Positive Concordant Pattern: Masquerading BBB

Report:

Sinus rhythm

Left atrial abnormality

Possible right atrial abnormality

First degree AV block

PR interval 0.22”

Alternating atrial (?sino-atrial) pacemaker (rhythm strip)[!xe "Alternating atrial pacemaker!]

Atrial bigeminy

Right bundle branch block

Left anterior hemiblock

Masquerading bundle branch block

Standard + precordial form

Old anterior infarction

Comment:

This is a case of RBBB with high-grade LAHB that has come to resemble LBBB in both the frontal and left precordial leads. As always, lead V1 provides the correct diagnosis of basic RBBB: all the delay is in the right ventricular (positive) territory of that lead. The masquerade can be confined to only one set of leads, usually the limb leads (standard form); in this case it is present in both.

This is also one of the causes of positive concordant precordial pattern. It is easy to see than an SVT with this morphology would “pass” for a VT on morphological grounds. In AF (Fig 14a), only the relatively slow ventricular rate and the Q wave in V6 distinguish it from WPW ‘A’ conduction.

Fig 14a. AF.

Fig 15. 73 year old man with diabetes, cardiomegaly and peripheral vascular disease. He sustained an MI 12 years previously and is admitted for carotid endarterectomy.