An Evaluation of Long‐term Stimulation Thresholds by Measurement of Chronic Strength Duration Curves

Successful long‐term cardiac pacemaker therapy requires both reliable generator output and stable, altainable chronic stimulation thresholds. Strength duration curves, which display cardiac stimulalion thresholds as a function of impulse duration, provide needed data to evaluate more thoroughly acute and chronic lead thresholds. We measured chronic strength duration curves at the time of generator replacement in 47 patients with three different types of lead systems of variable geometry and surface area and compared these curves with acute strength duration curves measured at the time of initial lead implantation in 19 patients. We found that strength duration curves have a characteristic shape; however, chronic strength duration curves were shifted upward and to the right of acute strength duration curves, regardless of electrode tip surface area or geometric design. Our data suggest that variable pulse width exceeding 1 ms may not significantly reduce stimulation thresholds.