Resting myocardial blood flow, coronary flow reserve, and contractile reserve in hibernating myocardium: implications for using resting myocardial contrast echocardiography vs. dobutamine echocardiography for the detection of hibernating myocardium

Controversy exists regarding the relative status of resting myocardial blood flow (MBF), coronary flow reserve (CFR), and contractile reserve (CR) in hibernating myocardium (HM). We hypothesized that CFR is more profoundly affected than resting MBF parameters in HM. Thus, resting MBF assessed by myocardial contrast echocardiography (MCE) will be more sensitive than CR elicited by dobutamine stress echocardiography (DSE) for the detection of HM. Accordingly 27 patients with ischaemic cardiomyopathy underwent resting MCE and DSE prior to revascularisation, of which 23 patients underwent follow-up echocardiography at 179 +/- 66 days after revascularization. Qualitative and quantitative MCE [contrast intensity (A, dB)], MBF (represented by blood velocity beta, dB/s), and CFR (vasodilator beta/rest beta, beta reserve) were obtained. CR was obtained during DSE. Resting contrast intensity (7.2 +/- 2.3 dB) and beta (0.67 +/- 0.47 dB/s) were significantly (P < 0.005 and < 0.01, respectively) reduced in HM vs. remote normal myocardium but significantly higher compared with non-viable segments (4.4 +/- 2.3 dB and 0.43 +/- 0.32 dB/s, respectively). However, CFR was significantly (0.82 +/- 3.2 (P = 0.01)) lower in HM compared with normal (1.8 +/- 1.02) but not significantly reduced when compared with non-viable myocardium (1.1 +/- 3.3). Sensitivity for the detection of HM with qualitative and quantitative MCE were 82 and 87%, respectively, compared with 67% (P < 0.0001) by DSE with similar specificity of 55 and 67%, respectively, compared with 63% with DSE. Resting MBF but not CFR distinguished HM from non-viable myocardium. Resting MCE and not DSE was more accurate for the prediction of HM.