Absence of left atrium-coronary sinus musculature electrical connection at coronary sinus ostium unmasked by unique double coronary sinus potentials pattern.

We describe a 77-year-old man with Wolff-Parkinson-White syndrome exhibiting double coronary sinus (CS) potentials during retrograde conduction over accessory pathway (AP). The first, low-frequency potential (DP1) was first recorded in the left posterolateral region, while the second, higher frequency signal (DP2) was recorded in a lateral-to-septal direction. The two signals were fused near the left lateral wall. Successful ablation of the AP was obtained at its ventricular insertion site in the postero-septal region. The unexpectedly delayed activation of the paraseptal RA following activation of the paraseptal left atrium (DP1) can be explained by the absence of a LA-CS musculature (CSM) electrical connection at the proximal CS, which forces a detour of the activation wavefront from LA to RA via the distal CS (DP2). This is a rare case exhibiting unique double CS potentials which unmasked the absence of a LA-CSM electrical connection at CS ostium.