Ambulatory Blood Pressure Monitoring: When Should It Be Used?

Henry R. Black, MD; William B. White, MD


July 15, 2015

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Is Out-of-Office Blood Pressure Monitoring for Everyone?

Henry R. Black, MD: I'm Dr Henry Black, adjunct professor of medicine at the New York University Langone School of Medicine.

William B. White, MD: I'm William White from the University of Connecticut (UConn) Health Center in Farmington, Connecticut. I'm a professor in the Department of Cardiology and a long-time clinical practitioner and researcher in clinical research in hypertension and vascular medicine.

Dr Black: A couple of weeks ago I was asked what I thought was the biggest advance in blood pressure management in the past 20 years. It was an easy question to answer. It wasn't a new drug or a new diet. It was the use of out-of-office blood pressure monitoring. It goes back a very long way, but it has really improved, and you have been one of the leaders in this field. Would you agree with that assessment? Tell us how to use out-of-office blood pressure.

Dr White: I have a tendency to agree, but maybe I'm a little biased. On the other hand, we make major decisions based on single or duplicate readings of blood pressure in a doctor's office. In reality, that does not necessarily represent the true blood pressure of a person. We have learned over the past four decades that blood pressure varies substantially in different environments according to the timing of medications, salt/water intake—all kind of things. Looking at just a couple of readings is like treating diabetes with just one blood sugar, whether it's fasting or random, and not having a better picture. It's just not appropriate anymore to base the treatment and management of people with hypertension on just a couple of in-office values.

Dr Black: In whom would you recommend doing ambulatory blood pressure monitoring? Would we be like the English, who do it on everyone diagnosed with hypertension, or should we limit it to a certain subset of our patients?

Dr White: I have to be somewhat pragmatic. Part of the issue is the ease of having ambulatory monitoring performed. Not everybody can do it where they live and work. In addition, there are some important issues with respect to reimbursement for the patients, for the procedure, and the interpretation. In an ideal world, where those problems are less significant, like New York City or Hartford, Connecticut, we have lots of people who do this monitoring. You could make an argument that most people would probably want to get a 24-hour monitor when first diagnosing a patient with stage 1 or early stage 2 hypertension to determine whether it is real, the extent of it, and the profile (whether blood pressures are elevated at night).

In contrast, we know enough now that if the blood pressure in the doctor's office is in the high stage 2 range (eg, > 160-170 mm Hg systolic and > 100 mm Hg diastolic). Either with or without target-organ disease, there will be little extra benefit in most cases to do a 24-hour monitor. You start treatment on that individual because the yield of finding a totally normal ambulatory blood pressure in somebody with severe hypertension is probably well under 5%.

I'm not an advocate of doing ambulatory blood pressures in everybody at the beginning of diagnosis. We are talking diagnosis here, not treatment. That is reasonable. The US Preventive Services Task Force published a draft in the Annals of Internal Medicine,[1] suggesting that everybody should have an ambulatory blood pressure before being put on medication. I appreciate that suggestion. On the other hand, it's not feasible for a lot of individuals. We are not ready to do that in the United States. Should we plan on doing that in the future? We probably should, because as more data emerge, we have clearly learned that it's better for predicting harm, and it's better when managing drugs to have the out-of-office measurements.

Unmasking Hypertension

Dr Black: We have often heard about white coat hypertension and how common it is. What is new that we have learned from using ambulatory blood pressure is a phenomenon called "masked hypertension," in which people have normal readings in the office but elevated readings outside of the office. How do you deal with that, and when do you look for that?

Dr White: By definition, masked hypertension is when the values in the physician's office setting are relatively normal, with or without an antihypertensive drug. When the patient wears a 24-hour monitor, the value is much higher because of increased activity, sympathetic stimulation during the day, or because they have high nocturnal blood pressures during sleep. It doesn’t matter. Their readings are going to be higher. That has been called masked hypertension, and that syndrome is clearly associated with an increase in target-organ disease as well as an increase in bad cardiovascular outcomes, including stroke and heart failure.

We need to take it seriously. The problem is that it would be hard to use this method in the average normotensive patient walking into a doctor's office. You would have to have some other reason for it. For example, has a stress test been performed in which the exercise blood pressure was very high? Is there evidence of target organ involvement that is unexplained by the clinical blood pressure, so that you want to evaluate this in a patient?

It's somewhat easier to evaluate patients for masked hypertension who are already diagnosed and on therapy but still having some symptoms, or they might be taking readings on their own using a home or self-monitored device, and those values are much higher than what the physician is getting in the office. In those circumstances, I can make a good case for doing 24-hour monitoring on somebody to look for masked hypertension.

We have been doing a project for about 4 years, funded by the National Institute on Aging, in people aged 82-84 on average, and we find that 30%-40% of people in this age group have masked hypertension.[2] Much of it is due to nocturnal hypertension, and it's a substantial problem for this population who are older with stiff arteries and don't have declines in blood pressure when they are sleeping.

Home Blood Pressures: A Substitute?

Dr Black: Some of the people who had what we thought were unexplained strokes were probably people with masked hypertension that we didn't detect without doing 24-hour monitoring. What about home blood pressure? Is that a reasonable competitor or something we should do instead of ambulatory monitoring? I personally don't think so. What do you think?

Dr White: There are issues with it. One or two of the home blood pressure (self-monitoring) devices are able to measure blood pressure during sleep, but the vast majority can’t. You are basically asking the patient to obtain a few readings when they can, either at work or at home.

The problem with home blood pressures in my mind is that we don't have a good systematic approach. With ambulatory monitoring, you put the patient on the device. They keep a diary. We get many daytime and nighttime readings. They have been shown to be highly reproducible. We have less evidence on home blood pressures, and we have more problems with patient bias because they will report what they want to report, just like they report blood sugars that they want to report. From a clinical management perspective, home blood pressures are helpful when people are trying to do a good job of taking them systematically at the same time of day with respect to the dosing of their medications. They are helpful in making sure that the patient's blood pressures are different at home from those in the doctor’s office.

I don't rely on home blood pressures alone, however. That could be dangerous because those values are not necessarily true. Going back to the study that we are conducting in older people, we find that home blood pressures are not very good predictors of ambulatory blood pressure. In fact, they are worse than the standard digital measurements that we take in the office setting.

Uses for Ambulatory Blood Pressure Monitoring

Dr Black: Do you use ambulatory blood pressure monitoring to see how well a particular regimen—nutritional, diet, or medication—is working?

Dr White: We do at least one time, particularly in a patient who has white coat or masked hypertension and we have initiated some sort of intervention, either drug or nondrug. If I don't believe that the clinical measurements in the doctor’s office represent an individual's true blood pressure, I will advocate for ambulatory monitoring after the patient is stabilized.

We haven't reached the point at which we are using ambulatory blood pressure monitoring routinely at 6- or 12-month intervals, although that could change with time. The research that I'm doing evaluates the practicality of doing that. We have another 2-3 years on that project to determine whether it makes more sense to use ambulatory blood pressure monitoring to target therapy and reduce the accumulation of target-organ disease, particularly in older people who might have microvascular disease of the brain or some issues with control during the nighttime.

Dr Black: Do you have a favorite machine that you use for 24-hour blood pressure monitoring, or a regimen that you use, or doesn't it matter? There are probably several very good approved ambulatory monitors.

Dr White: We have had experience with three different devices for the past 30 years, during which we have often used the Spacelabs (Hawthorne, California) recorders. We still use that device in clinical practice. We have also used the device that was formerly made by Welch Allyn (Skaneateles Falls, New York). It's a Quiet Track device. We have used the SunTech Oscar 2™ (Morrisville, North Carolina). These are all oscillometric devices. We used to use a device that measured first Korotkoff sound, but it's not clinically or commercially available right now. We have not been using the Quiet Track lately because of equipment failures. It was less expensive, but the hardware was not as tenacious as that in the Spacelabs or the SunTech units.

From the standpoint of software that is easy for doctors and nurses to use, we found that the SunTech software has been easier to use clinically. It has a nice color printout that you can use to show patients when they are hypertensive and when they are not. I am not saying that these are the only devices. There are other devices out there that have emerged over time, but I don't have clinical experience with any of the others.

Dr Black: This is likely to be a field that improves as we go along. Thank you very much for your time and expertise. You are my go-to guy for ambulatory monitoring.


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