Quantitation of the extent of acute myocardial infarction by phosphorus-31 nuclear magnetic resonance spectroscopy

Abstract

Phosphorus-31 nuclear magnetic resonance (P-31 NMR) spectroscopy is able to identify alterations in myocardial high energy phosphate metabolism associated with acute infarction. It was hypothesized that the extent of acute myocardial infarction could be quantitated from changes in the tissue content of inorganic phosphate (P1), phosphocreatine (PCr) and adenosine triphosphate (ATP) derived from P-31 NMR spectra.Nine isolated, perfused rat hearts were studied at 121.5 MHz. After baseline spectra were obtained, varying locations of either the right or the left coronary artery were occluded without removing the heart from the spectrometer. Spectra were then collected during regional ischemia at 15 and 45 min after occlusion. Phosphate metabolites were quantitated from the baseline and 45-min regional ischemia spectra, times at which the metabolites are at steady state for the normal and ischemic conditions. The heart was removed from the spectrometer, perfused for a total duration of 2 h and sectioned into 2-mm thick slices for triphenyltetrazolium chloride staining. Percent infarct was determined by manual tracing of magnified, digitized images of the stained sections. Coronary blood flow, heart rate and blood pressure were monitored throughout the experiment.Significant linear relations were found between percent infarct (by triphenyltetrazolium chloride staining) and the percent change of beta-ATP (r = −0.74), Pi(r = 0.83) and the PCr/P1 ratio (r = −0.71) at 45 min after coronary occlusion. Coronary Row was also found to correlate significantly with percent infarct (r = −0.70).These results are applicable to in vivo P-31 NMR studies of acute infarction where the volume of interest may include both normal and acutely infarcled myocardium. It is concluded that changes in P-31 NMR spectra allow quantitation of the extent of acute myocardial infarction.