Mechanical Versus Manual Chest Compression For Out-of-hospital Cardiac Arrest: A Cluster Randomized Trial by Perkins, G, Lall, R, Quinn, T, Deakin, C, Cooke, M, Horton, J, Lamb, S, Slowther, A, Carson, A, Smyth, M, Whitfield, R, Williams, A, Pocock, H, Black, J, Wright, J, Han, K, Gates, S, Collaborators, PARAMEDICT