Right bundle branch block

Right bundle branch block
ECG characteristics of a typical RBBB showing wide QRS complexes with a terminal R wave in lead V1 and slurred S wave in lead V6.
Classification and external resources
Specialty	Cardiology
ICD-10	I45.1
ICD-9-CM	426.4
DiseasesDB	11620
eMedicine	ped/2500

A right bundle branch block (RBBB) is a heart block in the electrical conduction system.^[1]

During a right bundle branch block, the right ventricle is not directly activated by impulses travelling through the right bundle branch. The left ventricle however, is still normally activated by the left bundle branch. These impulses are then able to travel through the myocardium of the left ventricle to the right ventricle and depolarize the right ventricle this way. As conduction through the myocardium is slower than conduction through the Bundle of His-Purkinje fibres, the QRS complex is seen to be widened. The QRS complex often shows an extra deflection which reflects the rapid depolarisation of the left ventricle followed by the slower depolarisation of the right ventricle.

In most cases right bundle branch block has a pathological cause though it is also seen in healthy individuals.^[2]

Diagnosis

Normal electrical conduction system of the heart (Schematic). All myocardial segments are excited almost simultaneously (purple staining).

1. Sinoatrial node
2. Atrioventricular node

Conduction in RBBB (Schematic): With a blockage in the right bundle branch (red), the left ventricle is excited in time (purple), while the excitation of the right ventricle takes a detour via the left bundle branch (blue arrows).

The criteria to diagnose a right bundle branch block on the electrocardiogram:

• The heart rhythm must originate above the ventricles (i.e. sinoatrial node, atria or atrioventricular node) to activate the conduction system at the correct point.
• The QRS duration must be more than 100 ms (incomplete block) or more than 120 ms (complete block)^[3]
• There should be a terminal R wave in lead V1 (e.g. R, rR', rsR', rSR' or qR)
• There should be a slurred S wave in leads I and V6.

The T wave should be deflected opposite the terminal deflection of the QRS complex. This is known as appropriate T wave discordance with bundle branch block. A concordant T wave may suggest ischemia or myocardial infarction.

A mnemonic to distinguish between ECG signatures of left bundle branch block (LBBB) and right, is WiLLiaM MaRRoW; i.e., with LBBB, there is a W in lead V1 and an M in lead V6, whereas, with RBBB, there is an M in V1 and a W in V6.

• 
  RBBB with associated first degree AV block
• 
  RBBB with associated tachycardia
• 
  RBBB

Causes

An atrial septal defect is one possible cause of a right bundle branch block.^[4] In addition, a right bundle branch block may also result from Brugada syndrome, right ventricular hypertrophy, pulmonary embolism, ischaemic heart disease, rheumatic heart disease, myocarditis, cardiomyopathy or hypertension.

Epidemiology

Prevalence of RBBB increases with age.

Treatment

The underlying condition may be treated by medications to control hypertension or diabetes, if they are the primary underlying cause. If coronary arteries are blocked, an invasive coronary angioplasty may relieve the impending RBBB.^[5]

See also

• Bundle branch block
• Left bundle branch block

References