Characterization of the ischemic process by regional metabolism.

The myocardial cell requires energy for contractile activity and for the work of internal maintenance. With the onset of ischemia mechanical performance is compromised. If the ischemia is severe and persistent, the energy necessary to maintain the internal millieu proves inadequate and cell death ensues. Ischemic heart disease is a regional phenomenon with normal and abnormal cell metabolism occurring side by side. The ischemic cell demonstrates hemodynamic, electrical and biochemical instability; its passage from a state of reversible to irreversible injury may persist for as long as 7 days and offers an opportunity to introduce interventions that may protect it and reduce ultimate infarct size. There is as yet no adequate objective means for predicting the mass of infarcted tissue. However, studies of regional metabolism, if properly conducted, may help define the adequacy of coronary vascular reserve and characterize the ischemic process. Current techniques utilize a myocardial pacing stress to induce an ischemic response. Although virtually every metabolic pathway is disrupted by severe ischemia, the assay of selected metabolities in arterial and coronary venous blood samples has provided information of diagnostic significance.