The impact of type 2 diabetes on short term myocardial morphological, functional, and energetic recovery post coronary artery bypass surgery in patients with ischemic heart disease

Abstract Background Type 2 diabetes (T2D) confers three times higher mortality in patients with ischemic heart disease (IHD). Moreover, amongst patients with IHD those with diabetes were shown to have higher long-term mortality from heart failure despite angiographic or surgical revascularisation with coronary artery bypass grafting (CABG). Impaired myocardial structural, functional, and energetic recovery may underpin this epidemiological observation. Consequently, using cardiovascular magnetic resonance and phosphorus-magnetic resonance spectroscopy scans, we aimed to assess the effect of T2D comorbidity on myocardial structural, functional, perfusion, and energetic recovery post-CABG in patients with IHD. Methods Seventy-seven IHD patients with (n=39) and without T2D (n=38) awaiting CABG were recruited. One-month pre- and 6-months post-CABG, cardiac phosphocreatine to ATP ratio (PCr/ATP), global longitudinal shortening (GLS) and 6-minute walk-distance (6MWD) were assessed in the study cohorts. The rest and adenosine-stress myocardial blood flow (MBF) assessments were only performed 6-months post-CABG. Results Pre-CABG, IHD-T2D patients had higher LV concentricity (LV mass to LV end diastolic volume ratio) (IHD-T2D:0.84[0.74,0.93],IHD-noT2D:0.72[0.67,0.77]g/mL,P=0.03]. worse PCr/ATP T2D (IHD-T2D:1.5[1.4,1.7],IHD-noT2D:1.8[1.6, 2.0];P=0.03) and shorter 6-minute walk distance (IHD-T2D:338[307,370],IHD-noT2D:399[364,434]m,P=0.007). There were no significant differences in LV volumes, ejection fraction or GLS between the two groups pre-CABG. Post-CABG, there was no longer a significant difference in cardiac energetics or 6-minute walk distances between the two groups due to a significant improvement in PCr/ATP in the IHD-T2D group. LV concentricity remained significantly elevated in the IHD-T2D group post CABG (IHD-T2D:0.82[0.75,0.88],IHD-noT2D:0.73[0.68,0.79]g/mL,P=0.04). Neither group showed a significant change in LVEF or GLS from the pre-CABG values, and post-CABG there were no differences in the rest or stress myocardial blood flows between the two groups. Conclusions Six months after CABG, neither IHD patients with T2D, nor IHD patients without T2D show any significant changes in LV structural remodelling or in contractile function. T2D does not jeopardise the short-term recovery in myocardial energetics or exercise distance post-CABG, with IHD patients with T2D showing more pronounced improvements post-CABG in both these assessments than patients without T2D. Larger longitudinal studies are needed to better understand the mechanisms of adverse longer-term cardiovascular outcomes suggested by epidemiological studies in IHD patients with T2D.