Circulation on the Run

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Dec 5, 2016

Dr. Carolyn Lam:
Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr. Carolyn Lam, associate editor from the National Heart Center and Duke National University of Singapore. Our feature discussion is regarding the exciting results of the masked hypertension study showing that clinical blood pressure underestimates ambulatory blood pressure, but first here's your summary of this week's issue.

The first study reviews the largest clinical experience so far with pulmonary vein stenosis following ablation for atrial fibrillation. First author Dr. Fender, corresponding author Dr. Packer and colleagues from Mayo Clinic Rochester, Minnesota evaluated the presentation of 124 patients with severe pulmonary stenosis between 2000 and 2014 and examined the risk for re-stenosis after intervention utilizing either balloon angioplasty alone or balloon angioplasty with stenting. All 124 patients were identified as having severe pulmonary vein stenosis by CT in 219 veins. 82% were symptomatic at diagnosis with the most common symptoms being dyspnea, cough, fatigue and decreased exercise tolerance. 92 veins were treated with balloon angioplasty, 86 with stenting and 41 veins were not intervened on. The acute procedural success rate was 94% and did not differ by initial management. Overall, 42% of veins developed re-stenosis, including 27% of veins treated with stenting and 57% of veins treated with balloon angioplasty.

The three-year overall rate of re-stenosis was 37% with 49% of balloon angioplasty treated veins compared to 25% of stented veins developing re-stenosis. This was a difference that remained significant even after adjusting for age, CHADS2 VASC score, hypertension and time period of the study with an adjusted [inaudible 00:02:30] ratio of 2.46 for risk of re-stenosis with balloon angioplasty versus stenting. In summary, this study shows that the risk for pulmonary vein re-stenosis is significant following atrial fibrillation ablation. The diagnosis is challenging due to non-specific symptoms and while there is no difference in acute success by type of initial intervention, stenting significantly reduces the risk of subsequent pulmonary vein re-stenosis compared to balloon angioplasty.

The next paper shows that the index of microvascular resistance, which is a novel invasive mreasure of coronary microvascular function, has emerging clinical utility as a test for the efficacy of myocardial re-perfusion in invasively managed patients with acute ST elevation myocardial infarction. In this study by first author Dr. [Carrick 00:03:30], corresponding author Dr. Barry and colleagues from the University of Glasgow in Scotland, index of microvascular resistance and coronary flow reserve were measured in the culprit artery at the end of percutaneous coronary intervention in 283 patients with ST elevation myocardial infarction. Authors found that compared with standard clinical measures of the efficacy of myocardial re-perfusion, such as ischemic time, ST segment elevation and angiographic blush grade, the index of microvascular resistance was more consistently and strongly associated with myocardial hemorrhage, microvascular obstruction, changes in left ventricular ejection fraction and left ventricular end diastolic volume at six months as well as all caused death of heart failure during the median follow up of 845 days.

In fact, compared with an index of microvascular resistance greater than 40, the combination of this index and coronary flow reserve less than two did not have incremental prognostic value. The take-home message is therefore that an index of microvascular resistance above 40 represents a prognostically validated reference test for failed myocardial re-perfusion at the end of primary percutaneous coronary intervention. This study supports further research into microvascular resistance based therapeutic strategies in these patients.

The next study provides experimental data regarding molecular mechanisms underlying calcific aortic valve disease. First author, Dr. Haji, and corresponding authors Dr. Matthew and [Bose 00:05:24] from the Quebec Heart and Lung Institute in Canada performed genomic profiling and in-depth functional assays in human aortic valves. They demonstrated for the first time that the promotor region of the long non-coding RNA H19 is hypomethylated in patients with calcific aortic valve disease. This hypomethylation in turn increases H19 expression in the valve interstitial cells where it prevents Notch 1 transcription by blocking or out-competing P53’s recruitment to the Notch 1 promotor. Thus, H19 appears to be the missing link connecting Notch 1 to idiopathic calcific aortic valve disease. It may therefore represent a novel target in calcific aortic valve disease to decrease osteogenic activity in the aortic valve.

The next paper describes the largest cohort of mycotic abdominal aortic aneurysms to date and is from Dr. [Sorelias 00:06:37] and colleagues of Uppsala University in Sweden.  These authors identified all patients treated for mycotic abdominal aortic aneurysms in Sweden between 1994 and 2014. Among the 132 patients, they noted that the preferred operative technique shifted from open repair to endovascular repair after 2001 with the proportion treated with endovascular repair increasing from 0% in 1994 to 2000 to 60% in the 2008 to 2014 period. Survival at three months was lower for open repair compared to endovascular repair at 74% versus 96% respectively with a similar trend present at one year. A propensity score adjusted analysis confirmed the early better survival associated with endovascular repair. During a median follow up of 36 months for open repair and 41 months for endovascular repair. There was no difference in long-term survival, infection-related complications or re-operation. The take-home message is that endovascular repair appears to be a durable surgical option for treatment of mycotic abdominal aortic aneurysms.

The final study provides insights into the molecular mechanisms by which aldosterone triggers inflammation and highlights the particular role of NLRP3 inflammasome, which is a pivotal immune sensor that recognizes endogenous danger signals and triggers sterile inflammation. Authors Dr. Bruden [Esimento 00:08:32], Dr. [Tostes 00:08:33] and colleagues from the University of Sao Paulo in Brazil analyzed vascular function and inflammatory profiles of wild-type NLRP3 knockout, caspase-1 knockout and interleukin-1 receptor knockout mice, all treated with vehicle or aldosterone while receiving 1% saline. They found that mice lacking the interleukin-1 beta receptor or lacking inflammasome components such as NLRP3 and caspase-1 were protected from aldosterone-induced vascular damage. In-vitro, aldosterone stimulated NLRP3-dependent interleukin-1 beta secretion by bone marrow derived macrophages. Chimeric mice reconstituted with NLRP3 deficient hematopoietic cells showed that NLRP3 in immune cells mediated the aldosterone-induced vascular damage.

In addition, aldosterone increased the expressions of NLRP3, caspase-1 and mature interleukin-1 beta in human peripheral blood mononuclear cells. Finally, hypertensive patients exhibited increased activity of NLRP3 inflammasome. Together these data demonstrate that NLRP3 inflammasome via activation of interleukin-1 receptor is critically involved in the deleterious vascular effects of aldosterone, thus NLRP3 is a potential target for therapeutic interventions in conditions with high aldosterone levels.

That wraps it up for our summaries. Now for our feature discussion.

On today’s podcast we are going to be discussing the very important issue of masked hypertension. This is an issue that gets a lot less attention than I think compared to white coat hypertension. I’m so pleased to have the first and corresponding author of the masked hypertension study, Dr. Joseph Schwartz, from Stony Brook University and Columbia University in New York. Welcome to the show, Joe.

Dr. J. Schwartz:
My pleasure. I’m delighted to join you.

Dr. Carolyn Lam:
We have a regular on the show today as well, Dr. Wanpen Vongpatanasin, associate editor from UT Southwestern. Welcome back Wanpen.

Dr. Wanpen V.:
Thank you so much. Happy to be here.

Dr. Carolyn Lam:
Joe, I want to start by addressing the common misperception that ambulatory blood pressure is usually lower than clinical blood pressure. That seems to make a lot of sense to us clinically because, for example, I always use ambulatory blood pressure to diagnose white coat hypertension and so the assumption there is that my clinically measured blood pressure is higher than what I’m going to be finding if this patient measures the blood pressure on an ambulatory 24-hour basis. It’s also from the cutoffs that we use. For example, ambulatory blood pressure we use a 24-hour cutoff of 130/80 to make the diagnosis whereas with clinical blood pressure we use a cutoff of 140/90 so all of this kind of reinforces that ambulatory blood pressure is usually lower. Your study, though, tells us otherwise so please fill us in here.

 Dr. J. Schwartz:
You're right that in the doctor's office there are a certain set of people who probably get anxious when they're around a doctor and with that anxiety may cause a temporary increase in their blood pressure, a temporary elevation, and that's the basis of where we think white coat hypertension comes from. That's a very widespread belief among doctors and it's even been in previous guidelines, there have been statements to that effect. When I talk to people out in the general public and tell them I'm doing a study comparing blood pressure out in the real world compared to blood pressure in the doctor's office, all of them tell me, "Well, usually when I'm in a doctor's office that's a relatively calm period for me unless there's really something wrong with me and out in the everyday world I have to face a variety of stressors. I have deadlines. I have places I need to get to. Sometimes I have people yelling at me. Sometimes I'm just in a hurry."

All these things elevate your blood pressure out in the real world and so when we were trying to recruit people for the study, and we were very agnostic in recruiting them, telling them that we were interested in the differences in blood pressures between the doctor's office and the ambulatory blood pressure and they might go in either direction. When I told them about the fact that their ambulatory blood pressure or real world blood pressure might be higher than in the doctor's office, the vast majority of people nodded affirmatively and said, "It wouldn't surprise me at all."

Dr. Carolyn Lam:
Could you define masked hypertension compared to white coat hypertension and tell us a little bit about the population you studied.

Dr. J. Schwartz:
Sure. First with the definition. I'm going to say something a little bit different from something you said before. You mentioned cutoffs that we typically used for ambulatory blood pressure of 130/80 and those are the cutoffs that are used if you compute an average blood pressure over the entire 24 hours. What many people do, and what we did for this study, was compare the average blood pressure when people were awake to their blood pressure in the doctor's office because obviously in the doctor's office everybody is awake. The typical cutoffs there are 135/85, recommended by numerous guidelines in this country and with our international collaborators. The definition of masked hypertension is having a blood pressure in the clinic setting that's below 140/90 but having an ambulatory blood pressure where either the systolic blood pressure is above 135 or the diastolic is above 85 millimeters of mercury.

In terms of the sample, for years I've had a particular strategy for trying to recruit participants. I do worksite-based studies and so I identify large organizations that will allow me to recruit their employees and then what we did for this study is go to individual departments, both here at Stony Brook University, at Columbia University, at a residential veterans' home that's affiliated with Stony Brook University and then also at a local private hedge fund management company. We would go to these sites, I talk to the head of a department and tell them a little bit about masked hypertension and what the study was about and ask them if they would be willing to have their employees participate in the study. Once I had the okay from the department head then we would conduct public health screenings, blood pressure screenings. My staff and I would go into the department for multiple days and invite anybody who was interested to have their blood pressure taken on site and while we were taking those blood pressures carefully.

The proper way to take those is to take three readings and leave a minute or two interval between them and rather than just have silence then between the readings we would tell them a little bit about our study. At the end of the study if they didn't have extremely high blood pressure and were not taking blood pressure medication we would ask them if they might be interested in participating in the study that we just described. That's how we identified potential participants and about 2/3 of the people that we talked to who looked eligible indeed chose to participate.

Dr. J. Schwartz:
The one other thing I might mention that I think we mentioned, I hope we mentioned as a limitation of the study, is that everybody in the study had health insurance and at least until recently there were very large portions of the population that didn't have health insurance, everybody by virtue of their employment by the organizations that participated in the study, did have employer-based health insurance.

Dr. Carolyn Lam:
Thanks for clarifying the population so well. Could you just give us the top line of your findings. How big a difference did you find, which direction and that intriguing effect of age?

Dr. J. Schwartz:
Sure. The first thing we found is that on average the systolic blood pressure is seven millimeters mercury higher out in everyday life than it is in the clinic setting where we take our clinic readings. I should mention that unlike most studies, and all studies at the time that we began our study, we brought people in three separate times to take the clinic blood pressure. Up until that, almost all of the studies of ambulatory blood pressure monitoring only had clinic blood pressures from a single visit. I think we have a very reliable measure of the clinic blood pressure as well as reliable measure of ambulatory blood pressure. We see a seven millimeter difference in the systolic blood pressure and a 2 millimeter difference, again the ambulatory being higher for diastolic blood pressure.

What's more remarkable is if you think about what's a sizable difference. If you think if we perhaps somewhat arbitrarily say 10 millimeters of systolic blood pressure is a large difference. More than 35% of the population has an ambulatory blood pressure that is more than 10 millimeters higher than their clinic blood pressure whereas only 3% of our sample had that large a difference in the opposite direction, what many people would call a white coat effect. It's more than a 10 to 1 difference in numbers of people who have elevated ambulatory versus elevated clinic.

You asked me to mention something about the age difference. When you look at how that difference in systolic blood pressure varies by age, it's quite a bit larger for people who are younger. If you're under 30 the difference is, on average, 10 millimeters rather than seven millimeters and if you go up as you approach 60 years of age or so the difference becomes relatively small, perhaps in the neighborhood of two millimeters. We don't have enough people because it's a working population over 65 to say very much about what would happen. In fairness to prior research, which often is on older populations and particularly hypertensive populations, the studies that have historically shown that ambulatory blood pressure tends to be lower than clinic blood pressure are in these older populations and populations that have elevated blood pressure to start with.

My speculation there, and you haven't asked me to mention it but I will, is that older people and those with hypertension have a reason to be more nervous or more anxious when they go to the doctor than people who are not taking medication and probably don't even know that they have hypertension. People who are just being screened perhaps during a routine physical for the possibility of hypertension, because the doctors take a blood pressure reading every time you go in, they're doing that in order to see whether you might have hypertension, but most people who are going in for what we call a well patient visit are not nervous about their blood pressure being high.

Dr. Carolyn Lam:
I have to say, the take-home message for me when I read this was, I am not paying enough attention to masked hypertension and then another thing was, maybe I need to think about more white coat hypertension in the older and masked hypertension in the younger. Wanpen, do you think it's as simple as that? What were your take-home messages?

Dr. Wanpen V.:
I think this is a very important study that examines this in a systematic way. I'm not surprised that Joe found as much masked hypertension here. I think that he's absolutely right. We looked at this in Dallas Heart Study as well recently and we found that in the population-based sample in Dallas almost 20% of people have masked hypertension and white coat we found only like 3% and the average in the Dallas Heart Study was very close to those samples, about mid-40s. I think that's a very important finding in that the people with masked hypertension would not be suspected otherwise to have problems. Also, in the Dallas Heart Study they used home readings but Dr. Schwartz used ambulatory blood pressure monitoring. Unless extra out of office monitoring is being done we will totally miss these people who are more likely to have target organ damage from high blood pressure. I think that's absolutely important.

Dr. Carolyn Lam:
Actually, Wanpen you brought up something I was going to bring up as well. Where does home blood pressure fit in with this? Do you think it's home blood pressure versus ambulatory blood pressure?

Dr. Wanpen V.:
The US Preventive Services Task Force has issued a little bit of recommendations recently that we need to either use ambulatory blood pressure monitoring or home blood pressure monitoring to confirm diagnosis of hypertension in the office. If someone shows up with elevated blood pressure in the office either home blood pressure or ambulatory blood pressure needs to be done. If we just followed that guidelines we're still going to miss people with masked hypertension because by definition they don't have elevated blood pressure in the office. I think that from these findings and Dr. Schwartz' study I think to catch these people we really need to pay attention to people with pre-hypertension type of blood pressure because it seems like those are the group that has the most probability to have elevated ambulatory blood pressure so anyone with borderline blood pressure in the clinic, those are the ones who the doctor needs to tell the patient to monitor blood pressure at home or order ambulatory blood pressure themselves if that's available in their facility.

Dr. Carolyn Lam:
Wanpen, I fully agree. What an important message. Joe, I'd like to give you the final word but I'd love to hear how you have maybe taken this into your own practice.

Dr. J. Schwartz:
I think we mostly focused on and indeed the paper mostly focuses on the difference between clinic blood pressure and ambulatory blood pressure. When we talk about the young people, the young people have a bigger difference but those differences are for the most part all in the normal range. You might see a 10- or a 12-point difference but it might be that the ambulatory is 124 and the clinic is 112 and no doctor is going to worry about that very much. There are really always two things that we're trying to look at simultaneously: The first is what is that difference between the ambulatory and the clinic, but the second is for whom does the clinic stay under the threshold for diagnosis of hypertension but the ambulatory is over? That's the diagnosis of masked hypertension.

We haven't said it today so I'll say it: Of those people who had normal clinic blood pressures averaged across three repeated visits, 15.7% of them had elevated ambulatory blood pressure and would have been diagnosed as having hypertension based on their average daytime ambulatory blood pressure reading. That's one message.

The last message is unfortunately there is almost no research yet telling us what we should do in terms of treating people with masked hypertension. We are now at the point where we can identify these people and we're also at the point where we now know that there are a lot of such people and we don't even have any research to base guidelines on for deciding what we should do with them. The most obvious thing is to recommend lifestyle changes. If they're overweight we could suggest that they lose weight. We could suggest that they exercise more. We might think about treating some of those people, especially if their ambulatory blood pressure is well above 140/90. There are no statements out in the literature by any of the organizations, and in fact there's no research examining whether there's a benefit or not a benefit to perhaps putting some of those people on medications. I think that's a big question that future research needs to address.

Dr. Carolyn Lam:
Joe, thank you so much. I think your last statements just really emphasize how important this paper is. It increases awareness and it's going to open the door to much more needed research in this area. Thank you so much. Thank you Joe and Wanpen for being on the show today.

Thank you listeners for joining us. Don't forget to join us next week for even more news and exciting discussions.