Registered Cardiovascular Invasive Specialist (RCIS) Practice Test

When the heart rate slows down, the myocardial contractile force, often quantified as the rate of pressure change over time (dp/dt), typically increases. This phenomenon can be attributed to the relationship between heart rate and cardiac filling times. As heart rate decreases, the duration of diastole, the phase of the cardiac cycle when the heart muscles relax and the chambers fill with blood, increases. With longer filling times, the ventricles can accommodate more blood, leading to a more significant stretch of the myocardial fibers. According to the Frank-Starling law of the heart, increased stretching of the myocardial fibers results in a stronger contraction during systole, thereby enhancing the contractile force (dp/dt). This means that as the heart has more time to fill, the force exerted during the subsequent contraction increases, demonstrating a direct effect of heart rate on myocardial performance. While cardiac conditions, other physiological responses, or medications might affect this relationship, in a general context of decreased heart rate, the myocardial contractility typically reflects this increase in force generation.