Acute myocardial infarction: triggers, interventional management, and outcomes

The open artery theory of acute myocardial infarction states that rapid reperfusion of an occluded coronary artery is the most effective therapy for such patients. The evidence is overwhelming: mortality has declined from 15–20% to ∼5–7% in experienced centres. However, reperfusion after prolonged occlusion may also further increase the damage to the myocardium due to oxidative stress, inflow of inflammatory cells, and release of chemokines and cytokines.1 A Current Opinion entitled ‘Targeting reperfusion injury inpatients withST-segment elevation myocardial infarction: trials and tribulations’, by David Garcia-Dorado and colleagues from the Hospital Universitari Vall d’Hebron in Barcelona, Spain addresses and updates this issue.2 As the authors remind us, despite timely reperfusion by primary percutaneous coronary intervention, mortality and morbidity following an acute ST-segment elevation myocardial infarction remain significant, with 5–7% death and up to 20% prolonged or new hospitalization for heart failure at 1 year, particularly in those with large infarcts. Although reperfusion is essential to salvage viable myocardium, the process of restoring blood flow to ischaemic myocardium can by itself induce the death of cardiomyocytes, a phenomenon known as ‘myocardial reperfusion injury’, which is thought to contribute up to 50% of the final myocardial infarct size. Unfortunately, many trials failed to prove the reperfusion hypothesis.3–5 As such, provided the reperfusion injury paradigm is correct, new treatments capable of targeting myocardial reperfusion injury effectively would be required to reduce myocardial infarct size, to preserve left ventricular systolic function, and prevent the heart failure. However, the search for such effective therapies remains challenging either because the right target has not been found yet or because the concept is false. In this consensus article, the authors further discuss the potential reasons underlying the neutral results of recent clinical trials, and explore the future possibilities for reducing myocardial infarct size and improving clinical outcomes in patients with reperfused ST-segment elevation myocardial infarction. Infarctions of any kind commonly lead to left ventricular dysfunction of various degrees.6,7 However, the nomenclature used to describe different states of myocardial dysfunction is poorly defined, which can lead to difficulties in interpreting and applying trial outcomes. In their clinical review entitled ‘Taxonomy of segmental myocardial systolic dysfunction’, Adam Kenneth McDiarmid and colleagues from the University of Leeds in the UK note that the terms ‘viable’ and ‘hibernating’ are commonly applied interchangeably and incorrectly.8 The range and inherent differences between imaging modalities used to define myocardial health and disease add further challenges to a consistent definition. The unexpected results of several large trials have led to renewed discussion regarding the definition of dysfunctional myocardial segments, and drive the need for an appropriate taxonomy. This article aims to define the diverse myocardial pathologies that may affect the myocardium in ischaemic heart disease and cardiomyopathy, and how they may be assessed with non-invasive imaging techniques. Distribution of hospitals’ performance according to the European Society Cardiology; Acute Cardiovascular Care Association quality indicators for acute myocardial infarction (from Bebb O, Hall M, Fox KAA, Dondo TB, Timmis A, Bueno H, Schiele F, Gale CP. Performance of hospitals according to the ESC ACCA quality indicators and 30-day mortality for acutemyocardial infarction: national cohort study using the United Kingdom Myocardial Ischaemia National Audit Project (MINAP) register. See Pages 974–982). Nevertheless, environmental factors such as air pollution and noise13 may still act more consistently as triggers of acute myocardial infarction. Indeed, a growing body of evidence suggests that chronic low-grade inflammation is involved in acute coronary syndromes.14 In a clinical review entitled ‘Climate and environmental triggers of acute myocardial infarction’, Marc J. Claeys and colleagues from the University Hospital Antwerp in Belgium highlight the increased risk of acute myocardial infarction caused by exposure to air pollution and cold temperatures.15 Such risk factors would be of considerable interest as they are a modifiable risk in nature. The current body of evidence about the biological mechanisms linking environmental changes to atherothrombotic events and the impact of climate change on cardiovascular health are discussed. Finally, recommendations for prevention and public policy are presented. Summarized ROC curves on a pervessel basis (from Danad I, Szymonifka J, Twisk JWR, Norgaard BL, Zarins CK, Knaapen P, Min JK. Diagnostic performance of cardiac imaging methods to diagnose ischaemia-causing coronary artery disease when directly compared with fractional flow reserve as a reference standard: a meta-analysis. See Pages 991–998). Although guidelines recommend specific interventions for the management of patients with acute coronary syndromes, their efficacy and safety also depend on the quality of care in individual medical institutions. In their research manuscript, ‘Performance of hospitals according to the ESC ACCA quality indicators and 30-day mortality for acute myocardial infarction: national cohort study using the United Kingdom Myocardial Ischaemia National Audit Project (MINAP) register’, Owen John Bebb and colleagues from the University of Leeds in the UK investigated the application of the European Society of Cardiology Acute Cardiovascular Care Association quality indicators for acute myocardial infarction for the study of hospital performance and 30-day mortality.22 The national cohort study had 118 075 patients from 211 hospitals available within the MINAP registry for the years 2012 and 2013. Overall, 16 of the 20 quality indicators could be calculated. Eleven quality indicators had a significant inverse association with GRACE risk-adjusted 30-day mortality. The association with the greatest magnitude was high attainment of the composite opportunity-based quality indicators in the range of 80–00% as compared with zero attainment with an odds ratio of 0.04. Increasing attainment from low with an odds ratio of 0.42 to intermediate with an odds ratio of 0.15 was also significantly associated with a reduced risk of 30-day mortality. A 1% increase in attainment of this quality indicator was associated with a 3% reduction in 30-day mortality. The quality indicators with the widest hospital variation was ‘fondaparinux received among NSTEMI’ and the least variation was seen with ‘centre organization’, while seven quality indicators had minimal variation. GRACE risk score-adjusted 30-day mortality with a median of 6.7% varied by hospital from 5.4% to 7.9%. Bebb and collegues conclude that 11 quality indicators were inversely associated with 30-day mortality. Increasing patient attainment of the composite quality indicator was the most powerful predictor. A 1% increase in attainment resulted in a 3% decrease in 30-day mortality. Thus, it appears that the ESC quality indicators for acute myocardial infarction are applicable in a large health system and have the potential to improve care and reduce unwarranted variation in death from acute myocardial infarction. This issue concludes with a meta-analysis entitled ‘Diagnostic performance of cardiac imaging methods to diagnose ischaemia-causing coronary artery disease when directly comparedwithfractional flow reserve as a reference standard: a meta-analysis’ by James K. Min and colleagues from the Weill Cornell Medical College in New York.23 The authors determined the diagnostic performance of single photon emission computed tomography, stress echocardiography, invasive coronary angiography, coronary computed tomography angiography, fractional flow reserve derived from coronary computed tomography angiography (FFRCT), and cardiac magnetic resonance imaging, with fractional flow reserve as a reference standard. PubMed and the Web of Knowledge were searched for published articles between 1 January 2002 and 28 February 2015. Twenty-three studies, 3788 patients, and 5323 vessels in which fractional flow reserve was performed were identified. On a per-patient basis, the sensitivity of coronary computed tomography angiography, FFRCT, and cardiac magnetic resonance averaged 90% and were higher than for single photon emission computed tomography with 70%, stress echocardiography with 77%, or invasive coronary angiography with 69%. The highest and lowest per-patient specificity was observed for cardiac magnetic resonance, with 94%, and for coronary computed tomography angiography with 39%. Similar specificities were noted for single photon emission computed tomography, with 78%, stress echocardiography with 75%, FFRCT with 71%, and invasive coronary angiography with 67%. On a per-vessel basis, the highest sensitivity was for coronary computed tomography angiography at 91%, for cardiac magnetic resonance at 91%, and for FFRCT at 83%, with lower sensitivities for invasive coronary angiography with 71% and single photon emission computed tomography with 57%. Per-vessel specificity was highest for cardiac magnetic resonance with 85%, FFRCT with 78%, and single photon emission computed tomography with 75%, whereas invasive coronary angiography reached a lower specificity of 66% and coronary computed tomography angiography a specificity of 58%. The authors conclude that when comparing cardiac imaging modalities directly with fractional flow reserve, cardiac magnetic resonance had the highest performance for diagnosis of ischaemia in patients with coronary artery disease, with lower performance for single photon emission computed tomography and stress echocardiography. Anatomical methods of coronary computed tomography angiography and invasive coronary angiography yielded lower specificity, with functional assessment of coronary atherosclerosis by stress echocardiography, single photon emission computed tomography, and FFRCT improving accuracy. The editors hope that readers of this issue of the European Heart Journal will find it of interest.