A version of this commentary appeared in the Huffington Post, Winnipeg Free Press and the Miramichi Leader
Have you been told by your health care professional that you have high blood pressure, high cholesterol or type 2 diabetes and you need to do something to improve your “numbers”? If so, it is likely their recommendations were based on national clinical practice guidelines written by experts in cardiovascular health.
On the face of it, following guidelines seems a very reasonable approach. What could be the problem?
Well, a recent evaluation of cardiovascular patient guidelines reveals that only 12% of the recommendations are based on randomized controlled trials (the highest level of evidence). In contrast, 54% of the recommendations are based purely on opinion and consensus.
Here’s what we know well: Evidence from the last 30 years provides pretty solid support that lowering what would be considered higher levels of blood pressure (above 160 to 170 mmHg systolic), especially in type 2 diabetics, reduces cardiovascular events (heart attacks and strokes) to what many, if not most, would consider a clinically important degree. Statins reduce the chance of cardiovascular events and one can control symptoms and improve outcomes when very high glucose levels are reduced.
But the evidence for reducing the risk of cardiovascular disease is not nearly as impressive or definitive when it comes to aggressively getting numbers below the commonly recommended lower number thresholds for blood pressure (<140/90 mmHg), diabetes (hemoglobin A1c <7%) and cholesterol (LDL < 2.0 mmol/L). This is important because reducing the chance of cardiovascular events is the only reason we aim to change numbers in the first place.
Given this, it is unfortunate how many patients and their families worry and become obsessed with these quite arbitrary breakpoints. A recent British Medical Journal analysis goes so far to say that our idolizing obsession with changing patient numbers is “damaging patient care.”
Beware the spin
One of the more tricky aspects surrounding cardiovascular disease numbers is how the magnitude of the cardiovascular benefits is typically presented.
A news report may, for example, state that a five-year study of a drug has shown it reduces cardiovascular disease by 25%. Sounds convincing, right?
While this number may be technically correct, it’s actually misleading.
That’s because a typical study result may find those patients who go without medication over five years have an 8% chance of a cardiovascular event, whereas if they take the medication in question, their chance decreases to 6%.
Mathematically, it is true that six is 25% lower than eight (a ‘relative’ difference). But the number that matters — the ‘absolute’ number — is actually 2% (8 minus 6). In other words, 2% of people obtained a benefit, but 98% of people on the medication received no cardiovascular benefit. The benefit is hopefully greater over a longer period of time, but studies rarely extend beyond five years.
In the case of statins, a class of drugs routinely prescribed to lower cholesterol, evidence shows the absolute difference in cardiovascular events achieved over a five year period is roughly 1 to 1.5% in patients who have never had a heart attack or a stroke. Other popular drugs (ezetimibe, niacin, fibrates) that lower cholesterol numbers have not been shown to consistently reduce the chance of cardiovascular events.
Most blood pressure drugs (but not atenolol or doxazosin), when used in patients with systolic blood pressures around 160 to 170 mmHg, lead to a difference in cardiovascular events of around 2% to 5%, and there is a 5 to 8% reduction when a drug called metformin is used in newly diagnosed diabetics.
Interestingly, other drugs used to lower blood glucose in diabetes have either been shown to have less of a benefit, no benefit at all or have not been studied to see if they reduce the chance of cardiovascular disease. And we can’t forget the possible side effects and the costs for medications, which patients must consider. Since the majority of patients will not get a cardiovascular benefit from these medications, any side effects really become unacceptable.
Informed decision making
Medical guidelines are oddly silent on patient preferences. A recent look at five main Canadian cardiovascular guidelines reveals that only 99 of the 90,000 words in the documents addresses patients’ values and preferences.
So, given all of this, what’s a patient to do?
Let’s forget the numbers for a moment and focus on what patients can and should do for themselves. The best available data show that stopping smoking, eating in moderation (the Mediterranean diet has the best evidence), and being active are the three most important things a person can do to reduce cardiovascular risk (even if these things don’t change your numbers).
Patients should ask their doctors, if a medication is recommended, whether that specific drug has been shown in well-designed clinical trials to reduce cardiovascular disease, and if so, by how much (in absolute numbers). They should also always have a discussion about the possible side effects and costs of any medication.
The bottom line: The goal is reducing the chance of cardiovascular disease not just lowering numbers.
In the end, a health care provider should support the patient decision regardless of the path the patient chooses and not make them feel guilty if they don’t blindly follow the latest guideline recommendations.
James McCormack is an expert advisor with EvidenceNetwork.ca and professor with the Faculty of Pharmaceutical Sciences at the University of British Columbia in Vancouver. He co-hosts a weekly radio show that is regularly rated one of the top medical podcasts available through Apple iTunes.
This work is licensed under a Creative Commons Attribution 4.0 International License.