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The seventeenth century London neuroanatomical school headed by Thomas Willis published the first images of the sympathetic nervous system. Nineteenth century European physiologists characterised these as the “pressor nerves”. Von Euler’s demonstration that the sympathetic transmitter was norepinephrine brought the field into the modern era. Sympathetic nervous system responses are regionally differentiated; human regional sympathetic activity is best studied by recording from postganglionic sympathetic efferents directed to the skeletal muscle vasculature (clinical microneurography) and by measurement of organ-specific norepinephrine release to plasma from sympathetic nerves (regional “norepinephrine spillover”). With these techniques, the sympathetic nervous system became accessible to clinical scientists, allowing the demonstration that sympathetic nervous system activation is crucial in the development and outcomes of cardiovascular disorders, most notably heart failure and essential hypertension. Activation of the renal sympathetic outflow is pivotal in the pathogenesis of essential hypertension. An important goal for clinical scientists is translation of knowledge of pathophysiology, such as this, into better treatment for patients. Although disputed, the case is strong that in hypertension, we are now on the cusp of effective “mechanisms to management” transition, with the use of catheter-based renal sympathetic nerve ablation for treating drug-resistant hypertension.

Renal denervation (RDN) with radiofrequency ablation substantially reduces blood pressure in patients with treatment-resistant hypertension. We assessed the long-term antihypertensive effects and safety. Symplicity HTN-1 is an open-label study that enrolled 153 patients, of whom 111 consented to follow-up for 36 months. Eligible patients had a systolic blood pressure of at least 160 mm Hg and were taking at least three antihypertensive drugs, including a diuretic, at the optimum doses. Changes in office systolic blood pressure and safety were assessed every 6 months and reported every 12 months. This study is registered with ClinicalTrials.gov, numbers NCT00483808, NCT00664638, and NCT00753285. 88 patients had complete data at 36 months. At baseline the mean age was 57 (SD 11) years, 37 (42%) patients were women, 25 (28%) had type 2 diabetes mellitus, the mean estimated glomerular filtration rate was 85 (SD 19) mL/min per 1·73 m2, and mean blood pressure was 175/98 (SD 16/14) mm Hg. At 36 months significant changes were seen in systolic (−32·0 mm Hg, 95% CI −35·7 to −28·2) and diastolic blood pressure (−14·4 mm Hg, −16·9 to −11·9). Drops of 10 mm Hg or more in systolic blood pressure were seen in 69% of patients at 1 month, 81% at 6 months, 85% at 12 months, 83% at 24 months, and 93% at 36 months. One new renal artery stenosis requiring stenting and three deaths unrelated to RDN occurred during follow-up. Changes in blood pressure after RDN persist long term in patients with treatment-resistant hypertension, with good safety. Ardian LLC/Medtronic Inc.

To the Editor: The renal sympathetic nerves have been identified as a major contributor to the complex pathophysiology of hypertension in both experimental models and in humans. 1 Patients with essential hypertension generally have increased efferent sympathetic drive to the kidneys, as evidenced by elevated rates of renal norepinephrine spillover, defined as the amount of transmitter that escapes neuronal uptake and local metabolism and thus “spills over” into the circulation. Hypertension is also characterized by an increased rate of sympathetic-nerve firing, possibly modulated by afferent signaling from renal sensory nerves. 2 – 4 A 59-year-old male patient with long-standing essential hypertension that was . . .

Renal sympathetic hyperactivity is associated with hypertension and its progression, chronic kidney disease, and heart failure. We did a proof-of-principle trial of therapeutic renal sympathetic denervation in patients with resistant hypertension (ie, systolic blood pressure ≥160 mm Hg on three or more antihypertensive medications, including a diuretic) to assess safety and blood-pressure reduction effectiveness. We enrolled 50 patients at five Australian and European centres; 5 patients were excluded for anatomical reasons (mainly on the basis of dual renal artery systems). Patients received percutaneous radiofrequency catheter-based treatment between June, 2007, and November, 2008, with subsequent follow-up to 1 year. We assessed the effectiveness of renal sympathetic denervation with renal noradrenaline spillover in a subgroup of patients. Primary endpoints were office blood pressure and safety data before and at 1, 3, 6, 9, and 12 months after procedure. Renal angiography was done before, immediately after, and 14–30 days after procedure, and magnetic resonance angiogram 6 months after procedure. We assessed blood-pressure lowering effectiveness by repeated measures ANOVA. This study is registered in Australia and Europe with ClinicalTrials.gov, numbers NCT 00483808 and NCT 00664638. In treated patients, baseline mean office blood pressure was 177/101 mm Hg (SD 20/15), (mean 4·7 antihypertensive medications); estimated glomerular filtration rate was 81 mL/min/1·73m 2 (SD 23); and mean reduction in renal noradrenaline spillover was 47% (95% CI 28–65%). Office blood pressures after procedure were reduced by −14/−10, −21/−10, −22/−11, −24/−11, and −27/−17 mm Hg at 1, 3, 6, 9, and 12 months, respectively. In the five non-treated patients, mean rise in office blood pressure was +3/−2, +2/+3, +14/+9, and +26/+17 mm Hg at 1, 3, 6, and 9 months, respectively. One intraprocedural renal artery dissection occurred before radiofrequency energy delivery, without further sequelae. There were no other renovascular complications. Catheter-based renal denervation causes substantial and sustained blood-pressure reduction, without serious adverse events, in patients with resistant hypertension. Prospective randomised clinical trials are needed to investigate the usefulness of this procedure in the management of this condition. Ardian Inc.

Conclusive evidence demonstrates that the sympathetic nervous system activation is a hallmark of congestive heart failure. This has been shown via a variety of biochemical, neurophysiological, and neuroimaging approaches for studying human sympathetic neural function. The sympathetic activation appears to be an early phenomenon in the clinical course of the disease, closely related to its severity and potentiated by the concomitant presence of other comorbidities, such as obesity, diabetes mellitus, metabolic syndrome, hypertension, and renal failure. The adrenergic overdrive in heart failure is associated with other sympathetic abnormalities, such as the downregulation of beta-adrenergic adrenoreceptors at cardiac level, and exerts unfavorable consequences on the cardiovascular system. These include the endothelial dysfunction, the development of left ventricular hypertrophy, the atherosclerosis development, as well as the generation of atrial and ventricular arrhythmias, and, at very extreme levels of sympathetic activation, the occurrence of microscopic myocardial necrosis. Given the close direct independent relationships detected in heart failure between sympathetic activation and mortality, the adrenergic overdrive has become a target of neuromodulatory therapeutic interventions, which include non-pharmacological, pharmacological, and device-based interventions. For some of these approaches (specifically bilateral renal nerves ablation and carotid baroreceptor stimulation), additional studies are needed to better define their impact on the clinical course of the disease.

Successful treatment of hypertension is difficult despite the availability of several classes of antihypertensive drug, and the value of strategies to combat the effect of adverse lifestyle behaviours on blood pressure. In this paper, we discuss two promising therapeutic alternatives for patients with resistant hypertension: novel drugs, including new pharmacological classes (such as vasopeptidase inhibitors and aldosterone synthase inhibitors) and new molecules from present pharmacological classes with additional properties in blood-pressure or metabolism pathways; and new procedures and devices, including stimulation of arterial baroreceptors and catheter-based renal denervation. Although several pharmacological targets have been discovered with promising preclinical results, the clinical development of novel antihypertensive drugs has been more difficult and less productive than expected. The effectiveness and safety of new devices and procedures should be carefully assessed in patients with resistant hypertension, thus leading to a new era of outcome trials and evidence-based guidelines.

Activation of renal sympathetic nerves is key to pathogenesis of essential hypertension. We aimed to assess effectiveness and safety of catheter-based renal denervation for reduction of blood pressure in patients with treatment-resistant hypertension. In this multicentre, prospective, randomised trial, patients who had a baseline systolic blood pressure of 160 mm Hg or more (≥150 mm Hg for patients with type 2 diabetes), despite taking three or more antihypertensive drugs, were randomly allocated in a one-to-one ratio to undergo renal denervation with previous treatment or to maintain previous treatment alone (control group) at 24 participating centres. Randomisation was done with sealed envelopes. Data analysers were not masked to treatment assignment. The primary effectiveness endpoint was change in seated office-based measurement of systolic blood pressure at 6 months. Primary analysis included all patients remaining in follow-up at 6 months. This trial is registered with ClinicalTrials.gov, number NCT00888433. 106 (56%) of 190 patients screened for eligibility were randomly allocated to renal denervation (n=52) or control (n=54) groups between June 9, 2009, and Jan 15, 2010. 49 (94%) of 52 patients who underwent renal denervation and 51 (94%) of 54 controls were assessed for the primary endpoint at 6 months. Office-based blood pressure measurements in the renal denervation group reduced by 32/12 mm Hg (SD 23/11, baseline of 178/96 mm Hg, p<0·0001), whereas they did not differ from baseline in the control group (change of 1/0 mm Hg [21/10], baseline of 178/97 mm Hg, p=0·77 systolic and p=0·83 diastolic). Between-group differences in blood pressure at 6 months were 33/11 mm Hg (p<0·0001). At 6 months, 41 (84%) of 49 patients who underwent renal denervation had a reduction in systolic blood pressure of 10 mm Hg or more, compared with 18 (35%) of 51 controls (p<0·0001). We noted no serious procedure-related or device-related complications and occurrence of adverse events did not differ between groups; one patient who had renal denervation had possible progression of an underlying atherosclerotic lesion, but required no treatment. Catheter-based renal denervation can safely be used to substantially reduce blood pressure in treatment-resistant hypertensive patients. Ardian.

Multiple sham-controlled clinical trials have demonstrated significant reductions in both office and 24-h blood pressure (BP) following radiofrequency renal denervation (RDN) in the uncontrolled hypertension population. Notably, the blood pressure response varies widely within individual participants, thus showing a clinical need to identify potential RDN “responders” prior to the procedure. Despite multiple analytic efforts, no single parameter, aside from baseline blood pressure, has been consistently associated with BP reduction following RDN. However, this failure may be due to limitations in empiric definitions of responders. Indeed, commonly applied responder definitions based on the difference between two point-in-time BP measurements are fraught due to visit-to-visit variability in office and 24-h blood pressure endpoints. Several factors should be considered to develop a more clinically useful operational definition of procedural response including relative changes in office and 24-h BP, consideration of the temporal response to RDN, as well as adjustment for baseline BP. The current evidence may provide incentives for future expert consensus to precisely define responders to hypertension treatments.

[...]ambulatory blood pressure is the state-of-the-art technique for measuring blood pressure in patients with treatment-resistant hypertension.2 Poor drug adherence is common in treatment-resistant hypertension,3 but this was not monitored in SYMPLICITY HTN-2, making the study susceptible to the Hawthorne effect.4 The SYMPLICITY HTN-3 trial5 included a sham control and ambulatory blood pressure measurement to balance out the Hawthorne effect, as well as other patient and investigator unspecific effects, and the blood pressure lowering effect of renal denervation was not significant in this trial. [...]the meta-analyses showed that renal denervation did not lead to severe adverse events and could be considered safe.6,7 Third, the evidence for the role of the sympathetic system in the pathophysiology of hypertension is strong.8,9 Finally, the clinical problems that interfered with renal denervation could be overcome.10,11 However, because of the clinical problems and findings of the meta-analyses, actually showing a blood pressure lowering effect of renal denervation seemed like an uphill battle. Future research also needs to confirm whether there is a sustained blood pressure lowering effect, which could then be cost-effective,16 and whether the procedure is safe in the long term, beyond the initial 6 months.6,7 Additionally, future research will need to show whether the blood pressure reduction caused by renal denervation has protective effects on the brain, heart, kidneys, and large arteries, and, eventually, whether it lowers cardiovascular morbidity and mortality.

Amongst other immune cells, neutrophils play a key role in systemic inflammation leading to cardiovascular disease and can release inflammatory factors, including lipocalin-2 (LCN2). LCN2 drives cardiac hypertrophy and plays a role in maladaptive remodelling of the heart and has been associated with renal injury. While lifestyle factors such as diet and exercise are known to attenuate low-grade inflammation, their ability to modulate plasma LCN2 levels is unknown. Forty-eight endurance athletes and 52 controls (18–55 years) underwent measurement for various cardiovascular health indicators, along with plasma LCN2 concentration. No significant difference in LCN2 concentration was seen between the two groups. LCN2 was a very weak predictor or absent from models describing blood pressures or predicting athlete status. In another cohort, 57 non-diabetic overweight or obese men and post-menopausal women who fulfilled Adult Treatment Panel III metabolic syndrome criteria were randomly allocated into either a control, modified Dietary Approaches to Stop Hypertension (DASH) diet, or DASH and exercise group. Pre- and post-intervention demographic, cardiovascular health indicators, and plasma LCN2 expression were measured in each individual. While BMI fell in intervention groups, LCN2 levels remained unchanged within and between all groups, as illustrated by strong correlations between LCN2 concentrations pre- and 12 weeks post-intervention ( r  = 0.743, P  < 0.0001). This suggests that circulating LCN2 expression are stable over a period of at least 12 weeks and is not modifiable by diet and exercise.