Histochemical correlates of O-15-water-perfusable tissue fraction in experimental canine studies of old myocardial infarction

A method has been proposed to quantitate the myocardial water-perfusable ti ssue fraction (PTF) in the area of hypoperfused asynergic segments using O- 15-water ((H2O)-O-15) and PET. This study investigated the histochemical co rrelates of PTF (and perfusable tissue index, PTI) in a canine model of old myocardial infarction, Methods: Myocardial infarction was produced in 12 m ongrel dogs, and PET was performed I mo later, providing quantitative param etric images of PTF, regional myocardial blood flow (MBF), and extravascula r density from (H2O)-O-15, O-15-carbon monoxide, and transmission datasets. At the end of scanning, the myocardium was sectioned, and the PET images w ere compared directly with the corresponding myocardial sections. Results: The distribution of tissue necrosis identified by histochemical staining co rresponded well with the defect in PTF but not in MBF. PTF agreed with the equilibrium images of myocardial (H2O)-O-15 distribution, obtained after in jection of a large bolus of (H2O)-O-15. The defect surface area identified on PTF agreed well quantitatively with the morphometric estimates of the su rface area of myocardial infarction. PTI agreed with the absolute proportio n of histochemically defined normal myocardium (0.87 +/- 0.09 and 0.83 +/- 0.08, respectively; P < 0.01). Both PTF and PTI decreased significantly in segments of myocardial infarction and showed a significant difference betwe en the transmural and nontransmural myocardial infarction. Conclusion: The absolute mass and proportion of histochemically defined noninfarcted tissue may be quantitated with PTF and PTI in the area of myocardial infarction s egments.