Heart Attack (Acute Myocardial Infarction)

What is a heart attack(Acute Myocardial Infarction?)

Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die. 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 (cholesterol and fatty acids) and white blood cells (especially macrophages) in the wall of an artery. The resulting ischemia (restriction in blood supply) and ensuing oxygen shortage, if left untreated for a sufficient period of time, can cause damage or death (infarction) of heart muscle tissue (myocardium). After a heart attack, the affected area of the heart(heart muscle) remains irreversibly damaged.


  • What does the cardiovascular system do?
  • Poor or abnormal function
  • Signs and Symptoms
  • Diagnosis and treatment
  • What happens in Intensive Care or Coronary Care?
  • How long will your loved one remain in Intensive Care or Coronary Care?
  • Internet Links
  • Publication Information


What does the cardiovascular system do?

The essential components of the human cardiovascular system are the heart, lungs, blood, and blood vessels. It includes: the pulmonary circulation, a “loop” through the lungs where blood is oxygenated and the systemic circulation, a “loop” through the rest of the body to provide oxygenated blood. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of their total body weight. Blood consists of plasma, red blood cells, white blood cells, and platelets. Also, the digestive system works with the circulatory system to provide the nutrients the system needs to keep the heart pumping.

The heart is at the centre, basically distributing blood from the ‘central pump’ with the blood vessels the pipes of the body, trying to reach every corner of the body. The cardiovascular system also passes nutrients (such as amino acids, electrolytes and lymph), gases(Oxygen and Carbon Dioxide), hormones, blood cells, etc. to and from cells in the body to help fight diseases, stabilize body temperature and pH, and to maintain blood pressure.

In the heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle. The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is de-oxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation(inhalation) and removal of carbon dioxide(exhalation). The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.The left side of the heart then receives oxygen rich blood from the lungs and pumps this blood into the Aorta and arteries of the body. This pumping action is a complex well-coordinated activity that cannot be fully explained here. The heart itself, receives oxygenated blood supply via the left and right coronary arteries.

Man with hand over heart

Poor or abnormal function of the cardiovascular system

May be a result of:

  • Insufficient blood supply due to dehydration, bleeding or swelling;
  • Insufficient blood supply to the heart due to ‘clotted’ arteries
  • A poor blood supply to the heart, where there is not enough oxygen and other nutrients for its work;
  • Poor lung function or obstruction to blood flow in the lungs, which places a strain on the heart muscle;
  • Too many or too few electrolytes (eg. potassium, magnesium) that cause irregular heartbeats or dangerous rhythms in the heart.
  • Weakness of blood vessel walls
  • Heart muscle weakness Cardiomyopathy
  • unhealthy lifestyle such as alcohol consumption, smoking, obesity

This image was sourced using a google image search

Signs and Symptoms

Typical symptoms of acute myocardial infarction include sudden retrosternal 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. A sizable proportion of myocardial infarctions (22–64%) are “silent”, that is without chest pain or other symptoms.

The onset of symptoms in myocardial infarction (MI) is usually gradual, over several minutes, and rarely instantaneous. Chest pain is the most common symptom of acute myocardial infarction and is often described as a sensation of tightness, pressure, or squeezing. Chest pain due to ischemia (a lack of blood and hence oxygen supply) of the heart muscle is termed angina pectoris. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and epigastrium, where it may mimic heartburn.

Shortness of breath (dyspnea) occurs when the damage to the heart limits the output of the left ventricle, causing left ventricular failure and consequent pulmonary edema. Other symptoms include diaphoresis (an excessive form of sweating), weakness, light-headedness, nausea, vomiting, and palpitations. These symptoms are likely induced by a massive surge of catecholamines from the sympathetic nervous system which occurs in response to pain and the hemodynamic abnormalities that result from cardiac dysfunction. Loss of consciousness (due to inadequate cerebral perfusion and cardiogenic shock) and sudden death (frequently due to the development of ventricular fibrillation) can occur in myocardial infarctions.

arteriogram showing coronary arteries of healthy h

Diagnosis and treatment:

The diagnosis of myocardial infarction can be made after assessing Patient’s complaints and physical status. ECG changes, coronary angiogram and levels of cardiac markers(Troponin, CK) help to confirm the diagnosis. ECG gives valuable clues to identify the site of myocardial damage while coronary angiogram allows visualization of narrowing or obstructions in the heart vessels.

A chest x-ray and routine blood tests may indicate complications or precipitating causes and are often performed upon arrival to an emergency department. New regional wall motion abnormalities on an echocardiogram are also suggestive of a myocardial infarction. Echo may be performed in equivocal cases by the on-call cardiologist.In stable Patients whose symptoms have resolved by the time of evaluation, a “thallium scan”(contrast scan) can be used in nuclear medicine to visualize areas of reduced blood flow in conjunction with physiologic or pharmacologic stress. Thallium may also be used to determine viability of tissue, distinguishing whether non-functional myocardium is actually dead or merely in a state of hibernation or of being stunned.

WHO criteria formulated in 1979 have classically been used to diagnose MI; 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(CK) and troponin


Treatment of a heart attack may include

  • Oxygen therapy
  • Nitroglycerin(GTN spray, GTN patch or GTN infusion) to treat acute chest pain
  • Aspirin and/or Clopidogrel(Antiplatelet therapy)
  • Beta- Blockers(i.e. Metoprolol) to reduce Heart rate and reduce Blood pressure
  • Heparin therapy
  • Thrombolysis(Streptokinase/ Urokinase) for breaking down blood clots quickly
  • Intra-Aortic Balloon pump insertion (Intra-Aortic Balloon Pump (IABP)
  • Cardiac Surgery(Coronary Artery Bypass Graft (CABG)
  • Angiogram followed by possible Angioplasty(Stenting of the heart)

What happens in the Intensive Care Unit or in Coronary Care?

Complications that may occur following a heart attack may include:

  • A Cardiac Arrest(where a Patients’ heart and breathing stops and the Patient requires immediate resuscitation)
  • Abnormal cardiac rhythms/heart beat such as AF, SVT, VT, VF.
  • Further heart attack extending the damage already done
  • Heart Failure
  • Cardiogenic Shock

How long will your loved one remain in Intensive Care/Coronary Care?

Length of stay in Coronary Care or Intensive Care depends on varying factors such as the severity of the Heart Attack, the symptoms and the treatment. Most Heart Attacks require admission at least to a Coronary Care Unit, but depending on the condition of your loved one, Intensive Care admission may be necessary. Usually your loved one will remain in the intensive/coronary care unit until your loved one is stabilised, followed by cardiac interventions such as angiogram, cardiac stenting or cardiac surgery (CABG)

Internet Links

Any Questions?

Of course, if you have any questions or concerns, please discuss them with the ICU nurses and doctors.

All Intensive Care interventions and procedures carry a degree of potential risk even when performed by skilled and experienced staff. Please discuss these issues with the medical and nursing staff who are caring for your loved one.

The information contained on this page is general in nature and therefore cannot reflect individual patient variation. It is meant as a back up to specific information which will be discussed with you by the Doctors and Nurses caring for your loved one. INTENSIVE CARE HOTLINE attests to the accuracy of the information contained here BUT takes no responsibility for how it may apply to an individual Patient. Please refer to the full disclaimer.

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