Authors (including presenting author) :
Lo L(1), Hung WS(1), Chan SW(1), Fung HT(1), Chan PF(1), Chao DVK(1)
Affiliation :
(1)Department of Family Medicine and Primary Health Care, United Christian Hospital
Introduction :
International researches, mostly European and Japanese studies, suggest that patients whose blood pressure does not drop normally at night are associated with a higher risk of stroke, heart disease and cardiovascular death. Whether this association applies to patients of Chinese ethnicity remains untested.
Objectives :
This study aims to investigate whether an abnormal nocturnal blood pressure drop results in increased cardiovascular morbidity and mortality in Chinese patients. It investigates a cohort of 1100 patients from five general out-patient clinics in Kowloon East Cluster. This interim report reveals the initial results of one pilot clinic.
Methodology :
This interim report reviews retrospectively a cohort of 304 patients who underwent 24-hour ambulatory blood pressure monitoring (ABPM) in RAMP HT Clinics in year 2012-2014, and follows their cardiovascular outcomes after a median of 6.1 years. Patients with secondary hypertension, OSAS or LUTS are excluded. Patients are segregated into the four nocturnal blood pressure dipping patterns according to their night-day BP ratio, calculated as [night-time BP / daytime BP]: Extreme dippers [=0.00]. Subsequent cardiovascular events including acute myocardial infarction, acute cerebral vascular accident, congestive heart failure, transient ischaemic attack, re-vascularisation, CV-related hospitalisation, peripheral vascular disease, progressive renal failure, new diagnosis of IHD / AF, cardiovascular mortalities and total mortalities are traced. Survival analysis of the four BP dipping patterns are presented in Kaplan–Meier curves, and compared for statistically significant difference between curves. The night-day BP ratio of individual patients is analysed by a multivariate Cox proportional hazard regression model, with adjustment of confounding variables including gender, age, smoking status, pre-existing coronary heart disease / cerebral vascular disease, diabetes mellitus, hyperlipidaemia, chronic kidney disease (eGFR < 60 mL/min/1.73m2), obesity, and anti-hypertensive treatment.
Result & Outcome :
Of the 270 patients analysed, 5.9% (n=16) were extreme dippers, 38.1% (n=103) normal dippers, 39.3% (n=106) non-dippers, and 16.7% (n=45) reverse dippers. A total of 19 cardiovascular events and 10 non-CV mortalities were reported. Pairwise log rank statistics showed that the 4 dipping patterns did not demonstrate statistically different survival from total cardiovascular events on a Kaplan-Meier plot. For total cardiovascular events, the Cox regression model did not reveal difference in hazards between the 4 dipping patterns. And all co-variates did not reach statistical significance though pre-existing CVD (p=0.089) and mean 24-hr SBP (p=0.072) were the more probable independent factors. For total mortality, the 4 dipping patterns and all co-variates did not show statistical significance. Smoking (p=0.081) was the most important independent factor in the Cox regression analysis. Conclusions: In a limited sample of Chinese hypertensive patients, abnormal nocturnal blood pressure dipping is not associated with adverse cardiovascular outcome. This is contradictory to current international meta-analyses. Further analysis on a larger cohort of Chinese patients is indispensable.
