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Heart health not just a numbers game

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VANCOUVER -- Have you been told by your health-care professional 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 only 12 per cent of the recommendations are based on randomized controlled trials (the highest level of evidence). In contrast, 54 per cent 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 < 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 as to say our idolizing obsession with changing patient numbers is "damaging patient care."

One of the more tricky aspects 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 per cent. Sounds convincing, right?

While this number may be technically correct, it's actually misleading.

That's because a typical study may find those patients who go without medication over five years have an eight per cent chance of a cardiovascular event, whereas if they take the medication in question, their chance decreases to six per cent.

Mathematically, it is true six is lower than eight (a 'relative' difference). But the number that matters is actually two per cent (8 minus 6). In other words, two per cent of people obtained a benefit, but 98 per cent of people on the medication received no cardiovascular benefit.

In the case of statins, drugs routinely prescribed to lower cholesterol, evidence shows the absolute difference in cardiovascular events achieved over a five-year period is roughly one to 1.5 per cent 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, lead to a difference in cardiovascular events of two to five per cent, and there is a five to eight per cent reduction when a drug called metformin is used in newly diagnosed diabetics.

Interestingly, other drugs used to lower blood glucose in diabetics have either been shown to have less of a benefit, no benefit or have not been studied. 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.

Medical guidelines are oddly silent on patient preferences. A recent look at five main Canadian cardiovascular guidelines reveals only 99 of the 90,000 words in the documents address patients' values and preferences. So what's a patient to do?

The best available data show stopping smoking, eating in moderation (the Mediterranean diet has the best evidence), and being active are the three most important things 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). Also, always have a discussion about 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 adviser with EvidenceNetwork.ca and professor with the faculty of pharmaceutical sciences at the University of British Columbia in Vancouver.

 

Republished from the Winnipeg Free Press print edition May 5, 2012 A17

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