The crochetage sign is an electrocardiographic pattern often observed in patients with atrial septal defect (ASD). It consists of a notch of the R wave in inferior limb leads. This early notch of the R wave in inferior leads was first observed 59 years before in a small group of patients with ostium secondum defect.
Heller et al. first studied this ECG pattern in ASD patients. Crochetage sign had sensitivity and specificity for ASD diagnosis, respectively, 73.1% and 92.6% if present in a single inferior lead, 58.1% and 97.2% if present in two leads and 27.8% and 100% if present in three inferior leads. The crochetage sign is independent of the frequency of incomplete right bundle branch block (iRBBB), but the association of iRBBB and crochetage sign increases the specificity of ASD diagnosis. Even more, the presence of crochetage pattern correlates with shunt severity, even in the presence of pulmonary hypertension but the underlying pathophysiology still remains unknown.