Q: Which phase of the cardiac pacemaker cell action potential is primarily responsible for the spontaneous depolarization that initiates each heartbeat?

Pacemaker potential phase, due to slow Na\textsuperscript{+} channel influx

Q: Calculate the cardiac output (CO) for a patient with a heart rate (HR) of 90 beats/min and a stroke volume (SV) of 65 mL/beat. Use the formula $$CO = HR \times SV.$$

$$CO = 90 \times 65 = 5850\ \text{mL/min}$$

Q: Which ion imbalance is most dangerous to heart function and can lead to life-threatening arrhythmias?

Potassium (K\textsuperscript{+})

Q: Which of the following is a direct effect of acetylcholine released by the parasympathetic nervous system on pacemaker cells?

Decreases heart rate by opening K\textsuperscript{+} channels

Question 1

Which phase of the cardiac pacemaker cell action potential is primarily responsible for the spontaneous depolarization that initiates each heartbeat?

Accepted Answer

Pacemaker potential phase, due to slow Na	extsuperscript{+} channel influx

Question 2

A patient presents with a prolonged QT interval on their ECG. What is the most significant clinical risk associated with this finding?

Accepted Answer

Increased risk of ventricular arrhythmias

Question 3

Which structure in the intrinsic cardiac conduction system is responsible for delaying the electrical impulse, allowing the atria to contract before the ventricles?

Accepted Answer

Atrioventricular (AV) node

Question 4

If the AV node is defective and fails to conduct impulses, which condition is most likely to occur?

Accepted Answer

Heart block

Question 5

During which phase of the cardiac cycle does ventricular pressure rise, causing the closing of AV valves but not yet opening the semilunar valves?

Accepted Answer

Isovolumetric contraction

Question 6

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

Accepted Answer

Second sound (dup)

Question 7

Calculate the cardiac output (CO) for a patient with a heart rate (HR) of 90 beats/min and a stroke volume (SV) of 65 mL/beat. Use the formula $$CO = HR 	imes SV.$$

Accepted Answer

$$CO = 90 	imes 65 = 5850\ 	ext{mL/min}$$

Question 8

Which of the following would most likely cause a heart murmur characterized by a high-pitched sound or clicking?

Accepted Answer

Stenotic valve

Question 9

A patient with persistent high blood pressure (aortic pressure \u003e90 mmHg) is at risk for which cardiac complication?

Accepted Answer

Myocardial hypertrophy and weakness

Question 10

Which hormone increases heart rate and contractility by acting on the heart, and also enhances the effects of norepinephrine and epinephrine?

Accepted Answer

Thyroxine

Question 11

Which ECG feature represents the depolarization of the ventricles and is typically the largest wave?

Accepted Answer

QRS complex

Question 12

A patient with congestive heart failure (CHF) presents with pulmonary congestion. Which side of the heart is most likely failing?

Accepted Answer

Left side

Question 13

Which of the following factors would most likely increase heart rate in a healthy adult?

Accepted Answer

Increased sympathetic stimulation

Question 14

What is the primary function of the Purkinje fibers in the cardiac conduction system?

Accepted Answer

Transmit impulses to ventricular muscle cells for coordinated contraction

Question 15

Which ion imbalance is most dangerous to heart function and can lead to life-threatening arrhythmias?

Accepted Answer

Potassium (K	extsuperscript{+})

Question 16

Which of the following is a direct effect of acetylcholine released by the parasympathetic nervous system on pacemaker cells?

Accepted Answer

Decreases heart rate by opening K	extsuperscript{+} channels

Question 17

A 25-year-old athlete has a resting heart rate of 50 beats/min. Which term best describes this condition, and what is its likely significance?

Accepted Answer

Bradycardia; may be a desirable result of endurance training

Question 18

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

Accepted Answer

The intrinsic cardiac conduction system generates its own action potentials

Question 19

Which of the following would most likely be observed in a patient with right-sided heart failure?

Accepted Answer

Peripheral edema

Question 20

A patient’s ECG shows an elevated ST segment. What is the most likely clinical interpretation?

Accepted Answer

Cardiac ischemia

Cardiovascular System: Electrical and Mechanical Events of the Heart

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