Author + information
- Darragh J. Twomey, MBBS, PhD,
- Sam Riahi, MD, PhD,
- Andrew J. Turley, MBChB and
- Simon James, MBBS∗ ()
- ↵∗Cardiology Department, James Cook University Hospital, Marton Road, Middlesbrough TS4 3BW, United Kingdom
A subset of patients with heart failure and prolonged QRS duration cannot derive benefit from cardiac resynchronization therapy (CRT). This is predominantly secondary to implant failure due to unsuitable coronary venous anatomy. An additional group of patients do not respond due to failure caused by suboptimal lead position. Randomized controlled trials of left ventricle (LV) lead placement guided by speckle tracking have demonstrated significant improvement in clinical outcomes when pacing occurs at the site of latest mechanical activation (1).
The wireless (WiSE) CRT system (EBR Systems, Inc., Sunnyvale, California) is a leadless endocardial LV pacing system that allows CRT in patients who are unable to undergo or do not respond to standard LV lead implantation. This study examined the threshold trends of the endocardial LV electrodes of patients recruited to the SELECT-LV (Safety and Performance of Electrodes Implanted in the Left Ventricle; NCT01905670) study, a prospective, multicenter evaluation of the WiSE CRT system (2).
All patients enrolled to the SELECT-LV trial were studied. The 2-part procedure involved the surgical implantation of a subcutaneous ultrasonographic transmitter and battery. The 9.1- × 2.7-mm electrode is subsequently implanted on the endocardial surface of the LV by using a 12-F femoral arterial delivery sheath. Electrode stability is assessed by using contrast injections, and acceptable function is confirmed by the presence of satisfactory pacing parameters.
The transmitter transfers energy acoustically to the endocardial LV receiver electrode, which converts the acoustic energy to an electrical pacing pulse. The system uses the right ventricular (RV) pacing signal from a previously implanted pacemaker or insertable cardioverter-defibrillator (ICD) to trigger LV stimulation. Biventricular capture is confirmed by comparison of QRS morphology during RV-only pacing.
Pacing parameters were measured at 1 week, 1 month, 2 months, 6 months, 1 year, and 2 years after implantation. There is no conventional voltage threshold for these electrodes. The reported threshold is determined by the energy used to generate an ultrasound wave large enough to ensure LV capture. This value is a function of amplitude, pulse width, and ultrasound array size.
The WiSE CRT system was successfully implanted in 34 of 35 patients (mean 65.4 ± 7.9 years of age, 85% male). Indications for implantation were adverse anatomy in 20 patients (57%), CRT nonresponse in 10 patients (29%), prior infection or upper extremity occlusion in 3 patients (9%), and other reasons in 2 patients (6%).
LV pacing threshold data were available in 33 of 34 patients (97.0%) at 1 month, 30 of 34 patients (88%) at 6 months, and 23 of 34 patients (68%) at 1 year, as shown in Figure 1. At 1 week, the mean energy required for LV capture was 0.38 ± 0.47 mJ. At 1 and 6 months after implantation, there were no significant changes in this value. There was a numerical reduction in energy requirement at 1 year (0.19 ± 0.17 mJ) and 2 years (0.25 ± 0.21 mJ), but this did not reach statistical significance.
The threshold trend of the novel WiSE CRT system has not been previously reported in the short or medium term. The present study demonstrated that LV endocardial pacing using this system was reliable over a 2-year period. There was no significant increase in energy requirement over time; in fact, there was a numerical reduction at 1 and 2 years after implantation. The variations in energy requirements among patients were primarily related to the distance from transmitter to electrode, the amount of subcutaneous tissue, and the degree of lung encroachment.
Conventional LV leads placed through the coronary sinus showed a significant increase in pacing threshold in both the medium and the long term (3). More recently, leadless endocardial electrodes placed in the RV have been shown to have a stable pacing threshold over a 1-year period (4). The results of this study suggest that this novel endocardial LV pacing system is equally reliable in the medium term.
The endocardial electrode of the WiSE CRT endocardial LV pacing system has a stable threshold over a 2-year period. These results support the use of this system for patients in whom conventional LV pacing is not possible or is ineffective. Continued monitoring is warranted to evaluate long-term threshold data in a larger cohort.
Please note: This research did not receive funding from any public, commercial, or not-for-profit agency. The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
All authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
- 2019 American College of Cardiology Foundation
- Khan F.Z.,
- Virdee M.S.,
- Palmer C.R.,
- et al.
- Reddy V.Y.,
- Miller M.A.,
- Neuzil P.,
- et al.
- Knops R.E.,
- Tjong F.V.,
- Neuzil P.,
- et al.