What are typical physiologic responses to bradycardia to maintain cardiac output?

What are typical physiologic responses to bradycardia to maintain cardiac output?

• A. Increased stroke volume via increased venous return/Frank-Starling, or sympathetic activation; in severe cases, pharmacologic or pacemaker intervention
• B. Decreased stroke volume
• C. No change
• D. Decreased venous return

Answer: (A)

When bradycardia lowers heart rate, cardiac output tends to fall unless stroke volume rises to compensate. Since CO = heart rate × stroke volume, the body’s priority is to boost stroke volume. This happens by increasing venous return ( preload ), which stretches the ventricular fibers more and, via the Frank-Starling mechanism, makes the next contraction stronger. Sympathetic activation also enhances contractility and can constrict veins to push more blood back to the heart, further increasing stroke volume. In more severe cases, pharmacologic support to raise heart rate and contractility or a pacemaker to restore a normal rate may be needed to preserve output. Decreased stroke volume or decreased venous return would worsen CO rather than compensate for the slower rate, and no change would not maintain adequate output when the heart is beating slowly.

When bradycardia lowers heart rate, cardiac output tends to fall unless stroke volume rises to compensate. Since CO = heart rate × stroke volume, the body’s priority is to boost stroke volume. This happens by increasing venous return ( preload ), which stretches the ventricular fibers more and, via the Frank-Starling mechanism, makes the next contraction stronger. Sympathetic activation also enhances contractility and can constrict veins to push more blood back to the heart, further increasing stroke volume. In more severe cases, pharmacologic support to raise heart rate and contractility or a pacemaker to restore a normal rate may be needed to preserve output.

Decreased stroke volume or decreased venous return would worsen CO rather than compensate for the slower rate, and no change would not maintain adequate output when the heart is beating slowly.