Relation of the Contractile Reserve of Hibernating Myocardium to Myocardial Structure in Humans

Abstract

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 201 Tl 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.