- 17 Sep 2019
- 14 min
- 17 Sep 2019
- 14 min
Justin Coleman interviews Emily Atkins about the tricky topic of when to start treating someone’s high blood pressure. Read the full article in Australian Prescriber.
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Welcome to this Australian Prescriber Podcast. I'm Dr Justin Coleman, a GP on the Tiwi Islands in the Northern Territory where I'm no stranger to treating high blood pressure in those at high cardiovascular risk. Today, I'm speaking with Dr Emily Atkins, who's a research fellow at the George Institute for Global Health and who has a PhD in cardiovascular medicines. Dr Atkins was lead author on the paper, Blood Pressure: At What Level is Treatment Worthwhile? The answer is apparently more complicated than when it gets too high. Dr Emily Atkins, welcome to our internationally acclaimed, yet humble podcast.
Thanks. It's a pleasure to be on the show.
Fantastic to have you. Look, back in the days when I used to wear a white coat, you wouldn't remember those days, you either had high blood pressure or you didn't. Therefore, you either treated it or you didn't. Should we yearn for the good old days Emily?
I think those days are gone. We're past them. Now what we need to do is balance the risks and benefits for our patients, so it's not one size fits all anymore.
That is a very good thing for our patients because I guess back in the old days there was a lot of undertreatment and overtreatment going on, so people who probably didn't need blood pressure treatment would get it just because the numbers said they needed it. Those at high cardiovascular risk, we were probably far too lax about giving blood pressure probably because there wasn't the evidence available. That's what we're going to talk about today. The main two factors in your article covered are at what blood pressure should we start treatment and secondly, at what target level of blood pressure should we aim for? Then I did want time to discuss your section entitled, Are Australians being undertreated or are Americans being overtreated? Because I think we might have differing slants on this, and I'd like to save a little bit of juicy controversy for our listeners towards the end, but enough about that. Let's start with the very simple act of taking a blood pressure. When we measure blood pressure, what's the recommended methodology because I noticed that it's slightly different from those used in the trials?
Ah, yes. In Australia, we are recommended to take three measures after a five minute rest and take the average of those measures.
Okay. In some of the trials different methods were used?
Yeah. What happens in some of the more recent trials is they have blood pressure machines that are programmed to take these three measures automatically, so you don't need to be standing there as the doctor pressing the button for it to start each time. This does mean that you can leave the room and you can do an unattended blood pressure measure, which can help make your patient more relaxed and reduce that white coat effect.
Okay. Although that's not actively recommended, but it suits the trials. Of course, many GPs these days, many of us have automated blood pressure machines, but we rarely leave the room while it happens, so I guess the white coat, not that we wear them anymore – as I pointed out earlier on – may still apply.
Dr Emily Atkins, at what blood pressure should we start treatment? That's a hard question to answer.
Yeah, it depends on the patient's underlying cardiovascular risk. For people who have a low cardiovascular risk, so under 10%, we would look at starting treatment if their blood pressure is persistently above 160 over 100.
That's 10% five-year cardiovascular risk?
Yes. Then you can do the cardiovascular risk calculation on cvdcheck.org.au.
Oh, of course. We even get a special Medicare item number for it these days, although many of us haven't yet used it.
That's below 10% risk. In the people who are at moderate risk, so 10 to 15%, you would look at if they have a persistently high blood pressure, so over 160, if they've got a family history of early cardiovascular disease, or if they're Aboriginal or a Torres Strait Islander. If they have those extra risk factors, then you look at starting blood pressure lowering therapy if their systolic blood pressure is in the 140 to 160 range. If they're in that 130 to 140 range, then you'd start your lifestyle advice and then review it again in six months. For people who are at high risk, so over 15%, you'd want to look at starting blood pressure lowering treatment immediately if their blood pressure is over 140 over 90, and look at also managing their other risk factors as well. This would also include lifestyle interventions.
Okay, so in a general sense for people at lower risk, you're looking at around about 160 systolic. And for people at moderate and higher risk, you're looking at around 140 systolic.
Yes, that's right.
Are there any circumstances where we should look at starting treatment at below 140 systolic?
Yeah. For people who are at particularly high risk, there may be benefits of starting in that 130 to 140 range where there is an additional risk factor.
What sort of people might fall into that category?
Additional cardiovascular risk factors that might also need to be considered are atrial fibrillation, obesity, chronic kidney disease, and also women who experience high blood pressure during pregnancy.
Okay. And like so many things, it's somewhat of a grey area in the sense that it's not an automated thing that any single one of those risk factors automatically makes you want to treat them at that range, but more just it adds to the overall risk of the individual. I do note that cardiovascular risk calculators don't include a lot of that information. And in particular, I work with Aboriginal and Torres Strait Islander people and generally that's not a part of many of the risk calculators.
Yes, that's right. It's always about looking at a person's broader cardiovascular risk, and then taking it that step beyond what's in the classic calculator.
Excellent. Now we know which level to start people on anti-hypertensive treatment. The next question becomes how low should we go, and what level we should aim for? And again, that differs according to the individual.
Absolutely. For people who aren't at very high cardiovascular risk, the recommendation is aiming for below 140 over 90. For people who are at high cardiovascular risk, over 75 years, people with diabetes and people with kidney disease, our Australian treatment targets are below 120.
Some of the controversy I think has come into these targets with that quoted number of 120 and there are various caveats there, but certainly if we weren't to take into account potential side effects, and cost, and people not wanting to take medication etc, then I think it's something worth aiming for in terms of protecting kidney function and reducing the risk of stroke.
Yes, that's right. Our systematic review showed that aiming for a lower target is associated with a 15% reduction in cardiovascular events.
Emily, are the targets we're talking about higher or lower than the European and the American anti-hypertensive targets?
Targets for people who are at high cardiovascular risk, for people who are older, for people with diabetes, and for people with kidney disease are lower than the American and European guidelines. Their guidelines are aiming for a treatment target of less than 130 over 80. Whereas, we're aiming for less than 120.
What do you think leads to that difference in targets between countries?
I think it's partly due to the SPRINT trial results being published. The SPRINT trial recruited people who are at a high risk of cardiovascular events who had blood pressure of 130 or higher and then randomly allocated them to a target of 140, which was the usual target, or below 120, which was the lower target. They had to stop the trial early because there were more cardiovascular events in the group aiming for below 140. What this meant was that the Americans then changed their definition of hypertension to 130 over 80, and subsequently their treatment targets were below 130 over 80. The Europeans didn't change their definition of hypertension, so they still use 140 over 90 like we do, but they amended their treatment targets to a 130 over 80 target.
In some ways you could say that the Australian thresholds for when to start treating tend to be more conservative, generally 140 over 90. Whereas, the treatment targets tend to be more radical if you like, pushing lower unless there's side effects or substantial risk of side effects such as a hypertension, or in the frail or elderly, or interactions with other medications.
Yeah, that's right.
Getting back to the controversial question, Emily, so are Australians being undertreated or are Americans being overtreated? In your article, you tended to feel that perhaps the Australian threshold should be lowered.
I think it's a bit of both. There's a lot of people who experience cardiovascular events and their usual blood pressure is in that 130 to 140 range, so they might benefit from having earlier treatment. On the other hand, if people aren't at a particularly high cardiovascular risk, starting treatment in that time means they're deriving less benefit.
Yeah. I guess one of the concerns as a GP is that an enormous number of people seem to come in at that sort of range you're talking about, and there are some concerns about sort of pathologising a large proportion, if not the majority of the population and medicalising their treatment. Sometimes I think at the expense of lifestyle changes, not that GPs wouldn't talk about lifestyle changes of course, but people just do sometimes tend to feel that if they're on a pill they can get away with some of their imperfect lifestyles.
One of the challenges with blood pressure is it's a continuous risk, so as your blood pressure gets higher, your cardiovascular risk gets higher. It's not so much a yes or no thing. It's at what point does that treatment become more beneficial?
There is some point where every single guideline and every clinician would agree that the harms of treatment do outweigh the benefits of treatment. No one suggests putting someone with 110 on blood pressure medication. What are those harms? I think looking at those might help us take into account why there is such controversy around these grey areas.
Yeah, with blood pressure lowering therapy there is an effect of the treatment, which means that your blood pressure gets lower and then at some point that can become a little bit problematic. For people whose blood pressure is already quite low, additional blood pressure lowering might not derive as much benefit and you might be better going for other treatment strategies to lower cardiovascular risks. For the frail elderly, you might be looking at balancing the risk from the high blood pressure against other risks for that patient.
I guess it's true to say that just as the treatment is a spectrum and the benefits or harms are also a spectrum, so there is no absolute cut off where harms start occurring. In other words, there would no doubt be people in the world if you lower their blood pressure of 160 to 150 you could be doing them harm, so it's like two spectrums crossing over each other and that's why it's hard to find an absolutely reliable threshold. The threshold probably does differ slightly for each individual, but I guess we have to use these large numbers to try to categorise people and treat people within that one category to the same target.
Absolutely. We're looking at, for most of the population, this is where we reckon the most benefit will happen, but it always needs to be tailored for the patient in front of you and balancing their treatment preferences, their lifestyle, their risk aversion against the treatment choices.
Thank you, Emily. I think it's an excellent article. I recommend GPs go back and read it to remember those numbers we've been bandying about. Thank you very much, Dr Emily Atkins for speaking with us today.
Thank you. It was a great pleasure.
My guests’ views are their own and don't represent Australian Prescriber, and my views are certainly all mine. I'm Dr Justin Coleman. Thanks for listening to another Australian Prescriber Podcast.