Assessment of myocardial salvage after ischemia and reperfusion using magnetic resonance imaging and spectroscopy.

Abstract

To test the hypothesis that contrast-enhanced magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) can differentiate reversible from irreversible myocardial injury, these modalities were used to study ischemia and reperfusion in a rat model. The presence of ischemia and reperfusion were confirmed with radiolabeled microspheres (n = 6). Groups of animals were subjected to either 16 (n = 17), 30 (n = 14), 60 (n = 11), or 90 (n = 14) minutes of left coronary artery (LCA) occlusion and 60 minutes reperfusion. After albumin-gadolinium (Gd)-DTPA injection, contrast-enhanced, T1-weighted, spin-echo proton images were acquired at baseline and every 16 minutes during LCA occlusion and reperfusion. In separate experiments, 31phosphorus (31P) spectra were acquired at similar time points during ischemia and reperfusion. After 16 minutes occlusion, normally perfused myocardium enhanced significantly compared with ischemic myocardium on MRI (104 +/- 7.9% vs. 61 +/- 11.0%, p less than 0.05, n = 5, mean +/- SEM, % of baseline value). MRS showed reduced phosphocreatine (PCr) and adenosine triphosphate (ATP) (58.8 +/- 2.4%, p less than or equal to 0.01; 81.4 +/- 2.4, p less than or equal to 0.01, n = 12). After 16 or 30 minutes ischemia, reflow resulted in uniform MRI signal intensity of the ischemic zone compared with normal myocardium (93.5 +/- 11.3 vs. 80.9 +/- 7.0, p = NS, n = 11, % of baseline value at 30 minutes reperfusion) and PCr recovery on MRS (94.3 +/- 4.0%, p = NS, n = 20, % baseline value at 30 minutes reflow). After 60 and 90 minutes ischemia, reflow resulted in marked enhancement of reperfused compared with normal myocardium on MRI (254.0 +/- 30.0 vs. 78.3 +/- 9.2, p less than or equal to 0.01, n = 10) and no recovery of PCr on MRS (64.1 +/- 3.0, p = NS, n = 14). Triphenyltetrazolium chloride (TTC) staining revealed transmural myocardial infarction (MI) in all hearts subjected to 60 or 90 minutes ischemia and reflow, and small nontransmural MIs in only 2/11 hearts subjected to 16 or 30 minutes ischemia and reperfusion. Thus, 1) MRI with albumin-Gd-DTPA is useful for identifying myocardial ischemia by enhancing the contrast between normally perfused and ischemic myocardia; 2) MRI with albumin-Gd-DTPA is useful for identifying reperfusion after myocardial ischemia; and 3) after reperfusion, reversible can be distinguished from irreversible myocardial injury by characteristic findings on MRI and MRS.