The fate of inorganic phosphate and pH in regional myocardial ischemia and infarction: A noninvasive31P NMR study

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Abstract
To determine the characteristic appearance of phosphorus (31P) nuclear magnetic resonance spectra in acute and chronic myocardial infarction in situ. cardiac‐gated depth‐resolved surface coil spectroscopy (DRESS) at 1.5 T was used to monitor 31P NMR spectra from localized volumes in the left anterior canine myocardium for up to 5 days following permanent occlusion of the left anterior descending coronary artery. Coronary occlusion initially produced regional ischemia manifested as significant reductions in the phosphocreatine (PCr) to inorganic phosphate (Pi) ratios and intracellular pH (P < 0.05, Student's t test) in endocardially displaced spectra acquired in periods as short as 50 to 150 s postocclusion. Spectra acquired subsequently revealed either (i) restoration of near‐normal phosphate metabolism sometime between 10 and about 50 min postocclusion or (ii) advancing ischemic phosphate metabolism at about an hour postocclusion, and/or (iii) maintenance of depressed PCI/P1 ratios for up to 5 days postocclusion with a return of the apparent pH to near normal values between 6 and 15 h postocclusion. Postmortem examination of animals exhibiting the first type of behavior revealed the existence of coronary collateral vessels. The last type of behavior indicates that P1 remains substantially localized in damaged myocardium for days following infarction. The location and size of infarctions were determined postmortem by staining excised hearts. The smallest infarctions detected by 31P DRESS weighed 4.9 and 7.5 g. The most acidic pH measured in vivo was 5.9 ± 0.2. Infarctions aged 1/2 day to 5 days were characterized by elevated but broad P1 resonances at 5.1 ± 0.2 ppm relative to PCr and significantly depressed PCr/P1 ratios (P < 0.002, Student's t test) relative to preocclusion values. Contamination of P1 resonances by phosphomonoester (PM) components is a significant problem for preocclusion P1 and pH measurements. These results should be applicable to the detection and identification of human myocardial infarction using 31P NMR and DRESS. © 1987 Academic Press, Inc.