Myocardial blood volume is associated with myocardial oxygen consumption: an experimental study with cardiac magnetic resonance in a canine model

Abstract

Understanding the oxygen consumption of the left ventricular myocardium provides important insight into the relationship between myocardial oxygen supply and demand. In other territories, cardiac magnetic resonance has been utilized to measure myocardial oxygen consumption with a blood level oxygen dependent (BOLD) technique. The BOLD technology requires repetitive sampling of stationary tissues and is frequently implemented in areas such as the brain. A limitation to utilizing BOLD cardiac magnetic resonance techniques in the heart has been cardiac motion. In this study, we document a methodology for acquiring BOLD images in the heart and demonstrate the utility of the technique for identifying associations between myocardial oxygen consumption and blood flow.

Figure 1. Imaging study protocol

The blood oxygen-level dependent (BOLD) method was used to evaluate the myocardial oxygen extraction fraction, and first-pass perfusion was utilized to evaluate both myocardial blood flow and volume. BOLD and first-pass perfusion scans were performed at rest and during either intravenous dipyridamole or dobutamine hyperemia. The numbers below the line represent the approximate time in minutes between events.

Figure 2. Representative short axis maps from a dog with a 96% LAD stenosis during Dipyridamole

The MBF map (A), and MBV map (B), derived from the first-pass perfusion images, clearly show an anterior perfusion defect. The OEF map (C), derived from the BOLD T₂-weighted images, shows higher OEF in the stenotic anterior region due to the decreased oxygen supply. The stenotic LAD region is marked with a yellow ROI. MBF scale units are ml/min/g (A); MBV scale units are ml/g (B). BOLD, blood oxygen-level dependent; LAD, left anterior descending; LV, left ventricle; MBF, myocardial blood flow; MBV, myocardial blood volume; OEF, oxygen extraction fraction; ROI, region of interest.

Figure 3. Regression analysis to discern relationships between MBF, MBV, and MVO₂ reserve during dipyridamole (orange circles) or dobutamine (brown circles)

Control dogs show only mild and moderate correlation between MBV reserve and MVO₂ reserve during dipyridamole and dobutamine, respectively (A). In stenotic regions, MBF reserve is slightly more correlated with MVO₂ reserve during dipyridamole (B). However, MBV reserve is more correlated with MVO₂ reserve during dobutamine (C). This supports the theory that MBV is required during inotropic stimulation when MVO₂ is more significantly increased. DIP, dipyridamole; DOB, dobutamine; LAD, left anterior descending; MBF, myocardial blood flow; MBV, myocardial blood volume; MVO₂, myocardial oxygen consumption.