MYOCARDIAL  INFARCTION [Symptoms / Pathogenesis / Risk Factors / Diagnosis / Complications of MI]


        When the myocardial ischemia progresses to a degree that irreversible necrosis of a part of myocardium occurs, an acute myocardial infarction (MI) is said to have occurred. An acute MI almost always results from an acute thrombotic obstruction of an atherosclerotic coronary artery.


Symptoms

     *Chest pain or discomfort, possibly described as pressure, squeezing, burning or fullness.

     *Pain in left arm, neck, jaw, shoulder or back accompanying chest pain

     *Nausea

     *Fatigue 

     *Shortness of breath

     *Sweating

     *Dizziness  

   In acute MI, the pain has same characteristics as angina, but it is far more severe, lasts longer, may radiate more widely, and not relieved by rest or nitroglycerin. Pain may be due to accumulation of anoxic metabolites as well as products of tissue necrosis. The pain is accompanied by greater psychogenic effects, i.e. feeling of impending death.


Pathogenesis

      Acute myocardial infarction (MI) indicates irreversible myocardial injury resulting in necrosis of a significant portion of myocardium(generally>1cm). Myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque. Ischemia induces profound metabolic and ionic perturbations in the affected myocardium. prolonged myocardial ischemia results in ischemia necrosis of the myocardium. The adult mammalian heart has negligible regenerative capacity, thus the infarcted myocardium heals through formation of a scar. Infarct healing is intertwined with geometric remodelling of the chamber , characterized by dilation, hypertrophy of viable segments, and progressive dysfunction.


   Cell membrane damage in acute MI leads to release of certain intracellular enzymes. Increase in their plasma levels is used as a diagnostic evidence of myocardial infarction.


Risk Factors 

     *Age: Men age 45 or older and women age 55 or older are more likely to have a heart attack than are younger men and women 

     *Tobacco; This includes smoking and long-term exposure to second- hand smoke.

     *High blood pressure; Over time, high blood pressure can damage coronary arteries.

    *High blood cholesterol or triglyceride levels; A high level of low-density lipoprotein (LDL) cholesterol is most likely to narrow arteries. A high level of triglycerides, a type of blood fat related to your diet, also ups your risk of heart attack.

     *Obesity; Obesity is associated with high blood cholesterol levels, high triglyceride levels, high blood pressure and diabetes.

     *Diabetes.

     *Family history of heart attack 

     *Lack of physical activity

     *Stress.  


Diagnosis

1. Electrocardiogram; An electrocardiogram (ECG) is a recording of the electrical activity of the heart. Abnormalities in the electrical activity usually occur with heart attacks and can identify the areas of heart muscle that are deprived of oxygen and/or areas of muscle that have died. In a patient with typical symptoms of heart attack and characteristic changes of heart attack on the ECG, a secure diagnosis of heart attack can be made quickly in the emergency room and treatment can be started immediately.

2. Blood tests; Cardiac enzymes are proteins that are released into the blood by dying heart muscles. These cardiac enzymes are creatine kinase (CK-MB),and troponin, and their levels can be measured in blood . these cardiac enzymes typically are elevated in the blood several hours after the onset of a heart attack. Currently, troponin levels are considered the perferred lab tests to use to help diagnose a heart attack, as they are indicates of cardiac muscle injury or death. A series of blood tests for the enzymes performed over a 24-hours period are useful not only in confirming the diagnosis of heart attack, but the changes in their levels over time also correlate with the amount of heart muscle that has died.



Complications of MI

     *Cardiogenic shock



     *Cardiac arrhythmias (Ventricular tachycardia or ventricular fibrillation are life- threating complications)

     *Congestive heart failure.