Persistent diastolic dysfunction in chronically ischemic hearts following coronary artery bypass graft

Objective: A porcine model was used to study diastolic dysfunction in hibernating myocardium (HM) and recovery with coronary artery bypass surgery (CABG).Methods: HM was induced in Yorkshire-Landrace juvenile swine (n = 30) by placing a c-constrictor on left anterior descending artery causing chronic myocar-dial ischemia without infarction. At 12 weeks, animals developed the HM phenotype and were either killed humanely (HIB group; n = 11) or revascularized with CABG and allowed 4 weeks of recovery (HIB+CABG group; n = 19). Control pigs were matched for weight, age, and sex to the HIB group. Before the animals were killed humanely, cardiac magnetic resonance imaging (MRI) was done at rest and during a low-dose dobutamine infusion. Tissue was obtained for histologic and proinflamma-tory biomarker analyses.Results: Diastolic peak filling rate was lower in HIB compared with control (5.4 +/- 0.7 vs 6.7 +/- 1.4 respectively, P = .002), with near recovery with CABG (6.3 +/- 0.8, P = .06). Cardiac MRI confirmed preserved global systolic function in all groups. Histology confirmed there was no transmural infarction but showed interstitial fibrosis in the endomysium in both the HIB and HIB+CABG groups compared with normal myocardium. Alpha-smooth muscle actin stain identified increased myofibroblasts in HM that were less apparent post-CABG. Cytokine and proteomic studies in HM showed decreased peroxisome proliferator-activator receptor gamma coactivator 1-alpha (PGC1-a) expression but increased expression of granulocyte-macrophage colony-stimulating factor and nuclear fac-tor kappa-light-chain enhancer of activated B cells (NFkB). Following CABG, PGC1-a and NFkB expression returned to control whereas granulocyte-macrophage colony-stimulating factor, tumor necrosis factor -a, and interferon gamma remained increased.Conclusions: In porcine model of HM, increased NFkB expression, enhanced my-ofibroblasts, and collagen deposition along with decreased PGC1-a expression were observed, all of which tended toward normal with CABG. Estimates of impaired relaxation with MRI within HM during increased workload persisted despite CABG, suggesting a need for adjuvant therapies during revascularization.