Why a lower BP threshold makes little sense

Local hypertension guidelines are reflecting the evidence and steering practice appropriately, experts say

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Australian experts have reiterated their support for local blood pressure guidelines amid a swirling controversy over the decision by US cardiologists to lower the threshold for hypertension. 

Dropping the current hypertension threshold from 140/90mmHg to 130/80mmHg would, with the stroke of a pen, double the proportion of Australian adults with the condition, increasing the number by 4.5 million. 

So any decision to do this had serious immplications, leading Australian cardiologist Professor Garry Jennings told The Medical Republic. 

The majority of patients who would be newly diagnosed with hypertension would most likely only be recommended lifestyle changes, but a significant proportion may be prescribed blood pressure-lowering medication. 

In a way, the decision to capture more patients was an academic one, Professor Jennings, who is Executive Director of Sydney Health Partners, said. 

“In a national survey, 71% of the population with blood pressure levels ? 140/90mmHg (our present threshold) were not aware they had hypertension,” he wrote in a Perspective in the MJA last week.

The fact very few members of the public realised that hypertension was the number one attributable risk factor for cardiovascular disease meant progress in tackling the condition was unlikely, Professor Jennings said. 

Before adding a medical label to more of these individuals, Professor Jennings and his co-authors prompted readers to consider whether we had effective ways of ensuring high-risk individuals engaged in healthy nutrition, exercise and medication adherence. 

Professor Jennings said the wide swathe of people who were at that lower end of severity should really be the impetus for the government to take population-based approaches more seriously.  This included serious efforts to limit the salt in our diets and address the obesogenic society that was such a major contributor to poor cardiovascular health.

But it also meant educating individuals about the real meaning of hypertension, he said.  “Hypertension has arguably been a sleeper in the Australian health scene.” 

While he welcomed discussion and debate over how to better address hypertension, Professor Jennings felt confident that Australian guidelines were reflecting the evidence and steering practice appropriately.

The US decision to lower the threshold was heavily based on the results of the SPRINT study, which found lower deaths and cardiovascular events when patients were aggressively treated to a systolic blood pressure of less than 120mmHg. 

However, there has long been controversy over the generalisability of these findings in the wider population, given the older and more high-risk study population. 

One major difference with adopting the new US guidelines, which have been endorsed by the American College of Cardiology and the American Heart Association, would be a shift away from Australia’s current focus on absolute risk and towards the singular metric of blood pressure. 

“However, the present national standard for assessing absolute risk is not valid for people aged less than 45 years in the non-Indigenous population and less than 35 years in Aboriginal and Torres Strait Islander Australians,” Professor Jennings and his colleagues wrote. 

Under the expanded definition, many young people would be included, but not be captured in an absolute risk calculator, creating the need for a new way of assessing overall risk. 

As countries around the world decide whether or not to follow the US lead, there is dissent even among medical colleagues in the United States over the new threshold. 

The America Academy of Family Physicians has refused to endorse the guidelines, citing fears of harmful overtreatment, among other reasons. 

MJA 2018; online 6 August