Question

Calcium channel blockers are sometimes prescribed to treat certain cardiovascular conditions. What is the most likely effect of a calcium channel blocker?

A. Delay repolarization of SA node cells

B. Decrease stroke volume

C. Prolong the plateau phase of contractile myocardium action potentials

D. Increase heart rate

*Choice B is the correct answer, please explain why choice B is correct, and why choice D is incorrect! Thank you!

Answer 1

Calcium channel blockers are the drugs that relax the blood vessels and Increase the supply of blood and oxygen to heart and also reduce the work load of heart.

Examples of calcium channel blockers are nifedipine , felodipine , amlodipinie.

Calcium channel blockers have negative chronotropic effect on SA node. Chronotropic effects are those that change the heart rate. Positive chrontropic effect increases the heart rate where as negative chrontropic effect decreases the heart rate.

Hence calcium channel blockers decreases the heart rate . This is to decrease the blood pressure in the vessels .In addition to negative chrontropic effect , they also dilate the blood vessels to decrease blood pressure.

Due to decrease in heart rate , the stroke volume decreases because of decreased ventricular contractility .

Hence the answer is B.decrease stroke volume and not D.increases heart rate.