Hypertension – What is the ideal treated blood pressure?
People often ask me whether their blood pressure is high. This is in some ways like being asked if they are tall. It is obvious that the person is tall if they are over 7 feet but what about if they are 6 feet or even 5 feet 9 inches (which incidentally happens to be my height)?
So how high does blood pressure have to be to be considered high? Various committees have spent years coming up with a single figure. It seems to have settled on 140/90mmHg. This is very convenient and means we all think we know what we are talking about. Its like saying 5feet 9inches is tall. The top figure is measured by occluding the arterial pulse with an inflatable cuff applied like a tourniquet around the upper arm and gradually allowing to the cuff to deflate until the pressure in the cuff is just below that required to cut off all the blood to the arm – the systolic pressure. The bottom figure is the highest pressure in the cuff at which all the blood flows along the artery with each pulse- the diastolic pressure.
Until recently we have always targeted our treatment for high blood pressure to get to a figure below 140/90mmHg. After all hypertension or high blood pressure was defined as a blood pressure above this figure. This never seemed to make complete sense to me – surely there may be more benefit in getting the blood pressure much lower than this. We have known for many years that the risk of complications (strokes and heart attacks) goes up steadily as the baseline blood pressure goes up even at very low levels. The effect is most pronounced for stroke. (see table 1 ).
ABC of hypertension BMJ Books Beavers G et al 2009
If you look and see the events that occur they are undoubtedly more common as the BP gets higher but there is still lower risk below a systolic BP of 136mmHg. The question therefore is how low should the blood pressure go to minimize your risk of having a heart attack or stroke?
The SPRINT trial has addressed this issue and published this year. 9361 patients aged over 50 with hypertension were randomized to a target blood pressure of either 120mmHg or 140mmHg. In fact they almost achieved this with the blood pressure being on average 121.5 and 134.6mmHg respectively in the two treatment groups. The trial had to be stopped early after only 3 years as they thought it was unethical to know that the more intensive treatment was better and let the trial continue. Primary events (heart attacks, strokes and death) occurred in 243 patients (1.65% per year) of the intensive treatment group and 319 (2.19% per year) of the standard treatment group. If you look at the deaths specifically 155 people died in the intensive group and 210 in the standard treatment group.
So are there any downsides to being treated more aggressively? In short yes. There was a very small increase in the likelihood of low blood pressure, fainting, abnormal blood tests and acute kidney injury. The patients also had to take an extra tablet on average to get their blood pressure lower.
These findings were backed up in a more diverse population (including those with diabetes and old heart attacks) in a summary of all the appropriate studies from 1966 until now. The authors, Ettehad et al, reviewed 123 hypertension studies which included more than half a million patients and concluded that benefit could be shown when treating blood pressures below 130mmHg. They could not show that there was any lower limit to the benefit of blood pressure lowering and overall showed that for a 10mmHg of blood pressure drop resulted in a 20% drop in the cardiovascular events and 13% drop in mortality irrespective of your starting blood pressure.
When assessing anyone’s risk of having a cardiovascular event it is important to keep in mind all risk factors (see ‘risk’). Remember it may seem very compelling to start treatment with something that gives a 20% reduction in the chance of having a heart attack but if there is very little chance of the heart attack occurring in the first place it still may not be worth starting the treatment. Giving antihypertensive treatment to a 40 year old man with a blood pressure of 140/90 gives much lower benefits compared to a 60 year old smoking diabetic man with the same blood pressure. The 60 year old has much more chance of having a heart attack and so a 20% reduction gives a greater absolute benefit. Furthermore there are natural ways of reducing your blood pressure and cardiovascular risk by losing weight and exercising which are universally applicable to all patients.
A Randomized Trial of Intensive versus Standard Blood-Pressure Control
The SPRINT Research Group
N Engl J Med 2015; 373:2103-2116
Blood pressure lowering for prevention of cardiovascular disease and death: a systematic review and meta-analysis
Ettehad D et al
www.thelancet.com Published online December 23, 2015 http://dx.doi.org/10.1016/S0140-6736(15)01225-8