Properties of ultrasonically marked leads

We have developed an ultrasonic marking system for pacing leads and the electrophysiological study of catheters. The aim of this study was to evaluate the accuracy of our system, its usability in the measurement of performance of implanted leads, and to investigate the potential of electrical shock and ultrasonic hazard. The measurements have shown that different applications require specific electronic design, involving some compromise between accuracy and sensitivity. A higher sensitivity at the beginning of the ultrasonically guided cardiac lead implantation yields poorer accuracy. Quantitative measurements show that accuracy can be subsequently improved by reduction of sensitivity of the marking system. The transponder marking circuit is better suited for general use and the passive electronic circuit is better suited for multiple electrode electrophysiological studies. Experiments concerning electrical safety show that in the worst failure case, the energy of the marking system released within the heart is less than 10(-9) J per pulse within the pacing frequency spectrum and the current was below 50 microamperes. Ultrasound intensities were within the safety limits set by international and national organizations. The experiments using the marking system for detection of the pacing lead failure showed that the system can yield an early warning of the lead malfunction. The system can significantly reduce the exposure of the medical staff and the patients to x rays as well as improve patient follow-up accuracy.