Q: Which equation correctly represents cardiac output (CO), and what are the typical resting values for heart rate (HR) and stroke volume (SV) in a healthy adult?

$$CO = HR \times SV$$; HR = 75 \text{ beats/min}, SV = 70 \text{ ml/beat}$

Question 1

Which structure in the intrinsic cardiac conduction system is responsible for setting the basic rhythm of the heart, and what is its typical rate of impulse generation?

Accepted Answer

Sinoatrial (SA) node; 75 impulses/min

Question 2

During the plateau phase (Phase 2) of the cardiac contractile cell action potential, which ion is primarily responsible for maintaining depolarization, and what is the physiological significance of this phase?

Accepted Answer

Ca$$^{2+}$$; allows sustained contraction for efficient blood ejection

Question 3

A patient presents with a heart rate of 45 beats per minute and an ECG showing absent P waves. Which part of the conduction system is likely acting as the pacemaker, and what is this rhythm called?

Accepted Answer

AV node; junctional rhythm

Question 4

Which equation correctly represents cardiac output (CO), and what are the typical resting values for heart rate (HR) and stroke volume (SV) in a healthy adult?

Accepted Answer

$$CO = HR 	imes SV$$; HR = 75 	ext{ beats/min}, SV = 70 	ext{ ml/beat}$

Question 5

A patient with persistent high blood pressure (aortic pressure \u003e 90 mmHg) is at risk for which of the following cardiac complications, and why?

Accepted Answer

Increased afterload, causing higher end-systolic volume and myocardial hypertrophy

Question 6

Which of the following best describes the Frank-Starling law of the heart?

Accepted Answer

The greater the preload (stretch), the greater the force of contraction and stroke volume

Question 7

Which ECG feature corresponds to ventricular depolarization, and what mechanical event does it trigger?

Accepted Answer

QRS complex; ventricular contraction (systole)

Question 8

A patient is diagnosed with ventricular fibrillation. What is the most immediate risk, and what is the recommended emergency treatment?

Accepted Answer

Loss of effective blood pumping; immediate defibrillation

Question 9

Calculate the stroke volume (SV) if the end-diastolic volume (EDV) is 130 ml and the end-systolic volume (ESV) is 55 ml. Use the formula $$SV = EDV - ESV.$$

Accepted Answer

$$SV = 75 	ext{ ml}$$

Question 10

Which of the following would most likely cause a heart murmur described as a 'swishing' sound immediately after the first heart sound (S1)?

Accepted Answer

Incompetent (insufficient) mitral valve

Question 11

Which of the following changes would most likely increase cardiac output during exercise?

Accepted Answer

Increased venous return and increased sympathetic stimulation

Question 12

A patient with hyperkalemia is at risk for which of the following cardiac effects?

Accepted Answer

Heart block and cardiac arrest

Question 13

Which of the following best explains why the action potential and contraction in cardiac muscle last much longer than in skeletal muscle?

Accepted Answer

The plateau phase due to Ca$$^{2+}$$ influx prolongs depolarization and contraction

Question 14

Which of the following is the correct sequence of excitation in the intrinsic conduction system of the heart?

Accepted Answer

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

Question 15

A patient with a second-degree heart block will have which of the following ECG findings?

Accepted Answer

More P waves than QRS complexes

Question 16

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

Accepted Answer

Decreases heart rate by opening K$$^+$$ channels in pacemaker cells

Question 17

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

Accepted Answer

Foramen ovale

Question 18

A patient with left-sided heart failure is most likely to develop which of the following complications?

Accepted Answer

Pulmonary congestion due to blood backing up in the lungs

Question 19

Which of the following is a direct effect of sympathetic stimulation on the heart?

Accepted Answer

Increased heart rate and force of contraction

Question 20

Which of the following congenital heart defects involves both mixing of oxygen-poor and oxygen-rich blood and increased workload due to narrowed vessels?

Accepted Answer

Tetralogy of Fallot

Electrical and Mechanical Events of the Heart: Cardiac Physiology and Regulation

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