DC Dysrhythmia Pathophysiology & Electrophysiology 1 — Questions and Answers
Question 1: What is the normal pacemaker of the heart and its intrinsic rate?
- AV node, 40–60 bpm
- Bundle of His, 20–40 bpm
- SA node, 60–100 bpm (Correct answer)
- Purkinje fibers, 60–100 bpm
Correct answer: SA node, 60–100 bpm
The sinoatrial (SA) node is the dominant pacemaker with an intrinsic firing rate of 60–100 bpm, the fastest rate in the cardiac conduction hierarchy, so it drives the normal rhythm.
Question 2: What is the primary function of the AV node in cardiac conduction?
- Initiate the cardiac impulse
- Delay impulse transmission to allow ventricular filling (Correct answer)
- Distribute the impulse through the ventricles via Purkinje fibers
- Prevent retrograde conduction from ventricles to atria
Correct answer: Delay impulse transmission to allow ventricular filling
The AV node delays the impulse by 0.12–0.20 seconds to allow atrial contraction to complete and ventricles to fill before ventricular systole begins, reflected as the PR interval on ECG.
Question 3: Which structure divides into the right and left bundle branches?
- Sinoatrial node
- AV node
- Bundle of His (Correct answer)
- Purkinje fibers
Correct answer: Bundle of His
The Bundle of His (common bundle) arises from the AV node and bifurcates into the right and left bundle branches at the superior interventricular septum.
Question 4: What is the intrinsic escape rate of AV junctional tissue if the SA node fails?
- 20–40 bpm
- 40–60 bpm (Correct answer)
- 60–100 bpm
- 100–150 bpm
Correct answer: 40–60 bpm
AV junctional tissue has an intrinsic rate of 40–60 bpm, serving as a secondary pacemaker that produces a junctional escape rhythm when the SA node fails to fire.
Question 5: In which direction does normal ventricular depolarization travel through the Purkinje network?
- From epicardium to endocardium
- Exclusively from right to left ventricle
- From endocardium to epicardium (Correct answer)
- From cardiac apex toward the base
Correct answer: From endocardium to epicardium
Normal ventricular depolarization travels from endocardium (inner wall) to epicardium (outer wall) via the Purkinje fibers, producing a narrow, organized QRS complex.
Question 6: What ECG change results from slowed conduction through the AV node?
- Widened QRS complex
- Prolonged PR interval beyond 0.20 seconds (Correct answer)
- Elevated ST segment
- Inverted T wave
Correct answer: Prolonged PR interval beyond 0.20 seconds
Slowed AV nodal conduction extends the PR interval beyond 0.20 seconds, producing first-degree AV block on the ECG without dropping any ventricular beats.
DC Dysrhythmia Pathophysiology & Electrophysiology 1
What is the normal pacemaker of the heart and its intrinsic rate?