What are the three major determinants of myocardial demand?

The three major determinants of myocardial demand are ventricular wall stress, heart rate, and contractility. Each of these factors plays a critical role in how much oxygen the heart muscle requires to function effectively.

Ventricular wall stress refers to the stress on the walls of the heart's ventricles during contraction. This stress increases as the heart pumps against higher pressures or when the heart's size increases due to conditions like ventricular hypertrophy. Higher wall stress means that the myocardium consumes more oxygen.

Heart rate, the number of beats per minute, directly impacts myocardial oxygen demand. As the heart rate increases, the heart requires more energy and thus more oxygen to sustain the increased activity. A higher heart rate leads to shorter diastolic filling times, which can also amplify the demand for oxygen.

Contractility is the intrinsic ability of the cardiac muscle to contract. When contractility increases, the heart works harder to pump blood, resulting in a greater need for oxygen. Conditions that enhance contractility, such as sympathetic stimulation, will lead to an increased demand for myocardial oxygen.

Understanding these determinants is crucial for perfusionists, as they need to manage the myocardial oxygen supply and demand balance during surgeries and in the management of patients with heart disease.