Framingham: Men at Twice the Risk of Sudden Cardiac Death as Women

Veronica Hackethal, MD

July 05, 2016

CHICAGO, IL — Men have at least twice the risk of dying from sudden cardiac death (SCD) as women do, at all ages, according to results from the long-running Framingham Heart Study published June 29, 2016 in the Journal of the American Heart Association[1].

Results also showed that those with more cardiovascular risk factors, as well as those with elevated blood pressure (BP) alone, had an increased risk for SCD.

The study is the first to determine lifetime risk for SCD, as well as the first to look at the impact of well-known risk factors on lifetime risk.

"The message conveyed by a study of this magnitude provides significant insight into the cumulative effect of multiple risk factors over a lifetime for the most serious cardiovascular event—sudden cardiac death," Dr Bode Ensam (University of London, UK), who was not involved in the study, commented to heartwire from Medscape in an email.

"The main contribution of this study is highlighting how large the burden of sudden cardiac death is, particularly in men," agreed Dr Sumeet S Chugh (Cedars-Sinai Heart Institute, Los Angeles, California) by phone to heartwire.

SCD is a leading cause of death in the US. Research suggests that the burden in terms of years of potential life lost because of SCD exceeds that of any type of cancer, another leading cause of death in the US, according to Chugh, who also was not involved in the study.

However, patients with obvious cardiac symptoms are the "tip of the iceberg," Ensam added. Asymptomatic individuals have the greatest risk for SCD. Currently no effective means exist for early identification of those at risk for SCD.

The study, led by Dr Brittany M Bogle (Feinberg School of Medicine, Northwestern University, Chicago, IL) included 2785 women and 2294 men with no evidence of heart disease on their first examination between 1948 and 2001 in the Framingham Heart Study. SCD was defined as death because of CHD occurring within 1 hour of symptom onset and not likely attributable to other causes. Researchers assessed cumulative lifetime risk for SCD at ages 45, 55, 65, and 75 years, and evaluated four risk factors for SCD: BP, total cholesterol, smoking, and diabetes.

During the study, 375 SCDs occurred, with the majority before age 70 years.

Across all age categories, men had a significantly higher lifetime risk of SCD than women.

Total Lifetime SCD Risk Estimates

Index Age, y Men, % (95% CI) Women, % (95% CI)
45 10.9 (9.4–12.5) 2.8 (2.1–3.5)
55 11.2 (9.9–12.6) 3.4 (2.7–4.1)
65 10.1 (8.7–11.5) 3.4 (2.7–4.2)
75 6.7 (5.3–8.1) 2.4 (1.7–3.1)

Participants with more risk factors had a higher lifetime risk for SCD. At every age, the lifetime risk for SCD in men with two or more major risk factors was more than 12%, or about one in eight.

Analyses of individual risk factors showed that, across ages and for both sexes, BP was a better indicator of risk for SCD than any other single factor. Men at age 45 years who fell into the highest BP category (systolic BP 160 mm Hg, diastolic BP 100 mm Hg, or on antihypertensive medication) had among the highest lifetime risk of SCD, at 16.3%.

The authors noted several limitations, including that all study participants were white and, as such, the results may not be generalizable to a more diverse population.

Chugh also mentioned other limitations. The study included only those who died, although survival after sudden cardiac arrest is highly dependent on chance. Roughly 90% of people who experience sudden cardiac arrest die, and that may depend on their accessibility to first responders. However, some are successfully revived. Because the study did not include the latter, it may underestimate the inciting event, sudden cardiac arrest, which is what prevention efforts are really targeting.

He pointed out that, nevertheless, the study underscores an important takeaway message, known for decades: effectively treating high BP may decrease the public-health burden of SCD. The same goes for the other risk factors: cholesterol, obesity, diabetes, and smoking. Another way to decrease the burden is to surgically implant cardiac defibrillators in those who need them. For that approach to work, providers need better ways of identifying individuals in the community who would most benefit.

"Currently, we use the ejection fraction, but that's not good enough. There are a lot of people who have SCD and a normal ejection fraction," he said. His team is working to identify genomic hot spots and new biomarkers for SCD.

Ensam also mentioned the potential for genetics and biomarkers to contribute to the creation of individualized risk profiles and seconded the importance of this study to public health.

"Future health initiatives must focus on the apparent at-risk groups, and the risk factors that appear to be most influential at each age: 45-year-old men with significant hypertension, diabetes in those over 65 years, and smoking in those under 65,” he stressed. "In addition, the presence of more than two major risk factors across all age groups and sexes must be cause for attention.

"In those who are asymptomatic, identification and modification of these risk factors remains far and away the most important mechanism by which we can reduce overall risk," he concluded.

Other issues that need to be addressed on a global scale include the effects of socioeconomic status and lifestyle factors besides smoking on the development of risk factors.

The study was supported by the National Science Foundation Graduate Research Fellowship and National Heart, Lung, and Blood Institute. The authors and Chugh report no relevant financial relationships. Ensam reports receiving a research grant and fellowship from Cardiac Risk in the Young, McColl's Retail Group, UK.

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