Precordial Masquerading Bundle Branch Block

Report :

Atrial fibrillation with rapid ventricular response 138/min

Northwest axis +260o

Right bundle branch block

(Probable) left anterior hemiblock

Possible old anterior myocardial infarction

Nonspecific ST/T changes

Positive concordant precordial pattern due to masquerading bundle branch block

Comment :

The rhythm is sufficiently irregularly irregular to establish the diagnosis of atrial fibrillation over, say, monomorphic but irregular ventricular tachycardia. The axis and the QRS complexes, however, are bizarre enough to include VT in the differential diagnosis. Another cause of bizarre complexes is anomalous conduction : this could be WPW ‘ A ‘ with totally anomalous conduction. This is, like VT, a classical cause of concordant precordial pattern. Against it is the (relatively, for WPW) slow ventricular response and absence of any normally or more normally conducted beats.

What is left is the masquerading bundle branch block. It is due to RBBB with a very high degree of LAHB. The masquerade is that of RBBB looking like LBBB in frontal leads (standard type) or precordial leads, as here (precordial type). The two types may be combined but here the extreme axis precludes certainty and may indicate, additionally, an old lateral infarction. There may have been a septal infarction as well, as some V1 complexes have a shallow but 0.04 sec long Q waves – beyond the Q waves that LAHB may contribute by itself.

Another recording is shown in Fig 110a.

Two more examples of masquerading BBB, from different patients, are shown below, in Figs 110 b and 110c.

110a. Another recording of AF. 110b. Standard + precordial masquerading BBB in a 66 year old outpatient with controlled heart failure. 110c. Standard masquerading BBB in a 59 year old man with anterior infarction. The precordial form is “spoiled” by the anteroseptal QR morphology. 111. 87 year old woman on digoxin, diuretics and nitrates admitted from a geriatric “village” with episodic bradycardia and hypotension. Parts of her Holter monitor study are shown below and on the next two pages.