The strength-duration curve and its importance in pacing efficiency: A study of 325 pacing leads in 229 patients

Pacemaker battery life is dependant on programmable parameters, principally pulse amplitude and pulse duration, Nigh factory default settings cause ex cessive current drain, The strength-duration curve relates pacing threshold to pulse duration. The most energy efficient pacing occurs at chronaxie, a value of pulse duration derived from the curve. Strength-duration curves w ere calculated for 325 acutely implanted pacing leads. Chronaxie and rheoba se were compared for atrial and ventricular leads. Chronaxie was compared w ith actual programmed pulse duration. There were 101 atrial and 224 ventric ular leads, all passive fixation. The curve fit was good, (mean error +/- S D) 0.024 +/- 0.06 Sr far atrial curves and 0.008 +/- 0.034 V for ventricula r curves, Mean (+/- SD) atrial and ventricular chronaxies were 0.24 +/- 0.0 7 ms and 0.25 +/- 0.07 ms, respectively. A "Z" value of 1.4 indicated that chronaxies might have been from the same population. Mean (+/- SD) atrial a nd ventricular rheobases were 0.51 +/- 0.2 V and 0.35 +/- 0.13 V, respectiv ely. A "Z" value of 7.1 (P < 0.002) suggested atrial and ventricular rheoba ses were from differing populations. All patients had factory default pulse durations of 0.45 ms or 0.5 ms, exceeding acute chronaxie by a factor of t wo, thus, demonstrating suboptimal pacing. We conclude that understanding t he strength-duration currie is critical. Sensible programming of other paci ng functions optimizes longevity. Battery drain is reduced by programming p ulse duration to chronaxie with a doubling of voltage threshold at this poi nt to achieve a safety margin. Further study of chronaxie drift with time i s required.