Hypertension Treatment with Renal Nerve Ablation

The neuroscience of hypertension covers several important domains.  Untreated hypertension can lead to central nervous complications such as stroke and vascular dementia.  Patients with essential hypertension show hyperactive renal sympathetic nerve outflow.  This produces several effects increasing blood pressure including: stimulation of renin, increased kidney sodium reabsorption and reduced blood flow to the kidney.  The kidney signals the brain areas controlling central sympathethic tone regulation.

Diet, weight loss and pharmacotherapy form the basics for treatment of hypertension.  Despite a variety of drugs with different mechanisms of action many patients fail to achieve satisfactory blood pressure control.  Obviously, new strategies for blood pressure control are needed.

One surgical strategy undergoing study is use of a endovascular cather to interrupt signals from the renal nerves to the kidney.  A recent study published in Lancet (The Sympliciity HTN-2summarized promising results from a randomized clinical trial using renal sympathetic denervation in a group of patients with treatment-resistant hypertension.  The key design elements of the study were:

• Subjects: 52 subjects randomized to surgical intervention, 54 controls not receiving the intervention
• Entry criteria: age 18-85 with systolic blood pressure of 160 mm Hg or greater despite compliance with three or more antihypertensive drugs (subjects could be enrolled if they had type 2 diabetes with a blood pressure of 150 mm Hg or more)
• Exclusion criteria: renal insufficiency, type 1 diabetes, contraindications to MRI, valvular heart disease, pregnancy, history of myocardial infarction, unstable angina or stroke in the last 6 months
• Procedure: A Symplicity catheter was inserted through the groin.  A series of low-power radiofrequency pulses was applied along both renal arteries with IV anxiolytics and narcotics used to control pain

The primary endpoint defined for the study was systolic blood pressure change at 6 months.  The drop in blood pressures were pretty impressive in the intervention group compared to controls:

• 6 month reduction in systolic 32 mm Hg intervention vs 1 mm Hg increase in controls
• 6 month reduction in diastolic blood pressure 12 mm Hg intervention vs 0 mm Hg in controls

Five subjects in the intervention group had no decrease in systolic blood pressure and did not appear to benefit.  No significant complications were noted in the intervention group.  Renal function remained stable after the intervention.  The authors note that the durability of the intervention is unknown.  It is possible nerve regeneration over time may occur resulting in return of hypertension.  In early trials, the effect of the intervention has not be lost in follow up lasting 2 years.

This intervention for hypertension appears very promising and deserves further study and long-term follow up.  If replicated it holds the potential to be a significant advance in treatment-resistant hypertension and the prevention on central hypertension complications of stroke and vascular dementia.

Figure on main complications related to hypertension courtesy of Wikipedia Commons public domain file authored by Mikael Haggstrom.

Symplicity HTN-2 Investigators, Esler MD, Krum H, Sobotka PA, Schlaich MP, Schmieder RE, & Böhm M (2010). Renal sympathetic denervation in patients with treatment-resistant hypertension (The Symplicity HTN-2 Trial): a randomised controlled trial. Lancet, 376 (9756), 1903-9 PMID: 21093036