Baroreflex activation device implant (Barostim)

Baroreflex activation therapy (BAT) Barostim is an advanced device that leverages the principles of baroreflex activation therapy to modulate the autonomic nervous system and treat conditions like resistant hypertension and heart failure with reduced ejection fraction (HFrEF). The device currently implanted by our vascular surgeons is the Barostim Neo2 designed by CVRX. A lead is placed on the carotid sinus via a small cutdown, tunneled under the subcutaneous tissue, and connected to a generator that is placed in the chest and can be controlled by an external programmer. Heart failure with reduced ejection fraction involves disturbances of the autonomic nervous system characterized by decreased baroreceptor sensitivity, increased sympathetic tone, and decreased parasympathetic tone. Baroreflex activation therapy (BAT) aims to restore balance to the autonomic nervous system by increasing parasympathetic output via electrical stimulation of the carotid baroreceptors. In clinical trials BAT has been shown to be safe and significantly improved QOL, exercise capacity, and NT-proBNP in patients with HFrEF. This approach helps mitigate the progression of heart failure by reducing neurohormonal activation.

Baroreflex activation device implant (Barostim)

Anesthesia type	General
Airway	ETT
Lines and access	PIV x2 +/- Arterial line
Monitors	Standard BIS +/- ABP
Primary anesthetic considerations
Preoperative	Heart failure symptoms
Intraoperative	Avoid baroreflex blunting medications
Postoperative	Standard
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Overview

Indications

• Barostim is indicated for patients who are NYHA Class III or Class II (who had a recent history of Class III) despite treatment with guideline-directed medical therapies (medications and devices), have a left ventricular ejection fraction of ≤ 35% and a NT-proBNP <1600 pg/ml.
• Refractory hypertension or inability to tolerate antihypertensive agents
• Contraindications to LVAD, heart transplant
• Autonomic Imbalance and Sympathetic Hyperactivity/POTS/Tachycardia

Contraindications

• Patient eligible for cardiac resynchronization therapy
• Bilateral carotid bifurcations located above the level of the mandible
• Baroreflex failure or autonomic neuropathy
• Uncontrolled, symptomatic cardiac bradyarrhythmias
• Carotid artery stenosis greater than 50% caused by atherosclerosis, as determined by ultrasound or angiographic evaluation
• Pregnancy
• Local or systemic infection

Surgical procedure

The procedure is well described by Weaver et al

Exposure

The first step in the procedure is exposing the carotid artery.

• The carotid bifurcation is exposed via a cutdown
  • The right carotid is preferentially used as it has been shown to be more sensitive

Mapping

The next step is to map the carotid sinus by testing the baroreceptor reflex at different areas.

• The surgeons will stimulate different areas of the carotid sinus with an electrode to test for a decrease in heart rate and/or systolic blood pressure
  • Mapping requires a lot of communication between surgery and anesthesia teams
  • Before the initiation of mapping, a stable baseline heart rate and blood pressure should be established
  • Peak responses in heart rate and pressure generally occur within 30-120 seconds of initiating stimulation
• Many common anesthetic medications can cause blunting of the baroreceptor reflex
  • Maintenance of anesthesia should be tailored to the patient to safely avoid baroreceptor blunting medications (see intraoperative management)

Anchoring and tunneling

The next step is to anchor the electrode to the point of maximal stimulus and tunnel the lead into the chest wall where it is attached to the generator.

Testing and closure

The next step is to test the lead and generator for adequate function and close the chest wall pocket and cutdown.

Preoperative management

Patient evaluation

System	Considerations
Cardiovascular	Only patients with significant heart failure history undergo BAT. They should be assessed for evidence of volume overload or current heart failure exacerbation. All patients will likely be on a beta blocker and should take it perioperatively
Pulmonary	SOB may be evidence of worsening heart failure or exacerbation. Patients with baseline orthopnea may require different positioning prior to induction
Hematologic	Likely anemic. Given proximity to great vessels, an active type and screen is recommended
Renal	HFrEF patients may have concomitant CKD
Endocrine	HFrEF patients may have concomitant diabetes

Labs and studies

• Type and Screen
• +/- TTE, TEE, EKG, Stress test

Operating room setup

• Arterial catheter and transducer
• Infusion and syringe pumps
• Vasopressor infusions available
• Push dose pressors drawn up

Patient preparation and premedication

• Cardiovascular medications are stopped 4-6 hours before surgery with the exception of beta-blocker therapy, which is down-titrated 1-2 days in advance to a level at which intraoperative bradycardia is not expected to interfere with observation of the baroreflex response
• If the patient is on DAPT or other anticoagulants they are held for the appropriate time given the indication and risk, as guided by discussion between surgeon and cardiologist
• Likely a lower than normal threshold for benzodiazepine use in elderly patients as the sedative hypnotics options are limited by baroreceptor reflex concerns

Regional and neuraxial techniques

• Regional anesthesia is NOT recommended in BAT implantation cases due to concerns for local anesthetic blunting of the baroreceptor reflex

Intraoperative management

Monitoring and access

• PIV x2
• Standard monitors
• BIS
• +/- Arterial line

Induction and airway management

• Standard induction for heart failure patient, ETT

Positioning

• Supine
• Arms usually tucked

Maintenance and surgical considerations

• Many of the medications routinely used for maintenance of general anesthesia modulate the baroreceptor reflex; including propofol, volatile anesthetics (in a dose dependent fashion), ketamine (in rabbits), and dexmedetomidine
  • Importantly, opioids, benzodiazepines, etomidate, and nitrous oxide all minimally affect the baroreceptor reflex
• Initial protocols for BAT device implantation recommend avoiding any of the blunting agents: Etomidate induction, benzodiazepine, opioid (as a bolus or infusion), and paralytic maintenance
  • These protocols are based on the theoretical benefit. There is no published data on the success or failure of baroreflex mapping with different regimens [source needed]. The device manufacturers also make suggestions, however, there are no sure recommendations
• BAT devices have been successfully implanted with different regimens. Safely achieving amnesia and immobility, while avoiding baroreflex blunting is the goal
  • Propofol is a reasonable choice for induction. While it does blunt the reflex, if used only for induction, the blunting effect dissipates in ~10 minutes - usually plenty of time to allow for draping, timeouts, and cutdown
  • Volatile anesthetics below 0.5 MAC limit blunting, are titratable, and allow for a more efficient emergence and recovery
  • Supplement with a remifentanil infusion, fentanyl boluses, or nitrous oxide to ensure adequate depth of anesthesia. Use BIS to help titrate medications
  • Avoid blunting agents which convey little benefit to efficiency and safety of the anesthetic (i.e., ketamine, dexmedetomidine)
  • Each strategy will of course have its drawbacks. A pure benzo-opioid regimen in a frail, elderly patient could necessitate a long recovery phase and increase the potential for delirium while using some of the blunting agents may require changing strategies mid-operation and/or risk failure
• During the mapping phase the goal is a stable dose of anesthetic, so that changes in HR and SBP can be attributed to sinus stimulation and not changes in medications. You will have transient bradycardia and hypotension during mapping. Be patient, but be prepared to intervene if the patient does not recover after stimulation ceases

Emergence

• Standard

Postoperative management

Disposition

• PACU

Pain management

• Mild pain procedure, low dose opioids generally sufficient

Potential complications

• Bradycardia, hypotension intraoperatively/postoperatively
• Other arrythmias
• Pneumothorax (during tunneling or pouch creation)
• Bleeding, hematoma
• Infection
• lead displacement
• Nerve injury