Quantitative optical frequency domain imaging assessment of in-stent structures in patients with ST-segment elevation myocardial infarction: impact of imaging sampling rate.

Background: The impact of the sampling rate (SR) of optical frequency domain imaging (OFDI) on quantitative assessment of in-stent structures (ISS) such as plaque prolapse and thrombus remains unexplored.
Methods and Results: OFDI after stenting was performed in ST-segment elevation myocardial infarction (STEMI) patients using a TERUMO OFDI system (Terumo Europe, Leuven, Belgium) with 160 frames/s and pullback speed of 20 mm/s. A total of 126 stented segments were analyzed. ISS were classified as either attached or non-attached to stent area boundaries. The volume, mean area and largest area of ISS were assessed according to 4 frequencies of SR, corresponding to distances between the analyzed frames of 0.125, 0.25, 0.50 and 1.0 mm. ISS volume was calculated by integrating cross-sectional ISS areas multiplied by each sampling distance using the disk summation method. The volume and mean area of ISS became significantly larger, while the largest area became significantly smaller as sampling distance became larger (1.11 mm(2) for 0.125 mm vs. 1.00 mm(2) for 1.0 mm, P for trend=0.036). In addition, variance of difference was positively associated with increasing width of sampling distance.
Conclusions: Quantification of ISS is significantly influenced by the applied frequency of SR. This should be taken into account when designing future OFDI studies in which quantitative assessment of ISS is critical for the evaluation of STEMI patients.