Pulmonary Blood Volume Variation Decreases after Myocardial Infarction in Pigs: A Quantitative and Noninvasive MR Imaging Measure of Heart Failure

Abstract

To prospectively evaluate the usefulness of magnetic resonance (MR) imaging for estimating pulmonary blood volume (PBV) and the variation in PBV throughout the cardiac cycle in experimental heart failure. The animal care committee approved this prospective study. Seven pigs were studied before and after myocardial infarction. PBV measurement was validated in a phantom and calculated as the product of cardiac output determined with velocity-encoded MR imaging and the pulmonary transit time for an intravenous bolus of contrast material to pass through the pulmonary circulation. The difference in arterial and venous pulmonary flow during the cardiac cycle was integrated for calculation of the PBV variation (expressed as percentage of stroke volume). Differences were evaluated with the Wilcoxon test. Calculated and direct phantom measurements of PBV differed by a mean of 4% +/- 3 (standard deviation) (R(2) = 0.97, P < .001). Infarction induced a decrease in left ventricular stroke volume (44 mL +/- 6 vs 27 mL +/- 7; P = .02), ejection fraction (55% +/- 5 vs 41% +/- 4; P = .02), and PBV variation (61% +/- 12 vs 43% +/- 15; P = .04) but not PBV (225 mL +/- 23 vs 211 mL +/- 42; P = .50). The mean pulmonary artery pressure increased after infarction (19 mm Hg +/- 6 vs 27 mm Hg +/- 4; P = .04). Following infarction, the PBV variation but not PBV decreased. PBV variation was the noninvasive measure exhibiting the greatest percentage of change following infarction. MR imaging can be used to assess the variation of the PBV during the cardiac cycle as a marker of heart failure.