ME & MY OPERATION
ULTRASOUND FOR HYPERTENSION
THE SPECIALIST
Dr MELVIN LOBO is a consultant cardiovascular physician. BLOOD pressure is the amount of pressure exerted on the walls of the arteries by blood flow.
The top number in your reading (systolic pressure) is the pressure exerted when the heart contracts and forces blood around the body.
The lower number (diastolic pressure) is when the heart relaxes between beats. A healthy reading is around 120/80.
When this pressure is consistently too high (more than 140/90) — known as hypertension — the heart has to work harder to pump blood, which weakens the heart muscle.
The increased pressure also damages blood vessel walls, so they’re prone to rupturing or forming clots, which can cause a stroke.
Around one million people in Ireland have hypertension. It can cause headaches, nausea, dizziness, blurred vision or breathlessness, but, like Ken, millions have no symptoms.
Hypertension can be caused by arteries stiffening as you age, stress, insufficient exercise and excess salt in the diet.
The initial treatment is lifestyle changes, such as diet and exercise. If these fail, then we try medication such as amlodipine, which relaxes the blood vessel walls to reduce pressure.
A small percentage of patients do not respond to drugs and many would like to come off them because it’s inconvenient or they struggle with side-effects.
For these patients, we can now offer a procedure called renal denervation, where we destroy nerves in the arteries that supply the kidneys. These nerves play a key role in regulating blood pressure — and high blood pressure can be caused by faulty signals transmitted by these nerves between the brain and kidneys.
One of the aims of this treatment is that patients could stop taking drugs altogether.
Since 2012, we have used radiowaves to destroy these nerves. This has been successful, but patients need several applications (sometimes up to six blasts in one procedure), as the energy is not that efficient in hitting its target. This means there is a risk that heat from the radiowaves could damage healthy tissue.
We are now involved in trials destroying these renal nerves using ultrasound. Ultrasound uses high-frequency soundwaves and may be preferable to radiowaves, as it is more controlled and penetrates deeper into the tissue, so is more effective and fewer applications are needed.
Also, unlike the radiowave probe, the ultrasound probe has a special balloon around it, which helps cool surrounding tissue and reduce damage to healthy cells.
We use around two to three burns per artery with the ultrasound, compared to six with radiowaves. And, because they are less likely to cause tissue damage, we can repeat the ultrasound treatment, unlike with radiowaves. The technique is the same as the one with radiowaves.
FIRST, we make a tiny incision in the right side of the groin and feed a guidewire through an artery, until it reaches one of the renal arteries. (There are two, one for each kidney. We treat both.)
We then pass a thin, flexible tube (a catheter) with a thin probe inside, called a transducer.
The probe is connected to an ultrasound machine controlled by the doctor.
When the probe is in position on the nerves, the doctor will activate a seven-second burst of ultrasound energy. This destroys the renal nerves and stops the faulty brain signals.
It takes about 40 minutes to treat both sides. The wound is sealed with a plaster and patients can go home the same day.
The results of the randomised international trial with ultrasound or sham treatment in which Ken took part were published in The Lancet in May.
They showed that in 146 patients, those who had ultrasound treatment saw their blood pressure drop by eight points or more, compared with only a slight reduction in the sham group.
We plan a larger trial to monitor patients long-term.