Myocardial infarction (MI)

Definition:

The complete necrosis of the myocardium due to complete cessation (occlusion) of blood supply is called myocardial infarction.

Etiology:

·         Atherosclerotic plaque (unstable)

·         Embolic occlusion of coronaries

·         Severe and prolonged vasospasm

·         Drugs (Cocain and Amphetamine)

Clinical features:

Symptoms:

Ø  Chest pain

o   Severe and prolonged means more than 30 min not relieved with nitrates

o   Left side of chest and then radiates to left arm to left arm or back or neck

Ø  Vomiting

Ø  Sweating

Ø  Symptoms of heart failure in case of massive MI

o   Dizziness

o   Drowsiness

o   Severe shortness of breath

o   Unconsciousness (in some cases)

Signs:

§  Fist sign

§  Sweating/ diaphoresis

§  Vomiting

§  BP will be either increased or decreased

§  Pulse:

o   Tachycardia: Due to anxiety, low cardiac output or arrhythmias

o   Bradycardia: If there is inferior wall infarction

§  Chest (pericardium) examination:

Usually normal examination of the heart or having the following

o   Ventricular septal defect (VSD)

o   Pain systolic murmur (PSM)

o   A soft first heart sound

o   Fourth heart sound

o   Third heart sound reflects left ventricular dysfunction

§  Lungs:

Crepts at the bases of lungs

Investigation of MI:

ECG:

Ø  ST segment elevation

Ø  May be tachycardia or bradycardia

o   V3-V4 show anterior wall MI due to LAD involvement

o   II, III, aVF show inferior wall MI due to RCA involvement

o   I, aVL show high lateral wall MI due to circumflex

Cardiac enzymes:

Troponin T and I are raised up to 2 weeks while CK-MB remains elevated up to 3 days. Creatine kinase (CK) has three isoenzymes.

§  CK-MB: present in heart

§  CK-MM: present in skeletal muscle

§  CK-BB: present in brain

Echocardiography:

ü  It asses the myocardial movements i.e. whether Hypokinetic or Akinetic (no movement)

ü  It also asses the valves, whole function of the heart and aorta.

Routine investigation:

·         CBC (Complete Blood Count)

·         RBS (Random Blood Sugar)

·         Urea, creatinine

·         Serum electrolytes (especially K)

·         Cardiac X-ray

Treatment:

All the patients with suspected myocardial infarction should be confined to strict bed rest and admitted in hospital preferably in CCU.

General:

v  The aim of general treatment is to relieve the symptoms.

v  To relieve the pain, so strong analgesics especially opoid group (Morphine, codein) and anti-emetics (Gravinate) are used.

v  Complete bed rest for 24 hrs.

v  To treat other co-morbidities (diseases like HTN, DM)

Specific:

Antiplatelets:

Aspirin 300mg and clopidogril 300 mg are given as first (loading) dose then 75mg OD.

Thrombolytics:

§  Streptokinase

§  If once it is used then the patient become allergic to it

Beta blockers:

Atenolol, Propranolol, Metaprolol (cardio selective)

Nitrates:

Angised, isoket (nitroglycerine) should be given to relieve chest discomfort.

ACE inhibitors (Angiotensin Converting Enzymes):

They prevent or at least reduce the left ventricular dilatation and cardiac failure following myocardial infarction. These are Ramipril and Captopril (Tab. Capoten 25mg).