Relation of the contractile reserve of hibernating myocardium to myocardial structure in humans

Background - Although dobutamine echocardiography (DE) is widely used to assess myocardial viability in humans, little is known about the relation between contractile reserve and myocardial structure. Methods and Results - We evaluated 20 patients with coronary disease (64± 13 years old, ejection fraction 28± 7.5%) with DE (up to 40 μg · kg^-1 · min^-1), rest- redistribution ²⁰¹Tl single photon emission CT, and quantitative angiography before bypass surgery. During surgery, patients underwent transmural myocardial biopsies (n=37) guided by transesophageal echocardiography to determine the extent of interstitial fibrosis and intracellular and interstitial proteins by histopathology and immunohistochemistry. Among the 37 segments biopsied, 16 recovered function as assessed 2 to 3 months later. Segments with postoperative functional recovery had more wall thickening at low-dose DE (28% versus 3%, P<0.001), higher thallium uptake (69% versus 48%, P=0.03), and less interstitial fibrosis (2% versus 28%, P<0.001). Quantitative angiographic parameters did not predict recovery of function. Segments with DE viability (contractile reserve and/or ischemia) had less fibrosis (2.7% versus 28%, P<0.001), less vimentin and fibronectin (both P<0.01), more glycogen (P=0.016), and higher thallium uptake (64% versus 35.5%, P<0.05) than those without viability. Viable segments by both DE and thallium had less fibrosis (1%) than those viable by 1 of the 2 techniques (9%) or not viable by both (28%, P=0.005). Thickening at low-dose DE correlated well with the extent of interstitial fibrosis (r=-0.83, P<0.01). Conclusions - Contractile reserve during DE correlates inversely with the extent of interstitial fibrosis and the amount of fibronectin and vimentin and directly with rest-redistribution thallium uptake.