Chapter 19.4, Problem 19BYGO

In the initial stages of ventricular fibrillation (during which the heart produces no functional contraction), tissue perfusion in the heart actually increases. Explain.

Why do the cardiac muscles cells demonstrate autorhythmicity?

Unlike skeletal muscle, cardiac muscle doesn’t undergo tetany. Explain how this is achieved and why is this necessary?

Why is the cardiac action potential propagated more slowly in an AV node cell then in an atrial or ventricular myocyte? How can be AV conduction affected by hypokalemia?  Briefly explain the mechanism by which the most popular beta-blocker metoprolol would affect cardiac muscle contractility and blood flow. How it affects heart rate and conduction?

Answer ALL parts of this question. In terms of heart failure there is a decrease in cardiac output. This is due to a contractile deficit in the individual cardiac myocytes. (a) Explain how this contractile deficit occurs. (b) What common cardiac problem is often associated with the changes in calcium handling often seen in cardiac cells of heart failure patients? Explain how this problem arises. (c) Describe the mechanism of action of levosimendan in the treatment of heart failure.

a) A consequence of the Frank-Starling law of the heart is that the outputs of the right and left ventricles match. Explain why this is important and how this match is made.b) The excitation-contraction matching mechanism within the heart muscle is different from that of the skeletal muscle. How might these differences be related to the difference between action potentials in cardiac muscle and skeletal muscle?

Mrs B had a heart transplant and as a result, she no longer has nerve supply to her heart. Keeping in mind the influence of venous return on the heart, do you think Mrs B will be able to increase her cardiac output during exercise? Explain.

Describe the events leading up to contraction in a cardiac contractile cell. (Where does the stimulus to “contract” come from?)

The entry of calcium into a ventricular muscle cell helps to maintain depolarization of the membrane during the plateau phase of the action potential, but this calcium also performs what other function?