Baroreflex activation therapy is an approach to treating

high blood pressure Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

and the symptoms of

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

. It uses an implanted device to electrically stimulate

baroreceptors Baroreceptors (or archaically, pressoreceptors) are sensors located in the carotid sinus (at the bifurcation of external and internal carotids) and in the aortic arch. They sense the blood pressure and relay the information to the brain, so that a ...

in the carotid sinus region. This elicits a

reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

response through the sympathetic and vagal nervous systems that reduces

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...

Medical uses

Baroreflex activation therapy is used to reduce the symptoms of heart failure in patients who do not qualify for cardiac resynchronization therapy.

Adverse effects

In common with pacemakers, implantation of baroreflex activation therapy devices carries risks of bleeding, bruising and infection. The location of the electrode, on the carotid artery, carries a theoretical risk of disturbing plaque inside the carotid artery that in principle could cause a stroke, although protocols typically include scanning the artery for plaques beforehand, and such events appear not to have occurred in the systematic trials. High stimulation voltages can cause an appreciable sensation which can be unpleasant. In typical use the device output voltage is adjusted to below the level that causes unpleasant sensations.

Devices

Device development benefited from the related technology of

pacemakers An artificial cardiac pacemaker (or artificial pacemaker, so as not to be confused with the natural cardiac pacemaker) or pacemaker is a Implant (medicine), medical device that generates electrical impulses delivered by electrodes to the Heart ...

which have markedly reduced in size and increased in efficiency since their introduction in 1958. The falling cost of the fundamental technology that combines a long-lasting battery, stimulating electrode and a microcontroller in a single device, made it possible to create specialized devices to activate baroreceptors. Examples are the Rheos and the Barostim Neo systems. In 2019, the FDA awarded the BAROSTIM NEO® a Breakthrough Device Designation and approved the device for the treatment of heart failure. It is currently available in Europe and the United States.

Procedure

The device is implanted into upper chest with the electrodes placed in the neck. First, an incision is made in the neck to visualize the carotid bifurcation. The electrode is placed over the carotid artery and positioned where stimulating through it elicits a blood pressure reduction. The electrode is then sutured in place. The main part of the device (also called the pulse generator) is then placed in a pocket underneath the skin. Adjustments of the stimulation pattern (size and frequency of pulses) are made using a device programmer which communicates with the implanted device through short-range radio signals. Stimulation is set at a level that reduces blood pressure but does not cause discomfort.

Mechanism

Baroreflex activation is distinct from vagal stimulation. Electrical stimulation of the external surfaces of the carotid sinus activates baroreceptors believed to be in the adventitia of the artery. This stimulates an afferent limb which activates central nervous system pathways that in turn exert two different but synergistic autonomic effects on the body. First, global sympathetic outflow is reduced and, second, vagal outflow is increased. These two autonomic effector pathways reduce heart rate and vasomotor tone, leading to a reduction in blood pressure. Effects can be seen within a few seconds of initiation of stimulation, a feature which is used in the initial implant procedure to aid positioning of the electrode.

History

Despite modern medications against high blood pressure, only around half of people with hypertension in England, USA and Canada have blood pressure at or below target levels. In many cases the situation can be resolved with increases in

antihypertensive Antihypertensives are a class of drugs that are used to treat hypertension (high blood pressure). Antihypertensive therapy seeks to prevent the complications of high blood pressure, such as stroke and myocardial infarction. Evidence suggests tha ...

medication. However in about 10% of patients, blood pressure is still above target (140/90mm Hg) despite at least 3 anti-hypertensives, a status known as resistant hypertension. Some patients prefer not to be prescribed progressively greater number of medications, because of side effects or the difficulty managing a complex medication regime. Despite the greater invasiveness, they may prefer the option of a device that can contribute to blood pressure control. Electrical stimulation of the carotid baroreceptor region is one such option to lower blood pressure.

References

{{reflist Hypertension Electrotherapy