Similar BP readings, CV outcomes with attended, unattended BP measures in SPRINT
Blood pressure (BP) readings appeared to be similar regardless of whether BP measurements were attended or unattended by staff, nor were CV outcomes different between the two techniques, according to a post hoc survey on participants following the SPRINT* trial.
Results of the SPRINT trial ─ showing that intensive treatment to a systolic BP (SBP) target of <120 mm Hg reduced the risk of cardiovascular disease (CVD) and mortality compared with standard treatment to a target of <140 mm Hg ─ have sparked ongoing debate about whether BP measurement techniques in the study were generalizable to routine practice. [N Engl J Med 2015;doi:10.1056/NEJMoa1511939]
“Recent publications from investigators not involved with SPRINT have stated that the BP measurement technique used in SPRINT was unattended, making the BP not comparable to other studies,” said Dr Karen Johnson of University of Tennessee Health Science Center, Memphis, Tennessee, US.
To address this concern, a survey was conducted immediately after SPRINT closeout visits on whether BP measurements were taken with or without staff attendance across 98 sites. Participants were categorized into four groups based on BP measurement techniques: always alone (n=4,082), never alone (n=2,247), alone for rest (n=1,746), and alone for BP measurement (n=716). [AHA 2017, abstract LBS.03]
Participants in the always-alone group were left alone both during the 5 minutes of rest before first BP measurement and during the three BP readings. Those who were never alone had attending staff in the room during the entire process. Those who were alone for rest were left alone only during rest period, while those in the alone-for-BP-measurement group were alone only when BP readings were taken using an automated measurement device.
Regardless of whether the participants were always alone or never alone during BP measurements, those who were randomized to intensive treatment in SPRINT had similarly reduced risk for the composite primary outcome of myocardial infarction, acute coronary syndrome, heart failure, stroke, and death from CVD, compared with those randomized to standard treatment (hazard ratios, 0.62 and 0.64 for the always-alone and never-alone groups, respectively).
The risk of all-cause mortality was also reduced with intensive vs standard treatment in both the always-alone and never-alone groups (HRs, 0.65 and 0.76, respectively).
No significant differences for the composite primary outcome or all-cause mortality were observed between intensive vs standard treatments in the alone-only-for-BP-measurements or the alone-only-for-rest groups.
Overall, the mean SBP achieved with intensive treatment group was 120 mm Hg across all four BP technique groups compared with 135 mm Hg with standard treatment.
The rates of serious adverse events (SAE) including bradycardia, acute kidney injury, and electrolyte abnormality were comparable between intensive- and standard-treatment groups, regardless of stratification of BP techniques.
Results not a surprise
The similar primary and all-cause mortality outcomes across BP technique groups were not surprising, said invited discussant Dr Sripal Bangalore of New York University School of Medicine in New York, New York, US, seeing that “the HR depends on the BP difference between intensive and standard treatments, rather than on the absolute BP values that are the matter of debate.”
The similar mean SBP achieved across BP technique groups was also “not surprising since the protocol mandated achieving a BP target,” according to Bangalore. “To conclude that absolute systolic BP values will not change whether attended or not attended based on indirect comparison is counter to many direct studies showing clear difference.”
“More importantly, the absolute SAE rates in the intensive arm were largely similar … [which is] reassuring but could be confounded by misclassification bias,” he added.
Given that BP readings from manual auscultatory measurement do not equal automated office or ambulatory BP values, “it is not prudent to have the same BP target for different BP-measurement techniques,” he cautioned.
Nonetheless, Johnson drew attention to other issues in BP measurements.
“To fully realize the benefits and minimize [the] risks associated with following the SPRINT intensive treatment algorithm, use of a validated automated BP device, staff training to allow for a quiet rest period, proper positioning, use of proper cuff size, and averaging multiple measurements, may be more important than whether the BP measurement is attended or unattended,” she said.