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Renal denervation to treat resistant hypertension: Guarded optimism

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ABSTRACTRenal sympathetic denervation has shown promise in treating hypertension resistant to drug therapy. This procedure lowers blood pressure via targeted attenuation of renal sympathetic tone, and it has a favorable safety profile. But although there is reason for cautious optimism, we should keep in mind that the mechanisms of hypertension are complex and multifactorial, and further study of this novel therapy and its long-term effects is needed.

KEY POINTS

  • Renal sympathetic nerves help regulate volume and blood pressure as they innervate the renal tubules, blood vessels, and juxtaglomerular apparatus. They carry both afferent and efferent signals between the central nervous system and the kidneys.
  • Surgical sympathectomy was done in the 1950s for malignant hypertension. It had lasting antihypertensive results but also caused severe procedure-related morbidity. A new percutaneous procedure for selective renal denervation offers the advantage of causing few major procedure-related adverse effects.
  • Selective renal denervation decreases norepinephrine spillover and muscle sympathetic nerve activity, evidence that the procedure reduces sympathetic tone.
  • The major clinical trials done so far have found that renal denervation lowers blood pressure significantly, and the reduction is sustained for at least 3 years.


 

References

Can a percutaneous catheter-based procedure effectively treat resistant hypertension?

Radiofrequency ablation of the renal sympathetic nerves is undergoing randomized controlled trials in patients who have resistant hypertension and other disorders that involve the sympathetic nervous system. Remarkably, the limited results available so far look good.

See related editorial

This article discusses the physiologic rationale for renal denervation, the evidence from studies in humans of the benefits, risks, and complications of the procedure, upcoming trials, and areas for future research.

DESPITE MANY TREATMENT OPTIONS, RESISTANT HYPERTENSION IS COMMON

Hypertension is a leading reason for visits to physicians in the United States and is associated with increased rates of cardiovascular disease and death.1,2 A variety of antihypertensive agents are available, and the percentage of people with hypertension whose blood pressure is under control has increased over the past 2 decades. Nevertheless, population-based studies show that the control rate remains suboptimal.3 Effective pharmacologic treatment may be limited by inadequate doses or inappropriate combinations of antihypertensive drugs, concurrent use of agents that raise the blood pressure, noncompliance with dietary restrictions, and side effects that result in poor compliance with drug therapy.

Resistant hypertension is defined as failure to achieve goal blood pressure in patients who are adhering to full tolerated doses of an appropriate three-drug regimen that includes a diuretic.1,4,5 If we use these criteria, many patients labelled as having resistant hypertension probably do not truly have it; instead, they are nonadherent to therapy or are on an inadequate or inappropriate regimen. Although the true prevalence of resistant hypertension is not clear, estimates from large clinical trials suggest that about 20% to 30% of hypertensive patients may meet the criteria for it.4 For the subset of patients who have truly resistant hypertension, nonpharmacologic treatments such as renal sympathetic denervation are an intriguing avenue.

SURGICAL SYMPATHETIC DENERVATION: TRIED AND ABANDONED IN THE 1950s

More than a half century ago, a surgical procedure, thoracolumbar sympathectomy (in which sympathetic nerve trunks and splanchnic nerves were removed), was sometimes performed to control blood pressure in patients with malignant hypertension. This was effective but caused debilitating side effects such as postural hypotension, erectile dysfunction, and syncope.

Smithwick and Thompson6 reported that, in 1,266 hypertensive patients who underwent this procedure and 467 medically treated controls, the 5-year mortality rates were 19% and 54%, respectively. Forty-five percent of those who survived the surgery had significantly lower blood pressure afterward, and the antihypertensive effect lasted 10 years or more.

The procedure fell out of favor due to the morbidity associated with this nonselective approach and to the increased availability of drug therapy.

THE SYMPATHETIC NERVOUS SYSTEM IS A DRIVER OF HYPERTENSION

A variety of evidence suggests that hyperactivation of the sympathetic nervous system plays a major role in initiating and maintaining hypertension. For example, drugs that inhibit the sympathetic drive at various levels have a blood-pressure-lowering effect. Further, direct intraneural recordings show a high level of sympathetic nerve activity in the muscles of hypertensive patients, who also have high levels of cardiac and renal norepinephrine “spillover”—ie, the amount of this neurotransmitter that escapes neuronal uptake and local metabolism and spills over into the circulation.7

Figure 1.

The kidneys are supplied with postganglionic sympathetic nerve fibers that end in the efferent and afferent renal arterioles, the juxtaglomerular apparatus, and the renal tubular system. Studies in animals and humans have shown that an increase in efferent signals (ie, from the brain to the kidney) leads to renal vasoconstriction and decreased renal blood flow, increased renin release, and sodium retention.8,9 Afferent signals (from the kidney to the central nervous system), which are increased in states of renal ischemia, renal parenchymal injury, and hypoxia, disinhibit the vasomotor center (the nuclei tractus solitarii) in the central nervous system, leading to increased efferent signals to the kidneys, heart, and peripheral blood vessels (Figure 1).10

Enhanced sympathetic activity in patients with hypertension may play a role in subsequent target-organ damage such as left ventricular hypertrophy, congestive heart failure, and progressive renal damage.11

Studies of renal denervation in animals, using surgical and chemical techniques, have further helped to establish the role of renal sympathetic nerves in hypertension.12,13

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