New results support the feasibility of an entirely extracardiac pacing method in a heterogeneous patient population, using a minimally invasive, parasternal delivery approach, with adequate sensing and thresholds suited for temporary pacing. The study, authored by Anne-Floor BE Quast, Niek EG Beurskens (University of Amsterdam, The Netherlands) and colleagues, was recently published in Circulation: Arrythmia and Electrophysiology.
One of the major findings of the study was that a total of 166 out of 174 patients, representing 95% of the cohort, had a viable lead access path through the fourth, fifth, or sixth intercostal space. In addition, accessing the targeted implant location using a custom delivery tool was successful in all five cadavers and three humans without the use of fluoroscopy, with an average lead delivery time of 121±52 seconds. No damage to the lung, pericardium, heart, or internal thoracic vessels occurred. Another important finding was that pacing performance was tested in six human subjects showing a threshold voltage of 4.7 volts, threshold pulse width of 1.8 ms, and an impedance of 1,205 Ohms. R-wave amplitudes measured 9.6 mV.
In order to test the feasibility of the pacing system, the investigators carried out a number of evaluations, including a retrospective computed tomography analysis to characterise anatomic variations related to lead access, accessing the anterior mediastinum in cadavers and human subjects using a custom delivery tool and acute clinical pacing performance.
Quast, Beurskens and colleagues remark that a completely extracardiac pacing system provides the potential for clinical advantages over existing device alternatives that require intravascular, endocardial, or epicardial contact, and that preliminary studies evaluating the feasibility of cardiac pacing with a lead in the anterior mediastinum, outside the pericardium and circulatory system have been completed. These studies examined the anatomic parasternal access route, the usability of a delivery tool to facilitate lead placement and the pacing performance of the extracardiac lead, they add.
“The current study has some limitations,” the authors comment, including the small number of human patients and cadavers included, and the retrospective assessment of the CT images in the anatomy study. Also, two standard transvenous pacemaker-leads, placed into the desired tissue location, were used for the evaluation of cardiac pacing performance and were not optimised for substernal pacing. “Future human studies are required to evaluate the safety and efficacy of the AtaCor extracardiac pacing system for temporary and permanent pacemaker therapy in different patient groups,” they remark.
Overall, Quast, Beurskens and colleagues conclude: “Temporary pacing is a logical initial clinical indication for this novel technology as it can leverage commercially available temporary pulse generators and is limited to in-hospital use where medical oversight exists,” and that, ultimately, “additional development efforts will be required to address other pacing indications including a 30-day ‘Bridge-to-Therapy’ system and permanent pacing options.”