Effect of renal sympathetic denervation on glucose metabolism in patients with resistant hypertension: a pilot study

Renal sympathetic denervation provides ventricular rate control but does not prevent atrial electrical remodeling during atrial fibrillation

Renal denervation (RDN) reduces renal efferent and afferent sympathetic activity thereby lowering blood pressure in resistant hypertension. The effect of modulation of the autonomic nervous system by RDN on atrial electrophysiology and ventricular rate control during atrial fibrillation (AF) is unknown. Here we report a reduction of ventricular heart rate in a patient with permanent AF undergoing RDN. Subsequently, we investigated the effect of RDN on AF-induced shortening of atrial effective refractory period, AF inducibility, and ventricular rate control during AF maintained by rapid atrial pacing in 12 pigs undergoing RDN (n=7) or sham procedure (n=5). During sinus rhythm, RDN reduced heart rate (RR-interval, 708±12 versus 577±19 ms; P=0.0021) and increased atrioventricular node conduction time (PQ-interval, 112±12 versus 88±9 ms; P=0.0001). Atrial tachypacing for 30 minutes increased AF inducibility and decreased AF cycle length. This was not influenced by RDN. RDN reduced ventricular rate during AF episodes by ≈24% (119±9 versus 158±19 bpm; P=0.0001). AF episodes were shorter after RDN compared with sham (12±3 versus 34±4 s; P=0.0091), but atrial effective refractory period was not modified by RDN. RDN reduced heart rate and reduced atrioventricular node conduction time during sinus rhythm and provided rate control during AF. AF-induced atrial electrical remodeling, AF inducibility, and AF cycle length were not modified, but duration of AF episodes was shorter after RDN. Modulation of the autonomic nervous system by RDN might provide rate control and reduce susceptibility to AF. Whether RDN may provide rate control in a larger number of patients with AF deserves further clinical studies.

Renal denervation for treatment-resistant hypertension

Hypertension is a major public health concern that is increasing in prevalence. Lifestyle and pharmacological management are not always sufficient to control blood pressure and treatment-resistant hypertension is a recognized clinical challenge. Renal sympathetic denervation (RSD) represents a new frontier in the treatment of resistant hypertension.

RESULTS

from the Symplicity HTN-1 and HTN-2 trials have demonstrated evidence that suggests RSD can safely reduce blood pressure in patients with this condition. More research is needed to verify these data, clarify unanswered questions and assess future applications of RSD. This review provides a detailed overview on the history of hypertension, treatment-resistant hypertension, the rationale behind RSD, current evidence and potential future applications of RSD. An overview of current and upcoming RSD devices is also included.

Potential lifetime cost-effectiveness of catheter-based renal sympathetic denervation in patients with resistant hypertension

AIMS

Recent studies have demonstrated the safety and efficacy of catheter-based renal sympathetic denervation (RDN) for the treatment of resistant hypertension. We aimed to determine the cost-effectiveness of this approach separately for men and women of different ages.

METHODS AND RESULTS

A Markov state-transition model accounting for costs, life-years, quality-adjusted life-years (QALYs), and incremental cost-effectiveness was developed to compare RDN with best medical therapy (BMT) in patients with resistant hypertension. The model ran from age 30 to 100 years or death, with a cycle length of 1 year. The efficacy of RDN was modelled as a reduction in the risk of hypertension-related disease events and death. Analyses were conducted from a payer's perspective. Costs and QALYs were discounted at 3% annually. Both deterministic and probabilistic sensitivity analyses were performed. When compared with BMT, RDN gained 0.98 QALYs in men and 0.88 QALYs in women 60 years of age at an additional cost of €2589 and €2044, respectively. As the incremental cost-effectiveness ratios increased with patient age, RDN consistently yielded more QALYs at lower costs in lower age groups. Considering a willingness-to-pay threshold of €35 000/QALY, there was a 95% probability that RDN would remain cost-effective up to an age of 78 and 76 years in men and women, respectively. Cost-effectiveness was influenced mostly by the magnitude of effect of RDN on systolic blood pressure, the rate of RDN non-responders, and the procedure costs of RDN.

CONCLUSION

Renal sympathetic denervation is a cost-effective intervention for patients with resistant hypertension. Earlier treatment produces better cost-effectiveness ratios.

[Renal denervation: current state and future perspectives]

Hypertension is a well-known risk factor for major cardiovascular events. Despite advances in medical therapy, sufficient treatment of hypertension remains unsatisfying in a substantial number of patients and is therefore one of the main challenges in modern medicine. In Germany 5-15 % of patients with hypertension suffer from resistant hypertension with elevated blood pressure despite the use of at least three antihypertensive drugs. Additionally patients often suffer from side effects. In patients with resistant hypertension the important role of the sympathetic nervous system with increased sympathetic activity is well known. In the past surgical sympathectomy with extended removal of sympathetic ganglia was performed to reduce blood pressure in patients with malignant hypertension. The positive effect of this highly invasive procedure on blood pressure led to the development of new strategies for the treatment of uncontrolled hypertension. One of the novel procedures includes catheter-based renal sympathetic denervation. The most common system is the radiofrequency ablation catheter (Symplicity®, Medtronic, Minneapolis, USA) which ablates the nerve fibers in the adventitia of the renal arteries by using high-frequency energy. As the results of the Symplicity trials (HTN-1 and HTN-2) showed significant reduction of systolic and diastolic blood pressure after renal denervation there is growing interest in this novel procedure. Moreover, by reducing the sympathetic activity after renal denervation early results indicate a positive impact on glucose metabolism, sleep apnea syndrome, as well as heart and renal failure. These effects led to the development of many different devices for renal denervation; however, trials with a higher number of patients and longer follow-up need to confirm these initially promising results and the value of newer devices. Until then renal denervation should not be regarded as standard therapy for arterial hypertension or an alternative to medical antihypertensive treatment and should be reserved for selected patients with resistant hypertension and specialized medical centres.

Health-related quality of life after renal denervation in patients with treatment-resistant hypertension

Recent studies have demonstrated the effectiveness of radiofrequency ablation of the renal sympathetic nerves in reducing blood pressure (BP) in patients with resistant hypertension. The effect of renal denervation on health-related quality of life (QoL) has not been evaluated. Using the Medical Outcomes Study 36-Item Short-Form Health Survey and Beck Depression Inventory-II, we examined QoL before and 3 months after renal denervation in patients with uncontrolled BP. For baseline comparisons, matched data were extracted from the Australian Diabetes, Obesity, and Lifestyle database. Before renal denervation, patients with resistant hypertension (n = 62) scored significantly worse in 5 of the eight 36-Item Short-Form Health Survey domains and the Mental Component Summary score. Three months after denervation (n = 40), clinic BP was reduced (change in systolic and diastolic BP, -16 ± 4 and -6 ± 2 mm Hg, respectively; P<0.01). The Mental Component Summary score improved (47.6 ± 1.1 versus 52 ± 1; P = 0.001) as a result of increases in the vitality, social function, role emotion, and mental health domains. Beck Depression Inventory scores were also improved, particularly with regard to symptoms of sadness (P = 0.01), tiredness (P<0.001), and libido (P<0.01). The magnitude of BP reduction or BP level achieved at 3 months bore no association to the change in QoL. Renal denervation was without a detrimental effect on any elements of the 36-Item Short-Form Health Survey. These results indicate that patients with severe hypertension resistant to therapy present with a marked reduction in subjective QoL. In this pre- and post-hypothesis generating study, several aspects of QoL were improved after renal denervation; however, this was not directly associated with the magnitude of BP reduction.

Effects of renal sympathetic denervation on arterial stiffness and central hemodynamics in patients with resistant hypertension

OBJECTIVES

This study investigated the effect of catheter-based renal sympathetic denervation (RD) on central hemodynamics in patients with resistant hypertension.

BACKGROUND

High central blood pressure (BP) increases cardiovascular events and mortality independently of peripheral BP. The effect of RD on central BP is unclear.

METHODS

A total of 110 patients underwent bilateral RD. Radial artery applanation tonometry and pulse wave analysis were used to derive central aortic pressure and hemodynamic indices at baseline and 1, 3, and 6 months after ablation. Ten patients with resistant hypertension not undergoing RD served as controls.

RESULTS

RD significantly reduced mean central aortic BP from 167/92 mm Hg to 149/88 mm Hg, 147/85 mm Hg, and 141/85 mm Hg at 1, 3, and 6 months (p < 0.001), respectively. Aortic pulse pressure decreased from 76.2 ± 23.3 mm Hg to 61.5 ± 17.5 mm Hg, 62.7 ± 18.1 mm Hg, and 54.5 ± 15.7 mm Hg 1, 3, and 6 months after RD (p < 0.001), respectively. Six months after RD aortic augmentation and augmentation index were significantly reduced by -11 mm Hg (p < 0.001) and -5.3% (p < 0.001), respectively. Carotid to femoral pulse wave velocity showed a significant reduction from 11.6 ± 3.2 m/s to 9.6 ± 3.1 m/s at 6 months (p < 0.001). Consistently, ejection duration and aortic systolic pressure load were significantly diminished, indicating improvement of cardiac work load by RD. No significant changes were obtained in control patients.

CONCLUSIONS

Besides the known effect of RD on brachial blood pressure, the study showed for the first time that this novel approach significantly improves arterial stiffness and central hemodynamics, which might have important prognostic implications in patients with resistant hypertension at high cardiovascular risk.

Cost-effectiveness and clinical effectiveness of catheter-based renal denervation for resistant hypertension

OBJECTIVES

The purpose of this study was to assess cost-effectiveness and long-term clinical benefits of renal denervation in resistant hypertensive patients.

BACKGROUND

Resistant hypertension affects 12% of hypertensive persons. In the Symplicity HTN-2 randomized controlled trial, catheter-based renal denervation (RDN) lowered systolic blood pressure by 32 ± 23 mm Hg from 178 ± 18 mm Hg at baseline.

METHODS

A state-transition model was used to predict the effect of RDN and standard of care on 10-year and lifetime probabilities of stroke, myocardial infarction, all coronary heart disease, heart failure, end-stage renal disease, and median survival. We adopted a societal perspective and estimated an incremental cost-effectiveness ratio in U.S. dollars per quality-adjusted life-year, both discounted at 3% per year. Robustness and uncertainty were evaluated using deterministic and probabilistic sensitivity analyses.

RESULTS

Renal denervation substantially reduced event probabilities (10-year/lifetime relative risks: stroke 0.70/0.83; myocardial infarction 0.68/0.85; all coronary heart disease 0.78/0.90; heart failure 0.79/0.92; end-stage renal disease 0.72/0.81). Median survival was 18.4 years for RDN versus 17.1 years for standard of care. The discounted lifetime incremental cost-effectiveness ratio was $3,071 per quality-adjusted life-year. Findings were relatively insensitive to variations in input parameters except for systolic blood pressure reduction, baseline systolic blood pressure, and effect duration. The 95% credible interval for incremental cost-effectiveness ratio was cost-saving to $31,460 per quality-adjusted life-year.

CONCLUSIONS

The model suggests that catheter-based renal denervation, over a wide range of assumptions, is a cost-effective strategy for resistant hypertension that might result in lower cardiovascular morbidity and mortality.

Catheter-based renal denervation for resistant hypertension: rationale and design of the SYMPLICITY HTN-3 Trial

Hypertension represents a significant global public health concern, contributing to vascular and renal morbidity, cardiovascular mortality, and economic burden. The opportunity to influence clinical outcomes through hypertension management is therefore paramount. Despite adherence to multiple available medical therapies, a significant proportion of patients have persistent blood pressure elevation, a condition termed resistant hypertension. Recent recognition of the importance of the renal sympathetic and somatic nerves in modulating blood pressure and the development of a novel procedure that selectively removes these contributors to resistant hypertension represents an opportunity to provide clinically meaningful benefit across wide and varied patient populations. Early clinical evaluation with catheter-based, selective renal sympathetic denervation in patients with resistant hypertension has mechanistically correlated sympathetic efferent denervation with decreased renal norepinephrine spillover and renin activity, increased renal plasma flow, and has demonstrated clinically significant, sustained reductions in blood pressure. The SYMPLICITY HTN-3 Trial is a pivotal study designed as a prospective, randomized, masked procedure, single-blind trial evaluating the safety and effectiveness of catheter-based bilateral renal denervation for the treatment of uncontrolled hypertension despite compliance with at least 3 antihypertensive medications of different classes (at least one of which is a diuretic) at maximal tolerable doses. The primary effectiveness endpoint is measured as the change in office-based systolic blood pressure from baseline to 6 months. This manuscript describes the design and methodology of a regulatory trial of selective renal denervation for the treatment of hypertension among patients who have failed pharmacologic therapy.

Renal Denervation: A New Approach to an Old Problem

Renal sympathetic hyperactivity is associated with hypertension. Renal denervation is an interventional approach to selectively denervate the renal sympathetic fibers. The reduction of systolic and diastolic blood pressure in patients with resistant hypertension has been demonstrated in the Symplicity HTN-1 and HTN-2 trials. Before the patient undergoes an interventional procedure, causes of secondary hypertension or pseudoresistance must be excluded.

Joint statement of the European Association for the Study of Obesity and the European Society of Hypertension: obesity and difficult to treat arterial hypertension

Obese patients are prone to arterial hypertension, require more antihypertensive medications, and have an increased risk of treatment-resistant arterial hypertension. Obesity-induced neurohumoral activation appears to be involved. The association between obesity and hypertension shows large inter-individual variability, likely through genetic mechanisms. Obesity affects overall cardiovascular and metabolic risk; yet, the relationship between obesity and cardiovascular risk is complex and not sufficiently addressed in clinical guidelines. The epidemiological observation that obesity may be protective in patients with established cardiovascular disease is difficult to translate into clinical experience and practice. Weight loss is often recommended as a means to lower blood pressure. However, current hypertension guidelines do not provide evidence-based guidance on how to institute weight loss. In fact, weight loss influences on blood pressure may be overestimated. Nevertheless, weight loss through bariatric surgery appears to decrease cardiovascular risk in severely obese patients. Eventually, most obese hypertensive patients will require antihypertensive medications. Data from large-scale studies with hard clinical endpoints on antihypertensive medications specifically addressing obese patients are lacking and the morbidity from the growing population of severely obese patients is poorly recognized or addressed. Because of their broad spectrum of beneficial effects, renin-angiotensin system inhibitors are considered to be the most appropriate drugs for antihypertensive treatment of obese patients. Most obese hypertensive patients require two or more antihypertensive drugs. Finally, how to combine weight loss strategies and antihypertensive treatment to achieve an optimal clinical outcome is unresolved.

Renal denervation therapies for refractory hypertension

The treatment of severe hypertension by the surgical obliteration of the renal sympathetic nerves was proposed almost 80 years ago. This approach, although highly effective in reducing blood pressure was associated with a significant amount of side effects and it was rapidly replaced by better tolerated medical therapy. The rapid progress in catheter based technologies occurring within the last 20 years facilitated the development of the first radio frequency renal artery denervation catheter. At the present time, several small trials have demonstrated the safety and efficacy of this approach among patients with refractory hypertension. Besides its effect on reducing blood pressure, other pleiotropic effects (ie, improving glycemia in diabetic patients) have been proposed. In this review, we discuss the anatomical and physiological rationale for this therapy, provide an update on the latest clinical data available and describe additional emerging technologies in this field.

Renal denervation for hypertension

Systemic hypertension is a major burden to the individual and society. Its association with major adverse cardiac and cerebral events and favorable effects of antihypertensive therapy are undisputed. However, despite multidrug therapy, blood pressures are frequently suboptimally controlled. Moreover, adverse drug effects often interfere with patients' lifestyles and affect compliance. Therefore, alternative treatment strategies have been explored. Most recently, attention has been redirected to the sympathetic nervous system (SNS) in the pathogenesis of hypertension. In addition, interruption of the renal SNS in humans with resistant hypertension has been studied with promising results. The following review provides an overview of the anatomy and physiology of the renal SNS, the rational for manipulating the SNS, and the results of therapeutic renal sympathetic denervation.

Renal hemodynamics and renal function after catheter-based renal sympathetic denervation in patients with resistant hypertension

Increased renal resistive index and urinary albumin excretion are markers of hypertensive end-organ damage and renal vasoconstriction involving increased sympathetic activity. Catheter-based sympathetic renal denervation (RD) offers a new approach to reduce renal sympathetic activity and blood pressure in resistant hypertension. The influence of RD on renal hemodynamics, renal function, and urinary albumin excretion has not been studied. One hundred consecutive patients with resistant hypertension were included in the study; 88 underwent interventional RD and 12 served as controls. Systolic, diastolic, and pulse pressure, as well renal resistive index in interlobar arteries, renal function, and urinary albumin excretion, were measured before and at 3 and 6 months of follow-up. RD reduced systolic, diastolic, and pulse pressure at 3 and 6 months by 22.7/26.6 mm Hg, 7.7/9.7 mm Hg, and 15.1/17.5 mm Hg (P for all <0.001), respectively, without significant changes in the control group. SBP reduction after 6 months correlated with SBP baseline values (r=-0.46; P<0.001). There were no renal artery stenoses, dissections, or aneurysms during 6 months of follow-up. Renal resistive index decreased from 0.691±0.01 at baseline to 0.674±0.01 and 0.670±0.01 (P=0.037/0.017) at 3- and 6-month follow-up. Mean cystatin C glomerular filtration rate and urinary albumin excretion remained unchanged after RD; however, the number of patients with microalbuminuria or macroalbuminuria decreased. RD reduced blood pressure, renal resistive index, and incidence of albuminuria without adversely affecting glomerular filtration rate or renal artery structure within 6 months and appears to be a safe and effective therapeutic approach to lower blood pressure in patients with resistant hypertension.

Spironolactone prevents chlorthalidone-induced sympathetic activation and insulin resistance in hypertensive patients

Recent studies from our laboratory indicate that chlorthalidone triggers persistent activation of the sympathetic nervous system and promotes insulin resistance in hypertensive patients, independent of serum potassium. Mechanisms underlying these adverse effects of chlorthalidone remain unknown, but increasing evidence in rodents suggests the role of angiotensin and aldosterone excess in inducing both sympathetic overactivity and insulin resistance. Accordingly, we conducted studies in 17 subjects with untreated stage 1 hypertension, measuring sympathetic nerve activity at baseline and after 12 weeks of chlorthalidone alone (25 mg/d), chlorthalidone plus spironolactone, and chlorthalidone plus irbesartan, using randomized crossover design. We found that chlorthalidone alone decreased 24-hour ambulatory blood pressure from 135±3/84±2 to 124±2/78±2 mm Hg and significantly increased sympathetic nerve activity from baseline (from 41±3 versus 49±4 bursts per minute; P<0.01). The addition of spironolactone to chlorthalidone returned sympathetic nerve activity value to baseline (42±3 bursts per minute; P>0.05), whereas the addition of irbesartan failed to alter the sympathetic nerve activity response to chlorthalidone in the same subjects (52±2 bursts per minute; P<0.01) despite a similar reduction in ambulatory blood pressure (121±2/75±2 and 121±2/75±2 mm Hg, respectively). Chlorthalidone alone also increased indices of insulin resistance, which was not observed when used in combination with spironolactone. In conclusion, our study demonstrates beneficial effects of spironolactone in attenuating both chlorthalidone-induced sympathetic activation and insulin resistance in humans, independent of blood pressure reduction. Because sympathetic overactivity and insulin resistance contribute to the poor prognosis in patients with cardiovascular disease, combination therapy of chlorthalidone with mineralocorticoid receptor antagonists may constitute a preferable regimen than chlorthalidone alone in hypertensive patients.

Renal denervation in moderate to severe CKD

Sympathetic activation contributes to the progression of CKD and is associated with adverse cardiovascular outcomes. Ablation of renal sympathetic nerves reduces sympathetic nerve activity and BP in patients with resistant hypertension and preserved renal function, but whether this approach is safe and effective in patients with an estimated GFR (eGFR) < 45 ml/min per 1.73 m(2) is unknown. We performed bilateral renal denervation in 15 patients with resistant hypertension and stage 3-4 CKD (mean eGFR, 31 ml/min per 1.73 m(2)). We used CO(2) angiography in six patients to minimize exposure to contrast agents. Estimated GFR remained unchanged after the procedure, irrespective of the use of CO(2) angiography. Mean baseline BP ± SD was 174 ± 22/91 ± 16 mmHg despite the use of 5.6 ± 1.3 antihypertensive drugs. Mean changes in office systolic and diastolic BP at 1, 3, 6, and 12 months were -34/-14, -25/-11, -32/-15, and -33/-19 mmHg, respectively. Night-time ambulatory BP significantly decreased (P<0.05), restoring a more physiologic dipping pattern. In conclusion, this study suggests a favorable short-term safety profile and beneficial BP effects of catheter-based renal nerve ablation in patients with stage 3-4 CKD and resistant hypertension.

Renal sympathetic denervation suppresses postapneic blood pressure rises and atrial fibrillation in a model for sleep apnea

The aim of this study was to identify the relative impact of adrenergic and cholinergic activity on atrial fibrillation (AF) inducibility and blood pressure (BP) in a model for obstructive sleep apnea. Obstructive sleep apnea is associated with sympathovagal disbalance, AF, and postapneic BP rises. Renal denervation (RDN) reduces renal efferent and possibly also afferent sympathetic activity and BP in resistant hypertension. The effects of RDN compared with β-blockade by atenolol on atrial electrophysiological changes, AF inducibility, and BP during obstructive events and on shortening of atrial effective refractory period (AERP) induced by high-frequency stimulation of ganglionated plexi were investigated in 20 anesthetized pigs. Tracheal occlusion with applied negative tracheal pressure (NTP; at -80 mbar) induced pronounced AERP shortening and increased AF inducibility in all of the pigs. RDN but not atenolol reduced NTP-induced AF-inducibility (20% versus 100% at baseline; P=0.0001) and attenuated NTP-induced AERP shortening more than atenolol (27±5 versus 43±3 ms after atenolol; P=0.0272). Administration of atropine after RDN or atenolol completely inhibited NTP-induced AERP shortening. AERP shortening induced by high-frequency stimulation of ganglionated plexi was not influenced by RDN, suggesting that changes in sensitivity of ganglionated plexi do not play a role in the antiarrhythmic effect of RDN. Postapneic BP rise was inhibited by RDN and not modified by atenolol. We showed that vagally mediated NTP-induced AERP shortening is modulated by RDN or atenolol, which emphasizes the importance of autonomic disbalance in obstructive sleep apnea-associated AF. Renal denervation displays antiarrhythmic effects by reducing NTP-induced AERP shortening and inhibits postapneic BP rises associated with obstructive events.

Effects of Renal Sympathetic Denervation on 24-hour Blood Pressure Variability

Background: In patients with arterial hypertension, increased blood pressure (BP) variability contributes to end organ damage independently from mean levels of arterial BP. Increased BP variability has been linked to alterations in autonomic function including sympathetic overdrive. We hypothesized that catheter-based renal sympathetic denervation (RDN) confers beneficial effects on BP variability. Methods and Results: Eleven consecutive patients with therapy-refractory arterial hypertension (age 68.9 ± 7.0 years; baseline systolic BP 189 ± 23 mmHg despite medication with 5.6 ± 2.1 antihypertensive drugs) underwent bilateral RDN. Twenty-four hour ambulatory BP monitoring (ABPM) was performed before RDN and 6 months thereafter. BP variability was primarily assessed by means of standard deviation of 24-h systolic arterial BP (SD_sys). Secondary measures of BP variability were maximum systolic BP (MAX_sys) and maximum difference between two consecutive readings of systolic BP (Δmax_sys) over 24 h. Six months after RDN, SD_sys, MAX_sys, and Δmax_sys were significantly reduced from 16.9 ± 4.6 to 13.5 ± 2.5 mmHg (p = 0.003), from 190 ± 22 to 172 ± 20 mmHg (p < 0.001), and from 40 ± 15 to 28 ± 7 mmHg (p = 0.006), respectively, without changes in concomitant antihypertensive therapy. Reductions of SD_sys, MAX_sys, and Δmax_sys were observed in 10/11 (90.9%), 11/11 (100%), and 9/11 (81.8%) patients, respectively. Although we noted a significant reduction of systolic office BP by 30.4 ± 27.7 mmHg (p = 0.007), there was only a trend in reduction of average systolic BP assessed from ABPM (149 ± 19 to 142 ± 18 mmHg; p = 0.086). Conclusion: In patients with therapy-refractory arterial hypertension, RDN leads to significant reductions of BP variability. Effects of RDN on BP variability over 24 h were more pronounced than on average levels of BP.

Renal sympathetic denervation reduces left ventricular hypertrophy and improves cardiac function in patients with resistant hypertension

OBJECTIVES

This study investigated the effect of catheter-based renal sympathetic denervation (RD) on left ventricular hypertrophy (LVH) and systolic and diastolic function in patients with resistant hypertension.

BACKGROUND

LVH and diastolic dysfunction are associated with elevated sympathetic activity and increased morbidity and mortality. The effect of RD on LVH and LV function is unclear.

METHODS

Forty-six patients underwent bilateral RD, and 18 patients served as controls. Transthoracic echocardiography was performed at baseline, and after 1 month and 6 months.

RESULTS

Besides reduction of systolic and diastolic blood pressure (-22.5/-7.2 mm Hg at 1 month and -27.8/-8.8 mm Hg at 6 months, p < 0.001 at each time point), RD significantly reduced mean interventricular septum thickness from 14.1 ± 1.9 mm to 13.4 ± 2.1 mm and 12.5 ± 1.4 mm (p = 0.007), and LV mass index from 53.9 ± 15.6 g/m(2.7) (112.4 ± 33.9 g/m(2)) to 47.0 ± 14.2 g/m(2.7) (103.6 ± 30.5 g/m(2)) and 44.7 ± 14.9 g/m(2.7) (94.9 ± 29.8 g/m(2)) (p < 0.001) at 1 month and 6 months, respectively. The mitral valve lateral E/E' decreased after RD from 9.9 ± 4.0 to 7.9 ± 2.2 at 1 month and 7.4 ± 2.7 at 6 months (p < 0.001), indicating reduction of LV filling pressures. Isovolumic relaxation time shortened (baseline 109.1 ± 21.7 ms vs. 85.6 ± 24.4 ms at 6 months, p = 0.006), whereas ejection fraction significantly increased after RD (baseline: 63.1 ± 8.1% vs. 70.1 ± 11.5% at 6 months, p < 0.001). No significant changes were obtained in control patients.

CONCLUSIONS

Besides the known effect on blood pressure, our study showed for the first time that RD significantly reduces LV mass and improves diastolic function, which might have important prognostic implications in patients with resistant hypertension at high cardiovascular risk.

Recent advancements in the treatment of resistant hypertension

The 2008 scientific statement from the American Heart Association defined resistant hypertension as blood pressure remaining above goal (< 140/90 mm Hg for the general population and < 130/80 mm Hg for patients with diabetes or renal disease) despite the concurrent use of optimal doses of 3 antihypertensive agents of different classes, ideally including a diuretic. Since then, there has been increasing recognition and characterization of patients with resistant hypertension and development of treatment strategies to treat this high-risk population. The role of aldosterone in resistant hypertension has gained increasing recognition. In particular, there has been development of a strong body of evidence for the use of spironolactone as a highly effective antihypertensive agent. Furthermore, there is increasing evidence to link aldosterone with both resistant hypertension and obstructive sleep apnea, with preliminary studies suggesting that aldosterone antagonists may potentially be effective in treating both conditions. Finally, recent work has directed increased attention toward novel invasive strategies for the treatment of resistant hypertension, specifically baroreflex activation therapy with carotid stimulation and percutaneous renal artery denervation. Initial randomized controlled trials have shown that both of these methods may be used to safely lower blood pressure, thereby providing exciting and promising new tools in the armamentarium of options to treat resistant hypertension.

Sympathetic nervous system: role in hypertension and in chronic kidney disease

PURPOSE OF REVIEW

A number of cardiovascular disease have been shown to be characterized by a marked increase in sympathetic drive to the heart and peripheral circulation. This is the case for essential hypertension, congestive heart failure, obesity, metabolic syndrome and chronic renal failure. This review focuses on the most recent findings documenting the role of sympathetic neural factors in the development and progression of the hypertensive state as well as of target organ damage. It also reviews the participation of sympathetic neural factors in the development of the earlier stages of renal failure.

RECENT FINDINGS

A marked increase in sympathetic neural discharge, as assessed via the microneurographic technique, has been shown to occur in the predialytic stage of chronic renal failure. Recent evidence, however, indicates that also in the earlier clinical phases of kidney disease, sympathetic activation is detectable. Further data show that sympathetic neural mechanisms participate in renal and/or hypertensive disease progression, favouring the development of target organ damage. Finally, recent findings indicate that the metabolic disarray frequently complicating the high blood pressure state (metabolic syndrome, dislipidemia, insulin resistance) may have as pathophysiological background a sympathetic overdrive. Altogether these data represent the rationale for employing in hypertension (and particularly in resistant hypertension) therapeutic interventions such as carotid baroreceptor stimulation and renal denervation, capable of exerting sympathoinhibitory effects.

SUMMARY

The sympathetic nervous system represents a major pathophysiological hallmark of both hypertension and renal failure and is an important target for the therapeutic intervention.

Risk of elevated resting heart rate on the development of type 2 diabetes in patients with clinically manifest vascular diseases

OBJECTIVE

Sympathetic nerve activation is causally related to insulin resistance as both a cause and a consequence. Resting heart rate (RHR) reflects sympathetic nerve activity. We investigated the effect of RHR on the incidence of type 2 diabetes mellitus (T2DM) in patients with clinically manifest vascular diseases.

DESIGN

Data were used from the second manifestations of arterial disease (SMART) study: a prospective cohort study of patients with clinically manifest vascular diseases (n=3646).

METHODS

RHR was obtained using an electrocardiogram. Patients were followed up for incident type 2 diabetes (n=289) during a median period of 5.5 (interquartile range 3.2-8.4) years. The relation between RHR and incident T2DM was estimated by Cox proportional hazard analysis. As age was an effect modifier (P=0.048), analyses were stratified for age.

RESULTS

Patients in quartile 4 (Q4) of RHR had a 65% increased risk of T2DM compared with those in Q1 (reference; hazard ratios (HR), 1.65; 95% confidence interval (95% CI), 1.15-2.36) adjusted for age, gender, smoking, estimated glomerular filtration rate, systolic blood pressure, location of vascular disease, and antihypertensive medication. Every 10 beats per minute (bpm) increase in RHR increased the risk for T2DM with 10% (HR, 1.10; 95% CI, 1.00-1.21) in the total population. This risk was particularly high in subjects aged 55-63 years (per 10 bpm: HR, 1.22; 95% CI, 1.04-1.43) and was independent of the location of vascular disease and beta-blocker use.

CONCLUSIONS

Increased RHR, an indicator of sympathetic nerve activity, is associated with an increased risk for T2DM in patients with manifest vascular diseases, particularly in middle-aged patients.

Evidence and consequences of the central role of the kidneys in the pathophysiology of sympathetic hyperactivity

Chronic elevation of the sympathetic nervous system has been identified as a major contributor to the complex pathophysiology of hypertension, states of volume overload – such as heart failure – and progressive kidney disease. It is also a strong determinant for clinical outcome. This review focuses on the central role of the kidneys in the pathogenesis of sympathetic hyperactivity. As a consequence, renal denervation may be an attractive option to treat sympathetic hyperactivity. The review will also focus on first results and the still remaining questions of this new treatment option.

Transcatheter renal artery sympathetic denervation for resistant hypertension: an old paradigm revisited

Resistant hypertension, defined as the failure to achieve target blood pressure despite concurrent use of 3 antihypertensive agents of different classes, is estimated to affect 20-30% of hypertensive patients. These patients are vulnerable to cardiovascular, cerebrovascular and renal complications. There is ample evidence that sympathetic nervous system hyperactivity contributes to the initiation, maintenance and progression of hypertension. The renal sympathetic nervous system, in particular, has been identified as a major culprit for the development and progression of hypertension, heart failure and chronic kidney disease in both preclinical and human studies. Traditional surgical sympathectomy proposed in 1940s was halted due to unacceptable operative risk and the emergence of anti-hypertensive medications. Recently, catheter-based renal sympathetic denervation by radiofrequency ablation has shown encouraging intermediate-term results with minimal complications in patients with resistant hypertension. This review summarizes the patho-physiological role of the renal sympathetic nervous system and the potential application of renal denervation therapy for the treatment of resistant hypertension.

Renal sympathetic denervation in hypertension

PURPOSE OF REVIEW

Despite the abundance of antihypertensive drugs, resistant hypertension remains a major clinical problem. Recent technological advances render interventional management of resistant hypertension one of the hottest topics in the hypertension field. The aim of this review is to present the pathophysiologic background and the mechanisms mediating blood pressure reduction after renal sympathetic denervation, to analyze recent findings with this fascinating approach and to critically suggest future research directions.

RECENT FINDINGS

Catheter-based, ablation-induced renal sympathetic denervation was initially studied in 45 patients with resistant hypertension in a proof-of-concept study. Impressive blood pressure reductions of about 30/15  mmHg were achieved at 6 months, without serious complications. A second, controlled, randomized (but not blinded) study confirmed the results, verifying the efficacy and safety of the procedure. A recent report revealed the 2-year durability of blood pressure reduction.

SUMMARY

Data published so far indicate that ablation-induced renal denervation is a feasible, effective, and well tolerated interventional approach for the management of resistant hypertension. The groundbreaking studies of renal denervation in drug-resistant hypertension pave the way for further research in other disease conditions in which sympathetic overactivity seems to play a critical role. This initial wave of enthusiasm needs to be followed by rigorous investigation, for the proper identification of the potential and the limitations, indications, and contraindications of this approach.

Effects of renal denervation on sympathetic activation, blood pressure, and glucose metabolism in patients with resistant hypertension

Increased central sympathetic drive is a hallmark of several important clinical conditions including essential hypertension, heart failure, chronic kidney disease, and insulin resistance. Afferent signaling from the kidneys has been identified as an important contributor to elevated central sympathetic drive and increased sympathetic outflow to the kidney and other organs is crucially involved in cardiovascular control. While the resultant effects on renal hemodynamic parameters, sodium and water retention, and renin release are particularly relevant for both acute and long term regulation of blood pressure, increased sympathetic outflow to other vascular beds may facilitate further adverse consequences of sustained sympathetic activation such as insulin resistance, which is commonly associated with hypertension. Recent clinical studies using catheter-based radiofrequency ablation technology to achieve functional renal denervation in patients with resistant hypertension have identified the renal nerves as therapeutic target and have helped to further expose the sympathetic link between hypertension and insulin resistance. Initial data from two clinical trials and several smaller mechanistic clinical studies indicate that this novel approach may indeed provide a safe and effective treatment alternative for resistant hypertension and some of its adverse consequences.

Renal Sympathetic Denervation for Treatment of Hypertension

OPINION STATEMENT: Sympathetic nervous system activation of the heart, kidney and peripheral vasculature increases cardiac output, fluid retention and vascular resistance and plays an important role in acute and chronic BP elevation. Renal sympathetic denervation via a percutaneous radiofrequency catheter based approach is a safe and effective procedure that lowers BP in patients with resistant hypertension. Exploratory studies in patients with resistant hypertension and a variety of comorbidities, including insulin resistance/metabolic syndrome, obstructive sleep apnea and the polycystic ovary syndrome, have shown benefit of renal denervation in attenuating the severity of the comorbid conditions, as well as reducing BP. However, more studies are needed to further address the long term effects of renal denervation and its safety and effectiveness in other disease states such as congestive heart failure.

The sympathetic nervous system and new nonpharmacologic approaches to treating hypertension: a focus on renal denervation

The sympathetic nervous system is activated in a variety of cardiovascular and metabolic diseases. This is particularly the case for essential hypertension, in which various indices of adrenergic activity, such as plasma norepinephrine, norepinephrine spillover, and sympathetic nerve firing rate, are all well above the reference range of values, thereby documenting sympathetic overdrive. Evidence is available that sympathetic neural factors participate in disease progression, as well as in the development of cardiac and renal organ damage. These findings represent the rationale for therapeutic interventions that counteract the adrenergic overdrive in the hypertensive state. This paper, after reviewing the key findings of the neuroadrenergic abnormalities occurring in hypertension, examines the rationale and the technical details, as well as the results achieved so far, with the use of a new technique that allows the elimination of afferent and efferent innervation of the kidney in resistant hypertension, ie, the ablation of renal nerves. Strengths and potential limitations of the renal denervation approach are briefly addressed.

Catheter-based radiofrequency renal-nerve ablation in patients with resistant hypertension

This review aims to describe the role and the results of catheter-based renal nerve ablation for the treatment of resistant hypertension. Despite the availability of multiple classes of orally active antihypertensive treatments, resistant hypertension remains an important public health issue in 2012 due to its prevalence and association with target-organ damage and poor prognosis. The failure of purely pharmacological approaches to treat resistant hypertension has stimulated interest in invasive device-based treatments based on old concepts. In the absence of orally active antihypertensive agents, patients with severe and complicated hypertension were widely treated by surgical denervation of the kidney until the 1960s, but this approach was associated with a high incidence of severe adverse events and a high mortality rate. A new catheter system using radiofrequency energy has been developed, allowing an endovascular approach to renal denervation and providing patients with resistant hypertension with a new therapeutic option that is less invasive than surgery and can be performed rapidly under local anaesthesia. To date, this technique has been evaluated only in open-label trials including small numbers of highly selected resistant hypertensive patients with suitable renal artery anatomy. The available evidence suggests a favourable blood pressure-lowering effect in the short term (6 months) and a low incidence of immediate local and endovascular complications. This follow-up period is, however, too short for the detection of rare or late-onset adverse events. For the time being, the benefit/risk ratio of this technique remains to be evaluated, precluding its uncontrolled and widespread use in routine practice.

Systemic and renal-specific sympathoinhibition in obesity hypertension

Chronic pressure-mediated baroreflex activation suppresses renal sympathetic nerve activity. Recent observations indicate that chronic electric activation of the carotid baroreflex produces sustained reductions in global sympathetic activity and arterial pressure. Thus, we investigated the effects of global and renal specific suppression of sympathetic activity in dogs with sympathetically mediated, obesity-induced hypertension by comparing the cardiovascular, renal, and neurohormonal responses to chronic baroreflex activation and bilateral surgical renal denervation. After control measurements, the diet was supplemented with beef fat, whereas sodium intake was held constant. After 4 weeks on the high-fat diet, when body weight had increased ≈50%, fat intake was reduced to a level that maintained this body weight. This weight increase was associated with an increase in mean arterial pressure from 100±2 to 117±3 mm Hg and heart rate from 86±3 to 130±4 bpm. The hypertension was associated with a marked increase in cumulative sodium balance despite an approximately 35% increase in glomerular filtration rate. The importance of increased tubular reabsorption to sodium retention was further reflected by ≈35% decrease in fractional sodium excretion. Subsequently, both chronic baroreflex activation (7 days) and renal denervation decreased plasma renin activity and abolished the hypertension. However, baroreflex activation also suppressed systemic sympathetic activity and tachycardia and reduced glomerular hyperfiltration while increasing fractional sodium excretion. In contrast, glomerular filtration rate increased further after renal denervation. Thus, by improving autonomic control of cardiac function and diminishing glomerular hyperfiltration, suppression of global sympathetic activity by baroreflex activation may have beneficial effects in obesity beyond simply attenuating hypertension.

Sympatho-renal axis in chronic disease

Essential hypertension, insulin resistance, heart failure, congestion, diuretic resistance, and functional renal disease are all characterized by excessive central sympathetic drive. The contribution of the kidney's somatic afferent nerves, as an underlying cause of elevated central sympathetic drive, and the consequences of excessive efferent sympathetic signals to the kidney itself, as well as other organs, identify the renal sympathetic nerves as a uniquely logical therapeutic target for diseases linked by excessive central sympathetic drive. Clinical studies of renal denervation in patients with resistant hypertension using an endovascular radiofrequency ablation methodology have exposed the sympathetic link between these conditions. Renal denervation could be expected to simultaneously affect blood pressure, insulin resistance, sleep disorders, congestion in heart failure, cardiorenal syndrome and diuretic resistance. The striking epidemiologic evidence for coexistence of these disorders suggests common causal pathways. Chronic activation of the sympathetic nervous system has been associated with components of the metabolic syndrome, such as blood pressure elevation, obesity, dyslipidemia, and impaired fasting glucose with hyperinsulinemia. Over 50% of patients with essential hypertension are hyperinsulinemic, regardless of whether they are untreated or in a stable program of treatment. Insulin resistance is related to sympathetic drive via a bidirectional mechanism. In this manuscript, we review the data that suggests that selective impairment of renal somatic afferent and sympathetic efferent nerves in patients with resistant hypertension both reduces markers of central sympathetic drive and favorably impacts diseases linked through central sympathetics-insulin resistance, heart failure, congestion, diuretic resistance, and cardiorenal disorders.

Norepinephrine reduces ω-conotoxin-sensitive Ca2+ currents in renal afferent neurons in rats

Sympathetic efferent and peptidergic afferent renal nerves likely influence hypertensive and inflammatory kidney disease. Our recent investigation with confocal microscopy revealed that in the kidney sympathetic nerve endings are colocalized with afferent nerve fibers (Ditting T, Tiegs G, Rodionova K, Reeh PW, Neuhuber W, Freisinger W, Veelken R. Am J Physiol Renal Physiol 297: F1427-F1434, 2009; Veelken R, Vogel EM, Hilgers K, Amman K, Hartner A, Sass G, Neuhuber W, Tiegs G. J Am Soc Nephrol 19: 1371-1378, 2008). However, it is not known whether renal afferent nerves are influenced by sympathetic nerve activity. We tested the hypothesis that norepinephrine (NE) influences voltage-gated Ca(2+) channel currents in cultured renal dorsal root ganglion (DRG) neurons, i.e., the first-order neuron of the renal afferent pathway. DRG neurons (T11-L2) retrogradely labeled from the kidney and subsequently cultured, were investigated by whole-cell patch clamp. Voltage-gated calcium channels (VGCC) were investigated by voltage ramps (-100 to +80 mV, 300 ms, every 20 s). NE and appropriate adrenergic receptor antagonists were administered by microperfusion. NE (20 μM) reduced VGCC-mediated currents by 10.4 ± 3.0% (P < 0.01). This reduction was abolished by the α-adrenoreceptor inhibitor phentolamine and the α(2)-adrenoceptor antagonist yohimbine. The β-adrenoreceptor antagonist propranolol and the α(1)-adrenoceptor antagonist prazosin had no effect. The inhibitory effect of NE was abolished when N-type currents were blocked by ω-conotoxin GVIA, but was unaffected by other specific Ca(2+) channel inhibitors (ω-agatoxin IVA; nimodipine). Confocal microscopy revealed sympathetic innervation of DRGs and confirmed colocalization of afferent and efferent fibers within in the kidney. Hence NE released from intrarenal sympathetic nerve endings, or sympathetic fibers within the DRGs, or even circulating catecholamines, may influence the activity of peptidergic afferent nerve fibers through N-type Ca(2+) channels via an α(2)-adrenoceptor-dependent mechanism. However, the exact site and the functional role of this interaction remains to be elucidated.

Treatment strategies for resistant arterial hypertension

BACKGROUND

Resistant hypertension is defined as blood pressure above the target range set by current guidelines despite the concurrent use of three or more antihypertensive drugs of different classes, including a diuretic, at their maximum or highest tolerated doses. This problem affects 5% to 15% of all hypertensive patients and is thus commonly seen by both primary care physicians and specialists.

METHODS

Review of current guidelines and pertinent literature revealed by a selective Medline search.

RESULTS

The treatment of resistant hypertension is multimodal, involving systematic identification of secondary causes of hypertension as well as the exclusion of pseudoresistance (inadequate treatment). Non-pharmacological treatment includes weight loss, dietary salt restriction, exercise, and abstinence from alcohol. Drug treatment consists of an individualized combination of antihypertensive agents with different mechanisms of action. Activation of the sympathetic nervous system is considered to be a major element in the pathogenesis of resistant hypertension; a new interventional treatment, selective denervation of the renal sympathetic nerves, results in clinically relevant and sustained blood pressure reduction in ca. 84% of the patients undergoing the procedure (a mean decrease of office systolic blood pressure by 32 mm Hg and by 12 mm Hg at six months, p <0.001). Among the 206 patients who underwent this procedure in the setting of published studies, 5 had complications; these included pseudoaneurysm of the femoral artery and dissection of the renal artery during the introduction of the ablation catheter.

CONCLUSION

The treatment of resistant hypertension is interdisciplinary and multimodal. The new and promising option of interventional renal sympathetic denervation can be considered for patients whose high blood pressure is inadequately controlled with medication.