The first key to treating a postoperative myocardial infarction is noticing it.
This is actually a significant challenge with ST-elevation myocardial infarction (STEMI) that occurs after surgery, Hitinder Gurm, MBBS, explained during a talk on treatment of postoperative MIs at the American Heart Association's 2019 Scientific Sessions, held in Philadelphia last November.
“I want to focus on STEMI. Because it's uncommon, it is often missed,” said Dr. Gurm, who is a professor of cardiology at University of Michigan in Ann Arbor.
Another challenge is that the symptoms of STEMI can be mistakenly attributed to other postoperative problems. “They look a little restless and so you give them some more morphine,” he said. “They go into shock and you're worried about bleeding.”
Clinicians may also get a false sense of reassurance if a patient has passed a preoperative stress test. “If the stress test was negative, we may make the assumption that the patient doesn't have cardiac disease so they can't have a cardiac complication,” said Dr. Gurm. That's not a safe assumption, he added. “Stress tests are not very good at picking up moderate coronary lesions, and these are usually the lesions that lead to ST-elevation myocardial infarction.”
Given all these factors, it may not be obvious that the issue is a STEMI until the patient is in ventricular fibrillation. “At that point, you realize it's cardiac, but the patient's already taken enough of a hit,” he said.
Once a postop STEMI is identified, rapid treatment is important. “The most important thing is we need to rescue them and we need to rescue them aggressively,” said Dr. Gurm. “Call your interventional colleagues. Take them to the cath lab for early angiography and revascularization.”
Not everyone does this, he noted, citing an analysis of perioperative MIs gathered from the National Inpatient Sample that was published in the European Heart Journal in 2017. “Only a quarter of the patients get an invasive approach when they have a STEMI,” he said.
A cohort analysis in that study also showed that the patients receiving invasive management had half the mortality rate of those treated conservatively. Coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI) were both used, with similar results, although the latter more often than the former. PCI is usually the preferred approach, but CABG should always be an option when necessary, Dr. Gurm added.
“Patients that go for CABG are very different patients than those who go for PCI, yet the mortality from postop MI is sort of similar. You don't need to send most patients to CABG early on, but when necessary, you should consider that,” said Dr. Gurm.
There is one other very simple intervention that should be part of the early response. “Get these patients on aspirin early as gastric absorption is delayed in postop patients,” he said.
Speaking of drugs, it's important to find out whether the patient is receiving epinephrine, for example, when they are transferred to the cath lab from the operating room. “Epinephrine is one of the most potent platelet agonists” and therefore can cause a stent to thrombose as soon as it's placed, explained Dr. Gurm.
Recommended treatment for these STEMI patients includes a P2Y12 inhibitor, but that class also faces the problem of delayed gastric absorption postoperatively. “A crushed ticagrelor gives you fairly good bioavailability even if the patient has poor gastric absorption, so that's our go-to drug,” he said.
Next, Dr. Gurm moved on to the more common postoperative MI, without ST-elevation (NSTEMI). “Now comes the hard part, which is what to do with NSTEMI,” he said. Challenges include limited research in this area and multiple possible causes.
“The problem is you don't know unless the patient has had an angiogram—or even if the patient has had an angiogram and they have obstructive disease, they could still have thrombotic disease, so you could have a mix of thrombotic disease and obstructive disease. And then patients who have had prior stents could have a stent-related problem,” said Dr. Gurm. “Those are all possible etiologies.”
Surgery adds the problems of sympathetic overdrive, hemodynamic instability, and hypercoagulability, among others, leading to type 1 MIs. “It's amazing that they don't thrombose more often,” he said. Type 2 MIs can be caused by demand ischemia mismatch, high or low blood pressure, or hypoxemia.
“So how do you treat that?” asked Dr. Gurm. “You try to normalize the physiology as best as you can, control the tachycardia, and manage hyper- or hypotension, just try to get it as normal as possible.”
Beta-blocker therapy can be considered, he said. Additional treatment for a postop NSTEMI includes maintaining normoxemia, managing anemia, and restarting antiplatelet therapy, especially in patients with an existing stent. “Beyond that we don't really know what you can do in the early phase to help these patients,” Dr. Gurm said.
Unstable patients should be sent for catheterization. “That's the easy part. It's the stable NSTEMI where we don't really have a good data set to help guide us,” he said, noting that there are case reports, but not randomized trials. “We only publish what works, we don't publish what doesn't work. So you have to be a little careful with that,” he said.
He wrapped up his talk with some recommendations for postdischarge NSTEMI care, including assessment of coronary ischemic burden, prescription of statin and aspirin therapy, and consideration of a dabigatran prescription.
He also reminded hospital physicians to assess these patients' overall cardiac function. “It's amazing how many patients with low EF [ejection fraction] go through the hospital and we sort of ignore that they have an option for a life-saving therapy that might have an impact down the road,” said Dr. Gurm. “If their EF is low, it might be low just because of the stress cardiomyopathy, but make sure that it's followed up.”
Patients must be discharged on guideline-recommended therapy and then evaluated as outpatients for potential implantable cardioverter-defibrillator placement if appropriate, he advised.