Pacemaker which adapts to minimize current drain and provide desired

Abstract

A cardiac pacemaker improves battery longevity by automatically providing a safe threshold and an associated pulse width leading to minimum current drain. The pacemaker stores a matrix of current drain characteristics for all of the possible pulse width-voltage pairs, and a revisable strength-duration curve for a patient. Either periodically or as a result of a loss-of-capture episode--whichever occurs first--the pacemaker calculates for each possible pulse width, a new threshold value based upon a measured rheobase and a derived chronaxie. Each threshold is multiplied by a predetermined safety margin. The pacemaker chooses as the pacing stimulation signal, the voltage-pulse width pair having the lowest associated current drain, and satisfying the desired safety margin.