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Background: Ambulatory BP monitoring (ABPM) is used to identify white coat hypertension (WCH). Some individuals however have mean daytime BP >135/85 mmHg on ABPM despite office BP in normal range, so called “masked hypertension”.

Aim: To establish the proportion of older-people with masked hypertension and compare survival with normotensive and hypertensive participants.

Methods: 330 adults aged ≥65 years had office BP recorded after 10 minutes supine, rest and underwent 24 hour ABPM. Participants were classified into 4 groups; normotensive (Office BP <140/90 mmHg and mean daytime BP < 135/85 mmHg), WCH (Office BP > 140/90 and mean daytime BP < 135/85), masked hypertension (Office BP <140/90 and mean daytime BP>135/85) and persistent hypertension (Office BP >140/90 and mean daytime BP > 135/85). Participants were followed up for 10 years. GP records and death certificates were reviewed to identify patients who had died. Cox regression modelling was used to compare survival among groups.

Results: 300 participants had ≥10 daytime BP recordings and were included in the analysis. 32% were normotensive, 20% had WCH, 32% had persistent hypertension and 17% had masked hypertension. Kaplan Myers curves showed similar survival for the WCH and normotensive group. These participants were therefore combined together to form 1 group “ABPM normotension”

Cox regression analysis adjusting for age and sex showed borderline association between mortality and masked hypertension [HR 1.74 (95% CI 0.95, 3.17), 0.07] and persistent hypertension [HR 1.57 (95% 0.96, 2.57)] compared to the ABPM normotensive group.

After adjusting for, smoking status, diabetes, BMI and antihypertensive medication, masked hypertension showed a stronger relationship with ten year mortality than persistent hypertension [HR 1.85 (95% CI 1.01, 3.40), p= 0.05) and [HR1.62 (95% CI 0.98, 2.69), p = 0.06] respectively.

Conclusion: Office BP measurements may miss individuals with masked hypertension. Masked hypertension shows stronger associations with mortality than persistent hypertension possibly due to poorer BP control.

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