Essentials of quantitative angiography for bifurcation lesions

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Introduction Visual estimation of vessel diameter and lesion length supported by balloon predilation (known length and diameter) has been a common strategy, when final stent implantation is anticipated. Quantitative coronary angiography (QCA) being highly accurate and reproducible can refine the visual estimate and provide several important parameters which have been accepted as surrogate endpoints in many clinical studies on new PCI technologies. However, stand-alone percent diameter/area stenosis measurements derived from conventional (single-vessel) twodimensional (2-D) QCA analysis fail to predict the functional significance of coronary vessel obstruction. This holds even more for the analysis of bifurcation lesions, where the discrepancy in vessel size proximal and distal to the carina (step-down phenomenon) results in stenosis being overestimated in the distal branches and underestimated in the proximal main vessel (PMV). Dedicated 2-D bifurcation software algorithms have been developed recently in order to make up for the shortcomings of 2-D singlevessel QCA by reporting angiographic parameters separately for the PMV and each of the distal branches. The proximal and the distal branches of a single bifurcation often do not lie on a single plane; thus vessel overlap and foreshortening together with the lesion eccentricity may compromise the results of 2-D angiographic analysis. In the last 10 years evidence has accumulated that three dimensional (3-D) angiographic reconstruction is accurate, precise and reproducible. Reduced time requirements for a single 3-D reconstruction facilitates realtime analysis; single-vessel as well as bifurcation lesions can be reconstructed and analysed via dedicated QCA algorithms. In this short review we will attempt to emphasise the relative merits of bifurcation QCA compared to visual assessment, report on the options currently available for 2-D and 3-D bifurcation QCA analysis and outline the challenges yet to be addressed.