Is a unified blood pressure threshold feasible in the current scenario?

There was a time when decision-making about hypertension was simple. The only apparatus available was the mercury sphygmomanometer and the blood pressure (BP) readings were taken in the office. The decisions about diagnosis and treatment targets were based on the office blood pressure (OBP) with the mercury sphygmomanometer. Even when the aneroid and hybrid BP apparatuses came into the market, these were calibrated against the mercury apparatus and the readings were the same for diagnosis and treatment targets. However, things changed when the ambulatory blood pressure (ABP) monitor became available and it was found that its readings differed from the OBP readings. Later on, home blood pressure (HBP) monitor was also introduced and its BP readings were also found to be different from OBP measurements. Lately, the introduction of the automated office blood pressure (AOBP) has added another dimension. In the present issue of this journal, an article titled “130/80 mmHg as a unifying hypertension threshold for office brachial, office central and ambulatory daytime brachial BP” has tried to resolve this issue. In this study, 1219 subjects with or without hypertension, but not on treatment, and with no history of cerebrovascular or cardiovascular disease were included and followed up prospectively over a 25 year period. OBP, office central BP and ABP were measured at the start. The threshold of 130/80 mmHg was defined retrospectively (as the cut off for hypertension diagnosis was 160/90 mmHg in 1992–1993) and outcome data was obtained from the Taiwanese National Health Insurance dataset and the National Death Registry. 72.8% of subjects were hypertensive by OBP, 59.6% by office central BP and 49.1% by daytime ABP. The authors claim that hazard ratios were similar for mortality and cardiovascular events for the three groups and so were the survival curves. Their conclusion is that office brachial hypertension, office central hypertension, and ambulatory daytime brachial hypertension defined by a unifying threshold of 130/80 mmHg may provide similar estimates of long-term risk for cardiovascular events but with differential precisions and cross-classification analyses suggest that adding office central hypertension or ambulatory daytime brachial hypertension may improve the prognostic value of office brachial hypertension. The limitations of the study as mentioned by the authors were that it included only one ethnicity (Han Chinese), did not ascertain the hypertension and treatment status of those subjects who were not put on treatment at the start but were subsequently put on treatment at some stage when either the new lower BP cut offs were introduced or their BP increased with age. Furthermore, the hypertension threshold of 130/80 was solely according to future cardiovascular risk and they were not able to assess whether BP lowering therapy based on the threshold could show the proven benefits. One problem with this study is that the OBP of 130/80 mmHg was defined retrospectively and thus arbitrarily. In their discussion it is stated that, “Specifically, concordant office central and office brachial hypertension identified a truly high-risk group, and office brachial hypertension alone might not be significantly associated with risk when combined with office central BP < 130/80 mmHg. Similarly, concordant ambulatory daytime brachial and office brachial hypertension might also identify a truly high-risk group, and office brachial hypertension alone might not be significantly associated with risk when combined with ambulatory daytime brachial BP < 130/80 mmHg.” This is borne out by a closer look at the survival curves in Figure 3 which clearly show that raised OBP alone has considerably less effect on survival than when combined with either raised office central BP or high daytime ABP. In this scenario, what is the role of isolated OBP > 130/80 mmHg? This is further highlighted by Supplemental Figure S1 in which Sensitivity, Specificity and Concordance for cardiovascular events for different combinations of cut-points for office brachial systolic and diastolic BP are graphically represented. Office brachial hypertension defined at 130/80 mmHg had a high sensitivity of 84.2%, low specificity of 32.1% and intermediate concordance of 47.8%. Comparative values for office brachial hypertension defined at 135/85 mmHg were 71.5%, 52.5% and 58.2% respectively. If OBP of 130/80 mmHg is the sole criterion for diagnosis and treatment, it would lead to a large number of people being treated for little or no benefit. In a consensus document on the management of hypertension in Asia from the HOPE Asia Network,1 the authors equate OBP of 130/80 mmHg to both HBP and daytime ABP of 130/80 mmHg. The article describes in detail the methodology for HBPM and ABPM but there is no mention of the methodology used for OBP. Their stress is on using HBPM and ABPM as they state, “HBPM is a better predictor of cardiovascular outcome than office BP. When there is a discrepancy of diagnosis between office and home BP, a home BP-based diagnosis should have priority and, when possible, be confirmed by ABP monitoring (ABPM)”. Another paper titled, “Could 130/80 mmHg be adopted as the diagnostic threshold and management goal of hypertension in consideration of the characteristics of Asian populations?”2 discusses the practical feasibility of the 2017 AHA/ACC guidelines3 for the management of hypertension for achieving a goal of zero cardiovascular events in Asia. It states that the shift of BP threshold to 130/80 mmHg will increase the number of patients with hypertension or uncontrolled hypertension to about 50% of all Asian adults and because of the stronger BP-dependent characteristics of cardiovascular disease in Asians compared to Westerners, the earlier treatment of hypertension will do much more to reduce the cumulative risk burden than the previous threshold of 140/90 mmHg. The authors have specifically focused on the morning home BP- guided approach as the most effective strategy and OBP, although equated with HBP, is not mentioned as it cannot determine the exaggerated morning surge in BP which may be more prevalent in Asian people. How do the various international guidelines deal with this unifying hypothesis? The 2017 AHA/ACC guidelines accepts the errors in OBP and the ‘growing evidence base supporting the use of AOBP’ but without committing to it. It also states that there is general agreement that OBP readings are often higher than HBP and ABP ones especially at higher BPs but defines hypertension by 130/80 mmHg for all three methods that is, OBP, HBP and daytime ABP. However, it recommends HBP or ABP for all adults with systolic BP 130–160 mmHg and diastolic BP 80–100 mmHg before diagnosis (Class IIa recommendation).3 The 2022 Guidelines of the Taiwan Society of Cardiology and the Taiwan Hypertension Society for the Management of Hypertension is similar to the American guidelines in defining hypertension at 130/80 mmHg for OBP, HBP and daytime ABP. However, it says that routine OBP should not be used for the diagnosis and management of hypertension unless standardized BP measurement protocol is followed and adds that this is generally not applicable in busy clinics. Thus, HBPM is recommended as the foundation for the diagnosis and grading of hypertension and also for the treatment thresholds and targets.4 The Hypertension Canada Guidelines give definite preference to AOBP and define hypertension at 135/85 mmHg for mean AOBP, HBP or awake ABP readings but 140/90 mmHg for mean OBP readings.5 The 2018 ESC/ESH Guidelines6 for the management of arterial hypertension gives similar definitions for hypertension for the various methods as the Canadian guidelines but mention OBP only and not AOBP. The 2019 NICE guidelines7 of hypertension from UK recommend that if clinic BP is between 140/90 mmHg and 180/120 mmHg, offer ABPM to confirm the diagnosis of hypertension and if ABPM is unsuitable, offer home blood pressure monitoring (HBPM) to confirm the diagnosis of hypertension. It also has the same cut offs for the various methods defining hypertension as the Canadian guidelines.5 The 2019 Japanese Society of Hypertension Guidelines8 for the management of Hypertension also define hypertension by OBP, HBP and daytime ABP values as the Canadian guidelines.5 It is appreciable that efforts are being made to have a single BP reading for the diagnosis of hypertension for the various methods used as it simplifies diagnosis and reduces chances of confusion. However, for this to be truly applicable, any one of the methods mentioned should be enough to make a definitive diagnosis in isolation and have similar cardiac end points. Neither the article published in this issue nor the two guidelines (American and Taiwanese) which equate OBP with HBP and daytime ABP readings and define hypertension at 130/80 mmHg achieve this. The article has been discussed above while both the guidelines do not recommend just OBP for diagnosis but need additional HBP or ABP for diagnosis. This is not surprising considering the variations in OBP due to device problems, methodological errors and especially the white coat phenomena.9 In a recent systematic review and meta-analysis of 31 articles comprising 9279 participants, systolic BP readings from routine OBP and systolic BP readings from research office BP measurement (standardized office BP) were substantially higher than systolic BP readings from AOBP, with pooled mean differences of 14.5 mmHg (p < .001) and 7.0 mmHg (p < .001), respectively.10 In the presence of marked variability in OBP readings, it is a futile exercise to try and equate it with HBP and awake/daytime ABP readings, which are a mean of multiple readings and also diagnose white coat hypertension.3-9 The unifying hypothesis will only be successful if firstly, there is a consensus on an OBP methodology which is prone to less variation and white coat effect and secondly, there are comparative cardiac end point and clinical outcome studies of this method versus HBP and ABP. None. The author declares no conflict of interest.

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