Computer-assisted mitral valve measurement using an optical tracking system - a new approach for planning of mitral valve reconstructions

Objectives: Intraoperative mitral valve analysis is mandatory for a successful mitral valve repair since it helps the surgeon to choose the surgical strategy by improving preoperative imaging findings. We developed a new method for mitral valve analysis based an optical tracking system that improves quantitative assessment of the complex 3D valve anatomy.

Methods: The tips of specially developed surgical instruments were tracked by an infrared stereo camera system (NDI Polaris™) in order to localize 16 anatomical landmarks. The data were processed by our own plugin in the open-source software MITK to create an anatomical geometric model of mitral valve including annulus, leaflets and chordae. Four surgeons made measurements on excised porcine hearts to assess feasibility, accuracy and variability. Annulus area, longitudinal and anterolateral diameters, coaptation line and distances between anterolateral and posteromedial papillary muscles to coaptation line were assessed.

Results:

mean ± SD	annulus area (mm2)	longitudinal diameter (mm)[point 2 - 5]	antero-lateral diameter (mm) [point 7 - 8]	distance anterolateral papillary muscle (mm) [point 11 - 15]	distance posteromedial papillary muscle (mm) [point 13 - 16]
surgeon 1	741 ± 11	32,6 ± 0,7	27,0 ± 1,0	7,3 ± 2,5	11,7 ± 1,4
surgeon 2	629 ± 15	30,9 ± 1,9	25,3 ± 1,5	12,9 ± 3,0	12,3 ± 1,5
surgeon 3	628 ± 105	34,6 ± 3,3	24,0 ± 1,4	7,2 ± 0,7	16,4 ± 0,3
surgeon 4	462 ± 30	28,6 ± 0,6	19,7 ± 1,6	9,3 ± 2,8	10,1 ± 0,9
interexpert	615 ± 114	31,7 ± 2,5	24,0 ± 3,1	9,2 ± 2,7	12,6 ± 2,7
95%-CI	543;688	29,9;33,5	22,1;26,0	7,1;11,2	11,0;14,3

These data (see table) were used for 3D-reconstruction of the mitral valve annulus and its relation to the subvalvular apparatus, as exemplary shown in the screenshot.

Fig. 1: screenshot

Conclusion: Anatomical parameters tracked by our infrared stereo camera system showed good accuracy and reproducibility. These computational models allow a more precise quantitative assessment of mitral valve geometry and present a new method for intraoperative mitral valve analysis providing precise sizing of anatomy that may:

1) guide the surgeon to choose the most suitable reconstruction procedure,

2) provide a learning tool and 3) improve outcome of mitral valve repair.