Clinical significance of conduction velocity orientation vectors on cardiac mapping surfaces

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Foundation. Main funding source(s): This work was supported by the Lefoulon Delalande Foundation OBJECTIVE: Electroanatomical maps using automated conduction velocity (CV) algorithms are now being calculated using 2D mapping tools. The basis of substrate-based functional assessment is to detect slow zones or slow CV of which isochronal late activation mapping (ILAM) is now commonly performed. We studied the accuracy of mapping surface 2D CV, compared to the 3D vectors, and the influence of mapping resolution in non-scarred animal and human heart models. METHODS: Two models were used: a healthy porcine Langendorff model with transmural needle electrodes and a computer stimulation model of the ventricles built from an MRI-segmented, excised human heart. Local activation times (LAT) within the 3D volume of the mesh were used to calculate true 3D CVs (direction and velocity) for different pixel resolutions ranging between 500 mm – 4 mm (3D CVs). CV was also calculated for endocardial surface-only LATs (2D CV). RESULTS: In the experimental model, surface (2D) CV was faster on the epicardium (0.509 m/s) compared to the endocardium (0.262 m/s, Figure 1). In stimulation models, 2D CV significantly exceeded 3D CVs across all mapping resolutions and increased as resolution decreased (Figure 2). 3D and 2D left ventricle CV at 500mm resolution increased from 429.2±189.3 mm/s to 527.7±253.8 mm/s (P<0.01), respectively with modest correlation (R=0.64). Decreasing the resolution to 4mm significantly increased 2D CV and weakened the correlation (R=0.46). The majority of CV vectors were not parallel (<30°) to the mapping surface providing a potential mechanistic explanation for erroneous LAT-based CV over-estimation. CONCLUSION: Ventricular CV is overestimated when using 2D LAT-based CV calculation of the mapping surface and is significantly compounded by mapping resolution. These findings have implications for the current methodology of functional substrate assessment with ILAM and surface CV assessment. [Figure: see text] [Figure: see text]