Night-time BP variability improves vascular risk prediction

Jul 15 2014

By Eleanor McDermid, Senior medwireNews Reporter

Measuring night-time variability in the blood pressure (BP) of patients with hypertension may help to predict their risk of having a cardiovascular (CV) event, show data from an international study.

Adding night-time BP variability (BPV) to predictive models significantly improved their discriminatory ability, suggesting that night-time BPV “may be a clinically useful tool”, say lead researcher Paolo Palatini (University of Padova, Italy) and colleagues.

The team studied 7112 participants of the Ambulatory Blood Pressure in Referred Hypertensive Subjects: an International Database Study. They were aged an average of 51 years and were not taking antihypertensive medications, but their office BP was at or above 140/90 mmHg. During a median follow-up of 5.5 years, these participants had 130 fatal and 455 nonfatal CV events.

Increasing night-time systolic and diastolic BPV, defined as the standard deviation (SD) of patients’ BP during overnight ambulatory monitoring, was significantly associated with CV events, CV mortality and total mortality, even after accounting for patients’ average ambulatory BP.

The risk increase associated with a 10 mmHg rise in the SD of BP ranged from 1.48-fold for the effect of systolic BPV on CV events to 3.34-fold for the effect of diastolic BPV on CV mortality. The associations were independent of age, gender, total cholesterol and serum creatinine levels, average ambulatory blood pressure, smoking and diabetes mellitus.

By contrast, daytime BPV did not predict CV outcomes, except for a weak association between diastolic BPV and CV mortality.

The researchers say this is not surprising, “given the fact that [a] patient’s nocturnal BPV may be more reproducibly representative of [a] patient’s true BPV.” They point out that daytime BPV is influenced by physical activity and stressful situations, whereas factors such as sleep apnoea may contribute to high night-time BPV.

When added to predictive models, night-time BPV as either a categorical or continuous variable significantly improved both the net reclassification index and the integrated discrimination improvement.

The team found that night-time BP SD cutoffs of 12.2 mmHg for systolic BP and 7.9 mmHg for diastolic BP best predicted which patients would have a CV event. Being above rather than below these cutoffs was associated with risk increases ranging from 41% to 132%.

This “underscores the potential clinical use of short-term BPV for risk evaluation as a simple binary measure”, write Palatini et al in Hypertension. “Whether selective reduction of BPV in hypertension could potentially improve patient outcomes should be tested in prospective randomized clinical trials.”

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