We need the final data before we can analyse SYMPLICITY HTN-3
Thomas Zeller states that we cannot determine the likely impact of SYMPLICITY HTN-3 until the final results are presented at the American College of Cardiology (ACC) annual meeting in March. He also reviews how renal denervation technology has evolved since the first system came on the market.
> How has catheter-based renal denervation technology developed since the intervention was first introduced?
The first renal denervation system (Symplicity, Medtronic) that was introduced had a very basic monopolar catheter (Flex), but we now have systems that have multi-electrode catheters - for example, St Jude Medical’s EnligHTN, and Boston Scientific’s Vessix. Medtronic now also has a four-electrode catheter (Spyral). These developments in catheter technology mean that the catheters are more flexible and, hopefully, more effective. Moreover, these newer devices reduce the treatment time and potentially reduce radiation exposure and contrast medium volume.
> What are the advantages of a multi-electrode catheter vs. a single electrode catheter?
Multi-electrode catheters provide the opportunity to ablate the renal nerves in a 3D fashion. That means the electrodes are positioned in all four different quadrants of the renal artery circumference. The Boston Scientific system (Vessix) has a bipolar catheter, which means it reduces the energy that needs to be applied. However, whether this lower energy system will be associated with an increase in safety and efficacy needs to be established.
> Aside from now having multi-electrode catheters, what other developments in renal denervation technology have there been?
We also now have renal denervation systems that provide an alternative option to radiofrequency energy. For example, ReCor Medical’s Paradise system uses ultrasound energy, rather than radiofrequency energy, to heat the tissue and ablate the nerves. A nice feature of the ReCor system is its centred balloon catheter, which keeps the distance between the probe and the tissue stable in all positions. This means that you have a more homogenous distribution of the ultrasound energy. Also, this centred balloon is used as a cooling device and this results in a significant decrease in temperature in the sections of the vessel wall that are close to the balloon (in particularly, the intima and the media). The heating is only applied to the adventitia and the tissue area around the artery; therefore, it is a targeted renal denervation procedure. Again, at the moment, we do not know if this new technology will result in improved efficacy or safety compared with radiofrequency.
> How do you think the news that SYMPLICITY HTN-3 did not meet its primary efficacy endpoint will affect the future of renal denervation technologies?
Nobody is able to say at the moment because we need the final data, which is due to be presented at the ACC meeting in March, before knowing what the impact of this study will be. The only information we have is that the primary efficacy endpoint was not met, which is not sufficient to analyse the study. However, the positive message from Medtronic is the device has proven its safety.
> Will there be any special sessions at the RHC that will review SYMPLICITY HTN-3?
We will not have any dedicated sessions because we do not have the full results and we are not able to provide any more information than what Medtronic has already released. However, we will review the trial during the Course. It is important to note that the Course focuses on the management of resistant hypertension as a whole and renal denervation is just one part of that. Therefore, as well as looking at renal denervation, we will also look at how to diagnose patients, how to exclude secondary causes of resistant hypertension, and review pharmacological treatment options.
> Of the sessions that do look at renal denervation, several focus on the practical aspects of renal denervation technologies, what are the key learning objectives of these sessions?
The key objectives are to understand the differences between the technologies that are available, but we cannot promote one device over another because we do not have any comparative data. One of the things we will discuss regarding SYMPLICITY HTN-3 is whether a sham-controlled trial using a different renal denervation technology would have met its primary efficacy endpoint, but we can only speculate as we do not have the data for this yet and do not have the complete results for SYMPLICITY HTN-3.
> If someone is particularly experienced with one renal denervation technology, what are the benefits of learning about other renal denervation technologies that are available?
It is important for a physician to consider becoming knowledgeable in more than one renal denervation technology because a second device may provide benefit when a first device does not (i.e. using an ultrasound device after a radiofrequency device). Additionally, there might be specific anatomical conditions where a particular device might have technical benefits in terms of easier delivery over others.