Burn away blood pressure

Back in the 1940s and 50s, there was a surge of interest in a surgical procedure called a sympathectomy for the treatment of primary hypertension.

This operation involved opening up the patient to gain access to the bundles of sympathetic nerves that run along the spine on the back, and severing them.

As the sympathetic nervous system - part of our autonomic, or involuntary, nervous system - plays a major role in elevating our blood pressure, it was thought that removing some of these nerves would help to lower the high blood pressure of hypertensive patients.

While the operation was fairly successful in terms of decreasing blood pressure, the less sophisticated equipment and technique of the times also meant that a fair number of patients experienced various surgical complications, and indeed, some died as a result of the surgery.

The development of the first effective anti-hypertensive drugs in the late 1950s, and subsequent advancements in this area of pharmaceuticals, meant that treatment for hypertension moved solely into the pharmacological realm.

As more about the disease was discovered, lifestyle modification, such as exercising, changing one's diet, and quitting smoking, were also adopted as part of the treatment regime for hypertension.

Now, we have come full circle, with the recent introduction in Malaysia and Singapore of a new surgical treatment for resistant hypertension, based on the same principles of the original sympathectomy.

Sympathetic surgery

Explains consultant interventional cardiologist Dr Yap Yee Guan: "In patients with high blood pressure, there is overstimulation of these (sympathetic) nerves, which in turn, will increase the secretion of certain hormones that we call renin, angiotensin, and aldosterone. These are hormones that are involved in the regulation of sodium and fluid volume in our body."

The amount of salt and water in our body affects our blood pressure - the more salt and water present, the higher our blood pressure.

These two elements are regulated by our kidneys through the three hormones mentioned above, which are produced by the adrenal glands located on top of the kidneys.

Dr Yap, who practises at a private hospital in Kuala Lumpur, adds that overstimulation of the sympathetic nerves also results in increased vascular tone, which causes our arteries to become constricted, thus, also raising blood pressure.

With the concept already proven over 60 years ago, and advancements in minimally invasive surgical procedures, the sympathectomy was revisited and tweaked for modern times in recent years.

In 2009, an international randomised clinical trial called the Symplicity HTN-2, was conducted to test a catheter-based renal nerve ablation, or denervation, procedure in the treatment of resistant hypertension.

Resistant hypertension is diagnosed when a patient can only control their blood pressure with four or more hypertensive medications.

Dr Yap shares that the trial, published in the Dec 2010 edition of The Lancet, showed a very significant drop in blood pressure for the group that underwent the renal nerve ablation.

"Clinical success in this study was defined as a reduction by 10 mmHg in the systolic blood pressure by the end of six months," he says.

A simple process

"At six months, of the patients in the ablation arm, 84 per cent had a 10 mmHg or greater drop in systolic blood pressure, compared with 35 per cent of the controls, which was statistically very significant."

In fact, the treated patients had an average drop of about 32/12 mmHg in their blood pressure, and recent follow-up visits confirmed that these reductions have been maintained two years after the procedure.

Nearly 40 per cent of these patients had also achieved blood pressure control - defined as a systolic blood pressure of <140 mmHg - by the end of the trial. This is in comparison to the average blood pressure reading of about 178/96 mmHg at the beginning of the study,

"This can translate to up to a 60 per cent decrease in stroke and heart attack risks," says Dr Yap.

It was also reported that one in five patients in the trial were able to reduce either the dosage or the number of medications they had been taking for their condition.

A simple process

The procedure itself is not too difficult, especially for practising cardiologists who are used to doing procedures like angiograms, says Dr Yap.

Patients are either heavily sedated or given general anaesthetic before the procedure; the main difference being that the former can be done as a daycare procedure, while the other requires an overnight stay in the hospital for monitoring purposes.

A catheter is inserted into the femoral artery via a small incision in the groin. The doctor then guides it up the femoral artery to either the right or left renal (kidney) arteries.

Dr Yap explains that the relevant sympathetic nerves lie within and immediately adjacent to the walls of the renal arteries.

Because of this proximity, all the doctor has to do is to place the tip of the catheter on the wall of the renal artery, and activate the generator attached to the wire that will create a radiofrequency wave to burn off the nerve cells.

As the site of these nerves cannot be accurately pinpointed, Dr Yap says that this procedure is repeated at four to six sites within the circumference and length of the artery in a systematic manner.

Once one artery is done, the doctor guides the catheter to the other renal artery and repeats the process. In total, the procedure takes about 40 minutes, according to Dr Yap.

"The procedure is no big deal; it's very simple. The most important part is the placement of the tip of the catheter to the artery wall," he shares, adding that so far, there have been no known complications from the procedure.

While this treatment is currently limited to those with resistant hypertension. Dr Yap is optimistic about the possibility of using it to treat all hypertensive patients in the future.

But he says: "Whether we can lower the criteria to less hypertensive patients is for further studies to determine."