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President's Message

Contributed by M. Mohsen Ibrahim, MD
Tuesday, 03 May 2016

President's Message

In Search for a Hypertension Threshold

Diagnosis of hypertension depends upon accurate and repeated blood pressure measurements, when exceeding a specific number; the individual is labeled as being hypertensive. The diagnosis is complicated by three factors: (1) the diagnostic accuracy of the measuring technique, (2) blood pressure variability, (3) disagreement on the diagnostic threshold.

1- Measuring Techniques

At present there are four different approaches to diagnose high blood pressure. A. Casual office or clinic blood pressure measurement (OBPM), B. Home blood pressure (HBPM). C. Ambulatory blood pressure monitoring (ABPM) and D. Automated office or sequential blood pressure measurement technique (AOBP).

a. OBPM has been the standard diagnostic procedure for many years. It is familiar to health personnel, readily available and not expensive. The procedure, however, is limited by blood pressure variability, necessitating frequent office visit to establish the diagnosis, the white coat effect, its failure to predict target organ damage (TOD) or cardiovascular events. Furthermore, it is subject to many sources of errors. Blood pressure measurements taken by health professionals in daily practice are higher than blood pressure measurements taken by well-trained observers within the framework of scientific studies and for research purposes.

Systolic blood pressure was higher when measured by a doctor (151 mmHg) than by a nurse (142 mmHg). Blood pressure recordings by the patient's own family physician during routine office visits were 18/10 and 20/12 mmHg higher than the corresponding mean awake ABPM and AOBP readings.

b. HBPM where measurements are taken by the individual himself or a family member. Blood pressure should be measured at least twice daily morning and evening for seven days and the average of the last six days is taken as the home readings. HBPM correlates with TOD, not expensive, avoids the white coat effect and can ensure a better patient compliance with drug therapy and lifestyle change. The diagnostic threshold of hypertension in HBPM is 135/85 mmHg. ABPM needs the purchase of equipment, its calibration, training of the individual, it may generate anxiety with obsession of unnecessary frequent measurements and may invite patient to change or to stop his mediations. It is recommended that HBPM should supplement and not to replace OBPM.

It has been found that treatment decisions based on clinic or home blood pressure alone might result in substantial over-diagnosis.

c. ABPM is recommended by many guidelines as the golden standard for high blood pressure diagnosis. It provides the definite diagnosis since it predicts TOD and future cardiovascular events. It can diagnose white coat and masked hypertension. Measurements are taken for the 24 hours, or only during daytime.

The technique is limited by its cost, inconvenience to the patient, not available in many clinics and not being suitable for follow-up and repeated measurements. The diagnostic hypertension threshold for daytime (awake) ABPM is 135/85 mmHg, for 24 hrs ABPM is 130/80 mmHg and for nocturnal (sleep) BP is 125/75 mmHg.

In PAMELA study done in Italy over a large number of individuals followed for years, comparison of ambulatory, home and clinic BP was made. In PAMELA, a daytime mean ABPM of 135 ± 14 mmHg corresponded to a mean clinic systolic pressure of 155 ± 22 mmHg.

d. AOBP is a relatively new technique that has been recently introduced in some guidelines. It uses a fully automated, validated electronic sphygmomanometer. The device takes multiple readings without requiring activation by the patient or health professional, usually 5 or more blood pressure readings are taken at 1-2 minutes intervals.

Patient should be resting in a quiet place without possibility of conversation. Mean AOBP values are comparable to awake ABPM and home BP values. Blood pressure levels are linked with TOD. It is more consistent during repeated office visits and similar both within and outside the physician's office. It eliminates office induced hypertension and is associated with less masked hypertension. Canadian hypertension education program (CHEP) has accepted an AOBP of 135/85 mmHg as the cut off for separating normal AOBP from hypertension. The ESH/ESC guidelines stated that "when feasible AOBP should be considered as the preferred electronics sphygmomanometer. The major limitations of AOBP are the cost (600-1000 USD) and the need for a separate examination room.

2- Blood Pressure Variability

Exaggerated blood pressure variability confounds the diagnosis of hypertension. In addition to diurnal (Circadian) variations, blood pressure can change within seconds to days as a result of anxiety (emotions), white coat, distended bladder, smoking, hypoglycemia, cold weather, pain, salt intake and medications. During panic attacks which are associated with severe anxiety blood pressure can reach very high levels and then decreases to within minutes to the normal range after subsidence of the panic attack.

Blood pressure checked weekly and monthly during repeated clinic visits showed a significant fall after just one week during the second clinic visit. Blood pressure continues to decrease on following visits to reach its lowest level after four weeks then to a plateau with little change after 4-6 weeks.

The mechanism underlying increased blood pressure variability include autonomic nervous system dysfunction namely sympathetic activation, vascular endothelial dysfunction, arterial wall stiffness and blood volume changes. Enhanced blood pressure variability independently contributes to TOD and cardiovascular complications of hypertension. However, many guidelines did not pay enough considerations to blood pressure variability. The European (ESH) guidelines stated that "hypertension should not be diagnosed on the basis of episodic rises in blood pressure, unless mean blood pressure is raised. Patients with variable clinic blood pressure should be assessed by 24hrs ABMP or self-measured at home or both (ESC/ESH 2007).

Large blood pressure variability is common in the elderly, suggesting the role of reduced compliance of large elastic arteries due to advanced atherosclerosis.

Averaging of repeated blood pressure measurement may help in reaching a blood pressure threshold. Repeated measurements are best obtained by an automated office blood pressure sequential measurements (AOBP) or through ABPM.

3- Diagnostic Threshold

Cardiovascular risk progressively increases with rising blood pressure levels starting from 115/75 mmHg. To define a hypertension diagnostic threshold at this level is not realistic and never reported in guidelines. The choice of a diagnostic threshold was based upon the blood pressure level at which benefits of drug therapy outweighed their adverse effects or the risks of hypertension exceed drugs adverse effects. The old diagnostic threshold recommended by WHO and old guidelines was 160/100 mmHg which changed to 140/90 mmHg. This threshold is accepted by the majority of guidelines these days.

The choice of 140/90 mmHg office readings was based upon consensus and expert opinion. An office blood pressure of 140/90 mmHg is equated to a mean home blood pressure or mean awake ABPM of 135/85 mmHg.

This relationship has been based on blood pressure readings carefully recorded in accordance with guidelines for proper blood pressure measurement (research quality office blood pressure readings) and may not reflect the blood pressure obtained by doctors, nurses and other health professionals in realistic office practice. Levels of 150/95 mmHg taken in routine practice correspond to 140/90 mmHg taken in research circumstances. Other factors besides the precision and accuracy of blood pressure measurements should be considered when trying to define a hypertension diagnostic threshold. These include the age, gender and the global cardiovascular risk profile. The recent British and American guidelines defined a higher diagnostic threshold of 150 mmHg systolic blood pressure for elderly subjects.

Reassessment of Framingham data has found that the levels at which systolic blood pressure is related to increases in all cause and cardiovascular disease mortality vary with age and sex. A substantial proportion of the populations with a systolic BP ≥ 140 mmHg are therefore at no increased risk. What complicates matters even further, is the fact that while a level of > 140/90 mmHg may be abnormal for one individual, may be acceptable for another but with different CV risk profile.

In a recent review meta-analysis of patients with mild hypertension (systolic blood pressure 140-159 mmHg and/or diastolic blood pressure 90-99 mmHg) and without cardiovascular disease, the effect of antihypertensive drug therapy or mortality and morbidity was examined. This review does not show any significant benefit of antihypertensive drug therapy in reducing mortality, heart attacks, strokes, or overall cardiovascular events.

Conclusion

It seems that the diagnostic threshold of hypertension is a moving target and not a single number but a range of measurements. For low risk individuals the threshold can be 150/95 mmHg while for high risk individuals it is 140/90 mmHg. The diagnostic threshold of hypertension is by no means the therapeutic target or threshold. Initiation of pharmacologic therapy depends not only on number, but also on the presence of risk factors, TOD and blood pressure response to lifestyle modifications.


President of the EHS

M. Mohsen Ibrahim, MD

Prof. of Cardiology- Cairo University

References & Suggested Readings

1- Rothwell PM. Limitations of the usual blood-pressure hypothesis and importance of variability, instability, and episodic hypertension. Lancet. 2010 Mar 13;375(9718):938-48

2- Hodgkinson J, Mant J, Martin U,Guo B, Hobbs F D R, Deeks J J et al. Relative effectiveness of clinic and home blood pressure monitoring compared with ambulatory blood pressure monitoring in diagnosis of hypertension: systematic review. BMJ 2011; 342 :d3621

3- Martin G Myers, Marshall Godwin, Martin Dawes, Alexander Kiss,Sheldon W Tobe, Janusz Kaczorowski. Measurement of blood pressure in the office: recognizing the problem and proposing the solution. Hypertension 2010 Feb 28;55(2):195-200.

4- Brueren MM, Petri H, van Weel C, van Ree JW. How many measurements are necessary in diagnosing mild to moderate hypertension? Fam Pract. 1997 Apr;14(2):130-5.

5- Parati G, Omboni S, Bilo G. Why Is Out-of-Office Blood Pressure Measurement Needed? Hypertension. 2009 Aug;54(2):181-7.

6- Parati G, Stergiou GS, Asmar R, Bilo G, de Leeuw P, Imai Y, Kario K, Lurbe E, Manolis A, Mengden T,O'Brien E, Ohkubo T, Padfield P, Palatini P, Pickering TG, Redon J, Revera M, Ruilope LM, Shennan A,Staessen JA, Tisler A, Waeber B, Zanchetti A, Mancia G; ESH Working Group on Blood Pressure Monitoring. European Society of Hypertension practice guidelines for home blood pressure monitoring. J Hum Hypertens. 2010 Dec;24(12):779-85.

7- Ogedegbe G, Pickering TG, Clemow L, et al. The Misdiagnosis of Hypertension: The Role of Patient Anxiety. Arch Intern Med.2008;168(22):2459-2465.

8- Lichtenstein MJ1, Steele MA, Hoehn TP, Bulpitt CJ, Coles EC. Visit frequency for essential hypertension: observed associations. J Fam Pract. 1989 Jun;28(6):667-72.

9- Sechrest L. Validity of Measures Is No Simple Matter. Health Services Research. 2005;40(5 Pt 2):1584-1604.

10- Head Geoffrey A, Mihailidou Anastasia S, Duggan Karen A, Beilin Lawrence J, Berry Narelle, Brown Mark A et al. Definition of ambulatory blood pressure targets for diagnosis and treatment of hypertension in relation to clinic blood pressure: prospective cohort study. BMJ 2010; 340 :c1104

11- Myers MG1, Kaczorowski J, Dawes M, Godwin M. Automated office blood pressure measurement in primary care. Can Fam Physician. 2014 Feb;60(2):127-32.

12- Brown Morris J, Cruickshank J Kennedy, MacDonald Thomas M. Navigating the shoals in hypertension: discovery and guidance. BMJ 2012; 344:d8218

13- Myers MG1, Valdivieso M, Kiss A. Use of automated office blood pressure measurement to reduce the white coat response. J Hypertens. 2009 Feb;27(2):280-6

14- Myers MG. The great myth of office blood pressure measurement. J Hypertens. 2012 Oct;30(10):1894-8.

15- Myers MG, Godwin M, Dawes M, Kiss A, Tobe SW, Kaczorowski J. Measurement of blood pressure in the office: recognizing the problem and proposing the solution. Hypertension. 2010 Feb;55(2):195-200.

16- Krause Taryn, Lovibond Kate,Caulfield Mark, McCormackTerry, Williams Bryan.Management of hypertension: summary of NICE guidance. BMJ 2011; 343 :d4891.

17- Pater C. Beyond the Evidence of the New Hypertension Guidelines. Blood pressure measurement – is it good enough for accurate diagnosis of hypertension? Time might be in, for a paradigm shift (I). Current Controlled Trials in Cardiovascular Medicine. 2005;6(1):6.

18- Diao D, Wright JM, Cundiff DK, Gueyffier F. Pharmacotherapy for mild hypertension. Cochrane Database Syst Rev. 2012 Aug 15;8:CD006742.

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Last Updated Tuesday, 03 May 2016