Question 1

Which of the following best describes the function of the intrinsic cardiac conduction system?

Accepted Answer

It initiates and distributes electrical impulses to coordinate depolarization and contraction of the heart.

Question 2

During the pacemaker potential in cardiac pacemaker cells, which ion movement is primarily responsible for the slow depolarization toward threshold?

Accepted Answer

Slow influx of $$\mathrm{Na^+}$$ ions

Question 3

Arrange the following components of the intrinsic conduction system in the correct order of impulse transmission:

Accepted Answer

SA node → AV node → AV bundle → bundle branches → Purkinje fibers

Question 4

A patient’s ECG shows absent P waves and a heart rate of 45 beats per minute. Which of the following is the most likely explanation?

Accepted Answer

The SA node is nonfunctional and the AV node is acting as the pacemaker.

Question 5

Which event occurs during the isovolumetric contraction phase of the cardiac cycle?

Accepted Answer

All heart valves are closed and ventricular pressure rises rapidly.

Question 6

Calculate the cardiac output ($$CO) $$for a patient with a heart rate ($$HR) of 80 $$beats/min and a stroke volume ($$SV) of 65 mL/$$beat. Use the formula $$CO = HR 	imes SV.$$

Accepted Answer

$$CO = 5,200\ \mathrm{mL/min}$$

Question 7

Which of the following would most likely increase end diastolic volume (EDV) and thus increase stroke volume (SV), according to the Frank-Starling law?

Accepted Answer

Increased venous return due to exercise

Question 8

A patient with persistent high blood pressure is at risk for which of the following changes in the heart?

Accepted Answer

Increased afterload, increased end systolic volume (ESV), and reduced stroke volume

Question 9

Which of the following best explains why cardiac muscle cannot undergo tetanic contractions like skeletal muscle?

Accepted Answer

The action potential and refractory period in cardiac muscle are much longer, preventing summation.

Question 10

A patient’s ECG shows an elevated S-T segment. What is the most likely clinical implication?

Accepted Answer

Cardiac ischemia

Question 11

Which of the following would be considered a positive inotropic agent that increases contractility of the heart?

Accepted Answer

High extracellular $$\mathrm{Ca$$^{2+}$$}$$

Question 12

If the vagus nerve to the heart were cut, what would most likely happen to the resting heart rate?

Accepted Answer

It would increase to approximately 100 beats per minute.

Question 13

A patient is experiencing ventricular fibrillation. Which of the following best describes the electrical activity in the heart?

Accepted Answer

Chaotic, disorganized action potentials occurring randomly throughout the ventricles

Question 14

Which of the following is the correct formula for stroke volume ($$SV$$)?

Accepted Answer

$$SV = EDV - ESV$$

Question 15

A 60-year-old male has a heart rate of 60 beats/min and an end diastolic volume (EDV) of 120 mL, with an end systolic volume (ESV) of 50 mL. What is his cardiac output ($$CO$$)? Use $$CO = HR 	imes SV$$ and $$SV = EDV - ESV.$$

Accepted Answer

$$CO = 4,200\ \mathrm{mL/min}$$

Question 16

Which fetal heart structure allows blood to bypass the pulmonary circulation by connecting the right and left atria?

Accepted Answer

Foramen ovale

Question 17

Which of the following would most likely result from right-sided heart failure?

Accepted Answer

Peripheral edema and blood pooling in body organs

Question 18

Which of the following best explains the effect of sympathetic stimulation on the heart?

Accepted Answer

It increases heart rate and contractility by releasing norepinephrine.

Question 19

A patient with a prolonged Q-T interval on their ECG is at increased risk for which of the following?

Accepted Answer

Ventricular arrhythmias

Question 20

Which of the following is a likely consequence of a total heart block?

Accepted Answer

No impulses reach the ventricles, which then beat at their own intrinsic rate.

Ch.18 pt.2: Electrical Events and Conduction System of the Heart

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