TIMI grade 3 flow in coronary arteries after thrombolysis is actually slower than normal (35.6 ± 20.8). Use of the more precise CTFC has resulted in a number of interesting observations. By using the continuous variable of CTFC, it is apparent that not all TIMI grade 3 flows are created equally, and TIMI grade 3 flow can be subdivided into a wide range of velocities, providing greater risk stratification within TIMI grade 3 flow. Flow in coronary arteries after myocardial infarction or percutaneous coronary intervention is uni-modally distributed across a broad range. Indeed, although patients often have TIMI grade 3 flow both before and after the intervention, the velocity may in fact double in these patients. Distance along coronary arteries measured using angioplasty guidewires may be combined with TIMI frame count measurements to give absolute velocity and flow assessments that are sensitive to small changes in perfusion. It is also correlated with volumetric flow and resting distal average peak velocity. The CTFC technique is a simple and inexpensive technique for calculation of coronary flow reserve, and is highly correlated ( r =0.88, P =0.0001) with coronary flow reserve measurements obtained using the Doppler guidewire. Pacing at a faster heart rate (20 beats/min) reduced the CTFC by 5 frames. Injections during diastole reduce the CTFC by 6 frames. It is therefore important to standardize use of nitrates in studies that involve CTFC measurement, or to at least confirm that nitrate use is well balanced across arms of the trial. Administration of nitrates, which cause enlargement of the artery and the volume to be filled with dye significantly, increases the CTFC by approximately 6 frames. Alterations in catheter size do not affect CTFC measurements.
#TIMI GRADE FLOW VS. TIMI RISK SCORE TRIAL#
Varying the force of dye injection may change the frame count by up to 2 frames, which is a relatively small and insignificant difference from a clinical trial perspective. Differences between observers are less than 0.75 frames and the correlation between observers is 0.97-0.99. Highly reproducible results are obtained with very low interobserver and intraobserver variability. For example, in the use of images acquired at 15 frames/s, frame counts are multiplied by a factor of 2 to derive the CTFC. Centers that use image acquisition at speeds other than the most widely used frame rate in the US of 30 frames/s need to adjust CTFC assessments accordingly. The number of frames from the first frame to the last frame when dye enters the standardized distal landmark is counted. The standardized distal landmarks are taken as the first branch of the posterolateral artery for the right coronary artery, most distal branch of the obtuse marginal branch for the circumflex, and the distal bifurcation for the LAD (also known as the 'whale's tail' branch of the LAD). The first frame taken for measurements is the frame in which dye touches both borders of the coronary artery and moves forward with at least 70% opacification of the vessel lumen. The frame count number after adjustment for vessel length is given the term 'corrected TIMI frame count'. A correction factor is required to compensate for the longer length of the left anterior descending artery (LAD) compared with the circumflex and right coronary arteries (the number of frames required for dye to traverse the LAD is divided by 1.7). In the CTFC method, the number of frames required for dye to reach a standardized distal landmark is counted.
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