Hibernating myocardium after coronary artery bypass grafting: evolution of electrocardiographic parameters

Background The main role of coronary artery bypass grafting (CABG) in ischemic heart failure (IHF) is the recovery of hibernating myocardium. Hypothetically, this improvement in contractile function might be associated with electrical conduction changes, and these may be detected by electrocardiogram (EKG). However, no data so far has evaluated specific EKG changes in hibernating myocardium. Purpose This study aims to compare EKG parameters of patients with IHF before and after CABG or medical therapy (MT) alone. Methods This is a prospective analysis of the EKGs of patients with multivessel coronary artery disease, left ventricle ejection fraction (LVEF) ≤ 35% and documented myocardial ischemia, randomized to CABG or MT. The EKGs were performed at inclusion and 6 months after CABG and at corresponding time points in MT. This study correlated the EKG data with echocardiography parameters and therapeutic strategies, using linear mixed effects models. Results A total of 316 EKGs from 158 patients (62 ± 7.5 years, 72% male) were analyzed, 71 in CABG and 87 in MT arm. Sinus rhythm was predominant (96% in both arms and stable overtime). In both arms, at baseline and 6 months later, the heart rate was 67 (± 12) and 66 (± 10) beats per minute. The LVEF was 33.6% and 35.9% at baseline, in CABG and MT, improving to 38.9% and 36.3%, respectively (p < 0.01). Interestingly, a shorter QRS complex and corrected QT interval were associated with CABG and higher LVEF - for every 40- millisecond decrease of QRS and QT, there was an increase of 1.6% and 0.8% in LVEF, respectively (p < 0.05). Absence of left ventricular hypertrophy was also associated with an improvement of 2.4% in LVEF (p < 0.05). Moreover, QRS axis deviation showed no association with LVEF, although the T-wave axis deviation to the right was related to a reduction in LVEF (p < 0.01). In parallel, a wider QRS-T angle was also associated with a lower LVEF (per each 10° increase, the LVEF was 0.2% lower (p < 0.01). Other parameters yielded inconsistent findings, including the presence of QRS fragmentation and the presence of pathological Q waves. Conclusion In ischemic heart failure, the recovery of contractile function in hibernating myocardium after CABG was associated with substantial improvement in main electrocardiographic parameters.