A Visiting Grandma Feels Short of Breath

ANSWER
This ECG shows normal sinus rhythm, a right bundle branch block (RBBB), and a left anterior fascicular block (LAFB). RBBB and LAFB are consistent with bifascicular block.

Criteria for an RBBB include a prolonged total QRS complex of 120 ms or longer and an RSR’ complex (“rabbit ears”) in lead V₁. LAFB criteria include a QRS of normal duration with an S wave greater than an R wave in leads II, III, and aVF and left-axis deviation (–48° in this case). 

The astute reader may question the disparity between RBBB and LAFB, since the criteria for the former include a prolonged QRS interval and the criteria for the latter include a normal QRS interval. It should be noted that the requirements for QRS duration for RBBB vary.

Bifascicular block (RBBB and either LAFB or left posterior fascicular block [LPFB]) is indicative of more advanced conduction system disease. However, it is not an indication for permanent pacemaker placement in an asymptomatic patient.

This patient was treated for a community-acquired right lower lobe pneumonia and a UTI.