the trigger zone if the ventricular event detected was a v sense within the trigger zone then path 108 is followed otherwise the ventricular event detected is paced and path 106 is followed if path 106 is followed then step 124 is executed in step 124 a determination is made as to whether the dynamic upper activity interval duai is greater than the upper activity interval uai the uai is the programmed minimum v2v escape for brady pacing the duai is the dynamic upper activity level this interval is greater than or equal to uai and less than or equal to vspv2v if the duai is not greater than uai at 124 then duai is already at minimum so there is no need to check further with respect to decreasing duai in this situation path 126 is followed and step 100 is executed again waiting for the next ventricular event if the duai is greater than the uai then path 128 is followed from step 124 to step 130 in step 130 a determination is made as to whether all of the last n v2v intervals are greater than or equal to dv2v the minimum v2v interval ending in a ventricular pace that is long enough such that it will not interfere with detection if all of the last n v2v intervals are not greater than or equal to dv2v at 130 then path 134 is followed and step 120 is executed in step 120 the dynamic upper activity interval duai is used as the upper activity interval uai in calculating the current v2v escape after execution of step 120 path 122 is followed returning control.