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A clinical classification of hypertension

WANG, Mou-yue; LIU, Huan

Editor(s): George, Thomas

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Hypertension is a common cardiovascular problem worldwide. As with any other disease it is important to assess the severity of the disease. However the present classification of hypertension by the Joint National Committee in its seventh report (JNC 7) with numerical values staging the severity of hypertension is theoretically correct but difficult to apply in practice (Table 1).1 Admittedly this is a step in the right direction with lesser number of stages compared to the sixth report.2 The World Health Organization- International Society of Hypertension (WHO-ISH)-1999 3and the European Society of Hypertension - European Society of Cardiology (ESH-ESC)4 guidelines follow similar numerical classifications (Table 2). All these papers are referred to as ‘guidelines’ in this article.

Table 1
Table 1:
JNC-7 classification of hypertension
Table 2
Table 2:
ESH-ESC 2003 classification of hypertension

Blood pressure (BP) is a biological variable and so absolute values cannot be determined. There is a wide variability in the BP readings of the same individual. The guidelines agree to this. Again when we consider BP measurement, more often than not the guidelines cannot be strictly followed. For example, cuffs of prescribed size may not be available. There is a psychological tendency to round off BP readings to the nearest 10's. Being a continuous variable we cannot have precise cut-off points. So it is imprecise to have precise values to categorize a patient into a particular ‘stage’ or ‘grade’. As per the present classifications, would a BP of 160 /100 mmHg (all BP values in this article are in millimeters of mercury - mmHg) fall in stage 1 or 2 Considering the least count of the manometer to be 2 mmHg, a BP of 100 mmHg could mean a reading any where between 98 and 102 mmHg. Thus although accurate BP readings are desirable, it is difficult in practice. Ambulatory BP recordings are also fraught with problems and are difficult to fit into ‘stages’.5 Excellent discussions on the pitfalls in BP measurement are given elsewhere.6-8 The numerical ‘stages’ and ‘grades’ are conceptually correct but are difficult to apply in practice. These grading numbers form a formidable memory test. Thus it would be better if we relied less on numerical values as the sole criteria to classify hypertension. JNC-7 has unwittingly recognized this and reduced the number of stages.

Considering these problems in the present classifications, there is a need for an additional classification for hypertension. Response to treatment can be used as a classifying factor. Gersh et al9 have taken this approach. In their classification of unstable angina they have sub-classified unstable angina based on severity, clinical circumstances and intensity of treatment. The present classifications of hypertension do not consider the treatment outcomes that can give valuable insights.

Besides they do not incorporate the qualitative aspects of the disease and are not flexible enough to suit various categories of patients. Hence there is a need for a clinical classification of hypertension which can supplement the existing classifications.

CLASSIFICATION

The key to the clinical classification is the definition of ‘normal’ BP. The usual normal BP is defined as a BP of 120 mmHg systolic and 80 mmHg diastolic in adults. This is an arbitrary value taken from the existing classifications. The normal value could be different based on the clinical circumstance e.g. pediatrics, pregnancy and isolated systolic hypertension (vide infra). This should be an evidence-based value to be determined from time to time and situation to situation. Thus the only numerical variable in this classification is the ‘normal BP’ value. Hypertension is defined as any value above this. The principle of this classification is to find out the intensity of treatment required to bring down the BP to ‘normal’ levels. This ‘normal BP’ would mean the target BP when treating a case.

In this classification there is a category of ‘low normal’ where the BP is lower than the ‘normal’ BP in perfectly healthy individuals who require no treatment. ‘High normal’ can be controlled by life style modifications. This class will also include drug-induced hypertension, which can be controlled by stopping the offending drugs. Drugs causing hypertension include alcohol, oral contraceptives, steroids, liquorice, etc. It would be unreasonable to try lifestyle modifications in secondary hypertension. Such patients should be excluded from the ‘high normal’ category.‘Mild to moderate hypertension’ includes cases that require medications for control. Patients with cardiovascular risk factors like diabetes would also come in the ‘mild to moderate’ category. This is in agreement with the guidelines that recommend drug treatment for such patients. For convenience, this class can be arbitrarily sub-classified into ‘mild’ and ‘moderate’. ‘Mild hypertension’ can be controlled with one anti-hypertensive medication. This is consistent with the sequential drug monotherapy.10,11 ‘Moderate hypertension’ requires 2 or more anti-hypertensive drugs for control.

‘Severe hypertension’ includes cases where optimum therapy fails to achieve adequate BP control to reach target. This is after excluding all the factors of inadequate response to treatment as mentioned in the guidelines. Optimum therapy would strike a balance between therapeutic effect and side effects. Similarly patients with target organ damage, malignant hypertension and patients presenting with hypertensive emergencies and urgencies would come in this category.

USAGE

This classification can be used in different clinical situations like paediatric hypertension, isolated systolic hypertension, pregnancy hypertension etc. In all these cases the optimum BP for each group as suggested by the guidelines/evidence base should be taken as ‘normal’ or ‘target’ BP. This should be mentioned with the classification head. For example a hypothetical case with initial BP of 170/100 mmHg without risk factors or complications, controlled with one drug will be described as "mild hypertension controlled to a target of 110/70 mmHg" if the ‘normal BP’ is defined as 110/70 mmHg.

The advantages of this system are many. The classification provides an easy qualitative assessment of the disease. Sometimes the so-called stage 1 could be more resistant to treatment and the so-called stage 2 could be more easily controlled. This fact has been alluded to in the WHO-ISH 1999 guidelines, which states, "It is emphasized that the term mild hypertension does not imply a uniformly benign prognosis". The possibility of a ‘dual response’ to known and unknown stressors needs to be evaluated. The initial response of the vascular bed could be ‘reactive’ with reversible changes and the later response could be structural and irreversible. 12,13 During the reversible stage hypertension could be easily controlled irrespective of the numerical value of BP whereas in the latter stages it could become more difficult to control. More importantly, it will make the physician control the BP adequately at the same time avoid unnecessary treatment.

Another aspect of this classification is that stress is laid on the qualitative aspects of hypertension like hypertension causing drugs, risk factors and target organ damage. By following this classification it would become mandatory for the physician to look for these factors. The classification is very adaptive and universal. It can be used for various age/ethnic groups and disease states. It can be used in the case of pulse pressure too. The only requisite is that a ‘normal value’ or target BP for each situation is to be determined and specified. It is also future-proof. If for example, some future studies show that the optimum BP is 110/70 mmHg even then this classification will hold good. It will encourage more research into the subject. In contrast to the present guidelines, patients under treatment are ipso facto included in this classification. The classification will emphasize treatment for hypertension because it evolves in the course of treatment.

The critic may find a few drawbacks in this classification. However these drawbacks are similar to the drawbacks in the existing numerical classifications. For example we assume the equipotence of different drugs - a patient controlled with a thiazide will be equated with a patient controlled with a beta-blocker. This need not pose a serious problem as in the measurement of BP itself we assume the equivalence of every instrument and observer. Another problem that could be raised is that the dosage range is not considered. For example a patient with mild hypertension may be controlled with 12.5-50 milligrams of hydrochlorothiazide. But this is similar to the BP range of say 140/90 to 159/99 mmHg (stage 1, JNC). Here the class is more homogenous. Finally the demarcation between mild and moderate hypertension is a bit blurred. And the class under which the patient falls will depend on the treating physician's choice of drugs. This however is in no way different from the existing classifications in which the grade or stage in the gray areas will depend on the BP reading decided by the physician. When in doubt this group can be left as ‘mild to moderate’ without sub-classification. As a stand-alone classification it will take some time before the severity is assessed. This is similar to the present system where repeated readings over a period of time are required before the index level of BP is registered. The limits of ‘high normal’ are not stated. However it would be unreasonable to try lifestyle modifications alone for very high BP readings (say, a diastolic BP greater than 120 mmHg). The physician has to use his discretion in such cases. The highest level of BP which could be managed by lifestyle modifications could be determined by large scale clinical trials.

‘Normal’ values or target BP should be based on large-scale studies on hypertension in different clinical circumstances (like diabetes or ethnic groups). If there is a range of normal values this range can be taken for classification. For the present we can take the normal values from the guidelines. In this classification the group of patients inadequately controlled in spite of optimum treatment comes under the category of severe hypertension. However, inadequate control could be due to improper use of drug combinations. While every effort should be used to bring the BP under control, when in doubt, we can classify such patients as ‘moderately-severe’. Similarly low dose combinations are recommended for the so-called ‘mild’ hypertension.14 According to this classification they would automatically come in the ‘mild to moderate’ category.

This classification can be used in clinical practice by the following algorithm. Evidence based value for ‘normal BP’ or target BP is determined for the particular category of patients. BP readings are taken as recommended. If the value is greater than the ‘normal BP’ then the patient has hypertension. Look for target organ damage. If present, the category is ‘severe’. Similarly if the presenting symptom is hypertensive emergency or urgency then too the category is ‘severe’. If target organ damage or hypertensive emergency /urgency are absent, look for cardiovascular risk factors. If present, the category is ‘mild to moderate’. Institute drug treatment (see below) as per the guidelines. If no risk factors present, try life style modification. If successful, the category is ‘high normal’. If not successful, try one drug and titrate till maximum dose. If the BP is controlled to the target, then the category is ‘mild’. If not, add additional medications till control achieved or side effects occur. If the BP gets controlled the category is ‘moderate’. If not controlled then again the category is ‘severe’. When it is necessary to begin treatment with 2 drugs, the starting category will be ‘mild to moderate’.

CONCLUSION

Hypertension is a difficult disease for easy classification. However an assessment of the severity of the disease is important for proper management. This classification of hypertension is minimally dependant on the numerical values and is based on commonsense. Higher values may turn out to be more benign and lower values may need more powerful treatment regimes. Thus this classification will answer the following key questions. Does the patient have hypertension If so does he need medication Is it iatrogenic And does he have any complications of the disease As the classification less dependant on numerical values it provides a simple, practical and qualitative classification of hypertension. For a biological variable like hypertension precise numerical compartmentalization is difficult. What we need is a practical idea of the severity of the disease. This classification appears simple but satisfies this need.

REFERENCES

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Keywords:

hypertension; classification, clinical; treatment outcomes; qualitative aspects

© 2006 Chinese Medical Association