by Dr Geoffrey Modest
The SPRINT hypertension study assessed different blood pressure targets on clinical outcomes, finding the lower the pressure, the better. A subsequent ambulatory blood pressure substudy of SPRINT looked at the relationship between the achieved ambulatory versus clinic-based blood pressures (see DOI: 10.1161/HYPERTENSIONAHA.116.08076.)
Details:
— the SPRINT study randomized patients to aggressive vs less aggressive blood pressure control, achieving a systolic of 121 mmHg versus 136 mmHg, respectively. The primary clinical outcome (MI, acute coronary syndromes, stroke, heart failure, or death from cardiovascular causes) was 25% less frequent in those having tighter control. (see here for details)
— in the current ancillary study on ambulatory blood pressure monitoring (ABPM), they performed ABPM at the 27-month study visit in a subgroup of 897 SPRINT participants
— for this ancillary study, mean age 71, 29% female, 66% white/28% black/3% Hispanic, BMI 30, 46% never smoker, 38% nondrinker/26% moderate drinker/10% heavy drinker, 21% CVD at baseline, eGFR 67, LDL 108/HDL 53/triglycerides 100, number of antihypertensive meds at the 27 month visit = 2.9 with 78% on ACE-I/ARB, 60% on calcium-blocker, 76% diuretics, 40% beta-blocker
— at the 27 month clinic visit:
— clinic-based systolic 120 mmHg
— nighttime ABPM systolic 116 mmHg
— daytime ABPM systolic 127 mmHg
— 24-hour ABPM systolic 123 mmHg
Results:
— for those on intensive therapy:
— decreased clinic-based systolic BP by 16.0 mmHg
— decreased nighttime systolic BP by 9.6 mmHg
— decreased daytime systolic BP by 12.3 mmHg
— decreased 24 hour systolic BP by 11.2 mmHg
–there was poor agreement in participants between clinic-based systolic BP and daytime systolic ABPM
Commentary:
— the role of ABPM continues to evolve, with studies documenting its strong association with cardiovascular and renal clinical events. Data for the last decade or so have pretty convincingly shown that ambulatory blood pressure is more predictive of cardiovascular events than clinic-based blood pressure, leading ultimately to the USPSTF promoting ABPM in their most recent guidelines (see https://www.uspreventiveservicestaskforce.org/Page/Document/RecommendationStatementFinal/high-blood-pressure-in-adults-screening , and my blog on it )
— One issue with the SPRINT study has been the rather eclectic way they measured the clinic-based blood pressure, reducing its generalizability to our clinical practice (see here which comments on their approach). One advantage of ABPM is that it is an equalizer, where the target blood pressure is pretty reproducible from one ambulatory monitor to another, and does not depend on measuring blood pressure in a clinic setting based on a very structured and likely unreproducible methodology (even without the strict regimen in SPRINT, how many of us check blood pressures after the patient has been resting quietly in a dark room for 5 minutes??)
— Unfortunately, there are relatively limited data on ambulatory blood pressure monitoring as a means to follow up patients with hypertension on treatment. There are some studies which do suggest that it is useful: a Brazilian study (see Salles GF. AchInternMed.2008;168:2340), which looked prospectively at 556 patients with resistant hypertension for 4.8 years, found that ambulatory blood pressure monitoring predicted clinical endpoints, and that clinic-based blood pressure did not. And in fact 40% of those with clinic-based “resistant hypertension” did not even have hypertension on ABPM (adding to the studies finding that even “appropriately” documented clinic-based blood pressure is really a poor predictor, and sometimes pretty irrelevant, especially as compared to ABPM: see here for an array of blogs on this, including the quite impressively documented and prescient recommendations from NICE in the UK in their 2011 guidelines
So, this study adds further to the imperative to use ABPM, especially in those patients with blood pressures near the goal (ie, the patient with 200/110 mmHg can just be treated….). And, though much less well documented (but easier for many) to use home-based measurements. This study helps reinforce the utility of ABPM in those being treated (again, I would assume, especially so if the achieved blood pressure is pretty close to goal: eg the Brazilian study above on refractory hypertension finding no benefit for clinic-based blood pressures did not have granular data, but I would assume that those way above goal continued to need adjustment of their meds independent of the ABPM reading, and those near goal were more likely to be in-range with ABPM even though the clinic-based pressures were high.
And, again, this study does raise a pretty basic concern: how often do our accepted clinical approaches (in this case clinic-based blood pressures) not really reflect the reality of actual clinical outcomes, yet are passed down over time and accepted? Which all reinforces the importance of constantly challenging our existing models. Another example which I have commented on recently is with A1c as a surrogate marker for diabetes and macrovascular complications, suggesting that the issue may be less with the A1c achieved than with the medications we choose to put patients on, and it is probably most important to choose ones that have documented cardioprotection (see here )