Myocardial Infraction

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Myocardial infarction (from Latin: Infarctus myocardii, MI) or acute myocardial infarction (AMI) is the medical term for an event commonly known as a heart attack. It happens when blood stops flowing properly to part of the heart and the heart muscle is injured due to not receiving enough oxygen. Usually this is because one of the coronary arteries that supplies blood to the heart develops a blockage due to an unstable buildup of white blood cells, cholesterol and fat. The event is called “acute” if it is sudden and serious.
Myocardial infarction is the irreversible necrosis of myocardium occurring as a result of critical imbalance between the coronary bloods supply and myocardial demand.

Types of MI:

  1. Transmural: Involve due to full thickness of ventricular wall.
  2. Nontransmural: Involve only the endocardium & adjacent myocardium.

Aetiology: It occurs usually due to formation of occlusive thrombus at a site of rupture of an atheromatous plaque in a coronary artery.

Clinical features:

Symptoms:

  1. Chest pain:
    • Site: Central retrosternal.
    • Severity: Very sever.
    • Onset: Sudden or gradual, usually at rest.
    • Duration: Prolonged (lasts for more than ½ an hour).
    • Character: Tight, heavy, constricting.
    • Radiation: Left shoulder, neck, jaw, left arm, ulnar border of forearm and hand even to epigastrium & back.
    • Relief: Not by rest or vasodilators (GTN),only subside by strong analgesic like morphine.
  2. Associated symptoms:
    • Breathlessness.
    • Restlessness.
    • Anxiety (fear of impending death)
    • Nausea and vomiting.
    • Collapse/syncope.
  3. Symptoms of complication: Heart failure, shock.
  4. Silent MI in elderly and diabetic patients.

Physical signs:

  1. Signs of sympathetic activation:
    • Pallor.
    • Sweating.
    • Tachycardia.
  2. Signs of vagal activation:
    • Vomiting.
    • Bradycardia.
  3. Signs of impaired myocardial function:
    • Hypotension, oliguria, cold peripherals.
    • Raised JVP, Narrow pulse pressure.
    • Third heart sound, Quiet first heart sound.
    • Diffuse apical impulse.
    • Lung crepitations.
  4. Signs of tissue damage: Fever, high ESR.
  5. Signs of complications:
    • Pericarditis.
    • Mitral regurgitation (MR).
    • Arrhythmia.
    • Pansystolic murmur.

Risk factors: Myocardial infarction results from atherosclerosis. Smoking appears to be the cause of about 36% of coronary artery disease and obesity 20%.Lack of exercise has been linked to 7-12% of cases. Job stress appears to play a minor role accounting for about 3% of cases.

Risk factors for myocardial infarction include:z
• Age
• Sex: At any given age men are more at risk than women, particularly before menopause,[38] but because in general women live longer than men ischemic heart disease causes slightly more total deaths in women.
• Diabetes mellitus (type 1 or 2)
• High blood pressure
• Dyslipidemia/hypercholesterolemia (abnormal levels of lipoproteins in the blood), particularly high low-density lipoprotein, low high-density lipoprotein and high triglycerides
• Tobacco smoking, including secondhand smoke
• Short term exposure to air pollution including: carbon monoxide, nitrogen dioxide, and sulfur dioxide but not the ozone.
• Family history of ischaemic heart disease or myocardial infarction particularly if one has a first-degree relative (father, brother, mother, sister) who suffered a ‘premature’ myocardial infarction (defined as occurring at or younger than age 55 years (men) or 65 (women).
• Obesity (defined by a body mass index of more than 30 kg/m², or alternatively by waist circumference or waist-hip ratio).
• Lack of physical activity.
• Psychosocial factors including, low socio-economic status, social isolation, negative emotions and stress increase the risk of myocardial infarction and are associated with worse outcomes after myocardial infarction. Socioeconomic factors such as a shorter education and lower income (particularly in women), and unmarried cohabitation are also correlated with a higher risk of MI.
• Alcohol — Studies show that prolonged exposure to high quantities of alcohol can increase the risk of heart attack.
• Oral contraceptive pill – women who use combined oral contraceptive pills have a modestly increased risk of myocardial infarction, especially in the presence of other risk factors, such as smoking.
• Hyperhomocysteinemia (high homocysteine) in homocysteinuria is associated with premature atherosclerosis, whether elevated homocysteine in the normal range is causal is contentious.

Investigations:

  1. ECG:
    -Earliest changes is usually S-T segment elevation, later on there is diminution of R wave.
    -Pathological Q wave (transmural infraction)
    -Symmetrical T inversion (subendocardial infraction).
    2. Plasma biochemical markers.
    3. Blood TC, DC,ESR,C-reactive protein (CPR): Polymorphonuclear leucocytosis (peak on first day),raised ESR (for several days),elevated CRP (in acute MI)
    4. X-ray chest P/A view: May be pulmonary oedema, may be cardiomegaly pre-existing myocardial damage.
    5. Echocardiography:
    • Assessment of LV and RV function.
    • Detection of complication: VSD, MR, Pericardial effusion.
    6. Others:
    • Radionuclide scanning.
    • Coronary angiogram.
    • Blood sugar.
    • Serum lipid profile ( to assess risk factors).

D/D of chest pain:

  1. Cardiac:
    1. Unstable angina.
    2. Myocardial infarction.
    3. Pericarditis.
    2. Aortic: Dissecting aneurysm of aorta.
    3. Lung/Pleura: Pneumothorax, Pleurisy massive pulmonary embolism.
    4. Oesophageal: Oesophagitis, Oesophageal spasm Mallory Weiss syndrome.
    5. Musculoskeletal: Local tenderness (common), Fractured ribs.

Principles of treatment of MI:

  1. Relief of pain.
  2. Use of thrombolytic drugs.
  3. Prevention & treatment of complication.
  4. Rehabilitation of the patients.
  5. Prevention of recurrence.

Management of (acute MI):

[A]Early management:

  1. Immediate hospitalization (under ICU) and provide facilities for defibrillation.
  2. Absolute bed rest in propped-up position.
  3. Oral Aspirin 300 mg stat then 75-150 mg daily for at least 4 weeks.
  4. Oxygen inhalation (high flow)
  5. Maintain a secured i/v channel with 5% DA.
  6. Analgesics: Inj.Morphine (10-20 mg i/v stat).
  7. Antiemetics: Inj.Prochlorperazine (12.5-25 mg) i/v.
  8. Thrombolytic drugs:
    If patient comes within 6 hours of chest pain:
    a) Inj.Streptokinase:1.5 million units in 100 mg of saline as an i/v infusion over 1 hour or
    b) Alteplase (Human tissue plasminogen activator)
  9. Β-adrenoceptor antagonists: Inj Atenolol or Metoprolol.
  10. Monitoring of ECG.

[B] Late management:

  1. Risk stratification and further investigation:
    a) Left ventricular function: Assessed from physical findings (tachycardia,3rd heart sound, basal creps, elevated venous pressure),ECG changes, heart size on chest X-ray, echo or radionuclide imaging.
    b) Ischemia: ETT 4 weeks after infract, coronary angiography.
    c) Arrhythmia.
  2. Routine drug therapy:
    a) Aspirine 75 mg daily after meal.
    b) Beta-blocker: Atenolol 50 mg daily.
    c) ACE inhibitors: Captopril 50mg tds.
  3. Lifestyle modification:
    a) Cessation of smoking.
    b) Regular exercise.
    c) Diet (Weight control, lipid lowering)

[C] Rehabilitation: The patient should be gradually mobilized in a case of uncomplicated MI. When there are no complications the patient can sit in a chair by day 3 and go to the bathroom after day 5.If all goes well then the patient should be discharged after 2 weeks in hospital up to 6 weeks the patient should not go out of the house but move about normally within the house. From 6 weeks to 3 months the patient should do less than activity through he nay rejoin the office.

[D]Gradual socialization: Reassurance and mental support.

[E]Prevention of recurrence:

Primary prevention:
• Control of risk factors before attack of MI.
Secondary prevention:
• Stop smoking.
• Control of hypertension, DM, Hypercholesteraemia.
• Weight control (obesity)
• Regular exercise according to tolerance.
• Low dose of aspirin regularly (75-100 mg/day)
• Surgery: Coronary artery bypass surgery, angioplasty.

Complications of MI:

[A]Early complications:

  1. Arrhythmia: Common arrhythmias (in acute MI)
    • Ventricular fibrillation.
    • Ventricular tachycardia.
    • Accelerated idioventricular rhythm.
    • Ventricular ectopics.
    • Atrial fibrillation.
    • Atrial tachycardia.
    • Heart block.
  2. Ishaemia: Post infract angina (in 50% of patients)
  3. Cardiogenic shock.
  4. Pericarditis.
  5. Thromboembolism.
  6. Mechanical complication:
    • Papillary muscle damage.
    • Rupture of inter-ventricular septum.
    • Rupture of ventricle may lead to cardiac tamponade.

[B]Late complication:

  1. Ventricular aneurysm.
  2. Post MI syndrome (Dressler’s syndrome)
  3. Pericarditis, pleural effusion, persistent pyrexia.
  4. Recurrence of angina or further MI.
  5. Recurrence of arrhythmia & sudden death.
  6. Shoulder hand syndrome.

Reference:

  1. Davidson’s Principle and Practice of Medicine, 21st edition.
  2. Wikipedia the free encyclopedia.

 

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