Fat QRS Complexes

Report:

Sinus rhythm 1

First degree AV block (PR 0.24”) 1

Right bundle branch block (QRS 0.20”) 2

VEBs ? junctional premature beats (QRS 0.20”, one narrower 0.12”) 1

Demand pacemaker 2

LBBB morphology (QRS 0.20”) 0

Fusion beats (narrowest QRS 0.16”, shortest PR 0.10”!) 3

Comment:

The QRS duration correlates, in a general way, with the myocardial disease responsible for the conduction delay. In this example, the RBBB, the VEBs and the paced beats are all remarkably prolonged. The fusion beats are somewhat narrower at 0.16”. The ninth beat in the fourth strip, however, is relatively narrow at about 0.12”. It is not a fusion beat, since no P wave or pacing spike precede it at a suitable interval. It’s most likely a VEB that appears narrow in this lead but whose true girth would be revealed in another.

Normally, the fusion PR interval should not be more than 0.06” shorter than the basic PR interval - 0.06” being sufficient to depolarise the ventricles and exclude any newcomers. This situation is different, with the AV and ventricular conduction both slowed down. The converse is seen below, in the third beat of the bottom strip: what should really be a pseudofusion beat, with the pacemaker spike falling 0.04” after the onset ( Q wave) of the QRS, some fusion still takes place. Three pseudofusion beats follow.

It is often helpful to cover the QRSs and observe the ST/T variation in fusion, or the lack of it in pseudofusion.

There is no evidence of pacemaker malfunction.

Fig 83. 79 year old man in ICU following CABGs.