Myocardial infarction (MI) refers to tissue death (infarction) of the heart muscles (myocardium) due to ischemia (lack of oxygen). It is acute coronary syndrome which exhibits sudden or short-term changes in symptoms related to the blood supply of the heart.
The common phrase “heart attack” non-specifically refers to the sudden death of cardiac tissues i.e. myocardial infarction. The causes and symptoms of MI are different from cardiac arrest but MI can lead to cardiac arrest in chronic cases. The term cardiac arrest refers to the incompetence of the heart to contract properly so that blood supply to the vital organs is compromised. It can lead to instant death if the heart fails to pump blood towards the brain.
Just like any other muscle in the body, the heart requires a constant supply of oxygen and nutrients. The arterial supply to the heart is provided by its own specialized vascular system that comprises of three coronary arteries that supply oxygenated blood to the muscles of the heart. If any of these arteries get blocked by a blood clot, (thrombus or embolus), the blood supply to the corresponding tissues is compromised, this lack of oxygen for a longer duration leads to “cardiac ischemia”.
Angina is the early warning sign of a heart attack
When any of the coronary arteries are obstructed, the cardiovascular system of the body presents the symptoms known as “angina pectoris”. Angina simply refers to severe pain in the cardiac region that mimics the pain of a heart attack but the only difference is of severity. In angina, blood flow to the targeted tissue is restored shortly and the pain recedes within a few minutes and cardiac tissue is not permanently damaged.
In a heart attack, blood flow is critically reduced or fully blocked leading to intense, sharp and unbearable pain. The heart muscles are permanently damaged and may die without prompt treatment. Almost 25% of cases of MI are reported to occur without any warning signs or symptoms, which is referred to as silent ischemia in clinical terms. Due to unknown reasons, in silent ischemia, spasmodic interruptions of blood flow to the heart are painless, despite the fact that they damage the heart tissues significantly. This condition can only be detected by an ECG (electrocardiogram) which is normally performed as a screening test at primary care centers.
Diabetic patients often become the victim of silent ischemia!
Signs and symptoms
Chest pain is the most common symptom of acute myocardial infarction and is commonly described as a sensation of pressure, tightness or squeezing. Pain commonly radiates to the left arm but may also radiate towards lower jaw, neck, back, right arm and upper abdomen.
Levine’s sign has classically been thought to be predictive of cardiac pain although observational studies show that it has poor positive predictive value. The patient localizes the chest pain by clenching one or both fists over the sternum (chest bone).
Common signs and symptoms of a heart attack include:
• Severe intense pain, pressure, tightness or squeezing sensation in chest or arms that may spread to shoulders, neck, jaws or back (particularly in the left side of the body)
• Breathlessness (Shortness of breath)
• Abnormal heart rate and blood pressure
• Indigestion or abdominal pain
• Lightheadedness or dizziness
• Cardiogenic shock
• Sudden death
In females, myocardial infarction may present with varied symptoms. The classic symptom of chest pain occurs in 50% of women. The other 50% commonly experience pain in back, neck or jaw, heartburn, indigestion, dizziness, fatigue, nausea, and vomiting.
Common causes and risk factors
The predominant factors for myocardial infarction include old age, chronic smoking, high blood pressure, high blood cholesterol, and HDL (high-density lipoproteins) level and diabetes mellitus. Other less common risk factors include coronary artery disease, male sex, low levels of physical activity, obesity, positive family history, and alcohol.
At any given age, men are at greater risk for the development of cardiovascular diseases.
Smoking appears to be the cause of 36 % and obesity (20%) of coronary artery disease. Lack of physical activity is linked to 7-12% of the total cases. Job-related stress and chronic high-stress levels account for about 3% of cases.
According to current consensus, an acute myocardial infarction is defined by elevated cardiac biomarkers with a rising or falling trend of the following parameters:
• Marked changes on electrocardiogram such as broad ST segments, new left bundle branch block or Q waves
• Changes in the movement of the heart wall during radiography
• The depiction of thrombus or embolus on angiogram or autopsy
• Symptoms related to ischemia
Common diagnostic tools are:
• Non-invasive imaging techniques including echocardiography, ultrasound, etc.
• Radioactive tests such as SPECT CT scan or PET scan (nuclear scans can visualize the perfusion of heart muscles)
Regular screening tests at primary care centers can help detect heart abnormalities at the earliest possible stage.
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