Prehospital randomised assessment of a mechanical compression device in out-of-hospital cardiac arrest (PARAMEDIC): a pragmatic, cluster randomised trial and economic evaluation by Gates, S, Lall, R, Quinn, T, Deakin, C, Cooke, M, Horton, J, Lamb, S, Slowther, A, Woollard, M, Carson, A, Smyth, M, Wilson, K, Parcell, G, Rosser, A, Whitfield, R, Williams, A, Jones, R, Pocock, H, Brock, N, Black, J, Wright, J, Han, K, Shaw, G, Blair, L, Marti, J, Hulme, C, McCabe, C, Nikolova, S, Ferreira, Z, Perkins, G