According to some methods, for example, preprogrammed in a microprocessor element of an implantable cardiac pacing system, at least one of a number of periodic pacing threshold searches includes steps to reduce an evoked response amplitude threshold for evoked response signal detection. The conveying path is disposed in the casing to convey a recording sheet. The receiver block is spaced a distance from the transmitter block so as to define a sensor field of view therebetween whereby at least a portion of the at least one web material traveling along a predetermined travel path interferes with at least a portion of the ultrasonic signals transmitted by the at least one transmitter block.