Bunny Ear Sign in ECG

1. What is the Bunny Ear Sign?

The Bunny Ear Sign refers to the RSR′ pattern seen most prominently in lead V1 on ECG, commonly indicating Right Bundle Branch Block (RBBB).

2. Main condition associated?

This sign is most commonly associated with Right Bundle Branch Block (RBBB), either complete or incomplete.

3. Meaning of R and R′ waves?

The initial R reflects septal depolarization; the R′ represents delayed depolarization of the right ventricle.

4. Which is taller: R or R′?

The R′ wave is usually taller in lead V1, giving the ‘bunny ear’ appearance.

5. QRS duration in complete RBBB?

QRS duration exceeds 120 ms in complete RBBB with Bunny Ear morphology.

6. Incomplete RBBB criteria?

Shows a similar RSR′ pattern but with QRS duration between 100–120 ms.

7. Differential diagnostic value?

Helps differentiate SVT with aberrancy from Ventricular Tachycardia.

8. Lead I finding in RBBB?

A wide or slurred S wave is commonly seen in lead I due to delayed RV activation.

9. T wave behavior in V1?

In RBBB, the T wave in lead V1 is usually inverted due to discordant repolarization.

10. Most useful ECG leads?

The Bunny Ear Sign is best seen in horizontal (precordial) leads, especially V1 and V2.

11. Mimics to consider?

Brugada syndrome, ventricular pacing, and artifact must be ruled out as mimics.

12. Bunny Ear in ventricular pacing?

Paced rhythms may produce broad R waves in V1 resembling Bunny Ear morphology.

13. Electrical axis in isolated RBBB?

Axis is typically normal in isolated RBBB unless coexisting with RV hypertrophy (RAD).

14. Is Bunny Ear always pathologic?

No, it can be benign in asymptomatic individuals, especially in athletes.

15. Seen in LBBB?

No, LBBB affects V5–V6 and does not produce an RSR′ pattern in V1.

16. Conduction delay represented?

The R′ reflects delayed conduction through the right ventricle via the Purkinje system.

17. Acute cause of transient Bunny Ear?

Acute pulmonary embolism can transiently cause RBBB and Bunny Ear due to right heart strain.

18. V1 findings in complete RBBB?

V1 shows a prominent R′ and QRS > 120 ms, classic for complete RBBB.

19. Bunny Ear in athletes?

Benign RBBB with Bunny Ear morphology may be a normal finding in well-trained individuals.

20. Role in arrhythmia differentiation?

Helps distinguish aberrant SVT from ventricular arrhythmias by recognizing bundle branch patterns.

#	Advanced Point
1	The Bunny Ear Sign refers to an RSR′ pattern most commonly seen in lead V1.
2	It is a hallmark of Right Bundle Branch Block (RBBB), both complete and incomplete forms.
3	The first R wave represents early septal depolarization, while R′ reflects delayed right ventricular activation.
4	The R′ wave is typically taller than the initial R in lead V1, forming the ‘bunny ear’ appearance.
5	QRS duration > 120 ms indicates a complete RBBB when Bunny Ear pattern is present.
6	An incomplete RBBB shows a similar RSR′ but with QRS duration between 100–120 ms.
7	The Bunny Ear Sign helps distinguish SVT with aberrancy from ventricular tachycardia.
8	RBBB leads to a wide S wave in leads I and V6, often with slurred morphology.
9	The T wave is usually inverted in lead V1 due to repolarization discordance.
10	The pattern is most prominent in the horizontal plane, especially V1 and V2 leads.
11	Bunny Ear appearance must be differentiated from patterns seen in Brugada syndrome or ventricular pacing.
12	In some ventricular paced rhythms, the QRS morphology mimics Bunny Ears due to similar conduction delays.
13	The axis remains normal in isolated RBBB unless accompanied by RVH (causing right axis deviation).
14	Clinical correlation is crucial — RBBB with Bunny Ear pattern may be benign or pathological.
15	Bunny Ear pattern does not occur in Left Bundle Branch Block, which alters V5–V6 instead.
16	The R′ deflection indicates delayed conduction through the right ventricular Purkinje system.
17	Bunny Ear sign may appear transiently in acute pulmonary embolism, due to acute right heart strain.
18	A prominent R′ in V1 with QRS prolongation should raise suspicion of complete RBBB.
19	Some athletes may exhibit benign RBBB patterns with Bunny Ear morphology on ECG.
20	Recognizing the Bunny Ear Sign assists in distinguishing conduction delays from true arrhythmias.

Bunny Ear Sign in ECG

ECG criteria for a right bundle branch block include the following:

QRS duration greater than 120 milliseconds
rsR’ “bunny ear” pattern in the anterior precordial leads (leads V1-V3)
Slurred S waves in leads I, aVL and frequently V5 and V6

Common Causes of RBBB:

Category	Examples
🔹 Structural Heart Disease	– Ischemic heart disease (especially anterior MI) – Cardiomyopathies (dilated, hypertrophic) – Valvular heart disease (e.g., aortic stenosis)
🔹 Pulmonary Causes	– Pulmonary embolism (PE) – Chronic lung disease (e.g., COPD, cor pulmonale) – Pulmonary hypertension
🔹 Congenital Conditions	– Atrial septal defect (especially secundum type) – Tetralogy of Fallot – Other congenital heart defects
🔹 Post-Intervention	– Cardiac surgery (e.g., valve replacement) – Catheter ablation – Right heart catheterization
🔹 Degenerative Conduction Disease	– Lenègre’s or Lev’s disease – Age-related fibrosis of conduction tissue
🔹 Electrolyte / Metabolic	– Hyperkalemia (less common) – Drug toxicity (e.g., flecainide, beta-blockers)
🔹 Normal Variant	– May be seen in asymptomatic individuals, especially in younger people or athletes (less common than LBBB as benign)

🔍 Key ECG Features of RBBB:

QRS duration ≥ 120 ms (wide QRS)
RSR’ (“bunny ears”) in V1–V3
Wide, slurred S waves in leads I and V6
Delayed right ventricular activation

Bunny Ear Sign in ECG