Q: Which formula can be used to calculate heart rate from an ECG if the time between two consecutive R waves is $$0.8$$ seconds?

$$\text{Heart Rate} = \frac{60}{\text{R-R interval (sec)}}$$

Q: Which equation would you use to determine the duration of the cardiac cycle if the heart rate is 75 beats per minute?

$$\text{Cardiac Cycle Duration (sec)} = \frac{60}{\text{Heart Rate (bpm)}}$$

Question 1

Which structure in the heart initiates the electrical impulse that sets the pace for the heartbeat, and what is its typical rate in beats per minute?

Accepted Answer

Sinoatrial (SA) node; 70-80 beats per minute

Question 2

During a normal ECG tracing, which wave corresponds to atrial depolarization?

Accepted Answer

P wave

Question 3

What is the primary function of the AV node in the cardiac conduction system?

Accepted Answer

To delay the electrical impulse, allowing the atria to contract before the ventricles

Question 4

If the AV bundle is damaged, which part of the ECG tracing would most likely be affected?

Accepted Answer

The QRS complex

Question 5

Which of the following correctly describes the sequence of electrical conduction through the heart?

Accepted Answer

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

Question 6

A patient presents with a prolonged P-R interval on their ECG. Which part of the conduction system is most likely affected?

Accepted Answer

AV node

Question 7

Which formula can be used to calculate heart rate from an ECG if the time between two consecutive R waves is $$0.8$$ seconds?

Accepted Answer

$$	ext{Heart Rate} = \frac{60}{	ext{R-R interval (sec)}}$$

Question 8

Which of the following best explains why the AV node delays the electrical impulse before passing it to the ventricles?

Accepted Answer

To allow the atria to contract and complete ventricular filling

Question 9

A blockage in the bundle branches would most directly affect which phase of the cardiac cycle?

Accepted Answer

Ventricular depolarization

Question 10

Which part of the conduction system is responsible for rapidly distributing the electrical impulse throughout the ventricles, ensuring coordinated contraction?

Accepted Answer

Purkinje fibers

Question 11

If the SA node fails to function, which structure can take over as the pacemaker, and what is the expected heart rate?

Accepted Answer

AV node; 40-60 beats per minute

Question 12

Which of the following is the correct order of events during the cardiac conduction cycle as seen on an ECG?

Accepted Answer

P wave → QRS complex → T wave

Question 13

A patient’s ECG shows no P wave but a normal QRS complex and T wave. Which part of the conduction system is most likely malfunctioning?

Accepted Answer

SA node

Question 14

Which of the following best describes the role of internodal pathways in the heart?

Accepted Answer

They connect the SA node to the AV node, allowing rapid conduction through the atria

Question 15

If the conduction through the Purkinje fibers is slowed, what would be the expected effect on the ECG?

Accepted Answer

Prolonged QRS complex

Question 16

Which equation would you use to determine the duration of the cardiac cycle if the heart rate is 75 beats per minute?

Accepted Answer

$$	ext{Cardiac Cycle Duration (sec)} = \frac{60}{	ext{Heart Rate (bpm)}}$$

Question 17

Which of the following would most likely result from a complete block at the AV node?

Accepted Answer

Ventricles would contract at a slower rate, independent of atrial rhythm

Question 18

Which part of the ECG tracing represents ventricular repolarization?

Accepted Answer

T wave

Question 19

A patient has a heart rate of 60 beats per minute. What is the duration of one cardiac cycle?

Accepted Answer

$$1$$ second

Chapter 21: Blood Vessels and Cardiac Conduction System

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