Q: Calculate the cardiac output (CO) if the heart rate (HR) is 80 beats/min and the stroke volume (SV) is 65 mL/beat. Use the formula $$CO = HR \times SV.$$

$$CO = 80 \times 65 = 5200 mL/$$min

Question 1

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

Accepted Answer

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

Question 2

During the pacemaker potential phase in cardiac pacemaker cells, which ion channels are primarily responsible for the gradual depolarization?

Accepted Answer

Slow Na$$^+$$ channels

Question 3

What is the correct sequence of excitation through the intrinsic conduction system of the heart?

Accepted Answer

SA node → AV node → AV bundle → Right and left bundle branches → Purkinje fibers

Question 4

A patient presents with a heart rate of 45 beats per minute and absent P waves on their ECG. Which of the following is the most likely explanation?

Accepted Answer

The AV node has taken over as the pacemaker, resulting in a junctional rhythm.

Question 5

Which event is represented by the QRS complex on an ECG?

Accepted Answer

Ventricular depolarization and atrial repolarization

Question 6

What is the primary benefit of the plateau phase in the action potential of contractile cardiac muscle cells?

Accepted Answer

It prevents tetanic contractions, ensuring efficient ejection of blood.

Question 7

Calculate the cardiac output (CO) if the heart rate (HR) is 80 beats/min and the stroke volume (SV) is 65 mL/beat. Use the formula $$CO = HR 	imes SV.$$

Accepted Answer

$$CO = 80 	imes 65 = 5200 mL/$$min

Question 8

Which of the following would most likely result from a defective AV node that fails to conduct some SA node impulses?

Accepted Answer

Second-degree heart block

Question 9

A patient with persistent high blood pressure has an aortic pressure of 100 mm Hg. How does this affect afterload and stroke volume?

Accepted Answer

Afterload increases, leading to reduced stroke volume.

Question 10

Which of the following best explains why the heart can continue to beat after all nervous connections to it are severed?

Accepted Answer

The intrinsic conduction system allows the heart to depolarize and contract without nervous system stimulation.

Question 11

Which phase of the cardiac cycle is characterized by all heart valves being closed and no change in ventricular volume?

Accepted Answer

Isovolumetric contraction

Question 12

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

Accepted Answer

Cardiac ischemia

Question 13

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

Accepted Answer

$$SV = EDV - ESV$$

Question 14

Which of the following would most likely increase preload and thus increase stroke volume according to the Frank-Starling law?

Accepted Answer

Increased venous return

Question 15

Which of the following is a positive inotropic agent that increases contractility?

Accepted Answer

Epinephrine

Question 16

A patient with congestive heart failure (CHF) has blood backing up in the lungs. Which side of the heart is most likely failing?

Accepted Answer

Left side

Question 17

Which of the following best describes the effect of acetylcholine on the heart?

Accepted Answer

It decreases heart rate by opening K$$^+$$ channels.

Question 18

A patient is experiencing rapid, irregular contractions that make the heart useless for pumping blood. What is the most likely diagnosis?

Accepted Answer

Fibrillation

Question 19

Which heart sound is associated with the closing of the semilunar (SL) valves?

Accepted Answer

Second sound (dup)

Question 20

Which of the following would most likely be heard in a patient with an incompetent (insufficient) heart valve?

Accepted Answer

A swishing sound as blood regurgitates backward

Electrical and Mechanical Events of the Heart: Cardiac Conduction, ECG, and Cardiac Cycle

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