MYOCARDIAL INFARCTION

Myocardial infarction refers to the process by which areas of myocardial cells in the heart are permanently destroyed.

Definition 

  • Myocardial infarction is defined as a diseased condition which is caused by reduced blood flow in a coronary artery due to atherosclerosis & occlusion of an artery by an embolus or thrombus. MI or heart attack is the irreversible damage of myocardial tissue caused by prolonged ischaemia & hypoxia.
  • There is a prolonged decrease in oxygen supply because of insufficient coronary blood flow subsequently leading to necrosis or "death" of the myocardial tissue occurs.

Incidence

  • Men > Women
  • 45% of myocardial infarction → Under 65 years
  • 5% of myocardial infarction → Under 40 years

Causes 

  • Atherosclerosis 
  • Thrombosis or embolism 
  • Vasospasm 
  • Hemorrhage or Anemia 
  • Trauma
  • Vasculitis
  • Drug use (cocaine)
  • Aortic dissection

Nonmodifiable

  • Sex
  • Age
  • Family history
  • Male pattern baldness

Modifiable

  • Smoking
  • Dyslipidemia
  • Diabetes mellitus
  • Hypertension
  • Obesity
  • Sedentary lifestyle
  • Poor oral hygiene
  • Presence of peripheral vascular disease
  • Elevated levels of homocysteine


Sign and Symptoms 

  • Ischemia
  • Severe chest pain, not relieved by nitroglycerin
  • Pain radiates to arms (commonly the left), shoulders,neck, back and jaw
  • Nausea or dizziness
  • Weakness and fatigue
  • Palpitation, cold sweat or paleness
  • Hypertension or hypotension
  • Bradycardia or tachycardia
  • Disorientation, confusion and restlessness
  • Nausea, vomiting, hiccups
  • Epigastric or abdominal distress

Pathophysiology 

Reduced blood flow (due to atherosclerosis, occlusion by thombus in ocoronary artery)➡️Less O₂ to the tissues➡️Cell are deprived of O₂➡️Ischemia➡️Infarction➡️Death of cells➡️Myocardial infarction

Physical Examination

  • Note the vital signs of the patient
  • Heart rate may disclose tachycardia, atrial fibrillation, or ventricular arrhythmia
  • Presence of Unequal pulses if the patient has an aortic dissection
  • Blood pressure is usually high, but patient presents hypotension if in shock
  • Tachypnea and fever
  • Distended Neck veins indicating right ventricular failure
  • Heart: lateral displacement of apical impulse, soft S1, palpable S4, new mitral regurgitation murmur. A loud holosystolic murmur radiating to the sternum may be indicative of ventricular septal rupture.
  • When the patient has developed pulmonary edema, wheezing and rales are common
  • Extremities may show edema or cyanosis and will be cold.

Diagnostic Tests

  • History taking
  • ECG: Demonstrates dysrhythmias and changes consistent with left ventricular hypertrophy, sinus tachycardia, ST segment changes.
  • Chest X-ray: Heart enlargement and pulmonary congestion
  • Echocardiogram to identify the structure and function of ventricles
  • Cardiac catheterization coronary artery disease (CAD)
  • Endomyocardial biopsy to analyze myocardial tissue cells
     

 Management

Therapy is aimed at the protection of ischemic and injured heart tissue to preserve muscle function, reduce the infract size and prevent death.

  1. Oxygen Therapy-Improve oxygenation to ischemic heart muscle.
  2. Pain Control-Analgesic therapy-Morphine is used to relieve pain
  3. Anxiety relief-Meperidine: For pain management in those patients who are allergic to morphine
  4. Vasodilator therapy-Nitroglycerin (sublingually, IV): Promotes venous and arterial relaxation and prevent of coronary spasm.
  5. Benzodiazepines- Used with analgesics when anxiety complicates chest pain and its relief.
  6. Thrombolytic agent: Such as tissue plasminogena vator (Activase), streptokinase (Streptase), reestablish blood flow in coronary vessels by dissolving the obstruct ing thrombus.
  7. Anticoagulation therapy is useful as an adjunct to thrombolytic therapy.
  8. B-adrenergic blocking agent improve oxygen supply and demand, promote blood flow in the small vessels of the beurt
  9. Antidysrhythmic therapy: Lidocaine (Xylocaine) decreases ventricular irritability.
  10. Calcium channel blockers: Improve the balance between oxygen supply and demand by decreasing heart rate, blood pressure and dilating coronary vessels. E.g. Diltiazem

Surgical  Management 

  • Coronary Artery bypass Graff (CABG)
  • Percutaneous transluminal coronary arteriography
  • Coronary  Sent 
  • Atherectomy is a minimally invasive procedure healthcare providers use to remove plaque buildup and open narrow or blocked arteries
  • Transmyocardial Laser Revascularization (TMLR)- is a type of surgery that uses a laser to make tiny channels through the heart muscle and into the lower-left chamber of the heart (the left ventricle). The left ventricle is the heart’s main pumping chamber.

Nursing Management

Reducing Pain

  • Start IV infusion, obtain baseline vital signs and attach electrodes for continuous ECG monitoring.
  • Administer oxygen by nasal cannula and encourage to take deep breaths.
  • Administer nitroglycerin, check blood pressure, heart rate, and respiratory rate before and after dose.
  • Administer narcotics, morphine and meperidine.

Improving Respiratory Function

  • Regular and careful assessment of respiratory function.
  • Encouraging the patient to take deep breath.
  • Change the position frequently as it keeps fluid from pooling in the lung bases.

Maintaining Tissue Perfusion

  • Keeping the patient on bed or chair help in reducing the myocardial oxygen consumption.
  • Check skin temperature and peripheral pulse.
  • Administer oxygen

Reducing Anxiety

  • Develop a trusting and caring relationship.
  • Explain the reason for hospitalization, equipment, procedures, diagnostic tests and therapies.
  • Administer antianxiety agents.

Maintaining Hemodynamic Stability

  • Monitor bypass surgery after every 2 hours
  • Monitor respiratory and lung fluids every 2-4 hours
  • Observe for edema
  • Monitor vitals

Increasing Activity Tolerance

  • Promote rest with early gradual increase in mobilization
  • Encourage passive and active exercise
  • Promote restful divisional activities
  • Elevate patients feet when out of bed in chain to promote venous return

Preventing Bleeding

  • Observe for hematomas or skin breakdown
  • Observe for blood in stool, emesis, and urine.
  • Avoid trauma to patients, monitor prothrombin time (PT), partial thromboplastin time (PTT) and hemoglobin.
  • Administer antacid to prevent stress ulcers
  • Avoid vigorous oral suctioning

Strengthening Coping Abilities

  • Listen carefully to the patient's and his family members.
  • Assist patients to establish a positive attitude toward illness.
  • Check for sleep deprivation, irritability and disorien-tation.

Complications

  • Acute pulmonary edema
  • Congestive heart failure
  • Cardiogenic shock
  • Cardiac tamponade
  • Myocardial rupture
  • Dysrhythmias
  • Cardiac arrest
  • Pericardial effusion

 

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