Complications during vascular surgery: basic principles and management of cardiac ischaemia

Systematic management of cardiac ischaemia requires an understanding of both the determinants of myocardial oxygen consumption, MVO2and coronary perfusion. This chapter discusses the mechanical and pharmacological determinants of MVO2using primarily end-systolic pressure–volume relation, ESPVR, and the relation of the pressure–volume area, which is based upon the ESPVR to MVO2. First, the mechanical determinants of cardiac performance are discussed, followed by their interaction with MVO2. Emphasis is placed upon the effects of heart rate, changes in cardiac loading, and in contractility on MVO2using the PVA as a basis for analysis. It will be shown that the effects of blood pressure on MVO2depend mostly on the contractile state of the heart, whereas when considered per beat heart rate probably does not affect MVO2. The concept of increasing contractility causing oxygen wasting and the controversy surrounding this concept is also discussed.