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New ACCP Thrombosis Guidelines Offer Weak Support for Aspirin in Primary Prevention

Fri, Feb 17, 2012

Clinical News Room


primary prophylaxis. Individuals who value preventing an MI substantially higher than avoiding a GI bleed will be, if they are in the moderate or high cardiovascular risk group, more likely to choose aspirin.”

Head of the guidelines committee, Dr Gordon Guyatt (McMaster University, Hamilton, ON), added: “We agonized over this recommendation endlessly, with some heated discussions. Some people thought we should recommend aspirin for everyone; others were adamant that no primary-prevention patient should take it. The right message is that there are trade-offs to be made and a lot of uncertainty. In this situation, it is inevitable that individual patient values and preferences will bear in the decision.”

He noted that this approach of collaborating with the patient in making the decision to take antithrombotic therapy or not was a big feature throughout these guidelines. “In many cases, the trade-offs between benefit and risk are very small, so we need to ask the patient more questions, really push for information to make the decision as to whether antithrombotic treatment is the right way to go.”

Opinion Leaders Less Involved Than Before

Guyatt also explained that there were big process changes in the way the guidelines were formulated this time. In particular, instead of having world experts in the field of antithrombotics in charge of each guideline section, it was decided this year to choose instead clinicians who were experts in methodology and interpretation of the evidence. “It was felt that the experts in the field were maybe a little too close to the information, and they often have intellectual and/or financial conflicts. While thrombosis experts were still included on the panel, they did not have the same weight as in previous occasions.”

Vandvik added: “If you performed the study that we were referring to you could not participate in the final discussions of what recommendations should be made.”

Asked what the antithrombotics experts on the panel thought of the new system, Guyatt said, “We made a lot of converts because our approach was so rigorous. Most acknowledged that it was a superior process. Some, however, were still a little grumpy!” Vandvik added: “This is somewhat an experiment, in terms of the academic conflict of interest, but I think it will catch on.”

Less Strong Recommendations

Not surprisingly, this new process has resulted in a set of guidelines that recommends antithrombotic treatment less often and less strongly than before. “The guidelines panel felt that the strength of the evidence in favor of antithrombotic therapy was less than has been thought in the past. Consequently, our recommendations tend to be weaker than in previous guidelines,” Guyatt says. “There is recognition that not everyone in the hospital needs antithrombotic therapy, and we need to individualize such therapy more.

“From an outside view, it appears that antithrombotics may have been used a little too much in North America, although the situation is very variable,” he adds. “In many cases, the risk of thrombosis is very small, and this has to be balanced by the risk of bleeding, the cost, and the inconvenience,” Guyatt noted.

He explained that in making this trade-off, one stroke was thought to be equal to three bleeds. He gave the example of an AF patient at a low risk of stroke. If a patient has a 1% risk of stroke over a year, and this risk is halved by antithrombotic treatment, 200 patients would need to be treated to prevent one stroke. But if the bleeding risk was 3%, that would mean six bleeds in the 200 patients, with the balance of six bleeds vs one stroke going against antithrombotic treatment.

However, in another patient with a 6% risk of stroke and a 3% risk of bleeding, this would translate into six strokes vs three bleeds, so antithrombotic therapy would be the right option in this case.

“We have got to be much more quantitative than we have been in the past. We may not have the greatest ways of assessing stroke and bleeding risk, but we have to offer clinicians something,” Guyatt says. The guidelines have opted for the CHADS2 score for stroke, rather than the CHA2DS2-VASc score as the first choice. “We also need to consider the values and preferences of the patient. Some people are more stroke averse; others are more bleeding averse. Some will be better than others at managing warfarin.”

The guidelines do not advise passengers on long-haul flights to take antithrombotic prophylaxis unless they have known risk factors. Guyatt says: “The risk is very small. If your risk of [venous thromboembolism] VTE is one in 1000 and a long-haul flight doubles this risk, then your risk is still very low. But if your baseline risk is one in 100, then it would become one in 50, and then you start to worry.”

Dabigatran Recommended for AF

But the guidelines do appear to welcome the new oral anticoagulants as an alternative to warfarin. For patients with atrial fibrillation in whom oral anticoagulants are indicated (CHADS2 score of >1), they recommend dabigatran rather than warfarin as long as the patient does not have severe renal impairment.

MedScape News Today; February 15, 2012; Written by Sue Hughes

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