Extravascular ICD therapy is feasible

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Studies presented at the 37th Heart Rhythm Society Scientific Sessions (HRS; 4–7 May, San Francisco, USA) have shown the feasibility of a novel approach to implantable cardioverter defibrillator (ICD) using Medtronic’s EV-ICD system. The studies were the first to evaluate “extravascular” ICD therapy.

ICD therapy involving leads placed outside the heart and veins, and under the rib cage may provide the same benefits achieved with conventional ICDs, including pacing the heart in patients at risk of dangerous heart rhythms, according to the presentations.

Joseph Chan, Prince of Wales Hospital, Hong Kong, who led one of the studies presented at Heart Rhythm, says,  “The feasibility results presented are encouraging, and show that the extravascular ICD approach may be the solution physicians are seeking.”

The investigational Medtronic EV-ICD system consists of an implanted device, a newly designed lead, and procedure tools to guide the efficient delivery of the system. Like transvenous ICD systems, the Medtronic EV-ICD is projected to have longevity of approximately 10 years and an expected device volume of approximately 33cc. In addition, the EV-ICD approach is designed to prevent the rare, but potentially serious, risks that can occur when leads are implanted inside the vasculature and the heart.

In an oral abstract session, Chan presented the results from a prospective, non-randomised study of 16 patients scheduled to undergo a midline sternotomy or implant of an ICD, who were enrolled at five sites in Europe and Hong Kong. Using an introducer to guide the delivery of the defibrillation lead under the rib cage, the study determined that defibrillation is possible in this location with defibrillation results consistent with conventional ICDs.

In a second oral abstract session, Darius Sholevar presented the results from a prospective, multicentre trial that assessed the feasibility of extravascular cardiac pacing. Substernal Pacing Acute Clinical Evaluation (SPACE) studied 26 patients from eight sites in the USA and Canada, and preliminary data demonstrated that pacing is possible from this extravascular space, with the majority of patients achieving consistent and appropriate ventricular pacing results.

These clinical data were supported by other pre-clinical abstracts presented during Heart Rhythm, which assessed the feasibility of pacing and defibrillation with leads outside the heart and under the rib cage:

  • Researchers developed a model to compare the amount of energy required for effective defibrillation in conventional ICDs, subcutaneous ICDs, and the investigational EV-ICD approach. The model showed that lead placement under the rib cage requires slightly more energy, on average, for defibrillation compared to conventional ICDs, and about half as much, on average, as current subcutaneous ICDs. These data were further supported by a second abstract demonstrating that the EV-ICD approach requires lower energy (defibrillation thresholds) than subcutaneous devices and comparable energy to conventional ICDs.
  • A final abstract reinforced that pacing can be achieved with the lead placed in this extravascular space.
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