MYOCARDIAL INFARCTION

MYOCARDIAL INFARCTION

Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, is the interruption of blood supply to part of the heart, causing heart cells to die.

Description:

This is most commonly due to occlusion (blockage) of a coronary artery following the rupture of a vulnerable atherosclerotic plaque, which is an unstable collection of lipids (fatty acids) and white blood cells (especially macrophages) in the wall of an artery. The resulting ischemia (restriction in blood supply) and oxygen shortage, if left untreated for a sufficient period of time, can cause damage or death (infarction) of heart muscle tissue (myocardium).Classical symptoms of acute myocardial infarction include sudden chest pain (typically radiating to the left arm or left side of the neck), shortness of breath, nausea, vomiting, palpitations, sweating, and anxiety (often described as a sense of impending doom). Women may experience fewer typical symptoms than men, most commonly shortness of breath, weakness, a feeling of indigestion, and fatigue. Approximately one quarter of all myocardial infarctions are silent, without chest pain or other symptoms.

Classification:

There are two basic types of acute myocardial infarction:

• Transmural: associated with atherosclerosis involving major coronary artery. It can be subclassified into anterior, posterior, or inferior. Transmural infarcts extend through the whole thickness of the heart muscle and are usually a result of complete occlusion of the area's blood supply.
• Subendocardial: involves small area in the subendocardial wall of the left ventricle, ventricular septum, or papillary muscles. Subendocardial infarcts are thought to be a result of locally decreased blood supply, possibly from a narrowing of the coronary arteries. The subendocardial area is farthest from the heart's blood supply and is more susceptible to this type of pathology.

Signs and symptoms:

Although chest pain or pressure is the most common symptom of a heart attack, heart attack victims may experience a variety of symptoms including:

• Pain, fullness, and/or squeezing sensation of the chest

• Jaw pain, toothache, headache

• Shortness of breath

• Nausea, vomiting, and/or general epigastric (upper middle abdomen) discomfort

• Sweating

• Heartburn and/or indigestion

• Arm pain (more commonly the left arm, but may be either arm)

• Upper back pain

• General malaise (vague feeling of illness)

• No symptoms (Approximately one quarter of all heart attacks are silent, without chest pain or new symptoms. Silent heart attacks are especially common among patients with diabetes mellitus.)

Risk factors:

Risk factors for atherosclerosis are generally risk factors for myocardial infarction:

• Diabetes (with or without insulin resistance) - the single most important risk factor for ischaemic heart disease (IHD)
• Tobacco smoking
• Hypercholesterolemia (more accurately hyperlipoproteinemia, especially high low density lipoprotein and low high density lipoprotein)
• High blood pressure
• Family history of ischaemic heart disease (IHD)
• Obesity^: (defined by a body mass index of more than 30 kg/m², or alternatively by waist circumference or waist-hip ratio).
• Age: Men acquire an independent risk factor at age 45, Women acquire an independent risk factor at age ; in addition individuals acquire another independent risk factor if they have a first-degree male relative (brother, father) who suffered a coronary vascular event at or before age. Another independent risk factor is acquired if one has a first-degree female relative (mother, sister) who suffered a coronary vascular event at age 65 or younger.
• Hyperhomocysteinemia (high homocysteine, a toxic blood amino acid that is elevated when intakes of vitamins B₂, B₆, B₁₂ and folic acid are insufficient)
• Stress (occupations with high stress index are known to have susceptibility for atherosclerosis)
• Alcohol Studies show that prolonged exposure to high quantities of alcohol can increase the risk of heart attack
• Males are more at risk than females.

Diagnosis:

A patient is diagnosed with myocardial infarction if two (probable) or three (definite) of the following criteria are satisfied:

1. Clinical history of ischaemic type chest pain lasting for more than 20 minutes
2. Changes in serial ECG tracings
3. Rise and fall of serum cardiac biomarkers such as creatine kinase-MB fraction and troponin

1. Physical examination 2. Electrocardiogram

3. Cardiac markers 4. Angiography

5. Histopathology

Prevention:

• Antiplatelet drug therapy such as aspirin
• Beta blocker therapy
• ACE inhibitor therapy should be commenced 24–48 hours post
• Statin therapy
• The aldosterone antagonist agent
• Omega-3 fatty acids,

Management:

1. Antiplatelet agents 2. Nitroglycerin

2. Reperfusion 4. Rehabilitation

Complications:

1. Congestive heart failure 2. Myocardial rupture

3. Arrhythmia 4. Pericarditis

5. Cardiogenic shock