ACUTE MYOCARDIAL INFARCTION


Definition:

  • Myocardial infarction is myocardial necrosis occurring as a result of a critical imbalance between coronary blood supply and myocardial demand.
  • Usually due to atheromatous thrombus in coronary artery.
  • Hypercoagulable state in youngs result in MI.
  • Use of cocaine is another cause of MI. Cocaine produces hypercoagulable state on the vasospasm of coronary arteries.

Clinical features:

Symptoms:

  • 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.
  • Other are breathlessness, syncope, vomiting and extreme tiredness.
  • Pain may be absent in some patients.

Signs:

  • Mild fever
  • Pallor, sweating
  • Tachycardia or bradycardia
  • Arrhythmias
  • Narrow pulse pressure
  • Raised JVP
  • Diffuse apical impulse
  • Soft first heart sound
  • Third heart sound
  • Pericardial friction rib
  • Systolic murmur
  • Basal crepitations
  • Complications:

A) Arrhythmias

  • Sinus bradycardia, sinus tachycardia.
  • Atrial tachycardia, atrial fibrillation.
  • Ventricular ectopic beats.
  • Ventricular tachycardia, ventricular fibrillation.
  • Heart blocks.
  • Accelerated idioventricular rhythm.

B) Cardiogenic shock

  • May be caused by arrhythmias, excessive diuretic therapy.
  • May be due to extensive myocardial damage.

C) Other

  • Cardiac failure.
  • Infarction papillary muscle-mitral regurgitation.
  • Pulmonary edema.
  • Interventricular septum rupture.
  • Cardiac tamponade.
  • Cerebral and peripheral embolism.
  • Deep vein thrombosis.
  • Ventricular aneurysm.
  • Dressler’s syndrome- autoimmune reaction to necrosed muscles- fever, pericarditis, pleurisy- treatment 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 are 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
  • Cardiac troponins remains elevated for 100-200 hrs
  • Delayed presentation.

3) Other investigations

  • Leukocytosis
  • Raised ESR
  • Elevated C reactive protein
  • Chest radiography- pulmonary edema
  • Radionuclide scanning
  • Echocardiography.

Management:

  •  1) Initial treatment:
  • Attach a cardiac monitor
  •  IV line
  •  Oxygen
  •  Sublingual nitrate
  •  IV morphine 3-5 mg along with antiemitics
  •  Aspirin 150 mg, Clopidogrel 300 mg

    2) Confirm diagnosis
  •  ECG
    3) Specific treatment
  •  Thrombolysis
  •  IV beta blocker
  •  Treatment complication like arrhythmia, CCF, shock
  •  Admit in ICU
  • Oxygen:
  • Administer oxygen in suspected MI.
  • Nitrates:
  • Nitrates reduce oxygen demand of myocardium.
  • IV nitroglycerine is given.
  • Control of pain:
  • Morphine 3-5 mg IV every 10-15 min along with antiemetics.
  • Morphine also reduce the preload.
  • Antiplatelet agents.
  • Aspirin and clopidogrel.
  • Beta blocker:
  • Decreases oxygen demand by decreasing blood pressure and heart rate.
  • Given orally or IV, metoprolol and esmolol.
  • Calcium channel blocker are not recommended.

ACE inhibitor:

  • Improves myocardial function by reducing myocardial remodeling.
  • Given within 24 hrs.
  • Initially short acting captopril 12.5 mg is given.
  • Dose may be increase up to 25 mg 8 hourly.
  • Thrombolytic therapy:
  • Streptokinase, urokinase and recombinant plasma activator (alteplase).
  • Leads to generation of plasmin which lysis clot.
  • Prophylactic anticoagulants:
  • Low dose heparin 5000 units twice daily SC to prevent DVT and pulmonary embolism.
  • Per cutaneous coronary interventions:
  • Angioplasty or stent placement in coronary artery.
  • Indicated in cardiogenic shock and presence of contraindications to thrombolytic therapy.
  • Coronary artery bypass grafting:
  • Benefit in patients with acute MI with persistent pain or deteriorating hemodynamic status.
  • Management of RV infarction
  •  Volume expansion is the initial treatment.
  •  Inotropic vasodilators may be required.
  • Management of complications

(1) Arrhythmia

  • Pain relief, Reassurance, Rest
  • Correction of hypokalemia
  • Manage CCF
  • Lignocaine after resuscitation
  • DC cardioversion is treatment for ventricular
  • Fibrillation
  • Verapamil, Diltiazem, Esmolol or Digoxin is used to treat atrial tachycardia, fibrillation and flutter.
  • Atropine used to treat 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

  • Control of obesity.
  • Exercise.
  • Cessation of smoking.
  • Control of lipids by diet and drugs.

(4) Medications

  • Aspirin 75-100 mg daily.
  • Clopidogrel 75 mg daily up to 12 months.
  • Beta blockers unless contraindicated , can be continued.
  • ACE inhibitors given early after acute coronary syndrome.
  • Statin therapy for all patients of CHD.
  • Nitrates for chest pain.
  • Warfarin for those at high risk of thromboembolism.