DEVICE THERAPY IN HYPERTENSION

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Resistant Hypertension

Resistant Hypertension: Blood pressure that remains above target levels despite adherence to a regimen of three antihypertensive drugs, one of which must be a diuretic, all at optimal or maximally tolerated doses. Additionally, blood pressure requiring four or more medications to achieve control is also considered resistant.

Pseudoresistance

Before diagnosing true resistant hypertension, it is important to rule out pseudoresistance, which refers to falsely elevated blood pressure readings due to:

• Poor adherence to medication.

• White coat effect: Elevated blood pressure readings in a clinical setting that are normal at home.

• Improper blood pressure measurement technique.

Causes of Resistant Hypertension

1.  Patient-Related Factors

• Nonadherence to Medication: Failure to take medications as prescribed is a common cause of resistant hypertension. This may be due to side effects, cost, or misunderstanding of the treatment plan.

• Suboptimal Treatment Regimen: Inadequate dosing, improper drug combinations, or insufficient use of diuretics may contribute to uncontrolled blood pressure.

• Lifestyle Factors:

  • Excessive Sodium Intake: High salt consumption can negate the effect of antihypertensive medications.

  • Obesity: Excess weight contributes to increased cardiac output and vascular resistance.

  • Physical Inactivity: Lack of exercise contributes to overall poor cardiovascular health.

  • Excessive Alcohol Intake: High alcohol consumption can raise blood pressure and reduce the efficacy of antihypertensive drugs.

• Medication Interference: Certain medications can increase blood pressure or counteract antihypertensive drugs, including:

  • Nonsteroidal Anti-inflammatory Drugs (NSAIDs).

  • Corticosteroids.

  • Oral Contraceptives.

  • Sympathomimetics (e.g., decongestants).

2.  Secondary Causes of Hypertension

Secondary hypertension is responsible for a significant number of resistant hypertension cases and includes the following:

• Primary Aldosteronism: Excess aldosterone production leads to sodium and water retention, contributing to elevated blood pressure.

• Chronic Kidney Disease (CKD): Impaired kidney function can lead to volume overload and increased systemic vascular resistance.

• Renal Artery Stenosis: Narrowing of the renal arteries results in decreased renal perfusion, triggering the renin-angiotensin system and increasing blood pressure.

• Obstructive Sleep Apnea (OSA): OSA is associated with intermittent hypoxia, sympathetic activation, and increased blood pressure.

• Pheochromocytoma: This rare adrenal gland tumor releases catecholamines, leading to episodic or sustained hypertension.

• Cushing’s Syndrome: Excess cortisol production leads to sodium retention and increased blood pressure.

• Thyroid Disorders: Hyperthyroidism and hypothyroidism can both contribute to blood pressure abnormalities.

Table: Causes of Resistant Hypertension

Category

Specific Causes

Patient-Related Factors

Nonadherence to medication

Suboptimal treatment regimen

Excessive sodium intake

Obesity

Physical inactivity

Excessive alcohol intake

Medication interference (NSAIDs, corticosteroids, etc.)

Secondary Hypertension

Primary aldosteronism

Chronic kidney disease

Renal artery stenosis

Obstructive sleep apnea

Pheochromocytoma

Cushing's syndrome

Thyroid disorders

Refractory Hypertension

Refractory hypertension is a more severe form of hypertension that remains uncontrolled despite aggressive treatment with at least five antihypertensive medications of different classes, including a diuretic. Unlike resistant hypertension, where blood pressure remains elevated despite using three or more drugs, refractory hypertension persists even when multiple drug classes are employed at their optimal or maximally tolerated doses, indicating a failure to respond to traditional therapeutic approaches.

Key Characteristics of Refractory Hypertension:

1. Failure to Achieve Target Blood Pressure: Blood pressure remains above goal levels despite the use of at least five different antihypertensive agents, including a long-acting diuretic.

2. Persistent High Sympathetic Activity: Patients with refractory hypertension often have significantly heightened sympathetic nervous system activity.

3. Inadequate Response Despite Adherence: Unlike resistant hypertension, which can sometimes be attributed to nonadherence or incorrect medication use, refractory hypertension persists even with good patient adherence and lifestyle management.

Comparison: Resistant vs. Refractory Hypertension

Parameter

Resistant Hypertension

Refractory Hypertension

Number of Medications

Uncontrolled on 3 or more drugs, including a diuretic

Uncontrolled on 5 or more drugs, including a diuretic

Persistence

Can be managed or controlled with optimized treatment

Remains uncontrolled despite optimization and multiple therapies

Treatment

May respond to modification of therapy, lifestyle changes

Often requires novel interventions, including device therapy

Potential Causes of Refractory Hypertension:

1. High Sympathetic Tone: Persistent activation of the sympathetic nervous system plays a significant role in maintaining elevated blood pressure in refractory hypertension.

2. Secondary Hypertension: Conditions such as primary aldosteronism, chronic kidney disease, or pheochromocytoma may contribute significantly to refractory cases.

3. Volume Overload: Despite diuretic therapy, some patients may have unrecognized volume overload, contributing to uncontrolled blood pressure.

4. Structural Vascular Changes: Long-standing hypertension may cause arterial stiffness, making blood pressure control more challenging.

Management Considerations:

• Device-Based Therapies: Patients with refractory hypertension may benefit from device-based therapies such as renal denervation or baroreflex activation therapy to reduce sympathetic activity.

• Lifestyle Optimization: Although lifestyle changes alone may not be sufficient, optimizing dietary intake, physical activity, and reducing alcohol consumption are still important components.

Device Therapy for Hypertension

Device-based therapies for hypertension have emerged as an alternative to conventional pharmacotherapy, especially in patients with resistant or poorly controlled hypertension. These therapies primarily target the autonomic nervous system and aim to modulate the physiological mechanisms responsible for blood pressure regulation. Below is an overview of device therapies and their general indications in hypertension:

1. Renal Denervation (RDN)

• Indications:

  • Patients with resistant hypertension who remain uncontrolled despite the use of three or more antihypertensive drugs, including a diuretic.

  • Suitable for patients with overactive sympathetic drive contributing to elevated blood pressure.

• Purpose: RDN aims to reduce renal sympathetic nerve activity, which is crucial in the development and maintenance of high blood pressure. It can be performed using radiofrequency, ultrasound, or chemical denervation methods.

• Key Devices: Symplicity Spyral catheter (radiofrequency) and Paradise System (ultrasound-based).

2. Baroreflex Activation Therapy (BAT)

• Indications:

  • Patients with resistant hypertension, particularly those who do not respond to standard medical therapies.

  • Often used when conventional antihypertensive drugs are not effective or cause significant side effects.

• Purpose: BAT involves stimulating baroreceptors in the carotid sinus to reduce sympathetic nervous system activity and lower blood pressure.

• Devices: Barostim Neo, a second-generation system that includes a unilateral electrode for carotid sinus stimulation.

3. Endovascular Baroreflex Amplification

• Indications:

  • Patients with resistant hypertension, particularly when pharmacological approaches are insufficient.

• Purpose: This therapy enhances baroreceptor sensitivity by reshaping the carotid sinus, thus promoting a decrease in sympathetic outflow.

• Device: MobiusHD, a nitinol stent that increases strain on the carotid sinus to stimulate baroreceptors.

4. Carotid Body Ablation

• Indications:

  • Patients with resistant hypertension characterized by overactive chemoreflex sensitivity, leading to increased sympathetic drive.

• Purpose: Ablation of the carotid body aims to reduce sympathetic overactivity by targeting the afferent signaling from the chemoreceptors located at the carotid bifurcation.

5. Pacemaker-Mediated Programmable Hypertension Control

• Indications:

  • Patients with uncontrolled hypertension who have a coexisting indication for pacemaker therapy.

• Purpose: This therapy modulates atrioventricular intervals to influence cardiac output and blood pressure. It aims to manage hypertension in patients requiring a dual-chamber pacemaker.

• Device: Moderato System, which regulates the atrioventricular interval to control blood pressure.

6. Central Iliac Arteriovenous Anastomosis (cAVA)

• Indications:

  • Patients with resistant hypertension who have failed to achieve adequate blood pressure control with both pharmacological and neuromodulatory therapies.

• Purpose: Creation of a controlled arteriovenous shunt in the iliac region helps in reducing systemic vascular resistance, thereby lowering blood pressure.

• Device: Coupler, which forms a conduit between the external iliac artery and vein

Summary Table: General Indications for Device Therapy in Hypertension

Device Therapy

Indications

Purpose

Renal Denervation (RDN)

Resistant hypertension with sympathetic overactivity

Reduce renal sympathetic nerve activity

Baroreflex Activation Therapy (BAT)

Resistant hypertension not responsive to medications

Modulate baroreceptor response to lower BP

Endovascular Baroreflex Amplification

Resistant hypertension

Enhance baroreceptor sensitivity and reduce BP

Carotid Body Ablation

Resistant hypertension with chemoreflex overactivity

Reduce chemoreceptor-mediated sympathetic activity

Pacemaker-Mediated Hypertension Control

Uncontrolled hypertension with a pacemaker indication

Control BP by modulating AV interval

Central Iliac Arteriovenous Anastomosis

Resistant hypertension after failure of other therapies

Reduce systemic vascular resistance