Reliability of fractional flow reserve measurements in patients with associated microvascular dysfunction: importance of flow on translesional pressure gradient.

Fractional flow reserve (FFR) has been applied with success as a lesion-specific functional indicator of stenosis severity, at least in patients with normal microcirculation. This study sought to assess the reliability of FFR calculations in patients with associated microvascular dysfunction (e.g., post myocardial infarction, or post-MI). First, the effect of coronary flow changes on translesional pressure gradient was assessed. Therefore, intracoronary pressure and flow was recorded simultaneously across 19 non-infarct-related lesions (both pre- and postinterventional lesions with a mean diameter stenosis of 47% +/- 12%). Measurements were performed by means of a pressure and Doppler wire during maximal hyperemia and also during submaximal hyperemia induced by low-dose adenosine. The drop of coronary flow from 48 +/- 23 ml/min during maximal hyperemia to 36 +/- 18 ml/min during submaximal hyperemia was associated with a small decrease in translesional pressure gradient (from 22 +/- 12 mm Hg to 19 +/- 12 mm Hg; P = 0.02) and a small increase in the mean distal/arterial pressure ratio (Pd/Pa) going from 77% +/- 11% to 81% +/- 11% (P = 0.003). Then, intracoronary pressure and flow measurements were compared across 21 non-infarct-related lesions vs. 22 matched infarct-related lesions. For a similar angiographic stenosis severity (% DS = +/- 44%), maximal flow was 48 +/- 22 ml/min in the non-infarct arteries and 37 +/- 26 ml/min in the infarct arteries (P = 0.03), confirming the presence of severe microvascular dysfunction in infarct regions. Similar to the earlier findings, this hyperemic flow reduction in MI patients was associated with a small increase of FFR (= Pd/Pa): 79% +/- 12% in no MI vs. 83% +/- 12% in MI patients (P = 0.3). A reduction of hyperemic flow by +25%, [correction] such as can be found in patients with severely impaired microvascular function, has a limited effect on FFR calculations (+ 5%). This finding allows the application of standard FFR calculations in a more general population of ischemic heart disease, including patients with recent MI. Copyright 2001 Wiley-Liss, Inc.