The Epidemiology, Diagnosis of Resistant Hypertension, with Swapnil Hiremath, MD, MPH

Swapnil Hiremath, MD, MPH

Credit: University of Ottawa

Over time, the prevalence of resistant hypertension has increased, partly due to factors like aging populations and rising rates of conditions like diabetes and chronic kidney disease.

24-hour ambulatory blood pressure monitoring (ABPM) is generally used to confirm a diagnosis of resistant hypertension, as it helps to distinguish between true hypertension and factors such as the white coat effect. However, access to this monitoring can be limited, and there are challenges with the validation and accuracy of home blood pressure monitoring devices, which are sometimes used as alternatives.

In an interview with HCPLive, Swapnil Hiremath, MD, MPH, dives into his National Kidney Foundation (NKF) 2024 Spring Clinical Meeting presentation, “Resistant Hypertension: Epidemiology, Diagnosis and Pathophysiology, Evidence-Based Approach.” Hiremath is a staff nephrologist at the Ottawa Hospital, an associate professor in the Faculty of Medicine at the University of Ottawa, and an associate scientist in the Clinical Epidemiology Program at the Ottawa Hospital Research Institute.

HCPLive:Can you describe the current epidemiology of resistant hypertension and how it's evolved over the years?

Hiremath: Hypertension itself is pretty common—roughly 1 in 5 adults have high blood pressure. If you look at the estimates in the literature, anywhere from 10-30% of all the people with high blood pressure—which is 20% of the population—may have resistant hypertension. Now, that's a very large range and it’s not very useful. The reason it's like that is because it depends on how rigorously you define it, the methods you use to look at blood pressure, and what kind of populations you're looking at.

The lower end of that estimate would be if you take all comers, such as in studies using the general population, but there are many other studies which focus on older populations, diabetics, or those with chronic kidney disease where the prevalence of resistant hypertension starts going up.

Over the past 60 years or so, the overall life expectancy has gone up. For older people, who are more likely to have hypertension, there's going to be more resistant hypertension. Once you standardize for age, this increasing epidemiology over time, an increasing prevalence of resistant hypertension over time, gets attenuated substantially. There are other factors—such as the increased rates of diabetes over time—which contribute to resistant hypertension, but it probably has nothing to do with hypertension, per se, it's just the case mix of the people who have high blood pressure.

HCPLive: What are some of the key challenges in diagnosing resistant hypertension accurately?

Hiremath: Resistant hypertension is defined differently in organizations like the American Heart Association, the Hypertension Canada, and the European Society of Hypertension. They all have slightly different definitions. However, what is common for all of them is that they need blood pressure to be above a certain level. In the United States, it is 130/80. In Canada, it's 140/90.

Those differences aside, what is also common for all of them is that you need to be on at least 3 different blood pressure lowering drugs, which are usually an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin receptor blocker (ARB), a calcium channel blocker, and a diuretic. These drugs also need to be given at an optimal, maximum tolerated dose. If a patient is receiving a small dose of hydrochlorothiazide and there is room to increase it, a clinician shouldn’t diagnose it as resistant hypertension.

The other aspect is how we measure blood pressure. Ideally, it is with an out of office measurement, which is typically a 24-hour ABPM.

HCPLive: Can you elaborate on the role of 24-hour ABPM in diagnosing resistant hypertension?

Hiremath:Normally, when you go and see a doctor, they check blood pressure in-office with a cuff. The problem with that is a certain number of people have what is called a “white coat effect.” Essentially, it is when a patient has higher blood pressure in the office, although it is lower at home or at work. It has to do with the stress of coming to the hospital and the stress of the doctor or nurse being there that drives the blood pressure up in a certain proportion. Approximately 10% of people may have white coat hypertension.

They do have hypertension, but white coat hypertension will be when the numbers are 135 versus 125, for example. 125 is acceptable and 135 is not. These patients could benefit from ABPM, although it is not routinely done. In the United States, it wasn't even available unless a provider said this patient has white coat hypertension.

HCPLive: How has the availability of 24-hour ABPM evolved, and what impact has it had on diagnosing and managing resistant hypertension?

Hiremath: A couple of years ago, more widespread use of 24-hour ABPM became available. In certain countries, you cannot diagnose hypertension without doing a 24-hour ABPM. In Canada, it's kind of hodgepodge—in some centers we have it and in some centers we don't.

The biggest challenge is that you need a 24-hour blood pressure monitoring to be performed because otherwise you may be labeling something as resistant hypertension when they actually don't have it. You need to have that white coat effect ruled out.

Some people argue if you can't do 24-hour ABPM, you can do blood pressure measurements at home. These days, you can buy home monitors from Walmart, Amazon, or any pharmacy. That would be fine except oftentimes these monitors are not validated and may not be giving you the correct numbers.

The licensing for devices is very different than the licensing for drugs. The US Food and Drug Administration (FDA) will approve a device if it will not physically harm the patient, but they don't look at if the numbers are accurate or not. In Canada, a study showed that only about 30% of the devices sold on Amazon were validated, whereas in pharmacies, it was roughly 50-60%. Essentially, if your patient has a home blood pressure monitor, it may not be giving them accurate numbers.

At our center, our patients bring in their monitoring and we check it to make sure it’s an accurate representation. However, a family doctor or internist may not have the resources to do that. Blood pressure monitoring is currently a big limitation.