By Dr. Geoffrey Modest
A recent study of older community-dwelling high-risk hypertensive patients looked at the relationship between their achieved blood pressure and cardiovascular outcomes (see Myers MG Hypertension. 2016;68:866).
Details:
- 6183 community-dwelling Ontario residents >65yo on antihypertensive therapy, followed mean of 4.6 years (the CHAP study: Cardiovascular Health Awareness Program)
- Blood pressure measured (as in the SPRINT trial) by AOBP (electronic automated office blood pressure). In Ontario, the protocol was that the person rest seated in a quiet place, undisturbed before and during the readings. The research staff did not speak to the subjects or interact with them. The patient did not wait 5 minutes, but the AOBP recorded the blood pressure each minute for 5 minutes and computed the mean value. The AOBP was recorded in community pharmacies, which a different study found to be similar to AOBP done in the office of the patient’s own family physician. In the SPRINT trial, the initial reading was after the patient seated and wait 5 minutes in quiet, then the blood pressure was measured using a similar automated machine as in the Ontario study
- Mean age 76, 42% male, 6% self-reported smokers, 48% self-reported high blood cholesterol, 27% diabetic, 12% congestive heart failure
- Mean AOBP: 134.3/72.9 mmHg. Mean number of antihypertensive meds = 1.8-1.9 for each 10mm blood pressure category
Results:
- 904 nonfatal and fatal cardiovascular events during the follow-up period
- Multivariate adjustment (adjusting for age, sex, coronary artery disease, cerebrovascular disease, congestive heart failure, diabetes, number of anti-hypertensive meds, hypercholesterolemia, smoking, self-reported health status, BMI, number of unique drugs) found that, as compared to an achieved systolic of 110-119 mmHg [n=837]:
- <110 mmHg: HR 1.38 (1.04-1.81) [n=546]
- 120-129mmHg: HR 1.30 (1.01-1.66)[n=1308]
- 130-139mmHg: HR 1.23 (0.96-1.58), nonsignificant [n=1259]
- 140-149mmHg: HR 1.18 (0.90-1.54), nonsignificant [n=984]
- 150-159mmHg: HR 1.43 (1.08-1.90) [n=604]
- 160+ mmHg: HR 1.85 (1.42-2.41) [n=645]
- Multivariate adjustment for achieved diastolic blood pressure, as compared to referent of 60-69 mmHg [n=1788]:
- <60 mmHg: HR 1.31 (1.07-1.61) [n=636]
- 70-79 mmHg: HR 1.02 (0.87-1.21), nonsignificant [n=2212]
- 80-89 mmHg: HR 1.08 (0.88-1.32), nonsignificant [n=1133]
- 90+ mmHg: HR 1.14 (0.86-1.52), nonsignificant [n=414]
- Multivariate adjustment for pulse pressure (systolic minus diastolic), with 50-59 mmHg being referent [no comment on how many people were in each group]:
- <50 mmHg: HR 1.06 (0.87-1.29), nonsignificant
- 60-69 mmHg: HR 1.07 (0.87-1.30), nonsignificant
- 70-79 mmHg: HR 1.10 (0.88-1.38), nonsignificant
- 80-89 mmHg: HR 1.33 (1.03-1.72)
- 90+ mmHg: HR 1.83 (1.42-2.34)
- No difference in outcome in the 1673 patients with diabetes vs the 4510 nondiabetics
Commentary:
- So, overall, this study found increased CV outcomes in patients with achieved systolic blood pressure below 110 mmHg or if 120-129 mmHg (vs the nadir of 110-119 mmHg), and not again until >150 mmHg; an increase only with diastolics <60 mmHg; and an increase when the pulse pressure was >80 mmHg (the latter likely reflecting stiff arteries, as with diffuse atherosclerosis). By the way, this nadir of SBP 110-119 mmHg was the same as in the SPRINT trial
- This observational study, as with many observational studies, did find a J-curve in clinical outcomes in hypertensive patients, with increased morbidity/mortality in those with both lower and higher achieved blood pressure. This was not found in the prospective randomized-controlled SPRINT or ACCORD trials, where the lower blood pressure was better, suggesting that there might be a selection bias here: i.e., are those with lower blood pressure different from the others? Do they have non-blood pressure related terminal illnesses, like cancer or infections or perhaps worse cases of diabetes or heart failure, which leads to lower blood pressure and also to higher morbidity/mortality?)
- One thing I have commented on in the past: there is a rather strong trend in the medical literature to put many study details in a “supplement”, which i think often includes critical details. In the above study, for example, there were no data on the number of patients in each cell of achieved systolic and diastolic blood pressures, except in the supplement, and none anywhere on the pulse pressure categories. It seems to me to be very important information (was the lack of statistical significance in some groups due to small numbers of patients??). My guess is that pretty few readers go to the trouble of going online to get this information; it is much less of a hassle to just accept the authors’ interpretations in the main article. And if we just got the PDF from the author by email, the supplementary material is not included (at least in my experience). And I pretty often do find very important information buried in the supplements, in the relatively few times I scour them, and this information sometimes changes my interpretation of the article.
- One of my biggest concerns with clinical management of hypertension is that in the typical rushed clinical environment, most of us simply accept the automated blood pressure readings of the medical assistants as being accurate. This brings up several very important issues in probably what is the most common clinical issue we see in adult patients and one that we can potentially positively affect:
- The automated machine is not always accurate (e.g. in patients with atrial fibrillation or frequent dysrhythmias)
- Typically the patient walks into the room and has the blood pressure done quickly in a not-so-restful environment (and many of my patients are pretty unfit physically/deconditioned, so have a much much higher blood pressure than when I retake a manual pressure when they are sitting quietly in the exam room)
- I do routinely recheck blood pressures in the exam room, typically after leaving the patient sitting on the exam table for about 2 minutes, often with the lights out (I go into the other room to write my note), and find in this not-very-scientific study that about 50% of the medical assistant blood pressures are really pretty close to what I get, 40+% are much lower than the medical assistant pressures (and often by 20-40 mmHg!!!), and the rest are much higher than the medical assistant values (not sure why, but i sometimes get manual pressures of 190/108, when the medical assistants get 118/77…..)
- There is a significant literature suggesting that clinical outcomes track much better with 24-hour ambulatory blood pressure monitoring (ABPM) or home-based blood pressure (I do ask patients to bring in their cuff and make sure it compares well with the manual recording I get, done at the same time). See the URLs below for more articles on this. and the USPSTF does now (finally) endorse non-clinic based blood pressures (see below)
- Using AOBP in this Ontario study, similar to the SPRINT study, is an interesting hybrid, which sounds pretty good to me, though i have not seen much in the literature on this. But again, to apply these trials to clinical practice, we need to get blood pressure readings that approximate how it was done in the studies (i.e., at least with having the patient rest in a quiet room for awhile, or using ABPM; though with ABPM, there is only one cutpoint: either above or below 135/85, not with the fine gradations of the SPRINT or other trials assessing treating blood pressure to different targets.
- One of the strengths of this study is that it was not a formal study with selected patients according to specific inclusion and exclusion criteria, but more of a community approach, likely more reflective of our actual clinical practice (i.e., there is decreased internal validity in that there may have been very uneven distribution of patients in the different categories of achieved blood pressure, perhaps with healthier patients overall able to achieve an SBP in the 110-119 range, or their clinicians were more aggressive in trying to lower their blood pressure; yet more external validity in that it more closely reflects real-world clinical practice. one drawback to the study was that AOBP was measured only one point in time. and they did not have much granular data, such as how long the patient had hypertension or what time of day the AOBP was recorded, or how bad the heart failure was, etc. But it was intriguing that the results (best to have SBP 110-119) was so similar to that of the rigorous SPRINT trial.
See https://stg-blogs.bmj.com/bmjebmspotlight/category/hypertension/ for an array of articles/reviews on hypertension, including a recent one showing that blood pressure variability is associated with more cardiovascular disease
See https://stg-blogs.bmj.com/bmjebmspotlight/2015/01/15/primary-care-corner-with-geoffrey-modest-md-uspstf-recs-on-ambulatory-blood-pressure-monitoring/ for a brief review of ambulatory BP monitoring and the USPSTF recommendations
See https://stg-blogs.bmj.com/bmjebmspotlight/2015/11/19/primary-care-corner-with-geoffrey-modest-md-tighter-blood-pressure-control-the-sprint-trial/ for the overall SPRINT trial
See https://stg-blogs.bmj.com/bmjebmspotlight/2016/06/02/primary-care-corner-with-geoffrey-modest-md-sprint-trial-elderly-subgroup-study-of-lower-blood-pressure-goal/ for an analysis of the elderly subgroup of the SPRINT trial, finding improvement in cardiac outcomes in those >75 yo with achieved SBP of 123
See https://stg-blogs.bmj.com/bmjebmspotlight/2016/05/03/primary-care-corner-with-geoffrey-modest-md-home-blood-pressure-monitoring/ for some of the data on home blood pressure monitoring
See https://stg-blogs.bmj.com/bmjebmspotlight/2015/10/13/primary-care-corner-with-geoffrey-modest-md-bp-self-monitoringself-titrating-decreases-bp/ shows the benefits of patient self-monitoring blood pressure and self-titrating meds
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