Is ‘time at target' a useful concept for controlling blood pressure?

The concept of “time in range” has been used in warfarin monitoring and glycemic management for diabetic patients, but it hasn’t quite caught on as a useful metric in hypertension control.

But a study published Sept. 5 in PLOS One suggests the proportion of time patients spend at ideal blood pressure (BP) levels is significantly predictive of adverse cardiovascular events, making it worthwhile to explore ways to increase that percentage.

Sheng-Chia Chung, PhD, with the University of College London, and colleagues studied nearly 170,000 patients with newly identified high BP who were free of cardiovascular disease at baseline. High BP was defined as above 140/90 mm Hg, and patients were treated to below that threshold unless they were in their 60s or older, in which case a 150/90 mm Hg target was used.

Using all available measurements—an average of 1.6 per year per patient—Chung et al. estimated the proportion of each year patients spent below those predefined BP thresholds. When the BP control status changed between two measurements, the authors explained, they assumed a linear increase or decrease, allowing them to estimate the amount of days each person spent inside or outside of the ideal range.

Notably, only 0.6 percent of patients achieved a time at target (TITRE) above 11 months per year. The median TITRE among all patients was 2.8 months.

But for those achieving a TITRE of even three to six months, the risk of cardiovascular death, myocardial infarction and stroke was cut by 75 percent compared to those who remained outside the target range for the duration of the study. It was dropped an additional three percent for those who had a TITRE of six to nine months.

Likewise, the odds of heart failure were reduced by 63 percent for those who managed to control their blood pressure for three to six months per year.

“The gradient of risk of cardiovascular diseases across different TITRE categories demonstrates not only its capability to better quantify the attributable risk to differences in longitudinal BP management, but also its potential to better characterize the benefits of BP-lowering interventions in reducing cardiovascular risk and mortality,” the authors wrote.

Chung et al. said the average of 1.6 BP measurements per patient per year may not be ideal, but it is reflective of current clinical practice. Also, even those infrequent measurements allowed for a prognostically relevant estimation of TITRE.

“Despite hypertension being a chronic condition, current clinical convention is to assess BP ‘control’ at a one-off time point, and guidelines do not make recommendations of the frequency of measurement, how repeated measures might be used, nor evaluating longitudinal control,” Chung and colleagues wrote. “These findings suggest the need for more frequent measurement of BP in usual care and further research to understand how it may inform better blood pressure control.”

Another problem with evaluating BP measures as singular events, the researchers said, is patients who have one sufficient reading might be prematurely taken off their medications. This study demonstrates many individuals are likely to vacillate between a target and an above-target range.