Hibernating myocardium: morphological correlates of inotropic stimulation and glucose uptake

Background-In patients with postischaemic left ventricular dysfunction, seg ments recovering function after revascularisation (hibernating myocardium) may not respond during dobutamine echocardiography, despite preserved [F-18 ] 2-fluoro-2-deoxy-D-glucose (FDG) uptake at position emission tomography. Objective-To investigate whether this lack of response might reflect the de gree of ultrastructural change in hibernating myocardium. Methods-Transmural biopsies were obtained from 22 dysfunctional segments in 22 patients during coronary artery bypass grafting and examined by light a nd electron microscopy. Wall motion scores and coronary vasodilator reserve were assessed before and after coronary artery bypass grafting (CABG). Results-Mean (SD) wall motion score improved in all segments following CABG (from 2.24 (0.4) to 1.55 (0.4); p < 0.0001), confirming hibernating myocar dium. In these segments myocardial blood flow (positron emission tomography with (H2O)-O-15) before CABG was similar to that in normal volunteers (1.0 2 (0.24) v 1.02 (0.23) ml/min/g), while the coronary vasodilator reserve wa s blunted (1.26 (0.7) v 3.2 (1.6); p < 0.0001). Myocardial blood flow was u nchanged after CABG, whereas coronary vasodilator reserve increased to 2.10 (0.90) (p < 0.0007). In hibernating myocardium myofibrillar loss, intersti tial fibrosis, and glycogen-rich myocytes were more marked than in control donor hearts. On the basis of the response to dobutamine before CABG, two f unctional groups were identified: group A, segments with inotropic reserve (n = 15); group B, segments without inotropic reserve (n = 7). FDG uptake w as similar in group A and group B (0.40 (0.1) v 0.44 (0.1) mu mol/min/g). I n group B there was more myofibrillar loss (26 (8)% v 11 (5)%; p = 0.0009) and glycogen-rich myocytes (28 (11)% v 17 (10)%; p = 0.02), whereas interst itial fibrosis, myocardial blood flow, and coronary vasodilator reserve wer e similar in the two groups. Myofibrillar loss was the only independent pre dictor of inotropic reserve (p = 0.01). Conclusions-Hibernating myocardium is characterised by a reduced coronary v asodilator reserve which improves on revascularisation and shows a spectrum of ultrastructural changes that influence the response to dobutamine, whil e FDG uptake is invariably preserved.