Device profile of the MobiusHD EVBA system for the treatment of resistant hypertension: overview of its mechanism of action, safety and efficacy

INTRODUCTION

Early promising results of renal nerve denervation awakened interest in developing medical device alternatives for patients with resistant hypertension. The subsequent sham-controlled renal nerve denervation randomized trials were disappointing leading researchers and innovators to explore alternative device and trial designs to address this significant unmet need. We describe the innovation process leading to the first endovascular carotid baroreflex amplification device currently undergoing clinical trials in the United States and Europe.

AREAS COVERED

We provide a brief overview of carotid baroreceptor physiology and then couple this knowledge with the fundamental principles of strain pattern changes that led to the proposed innovation. The mechanism of blood pressure reduction via enhancing innate physiologic carotid sinus baroreceptor signaling through changes in pulsatile focal carotid bulb strain is described alongside preclinical testing and early clinical results.

EXPERT OPINION

The collective data to date suggest endovascular carotid baroreflex amplification may be an innovative alternative for resistant hypertension patients. However, well-controlled studies will be needed to assess efficacy, safety, durability, and risk: benefit of this permanent intravascular carotid implant.

SUBJECT CODES

high blood pressure, hypertension, treatment, physiology.

Blood Pressure: Return of the Sympathetics?

This brief review highlights new ideas about the role of the sympathetic nervous system in human blood pressure regulation. We emphasize how this role varies with age and sex and use our findings to raise questions about the sympathetic nervous system and hypertension in humans. We also focus on three additional areas, including (1) novel ideas about the carotid body and sympathoexcitation as it relates to hypertension, (2) clinical trials of renal denervation that attempted to treat hypertension by reducing ongoing sympathoexcitation, and (3) new ideas about resistant hypertension and cerebral blood flow. We further highlight that success of device-based therapy to modulate the sympathetic nervous system relies heavily on patient selection. Furthermore, data suggest that the majority of patients respond to anti-hypertensive therapy and the major cause of "resistant" hypertension is poor patient adherence. While the enthusiasm for device therapy or perhaps even "precision medicine" is high, it is likely that by far the most benefit to the most patients will occur via better screening, more aggressive therapy, and the development of strategies that improve patient adherence to medication regimens and lifestyle changes.

Deep brain stimulation for the treatment of resistant hypertension

Hypertension is a leading risk factor for the development of several cardiovascular diseases. As the global prevalence of hypertension increases, so too has the recognition of resistant hypertension. Whilst figures vary, the proportion of hypertensive patients that are resistant to multiple drug therapies have been reported to be as high as 16.4 %. Resistant hypertension is typically associated with elevated sympathetic activity and abnormal homeostatic reflex control and is termed neurogenic hypertension because of its presumed central autonomic nervous system origin. This resistance to conventional pharmacological treatment has stimulated a plethora of medical devices to be investigated for use in hypertension, with varying degrees of success. In this review, we discuss a new therapy for drug-resistant hypertension, deep brain stimulation. The utility of deep brain stimulation in resistant hypertension was first discovered in patients with concurrent neuropathic pain, where it lowered blood pressure and improved baroreflex sensitivity. The most promising central target for stimulation is the ventrolateral periaqueductal gray, which has been well characterised in animal studies as a control centre for autonomic outflow. In this review, we will discuss the promise and potential mechanisms of deep brain stimulation in the treatment of severe, resistant hypertension.

Tonic arterial chemoreceptor activity contributes to cardiac sympathetic activation in mild ovine heart failure

Heart failure (HF) is associated with a large increase in cardiac sympathetic nerve activity (CSNA), which has detrimental effects on the heart and promotes arrhythmias and sudden death. There is increasing evidence that arterial chemoreceptor activation plays an important role in stimulating renal sympathetic nerve activity (RSNA) and muscle sympathetic nerve activity in HF. Given that sympathetic nerve activity to individual organs is differentially controlled, we investigated whether tonic arterial chemoreceptor activation contributes to the increased CSNA in HF. We recorded CSNA and RSNA in conscious normal sheep and in sheep with mild HF induced by rapid ventricular pacing (ejection fraction <40%). Tonic arterial chemoreceptor function was evaluated by supplementing room air with 100% intranasal oxygen (2-3 l min(-1)) for 20 min, thereby deactivating chemoreceptors. The effects of hyperoxia on resting levels and baroreflex control of heart rate, CSNA and RSNA were determined. In HF, chemoreceptor deactivation induced by hyperoxia significantly reduced CSNA [90 ± 2 versus 75 ± 5 bursts (100 heart beats)(-1), P < 0.05, n = 10; room air versus hyperoxia] and heart rate (96 ± 4 versus 85 ± 4 beats min(-1), P < 0.001, n = 12). There was no change in RSNA burst incidence [93 ± 4 versus 92 ± 4 bursts (100 heart beats)(-1), n = 7], although due to the bradycardia the RSNA burst frequency was decreased (90 ± 8 versus 77 ± 7 bursts min(-1), P < 0.001). In normal sheep, chemoreceptor deactivation reduced heart rate without a significant effect on CSNA or RSNA. In summary, deactivation of peripheral chemoreceptors during HF reduced the elevated levels of CSNA, indicating that tonic arterial chemoreceptor activation plays a critical role in stimulating the elevated CSNA in HF.