Myocardial Infarction

Pathophysiology 90% caused by artherosclerosis nonatherosclerotic  in younger patients: infected cardiac valve through a patent foramen ovale (PFO), coronary occlusion secondary to vasculitis, primary coronary vasospasm (variant angina), cocaine use, or other factors leading to mismatch of oxygen supply and demand, as may occur with a significant gastrointestinal bleed.

Epidemiology 5/1000 per year for ST segment elevation African American, Hispanic, and white populations in the United States. male, age 70 years when the sexes converge to equal incidence. Premenopausal women appear to be somewhat protected from atherosclerosis, possibly owing to the effects of estrogen. Incidence increases with age. Most patients who develop an acute myocardial infarction are older than 60 years. Elderly people also tend to have higher rates of morbidity and mortality from their infarcts.

Risk Factor Non modifiable: age, gender, family history Modifiable: smoking, hypertension, DM,, hyperlipidaemia, obesity, sedentery lifesyle Controversial: stress, type A personality, ↑ of apoprotein A & fibrinogen, hyperinsulinaemia, homocystein, ACE genotype, cocaine

Presentation acute central chest pain > 20min ass with sweatiness, nausea, SOB, palpitations. Silent infarct in elderly and diabetics- syncope, pulmonary oedema, epigastric pain and vomiting, post-op hypotension, oliguria, acute confusional state, stroke, diabetic hyperglyceamic state distress, anxiety, pallor, pulse and BP ↑ or ↓, S4, sign of heart failure (↑  JVP, S3 and basal crepitations) or a pansystolic mumur (papillary muscle dysruption, rupture) low grade pyrexia later: pericardial rub or peripheral oedema

Diagnostic criteria WHO criteria: 2 out of 3 Typical history of ischaemic type chest pain lasting for more than 20 minutes Changes in serial ECG tracings Rise and fall of serum cardiac biomarkers such as creatine kinase-MB fraction and troponin + typical symptoms, pathological Q waves, ST elevation or depression or coronary intervention are diagnostic of MI.

Investigation

ECG	hyperacute (tall) t waves, ST elevation or new LBBB within hours of acute Q wave (transmural infarction). T wave inversion and development of pathological Q wave follows over hours to days. St depressiion, T inversion, non-specific changes, or normal normal in 20% of MI
CXR	Cardiomegaly, pulmonary odema, widened mediastinum (?aorta dissection)
Blood	FBC, U&E, glucose ↑, lipids ↓,
Cardiac enzyme	(CK, AST, LDH, troponin) ↑, CK is found in myocardial and skeletal muscle: ↑ in MI, after trauma, prolonged exercise, myositis, afro-carribeans, hypothermia, hypothyroidism Check CK-MB isoenzyme levels if there is doubt as to the source (normal CK-MB:CK ratio <5%) Troponin T better shows MI (peaks at 12-24H, elevated for >1wk) If normal >6h after onset of pain, and ECG normal, risk of  missing  MI is tiny (0.3%). peak post MI levels also help risk stratification.

Differential Diagnosis Angina, pericarditis, myocarditis, aortic dissection, pulmonary embolism, PE, oesophageal reflux

Management

Pre-hosp

MONA Arrange emergency ambulance. Oxygen, (12-15L) Aspirin 300MG chewed and GTN sublingual Analgesia (morphine 5-10mg IV + metoclopramide 10mg IV (not IM- risk of bleeding)

Hospital

Morphine, O2, Aspirin, IVI

check for ST elevetaion

ST-segment elevation

No ST segment elevation

Thrombolysis or primary angioplasty B-blocker eg. atenolol 5mg IV ACEi (eg lisinopril 2.5mg) start in all normotensive pt within 24h of acute MI, especially if there is clinical evidence of heart failure or echo evoidence of LV dysfunction

B-blocker eg. atenolol 5mg IV LMWH (eg enoxaparin 1mg/kg/12H SC for 2-8d Nitrates High risk pt (persistent or recurrent ischaemia, ST depression, diabetes, ↑troponin) require infusion of GPIIb/IIIa antagonist (eg tirofiban) and ideally urgent angiography. Aspirin + copidogrel considered for up to 12 months. Low risk pt (no further pain, flat or inverted T waves, or normal ECG and negative troponin) can be discharged if a repeat troponin is negative. Treat medically and arranged for stress test, angiogram ect.

Contraidication for thrombolysis

Absolute Previous intracranial bleeding at any time, stroke in less than 3months,closed head or facial trauma within 3 months,suspected aortic dissection ,ischemic stroke within 3 months(except in ischemic stroke within 3hours time), active bleeding diathesis, uncontrolled high blood pressure (>180 systolic or >100 diastolic),known structural cerebral vascular lesion viz av malformations. Relative Current anticoagulant use, invasive or surgical procedure in the last 2 weeks, prolonged cardiopulmonary resuscitation (CPR) defined as more than 10 minutes, known bleeding diathesis, pregnancy, hemorrhagic or diabetic retinopathies, active peptic ulcer, controlled severe hypertension

Subsequent management: bed rest for 48H, continuous ECG monitoring Daily examination of heart, lungs and legs complications Daily 12-lead ECG, U&E, cardiac enzymes for 2-3d Prophylaxis against thromboembolism, eg heparin 5000u/12h, until,fully mobile. If large anterior MI, consider warfarin anticoagulation for 3months as prophylaxis against systemic embolism from LV mural thrombus. Continue daily low-dose aspirin (75-150mg) -reduce vascular events (MI, stroke, vascular death) by 29% oral B-blocker (metoprolol 50mg/6h decrease pulse <60, continue for at least 1 year. Long term- reduce mortality by 25% in pt who had previous MI. If CI: verapamil or diltiazem ACEi in all pt ↓ 2y mortality by 25-30% Statin - ↓ cholesterol for all pt or if total cholesterol >4mmol/L discourage smoking, encourage exercise, treat DM, HTN and hyperlipidaemia exercise EC: in risk stratification 3-4wk post MI, in non STEMI or troponin rise if uncomplicated : discharged after 5-7d. Return to work after 2M, x start post MI: airline traffic, divers. Lighter jobs. Diet: oily fish, veg, fibre, low in saturated fat. Exercise. Avoid sex for 1 month, avoid air travel for 2 months Review symptoms at 5wks Review at 3 months: check fasting lipids

Complications Cardiac arrest Unstable angina bradycardia or heart block Tachyarryhtmias LVF/RVF Pericarditis DVT, PE, systemic embolism Cardai tamponade Mitral regurgitation, VSD Late malignant ventricular arryhtmias Dressler's syndrome – recurrent pericarditis Left ventricular aneurysm

Mortality

50% deaths occur within 2h onset of symptom