The fate of inorganic phosphate and pH in regional myocardial ischemia and infarction: A noninvasive ³¹P NMR study

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 less than 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 PCr/Pi 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 Pi 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 Pi resonances at 5.1 +/- 0.2 ppm relative to PCr and significantly depressed PCr/Pi ratios (P less than 0.002, Student's t test) relative to preocclusion values. Contamination of Pi resonances by phosphomonoester (PM) components is a significant problem for preocclusion Pi and pH measurements. These results should be applicable to the detection and identification of human myocardial infarction using 31P NMR and DRESS.

The effect of cardiopulmonary bypass on brain and heart metabolism: A 31P NMR study

“…In well-oxygenated undamaged brain and myocardium, the Pi peak is small. During ischemia, this peak broadens and may be more difficult to detect (6). The need to eliminate the interference of 2,3-DPG was a major reason for selecting older sheep for this study.…”

“…Nuclear magnetic resonance (NMR) spectroscopy is a useful, nondestructive technique for the measurement of phosphorus containing metabolites and intracellular pH in the brain and heart in vivo (1)(2)(3). In particular, the precise evaluation of the time course and extent of metabolic perturbations induced by cerebral and myocardial ischemia depends on continuous measurements of intracellular pH and high energy phosphate content which can be made using NMR techniques (4)(5)(6)(7). A quantitative comparison of the relative effects of treatment modalities can be made with the added advantage of each animal serving as its own control.…”

Contractile function assessment by intraventricular balloon alters the ability of regional ischaemia to evoke ventricular fibrillation

“…Indeed, in the ‘no IVB’ group, the UZ P i values during ischaemia at no time increased above pre‐ischaemia values (Figure F). Before ischaemia, PCr, β‐ATP, intracellular pH and P i values were all normal, and during ischaemia, values changed in accordance with published findings (Bottomley et al ., ; Ishibashi et al ., ; Cross et al ., ; Takaoka et al ., ) with no significant differences between groups. These findings are entirely consistent with generation of partial ischaemia in the UZ (localized and small in extent, presumably endocardial because total UZ coronary flow was not lowered versus the no IVB and IVB groups) as a consequence of IVB inflation.…”

Mr Spectroscopy in Clinical Research

“…of the Pi peak because 2-DPG signals from the blood resonates at the same frequency. BOTTOMLEY and coworkers (35,36) have studied patients with myocardial infarction by 31p MRS using the DRESS technique for localisation in a slice. They found a significant reduction in the PCr/P i ratio in the patients together with an increase in P/ ATP ratio.…”