Paradigm shift in lead design.

Area of Science:

• Biomedical Engineering
• Electrophysiology
• Medical Device Technology

Background:

• Over 30 years, electrode technology has evolved from bulky (90 mm2) to micro-sized (1.0 mm2) designs.
• This miniaturization has led to a significant increase in impedance, from 110 Ohms to over 1 kOhms, a notable shift in lead design.

Purpose of the Study:

• To investigate the relationship between electrode size, impedance, and energy consumption in cardiac pacing.
• To derive a formula for voltage threshold based on electrophysiology and electrophysics, optimizing electrode design.

Main Methods:

• A theoretical model was developed assuming a nonexcitable tissue layer between the electrode and myocardium.
• Calculations were performed for voltage threshold, impedance, and energy as a function of electrode surface area, considering chronaxie and pulse duration.

Main Results:

• The study estimates the nonexcitable tissue thickness at 1.5 mm based on chronic threshold data.
• Optimal voltage threshold (0.62 V) with a 0.5 ms pulse duration is achieved at a surface area of 4 mm2, resulting in 1 kOhms impedance and 197 nJ energy.
• Further reduction in surface area below 1.6 mm2 does not substantially decrease energy if pulse duration remains 0.5 ms.

Conclusions:

• Electrode shape appears to have a minor role in efficiency; a hemispherical model accurately approximates experimental results for various shapes.
• Significant energy reduction (<100 nJ) is achievable by reducing pulse duration to match chronaxie, with surface areas ≤1.5 mm2.
• A paradigm shift in cardiac pacing requires acceptance of electrostimulation fundamentals combined with electrophysics principles.