Renal sympathetic denervation | |
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Other names | Renal denervation |
Renal sympathetic denervation (RSDN) is a minimally invasive, endovascular catheter based procedure using radiofrequency ablation or ultrasound ablation aimed at treating resistant hypertension (high blood pressure not controlled by medication). [1] Nerves in the wall of the renal artery are ablated by applying radiofrequency pulses or ultrasound to the renal arteries. This causes reduction of sympathetic afferent and efferent activity to the kidney and blood pressure can be decreased. [2] Early data from international clinical trials without sham controls was promising - demonstrating large blood pressure reductions in patients with treatment-resistant hypertension. [2] [3] However, in 2014 a prospective, single-blind, randomized, sham-controlled clinical trial failed to confirm a beneficial effect on blood pressure. [4] A 2014 consensus statement from The Joint UK Societies did not recommend the use of renal denervation for treatment of resistant hypertension on current evidence. [5] More recent sham-controlled trials suggest renal denervation can lead to lower systolic blood pressure. [6] [7] [8]
Prior to pharmacological management of hypertension, surgical sympathectomy was a recognized treatment for hypertension. [9] This was often successful in reducing blood pressure but due to its non-selective nature the side effects of the procedure were poorly tolerated. Side effects included orthostatic hypotension, palpitations, anhydrosis, intestinal disturbances, loss of ejaculation, thoracic duct injuries and atelectasis. [10] Modern antihypertensive pharmacological interventions have improved the control of hypertension, but only 34–66% of people with hypertension in England, US and Canada have blood pressure at or below target levels. [11] Resistant hypertension is defined as blood pressure above target (140/90mm Hg) despite concomitant use of three or more anti-hypertensives – one of which should be a diuretic. [12] It has been estimated that 8–10% of people with hypertension fall into this category. [5]
Several commercial devices exist. [13] These include Medtronic's Symplicity Renal Denervation System, St. Jude Medical's EnligHTN System, Boston Scientific's Vessix V2 Renal Denervation System, Covidien's OneShot System, Recor's Paradise System, Terumo's Iberis System and Cordis Corporation's RENLANE Renal Denervation System. Currently[ when? ], no renal denervation device has FDA approval.[ citation needed ]
The procedure involves endovascular access via the femoral artery with advancement of a catheter-mounted device into the renal artery. The device uses radiofrequency or ultrasound to ablate the renal nerves. Typically, numerous ablations are applied at a different longitudinal and rotational positions to ensure maximal denervation. [13] The procedure does not involve a permanent implant.[ citation needed ]
The most widely discussed studies to date are the Symplicity HTN-1, HTN-2 and HTN-3 trials, conducted with Medtronic's Symplicity RDN System.[ citation needed ]
Symplicity HTN-1 [3] looked at outcomes in 153 patients that underwent catheter-based renal denervation. Three-year follow-up data have demonstrated an average blood pressure reduction of -33/-19mm Hg.
Symplicity HTN-2 was a randomized, [2] controlled trial that compared 54 control patients with 52 patients who underwent catheter-based renal denervation. Six month follow-up data demonstrated a blood pressure reduction of -32/12 mm Hg in the treated group compared with a change of 1/0 mm Hg in the control group.
Meta-analyses of renal denervation have yielded conflicting results. [14] Whilst office systolic blood pressure reductions typically average around 30 mmHg, reductions observed on ambulatory blood pressure monitoring are typically much smaller, around 10 mmHg. [15] Explanations offered for this mismatch include renal denervation obliterating the white coat response, thereby disproportionately reducing clinic pressures, [14] or inadvertent bias arising from the unblinded design and lack of sham control procedure in almost all renal denervation trial designs to date. [15] [16]
A study published in 2014, Symplicity HTN-3, was a prospective, single-blind, randomised, sham-controlled trial in which 535 patients with severe resistant hypertension were randomized to undergo renal denervation or a sham procedure (in a 2:1 ratio). The results showed no statistically significant difference between renal denervation and the sham procedure. [4]
Following the publication of Symplicity HTN-3 the Joint UK Societies produced a consensus statement that did not recommend the use of renal denervation for treatment of resistant hypertension in routine clinical practice. However they advocated further research with better designed randomised studies. [5]
More recent sham-controlled trials suggest renal denervation can lead to lower systolic blood pressure. [6] [7] [8] [17]
The Symplicity HTN-1, HTN-2 and HTN-3 trials have demonstrated acceptable safety profiles for catheter based renal denervation. Patients may experience pain during application of radiofrequency pulses and intraprocedural bradycardia requiring atropine has also been reported. [2] Other documented procedure related complications include femoral artery pseudoaneurysm and renal artery dissection.[ citation needed ]
Of particular concern is the theoretical risk of damage to renal arteries during delivery of radiofrequency energy. An animal study using swine showed no damage to the renal arteries at 6 month follow up. This finding is further supported in human studies in the HTN-1 and HTN-2 trial where follow up imaging has not demonstrated renal vascular damage. [18]
Other diseases may be associated with an overactive sympathetic drive and therefore, in theory, renal denervation could be of benefit. Congestive heart failure (CHF), left ventricular hypertrophy (LVH), atrial fibrillation (AF), obstructive sleep apnea (OSA), and insulin resistance/type 2 diabetes mellitus (DM) all have been associated with increased activity of the sympathetic nervous system.[ citation needed ] Current clinical trials are examining the effect of renal denervation in these conditions. [19]
Angiotensin-converting-enzyme inhibitors are a class of medication used primarily for the treatment of high blood pressure and heart failure. This class of medicine works by causing relaxation of blood vessels as well as a decrease in blood volume, which leads to lower blood pressure and decreased oxygen demand from the heart.
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Hypertension, also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. It is, however, a major risk factor for stroke, coronary artery disease, heart failure, atrial fibrillation, peripheral arterial disease, vision loss, chronic kidney disease, and dementia. Hypertension is a major cause of premature death worldwide.
Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. Healthy pulse pressure is around 40 mmHg. A pulse pressure that is consistently 60 mmHg or greater is likely to be associated with disease, and a pulse pressure of 50 mmHg or more increases the risk of cardiovascular disease. Pulse pressure is considered low if it is less than 25% of the systolic. A very low pulse pressure can be a symptom of disorders such as congestive heart failure.
Antihypertensives are a class of drugs that are used to treat hypertension. Antihypertensive therapy seeks to prevent the complications of high blood pressure, such as stroke, heart failure, kidney failure and myocardial infarction. Evidence suggests that reduction of the blood pressure by 5 mmHg can decrease the risk of stroke by 34% and of ischaemic heart disease by 21%, and can reduce the likelihood of dementia, heart failure, and mortality from cardiovascular disease. There are many classes of antihypertensives, which lower blood pressure by different means. Among the most important and most widely used medications are thiazide diuretics, calcium channel blockers, ACE inhibitors, angiotensin II receptor antagonists (ARBs), and beta blockers.
Indapamide is a thiazide-like diuretic drug used in the treatment of hypertension, as well as decompensated heart failure. Combination preparations with perindopril are available. The thiazide-like diuretics reduce risk of major cardiovascular events and heart failure in hypertensive patients compared with hydrochlorothiazide with a comparable incidence of adverse events. Both thiazide diuretics and thiazide-like diuretics are effective in reducing risk of stroke. Both drug classes appear to have comparable rates of adverse effects as other antihypertensives such as angiotensin II receptor blockers and dihydropyridine calcium channel blockers and lesser prevalence of side-effects when compared to ACE-inhibitors and non-dihydropyridine calcium channel blockers.
Candesartan is an angiotensin receptor blocker used mainly for the treatment of high blood pressure and congestive heart failure. Candesartan has a very low maintenance dose. Like Olmesartan, the metabolism of the drug is unusual as it is a cascading prodrug. Candesartan has good bioavailibility and is the most potent by weight of the AT-1 receptor antagonists.
Moxonidine (INN) is a new-generation alpha-2/imidazoline receptor agonist antihypertensive drug licensed for the treatment of mild to moderate essential hypertension. It may have a role when thiazides, beta-blockers, ACE inhibitors, and calcium channel blockers are not appropriate or have failed to control blood pressure. In addition, it demonstrates favourable effects on parameters of the insulin resistance syndrome, apparently independent of blood pressure reduction. It is also a growth hormone releaser. It is manufactured by Solvay Pharmaceuticals under the brand name Physiotens & Moxon.
Secondary hypertension is a type of hypertension which by definition is caused by an identifiable underlying primary cause. It is much less common than the other type, called essential hypertension, affecting only 5-10% of hypertensive patients. It has many different causes including endocrine diseases, kidney diseases, and tumors. It also can be a side effect of many medications.
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Denervation is any loss of nerve supply regardless of the cause. If the nerves lost to denervation are part of the neuronal communication to a specific function in the body then altered or a loss of physiological functioning can occur. Denervation can be caused by injury or be a symptom of a disorder like ALS, post-polio syndrome, or POTS. Additionally, it can be a useful surgical technique to alleviate major negative symptoms, such as in renal denervation. Denervation can have many harmful side effects such as increased risk of infection and tissue dysfunction.
The modern history of hypertension begins with the understanding of the cardiovascular system based on the work of physician William Harvey (1578–1657), who described the circulation of blood in his book De motu cordis. The English clergyman Stephen Hales made the first published measurement of blood pressure in 1733. Descriptions of what would come to be called hypertension came from, among others, Thomas Young in 1808 and especially Richard Bright in 1836. Bright noted a link between cardiac hypertrophy and kidney disease, and subsequently kidney disease was often termed Bright's disease in this period. In 1850 George Johnson suggested that the thickened blood vessels seen in the kidney in Bright's disease might be an adaptation to elevated blood pressure. William Senhouse Kirkes in 1855 and Ludwig Traube in 1856 also proposed, based on pathological observations, that elevated pressure could account for the association between left ventricular hypertrophy to kidney damage in Bright's disease. Samuel Wilks observed that left ventricular hypertrophy and diseased arteries were not necessarily associated with diseased kidneys, implying that high blood pressure might occur in people with healthy kidneys; however, the first report of elevated blood pressure in a person without evidence of kidney disease was made by Frederick Akbar Mahomed in 1874 using a sphygmograph. The concept of hypertensive disease as a generalized circulatory disease was taken up by Sir Clifford Allbutt, who termed the condition "hyperpiesia". However, hypertension as a medical entity really came into being in 1896 with the invention of the cuff-based sphygmomanometer by Scipione Riva-Rocci in 1896, which allowed blood pressure to be measured in the clinic. In 1905, Nikolai Korotkoff improved the technique by describing the Korotkoff sounds that are heard when the artery is ausculted with a stethoscope while the sphygmomanometer cuff is deflated. Tracking serial blood pressure measurements was further enhanced when Donal Nunn invented an accurate fully automated oscillometric sphygmomanometer device in 1981.
Hypertension is managed using lifestyle modification and antihypertensive medications. Hypertension is usually treated to achieve a blood pressure of below 140/90 mmHg to 160/100 mmHg. According to one 2003 review, reduction of the blood pressure by 5 mmHg can decrease the risk of stroke by 34% and of ischaemic heart disease by 21% and reduce the likelihood of dementia, heart failure, and mortality from cardiovascular disease.
Baroreflex activation therapy is an approach to treating high blood pressure and the symptoms of heart failure. It uses an implanted device to electrically stimulate baroreceptors in the carotid sinus region. This elicits a reflex response through the sympathetic and vagal nervous systems that reduces blood pressure.
Hypertension is a condition characterized by an elevated blood pressure in which the long term consequences include cardiovascular disease, kidney disease, adrenal gland tumors, vision impairment, memory loss, metabolic syndrome, stroke and dementia. It affects nearly 1 in 2 Americans and remains as a contributing cause of death in the United States. There are many genetic and environmental factors involved with the development of hypertension including genetics, diet, and stress.
Refractory Hypertension, also known as a refractory hypertensive state, RfHTN, or status angiotensus, is a hypertensive condition which can occur, for no apparent reason, in patients with previously well-managed hypertension. Refractory hypertension is characterized by a blood pressure that remains uncontrolled on maximal or near-maximal therapy, which is the use of ≥5 antihypertensive agents of different classes, including a long-acting thiazide-like diuretic and spironolactone. Patients with refractory hypertension typically exhibit increased sympathetic nervous system activity. The phenotype of refractory hypertension was first proposed in a retrospective analysis of patients referred to the University of Alabama at Birmingham Hypertension Clinic whose blood pressure could not be controlled on any antihypertensive regimen.