Relationship between regional myocardial blood flow and tissue ATP content in acute ischemia

This study was undertaken to determine the relationships between myocardial mitochondrial function, regional myocardial blood flow (MBF), and tissue ATP content in acute ischemia. Fifty-one anesthetized dogs were used in the tests. MBF was measured by the H2 gas clearance method in order to define the ischemic area, during periods of coronary occlusion of 10, 20, 60, and 90 min. The correlation between MBF and myocardial ATP content in the ischemic area was positive and significant in each group (r = 0.54-0.82). The ATP content in the true ischemic area (where MBF was less than 20 ml/min/100 Gm) decreased significantly even after 10 min of occlusion, but mitochondrial function decreased only after 20 min of coronary occlusion when compared to the nonischemic area. Although ischemia induces mitochondrial dysfunction, a very short period of ischemia did not cause significant disturbance of mitochondrial function. Moreover, in the areas with MBF of 20-40 ml/min/100 Gm, the ATP content began to decrease 60 min after occlusion, whereas 10 or 20 min of occlusion did not reduce the ATP content. These results suggest that normal maintenance of ATP levels depends not only on MBF itself but also on the duration of ischemia plus the degree of damage to mitochondrial function, and that critical blood flow, defined as the minimum flow necessary to maintain the level of myocardial ATP, varies with the duration of ischemia.