What is it mean that angioplasty of the diagonal branch artery can or may compromise the lad ? thank you.

Angioplasty: In an ostial or proximal stenosis affecting a diagonal branch of the LAD dilation necessarily extends proximally and into the LAD thus risking the more major vessel via a variety of issues including a "snowplough" effect; experienced intervetionalists can handle such potential procedural complications.

A fork in the road: The Dx comes off the LAD. A branch point. Usually the stenosis or blockage is near the bifurcation. If a PTCA or ballooning is done near the beginning of the diagonal, it can push tissue across to the adjacent vessel, the LAD.