What is Renovascular Hypertension?
High blood pressure, or hypertension, impacts about 75 million adults in the U.S and is a common reason for primary doctor visits. One of the typical reasons behind high blood pressure is called renovascular hypertension, often leading to stubborn, resistant hypertension. This condition occurs when you have high blood pressure due to reduced blood flow to the kidneys, generally because of a blockage in the main renal (kidney) artery.
What Causes Renovascular Hypertension?
Renovascular hypertension is a condition characterized by high blood pressure caused by kidney problems. It can occur when the blood flow to the kidneys is disrupted. Some common causes of renovascular hypertension include kidney artery narrowing, fibromuscular dysplasia, vasculitis, external compression of the artery, kidney artery tear or infarction, scarring from radiation treatment, and blockage from a graft.
Risk Factors and Frequency for Renovascular Hypertension
Treating uncontrolled high blood pressure costs about $48.6 billion each year. Although most of these cases are due to primary high blood pressure, about 10% result from secondary high blood pressure. In fact, studies show that about 75% of the cases of secondary high blood pressure are due to renovascular high blood pressure, a type that affects kidney blood vessels.
Renovascular high blood pressure can affect anyone, regardless of their age. However, narrowing of the renal arteries, mostly due to the buildup of fats and cholesterol (a condition called atherosclerosis), is the most common cause and usually occurs in adults over 65 years of age. This condition is more common in people who have known atherosclerotic disease, like coronary artery disease, disease of the peripheral arteries, or narrowing of the carotid artery. Autopsy studies have shown that more than one in four patients who die of cardiovascular disease have some degree of renal artery narrowing.
A condition called Fibromuscular dysplasia (FMD) is another cause of renovascular high blood pressure. It usually affects young women and contributes to around 10% of renovascular high blood pressure cases and 5.8% of secondary high blood pressure cases. FMD can affect any group of arteries, but it most frequently affects the last two-thirds of the renal artery.
Signs and Symptoms of Renovascular Hypertension
Renovascular hypertension is a condition caused by blockage of the arteries that carry blood to the kidneys. To help determine if a patient has renovascular hypertension, doctors look for certain hints in the patient’s medical history. These hints include:
- High blood pressure that doesn’t respond well to medication, even when the patient is taking two or three different types from different classes, including water pills
- A history of trials with multiple medications to control blood pressure
- Repeated hospitalization due to severe high blood pressure episodes
- A 30% increase in creatinine, a waste product in the blood, after starting a medication class known as ACE inhibitors
- Older patients with blockages in the renal arteries (which supply the kidneys) often have other blockages in their body, such as in the arteries to the neck (carotid), legs (peripheral), or heart (coronary)
- Women of childbearing age (between 15 and 50 years old) who have high blood pressure are likely to have a condition called fibromuscular dysplasia
- A long-term history of smoking
Other clues of the presence of renovascular hypertension can include patients with a type of blood vessel inflammation known as vasculitis affecting the renal arteries, repeated episodes of sudden lung water logging or unexplained heart failure, unexplained increase in waste products in the blood, an increase in creatinine levels after starting ACE inhibitors, unexplained low levels of potassium and a condition where the blood has too much bicarbonate, or a shrunken or small kidney on one side. A physical examination might reveal a swishing noise in the abdomen, which can indicate the presence of blockages in the renal arteries.
Testing for Renovascular Hypertension
For patients with renovascular hypertension, a type of high blood pressure caused by narrowing of the arteries that carry blood to the kidneys, numerous tests may be required to identify the cause of the uncontrolled high blood pressure.
In a lab, several tests might be conducted. These include urine tests to check for protein and blood in the urine which might indicate kidney problems; blood tests to assess the kidney’s functionality; basic metabolic tests to measure electrolyte levels and see how the body’s cells are metabolizing nutrients; complement and autoimmune tests in cases where autoimmune diseases are suspected, among others. These tests help to rule out conditions such as pheochromocytoma (a rare kind of tumour), hyperaldosteronism (excessive production of a hormone called aldosterone), and Cushing’s syndrome (a hormonal disorder).
However, testing often goes beyond the lab. Several types of imaging techniques can be used in these cases. The preferred diagnostic test is renal arteriography, an imaging technique that visualises the arteries in the kidneys. Yet, as it is invasive, costly, and can potentially lead to complications like cholesterol buildup or tearing of the renal artery, other techniques are also employed.
Duplex ultrasonography, which uses sound waves to create images, is often the first choice. It is cost-effective, non-invasive, and doesn’t involve the use of contrast dyes or radiation. This technique uses various parameters to detect presence of renal artery stenosis (a condition characterized by narrowing of the arteries that carry blood to the kidneys), with the peak systolic velocity being the most important. A high peak systolic velocity indicates the presence of considerable stenosis, or narrowing of the arteries.
Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are other possible imaging tests. CTA involves the use of intravenous contrast to generate detailed images of blood vessels, and MRA uses a magnetic field, radio waves, and a contrast agent to visualize blood vessels and surrounding areas. While both tests have high sensitivity and specificity, they have their limitations such as the exposure to radiation in CTA, and overestimation of the grade of stenosis or difficulty visualizing the renal arteries in MRA.
In cases where the results of other tests aren’t consistent, or when an intervention might be necessary, catheter angiography is often preferred. This technique, which can accurately assess renal arteries and locate potential blockages, uses a narrow tube (catheter) that is guided through the blood vessels to the area of interest.
In conclusion, diagnosing renovascular hypertension involves a combination of lab tests and imaging techniques, each offering unique information about the kidneys and the renal arteries to determine the cause behind this type of high blood pressure.
Treatment Options for Renovascular Hypertension
The goal of treating renovascular hypertension, a type of high blood pressure caused by issues with the arteries in the kidneys, is to address the root problem. There are several ways to treat this, which include medication and procedures.
Starting with medications, the American College of Cardiology and the American Heart Association recommends drug therapy as the first response to renal artery stenosis, a narrow artery in the kidney. Blood pressure medications like ACE inhibitors and angiotensin receptor blockers are often used because these drugs affect the system that controls the dilation of blood vessels and the balance of salt and water in the body. Still, more than one type of medication may be required. Other effective drugs include calcium channel blockers, thiazides, beta-blockers, and hydralazine. There are also direct renin inhibitors, like aliskiren, that have been investigated. While these drugs work for high blood pressure, they haven’t been proven effective specifically for renovascular hypertension.
Although these medications can control blood pressure, they can potentially worsen kidney function. This is especially a concern for those who have only one working kidney or if both kidneys are affected.
Another treatment option is percutaneous angioplasty, a procedure to restore blood flow through the arteries. This is commonly used for patients with hypertension caused by fibromuscular dysplasia (a disease that affects the growth of arterial walls) or for those with atherosclerotic renal artery stenosis who aren’t responding to medication. Guidelines suggest certain situations when this procedure should be considered — such as patients with significant narrowing of the renal artery and heart-related complications.
For patients with fibromuscular dysplasia, this procedure has been shown to lower baseline blood pressure. However, in the case of atherosclerotic renal artery stenosis (where the narrowing is due to fatty deposits), it’s still doubted whether the procedure is more beneficial compared to medication alone. Recent studies have shown no difference in blood pressure or the amount of blood pressure medication needed between patients who had the procedure and those who just received medication.
In situations where the renal artery stenosis keeps recurring, or medication and angioplasty are not controlling the blood pressure, renal bypass surgery could be considered. This complex surgery involves connecting the kidney to the aorta with a vein or synthetic tube, bypassing the blocked artery. This procedure is rarely used and is recommended in certain situations.
Some studies have also looked at the possible benefits of removing one kidney in patients with renovascular hypertension. The results showed improvements in controlling the blood pressure, kidney function, and a reduction in the use of blood pressure medications. Nonetheless, it’s a serious surgery with its risks, and the long-term effects are still not fully understood.
What else can Renovascular Hypertension be?
When trying to diagnose renovascular hypertension, which is high blood pressure caused by issues with the arteries leading to your kidneys, doctors consider other conditions that may also cause high blood pressure. These include:
- Pheochromocytoma: This condition usually comes with symptoms like flushing, headaches, a fast heartbeat, and sudden uncontrolled high blood pressure.
- Primary hyperaldosteronism: This is a hormone condition that can cause low levels of potassium in the blood and a disturbance in the body’s acid-base balance.
- Obstructive sleep apnea: This condition is most often seen in people who are overweight. Common symptoms include loud snoring and frequent pauses in breathing during sleep. It’s typically diagnosed with a sleep study.
- Coarctation of the aorta: This is a narrowing of the large blood vessel that delivers oxygen-rich blood from the heart to the body. Symptoms include a heart murmur, a delay in the pulse between the upper arm and the thigh, and high blood pressure in the upper body. It’s usually diagnosed with an MRI or CT scan.
- Cushing syndrome: This is a hormone disorder that can cause symptoms like a round face, a fatty hump between the shoulders, weak muscles, high blood sugar, stretch marks in the skin, and weight gain mostly in the stomach area.
These conditions can produce similar symptoms or effects as renovascular hypertension, so it’s crucial for doctors to conduct detailed tests to provide an accurate diagnosis.
What to expect with Renovascular Hypertension
Atherosclerotic renal artery stenosis is a condition that progressively narrows the renal arteries, potentially leading to kidney failure. Previous studies have found that over three years, the disease progressed in 18% of patients with normal arteries, 28% of patients with less than 60% stenosis (or narrowing), and 49% of patients with more than 60% stenosis.
The rate of disease progression increases in those who have high blood pressure (above 160 mm hg), diabetes, or high-grade stenosis (over 60% obstruction). If left untreated, this condition, known as renovascular hypertension, can result in end-stage renal failure. The median survival time in such cases is 25 months, and the 4-year mortality rate is 35%.
The main treatment goal for renovascular hypertension is addressing the root cause. For patients with the condition due to atherosclerotic renal artery stenosis, medication is the primary management strategy. This is because many studies have found that invasive treatments don’t significantly improve kidney or heart outcomes.
Possible Complications When Diagnosed with Renovascular Hypertension
Renovascular hypertension can lead to various complications, mostly resulting from high blood pressure. These potential complications include:
- Kidney failure
- Heart attack
- Stroke
- Fluid in the lungs
- Eye damage (retinopathy)
- Left ventricular hypertrophy (thickening of heart muscle)
- Heart failure
- Aneurysm (blood vessel bulge)
- Vascular dementia (reduced blood flow to the brain)
Preventing Renovascular Hypertension
Renovascular hypertension is a condition in which the blood flow to the kidneys becomes constrained, resulting in high blood pressure due to a hormonal reaction from the affected kidney. This could potentially lead to serious complications such as heart attacks, strokes, and even death. People who are taking several blood pressure medications and still experience high blood pressure should consider discussing the likelihood of renovascular hypertension with their healthcare provider. Medical professionals should also be alert to this possibility in patients with persistent high blood pressure and pursue the right tests for a diagnosis.
