Patients with a history of cardiovascular disease, compared with those without, had a higher incidence of sudden cardiac death (SCD), according to a study of 5.5 million Danish citizens in 2010, published in JACC: Clinical Electrophysiology.

In a study designed to examine differences in SCD cases between patients who did and did not have a history of cardiovascular disease, Tobias Skjelbred, MD, et al., identified 6,851 deaths from SCD between Jan. 1 and Dec. 31, 2010 through autopsy records, the Danish National Patient Register and the National Causes of Death Register. A history of cardiovascular disease was defined as one or more hospital in- or outpatient contact(s) coded as cardiovascular disease as a primary or secondary diagnosis from Jan. 1, 1994, onward. All deaths were usually reviewed by one physician and two if the death was sudden and unexpected.

Results showed that of the SCD cases, 3,805 (55.5%) had a history of cardiovascular disease while 3,046 (44.5%) did not. The incidence rate of SCD increased with age, and was higher in those with a history of cardiovascular disease in all age groups.

Of note, the difference in incidence rates decreased with age from 21.6 in those ≤19 years old to only 1.8 in those >90 years.

The average age of SCD cases was younger for those without vs. with a history of cardiovascular disease (73 vs. 80 years). Also, those without cardiovascular disease who had SCD were more likely to be female and less likely to have comorbidities, cancer and/or psychiatric illnesses. Furthermore, the odds of having cardiovascular disease before SCD were lower in women (odds ratio [OR], 0.66) and those living alone (OR, 0.75).

"Despite having information on all hospital in- and outpatient visits since 1994, there are still 45% of SCD cases that did not have a history of [cardiovascular disease]," write the authors. "This finding raises the question of whether there might be an undisclosed noncardiac cause in cases without prior [cardiovascular disease], if SCD is the first sign or symptom of an underlying cardiac disease in these individuals, or if heart disease is underdiagnosed in these individuals."