Renal Artery Denervation for the Treatment of Hypertension: Opening up New Horizons

Abstract

Hypertension is a major global public health concern. Anestimated 30–40% of the adult population in the developedworld suffer from this condition [1, 2]. Currently the role ofinterventional radiology is limited to the few cases inwhich the renin–angiotensin–aldosterone system is acti-vated by renal artery stenosis. However, stenosis of therenal artery accounts for elevated blood pressure in much\5% of patients, and the effect of renal stenting on bloodpressure is not as high as expected in the past [3, 4]. In themajority of patients, hypertension is deemed ‘‘essential,’’meaning that no direct cause can be identified and it isbelieved to be related to both genetic disposition andenvironmental influences. These patients need lifelongpharmacological therapy. Despite a plethora of antihyper-tensive drugs, hypertension remains resistant in a consid-erable number of patients. A new interventional procedure,the catheter-based renal sympathetic denervation (RSD),promises help in such cases of resistant hypertension.There is increasing evidence that renal efferent sympa-thetic nerves and afferent sensory nerves that lie within andimmediately adjacent to the wall of the renal artery arecrucial for initiation and maintenance of systemic hyper-tension [5–8]. Efferent renal sympathetic activation leadsto volume retention via sodium reabsorption, a reduction ofrenal blood flow by pre- and postglomerular vasocon-striction, and activation of the renin–angiotensin–aldosterone system. Afferent renal sensory nerve activitydirectly influences sympathetic outflow from the centralnervous system to the kidneys and other highly innervatedorgans involved in cardiovascular control, such as the heartand peripheral blood vessels, by modulating hypothalamicactivity [9]. Hence, functional denervation of the humankidney by targeting both efferent sympathetic nerves andafferent sensory nerves seems to be a valuable treatmentstrategy for hypertension [10].Renal denervation has been used successfully as atherapeutic strategy to prevent hypertension in a variety ofexperimental models. In humans, radical surgical methodsfor thoracic, abdominal, and pelvic sympathetic denerva-tion were successfully applied as early as the 1930s tolower blood pressure in patients with malignant hyperten-sion. However, the so-called Smithwick intervention wasassociated with high perioperative morbidity and mortalityand long-term complications, such as bowel, bladder, anderectile dysfunction, and severe postural hypotension[11–13].For RSD, the treatment catheter (Symplicity, Ardian,Inc., Palo Alto, CA) is introduced into the renal artery viafemoral access. Radiofrequency ablations lasting up to2 min each are applied to four to six discrete points in therenal artery. To destroy the nerve tissue in the whole cir-cumference of the artery, the tip of the ablation wire has tobe pulled in a helical manner backward toward the renalartery ostium by 5-mm steps between each ablation. Thetreatment is analogical to the radiofrequency ablation ofaberrant nerve bundles in the heart, which has been per-formed for many years. At first for safety reasons, theprocedure was only performed on one artery per session.After establishing the safety of the technique, a simulta-neous bilateral renal artery denervation is normally per-formed [14].