Terminologies in Cardiovascular Diseases

Preload and Afterload: Preload is the volume in the ventricles at the end of diastole, reflecting how much the heart is filled before it contracts. Afterload is the resistance the heart must overcome to eject blood during systole.

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Tachycardia and Bradycardia: Tachycardia is a fast heartbeat, usually greater than 100 beats a minute. Bradycardia is a heart rate that is too slow, usually less than 60 beats a minute.

Frank-Starling Mechanism

Cardiac output (CO) increases in response to an increase in blood volume within the heart chambers. The increase in blood volume stretches the myocardial fibers, causing the cardiac muscle to contract more forcefully with increase in its mechanical performance. Intraatrial pressure controls atrial stretch. The Frank-Starling mechanism in the atrium is manifested in two phases. An increase in the amplitude of the calcium transient and a decrease in the time constant of Ca2+ transient decay are accompanied by the development of increased contraction force after stepwise increase of stretch. Thus, immediately after the stretch, the contraction force is increased, and an additional increase in force is followed instantly afterwards. An increase in muscle length results in a gradual augmentation of Ca2+ transient amplitude, which modulates the action potentials through increased Na+/Ca2+-exchange inward current. Troponin C is the calcium binding part of the contractile machinery, and is sensitive to muscle length. Experiments show that troponin C affinity change is needed to produce the immediate increase of contraction force and stretch, modulate the Ca2+ transient and stabilize the diastolic Ca2+ concentration. The same mechanism that caused the normal physiologic responses to stretch could also generate arrythmogenic after potentials at high stretch levels in the model. Using a bivariate regression model with the assumption that variability is constant as a percentage of the expected value, a regression equation and graphs was developed that allowed calculation of a 95% prediction interval for several echocardiographic measurements as a function of the subject’s age and either body weight or body surface area. With a stepwise decrease in the pacing heart rate, the LA dimension increases just before atrial contraction, and LA systolic shortening increases as well. Nevertheless, a decrease in the left ventricular filling volume during atrial systole is seen. As the pulmonary venous flow during atrial systole is directed toward the left atrium, the left atrial inflow volume from the pulmonary venous flow decreases, and the Frank-Starling mechanism operates with a decrease in the pacing rate. However, due to the decrease in pulmonary venous flow to the left ventricle via the left atrium, left ventricular filling decrease

Mehrzad, R., Rajab, M., & Spodick, D. (2014). The Three Integrated Phases of Left Atrial Macrophysiology and Their Interactions. International Journal of Molecular Sciences, 15(9), 15146–15160. https://doi.org/10.3390/ijms150915146