Attended Versus Unattended Blood Pressure Measurement In Patients With Cardiovascular Disease: Does It Matter?

Introduction: Nearly one half of the subjects in SPRINT had their blood pressure (BP) measured absent an observer (unattended), whereas most prior trials have used attended measurement. This has created controversy in interpreting the relationship between achieved systolic BP (SBP) and outcomes in SPRINT. Accordingly, we prospectively examined the difference between attended and unattended office SBP measured using the same automated device used in SPRINT among patients with documented CV disease. Methods: We randomized patients attending a routinely scheduled cardiology clinic visit to have their BP measured using an attended, followed by an unattended method, or vice versa, after a controlled rest period. All study BP measurements were obtained in triplicate using the automated Omron HEM-907XL BP monitor, and averaged. The outcome of interest was the difference in SBP between the two measurement techniques. At the same visit, we obtained a routinely measured office BP from the medical record, and compared with attended and unattended measurements. Results: A total of 102 patients were enrolled, mean age was 63 years, 48% (49 of 102) men and 75% (76 of 102) were Caucasian. The mean attended and unattended SBP was 125.4 ± 20.4 and 122.6 ± 21.0 mm Hg, respectively. The mean SBP recorded by the clinic nursing staff was 130.6 ± 23.6 mm Hg. On average, the attended SBP was 2.7 mmHg higher than the unattended measurement (P=0.0002, 95% CI 1.3 to 4.1). The clinic staff SBP measurement was 5.2 mmHg higher than the attended SBP (P=0.0003, 95% CI 2.4 to 8.0) and 8.0 mmHg higher than the unattended SBP (P<0.0001, 95% CI 5.4 to 10.5). Conclusion: Among CVD patients being evaluated in a cardiology clinic, there is only a small (~3 mmHg) but statistically significant difference between attended and unattended automated SBP. More importantly, the routine office measured SBP was significantly higher than either the attended or unattended SBP. Our findings suggest that observing the BP measurement in patients with established CVD affects the BP, but much less than previously suggested. Factors such as measurement timing and non-standardized measurement technique are likely to have a larger impact on BP measurement than observer attendance.