Rate-Dependent LBBB
Report:
Sinus rhythm 90/min
SVEBs, blocked, in bigeminy
Left bundle branch block, rate-dependent
Comment:
The blocked atrial extrasystoles are discretely etched on the onset of the T wave. A sustained run could be mistaken for sinus bradycardia 50/min.
Complexes are conducted normally only in the pauses created by the SVEBs. The last normal complex, in the bottom strip, does not have a blocked SVEB in its wake (its T wave is quite smooth) and the LBBB reappears for the rest of the strip.
Below (Fig 77a) is another strip showing SVEB-mediated transition from LBBB to normal ventricular conduction.
Fig 77a.
Fig 78. 71 year old man with congestive cardiomyopathy (LV 7.2 cms) and 90% left circumflex artery stenosis. His ECG contains three FLBs with unusual consequences.
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