Myocardial infarction March 2018 | by EMauthor
The clinical classification of MI: •Type 1: Spontaneous MI related to ischaemia due to a primary coronary event such as plaqueerosion and/or rupture, fissuring, or dissection. •Type 2: MI secondary to ischaemia due to increased oxygen demand or decreased oxygen supply (e.g. coronary spasm, coronary embolism, anaemia, arrhythmias, hypertension). •STEMI — the thrombus completely occludes the lumen of the artery resulting in progressive necrosis of myocardium. The ECG shows acute ST-segment elevation. •Non-ST segment elevation myocardial infarction (NSTEMI) — the volume of thrombus is insufficient to occlude the artery or does so only temporarily. There is some myocardial necrosis, evidenced by a rise in cardiac biomarkers and often non-specific ECG abnormalities (e.g. ST-segment depression or T-wave inversion). Clinical features In the textbooks there is central chest tightness or heaviness. It may radiate to one or both arms, the neck, jaw or teeth. Don't get too obsessed with this presentation--it is becoming increasingly clear that atypical presentations are often overlooked. Also remember from above that 'symptoms of ischaemia' is one of only four features required to define an MI along with positive biomarkers. Atypical presentations include •Sudden shortness of breath which can manifest in the extreme as acute left ventricular failure •Pain in the arms, jaw, back, epigastrium or abdomen •Indigestion, even if relieved by antacids •Profound fatigue and weakness •Syncope or collapse •Acute confusion in the elderly Focused physical examination, including vital signs, general state of the patient, chest and heart examination and state of peripheral perfusion. This will more often than not be normal in acute MI. Investigations •Chest radiograph is useful in ruling out other causes of symptoms and examining the mediastinal width especially if intending to give Fondaparinux •Main basic description of ECG changes (best explained hands-on) oST segment elevation with reciprocal ST segment depression = STEMI oTall wide T wave (hyper-acute T wave, may become a STEMI) oNew onset left bundle branch block (STEMI equivalent) oPathological Q waves (more than 1/3 depth of the R wave and more than 0.04 seconds or one small square wide) o(Deep) T wave inversion oLoss of progression of R wave in the chest leads oTall wide R wave with ST depression in lead V1 and V2 (posterior MI) •Localisation of the ECG changes will determine the area of the infarcts oAntero-septal: V1 through to V3 oAnterior: V1 through to V4 oAntero-lateral: V4 through to V6, I and aVL oLateral: I and aVL oInferior: II, III, and aVF oInfero-lateral: II, III, aVF, V5 and V6 •Will need serial ECGs •If you have an interest in echocardiography then by all means scan, preferably with the assistance of a consultant or interested colleague, but obviously don't rule anything out based on a bedside scan. •We use a highly-sensitive cardiac troponin T assay in the trust which rises within hours (see the section on ROACS) which will usually have been drawn from the patient at triage. You only have to wait the result if it will change your management. Examples of when you do not have to wait for troponin result: oThe symptoms are suggestive of at least unstable angina in any case oThe sample has been drawn within about 2 hours of the patient's symptoms Initial treatment of NSTEMI •If SaO2 <90% or breathless, low flow O2 •Cardiac monitor •After screening for contraindications, give aspirin 300 mg and clopidogrel 300 mg oIf CXR normal and ongoing pain give fondaparinux 2.5 mg. •Morphine 2.5–10mg IV + metoclopramide 10mg IV •Pain can be controlled by GTN infusion (50 mg in 50 mL saline 0-10 mL per hour) •We usually hold beta blockers until the patient is admitted •Discuss with cardiology registrar in the CTC if oIncreasing GTN requirements oOngoing dynamic ECG changes oOther concerns e.g. recent discharge from CTC Initial treatment of STEMI •Cardiac monitor •Aspirin 300mg (unless already given by GP/paramedics) •Morphine 2.5–10mg IV + anti-emetic, eg metoclopramide 10mg IV •Fax ECG to PPCI hotline and discuss with cardiology SpR who will send the CNS to retrieve the patient Key point: remember to counsel the patient on the differential diagnosis and his / her treatment, including reporting side effects such as bleeding, which is a risk. Document that you have done this. Targets for STEMI NICE Guidelines •Do not use CGS or cardiogenic shock caused by suspected acute STEMI to determine whether a person is eligible for PCI •Offer coronary angiography for people with acute STEMI if: oPresentation < 12 hours of onset of symptoms and oPrimary PCI can be delivered within 120 minutes of the time when fibrinolysis could have been given. Myocardial infarction RCEM reperfusion standards: •Door to ECG 10 min •Door to Needle 30 min •Call to Needle 60 min •Aspirin given
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