"Crochetage" (Notch) on R wave in inferior limb leads: A new independent electrocardiographic sign of atrial septal defect. Heller J, et al. JACC 1996;27:877-882
Extract from above article:
"Crochetage" is a notch near the apex of R wave in inferior limb leads.
First reported in 1959 in 11 pts. with ASD. Mechanism of production of this crochetage is not known.
1) Crochetage is independent of Incomplete RBBB (iRBBB) seen in V1 for the following reasons:
(i) Crochetage may be present without iRBBB pattern
(ii) Crochetage disappears in immediate postoperative period while iRBBB - which is due to chronic RV volume overload persists longer
(iii) Crochetage always involves the first 80 ms of R wave, while iRBBB involves the last part of R wave.
Examples from 2 patients:Disappearance of "crochetage" 3 days after surgery for ASD:Crochetage is not unique to ASD...and is noted in normal children too!
But, it is highly specific (92-100%) for ASD and for other conditions:
For ASDs, crochetage is not any more sensitive than iRBBB.