Myocardial Infarction• Most common diagnosis in hospitalised patients.• Mortality rate 30%• Mortality rate after admission reduced by 30%• Worldwide mortality , 12 million deaths occur each year due to CVD.
DEFINITION• Irreversible necrosis of cardiac muscles secondary to prolonged ischemia.• Usually results from an imbalance of oxygen supply and demand.• Appearance of cardiac enzymes in the circulation generally indicates MI
Pathogenesis• MI occurs when there is a abrupt reduction reduction in coronary blood flow following a thrombotic occlusion of a coronary artery previously narrowed by artherosclerosis.• Infarction occurs when a coronary artery thrombus develops rapidly at a site of vascular injury.• This injury can be produced by: Hypertension Lipid accumulation Cigarette smoking• Rupture of an atherosclerotic plaque.
Stages of development of atherosclerosis.• Deposition of cholesterol beneath endothelium coronary arteries)• Invasion by fibrous tissue.• Necrotic stage.• Stage of calcification• Atherosclerotic plaque.
Severity of MI• Depends on 3 factors.• 1. The level of occlusion.• 2. the length of time of occlusion.• 3. The presence or absence of collateral circulation.
Precipitating factors• Vigorous physical exercise• Medical or surgical illness.• Emotional stress.
Risk factors• Age• Male sex• Family history of IHD.• Smoking• Hypertension.• Diabetes mellitus.• Hyperlipidemia.• Obesity.• Sedentary life style.
Risk of MI in cancer Patients• Hyper viscosity syndrome in malignancies(Lymphoprolipherative and myeloproliferative disorders).• Cardio toxic drugs (adriamycin , Daunorubicin)• Paraneoplastic syndromes as thromboembolism.• Anti oestrogen• Anaemia in malignancy.• RT to chest.
ECG changes that mimic MI Preexcitation syndromes• Pericarditis.• Pulmonary embolism.• Cardiomyopathy.• COPD.• Acute aortic dissection.• Acute cholecystitis(inferio ST elevation).
Cardiac enzymes Creatine kinase• CK-MB• CK-MM• CK-BB Non cardiac sources of Creatine kinase• Muscular disease including muscular dystrophy myopathes and polymyositis.• Electric cardio version.• Cardiac catheterisation.• Hypothyroidism.• Surgery.• Skeletal muscle damage secondary to trauma.• Convulsion.
Cardiac Troponins(cTnT, cTnI)• Have greater sensitivity and specificity for myocardial injury than those for CK-MB. Significance• In postoperative period.• Pt who present late 4 days after MI. Lactate dehydrogenise• LDH1/ LDH2 ratio>1.0 is consistent with MI.
Other non-invasive techniques• ECHO• Coronary angiography.• Left ventriculography.
Management1. Oxygen supply.2. Analgesia.• To reduce level of circulating catecholamine and reduce myocardial oxygen consumption.• 3. Sublingual nitro glycerine Given in the absence of• Hypotension systolic BP<90)• Sinus tachycardia (HR>110)• Excessive bradycardia (HR<50)• Inferior infarction complicated by RV infarction 4. Anti platelet therapy with aspirin• reduces mortality in patients with MI
• 5) Anticoagulation with heparin.• To maintain APTT of 1 ½ to 2 times of control.• 6) B- Adrenergic antagonists.• Should be avoided if:• a) HR <60• b) Systolic BP<90• c) Advanced heart block• d) Bronchial asthma• e) Peripheral vascular disease.
Acute coronary reperfusion• 90% of patients with acute MI and ST elevation have complete thrombotic occlusion of infarct related coronary artery.• Early restoration of perfusion reduces infarct size and reduce mortality
Indication for thrombolysis• Presentation within 12 hours of chest pain with:• a) ST elevation >2mm in 2 or more chest leads.• b) ST elevation >1mm in two or more limb leads.• c) new onset LBBB.• d) Posterior infarction (dominant R waves ST depression in V1_V3)
Contraindication (absolute)• Active bleeding.• surgical procedure within last 10 days.• Neurosurgical procedure within last 2 months.• Stroke/ TIA within last 12 months.• H/O CNS tumor, aneurysm or AVM.• Acute Pericarditis• Aortic dissection.• Active peptic ulcer disease.• Defective haemostasis.• Pregnancy.
Specific thrombolytic agents• I) Streptokinase: non selective fibrinolytic agent• Given in infusion 1.5 million units in 60 minutes.• 2) Recombinant tissue-plasminogen activator• More selective with no allergic reaction.• This agent results in 80% patency of infarct related artery in 90 min.•
Complications• Bleeding• ICH• Pt with persistent chest pain and St elevation at 60-90 min after thrombolytic therapy need urgent coronary angiography and rescue PTCA Other Indications for PTCA• a) C/I to thrombolytic therapy.• b) cardiogenic shock.• c) Increased risk of ICH.• d) Previous CABG.