Caroline Helwick

October 31, 2014

NEW ORLEANS — In patients undergoing noncardiac surgery after previous percutaneous coronary intervention (PCI) and stent implantation, the use of aspirin is unrelated to the occurrence of a major cardiac adverse event, a new study shows.

Canadian investigators evaluated whether antiplatelet therapy decreases the incidence of cardiac adverse events in patients undergoing noncardiac surgery, and found the use of aspirin to be largely irrelevant.

"Is aspirin protecting the patient? I don't think so," said Marcin Wasowicz, MD, from the University Health Network, which includes Toronto General Hospital, Toronto Western Hospital, and Princess Margaret Hospital.

The study findings, presented here at the American Society of Anesthesiologists 2014 Annual Meeting, support those from the recent double-blind randomized POISE-2 trial, Dr Wasowicz reported.

POISE-2 found that neither aspirin nor clonidine reduced the risk for death or nonfatal myocardial infarction when given concurrently with noncardiac surgery.

Within 1 year of PCI, 5% to 16% of patients will undergo noncardiac surgery, and they have a fairly high risk for perioperative major cardiac adverse events. Management is based on guidelines from the American Heart Association (AHA) and the American College of Cardiology (ACC), "but they are based mainly on expert opinion, which is a low level of evidence," Dr Wasowicz pointed out.

 
The 21% incidence of major cardiac adverse events is still very high, even though we followed the ACC/AHA guidelines.
 

"There is a never-ending discussion between anesthesiologists and our colleagues on the other side of the table as to what's more important: the risk of stent thrombosis or surgical bleeding? Needless to say, this question is unresolved," he said.

In their prospective cohort study, Dr Wasowicz and his colleagues evaluated 201 patients scheduled for elective noncardiac surgery who had received a stent during a previous PCI.

The primary outcome was cardiac adverse events, which included myocardial infarction, stent thrombosis, need for revascularization, sudden cardiac death, and stroke. Major bleeding was a secondary outcome.

Covariates in their model included factors known to contribute to perioperative heart trouble, such as time between PCI and subsequent surgery, type of stent (bare metal or drug-eluting), revised cardiac risk index, and urgency of surgery.

Of the 201 patients, 42 experienced an adverse event. "The 21% incidence of major cardiac adverse events is still very high, even though we followed the ACC/AHA guidelines," Dr Wasowicz explained.

Of these, 38 were myocardial infarctions, the majority of which were non-ST-segment elevation. The injury was in the territory of stent implantation in 72% of the patients. In addition, three patients died and one suffered a stroke.

Four of the cardiac cases occurred in patients who underwent surgery less than 42 days after PCI, he reported.

Major bleeding was observed in 30 patients (15%), "which is quite a significant number," Dr Wasowicz said. This was defined as the need for a transfusion of more than 2 units of red blood cells or the loss of more than 1000 cc of blood.

Almost 100% of the patients followed advice and continued aspirin up to the day of surgery. The Thromboelastography-Platelet Mapping Assay, which reflects the degree of platelet inhibition, showed that aspirin continued until surgery led to platelet inhibition of at least 50% in the majority of patients. Even patients who stopped aspirin 3 to 7 days before the procedure remained above 50% inhibition. The few patients who stopped aspirin more than 7 days before the procedure had somewhat lower inhibition.

"This is what is recommended by the manufacturer of the platelet mapping test, but, unfortunately, this did not correlate with our results," Dr Wasowicz explained. There was no association between platelet inhibition and cardiac adverse event risk.

Risk factors with an odds ratio of at least 2 included kidney injury, congestive heart failure, and high-risk surgery — which are part of the revised cardiac risk index — and preoperative or postoperative anemia. By optimizing preoperative hemoglobin levels and lowering the "transfusion trigger," the clinician might be able to ameliorate this risk factor, he suggested.

"The guidelines recommend bridging patients using low-molecular-weight heparin if you cannot use aspirin or clopidogrel, but we saw a very strong association with bleeding, and an association between bleeding and the incidence of adverse events," he added.

Dr Wasowicz concluded by saying, "We were surprised by the high incidence of major cardiac adverse events. We were surprised by our results."

How do we relate these results to the guidelines? he asked. "The timing of surgery after PCI continues to be important, but as for the use of aspirin — we are not sure anymore."

The lack of benefit of low-molecular-weight heparin in these patients is a take-home message, said session comoderator Jerrold Levy, MD, from Duke University in Durham, North Carolina. "The idea of using low-molecular-weight heparin for bridging makes very little sense to me," he said. "It speaks to the concept of needing better bridging strategies in clinical medicine."

Dr Wasowicz said he agrees. "To be honest, bridging with low-molecular-weight heparin, to replace aspirin or clopidogrel, mechanistically does not make sense. They have a totally different mechanism of platelet inhibition."

Dr Wasowicz and Dr Levy have disclosed no relevant financial relationships.

American Society of Anesthesiologists (ASA) 2014 Annual Meeting: Abstract BOC07. Presented October 14, 2014.

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