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For decades, the standard treatment for angina (chest pain) has been to rush patients into surgery for angioplasty and stenting, or coronary bypass surgery.

But a new blockbuster study shows that these common surgical interventions work no better than medications as a treatment for stable angina.

The International Study of Comparative Health Effectiveness with Medical and Invasive Approaches is one of the most thorough and costly clinical trials ever conducted. (It also has a clever acronym: ISCHEMIA, which is a restriction in blood supply to tissues and the underlying cause of angina.)

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The $100-million study included 5,179 patients – with an average age of 64, although only 23 per cent were women - with stable angina or suspected blockages. They underwent cardiac stress tests – which are generally done walking briskly on a treadmill – or magnetic resonance imaging.

Study participants were randomly assigned to either surgical intervention or optimal medical therapy. OMT consists of a combination of drugs such as Aspirin, statins, beta-blockers, ACE inhibitors and counselling on diet and exercise. The patients were then followed closely for 3.3 years on average and disease progression and complications monitored.

The commonly accepted wisdom was that surgery prevents heart attacks more effectively than drugs.

But the ISCHEMIA data showed that, after one year, 7 per cent of the patients in the surgery group had heart attacks, compared to 5 per cent in the medication group. After four years, 13 per cent of those in the procedure group had heart attacks, compared to 15 per cent in the medicine group.

In other words, it was a wash.

The same was true when researchers looked at other measures such as mortality, heart-related hospitalizations and resuscitation after cardiac arrest.

When the findings were presented recently at the annual conference of the American Heart Association conference, those in the know were blown away.

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“Cardiology changes today,” wrote Dr. John Mandrola, a Louisville, Ky., cardiac electrophysiologist and columnist for Medscape.

When guidelines are rewritten to reflect these findings, the take-home messages for patients with stable angina and their doctors will be: 1) try medication first; 2) surgery, if it is recommended, is not urgent.

Or, as Dr. Mandrola wrote: “That blockage is not a time bomb in your chest.”

Today, many – and now we know too many – patients with persistent chest pain or even a suggestion of coronary blockages, get either angioplasty and stenting or bypass surgery.

But the ISCHEMIA data are a reminder that while surgical interventions remove specific blockages, drugs probably clear blood vessels more broadly.

(To be clear, the findings don’t apply to patients who have had heart attacks or have unstable heart disease.)

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Whether the way patients with stable angina are treated actually changes remains to be seen.

It takes, on average, 17 years for findings of health research to become standard practice.

Physicians are a conservative lot and pretty adept at turf protection, not to mention that much medical practice is based on tradition more than hard evidence.

There is also a lot at stake. Consider that about 17 million or about 5 per cent of Americans are living with angina.

In the U.S., about 500,000 patients a year have stents implanted. That includes 100,000 people with stable angina and 23,000 with no chest pain. The researchers estimated that treating the latter group with drugs instead of surgery would save US$775-million.

(About 15,000 Canadians annually undergo bypass surgery and another 50,000 have angioplasty and stenting, according to data from the Canadian Institute for Health Information. However, not all the procedures are related to angina. Previous research has shown that per capita, Canadians undergo fewer heart procedures than Americans because there are incentives to over-treat in a for-profit system.)

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The ISCHEMIA study, among other things, is a reminder that there is very little rigorous study of the effectiveness of surgical practices. While new prescription drugs are tested in clinical trials, that is not the norm for innovations in surgery.

That we have been doing surgery that’s not particularly useful on heart patients for decades also underscores the power of intervention bias – the belief that doing something is better than doing nothing.

As legendary cardiologist Dr. Bernard Lown famously said, cardiac surgeons too often “think like plumbers rather than like scientists,” and are eager to unblock pipes as soon as possible.

Patients also tend to much prefer surgery over drug regimes. As Carolyn Thomas, who writes the popular Heart Sisters blog, notes, changing those ingrained cultural perceptions is going to be difficult.

Having good evidence is one thing; changing minds, and practices, is quite another.

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