Easing the pressure

An implantable device that triggers the body’s own blood pressure control system could provide treatment for those suffering high blood pressure but unable to tolerate drugs. Dave Wilson reports

The system electronically activates special arteries

Hypertension, or high-blood pressure, is a growing health issue that is implicated in many cardiovascular disorders.

Although there are many different kinds of drugs on the market, many people’s blood pressure is not adequately controlled by medication. Up to 30 per cent of people have to take three or more drugs and are considered resistant to therapy.

Now, a new implantable device is being readied for commercialisation in Europe that could help these resistant patients. The Rheos System, developed by Minneapolis-based CVRx, is a pacemaker-like device designed to reduce high blood pressure and address heart failure by electrically activating specific target areas at the carotid arteries in the neck.

The system comprises three components – a small device implanted beneath the collar bone, two thin lead wires that are implanted in contact with the left and right carotid arteries, plus an external unit to monitor the system’s functional characteristics and to program it via telemetry.

The carotid arteries on either side of the neck contain a specific location called the carotid sinus. Embedded in the walls of the arteries at that location are specialised receptors called baroreceptors, which are the body’s natural blood flow monitors.

They sense the pressure of blood flowing through the vessels, which causes them to send electrical impulses to the brain to let the brain know what the blood pressure is.

Engineers hope to develop a system where a physician could program in a patient’s required blood pressure

The implanted device works by electrically stimulating baroreceptors on the carotid arteries. This causes the baroreceptors to send signals to the brain that are interpreted as a rise in blood pressure that needs to be corrected. The brain acts to lower the blood pressure by reducing the workload of the heart in a chain of events that ultimately reduces risk of stroke, heart attack, heart failure and kidney disease.

According to Dr Robert Kieval, founder and chief technology officer of CVRx, three key parameters are used by the pulse generator to non-invasively regulate the activation energy from the device to the leads, and hence control the amount of stimulation delivered to a patient.

These parameters are the amplitude of the voltage of the pulses, their frequency and width. They are controlled by the external system via a telemetry communications link that allows a physician to program the microprocessor inside the device. This allows the physician to provide a therapy that is specific to each patient.

Since the device has primarily been used in clinical trials, key parameters are varied systematically by the external computer system used by a doctor in the presence of a CVRx representative until the most effective dose response – or optimal setting of the parameters – is found.

Then, in a series of regular check-ups, the dose response is checked again to ensure that a patient remains responsive. If not, the parameters can be modified to increase effectiveness.

’Clinical studies of the device have taken place across Europe and the US. A number of patients have been implanted with the device for more than four years and have experienced a significant and sustained drop in systolic blood pressure,’ said Kieval.

Eventually, the company’s engineers hope to develop a system where a physician would be able to program in the patient’s required blood pressure from a user interface and the embedded machine would then take appropriate action to stimulate the baroreceptors to do just that.

Design essential

The key facts to take away from this article

  • The Rheos System is a pacemaker-like device with three components
  • The implant works by stimulating receptors on the carotid arteries
  • An external system is used to program the internal microprocessor
  • Implanted patients have experienced a drop in systolic blood pressure