Sleep disordered breathing and atrial fibrillation are associated with dysregulation of circadian rhythm in human myocardium

Objective: Cardiovascular disease remains the leading cause of death worldwide. Cardiovascular high-risk patients with severe coronary artery disease are at increased risk for multiple comorbidities and secondary disorders, including sleep disordered breathing (SDB) and atrial fibrillation (AF) as the most frequent sustained arrhythmia. The role of myocardial circadian rhythm gene regulation for AF initiation and progression in this population is still elusive, but recent research implicates disturbance of circadian rhythm gene expression in the progression of different diseases.

Purpose: We evaluated the myocardial expression of relevant genes involved in the circadian rhythm (CLOCK, BMAL1, NR1D1, NR1D2) in patients with severe coronary artery disease.

Methods and Results:

Clinical data was acquired from 160 patients undergoing elective coronary artery bypass grafting, including a pre-operative test for SDB using polygraphy. SDB was defined as an apnea-hypopnea index (AHI) ≥ 15/h. Human myocardial tissue was analyzed from right-atrial appendage biopsies obtained intraoperatively in the morning. CLOCK, BMAL1, NR1D1, NR1D2 mRNA expression was quantified using real-time qPCR. In SDB patients, CLOCK expression (% ACTB) (median [IQR]) was reduced to 1.408 [1.174] when compared to patients without SDB 1.844 [1.292] (p < 0.001, Mann-Whitney test, Figure A, left panel). Additionally, CLOCK expression was negatively correlated with increasing SDB severity (AHI) (linear regression, r² = 0.061, p = 0.002, Figure A, right panel). BMAL1 expression was also reduced in SDB patients to 0.216 [0.207] compared to 0.459 [0.411] in controls (p < 0.001, Figure B, left panel) and negatively correlated with the AHI (r² = 0.050, p = 0.004, Figure B, right panel). NR1D2 expression was similarly reduced in SDB patients, while NR1D1expression was not significantly altered (not shown).

For further analysis, we defined a reduced CLOCK expression as an expression in the lowest quartile of the total population. Interestingly, patients with a reduced CLOCK expression presented more frequently with diagnosed AF at baseline (p = 0.017, Fisher’s exact, relative frequencies depicted in Figure C). Moreover, newly diagnosed postoperative AF (in patients without known AF) was over 4-fold more frequent in patients with a reduced CLOCK expression (p < 0.001, Figure D). Multivariate logistic regression analysis of 129 patients without AF diagnosis preoperatively revealed that reduced myocardial CLOCK expression was significantly associated with postoperative AF (OR 16.57, p<0.001), independent of other risk factors and comorbidities (age, sex, hypertension, diabetes, SDB).

Conclusion:

Disrupted myocardial expression of circadian rhythm genes may be indicative of a disturbed sleep/wake cycle in patients with sleep-disordered breathing. It is also associated with an increased risk of both pre-existing and newly diagnosed postoperative atrial fibrillation in patients undergoing coronary artery bypass surgery.