By Assoc Prof Chin Chee Tang,
Senior Consultant, Department of Cardiology

Taking long-term medication is always a challenge to many patients with hypertension, especially for those who continue to have high blood pressure despite lifestyle changes and medications. Renal Sympathetic Denervation, a minimally invasive procedure that uses radiofrequency waves, might be the answer for patients with resistant hypertension, Assoc Prof Chin shared.

High blood pressure (also known as hypertension) is the most common modifiable risk factor for diseases affecting the cardiovascular system – not just in Singapore, but worldwide. According to the recent European and United States guidelines on blood pressure management, the recommendation is to lower systolic blood pressure (SBP) to 120 to 130mmHg in most patients with hypertension. For the majority of people with high blood pressure, these targets can be achieved with appropriate lifestyle changes and drug treatment. Anti-hypertensive drugs (medications to reduce blood pressure) are widely available, relatively inexpensive, and generally do not have many side effects. Importantly, they have been shown to reduce blood pressure and improve cardiovascular outcomes such as reducing the chance of death, heart attacks and strokes. Studies involving hundreds of thousands of participants have shown that by reducing SBP by 10mmHg, the risk of having a heart attack or a stroke is reduced by 25% and 33% respectively.

However, many people find it difficult to take their medication consistently as directed, and this results in poor adherence to medications; which contributes to the poor control of blood pressure. In studies where blood or urine samples have been taken to measure drug levels, the rates of non-adherence in hypertension medications were as high as 66%; that implies only a third of patients take their blood pressure medications as prescribed by their doctor.

We know that there are patients who, despite adhering to lifestyle interventions and medications, continue to have very high blood pressure. This phenomenon, termed as resistant hypertension, is associated with very high rates of undesirable health outcomes. 

The sympathetic nervous system in the body is known to be involved in the progression and development of hypertension. A proportion of the nerves of the sympathetic nervous system that run along the blood vessels and supply blood to the kidneys (renal arteries) have been considered to be a target for interventions to improve blood pressure control.

From reports of operations performed in the 1950 to 1960’s, the removal of these nerves lowered blood pressure significantly. These results formed the basis for the development of contemporary minimally invasive approaches using radio-frequency, ultrasound, or injection of neurotoxic agents such as alcohol to affect the nerves located in the renal arteries.

Innovative Treatment That Targets Resistant Hypertension

The initial clinical trials1  of renal sympathetic denervation (RSD) that focused on patients with severe resistant hypertension have shown encouraging results, reporting large falls in blood pressure with a favourable safety profile. Based on this, NHCS performed the first case of RSD in Singapore in 2011, for a patient who had uncontrolled blood pressure despite taking five medications at maximally tolerated doses. Since then, NHCS continues to perform the procedure for selected patients with resistant hypertension – the majority have had significant blood pressure reduction, and importantly, none of them showed any complications from the procedure.

However, a study2 conducted in the United States in 2014 reported that resistant hypertension patients who were only on medications experienced blood pressure reductions that were similar to those of patients who underwent RSD. Because of the lack of an obvious benefit of RSD in resistant hypertension, the technological development in RSD slowed down.

Despite this, there were continued research efforts to develop and advance the technology for RSD. The results of the most recent studies are encouraging and have re-ignited interest in the potential of this technology.

In one recent study3, patients with hypertension had their medications stopped and were randomly allocated to undergo RSD with the latest device and technique. The study was designed to remove any bias that might be present because of medications and inconsistent medication consumption. Blood and urine tests were also performed to ensure that patients were not taking medications without the knowledge of the investigators. The results of the study showed that patients who underwent RSD had lower blood pressure levels after the treatment, while those who did not have the procedure had no change in their blood pressure levels.

A second study4 had a similar design but one major difference – medications were allowed. These medications were prescribed in a very tightly controlled manner, and regular blood and urine tests were performed to ensure that participants took the medications as directed. Similar to the previous study, patients who went through RSD had shown lower blood pressure levels after the treatment as compared to those that did not undergo RSD. 

From these two recent studies, results have shown no significant adverse effects or complications among the patients who underwent RSD. Now, with these latest results, there is fresh impetus for further studies involving more patients to understand how the treatment may be offered to different patient groups. For patients who have exhausted all possible management options, and yet continue to have high blood pressure levels, RSD may be the ‘last resort’. There is also a likelihood where individuals who would rather not take long term medications and are keen to explore an alternative option of a safe and one-time procedure, may benefit from RSD.

At NHCS, RSD is only offered to patients who are unable to achieve good blood pressure control despite taking their medications, and those who have multiple allergies or side effects with medicines and cannot tolerate long term drug therapy. NHCS continues to look forward to further developments in this treatment option to help our patients to improve their health outcomes in the long run. 



HOW THE RSD PROCEDURE WORKS
A plastic tube is inserted into the main blood vessel (aorta) to reach the blood vessel (renal artery) supplying blood to the kidney. A wire is passed into the renal artery and after this, the RSD catheter is inserted into the artery over the wire. When the RSD catheter is activated, energy is transmitted across the renal artery wall to the overactive sympathetic nerves and leads to decreased nerve activity

1Renal Sympathetic Denervation in Patients With Treatment-Resistant Hypertension (The Symplicity HTN-2Trial), 2010
2A controlled trial of renal denervation for resistant hypertension (Symplicity HTN-3), 2014
3Catheter-based renal denervation in patients with uncontrolled hypertension in the absence of antihypertensive medications (SPYRAL HTN-OFF MED), 2017
4Effect of renal denervation on blood pressure in the presence of antihypertensive drugs (SPYRAL HTNON MED), 2018

This article is from Murmurs Issue 33 (Jan – Apr 2019). Click here to read the full issue.