Recovery and Contractile Reserve on Cardiac MRI in Hibernating Myocardium
Post- CABG
Christopher T Holley, Laura Hocum Stone, Melanie Crampton, Rosemary F Kelly,
Edward O McFalls
Background. Clinical studies have suggested that functional recovery of hibernating myocardium
may not occur following coronary artery bypass graft (CABG) surgery. Using a swine model of
hibernating hearts and MRI estimates of circumferential strain (ECC), we tested whether
contractile reserve within hibernating hearts is present post-CABG. Methods. Ten pigs underwent
thoracotomy with placement of a constrictor around the LAD artery. At 12 weeks, they underwent
MRI imaging prior to off-pump revascularization with a left internal mammary artery graft to the
LAD artery. At 4 weeks post-CABG, MRI studies were repeated at baseline and during an
infusion of dobutamine (5 µg/kg/min).
Results: Following CABG, CT angiography confirmed a patent LIMA graft. MRI studies postCABG showed that baseline circumferential strain in the Hibernating (LAD) Region was lower than
the Remote Region (-13.330.50 versus -14.870.43; P<0.01). Despite reduced basal function,
contractile reserve was present in the Hibernating Region (Figure).
Summary: Baseline function in hibernating myocardium is depressed at 4 weeks post-CABG but
the presence of contractile reserve suggests that recovery may occur. Future studies should
assess temporal recovery of function and test whether additional interventions such as
administration of stem cells can lead to earlier recovery of function.