When Does a Left Anterior Descending Stenosis Alter Flow Across a Left Main Segment?: Interpreting Left Main Fractional Flow Reserve With Downstream Obstruction

M. J. Kern
2013 Circulation. Cardiovascular Interventions  
A ttributed 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
more » ... atio 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. 1,2 Article see p 161 Such 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. 3 Now for the not-so simple part, interpreting LM FFR in the more complicated angiographic scenario where there is downstream stenoses (ie, LM/LAD), the combination of LM/LAD stenoses requires understanding FFR and the interplay of 2 new conditions: (1) lesions acting in series and (2) potential reduction of the maximal LM blood flow (and myocardial bed size), as a function of the degree of obstruction of the downstream lesion. For serial lesions, an accurate FFR requires that maximal hyperemia be achieved across a target lesion. Each of the serial lesions blunts the hyperemia of the other, and thus simple pressure ratios (without using a distal coronary balloon occlusion pressure) 4,5 cannot produce accurate individual FFR values. In clinical practice, the summed FFR across both lesions (LM+LAD=FFR epicardial ) determines the need to treat; and a pressure pullback recording tells us which lesion to treat. The lesion with the largest pressure (ΔP, not FFR) is treated first, and then FFR across the remaining lesion determines the next treatment decision. Such a method can be used to assess serial LM with LAD disease, but this approach engenders a downside: accepting stenting of the unprotected LM, if after treating the LAD the LM FFR becomes abnormal. (Circ Cardiovasc Interv. 2013;6:128-130.)
doi:10.1161/circinterventions.113.000308 pmid:23591419 fatcat:yumdshv6lrdozg2accfbaq6kpy