Doctors miss many postop MIs because patients have no symptoms by Deborah Gesensway
Published in the July 2011 issue of Today's Hospitalist
WITH BOTH THE NUMBER and the age of people undergoing surgery on the rise, it's no surprise that the number of perioperative myocardial infarctions (MIs) is growing. What is surprising is how many postop MIs take place— and how profoundly they affect a patient's prognosis.
Even more startling news arrived in the April 19 Annals of Internal Medicine, which published the latest findings from the international POISE 1 (Perioperative Ischemic Evaluation) trial. According to the study, 5% of patients admitted for noncardiac surgery suffer a periop MI. But two-thirds of those
"These heart attacks without symptoms carry the exact same poor prognosis as the ones with symptoms."
–P.J. Devereaux, MD, PhD McMaster University
patients never complained of ischemic symptoms and pain, so their heart attacks would have been missed if researchers hadn't routinely been measuring cardiac biomarkers during the trial.
In a conversation with Today's Hospitalist, lead author P.J. Devereaux, MD, PhD, associate professor and cardiologist at McMaster University in Hamilton, Ontario, detailed several lessons that hospitalists can take away from the findings.
"Physicians should ask themselves if it were their loved one who suffered a perioperative MI, wouldn't they prefer more aggressive management than what currently occurs?" Dr. Devereaux says. "We think this publication is an important step to making physicians realize that we could be doing a much better job."
One of your main findings is that MI is the most common major vascular complication of surgery. But didn't we already know that?
People have not been aware of how much more prevalent MIs are than every other postoperative major cardiovascular complication. This paper also emphasizes how important MIs are, in that these patients have very poor outcomes.
Almost 12% of people who have a heart attack after surgery will die within 30 days. (The 30-day postop mortality rate is about 2% for patients who don't have a heart attack.) That's double the death rate of people with MIs in the nonoperative setting. In most centers in North America, if you show up in the emergency room with an MI, you have a 6% likelihood of dying within the next 30 days, whereas if you have a heart attack after surgery your likelihood of death is 12% within the subsequent month.
We are extremely—and appropriately—assertive about treating people in emergency rooms with heart attacks. But for the most part, we have been ignoring MIs when they happen after surgery.
Why do you think physicians are less aggressive in treating postop MIs?
Part of the reason these MIs are ignored—and this is the crucial message in the POISE 1 paper—is that two-thirds of patients who have heart attacks are not having any ischemic symptoms.
We think that's because 75% of those heart attacks happen in the first 48 hours after surgery, which typically is when patients are getting high-dose narcotics to blunt surgical discomfort. So it is not surprising that patients don't experience symptoms. The lack of ischemic symptoms likely influences physicians' perception as to the severity of an event, but these heart attacks without symptoms carry the exact same poor prognosis as ones with symptoms.
How should physicians detect these silent heart attacks?
We have a very simple test—troponin—that we can measure the first few days after surgery. We have to start monitoring troponins postop because if we don't we will miss the majority of these serious heart attacks.
Does the study indicate which patients should have troponins measured and when?
We are currently doing a 40,000-patient prospective cohort study called VISION [Vascular events In noncardiac Surgery patients cOhort evaluatioN] where we are measuring troponins and other biomarkers for the first few days postop. We will be reporting results in the next six months from the first half of that trial.
We now recommend monitoring troponins six to 12 hours postop, and then on day 1, day 2, and day 3 postop. Those are the periods when people are typically getting narcotics and are most at risk of having an event and not experiencing symptoms.
When physicians detect these silent heart attacks, what should they do?
Move patients to a monitored setting and do the things that we know work in nonoperative MIs.
If patients have a heart attack after surgery, I would argue that they are much better off not being on a surgical floor because that's not surgery's area of expertise. It is clear that patients presenting with a myocardial infarction to the emergency room benefit from a monitored setting, such as telemetry in the cardiac care unit. The same is likely true when a patient suffers a myocardial infarction after surgery.
We also found that compared to the heart attack in the emergency room, these periop MI patients get very low-level treatments. A third of them aren't even getting aspirin when they go home, and patients on aspirin had about half the 30-day mortality as those not on aspirin.
We need to become much more aggressive about their management. Another study we are doing— POISE 2—is testing low-dose aspirin and clonidine, starting before surgery and continuing into the postop period, to see if we can prevent major vascular complications during the first 30 days after surgery. But until we complete trials evaluating drugs to manage a perioperative MI, it's not OK to look the other way because these patients are doing so poorly.
Does this study speak to how hospitalists should assess cardiac risk during preop workups?
The VISION study will offer more insight into how to better risk-stratify patients up front. It's important to risk-stratify patients because patients have a right to make an informed decision about the risks and benefits of their potential surgery.
I think we are going to discover that there are biomarkers—like troponins—that can better help us risk-stratify people prior to surgery. Another example is measuring NT-pro BNP prior to surgery, which looks to be a strong predictor of who is going to get into trouble.
There is also a better understanding emerging of some risk factors, like sleep apnea. The field is about to change dramatically in the very short term.
Deborah Gesensway is a freelance writer based in Toronto who covers U.S. health care.