Right Bundle Branch Block Conduction Abnormalities(RsR’, incomplete RBBB, RBBB plus RVH)


Knowledge

Electrophysiology: Technically for right bundle branch block to be present, the QRS duration is 120 msec or greater, the R wave usually has a larger amplitude than the S wave in V 1 or V2 and the T wave vector is in the opposite direction to the QRS vector (T waves are inverted in V1 thru V3). The conduction abnormality appears as "rabbit ears" (rsR pattern) on the right side of the chest (V1,2), and the R wave complex in V 5 and V6 looks normal if the terminal S wave on the left side (V4,5,6) is disregarded.

Pathophysiology: The right bundle is a superficial and fragile structure on the right side of the septum. Conduction can be blocked or slowed by trauma (floating catheter), by increased right ventricular pressure or by ischemia or infarction. An incomplete RBBB has a QRS duration of less than 120 msec and a rsr' pattern in V1 and V2 without an R wave greater than the amplitude of the S wave. It sometimes is simply called a Rsr' pattern and usually is a normal finding but rarely is associated with an atrial septal defect. It is not necessarily a precursor of RBBB or any conduction abnormality. When left axis deviation is present, bifasicular block is said to be present due to involvement of the anterior fascicle of the left bundle. These patterns can precede complete heart block particularly when part of a myocardial infarction but can be a normal variant.


Recommendations

Right ventricular conduction patterns can be seen more frequently in youngsters and athletes but they can also be normal variants. While wide splitting of the second heart sound is often heard, fixed splitting of the second heart sound can be associated with an atrial septal defect. Remember that the abnormalities of the second heart sound must be heard in the sitting position since splitting is often wide in normals while supine. If present, an echocardiographic air contrast ("bubble") study is indicated. Any pulmonary disease process can be associated with RVCD and they can occur acutely with exacerbation of lung disease or a pulmonary embolus. Clinical correlation is necessary and then treatment of the lung disease or a VQ scan might be indicated. If the conduction abnormalities occur as part of the presentation of a MI, it becomes a "complicated MI" requiring more conservative therapy and possibly even a pacemaker if it progresses to CHB. If an exercise test is indicated due to possible coronary disease, the ST segments in the anterior leads cannot be interpreted while the other leads can be utilized. Be careful to locate the j-junction beyond the broad S wave.

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