Introduction

• The right and left bundle branches arise as bifurcations from the bundle of His, just below the level of the atrioventricular node.
• Right bundle branch block (RBBB) results from delayed or inhibited conduction along the right bundle branch or any of its more distal main ramifications.
• Left bundle branch block (LBBB) results from similar abnormalities to the main left bundle or its more distal components.
• Bundle branch blocks slow the conduction within the areas of the ventricular myocardium they supply and give rise to specific electrocardiographic findings.
• Because relative to the right bundle branch, the left bundle branch is better "developed" (ie it is thicker, ramifies more, and therefore conducts faster), it is less likely to be blocked when no organic heart disease is present. Bundle branch blocks, therfore, can be either a sign of significant underlying heart disease (LBBB) or found as an incidental finding (RBBB), potentially resulting from transient, self-limiting "fatigue" with no organic right-sided heart disease.

ECG Characteristics

Clinical significance

Treatment

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Rausch W P, Keene B K (2002) ECG of the month. Sinus tachycardia with left bundle branch block. JAVMA 220 (7), 980-981 PubMed.

Other sources of information

• Goodwin J K (2001) Electrocardiography. In: Manual of Canine and Feline Cardiology. 3rd edn. Tilley L P, Goodwin J K (eds), pp 43-70.