Implantable cardiac stimulation device having automatic capture/threshold capability using a dynamically adjustable safety margin

The present invention is generally directed to an implantable medical device, e.g., a cardiac stimulation device, and is particularly directed to an automatic capture/threshold pacing method for use in such a device. An improved system and method for performing automatic capture/threshold detection in an implantable cardiac stimulation device or any device capable of stimulating some organ or tissue in the body. In existing systems a threshold stimulation energy level is periodically determined and a working stimulation energy level is then set by increasing the threshold stimulation energy level by a fixed or preprogrammed safety margin, e.g., a fixed voltage level or a percentage safety margin. However, in certain circumstances this safety margin may not be sufficient, resulting in either frequent threshold level determinations or losses-of-capture. To avoid these situations which may be wasteful of battery energy or dangerous for the patient, embodiments of the present invention periodically increase and/or decrease the safety margin according to the performance of the stimulation device, i.e., based upon the frequency of capture.