Are alterations in adrenergic receptor densities associated with myocardial hibernation and contractile reserve in patients with ischemic ventricular dysfunction?
Graded and reciprocal changes in α- and β-adrenergic receptor densities occur in viable, hibernating myocardium, potentially explaining depressed resting function and preserved contractile reserve.
Background —Alterations in adrenergic receptor densities can potentially contribute to myocardial dysfunction. Their relevance to myocardial hibernation in humans is unknown. Methods and Results —Accordingly, 22 transmural myocardial biopsies were obtained in 11 patients with ischemic ventricular dysfunction during bypass surgery, guided by transesophageal echocardiography. Patients underwent dobutamine echocardiography (DE) and rest scintigraphic studies before revascularization and DE at 3 to 4 months. α- and β-receptor density (ARD and BRD) and extent of fibrosis were quantified from the myocardial biopsies. Of the 22 segments, 16 had abnormal rest function and 6 were normal. Severely hypokinetic or akinetic segments showed a 2.4-fold increase in ARD with a concomitant 50% decrease in BRD compared with normal segments. An increase in ARD, a decrease in BRD to a lesser extent, and thus an increase in ARD/BRD ratio were seen in dysfunctional segments with contractile reserve compared with normal segments and were most pronounced in those without contractile reserve ( P <0.001). Similar findings were observed if recovery of function or scintigraphic uptake was analyzed as a marker for viability. No significant relation between either ARD or BRD and percent myocardial fibrosis was noted ( r =0.37 and −0.39, respectively). Conclusions —Thus, graded and reciprocal changes in α- and β-adrenergic receptor densities occur in viable, hibernating myocardium and may account in part for the observed depression in resting myocardial function and preserved contractile reserve in this entity.
Shan et al. (Tue,) studied this question.