Myocardial Infarction (MI)

AMI scheme[1]

Myocardial infarction, commonly referred to as heart attack, is a condition characterized by necrosis of the heart muscles due to development of ischemia that stays on for prolonged periods. Such a condition develops when the heart does not receive oxygen and blood due to blockage in the coronary arteries.


Presentation

Development of sudden chest pain is the most common symptom of heart attack. The pain may radiate down the left arm or neck in majority of the cases. The chest pain may be mild or severe. The characteristics of chest pain can be explained as follows:

  • Feeling of tight band that surrounds the chest.
  • Experiencing symptoms mimicking bad indigestion.
  • Feeling of some kind of heavy object on chest.
  • The pain often lasts for about 20 minutes. In addition to chest pain, individuals can also suffer from anxiety, shortness of breath, palpitations, sweating, cough and fainting.
  • It is always better to seek medical intervention at the earliest when an individual experiences any of these symptoms. Early intervention can help prevent onset of debilitating conditions.
  • In many cases, individuals may not experience any symptoms at all; or would just complain of dull or vague symptoms such as fatigue and shortness of breath. Such individuals are known to have developed silent heart attacks [6].

Workup

A preliminary physical examination to determine the heart sounds, blood pressure and pulse rate will be quickly carried out. Following this, an electrocardiogram will be done to evaluate the extent of heart damage. A blood test will be conducted which would determine heart tissue damage. This test would also confirm heart attack.

Coronary angiogram would either be done immediately or after stabilizing the condition of the patient. In this test, a specialized dye is inserted which allows to evaluate areas of blockage. In addition, other tests such as nuclear stress test and exercise stress test would also be conducted [7].

Treatment

Heart attacks require emergency treatment. Once the patient arrives he is immediately admitted to the intensive care unit and is constantly monitored through heart monitor and is put on an external oxygen supply [8]. He is given medications such as nitroglycerin and morphine intravenously for reducing chest pain [9].

In addition, aspirin would also be given to prevent blood from clotting. In case, the individuals is having arrhythmias he would be given medications to bring the heart rate back to normal. Once the patient’s vital signs are stabilized he is prepared for angioplasty which is employed to open blocked blood vessels [10].

In case of greater degree of blockages, a bypass surgery may be recommended. In many cases, individuals are given drugs to breaks the clots. These drugs work best when given within 3 hours of chest pain. Such a type of method is known as thrombolytic therapy.

Prognosis

Prognosis of myocardial infarction greatly depends on the extent of damage the infarct has caused to the heart muscles as well as the left ventricular function. The prognosis of the condition is not very favorable in most of the cases. It has been reported that acute myocardial infarction causes mortality in 30% cases. In addition to this, about 5 to 10% individual who survive the condition, eventually die within the first year of suffering an attack. To add to this, about 50% of patients need to be hospitalized again within a year of suffering from myocardial infarction. Individuals with diabetes or hypertension are known to have a poor prognosis [5].

Etiology

Development of blockage in the coronary arteries that prevents the blood and oxygen from reaching the heart causes myocardial infarction. Occurrence of atherosclerosis is known to be major causative factor for development of most of the acute coronary syndromes. It has been reported that 90% cases of myocardial infarction occurs due to atherosclerotic coronary artery. Individuals with chronic disorders such as hypertension, diabetes and obesity are an increased risk of developing myocardial infarctions. Those in habit of smoking or living a sedentary lifestyle are also highly susceptible to heart attack [2].

Epidemiology

It has been estimated that about 1.5 million individuals suffer from myocardial infarctions each year in the US. Cardiovascular disease is the leading cause of mortality in the US causing 500,000 to 700,000 deaths each year. Worldwide, about 12 million deaths occur each year due to cardiovascular diseases. Male are more prone to contract myocardial infarctions than women [3].

Sex distribution
Age distribution

Pathophysiology

Buildup of plaque in the coronary arteries causes the arteries to block preventing the oxygen rich blood to reach the heart. The plaque is essentially made up of cholesterol and other cells. When plaque slowly and gradually builds up in the arteries, it causes them to narrow so much so that they gradually get blocked.

A heart attack can also occur when the plaque tears, causing the blood platelets along with other substances to form a clot. The clot is formed at the site which prevents the blood and oxygen to reach the heart causing an attack. Lack of oxygen supply, gradually reduces the muscular contractions and systolic wall motion in the affected area [4].

Prevention

Adopting certain lifestyle changes can help prevent onset of myocardial infarction. Exercising regularly and eating diet low in cholesterol and sodium will help in preventing the onset of chronic degenerative disorders and plaque formation. Individuals should also quit smoking in order to decrease their chances of developing heart attacks.

Summary

Individuals with acute myocardial infarction suffer from sudden onset of chest pain which is felt behind the sternum and in many cases the pain travels down the left arm. However, there are times when individuals experience absolutely no or some vague symptoms. This is known as silent myocardial infarctions. Heart attack requires immediate medical intervention to prevent development of irreversible damages [1].

Patient Information

Definition

Myocardial infarction is characterized by necrosis of heart cells due to blockage of the coronary arteries that supply blood and oxygen to the heart. It is a common occurrence affecting about 1.5 million individuals in US.

Cause

Heart attack occurs primarily due to plaque tear or narrowing of the arteries due to gradual deposition of the plaque in them. Formation of plaque in the coronary arteries cause it to block as a result of which blood and oxygen no longer reach the heart muscles.
Symptoms

Symptoms of myocardial infarction consist of sudden onset of chest pain that is characterized by feeling of tightness in the chest. The pain can even radiate along the left arm and neck. In addition, other symptoms include lightheadedness, nausea, cough, sweating and shortness of breath.

Diagnosis

A quick preliminary examination of the vital signs is made following blood tests to reveal extent of damage to the heart. In addition, electrocardiogram is also carried out to determine heart damage.

Treatment

Treatment begins with intravenous administration of nitroglycerine and morphine to decrease the chest pain. Medications to correct the blood clot are also given. Following this, angioplasty or bypass surgery is done depending on the extent of blockages.

Self-assessment

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References

  1. Siddiqui MA, Tandon N, Mosley L, Sheridan FM, Hanley HG.Interventional therapy for acute myocardial infarction. J La State Med Soc. Jun 2001;153(6):292-9.
  2. McCord J, Jneid H, Hollander JE, et al. Management of cocaine-associated chest pain and myocardial infarction: a scientific statement from the American Heart Association Acute Cardiac Care Committee of the Council on Clinical Cardiology. Circulation 2008; 117:1897.
  3. Rosamond WD, Chambless LE, Folsom AR, et al. Trends in the incidence of myocardial infarction and in mortality due to coronary heart disease, 1987 to 1994. N Engl J Med 1998; 339:861.
  4. Busko M. High-risk plaque predicts ACS in ER patients with chest pain. Heartwire [serial online]. July 18, 2014;Accessed July 21, 2014.
  5. Yan AT, Tan M, Fitchett D, et al. One-year outcome of patients after acute coronary syndromes (from the Canadian Acute Coronary Syndromes Registry). Am J Cardiol 2004; 94:25.
  6. Bahit MC, Cannon CP, Antman EM, et al. Direct comparison of characteristics, treatment, and outcomes of patients enrolled versus patients not enrolled in a clinical trial at centers participating in the TIMI 9 Trial and TIMI 9 Registry. Am Heart J 2003; 145:109.
  7. Anderson JL, Adams CD, Antman EM, Bridges CR, Califf RM, et al. ACC/AHA 2007 guidelines for the management of patients with unstable angina/non-ST-Elevation myocardial infarction: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 2002 Guidelines for the Management of Patients With Unstable Angina/Non-ST-Elevation Myocardial Infarction) developed in collaboration with the American College of Emergency Physicians, the Society for Cardiovascular Angiography and Interventions, and the Society of Thoracic Surgeons endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation and the Society for Academic Emergency Medicine. J Am CollCardiol. Aug 14 2007;50(7):e1-e157. 
  8. Cabello JB, Burls A, Emparanza JI, et al. Oxygen therapy for acute myocardial infarction. Cochrane Database Syst Rev 2013; 8:CD007160.
  9. Meine TJ, Roe MT, Chen AY, et al. Association of intravenous morphine use and outcomes in acute coronary syndromes: results from the CRUSADE Quality Improvement Initiative. Am Heart J 2005; 149:1043.
  10. Cantor WJ, Fitchett D, Borgundvaag B, Ducas J, Heffernan M, et al. Routine early angioplasty after fibrinolysis for acute myocardial infarction. N Engl J Med. Jun 25 2009;360(26):2705-18

Media References

  1. AMI scheme, CC BY-SA 3.0

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