The relationship between corrected TIMI frame count and myocardial fractional flow reserve

Thrombolysis in myocardial infarction (TIMI) frame count (TFC) is a reproducible, objective and quantitative index of coronary flow that allows standardization of TIMI flow grades. After myocardial infarction (MI), hyperemic and basal flows decrease in the infarct region due to residual stenosis and increased resistance in the microvasculature subtended by this infarct-related artery (IRA). Myocardial fractional flow reserve (FFRmyo) is a lesion-specific index for epicardial stenosis. FFRmyo can also be used as a criterion for assessing the success of revascularization therapy. The aim of this study was to investigate the relationship between improvement of the corrected TFC (CTFC) and change in FFRmyo, which were determined in the IRA in patients with recent MI who underwent mechanical revascularization.

Forty-one patients (28 male; age, 58.3 +/- 12.3 years) early after MI with > 60% narrowing in the IRA who underwent stent implantation for this residual stenosis were included in this study. After angiography, a fiber-optic pressure monitoring guidewire was positioned distal to the stenosis to be dilated. Means of aortic (Pa) and distal (Pd) pressures were recorded simultaneously under baseline and hyperemic conditions. FFRmyo (Pd/Pa) was determined under adenosine hyperemia before and after stent implantation, as was TFC. Percentage of the improvement in the CTFC and FFRmyo was calculated for each lesion. The first frame used for TFC was defined by a column of contrast extending across > 70% of the arterial lumen and last frame counted was that in which contrast first appeared in the distal, pre-defined landmark branches for each vessel. CTFC was calculated for the LAD by dividing TFC of the LAD by a factor of 1.7.

Eighteen patients had LAD, 10 had CX and 13 had RCA lesions. After stent implantation, the CTFC improved by 41% (from 32.3 +/- 3.4 to 19.2 +/- 2.1; p < 0.0001) and FFRmyo improved by 69% (from 0.53 +/- 0.11 to 0.90 +/- 0.15; p < 0.0001). There was a statistically significant correlation between the change in FFRmyo and improvement in the TFC (r = 0.85).

Improvement in CTFC is associated with change in FFRmyo in the IRA undergoing mechanical revascularization. After mechanical revascularization, CTFC decreases proportionally to improvement of the FFRmyo. These two parameters support each other in terms of successful revascularization and this relationship shows the recruitability of CTFC in terms of FFRmyo as well.