How critical is frame selection in quantitative coronary angiographic studies?

To analyse quantitatively a coronary arterial segment from a cineangiogram, and end-diastolic or neighbouring frame is usually selected. However, different cardiologists may select other (although usually neighbouring) frames, even when the same selection criteria are followed. It is also possible that the frames are selected from different cardiac cycles. In this study the effects of such phase shifts on the reproducibility of the quantitative measurements were studied. In a total of 38 consecutive patient films obtained at a filmspeed of 25 frames s^-1, the frame φ demonstrating the severity of a lesion optimally as judged by a senior cardiologist, the three preceding frames, the three following frames and one frame exactly one cycle prior to or following frame φ were selected; frame φ was always chosen in the end-diastolic phase of the cardiac cycle. In each film one coronary arterial segment with a focal lesion was analysed quantitatively in these total of 8 frames with the Cardiovascular Angiography Analysis System (CAAS). No significant differences were found in the mean difference and the standard deviations of the differences (variabilities) in the obstruction diameter, interpolated reference diameter, percent diameter stenosis, extent of the obstruction and area of atherosclerotic plaque obtained in the various frames with respect to frame φ. Therefore, it may be concluded that the selection of a cineframe for quantitative analysis in the end-diastolic phase of the cardiac cycle is not very critical. It is argued that the quality of mixing of the contrast agent in the arterial segment is a major source of the observed variations; filling artefacts are potentially present in each of the selected frames. For practical purposes, minimal threshold values for the changes in the obstruction parameters based on 95% confidence levels can be calculated at the individual patient level and at the group level for the exclusion or inclusion of possibly occurring changes in coronary vasomotor tone.