Question

A 63year old man suddenly felt a crushing pain beneath his sternum. He became weak and began to sweat profusely. He called 911 and was taken to the hospital where it was confirmed that he had suffered a heart attack due to occlusion in a major coronary artery.

1. When a coronary artery is occluded, the K+ concentration rises in the interstitial fluid of the ischemic region of the myocardium. What effect does the elevated K+ concentration have on the resting membrane potential of the myocardial cells in the ischemic zone?

A. Increases the resting membrane potential(hyperpolarizes the resting membrane potential)

B. Decreases the resting membrane potential (depolarizes the resting membrane potential)

C. Has no effect on the resting membrane potential

2. What effect does this change in resting membrane potential have on the propagation of the cardiac impulse?

A. The upstroke of the action potential will be steeper than normal

B. Propagation of the action potential will be slower than normal

C. More voltage-sensitive Na+ channels will be activated

D. The amplitude of the action potential will be increase

The patient had cardiac rhythm disturbances within minutes after he felt the chest pain. He was given an anti-arrhythmic drug that inactivated many of the fast Na+channels in the heart.

3. What effect would the anti-arrhythmic drug have on the resting membrane potential of the myocardial cells?

A. It will have very little effect on the resting membrane potential

B. It will depolarize the resting membrane potential

C. It will hyperpolarize the resting membrane potential

4.​What effect would this drug have on the action potential in the SA node?

A. It will increase the slope of the If component of the action potential

B. It will diminish the amplitude of the action potential

C. It will increase the duration of the action potential at the SA node

D. It will have very little effect on the action potential at the SA node

Soon after the patient arrived at the hospital, the activity in the vagus nerve fibers to the heart increased reflexively.

5. What electrophysiological effects would increased vagal activity have on the cells of the SA Node?

1. It will increase heart rate

2. It will decrease the slope of the If component of the action potential

3. It will depolarize the resting membrane potential

4. It will increase cellular levels of cAMP

Answer 1

1.  In hyperkalemia, the resting membrane potential is decreased, and the membrane becomes partially depolarized. Initially, this increases membrane excitability. However, with prolonged depolarization, the cell membrane will become more refractory and less likely to fully depolarize

2. Propagation of action potential decrease

3.  Cardiac arrhythmias arise from disturbances in the functioning of the specific ion channels that normally control excitation or from the functional expression of previously latent channels. Antiarrhythmic agents act by blocking the membrane sodium, potassium, and calcium channels, but no agent has exclusive action on a given type of channel. Arrhythmias resulting from reentry form the largest group of clinically significant arrhythmias. Most arrhythmias result from depressed sodium channel function. Hence resting membrane potential dec

4. Sodium-channel blockers comprise the Class I antiarrhythmic compounds according to the Vaughan-Williams classification scheme. These drugs bind to and block the fast sodium channels that are responsible for the rapid depolarization (phase 0) of fast-response cardiac action potentials.inc duration