Certified Registered Nurse Anesthetist (CRNA) Practice Exam

What cardiac effects does beta-1 receptor stimulation produce?

1. Negative dromotropic effect

2. Positive inotropic, chronotropic, and dromotropic effects

3. Decreased contractility

4. None of the above

The correct answer is: Positive inotropic, chronotropic, and dromotropic effects

Beta-1 receptor stimulation primarily impacts the heart by enhancing its performance in several key ways. The stimulation of these receptors results in positive inotropic, chronotropic, and dromotropic effects. Positive inotropic effects refer to an increase in the force of contraction of the heart muscle. When beta-1 receptors are activated, they increase the intracellular levels of cyclic AMP, which enhances calcium availability for myocardial contraction. This leads to stronger contractions of the cardiac muscle. Positive chronotropic effects occur as a result of increased heart rate. Beta-1 receptor stimulation accelerates the firing rate of the sinoatrial (SA) node, which is the heart's natural pacemaker, thus leading to an increased heart rate during periods of increased demand or stress. Positive dromotropic effects relate to the conduction velocity through the atrioventricular (AV) node. Stimulation of beta-1 receptors enhances electrical conduction, allowing impulses to be transmitted more rapidly from the atria to the ventricles, which is crucial during times of increased activity or stress. Together, these effects prepare the heart to respond more effectively to physiological demands, such as during exercise or stress, thereby maximizing cardiac output and overall performance.