The Strength‐Duration Curve and Its Importance in Pacing Efficiency: A Study of 325 Pacing Leads in 229 Patients

Abstract

Pacemaker battery life is dependent on programmable parameters, principally pulse amplitude and pulse duration. High factory default settings cause excessive 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 were calculated for 325 acutely implanted pacing leads. Chronaxie and rheobase were compared for atrial and ventricular leads. Chronaxie was compared with actual programmed pulse duration. There were 101 atrial and 224 ventricular leads, all passive fixation. The curve fit was good, (mean error +/- SD) 0.024 +/- 0.06 V for atrial curves and 0.008 +/- 0.034 V for ventricular curves. Mean (+/- SD) atrial and ventricular chronaxies were 0.24 +/- 0.07 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 and ventricular rheobases were 0.51 +/- 0.2 V and 0.35 +/- 0.13 V, respectively. A "Z" value of 7.1 (P < 0.001) suggested atrial and ventricular rheobases 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 two, thus, demonstrating suboptimal pacing. We conclude that understanding the strength-duration curve is critical. Sensible programming of other pacing functions optimizes longevity. Battery drain is reduced by programming pulse duration to chronaxie with a doubling of voltage threshold at this point to achieve a safety margin. Further study of chronaxie drift with time is required.

A Comparison of Chronaxies for Ventricular Fibrillation Induction, Defibrillation, and Cardiac Stimulation: Unexpected Findings and Their Implications

“…The mean stimulation chronaxie of 0.15 ms for the lead tip and 0.23 ms for the coil are situated at the lower edge of the 0.2 ms to 0.6 ms chronaxie range reported for electrodes with a surface area from 2 mm 2 to 10 mm 2 30 , 32–36 . In historical data, amplitude resolution was limited, with the finest voltage step being 20% to 40% of rheobase.…”

Disparity in Left Ventricular Stimulation Among Different Pacing Configurations in Cardiac Resynchronization Therapy

“…The use of peak instead of mean voltage in our study could decrease the accuracy of the strength-duration curves. 15,16 However, most published studies of clinical data of strength-duration curve have been performed using peak voltage. 3,6,8,12,17 (3) Strength-duration curves were constructed using the Lapicque formula (rheobase voltage and chronaxie).…”

Intraprocedural Assessment of Stimulation, Sensing, Detection, and Defibrillation

“…29-10). 56 Programming the PCTs at both extremes of too long a PW or amplitude will significantly increase battery drain and decrease battery longevity. A strength-duration curve is automatically constructed in most modern CIEDs to aid in the optimization of pacing output programming with the aim of prolonging battery longevity.…”

“…Subsequently, similar steps are taken with a fixed voltage amplitude and decrementing the PW to determine its minimal PCT. 56 The strength-duration curve has direct relevance to clinical practice. The identification of rheobase and chronaxie from the strength-duration curve is essential for such programming (Fig.…”