ABSTRACT
To detect abnormal regional myocardial coronary flow reserve, serial spin-echo MR tomograms of four control dogs and six with a partial balloon occlusion of the left anterior descending (LAD) coronary artery were acquired before and after dipyridamole infusion and during the paramagnetic effect of a bolus plus infusion of gadolinium-DTPA. Microsphere myocardial blood flow was measured for correlation with serial regional changes in MR signal intensity. Significant difference in gadolinium-enhanced MR signal intensity existed between the hypoperfused LAD and the hyperemic left circumflex perfusion beds (46 +/- 22% vs 78 +/- 29% above baseline, respectively; P less than 0.05). The percentage changes in gadolinium-enhanced MR signal and microsphere myocardial blood flow were significantly correlated (r2 = 0.93).
Subject(s)
Contrast Media , Coronary Circulation/drug effects , Coronary Disease/physiopathology , Dipyridamole/administration & dosage , Gadolinium , Hyperemia/physiopathology , Magnetic Resonance Imaging , Organometallic Compounds , Pentetic Acid , Animals , Coronary Disease/pathology , Disease Models, Animal , Dogs , Gadolinium DTPA , Vasodilation/drug effectsABSTRACT
To determine how administration of a hyperosmotic agent alters regional nuclear magnetic resonance (NMR) relaxation parameters and imaging characteristics in ischemic-reperfused myocardium, 7 dogs were infused with mannitol for 15 minutes before and after the release of a 3 hour left anterior descending coronary artery (LAD) occlusion. Nine control animals received normal saline during the 3 hour occlusion and 1 hour reperfusion periods. Normal posterior left ventricular (LV) wall and the ischemic anterior LV wall (risk area) myocardium was sampled for calculation of segmental microsphere myocardial blood flow, % tissue water content, NMR relaxation times (T1, T2) and myocyte ultrastructure using electron microscopy. Mean infarct T1 values were 14% greater than normal segments in saline-treated controls, but only 5% greater after mannitol. The difference in tissue water content between infarcted and normal segments was 4% in saline-treated (83 vs. 79%) compared to 2% in mannitol-treated dogs (79 vs. 77%). T1, T2 and % water content of control infarct segments were greater than treated infarcts (p less than 0.01). T1 and T2 rose as occlusion flow fell below 0.5 ml/min/g in control hearts but did not rise until flows were reduced to 0.1 ml/min/g in mannitol-treated hearts. Areas of increased signal in T1 and T2 NMR images correlated well with histochemical infarct volume (r = 0.98, SEE = 1.1 cc) in mannitol-treated dogs, but infarct borders were qualitatively less well-defined than in controls. We concluded that mannitol (1) diminishes tissue edema and reduces NMR relaxation parameters (T1, T2) in infarcted myocardium; and (2) attenuates the rise in T1 and T2 and ultrastructural myocyte injury in ischemic-reperfused myocardium.
