has also contacted the vast majority of family members to help them identify specific, targeted health interventions they can take.

The study will appear Tuesday in a special edition of Circulation, a journal by the American Heart Association.