What is the Difference Between Junctional and Idioventricular Rhythm

The key difference between junctional and idioventricular rhythm is that pacemaker of junctional rhythm is the AV node while ventricles themselves are the dominant pacemaker of idioventricular rhythm.

Sinoatrial node or SA node is a collection of cells (cluster of myocytes) located in the wall of the right atrium of the heart. Functionally, SA node is responsible for the rhythmic electrical activity of the heart. It is the natural pacemaker of the heart. An impulse created by the SA node causes two atria to contract and pump blood into two ventricles. When the SA is blocked or depressed, secondary pacemakers (AV node and Bundle of His) become active to conduct rhythm. Junctional and ventricular rhythms are two such rhythms. AV node acts as the pacemaker and creates junctional rhythm. When both the SA node and AV node fail to conduct rhythms, ventricles act as their own pacemaker and conduct idioventricular rhythm.

CONTENTS

1. Overview and Key Difference
2. What is Junctional Rhythm
3. What is Idioventricular Rhythm
4. Similarities –  Junctional and Idioventricular Rhythm
5. Junctional vs Idioventricular Rhythm in Tabular Form
6. Summary – Junctional vs Idioventricular Rhythm

What is Junctional Rhythm?

Junctional rhythm is an abnormal rhythm that starts to act when the Sinus rhythm is blocked. In an ECG, junctional rhythm is diagnosed by a wave without p wave or with inverted p wave. Junctional rhythm originates from a tissue area of the atrioventricular node. Therefore, AV node is the pacemaker of junctional rhythm. Due to junctional rhythm, atria begin to contract. But it does not occur in the normal fashion. During junctional rhythm, the heart beats at 40 – 60 beats per minute.

There are four types of junctional rhythms as junctional rhythm, accelerated junctional rhythm, junctional tachycardia, and junctional bradycardia. In accelerated junctional rhythm, the heartbeat will be 60 – 100 beats per minute. In junctional tachycardia, it is higher than 100 beats per minute, while in junctional bradycardia, it is lower than 40 beats per minute.

What is Idioventricular Rhythm?

Idioventricular rhythm is a slow regular ventricular rhythm. The heart beats at a rate of less than 50 bpm. It is also characterized by the absence of a p wave and a prolonged QRS interval. Idioventricular rhythm is generated when both the SA node and AV node are suppressed due to structural or functional damages. Ventricles themselves act as pacemakers and conduct rhythm. Accelerated idioventricular rhythm is a type of idioventricular rhythm during which the heart rate goes to 50-110 bpm. During ventricular tachycardia, ECG generally shows a rate greater than 120 bpm.

Idioventricular rhythm is a benign rhythm, and it does not usually require treatment. One of the causes of idioventricular rhythm is heart defect at birth. Drugs can also cause idioventricular rhythm. The major reason can be an advanced or complete heart block.

What are the Similarities Between Junctional and Idioventricular Rhythm?

• Junctional and idioventricular rhythms are cardiac rhythms.
• They originate mainly when the sinus rhythm is blocked.
• Both originate due to secondary pacemakers.
• The rhythm is regular in both rhythms.
• Both rhythms are benign.
• They can be diagnosed by an ECG.
• Patients with junctional or idioventricular rhythms may be asymptomatic.

What is the Difference Between Junctional and Idioventricular Rhythm?

Junctional rhythm is an abnormal cardiac rhythm caused when the AV node or His bundle act as the pacemaker. Idioventricular rhythm is a cardiac rhythm caused when ventricles act as the dominant pacemaker. So, this is the key difference between junctional and idioventricular rhythm. Junctional rhythm can be without p wave or with inverted p wave, while p wave is absent in idioventricular rhythm.

The below infographic lists the differences between junctional and idioventricular rhythm in tabular form for side by side comparison.

Summary – Junctional vs Idioventricular Rhythm

SA node is the default natural pacemaker of our heart and causes sinus rhythm. Sinus rhythm is the rhythm of our heartbeat. Junctional and idioventricular rhythms are two cardiac rhythms generating as a result of SA node dysfunction or the sinus rhythm arrest.  Both arise due to secondary pacemakers. AV node acts as the pacemaker during the junctional rhythm, while ventricles themselves act as the pacemaker during the idioventricular rhythm. Both can be diagnosed by an ECG. Thus, this is the summary of what is the difference between junctional and idioventricular rhythm.

Reference:

1. Gangwani, Manesh Kumar. “Idioventricular Rhythm.” StatPearls [Internet]., U.S. National Library of Medicine, 7 Apr. 2021.
2. Hafeez, Yamama. “Junctional Rhythm.” StatPearls [Internet]., U.S. National Library of Medicine, 19 July 2021.

Image Courtesy:

1. “Junctional Tachycardia” By James Heilman, MD – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Aivr (CardioNetworks ECGpedia)” By CardioNetworks: [ ] – CardioNetworks: Aivr.jpg (CC BY-SA 3.0) via Commons Wikimedia