Atrial fibrillation (AFib) is the most common cardiac rhythm abnormality, and affects more than 33 million individuals worldwide. It is associated with an increased risk of stroke, heart failure (HF), cognitive impairment, and death, and emerging evidence has begun to suggest that AFib may also contribute to one’s susceptibility to sudden cardiac death (SCD).

A study published April 30 in JACC: Heart Failure, sought to determine if a history of congestive HF is a cofounder of an association between AFib and SCD, and found that "a history of congestive HF, including both systolic and diastolic symptomatic dysfunction, may partially explain the AFib–SCD association."

The study, led by Kyndaron Reinier, PhD, Cedars-Sinai Medical Center, compared 652 SCDs in the Oregon Sudden Unexpected Death Study with age and sex-matched controls. The investigators found that AFib was much more common in SCD cases than matched controls (27 percent vs. 18 percent, p = .0001). After adjustments using logistic regression and propensity score matching however, the AFib-SCD association was no longer significant. In comparison to the controls patients with SCD more frequently had congestive HF (45 percent vs. 19 percent, p < .0001) and low ejection fraction (30 percent vs. 14 percent, p < .001). When the prevalence of AFib stratified by congestive HF status was compared in cases and controls, no difference (p=.13) was to be found. Conducting a number of sensitivity analyses using alternative definitions of congestive HF based upon left ventricular function and brain natriuretic peptide levels, all of which failed, Reinier and his colleagues failed to demonstrate an independent association of AFib and SCD.

The authors note that, "our findings underscore the need to further investigate the complex association between AFib and SCD, especially in the setting of diastolic congestive HF, before a causal association between the two conditions is confirmed."

"The findings from Reiner et al. have important implications for both cardiovascular investigators and clinicians," writes Jonathan Piccini, MD, MHS, FACC, Duke University Medical Center. "The relationship between AFib, congestive HF and SCD in this analysis serves as an important reminder of the clear and present danger of confounding in all observational studies. Further investigation is required to clarify whether AFib contributes to the risk of SCD. However, these data also highlight the risks of SCD in patients with concomitant AFib and congestive HF. Perhaps the best method for preventing SCD in patients with AFib is the prevention of congestive HF."

Keywords: Prevalence, Cognition, Stroke, Propensity Score, Ventricular Function, Left, Heart Failure, Death, Sudden, Cardiac, Logistic Models, Natriuretic Peptide, Brain