It's just one of the many funky things that can happen when you put the needle to the groove.
For these conditions a flow separation or 'breaking' of the second or third wave downstream of the original groove was a common occurrence.
At the same time the ice just downstream of the groove actually thickens slightly.
A long non-branching coronary artery emerges from the left-hand-facing sinus (sinus 2) and runs behind the pulmonary trunk to enter the left atrioventricular groove.
The myocardium of the rudimentary right ventricle is separated by the atrioventricular groove from the muscular floor of the blind-ending right atrium.
The coronary sinus courses within the atrioventricular groove behind the left atrium to open into the right atrium.
The interventricular grooves are shallow and identifiable only by the courses of the interventricular coronary arteries.
Sub-horizontal irregular grooves across fault surface are excavator marks, not primary features.
