Final answer:
Viability is assessed by noting the response of heart muscle to dobutamine infusion, particularly looking for improved contractility indicating viable myocardium. The assessment considers factors influencing heart function such as preload, afterload, and overall contractility while monitoring variations in blood flow and pressure.
Step-by-step explanation:
Viability in cardiac muscle can be assessed through a dobutamine stress echocardiogram (DSE), which primarily involves analyzing response to dobutamine infusion by assessing wall motion abnormalities. This technique includes the administration of dobutamine, a medication that increases heart rate and contractility, to simulate exercise conditions since not all patients can undergo physical exercise. As dobutamine is infused, the echocardiogram monitors the heart's motion and contractility, especially observing changes in wall motion. The focus is on the contractile response of the myocardium: if a segment of the myocardium improves in contractility during the stress test, it is likely to be viable.
Factors that affect heart contractility can be either positive or negative. Positive factors increase contractility, such as sympathetic stimulation and increased calcium ions in the myocardium, whereas negative factors decline contractility, for instance, parasympathetic stimulation or hypoxia. Stroke volume (SV) and, in turn, cardiac output are affected by preload, contractility, and afterload, all critical determinants of the heart's pumping capability. Cardiac response to variations in blood flow and pressure is complex and involves various intrinsic and extrinsic regulatory mechanisms to maintain efficient blood circulation.