Effect of repetitive brief episodes of cardiac ischemia on ³¹P magnetic resonance spectroscopy in the cat

Abstract

Angina is characterized by brief periods of ischemia followed by reperfusion; the cumulative effect of these episodes on energetics of the myocardium has not been fully elucidated. This study used an in vivo feline model for the assessment of high-energy phosphate compounds during brief sequential periods of ischemia and reperfusion. Nine adult, open-chest, anesthetized cats were prepared with a reversible occluder around the proximal left anterior descending artery and a 1.2-cm-inside diameter coil sutured on the myocardial surface in the distribution of the left anterior descending coronary artery. Levels of PCr, Pi, and ATP (beta-phosphate signal) were measured by 31P MRS in a GE CSI 2-T NMR spectrometer/imager. Measurements were obtained during a control period and during three successive occlusion-deocclusion periods of roughly 12 and 20 min' duration, respectively. The last deocclusion period was observed for 60 min. Electron microscopy was performed in two animals. PCr declined (P less than 0.01) rapidly following each occlusion to 51 +/- 5.2% (occlusion 1), 53 +/- 5.8% (occlusion 2), and 48 +/- 5.7% (occlusion 3) of the control value by 6 min. Pi rose (P less than 0.01) with the three sequential occlusions to 253 +/- 46, 288 +/- 57, and 277 +/- 46%, respectively. PCr and Pi returned to baseline promptly with reperfusion, while ATP showed a gradual decline throughout the experiment, decreasing to 77 +/- 7.2% of control at the end of the last reperfusion (P less than 0.05). Although PCr returned to baseline during reperfusion, ATP did not, suggesting a reduction in the nucleotide pool. These findings indicate that the repeated episodes of ischemia, which are insufficient to produce necrosis, can have an effect on myocardial high-energy phosphate metabolism as evidenced by mild depletion of ATP.

Complementarity of magnetic resonance spectroscopy, positron emission tomography and single photon emission tomography for the in vivo investigation of human cardiac metabolism and neurotransmission

“…Multiple, short, ischaemic episodes, as opposed to single ones, simulating repeated angina episodes, are not always followed by full recovery (Holt et al 1987). Reductions in coronary flow showed a close relation between PCr/P~ ratio, blood flow and contractility Schaefer et al 1990b).…”

“…The changes are accompanied by a decline in contractile function (Miller et al 1991). Full metabolic and functional recovery occurs after reperfusion for a complete ischaemia of 10 min or less (Holt et al 1987) but not for a longer period of ischaemia. Reperfusion after a short (24 s) ischaemia showed a dissociation between coronary flow and metabolism, with metabolism and function recovering faster than reactive hyperaemia ).…”