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Myocardial Infarction

Myocardial Infarction (MI) is also referred to as a heart attack or coronary thrombosis. It is a condition where a part of the heart muscle suddenly loses blood supply. Typically, a heart attack occurs due to a thrombosis (blood clot) formed within a coronary artery. This obstructs normal blood flow to some part of the heart. If left untreated, myocardial infarction can cause damage to the heart. Besides a severe myocardial infarction can be fatal. There is shortness of breath and profuse sweating. It is essential to seek immediate medical help if you feel that you are suffering a myocardial infarction. Sudden overwhelming stress or laborious exertion or physical activity might bring on a myocardial infarction.


A heart attack is felt as a sudden and severe chest pain that may also travel up and down both arms. The pain felt during myocardial infarction lasts longer than that felt during an angina. In rare cases, a person does not feel any noticeable symptoms and is even unaware that he has suffered a heart attack. Smoking, diabetes, hypertension, high cholesterol and obesity puts a person at increased risk of heart attacks. Heart attacks are more noticed in older men and women, though there is an increasing trend for younger persons to suffer heart disease too. Female sex hormones protect women from heart disease till menopause. Heart ailments and coronary heart disease is sometimes genetic.


An ECG (electrocardiograph) can help trace your heart activity and whether you have suffered a heart attack. A Doppler ultrasound helps examine the heart valves, muscles and blood flow. A coronary angiogram is a special x-ray procedure that tests the severity of the blood vessel block with the help of a dye. The presence of certain enzymes like Troponin-I and Creatinine Kinase (CK) are indicative of a heart attack.


Hospital treatment is essential for a person suffering from a MI. The nature of the treatment hinges on the extent of damage of the heart muscle as well as the blockage of the blood vessels. Medication for dissolving the blood clot is administered. The patient is given drugs to reduce the pain and breathe easier. Beta-blocker drugs may be given to reduce the chances of another heart attacks. ACE Inhibitors may be prescribed to prevent heart failure. Balloon Angioplasty may be recommended to improve blood flow to the heart.

Adenosine Stress Test

Coronary artery disease is diagnosed by many stress tests such as echocardiography and treadmill. They determine cardiac activity with details of blood circulation and blood pressure. The stress tests are measured based on activity of the heart when subjected to exertion. The coronary arteries are examined for accumulation of plaque through triglyceride estimation and various other tests. In many scenarios the results of stress test are correlated with the laboratory analysis to identify the underlying conditions such as atherosclerosis.

Stress examinations of the heart also help in the detection of ischemia and arrhythmia. The adenosine stress test is done to identify underlying coronary artery disease. Adenosine helps in inducing the vasodilation of the coronary artery directly through the activation of the A2A receptor. The myocardial blood volume increases to a greater extent through this activity. The stenotic coronary arteries display an attenuated hyperemic response in the myocardial region of the heart. The radio tracer for the identification of coronary artery disease undergoes heterogeneous distribution. Adenosine is an endogenous nucleoside predominantly produced in the arterial vascular region. Its action is mediated through the G protein coupled adenosine receptors.

Methodology of adenosine infusion

The adenosine infusion is administered at a rate of 140 mcg/kg/min. The echocardiogram is taken by attaching twelve leads. The values of ECG are taken every minute. Along with these procedures, the blood pressure is consistently monitored for stability during the entire procedure of adenosine stress testing.

A2A receptor protein plays a significant role in the regulation of inflammatory response and immune response. A2A agonists act as effective catalysts in the identification of various diseases such as myocardial infarction and infectious diseases. These receptors help in the reduction of tissue damage.

Patient information and risk factors

The patient is advised not to consume any solid food. Water and juices are allowed prior to the procedure. The nuclear technologist injects the cardiolite and adenosine into the blood stream through an intravenous line. The cardiolite is administered to capture the cardiac images.

Water is given to patients before the start of the imaging procedure through the induced cardiolite. Adenosine is introduced through the IV line after acquiring the resting images. Anticipated side effects of adenosine are generally nausea, angina, shortness of breath and flushing. Most of these side effects are monitored by the technicians. The side effects are usually short lived. A second round of cardiolite is administered after the adenosine to acquire the second set of images. In order to reduce the side effects, patients are advised to walk on the treadmill. The entire procedure lasts for a period of two and a half hours. A comparative account is made of both sets of images at resting stage and also during stress (exercise induced). Patients are advised to take fluids preferably juices after the procedure.


The adverse effects of adenosine stress test include wheezing, hypotension with a systemic hypotension of less than 80 mm of hg, second degree heart block and cyanosis. Pregnant and lactating women are not advised to undergo adenosine stress test because of radio tracers. Incidences of hypersensitivity to adenosine have also been reported. Although adenosine stress is pharmacologically recommended for myocardial stress, one of the predominant side effects during the procedure is myocardial infarction.


Platelets

Platelets or thrombocytes are cell fragments found in the blood with an average life span of about 5- 9 days. Typically a healthy adult has about 150,000 to 450,000 platelets per micro liter of blood. Platelets are crucial for the clotting process since they are involved in hemostatis. If the platelet count is too high or low, it can be indicative of some disorders. Abnormally high platelet count can lead to myocardial infarction, pulmonary embolism or a stroke. Very low platelet count can lead to excessive bleeding. Low platelets can happen due to medications, leukemia, hemolytic anemia or chemotherapy. Abnormally high platelet count can be due to anemia, thrombocythemia or recent spleen removal.

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Collection of Pages - Last revised Date: October 16, 2017