What is hypertension (high blood pressure, HTN)
Hypertension (high blood pressure, HTN) is defined as a condition in which blood pressure measurements are greater than the commonly accepted normal levels for age (systolic blood pressure = 135-140 mm Hg and / or diastolic blood pressure = 85-90 mm Hg).
Hypertension is an important risk factor for stroke, ischemic heart disease, chronic heart failure, end-stage renal disease and intermittent claudication (peripheral arterial disease in the legs).
Resistant hypertension (or malignant hypertension) is defined as the inability to regulate blood pressure using the maximum tolerated doses of three antihypertensive drugs, one of which should be a diuretic. The American Society of Hypertension states that the level of blood pressure should be below 130/80 mmHg for high-risk groups (like patients with diabetes, renal disease and proteinuria).
The prevalence of resistant hypertension is not precisely known but it appears that the proportion of resistant hypertension does not exceed 5% in the general hypertensive population. However, two large epidemiological studies from the U.S. and Spain determined that 9-12% of hypertensive patients do actually suffer from resistant hypertension.
Surgical treatment of resistant hypertension
In the middle of last century, Sympathectomy was a very popular surgical option and the only effective method of dealing with malignant hypertension. This method, however, had many serious side effects and fell out of favour with the advent of antihypertensive drugs. Today, we have developed a new surgical method for treating resistant hypertension called Renal Sympathetic Denervation (renal artery de-nervation, RDN, Ardian). This procedure is minimally invasive with excellent safety features and however the results from recent SYMPLICITY HTN-3 trial show that renal artery denervation did not prove to be effective treatment for hypertension, as initially thought.
The Renal Sympathetic Denervation works on the sympathetic nervous system. The kidneys have a dense sympathetic innervation of afferent and efferent nerves surrounding both renal arteries. Stimulation of the afferent sympathetic nerves leads to an increase in the production of the renal hormone renin, which causes water and “salt” to be retained in the body and a reduction in blood flow through the kidneys. This process results in further stimulation of efferent sympathetic renal nerves which influence the patient’s central nervous system. As a consequence, the central nervous system increases the tone of the afferent sympathetic renal nerves, creating a vicious cycle that contributes to disease development and maintenance of what we call resistant hypertension.
Sympathetic Renal Denervation is a new interventional treatment for resistant hypertension that uses a specially designed catheter (Simplicity Catheter System, Ardian, Mountain View, CA, USA). The procedure requires insertion of the special treatment catheter (Simplicity Catheter System, Ardian) into the patient’s femoral artery (groin) and then advancing it into the renal arteries of the kidneys. Through this special catheter “electricity” in the form of “heat” ablates (destroys) the overractive sympathetic nerves which surround the arteries of the kidneys (catheter-based radiofrequency ablation). This method is minimally invasive, is performed under light sedation and local anaesthetic, and requires a minimum time of 30-40 minutes in order to perform an effective denervation of both renal arteries. After the surgery, the patient is transferred to a cardiology ward for recovery. Here, the patient receives intravenous fluids and pain relief. The patient is then mobilized out of bed after six hours. The next day the patient is usually discharged home with written instructions following an evaluation by our team.
Causes of “pseudo-resistant hypertension”
A significant portion of patients “tagged” with resistant hypertension are in fact suffering from what we call “pseudo-resistant hypertension”. It is therefore extremely important to ensure that the correct diagnosis of resistant hypertension has been made before a patient is referred for treatment with sympathetic denervation of the renal arteries. This means that the patient has undergone a careful up-titration of antihypertensive medications, with adherence to appropriate administration of medical therapy, and with exclusion of the presence of “white coat” hypertension (whereby blood pressure goes up in the presence of a health professional). We therefore recommend a 24-hour recording of blood pressure or blood pressure measurements at home for a week, before committing the patient to the treatment of renal artery denervation (RDN, Ardian).
Another very important parameter in the evaluation process is a thorough assessment of the patients’ medical treatment for concomitant administration of medications that may increase his/her blood pressure. Medications like non-steroidal anti-inflammatory drugs (pain relief drugs), either classic or cyclo-oxygenase II inhibitors, which are taken by a large population of patients and often without a prescription, can be a cause of both an increase in blood pressure and deterioration in renal function. Other major causes of resistant hypertension include the expansion of patients’ intravascular volume by either overconsumption of fluid or salt (sodium) retention due to chronic renal disease, or by the administration of sub-therapeutic doses of diuretics.
Finally, all patients with resistant hypertension must be assessed for causes of secondary hypertension like kidney-parenchymal disease, reno-vascular hypertension, sleep apnea syndrome or primary aldosteronism.
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