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What is Anterior Myocardial Infarction?
A myocardial infarction or heart attack (MI) signifies the death of heart muscle cells due to lack of oxygen supply. This occurs when a coronary artery which supplies oxygenated blood to the heart is significantly blocked, commonly by plaques or cholesterol deposits. Depending on which of the branches of the coronary arteries is/are blocked, the area supplied is adversely affected and loses its function in the pumping action of the heart.
The coronary circulation consists of the right and left main coronary arteries. The left coronary artery further divides into the left circumflex artery and the left anterior descending artery (LAD). The LAD supplies the anterior (front) part of the left ventricle (the lower chamber of the heart). Depending on the extent of blockage to the LAD and its branches, the septum (wall between the left and right ventricles) and the lateral side of the ventricle may also be affected. Therefore an anterior myocardial infarction is the death of heart muscles of the front, and possibly the side and septum, of the left ventricle.
Depending on the extent of involvement, cardiac function may be compromised in terms of its ability to pump and deliver adequate blood supply to the rest of the body. If severe, cardiogenic shock resulting in death can occur.
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The factors that lead to anterior MI are similar to those causing damage in other parts of the heart which are supplied by other branches of the coronary arteries. Risk factors which may predispose one to develop a heart attack include:
- Age greater than 45 years (although younger people may also experience it)
- Family history of heart attack
- Male gender
- High cholesterol levels in the blood
- High blood pressure that is poorly controlled
- Type A personality
- Lack of exercise
Causes of anterior MI as well as in any part of the heart include:
- Atherosclerosis leading to plaque formation in the coronary arteries – most common cause
- Coronary artery vasospasm (constriction)
- Embolism or blood clots
- Carbon monoxide poisoning
- Left ventricular hypertrophy (enlargement)
- Drugs containing cocaine, amphetamines, and ephedrine
- Aortic dissection
- Coronary aneurysm
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A heart attack involving the left ventricle can compromise the pumping action of the heart and the blood supply to the rest of the body. This can lead to symptoms like:
- Chest pains – constricting, stabbing, squeezing type of pain under the breastbone or the left side of the chest; pains may radiate to the neck, back, shoulder and left arm
- Shortness of breath or difficulty in breathing
- Lightheadedness, may be accompanied by fainting
- Anxiety and a sense of impending doom
- Extreme paleness, with cold and clammy skin
- General weakness or fatigue
Upon medical examination the patient may be found to have low blood pressure due to failure of blood circulation with irregular heartbeats.
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An electrocardiogram (ECG) will reveal the electrical changes in particular areas of the heart. The evaluation of lead changes in V1-V5 will show abnormalities in the waves, particularly the appearance of Q-waves and R wave progression in anterior wall infarcts.
Specific biomarkers in the blood may also reveal the occurrence of an infarct. Serum level of troponin is the best biomarker because it has a high level of specificity and sensitivity. Other biomarkers include creatine kinase–MB and myoglobin. Myoglobin levels rise earlier than the two biomarkers, but it has poor specificity and may also increase in other conditions. Creatine kinase–MB rises within four hours but peaks only after 18-24 hours.
Imaging studies are useful in evaluating the extent and complications of coronary artery blockage and wall motion abnormalities. These include chest radiography, echocardiography, MRI, CT scanning and others.
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Emergency treatment of a heart attack focuses on restoration of effective circulation and oxygenation of the heart and the rest of the body. Pain relief and prevention of complications are also important in management.
These are accomplished by:
- Empirical treatment with morphine, oxygen, nitroglycerin and aspirin as recommended by the American Heart Association (AHA) protocol
- Use of antihypertensives like ACE inhibitors, calcium channel blockers and angiotensin receptor blocker to decrease myocardial oxygen demand
- Thrombolytic therapy to destroy blood clots that can further block arteries
Anterior myocardial infarct is just one of the different types of cardiac muscle death according to location and source of blood supply. Immediate recognition and medical management are necessary to prevent complications and death.
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Myocardial Infarction: http://www.nursingtheory.nhs.uk/Cardiac/Myocardial%20Infarction.htm