When Does a Left Anterior Descending Stenosis Alter Flow Across a Left Main Segment?

Attributed to Albert Einstein, the saying, “Everything should be made as simple as possible, but not simpler,” embodies a concept that certainly applies to our understanding and interpretation of fractional flow reserve (FFR) across the most clinically important stenosis interventionalists encounter, the left main (LM) stenosis. Remarkable technical advances supported by multicenter, long-term outcome studies have validated FFR for daily use in the cardiac catheterization laboratory. FFR, the ratio of coronary pressure beyond a stenosis to the aortic pressure (representing the normal coronary pressure in the absence of a stenosis), measured during maximal hyperemia (ie, minimal myocardial bed resistance) identifies the ischemic potential of the lesion. In practice, FFR guidance for multivessel percutaneous coronary intervention compared with angiographic guidance alone produces better clinical and economic outcomes.1,2Article see p 161Such as occurs with all diagnostic testing in medicine, the correct interpretation of results depends not only on the quality of the testing method, but also on the clinical circumstances under which the test is conducted. The same principle applies to FFR. Measuring FFR across an LM stenosis without disease in its branches is relatively simple. The pressure wire is advanced beyond the narrowing into the unobstructed branches, either the left anterior descending (LAD) or the circumflex (CFX) artery, and hyperemic coronary and aortic pressure ratios are computed as FFR. A few caveats for obtaining an accurate FFR include correct zeroing and equilibration of pressures, ensuring the guide catheter is not obstructing LM flow, and administering an adequate dose of adenosine (Table). For the slightly more complicated scenario of a distal LM bifurcation lesion, one should measure FFR in both branches. In either case, LM lesions treated medically for FFR >0.80 are associated with excellent 5-year major adverse cardiac event rates.3Now for the not-so simple …