Atrial fibrillation lasting 30 seconds or longer was detected in 45 of 280 patients ( 16.1 % ) in the intervention group , as compared with 9 of 277 ( 3.2 % ) in the control group ( absolute difference , 12.9 percentage points ; 95 % confidence interval [ CI ] , 8.0 to 17.6 ; P < 0.001 ; number needed to screen , 8 ) .