Myocardial infarction in a canine model monitored by two‐dimensional ³¹p chemical shift spectroscopic imaging

Abstract

We have developed a closed chest animal model that allows noninvasive monitoring of cardiac high energy phosphate metabolism before, during, and for at least 3 weeks after a myocardial infarction. Ten beagles underwent 2 h of coronary occlusion followed by 3 weeks of reperfusion. Myocardial high energy phosphates from 12-ml voxels were noninvasively tracked using 31P two-dimensional chemical shift imaging. Gadolinium enhanced 1H MRI identified the zone at risk, and radioactive microspheres assessed regional blood flow and partition coefficients. Occlusion of the left anterior descending coronary artery produced infarcts that were 13.7+/-8.8% (mean+/-SD) of the left ventricular volume. Rapid changes in the phosphocreatine and inorganic phosphate levels were observed during occlusion, whereas adenosine triphosphate levels decreased more slowly. All metabolites recovered to base-line levels 2 weeks after occluder release. Multiple inorganic phosphate peaks in the infarct voxel spectra indicated that more than one metabolically compromised tissue zone developed during occlusion and reperfusion. Microsphere data indicating three distinct blood flow zones during ischemia and reperfusion (<0.3, 0.3-0.75, and >0.75 ml/min/g) supported the grouping of pH values into three distinct metabolic distributions.

Similar long-term cardiovascular effects of propofol or isoflurane anesthesia during ischemia/ reperfusion in dogs

“…20,21,23 The data were acquired from a 30-mm thick slice, positioned in the transverse plane, and centered just proximal to the most apical region of the heart. Multivoxel 31 P 2D-CSI [TR 500 msec, α 90°, field of view (FOV) 320 mm, Bandwidth ± 2 kHz, acquisition time 34 min] were obtained from this transverse slice once at B, twice during the occlusion period (O1 and O2), twice immediately upon reperfusion (R1 and R2) and once at each follow-up (D3 and D10 respectively).…”

“…These spectra were then fitted using FITMAN, a software package designed in our laboratory, which incorporates prior knowledge of the spectrum as determined from the literature and our previous results. 20,21,23,24 Each slice consisted of 2 x 2 cm 2 voxels through the 3-cm thick transverse slab, in a 16 x 16 grid that could be positioned retrospectively. This ensured that the volumes of interest (VOI) contained predominantly or exclusively, infarcted tissue, as opposed to non-infarcted tissue.…”

“…20,21,23 A spectral template was used to fit the blood peaks, allowing for the discrimination of the myocardial Pi peaks. If more than one Pi peak was fit within a spectrum then the peak corresponding to the most acidic environment was chosen as the intracellular pH for that VOI.…”

“…Blood flow determination (F, expressed in mL·min -1 ·g -1 ) has been previously described in detail. 20,21,23,26,27 Infarct ratio To minimize the biological variability between animals we normalized the infarct size based on the region at risk (RAR). The RAR was defined as the volume of tissue with myocardial blood flows less than 0.3 mL·min -1 ·g -1 during occlusion, as determined by the microsphere data.…”

Noninvasive assessment of pharmaceutical intervention during myocardial ischemia-reperfusion in a canine model using two-dimensional 31P chemical shift imaging

“…Previously we have reported (Farrall et al 1997) that 31 P NMRS can noninvasively monitor the changing metabolic state of myocardial tissue during 2 h of occlusion and during 3 weeks of reperfusion. These data were acquired using an externally applied surface coil in a canine model using a Siemen's clinical whole body 2-T imager-spectroscopy unit.…”