Effects of graded intensity of oxygen deficiency on function and energy metabolism in post-ischaemic myocardium

The effect of graded ischaemic injury on post-ischaemic myocardium was examined in rat hearts after three 4 min periods of asphyxia. Systolic function under steady state conditions and during isovolumic beats, the content of high energy phosphates and glycogen, and myocardial material properties were determined. Severity of the oxygen deficiency was varied by manipulating myocardial oxygen demand (MVO2) either by rapid atrial pacing or by vagal stimulation. After 20 min of post-asphyxial recovery, steady state haemodynamics were almost normal. In the high MVO2 group (atrial pacing) the dp/dtmax was reduced to 90%(NS). The isovolumic indices of function were decreased in all post-asphyxial groups. This was most pronounced in the high MVO2 group, with a reduction in peak left ventricular systolic pressure to 85.7 (SEM 3.4)% and a decrease in peak left ventricular systolic stress to 82.3(3.9)% (p less than 0.01). The post-asphyxial myocardial performance recovered better in the low MVO2 group (vagal stimulation). Material properties were altered only in the high MVO2 group. The decreased content of ATP and glycogen were comparable in all post-asphyxial groups. A phosphocreatine overshoot phenomenon was most marked in the high MVO2 group: 11.4(2.8) mumol.g-1 v 4.7(0.9) mumol.g-1 (control), p less than 0.01. The results indicate that post-ischaemic contractile dysfunction of reversibly injured is not closely related to the previous O2 deficit or to the functional impairment. We also obtained no correlation between ATP content and material properties in modestly injured post-ischaemic myocardium.