Characterization of high-energy phosphate compounds during reperfusion of the irreversibly injured myocardium using 31P MRS.

Phosphorus-31 magnetic resonance spectroscopy (MRS) was used to monitor regional changes in high-energy phosphorus compounds and intracellular pH during 60 min of acute regional ischemia (acute occlusion of left anterior descending artery) and reperfusion in open-chest cats using a 1.2-cm two-turn coil sutured to the myocardium. During the 60-min ischemic phase, phosphocreatine (PCr) intensity was reduced to 47 +/- 4.9% (mean +/- SE) of control (p less than 0.01) by 15 min postocclusion while adenosine triphosphate (ATP) intensity decreased more slowly with the decrease (66 +/- 5.6%) achieving significance (p less than 0.05) only at 60 min postocclusion. Inorganic phosphate (Pi) increased to a maximum of 397 +/- 42% of control (p less than 0.01) while the pH decreased progressively from 7.36 +/- 0.02 to 6.02 +/- 0.14 (p less than 0.01). After release of occlusion PCr intensity recovered to 86 +/- 12% of the initial control value at 15 min postreperfusion but showed a subsequent downward trend to 79 +/- 8.8%. The ATP did not recover but tended to decline further during reperfusion. The Pi intensity decreased to 260 +/- 38% of control while the pH increased to 7.01 +/- 0.23 by 15 min postreperfusion. Thus, the reperfused irreversibly injured myocardium is characterized by persistent depletion of PCr and ATP and elevation of Pi. Phosphorus-31 MRS provides a nondestructive method for characterizing the reperfused irreversibly damaged myocardium.