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Dr. Michael Lim's Articles

Lowdown on high blood pressure

There is strong evidence that the lowering of blood pressure can prevent stroke and heart disease

Whenever the heart pumps, it generates a pressure in the arteries. The pressure rises to a peak, which is recorded as the upper blood pressure(BP) reading or systolic BP(SBP) and then falls to a nadir, which is recorded as the lower BP reading or diastolic BP (DBP), after which the pressure in the arteries rises again with the next pumping action of the heart.

The BP is considered to be abnormal or a state of high BP(hypertension) if the constant elevation of the BP beyond a certain level of BP can result in damage to vital organs such as the heart, brain and kidney.

When should blood pressure be treated?

In 2014, the Eighth Joint National Committee (JNC 8) released their guidelines for the management of high BP in adults which was published in the Journal of the American Medical Association.

These recommendations are widely followed by the medical community. The latest guidelines use the age of 60 years as a dividing point for the different “normal” desired levels of BP for these 2 different age bands.

Unlike past guidelines, the new recommendations for those 60 years or more is to keep the BP below 150/90 mm Hg in contrast to previous recommendations of 140/90 mm Hg. While there is strong evidence that lowering the BP to less than 150/90 mm Hg can reduce stroke and heart disease, there is no evidence that there will be incremental benefit by lowering the SBP to 140 or less for this age group.

As there was no consensus among the experts, it was agreed that if the SBP had already been lowered to less than 140 mm Hg, there is no necessity to readjust the medication if the patient is well.

The target BP level of less than 140/90 mm Hg or less is recommended for those less than 60 years of age without other major medical illness. This target is also recommended for those 60 years or more who have underling diabetes mellitus or chronic kidney disease. Hence, if these “normal” desired levels of BP are exceeded, treatment to bring the BP to these desired levels should be initiated.

Is SBP or the DBP more important?

There are at least 5 major BP lowering trials where those aged 30 to 69 years were given medication to lower the DBP to less than 90 mm Hg. The data from these major trials showed that there was a significant reduction in stroke, heart failure and overall death.

The data to demonstrate benefit for reduction of the SBP to less than 140 mm Hg was less compelling for those less than 60 years of age. Hence, for those less than 60 years of age, the elevation of DBP is a more important factor than elevated SBP. For those 60 years or older, the SBP is more important than DBP.

Is lower BP better?

It has been a common practice to lower the BP to below 130/80 mm Hg for those with high BP and diabetes mellitus or chronic kidney disease. In contrast to other guidelines, the latest JNC 8 guidelines on examining the currently available evidence were of the view that there is no incremental benefit to lower the BP to less than 130/80 mm Hg as compared to less than 140/90 mm Hg.

While lowering BP appears to be beneficial, epidemiological data shows that if the SBP and DBP are lowered excessively, there appears to be a J-curve effect in which the benefits seen with BP lowering are reversed resulting in increased adverse outcomes including heart attacks, stroke and deterioration of kidney function.

The rationale for this is that when the BP drops excessively, there will not be enough blood flow to provide adequate oxygenation to the vital organs resulting in impairment of function. In the INVEST (International Verapamil SR/T Trandolapril) trial, more than 22000 heart artery patients with high BP showed a reduction in stroke and heart attacks in those in whom the DBP was reduced to between 80 and 89 mm Hg, and showed a reversed trend, with progressive increase in stroke and heart attacks, in those whom the DBP values were less than 80 and less than 70 mm Hg.

Of the 6400 patients in the INVEST trial who also had diabetes mellitus, there was a major reduction in stroke and heart attack when the SBP was reduced from more than 140 to between 130 to 139 mm Hg.

Again, there was a reversal of the trend, with an increase in stroke and heart attacks when the SBP was less than 130. When the SBP fell to 110, the risk of adverse outcomes was double that of those in the higher BP category.

This J-curve relationship is seen in those with high BP who have underlying blockage of the heart arteries but for those without blockage of heart arteries, the relationship between BP and heart attacks appears to be linear.

Does the choice of medication matter?

A wide array of drugs is used by physicians for the management of high BP. Based on available evidence, the JNC 8 panel has made some new recommendations. The new guidelines recommend the use of 4 classes of drugs as the initial choices: thiazide-type diuretics(including hydrochlorthiazide), calcium channel blockers (including amlodipine, diltiazem), angiotensin converting enzyme inhibitors (including perindopril, ramipril, lisinopril, enalapril), and angiotensin receptor blockers (including losartan, irbesartan, telmisartan).

Some of the other commonly used BP lowering drugs have not been recommended as first line drugs although they are widely used by many physicians; the reason being that the trial data does not favour the use of these drugs as compared to these 4 classes of drugs.

Which blood pressure reading is accurate?

If you have been to your doctor’s clinic and have been told that you have elevated blood pressure readings, it does not mean that you have persistent high blood pressure or hypertension.

There are some who exhibit an elevated BP transiently while in the doctor’s clinic but the BP reverts to normal when measured at home. This transient BP elevation due to stress or anxiety as a result of being in a medical setting is termed as "white-coat hypertension."

There are also those who have normal BP readings in a calm and quiet medical setting but have elevated BP readings in a stressful home environment. This condition is termed as "reverse white-coat hypertension" or "masked hypertension." For those who have elevated BP readings, home monitoring is encouraged and by monitoring the trend, your physician will be able to make the most appropriate decision on the need to commence medication.

How should one handle an elevated blood pressure reading?

If you have just been informed that you have an elevated BP reading, you should monitor and recheck the blood pressure. If you are less than 60 years of age or if you are 60 years or more but have underlying kidney disease or diabetes mellitus, your physician may commence medication if your BP is consistently 140/90 mm Hg or more.

If you are 60 years or more, with no kidney disease or diabetes mellitus, treatment should only be considered if your BP is 150/90 mm Hg or more.

You should discuss with your physician with regards to non-pharmacological measures (such as weight loss and reduction of salt intake) and the appropriate choice of medication, given that not all BP lowering drugs have the same efficacy.

While lowering the BP to below the elevated BP levels is beneficial, one should avoid excessive lowering of the BP especially if there is underlying heart artery disease or narrowing of brain arteries as excessively low BP levels may result in more strokes, heart attacks or kidney deterioration.

For those who are on BP lowering medication and have episodes of dizzy or near fainting spells, they may have “white-coat hypertension”, and hence when they leave the medical setting, the BP may drop to very low levels with the medication.

These patients do not require medication. Finally, if you have elevated BP readings, whether you eventually are confirmed to have high BP or not, home BP monitoring twice a day can help to prevent a wrong diagnosis of hypertension and to avoid unnecessary medication. A small investment in a BP monitor can save you from a lifetime of unnecessary medication.