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Diagnosis Am i



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  Diagnosis  A combined task force of major professional societies revised the definition of myocardial infarction in 2012 to reflect any event leading to myocardial ischaemia causing cardiac myocyte cell death, and suggested myocardial infarction be classified by its pathological cause into five types (Thygersen, 2012). In each case, the diagnosis of myocardial infarction relies on biomarker evidence of myocyte necrosis, and either electrocardiographic (ECG) criteria of ischaemia or infarction, or ischaemic symptoms, or both (Stone, 2014). Cardiac troponin (cTn) isoforms I and T have emerged as the preferred diagnostic biomarkers, because they are highly sensitive and specific for myocardial injury, detectable within 2−3 h, and peak within 24−28 hours (Morrow, 2007). The advent of high-sensitivity cardiac troponin T (hs-cTnT) has led to a 20% increase in the diagnosis of NSTEMI and concomitant reduction in the diagnosis of unstable angina (Roffi, 2016). The 2015 European Society of Cardiology (ESC) NSTE-ACS guidelines embrace using the change in hs-cTnT within 1 or 3 h to rule out NSTEMI where applicable. Although beyond the scope of the present review, when used in conjunction with ECG findings and overall clinical presentation, the negative predictive value for myocardial infarction in patients with hs-cTnT below the upper limit of normal on two consecutive checks at least 1 h apart might approach 98%, with a positive  predictive value of 75−80%  (Roffi, 2016). Although available in Europe, the hs-cTnT assays have yet to be approved in the USA. Creatine kinase myocardial band (CK-MB) follows similar kinetics as cTn; although a CK-MB to total CK ratio of 2·5% or more is specific for myocardial injury, it is relatively insensitive for detecting small myocardial infarctions, and both European and US guidelines emphasise the use of cTn as the preferred biomarker for diagnosis of acute myocardial infarction (Jneid, 2012). A limitation of cTn is that it can remain in the circulation up to for 7−10 days, or   longer in patients with renal failure. Thus, early ischaemic events might not be detected with serial cTn unless cTn is falling and subsequently rises again, or stays persistently elevated despite an expected fall. Although CK-MB can be used to detect recurrent myocardial injury, this might miss small repeat infarctions, because it is not as sensitive as cTn. Risk Assessment  Early risk stratification of patients with myocardial infarction allows for prognostication and triage via initiation of one of several vital treatment pathways. Several clinical prediction scores estimate short-term and long-term risks of recurrent ischaemic events and death after myocardial infarction. The TIMI risk score is easiest to use, whereas GRACE is more accurate, comprehensive, and applicable to both NSTEMI and STEMI (de Araújo, 2005). Dedicated STEMI risk scores also exist, but they largely predict death and are less used in clinical practice. Additionally, biomarkers such as C-reactive protein and B-type natriuretic peptide could help to further risk-stratify patients at intermediate risk. However, these biomarkers have yet to be incorporated into large, strategy-based studies. There are currently no guideline-approved treatment pathways based on any biomarker other than cTn.    Reperfusion and revascularisation strategies General principles In NSTEMI, antithrombotic therapy is thought to stabilise the vulnerable plaque and allow endogenous fibrinolysis to restore patency (Kumar, 2009). Percutaneous coronary intervention (PCI) is usually pursued to improve blood flow and prevent recurrent ischaemia. PCI should  be done within 24 h of NSTEMI if possible, but some studies suggest that PCI could be done in low-risk  patients up to 48−72 h without clinical consequence  (Cannon, 2001). However, doing PCI after 24 h has been associated with longer hospitalisation (Montalescot, 2009), which could increase costs, therefore reducing quality of care. Conversely, in STEMI, priority should be given to immediate reperfusion to limit infarct size, and antithrombotic therapy is used adjunctively (Steg, 2012). Similarly, patients with NSTEMI and high-risk features or elevated risk scores (figure 1) require urgent revascularisation, emphasising the importance of early risk stratification (Amsterdam, 2014). For STEMI, patients usually have complete arterial occlusion, and as such reperfusion is needed to restore patency as quickly as possible (eg, within 60−90 min). Patients who undergo fibrinolysis often have  residual stenosis, and a reduction in this stenosis with subsequent angioplasty or stenting, or both, improves perfusion and prevents acute reocclusion. For NSTEMI, the artery is usually patent but severely stenosed with a ruptured plaque. The goal is to prevent progression of the thrombus to complete occlusion. The timeframe is broader, measured in hours to days, but more immediate if there is active ongoing ischaemic pain or haemodynamic compromise (figure 1, panel 1). STEMI Both US and European guidelines recommend reperfusion therapy be administered as quickly and effectively as possible for STEMI (Windecker, 2014). Several large studies showed that  patients who receive reperfusion more rapidly have a smaller infarct size and lower mortality than those who have a delay in treatment (Cannon, 2000). The reperfusion strategy should be chosen balancing which therapy would most likely completely restore arterial patency in the shortest time.  Primary PCI  First medical contact to time of primary PCI Total ischaemic time should be kept to 120 min or less, and ideally 60 min or less. To achieve this goal, guidelines recommend a first medical contact to time of primary PCI (also known as first medical contact-to-device, or door-to- balloon time) of 90 min or less, because this time correlates with improved morbidity and mortality (Cannon, 2000). For patients just outside of the 90-min time window, results of the PRAGUE-2 and DANAMI-2 trials suggest that transfer to a PCI-capable hospital is safe and decreases mortality c ompared with fibrinolysis,19−21 and is advised if   it can be completed in 120 min or less (Steg, 2012).  Balloon angioplasty versus stenting Stent placement decreases target vessel revascularization and subsequent myocardial infarction compared with balloon angioplasty alone (Nordmann, 2004). Several studies and metaanalyses show that drug-eluting stents (DES) reduce target vessel revascularisation compared with bare-metal stents (BMS),24  –  26 and some studies suggest that DES might also reduce major adverse cardiac events (MACE) in some patients (Menichelli, 2007). Concurrently, the 2014 ESC revascularisation guidelines recommend DES exclusively in patients with acute myocardial infarction (Windecker, 2014). Routine aspiration thrombectomy Two recent trials (TOTAL30 and TASTE31) showed that routine aspiration thrombectomy does not reduce mortality, recurrent myocardial infarction, heart failure, or cardiogenic shock,  but might increase the risk of stroke within 30 days. As such, although catheter-based aspiration thrombectomy can be an effective adjunct therapy during primary PCI, it should be reserved for patients with a large thrombus burden and should not bethe default strategy. Fibrinolysis  Role in the triage of STEMI Thrombolytic agents promote the conversion of endogenous  plasminogen to plasmin, which lyses fibrin and dissolves clots. Fibrinolysis is estimated to reduce mortality by 29% compared with placebo in STEMI (French, 1999). That said, several trials indicate that primary PCI with balloon angioplasty or stenting, or both, should be  preferred to fibrinolysis because PCI more reliably and completely restores perfusion. In a meta-analysis of 23 trials, primary PCI improved short-term major adverse cardiac and cerebrovascular events (MACCE) compared with fibrinolysis (8% vs 14%; p<0·0001), with a  persistent long-term reduction (Keeley, 2003).
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