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Right Bundle Branch Block 891.e3

Differential Diagnosis TREATMENT (particularly with tachycardias). Because
• Right ventricular hypertrophy Treatment Overview and Acute most dogs have sinus arrhythmia and some
VetBooks.ir • Ventricular escape rhythm General Treatment the regularity of rhythm can be a helpful Diseases and Disorders
degree of irregularity of the heart rhythm,
• Ventricular ectopy
No specific treatment is necessary for RBBB:
clue.
• Motion artifact
Initial Database • RBBB does not result in clinical or hemo- • Supraventricular rhythms (e.g., sinus rhythm,
sinus tachycardia, atrial fibrillation) respond
dynamic sequelae and therefore does not
By definition, RBBB is an electrocardiographic require treatment. to vagal maneuvers with slowing of the heart
diagnosis. • The right bundle branch is anatomically rate, even when RBBB is present. Ventricular
• Electrocardiographic characteristics of vulnerable to injury, and RBBB may be arrhythmias do not.
complete RBBB observed in otherwise normal dogs.
○ Prolonged QRS complex duration (canine Technician Tips
> 0.08 second [> 0.07 second in toy Possible Complications The QRS waveform in this benign condi-
breeds]; feline > 0.06 second) • Misdiagnosis of RBBB as premature ven- tion can be easily mistaken for a pathologic
○ Wide QRS complexes with an S wave tricular complexes (PVCs) or ventricular ventricular beat.
in leads I, II, III, and aVF and the left tachycardia can lead to treatment—and
precordial leads (CV 6 LL [V 2 ] and CV 6 LU toxicosis—with antiarrhythmic drugs. SUGGESTED READING
[V 4]) • Complete block of the right and left bundle Côté E: Electrocardiography and cardiac arrhythmias.
○ Positive QRS complexes in leads aVR, branches produces complete (third-degree) In Ettinger SJ, et al, editors: Textbook of veterinary
aVL, and CV 5RL (V 1 or rV 2) AV block (rare). internal medicine, ed 7, St. Louis, 2010, Saunders,
• Electrocardiographic characteristics of pp 1059-1087.
incomplete RBBB PROGNOSIS & OUTCOME
○ When the morphology of the QRS ADDITIONAL SUGGESTED
complex as described above is noted, RBBB is not a progressive or deleterious entity, READINGS
but the QRS duration is normal or only and prognosis is good except when associated Kittleson MD: Electrocardiography: basic concepts,
slightly prolonged, incomplete RBBB with structural heart disease, in which case diagnosis of chamber enlargement, and intraven-
is suspected. It can be challenging to prognosis is the same as that of the underlying tricular conduction disturbances. In Kittleson MD,
differentiate this finding from right disorder. et al, editors: Small animal cardiovascular medicine,
ventricular hypertrophy, and assess- Philadelphia, 1998, Mosby, pp 90-94.
ment of the ventricle size and thickness PEARLS & CONSIDERATIONS Miller MS, et al: Electrocardiography. In Fox PR, et
(e.g., echocardiographically) is usually al, editors: Textbook of canine and feline cardiology,
Philadelphia, 1999, Saunders, pp 84-86.
required. If the ventricle is structurally Comments Tilley LP: Left bundle branch block. In Tilley LP,
normal, incomplete RBBB is diagnosed The bizarre QRS morphology seen with bundle editor: Essentials of canine and feline electrocardiog-
by exclusion. branch block can be confused with ventricular raphy, Philadelphia, 1992, Lea & Febiger, pp 75-77.
ectopy.
Advanced or Confirmatory Testing • If P waves are seen and the PR interval is AUTHOR: Meg M. Sleeper, VMD, DACVIM
• Thoracic radiographs can evaluate right consistent, the complex is likely coming EDITOR: Leah A. Cohn, DVM, DACVIM
ventricular enlargement; only moderate or from a supraventricular site (and the bizarre
severe enlargement is likely to be apparent QRS morphology is due to BBB rather than
radiographically, and false-positives are likely. ventricular ectopy). However, sometimes P
• Echocardiogram can assess heart structure waves are buried and not visible, although
and function. the rhythm is supraventricular in origin

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