First Human Demonstration of Cardiac Stimulation With Transcutaneous Ultrasound Energy Delivery: Implications for Wireless Pacing With Implantable Devices

First Human Demonstration of Cardiac Stimulation With Transcutaneous Ultrasound Energy Delivery: Implications for Wireless Pacing With Implantable Devices

Kathy L. Lee, Chu-Pak Lau, Hung-Fat Tse, Debra S. Echt, David Heaven, Warren Smith, Margaret Hood

The feasibility and safety of cardiac stimulation using a remote energy source, without pain or discomfort, has been shown acutely in patients for the first time. This new technology using ultrasound energy has the potential for application to permanent pacing systems. It has the advantages of avoiding the complications inherent to pacing leads and accessibility to different locations within various cardiac chambers, enabling selective site and multisite pacing. The development of implantable receiver electrodes holds promise for a new paradigm in pacemaker therapy.

Objectives

The purpose of this study was to evaluate the feasibility and safety of a novel technology that uses energy transfer from an ultrasound transmitter to achieve cardiac stimulation without the use of a pacing lead in humans.

Background

To overcome the limitations of pacemaker leads, a new technology enabling stimulation without the use of a lead is desirable.

Methods

A steerable bipolar electrophysiology catheter incorporating a receiver electrode into the tip and circuitry to convert ultrasound energy to electrical energy was inserted transvenously into the heart. An ultrasound transmitting transducer was placed on the chest wall with ultrasound gel. Ultrasound energy was amplitude-adjusted and transmitted at 313 to 385 kHz. The output waveform of the receiver electrode was monitored while the transmitter was moved on the chest wall to target the receiver. The ultrasound transmission amplitude was limited to a mechanical index of 1.9, the maximum allowed for ultrasound imaging systems. Ultrasound-mediated pacing with minimum voltage but consistent capture was obtained for 12 s.

Results

Twenty-four patients (48 ± 12 years) were tested during or after completion of clinical electrophysiology procedures. A total of 80 pacing sites were tested (mean 3.3 sites/patient): 12 right atrial, 35 right ventricular, and 33 left ventricular (31 endocardial) sites. The transmit-to-receive distance was 11.3 ± 3.2 cm (range 5.3 to 22.5 cm). Ultrasound-mediated pacing was achieved at all 80 test sites, with consistent capture at 77 sites. The mechanical index during pacing was 0.5 ± 0.3 (range 0.1 to 1.5). The mean ultrasound-mediated capture threshold was 1.01 ± 0.64 V. There was no adverse event related to ultrasound pacing. No patient experienced discomfort during pacing.

Conclusions

The feasibility and safety of pacing usng ultrasound energy has been shown acutely.