Part 6: Cardiac Function – Cardiac Output, ECG, Regulation of Cardiac Activity (25 MCQs)

Part 6: Cardiac Function – Cardiac Output, ECG, Regulation of Cardiac Activity (25 MCQs)

Q1. Stroke volume is defined as:

A. Blood pumped per minute
B. Blood pumped per beat by each ventricle
C. Total blood volume
D. Blood pressure

Answer: B

Explanation:

• A. Incorrect: Blood per minute = cardiac output.
• B. Correct: Stroke volume = blood pumped per beat (≈70 mL).
• C. Incorrect: Total blood volume = ≈5 L.
• D. Incorrect: Blood pressure is force, not volume.

Q2. Cardiac output is calculated as:

A. Stroke volume ÷ Heart rate
B. Stroke volume × Heart rate
C. Stroke volume + Heart rate
D. Stroke volume – Heart rate

Answer: B

Explanation:

• A. Incorrect: Not division.
• B. Correct: CO = SV × HR.
• C. Incorrect: Not addition.
• D. Incorrect: Not subtraction.

Q3. Average cardiac output in a healthy adult is about:

A. 2 L/min
B. 5 L/min
C. 10 L/min
D. 20 L/min

Answer: B

Explanation:

• A. Incorrect: Too low.
• B. Correct: Normal CO ≈ 5 L/min at rest.
• C. Incorrect: Possible during exercise, not rest.
• D. Incorrect: Extreme exercise, not normal.

Q4. End-diastolic volume (EDV) is:

A. Volume of blood in atria
B. Volume of blood in ventricles after diastole
C. Volume of blood ejected per beat
D. Volume of blood remaining after systole

Answer: B

Explanation:

• A. Incorrect: Atria fill ventricles.
• B. Correct: EDV = blood in ventricles at end of diastole (≈110–130 mL).
• C. Incorrect: That is stroke volume.
• D. Incorrect: That is end-systolic volume.

Q5. Ejection fraction is the ratio of:

A. Stroke volume ÷ EDV
B. Stroke volume ÷ ESV
C. EDV ÷ ESV
D. CO ÷ HR

Answer: A

Explanation:

• A. Correct: EF = SV ÷ EDV (normal ≈ 60%).
• B. Incorrect: Not SV/ESV.
• C. Incorrect: Not EDV/ESV.
• D. Incorrect: CO/HR = SV.

Q6. Which component of ECG corresponds to atrial depolarization?

A. P wave
B. QRS complex
C. T wave
D. U wave

Answer: A

Explanation:

• A. Correct: P wave = atrial depolarization.
• B. Incorrect: QRS = ventricular depolarization.
• C. Incorrect: T = ventricular repolarization.
• D. Incorrect: U wave not always present.

Q7. QRS complex in ECG represents:

A. Atrial depolarization
B. Atrial repolarization
C. Ventricular depolarization
D. Ventricular repolarization

Answer: C

Explanation:

• A. Incorrect: P wave = atrial depolarization.
• B. Incorrect: Atrial repolarization hidden in QRS.
• C. Correct: QRS = ventricular depolarization.
• D. Incorrect: T wave = ventricular repolarization.

Q8. T wave in ECG represents:

A. Atrial depolarization
B. Ventricular depolarization
C. Atrial repolarization
D. Ventricular repolarization

Answer: D

Explanation:

• A. Incorrect: That’s P wave.
• B. Incorrect: That’s QRS.
• C. Incorrect: Atrial repolarization hidden in QRS.
• D. Correct: T wave = ventricular repolarization.

Q9. Normal duration of a cardiac cycle is about:

A. 0.5 sec
B. 0.8 sec
C. 1.2 sec
D. 2 sec

Answer: B

Explanation:

• A. Incorrect: Too short.
• B. Correct: Normal = 0.8 sec at 72 bpm.
• C. Incorrect: Too long.
• D. Incorrect: Too long.

Q10. Heart rate is normally regulated by:

A. SA node
B. AV node
C. Purkinje fibers
D. Bundle of His

Answer: A

Explanation:

• A. Correct: SA node → natural pacemaker.
• B. Incorrect: AV node transmits impulse.
• C. Incorrect: Purkinje fibers distribute impulse.
• D. Incorrect: Bundle of His conducts impulse.

Q11. Which nerve decreases heart rate (parasympathetic control)?

A. Sympathetic nerve
B. Phrenic nerve
C. Vagus nerve
D. Glossopharyngeal nerve

Answer: C

Explanation:

• A. Incorrect: Sympathetic nerves increase HR.
• B. Incorrect: Phrenic controls diaphragm.
• C. Correct: Vagus nerve decreases HR.
• D. Incorrect: Glossopharyngeal controls taste/swallowing.

Q12. Which hormones increase heart rate?

A. Insulin and glucagon
B. Thyroxine and adrenaline
C. ADH and aldosterone
D. Estrogen and progesterone

Answer: B

Explanation:

• A. Incorrect: Glucose metabolism hormones.
• B. Correct: Thyroxine + adrenaline → increase HR.
• C. Incorrect: Regulate fluid balance, not HR.
• D. Incorrect: Sex hormones, not HR regulators.

Q13. Tachycardia means:

A. Slow heart rate (<60 bpm)
B. Rapid heart rate (>100 bpm)
C. Irregular heart rate
D. Stoppage of heart

Answer: B

Explanation:

• A. Incorrect: That is bradycardia.
• B. Correct: Tachycardia = >100 bpm.
• C. Incorrect: Irregular = arrhythmia.
• D. Incorrect: Stoppage = cardiac arrest.

Q14. Bradycardia refers to:

A. HR <60 bpm
B. HR >100 bpm
C. HR >200 bpm
D. Irregular heartbeat

Answer: A

Explanation:

• A. Correct: Bradycardia = slow HR <60 bpm.
• B. Incorrect: That’s tachycardia.
• C. Incorrect: Too high for bradycardia.
• D. Incorrect: That’s arrhythmia.

Q15. Which structure delays the impulse to allow atrial contraction before ventricles contract?

A. SA node
B. AV node
C. Purkinje fibers
D. Aorta

Answer: B

Explanation:

• A. Incorrect: SA initiates impulse.
• B. Correct: AV node delays impulse → atria empty into ventricles.
• C. Incorrect: Purkinje fibers distribute, no delay.
• D. Incorrect: Aorta not involved in conduction.

Q16. Which part of ECG is hidden within the QRS complex?

A. Atrial depolarization
B. Atrial repolarization
C. Ventricular repolarization
D. Ventricular depolarization

Answer: B

Explanation:

• A. Incorrect: That’s visible as P wave.
• B. Correct: Atrial repolarization is hidden under QRS.
• C. Incorrect: Ventricular repolarization = T wave.
• D. Incorrect: Ventricular depolarization = QRS.

Q17. The “pacemaker potential” is generated due to:

A. Na⁺ leakage into SA node cells
B. K⁺ outflow
C. Ca²⁺ storage
D. ATP breakdown

Answer: A

Explanation:

• A. Correct: Pacemaker potential = slow Na⁺ influx in SA node.
• B. Incorrect: K⁺ efflux repolarizes, not initiates.
• C. Incorrect: Ca²⁺ causes depolarization, not pacemaker potential.
• D. Incorrect: ATP breakdown provides energy, not potential.

Q18. Which wave is absent in ventricular fibrillation ECG?

A. P wave
B. QRS complex
C. T wave
D. All organized waves

Answer: D

Explanation:

• A. Incorrect: Not just P.
• B. Incorrect: Not just QRS.
• C. Incorrect: Not just T.
• D. Correct: Ventricular fibrillation = no organized ECG waves.

Q19. Which condition is diagnosed using ECG?

A. Blood sugar level
B. Cardiac arrhythmia
C. Oxygen saturation
D. Blood pressure

Answer: B

Explanation:

• A. Incorrect: Blood test for sugar.
• B. Correct: ECG detects arrhythmias.
• C. Incorrect: O₂ measured by oximetry.
• D. Incorrect: BP by sphygmomanometer.

Q20. First heart sound corresponds with:

A. Atrial systole
B. Closure of AV valves
C. Closure of semilunar valves
D. Opening of AV valves

Answer: B

Explanation:

• A. Incorrect: Not atrial systole.
• B. Correct: “Lub” sound = AV valves close.
• C. Incorrect: “Dub” sound.
• D. Incorrect: Valve opening is silent.

Q21. Which wave in ECG indicates ventricular repolarization?

A. P wave
B. QRS complex
C. T wave
D. U wave

Answer: C

Explanation:

• A. Incorrect: P = atrial depolarization.
• B. Incorrect: QRS = ventricular depolarization.
• C. Correct: T wave = ventricular repolarization.
• D. Incorrect: U wave is rare.

Q22. Atrial depolarization occurs just before:

A. Atrial systole
B. Ventricular systole
C. Atrial diastole
D. Ventricular diastole

Answer: A

Explanation:

• A. Correct: Depolarization → contraction = atrial systole.
• B. Incorrect: Ventricular systole follows atrial.
• C. Incorrect: Diastole is relaxation.
• D. Incorrect: Not related.

Q23. Increase in sympathetic activity leads to:

A. Decrease in HR
B. Increase in HR and force of contraction
C. Decrease in stroke volume
D. Complete heart block

Answer: B

Explanation:

• A. Incorrect: Parasympathetic decreases HR.
• B. Correct: Sympathetic ↑ HR + contractility.
• C. Incorrect: Stroke volume increases.
• D. Incorrect: Heart block due to conduction defect.

Q24. Which factor decreases heart rate?

A. Sympathetic stimulation
B. Vagus nerve stimulation
C. Thyroxine
D. Adrenaline

Answer: B

Explanation:

• A. Incorrect: Sympathetic increases HR.
• B. Correct: Vagus nerve decreases HR.
• C. Incorrect: Thyroxine increases HR.
• D. Incorrect: Adrenaline increases HR.

Q25. Which part of conduction system ensures ventricles contract simultaneously?

A. SA node
B. AV node
C. Bundle of His and Purkinje fibers
D. Atrial fibers

Answer: C

Explanation:

• A. Incorrect: SA initiates impulse.
• B. Incorrect: AV delays impulse.
• C. Correct: Bundle of His + Purkinje distribute impulse to both ventricles.
• D. Incorrect: Atrial fibers contract atria.

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