Perioperative myocardial infarction: in the twilight zone between surgery and cardiology

This editorial refers to ‘Perioperative acute myocardial infarction associated with non-cardiac surgery’†, by N.R. Smilowitz et al., on page 2409. Approximately 300 million patients undergo major non-cardiac surgery (NCS) per year. NCS may be associated with cardiovascular complications, and it is important that the Heart Team (in this case mainly anaesthesiologists, surgeons, and cardiologists) work to minimize the risk to patients by optimizing preventive strategies, early diagnosis, and treatment of such complications.1 , 2 A major issue in patients undergoing NCS is the occurrence of acute perioperative myocardial infarction (MI), and several mechanisms are important: (i) a mismatch in the supply–demand ratio of blood flow in response to metabolic demand due to a coronary artery stenosis that may become flow limiting by perioperative haemodynamic fluctuations (type 2 MI); (ii) acute coronary syndromes (ACS) due to stress-induced rupture of a vulnerable atherosclerotic plaque in combination with vascular inflammation and altered vasomotion, as well as changes in haemostasis; and (iii) development of acute stent thrombosis often in part due to interruption of antiplatelet therapy.1 , 3 In this issue of the journal, Smilowitz and co-workers4 evaluated trends in perioperative MI, management, and outcomes following NCS in the USA between 2005 and 2013. They report the incidence and outcome of acute MI in 9 566 277 hospitalizations for major NCS using registry data from the United States National Inpatient Sample. Perioperative acute MI occurred in 84 093 (0.9%) and was most frequent in patients undergoing vascular (2.0%), transplant (1.6%), and thoracic (1.5%) surgery. In-hospital mortality was much higher in patients with perioperative MI than in those without MI (18.0% vs. 1.5%). Over time, the rate of perioperative acute MI per 100 000 surgeries declined by 170, from 898 in 2005 to 729 in 2013 (P for trend <0.0001) and the mortality associated with perioperative acute MI also decreased over time. In a propensity-matched cohort of 34 650 patients with perioperative acute MI, invasive management was associated with lower mortality than conservative management (8.9% vs. 18.1%). The diagnosis of acute MI as well as the included surgical procedure were based on routine ICD (International Classification of Diseases) diagnosis. The external validity appears to be high. Of note, only patients older than 45 years of age were included, and patients who underwent cardiac procedures, bone marrow transplantation, ophthalmologic surgery, radiation therapy, dental surgery, and non-operating room procedures were excluded from the analysis. The incidence of perioperative MI of 0.9% signals a very large health problem. Further, the reported rate in this observational study relied on clinical routine diagnosis of MI being reported to registries, and the true incidence may thus be higher. There was a trend towards a slight decrease in the perioperative MI rate during the study years, and this was in particular reported for ST-elevation MI where the incidence declined from 261 to 116 per 100 000 operations during 2005–2013. This trend was noted in both women and men. It might in part be due to the general trend of a decrease in the incidence of ST-elevation MI in the western world,5 but may also be due to optimization of perioperative care. The percentage of patients with perioperative MI undergoing coronary interventions increased during the study period, and this group of patients had a better prognosis. As for other patients with MI, it appears intuitively understandable that visualization of the coronary arteries may identify stenoses or occlusions that, if treated, may improve prognosis.6 , 7 This calls for a timely evaluation with coronary arteriography and revascularization, when relevant, in patients with perioperative MI. It cannot be ruled out that a better prognosis for patients with perioperative MI undergoing coronary intervention in part may be due to improved medical therapy. Optimizing anti-ischaemic, anti-thrombotic, and anticongestive treatment as well as providing cardiovascular advice and counselling are important in these patients.1 , 2 Medical therapy that might prevent cardiovascular complications and in particular perioperative MI has been much in focus during the last decades. Beta-blockers have been evaluated in registries and in clinical randomized trials, and have been shown to reduce perioperative MI, but, on the downside, to increase stroke.1 , 2 , 8 The current recommendations are to continue beta-blockers in patients that already receive this therapy. In patients with high risk of perioperative MI, it may be considered to initiate beta-blockers pre-operatively.1 , 2 Low-dose aspirin has also been investigated in this context. The large randomized POISE-2 trial showed no benefit of aspirin in preventing perioperative MI and caused an increase in bleeding.9 Continuation of aspirin in patients already receiving this drug may be considered in the perioperative period, and should be based on an individual decision that depends on the perioperative bleeding risk weighed against the risk of thrombotic complications.1 Importantly, patients with coronary drug-eluting stent implantation should continue aspirin unless the specific operation contraindicates platelet inhibitors.1 , 10 , 11 The risk of perioperative cardiovascular complications depends on the condition of the patient before surgery, the prevalence of co-morbidities, and the urgency, magnitude, type, and duration of the surgical procedure.12 , 13 The report by Smilowitz et al. 4 confirms that acute surgery is associated with a high risk of perioperative MI. Vascular, thoracic, and transplantation surgeries were also associated with a high risk of perioperative MI, and this is in accordance with the current ESC Guidelines suggesting that these procedures, and also high-risk abdominal surgery, are associated with a high risk of cardiovascular complications.1 The study also showed that patients who had been treated with percutaneous coronary intervention are at high risk of perioperative MI. The vast majority of these patients had been treated with coronary stent implantation, and potential stent malapposition or delayed endothelial coverage of the stent make the issue of appropriate antiplatelet therapy more important due to the risk of stent thrombosis. Recent studies have shown that the risk for perioperative MI is high within the first month after stenting,11 – 13 and surgery should be avoided in this period. However, between 1 and 12 months after drug-eluting stent implantation, the risk of 30-day perioperative MI and death was similar to a matched background population without known ischaemic heart disease.13 Moreover, interruption of both the P2Y12 inhibitor and aspirin has been associated with an increased risk of perioperative MI in some10 , 11 but not all studies.12 , 14 Importantly, however, none of the studies could show any benefit of continuing dual antiplatelet therapy.11 , 12 , 14 Since most surgeons and cardiologists consider continuation of dual antiplatelet therapy as a relative contraindication in relation to major NCS, P2Y12 inhibitors should be paused for 3–7 days, but aspirin should be continued.1 Patients with low functional capacity and co-morbidities such as lung disease, diabetes, and renal failure also have an increased risk of complications during NCS. The NSQIP and Lee risk index K provide complementary prognostic perspectives and can help the clinician in the decision-making process.1 The ESC Guideline recommends use of these scoring systems for evaluation of cardiovascular risk, in particular for complex patients, when high- and intermediate risk NCS is planned. In high-risk patients more thorough cardiac examinations are recommended before NCS.1 Biomarkers for evaluation of risk related to NCS may be an important tool for identifying high risk patients planned for NCS. Troponin (Tn) and BNP plasma levels have been measured prior to and after surgery, and have additional prognostic value for long-term mortality and for cardiac events after major non-cardiac vascular surgery.15 , 16 Recently, the VISION study showed that among 21 842 patients undergoing NCS, peak post-operative high sensitivity TnT (hs-TnT) during the first 3 days after surgery was significantly associated with 30-day mortality.17 Elevated post-operative hs-TnT in patients without an ischaemic feature was also associated with 30-day mortality.17 In this important study, patients had hs-TnT measurements 6–12 h after surgery and daily for 3 days. In summary, perioperative MI in patients undergoing NCS is a common and potential devastating problem. Even though this twilight zone between surgery and cardiology is getting brighter, we must continue to shed more light on this issue. Studies on new diagnostics and scoring systems that can help us to identify high-risk patients, and randomized trials evaluating new and old antithrombotic and cardioprotective drugs, are greatly needed in order to improve patient outcome. Conflict of interest: none declared.