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Myocardial infarction


   - Myocardial infarction is myocardial necrosis occuring as a result of a critical imbalance betn coronary blood supply and myocardial demand
   - Usualy due to atheromatous thrombus in coronary artery.
   - Hypercoagulable state in youngs result in MI
   - Use of cocain is another cause of MI. Cocain produces hypercoagulable state an dvasospasm of coronay arteries

Clinical features:
Syptoms:
1) chest pain is cardinal symptom. It is at the left chest and medial aspect of the left arm. severe and prolonged, described as tightness, heaviness or constriction.
2) other are breathlessness, syncope, vomiting and extream tiredness
  - pain may b absent in some pts

Signs:
Mild fever
Pallor, sweating
Tachycardia or bradycardia
Arrythmias
Narrow pusle pressure
Raised JVP
Diffuse apical impulse
Soft first h sound
Third h sound
Pericardial friction rib
Systolic murmur
Basal crepitations
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Complications:
 A) arrythmias
     - sinus bradycardia, sinus tachycardia
     - atrial trachycardia, atrial fibrillation
     - ventricular ectopic beats
     - ventricular tachycardia, ventricula fibrillation
     - heart blocks
     - acclerated idioventricular rhythm
 B) cardiogenic shock
     - may b caused by arrythmias, excessive               diuretic therapy
     - may b due to extensive myocardial damge
 C) other
     - cardiac failure
     - infarction papillary muscle--mitral regurgitation
     - pulmonary oedema
     - interventricular septum rupture
     - cardiac tamponade
     - cerebral and peripheral embolism
     - deep vein thrombosis
     - ventricular aneurysm
     - Dressler's syndrome--autoimmine reaction to necrosed muscles--fever, pericarditis, pleurisy--Rx is NSAIDs and corticosteroids

Investigations:
1) electrocardiogram
     -typical changes seen
     - ST elevation > 1-2 cm
     - pathological Q waves
     - rarely MI T waves may become tall and               peaked. These r transient.
     - appearance of a new left bundle branch block

2) plasma enzymes
  - creatinine kinase (CK)
  - aspartate aminotransferase (AST)
  - lactate dehydrogenase (LDH)
  - myoglobin
  - troponins (cardiac specific)
* CK starts to rise at 4-6 hrs, peak at 12 hrs, fall     to normal by 48-72 hrs
* AST rise by 12 hrs, peak on 1st or 2nd day
* LDH rise aft 12 hrs, peak by 2-3 days, remain        elevated for a week
* myoglobin rises within 2-6 hrs and remains for       7-12 hrs
* cardia troponins remains elevated for 100-200 hrs
   Useful in pts presenting late

3) other investigations
    -leucocytosis
    -raised ESR
    -elevated C reactive protein
    -chest radiography- pul oedema
    -radionucleotite scanning
    - echocardiography

Management
1) initial rx:
  - attach a cardia monitor
  - iv line
  - oxygen
  - sublingual nitrate
  - iv morphine 3-5 mg along with antiemits
  - aspirin 150 mg, clopidogrel 300 mg
2) confirm diagnosis
  - ECG
3) specific rx
  - thrombolysis
  - iv beta blocker
  - rx complication like arrythmia, ccf, shock
  - admit in icu

Oxygen:
    Admister oxygen in suspected MI
Nitrates
    Nirates reduce o2 demand of myocarium.
    Iv nitrogycerine is given
Control of pain
    Morphine 3-5 mg iv every 10-15 min along with        antiemitics
    Morphine also reduce preload
Antiplatelet agents
    Aspirine and clopidogrel
Beta blocker
    Decreases O2 demand by decreasing bld              pressure and heart rate
    Given orally or iv, metoprolol and esmolol
Calcium chaneel blocker r not recommanded
ACE inhibitor
    Improves myocardial fucn by reducin myocardial     remodeling
    Givn within 24 hrs
    Intially short acting captopril 12.5 mg given
    Dose may be increase upto 25 mg 8 hrly
Thrombolytic theorapy
    Steptokinase, urokinase and recombinant plasma     activator (altiplase)
    Leads to generation of plasmin which lyses clot

Prophylactic anticoagulants:
   - low dose heparine 5000 units twice daily SC to prevent DVT and pulmonary embolism

per cutaneous coronary interventions
   - angioplasy or stent placement in coronary           artery
   - indicated in cardiogenic shock and presence of containdications to thrombolytic therapy

Coronary artery bypass grafting:
   - benifit in pts with acute MI with persistant pain or deteriorating haemodynamic status

Management of RV infarction
  - volm expansion is the initial rx
  - inotropic vasodilators may b required
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Management of complications
 (1) arrythmia
      - pain relief, reassurance, rest
      - correction of hypocalemia
      - manage CCF
      - lignocain aftr resuscitation
      - DC cordivesion is Rx for ventricular                   fibrillation
      - varapamil, diltiazem, ismolol or digoxin is used to treat atrial trachycardia, fibrillation and flutter
      - atropin used to rx symptomatic sinus bradycardia and heart block
      - temporary pacemaker in heart block complicating inferior wall MI
 
 (2) cardiogenic shock
      - treated by iv fluids

 (3) aftercare and rehabilitation
     - contol of obeysity
     - exercise
     - cesation of smoking
     - control of lipids by diet and drugs

 (4) medications
     - aspirin 75-100 mg daily
     - clopudogrel 75 mg daily upto 12 months
     - beta blockes unless contraindicated continued indefinately
     - ACE inhibitors given early aft acute coronary syndrome
     - statin therapy for all pts of CHD
     - nitrates for chest pain
     - warfarin for those at high risk of thromboem

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