Effect of potential confounding factors on the thrombolysis in myocardial infarction (TIMI) trial frame count and its reproducibility.

BACKGROUND The potential factors that introduce variability into TIMI frame count (TFC) have not been systematically investigated. The goal of this study was to determine if nitrate use, dye injection rate, catheter size, the phase of the cardiac cycle in which dye is injected, or heart rate affect the TFC and to investigate the reproducibility of the TFC. METHODS AND RESULTS The dye injection rate was increased 1 mL/s, and angiography was repeated. A coronary angiogram was taken first with an 8F catheter and then with a 6F catheter. After taking angiograms, intracoronary nitrate was given to the patient, and the second angiography was performed. Basal heart rate was increased 20 beats/min, and angiography was repeated. Dye injection was performed at the beginning of systole and diastole. The TFC was not significantly changed by increasing the dye injection rate (P=0.467) or by changing catheter size (P=0.693). Nitrate administration significantly increased the TFC from 26.4+/-11.9 to 32.8+/-13.3 frames (P<0.001). Dye injection at the beginning of diastole significantly decreased the TFC from 30.1+/-8.8 to 24.4+/-7.9 frames (P<0.001) for the left coronary artery and from 24.16+/-4.49 to 21. 24+/-4.45 frames (P<0.001) for the right coronary artery. Increasing heart rate significantly decreased the TFC from 30.4+/-6.1 to 25. 3+/-7.2 frames (P<0.001). Intraobserver and interobserver reproducibility of the TFC was good (mean difference, 1.33+/-1.24 and 2.57+/-1.72 frames, respectively). CONCLUSIONS Nitrate use, heart rate, and the phase of the cardiac cycle in which dye is injected had significant effects on the TFC. Therefore, studies comparing TFC need to consider these factors, and the use of nitrates should be either standardized or randomized.