Key for physicians in obtaining optimal patient outcomes and performing minimal, predictable ablation is having a direct understanding of the characteristics of the tissue they are ablating and how they are affecting that tissue. Impedance as it relates to electrophysiology is not a new measurement and provides insights into electrical coupling with cardiac tissue and radiofrequency (RF) delivery. However, recent studies of changes in local impedance during RF ablation have been shown to provide insight into tissue characteristics and RF lesion formation.
Now available in the U.S., the DIRECTSENSE Technology (Boston Scientific) provides electrophysiologists with novel insights before, during, and after an ablation procedure. In this article, Dr. Kenneth Stein, senior vice president and chief medical officer for Rhythm Management and Global Health Policy at Boston Scientific, discusses how this technology uses impedance principals and applies a localized measurement for a unique view into tissue resistivity and subsurface tissue heating during an ablation procedure.
Can you talk about the DIRECTSENSE Technology and why it’s important to track changes in local impedance?
The DIRECTSENSE Technology is a tool for monitoring the effect of RF energy delivery during cardiac ablation procedures. It provides data on the local impedance around the catheter tip as opposed to generator impedance, which measures the impedance from the catheter tip through all tissue between the catheter and the RF return patch. During ablation, the tool tracks the change in local impedance which, in conjunction with other measures, offers physicians a distinct understanding of tissue characteristics and how they are affecting that tissue. Specifically, changes sensed in the electrical field around the tip of the catheter reflect changes in tissue resistivity due to heating below the tissue surface. These changes may indicate temperature change in the tissue, helping to reduce the chances of over-ablation and avoid complications.
How is this new technology addressing an unmet need for electrophysiologists?
Measuring local impedance at the tip of the ablation catheter is unique and not something other electrophysiologists have been able to measure before. In the past, we’ve looked at the mechanical connection of catheter to tissue, but we have never had a direct measure of the electrical coupling of catheter to tissue.
The DIRECTSENSE Technology measures impedance very local to the catheter tip, which brings several different advantages. Importantly, we gain insight into the actual characteristics of the tissue itself, which can be used in planning pre-ablation. We also gather important information into the stability of the catheter tip and its proximity to tissue. In addition, it provides data to electrophysiologists during the procedure while they’re ablating, giving them an understanding of what’s happening during RF delivery and heating below the surface of the tissue.
How is this changing the way electrophysiologists understand local tissue characteristics before and during ablation?
The DIRECTSENSE Technology was approved and launched in Europe two years ago, and I’ve been impressed to see how it has been adopted and incorporated into workflows. It is used with the RHYTHMIA HDx Mapping System (Boston Scientific), which means the data can be quickly integrated into a 3D map. It helps physicians know their proximity to, and characteristics of the tissue, and gives them a sense of viable tissue or scar. The most provocative data that we’ve seen has come out of the LOCALIZE clinical trial presented at Heart Rhythm Society 2020 Science. In this retrospective analysis of the DIRECTSENSE Technology, a local impedance decrease of ≥16.6 ohms with an inter-lesion spacing of ≤6 mm showed a ≥98% positive predictive value of durable pulmonary vein block at three months in patients with paroxysmal atrial fibrillation. So, by adopting these kinds of measures in their practice, electrophysiologists are obtaining a more direct understanding of lesions and procedural efficiency to obtain optimal patient outcomes.
What impact do you think the DIRECTSENSE Technology will have on ablation procedures moving forward?
Knowing the change in impedance around the tip of the catheter provides unique information about local tissue characteristics and the development of the lesion, and this technology provides electrophysiologists with information that we’ve never had access to. In the past, we’ve looked at measurements like generator impedance to try to illustrate the impact of the ablation on tissue at the local level, but generator impedance is a poor surrogate for that because it’s affected by so many things outside of the local tissue level. By adding a measurement of local impedance, the DIRECTSENSE Technology assists physicians in evaluating pre-ablation tissue health, while supporting better clinical understanding of how they are influencing that tissue to guide minimal, predictable ablation during a procedure.
This article is published with support from Boston Scientific.
Disclosures: Dr. Stein reports being an employee and shareholder of Boston Scientific.