Control subjects had a higher mean compression rate both immediately ( 121 [ standard deviation { SD } = 21 ] vs. 109 [ SD = 15 ] cpm ; 95 % confidence interval [ CI ] of mean difference 4-19 ; p = 0.002 ) and at follow-up ( 120 [ SD = 20 ] vs. 111 [ SD = 13 ] cpm ; 95 % CI of mean difference 2-16 ; p = 0.014 ) .