Recent studies demonstrated that atrial fibrillation (AF) is independently associated with sudden cardiac death (SCD). But both AF and SCD share few common causal factors including congestive heart failure (CHF) that could explain this association. A recent case-control study - The Oregon-SUDS [Sudden Unexpected Death Study] tested the hypothesis that CHF could play a major confounding role in this association(1).

This study included 652 subjects who experienced SCD (sudden cardiac death - defined as abrupt loss of pulse within 1 hr. of symptom onset) in Oregon Metropolitan region between the years 2002 and 2012. They were age and sex matched to 652 alive controls diagnosed with known coronary artery disease (defined by a previous history of MI, CABG, PCI or >/=50% stenosis involving any major coronary artery), but no prior history of cardiac arrest or ventricular arrhythmias. All subjects included were above 18 years of age and had prior cardiac evaluation with either electrocardiogram (EKG) or/and echocardiogram. The subjects’ medical history was obtained from review of their outpatient/inpatient medical records including cardiac evaluations like EKG, echocardiogram, and coronary angiograms. Any documented history of AF or CHF in the patient records or investigations (labs/imaging studies) was noted. The relative risk of SCD in patients with and without AF was calculated using odds ratio and in a different model, CHF was added to study its interaction with AF and SCD.

A history of AF and CHF was more common in the case group (27% and 45% respectively) compared to the controls group (18% and 19% respectively). The prevalence of AF was similar in both the groups when stratified by CHF (p=0.13). Conversely when adjusted by AF alone, there was increased prevalence of CHF in the cases compared to controls when stratified by AF (p<0.001). Multivariate model adjusted to all variables except CHF showed significant association of AF with SCD (OR: 1.6; 95% confidence interval [CI]: 1.2 to 2.0; p = 0.002); but there was no statistical significance (OR: 1.1; 95% CI: 0.8 to 1.5; p = 0.45) with addition of CHF to the model (OR: 1.1; 95% CI: 0.8 to 1.5; p = 0.45). Univariate analysis revealed significant association between CHF and SCD (OR: 3.1; 95% CI: 2.4 to 4.1; p < 0.0001). Logistic regression analysis showed AF was not associated with SCD in patients with CHF (OR: 0.9; 95% CI: 0.6 to 1.4; p = 0.54) or without CHF (OR: 1.4; 95% CI: 0.9 to 2.0; p = 0.14). Subgroup analysis revealed that CHF was significantly associated with SCD in patients with AF (OR: 2.1; 95% CI: 1.2 to 3.4; p = 0.006) and without AF (OR: 3.6; 95% CI: 2.6 to 5.0; p < 0.0001).

This study showed AF is significantly associated with SCD but this may be partly related to history of congestive heart failure. So, more studies are needed to study the impact of CHF in predicting the risk of SCD in AF patients.

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1.         Reinier K, Marijon E, Uy-Evanado A et al. The association between atrial fibrillation and sudden cardiac death: the relevance of heart failure. JACC Heart failure 2014;2:221-7.