Sleep apnea and temporal changes in cardiac repolarization in patients undergoing coronary artery bypass grafting
Authors: Teo Y , Yong C L , Ou Y H , Tam W W , Koo C Y , Lee C H 
Published: October 2022

Abstract

Background
In coronary artery bypass grafting (CABG), despite re-establishing coronary reperfusion, myocardial recovery and restoration of contractility often occur later, and the risk of adverse cardiovascular events persists during the post-CABG period. The occurrence of adverse cardiovascular events is linked to abnorm-al cardiac repolarisation that can be measured by surface electrocardiograms (ECGs). Sleep apnoea is an emerging cardiovascular risk factor. The relationship between sleep apnoea, abnorm-al cardiac repolarisation, and the occurrence of adverse cardiovascular events is not well studied.

Purpose
We investigated the impact of sleep apnoea on the change in repolarisation after CABG, and if the change in repolarisation is associated with the occurrence of major adverse cardiac and cerebrovascular events (MACCE).

Methods
Between November 2013 and December 2018, 1007 patients from 4 hospitals underwent an overnight sleep study prior to a non-emergent CABG. ECGs were acquired prospectively within 48h before the CABG (T1), and within 24h after the CABG (T2). QTc intervals were measured in three consecutive heart beats in one lead - the preferential lead measurements were lead II, followed by lead V5. QTc intervals were measured using the BRAVO algorithm by Analysing Medical Parameters for Solutions (AMPS) LLC. The change of T2 from T1 for QTc (ΔQTc) was derived. The mean follow-up duration was 2.1 years. MACCE was a composite of cardiovascular death, myocardial infarction, stroke, and unplanned revascularisation.

Results
A total of 954 patients (median age: 62 years; male: 86%) survived the initial 24 hours and had quality ECGs for analysis. Lead II and V5 were measured in 72% and 25% of the cohort, respectively. A total of 115 patients developed MACCE (MACCE group). Compared with the non-MACCE group, the MACCE group was older, had (a) a higher prevalence of smoking, hypertension, diabetes mellitus, and chronic kidney disease, (b) higher apnoea-hypopnoea index (AHI) and oxygen desaturation index (ODI), and (c) a smaller ΔQTc (Table). In Cox regression analysis, a smaller ΔQTc was independently associated with occurrence of MACCE (HR: 1.003; 95% CI: 1.000–1.006; p=0.032).
Older age, history of previous stroke, chronic kidney disease, more severe sleep apnoea (higher AHI, ODI, and severe oxygen desaturation) were associated with smaller ΔQTc. After adjusting for the effects of confounding variables, a higher ODI was independently associated with a smaller ΔQTc (correlation coefficient: −0.58; p&lt;0.001).

Conclusions
In patients undergoing a non-emergent CABG, a smaller ΔQTc during the first 24 hours after the CABG is associated with a higher incidence of MACCE. A higher pre-operative ODI based on a sleep study is an independent predictor of a smaller ΔQTc. This suggests that change in QTc within 24 hours after CABG could be due to sleep apnoea, and it is a novel predictor of occurrence of MACCE at medium term follow-up.

Funding Acknowledgement
Type of funding sources: Public Institution(s). Main funding source(s): Transition Award and Clinician Scientist Award from the National Medical Research Council of Singapore (award numbers: NMRC/TA/012/2012; NMRC/CSA-INV/002/2015)