Cardiac muscle cell fatigue. There are two types of cells within the heart: the cardiomyocytes and the cardiac pacemaker cells. Cardiomyocytes make up the atria (the chambers in which blood enters the heart) and the ventricles (the chambers where blood is collected and pumped out of the heart). These cells must be able to shorten and lengthen their fibers and the fibers must be flexible enough to stretch. These functions are critical to the proper form during the beating of the heart. Cardiac pacemaker cells carry the impulses that are responsible for the beating of the heart. They are distributed throughout the heart
Heart rate turbulence Heart rate turbulence Heart rate turbulence (HRT) is the return to equilibrium of heart rate after a premature ventricular contraction (PVC). It consists of a brief speed-up in heart rate, followed by a slow decrease back to the baseline rate. An important feature of HRT is that PVCs occur naturally in most adults, so measuring the characteristics of a given person's HRT offers a noninvasive way to evaluate his or her cardiac function without applying artificial external stimuli. The measured values of HRT parameters have been shown to be a statistically significant predictor of the probability of dying from cardiac