Effects of coronary revascularisation on myocardial blood flow and coronary vasodilator reserve in hibernating myocardium

Abstract

Objective: Previous studies have suggested that resting myocardial blood flow is within normal limits in most chronically dysfunctional left ventricular segments which improve function after coronary artery revascularisation (hibernating myocardium). The aim of this study was to assess myocardial blood flow and coronary vasodilator reserve in hibernating myocardium before and after coronary revascularisation.

Patients and methods: 30 patients with multivessel coronary disease undergoing coronary revascularisation (21 patients with bypass grafting and nine with coronary angioplasty), and 21 age and sex matched healthy volunteers (controls). Myocardial blood flow (MBF, ml/min/g) was measured by positron emission tomography using oxygen-15 water at rest and after dipyridamole (MBFdip, 0.56 mg/kg in four minutes). Coronary vasodilator reserve was calculated as MBFdip/MBF. Regional wall motion was assessed with echocardiography.

Results: Before revascularisation there were 48 remote and 275 dysfunctional myocardial segments, of which 163 (59%) improved function after revascularisation (hibernating). In hibernating segments coronary vasodilator reserve before revascularisation was significantly lower than in remote segments (1.97 (0.7), p < 0.0001) and controls (3.2 (1.5), p < 0.0001). In hibernating segments, myocardial blood flow remained unchanged after revascularisation (0.94 (0.3) v 0.95 (0.3) ml/min/g, p = 0.3) while coronary vasodilator reserve increased (1. 47 (0.7) v 1.98 (1.0), p < 0.0001). Myocardial blood flow was similar in remote, hibernating segments before and after revascularisation and in controls.

Conclusions: This study confirms that myocardial blood flow at rest in hibernating myocardium is within normal limits in most segments, and that hibernating myocardium is characterised by an impaired coronary vasodilator reserve which improves significantly after coronary revascularisation.

Figure 1

Perfusion data on 163 hibernating myocardial segments before (baseline) and after coronary revascularisation. MBF, myocardial blood flow; MBFdip, post-dipyridamole myocardial blood flow; CVR, coronary vasodilator reserve.***p < 0.0001.

Figure 2

Comparison of myocardial blood flow between hibernating, remote (before and after revascularisation), and control myocardial segments. HIB, hibernation segments before revascularisation; REM, remote segments; -post refers to post-revascularisation.

Figure 3

Scatterplot showing the distribution of myocardial blood flow (uncorrected and corrected for the rate-pressure product) before revascularisation in the hibernating segments. The thresholds of 0.55 and 0.45 ml/min/g represent the mean value minus 2 SDs of myocardial blood flow in control segments (uncorrected and corrected for the rate-pressure product). MBF, myocardial blood flow uncorrected for the rate-pressure product; MBFcorr, myocardial blood flow corrected for the rate-pressure product.

Figure 4

Comparison of post-dipyridamole myocardial blood flow between hibernating, remote (before and after revascularisation), and control myocardial segments. See fig 2 for key to abbreviations.

Figure 5

Comparison of coronary vasodilator reserve between hibernating, remote (before and after revascularisation), and control myocardial segments. See fig 2 for key to abbreviations. ***p < 0.0001.