LBBB: Old Myocardial Infarction
Report:
Sinus rhythm 64/min
Third degree AV block
Junctional escape rhythm 36/min
Left bundle branch block
QRS 0.22”
Probable old anterior infarction
Comment:
The patient had LBBB since his original infarction; the present morphology is identical to that of conducted sinus rhythm before the AV block developed. The QRS rapid descent and slurred upstroke in V1 distinguish LBBB from ventricular ectopic complexes. The QRS is very wide, in keeping with advanced myocardial disease.
The ascending limb of the R wave is notched in leads 1, aVL and V6 (sign of Chapman6) and the S wave in V4 has a notch > 0.05” (Cabrera sign7). In addition, there is an RS morphology in lead V6 – all reasonably specific but quite insensitive signs of anterior infarction in LBBB. Oddly enough, the patient had another sign – thin tall R wave in V2 four years previously (below, Fig 10a), now extinct, for unknown reasons. The frontal axis has shifted markedly to the left over that time.
One has to keep in mind, however, that junctional rhythm may differ from conducted sinus rhythm in morphology (the non-phasic aberrancy), however slightly. Alternatively, the escape rhythm in Fig 10 may originate from the right bundle branch.
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