EHJ: Danish researchers refine evaluation of SCD in young
There are inherent problems and inconsistencies with calculating the number of sudden cardiac deaths (SCD) in the young. Danish researchers, however, used a rigorous method and found an incidence rate higher than previously reported, according to a study published online Dec. 2 in the European Heart Journal.

Bo Gregers Winkel, MD, from the Center for Cardiac Arrhythmia in Copenhagen, Denmark, and colleagues retrospectively studied all death certificates, the registration of all in- and outpatient activity on Danish hospitals and emergency rooms, as well as medical records and autopsy reports. For the study, they included all deaths in persons aged 1 to 35 years in Denmark between 2000 and 2006.

They found that 7 percent of all deaths in the young can be attributed to SCD, when including non-autopsied cases. The highest possible incidence rate of SCD in the young was 2.8 per 100,000 person-years including non-autopsied cases of sudden unexpected death (SUD). Excluding those, the incidence rate declined to 1.9 per 100,000 person-years.

They said that previous reports in the U.S. had shown the use of death certificate-derived data for identifying SCD yielded a "sensitivity of 59 percent and a positive predictive value of a mere 19 percent," which would "naturally lead to concern whether our initial use of death certificates would be a reliable method."

However, Danish death certificates, unlike those in the U.S., include a supplemental information field describing the circumstances surrounding the death including interviews with eyewitnesses and relatives, previous medical conditions, an external examination of the body and the preliminary conclusion before autopsy.

"This makes the Danish death certificates suitable to be a primary screening tool for identification of SUD in the young," the investigators said.

In the current study, an external exam was carried out in 84 percent of all SUD cases and the autopsy ratio was 75 percent. Winkel et al had a positive predictive value of 50 percent to identify SCD from death certificates. "This was calculated using only autopsied cases as the numerator and as such could never exceed the autopsy ratio of 75 percent. In essence, this suggests that death certificates contain a high level of information in our study," they said.

Researchers identified 625 cases of SUD (10 percent of all deaths), of which 156 were not autopsied. A total of 29 percent of autopsied SUD cases were unexplained.

Of the 469 autopsied SUD cases, 67 percent were SCD. The most common cardiac cause of death was ischemic heart disease (13 percent). The 1 percent rate of hypertrophic cardiomyopathy death was low compared to other studies. However, if researchers included idiopathic fibrosis and left ventricular hypertrophy in the definition of hypertrophic cardiomyopathy, "our incidence would increase to 9 percent, thereby being in concert with the other studies."

Winkel et al reported that arrhythmogenic right ventricular cardiomyopathy accounted for 5 percent of autopsied SCD. "Although less frequent when compared with [other studies], it is a significant cause of SCD in the young in Denmark."

In 45 percent of SCD cases, the death was witnessed, 34 percent died during sleep and 89 percent were out-of-hospital deaths.

Of the 11 percent SCD that occurred in-hospital, 27 percent collapsed and died in the emergency room, while 63 percent died sudden and unexpectedly during hospitalization.

Researchers noted that the in-hospital deaths and those that occurred during sleep "warrant for caution in the interpretation of figures that rely solely on out-of-hospital deaths and/or witnessed deaths as they are likely to underestimate the incidence of SCD."

The median age of the SCD population was 29 years, more than two-thirds were male and about two-thirds had no previous medical history. Researchers found that increasing age was associated with significantly increased risk of dying from SCD.

Investigators found that the median age of SUD and SCD victims was similar (27 vs. 28 years), but SUD deaths were less likely to be witnessed (34 vs. 62 percent SCD cases) and more likely to die during sleep (46 vs. 24 percent).

The researchers suggested that a family genetic evaluation might be in order for unexplained SUD as "some of these persons may harbor disease-causing mutations in, for instance, the KCNQ1 and SCN5A genes known to be associated with death during sleep due to primary arrhythmogenic diseases like the long QT syndrome and the Brugada syndrome."

The Danish researchers cautioned that they cannot rely solely on the information on the cause of deaths in the registry when it comes to identifying SCD cases because they found that "24 percent of all autopsied cases of SCD or SUD were not categorized in the Cause of Death Registry with an ICD-code denoting cardiac or ill-defined cause of death."

They also said that most cause of death registries "suffer from the inherent weakness of not registering whether a death was sudden and unexpected."