During coronary revascularisation involving a main vessel and a side branch, it is unclear whether ballooning of the side branch is a prerequisite for long term clinical success. Coronary physiology techniques such as Fractional Flow Reserve (FFR) provide a unique way to scientifically quantify whether a side-branch may need revascularisation following treatment of the main vessel.

Frequently it is difficult to rewire a side branch which involves passing a catheter through stents in the main vessel. This can be difficult with a conventional pressure wire. Newver systems such as the Acist Navvus Rapid Exchange FFR microcatheter runs over the regular work horse wire chosen by the operator. This means that it is possible to measure FFR more easily in heavily diseased and anatomically challenging vessels.