High impedance leads and safety margin. Electrical considerations based on a simplified expression of the 'paradigm'

Abstract

For physicians who are not familiar with the electrical basis of cardiac stimulation, high impedance leads previously (10 years ago) considered as bad electrodes (high voltage) are now considered as the 'epitome' of lead technology (low energy drain): clearly impedance is not a good parameter for characterizing the qualities of a pacing lead. Using a simplified approach to the electrostimulation 'paradigm', it is easy to establish that modern high impedance leads are in fact high current density leads and high efficiency leads (better description). It is also possible to establish that routine programming of the safety margin at 100% above threshold parameters is associated with a decrease in the penetration of the electric field according to the reduction of the cathode surface area. For safety and energy saving, a small tip electrode could be combined with a low polarization surface treatment and a reduction in fibrosis development between electrode and myocardium.

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

“…1 However, the reported voltage thresholds alone do not always correlate with energy delivered or current drain (known to affect battery longevity) because of different pacing impedances between LV configurations. 11 In addition to these studies, our data indicate that the lowest and highest calculated energy delivered and current drain at LV threshold are found in the Tip3 RV coil and Ring3 Can configurations, respectively.…”

“…We can only postulate that different current density and/or electric fields responsible for myocardial stimulation varies between LV configurations mostly due to different pacing impedances even when the same electrode (Tip or Ring) is used as cathode. 1,4,11 …”

“…We chose arbitrarily a calculated energy of Ͻ0.9 mJ and current drain Ͻ0.46 A at 0.4 ms, because a voltage threshold of 1.5 V (impedance, 1000 ⍀; battery voltage, 3.2 V; and pacing rate, 100 bpm) would require a pacing output programmed to 3 V at 0.4 ms for appropriate safety margin. 11 Puzzling to us is the difference in energy and current drain at LV threshold in the same patient between LV since configurations using the same electrode as cathode, because theoretically myocardial stimulation occurs at the same location. We can only postulate that different current density and/or electric fields responsible for myocardial stimulation varies between LV configurations mostly due to different pacing impedances even when the same electrode (Tip or Ring) is used as cathode.…”