Heart Attack (Myocardial Infarction)

Overview

By Tina Shahian, PhD

The coronary arteries deliver nutrient- and oxygen-rich blood to the pumping muscles of the heart. A block in the flow of blood to the heart can lead to tissue damage and death – otherwise referred to as a heart attack. Other common names for this condition are myocardial infarction and coronary syndrome. In the United States, there is an estimated one heart attack every 34 seconds. Heart attacks can be fatal and are a leading cause of death in adults.

A damaged or dead heart muscle is associated with various complications. Heart failure is a temporary or permanent condition where the heart can no longer pump ample blood to the body. Damaged heart muscles can also lead to irregular heartbeats (or arrhythmia) and heart valve damage, both of which can become fatal. The key to avoiding potentially permanent and deadly heart damage is to recognize the symptoms of a heart attack and seek immediate medical attention.

Causes and Risk Factors

cross section of the heartThe main cause of a heart attack is a blockage in the arteries that carry blood to the heart. This process begins with the gradual buildup of plaque in the arteries (called atherosclerosis), which over time narrows the blood pathways and leads to coronary artery disease. When a rupture occurs at the site of plaque buildup, the body senses the damage and attempts to repair the site by releasing blood-clotting factors. A large clot that fully blocks the path of blood to the heart will result in a heart attack.

Heart attacks may also occur because of severe spasms of the coronary arteries, which are triggered by certain drugs, stress, and smoking. Coronary artery spasms are not common. The following risk factors increase the chances of having a heart attack:

  • High fat and cholesterol. High levels of triglycerides (a type of fat) and low-density lipoprotein (LDL) cholesterol promote plaque formation in the arteries. High-density lipoprotein (HDL) cholesterol helps prevent coronary artery disease.
  • High blood pressure. Chronic high blood pressure, which is associated with obesity, diabetes, and smoking, can damage the coronary arteries.
  • Smoking. Tobacco use increases the chances of having a heart attack by promoting plaque formation and blood clotting in the arteries.
  • Age and gender. The risk of having a heart attack increases with age - over the age 45 in men and 55 in women - with men bearing a greater risk.
  • Family history. Individuals with a family history of heart attacks and heart disease are at greater risk for a heart attack.
  • Chronic stress. Daily stress that is alleviated by smoking, alcohol consumption and overeating can lead to increased risk of heart disease and heart attacks. There is also evidence suggesting that chronic stress boosts the levels of white blood cells in circulation; white blood cells are a known component of plaque.
  • Diabetes mellitus. Diabetes, a disease where the body does not produce sufficient insulin hormone in response to sugar, can increase the risk of having a heart attack.
  • Inactive lifestyle. The lack of routine physical activity can lead to obesity and high cholesterol, both of which are risk factors for coronary artery disease.
  • Obesity. High body weight is associated with high blood pressure and cholesterol, two risk factors for heart disease.
  • Preeclampsia. This pregnancy-related condition elevates the blood pressure and increases the risk of cardiovascular disease, including heart attacks.

 

Symptoms

The classic heart attack symptoms are sudden chest pain and tightness, and shortness of breath. It is important to keep in mind that symptoms can vary. In particular, in women the symptoms can vary and can begin weeks before the actual heart attack. Women commonly report shortness of breath, nausea, fatigue, and body ache.

A more complete list of heart attack symptoms includes:

  • Pressure and tightness in the chest
  • Shortness of breath
  • Upper body pain (e.g. arm, shoulder, jaw)
  • Cold sweats
  • Fatigue
  • Feeling lightheaded or dizzy
  • Difficulty sleeping
  • Nausea or discomfort in the abdomen
  • Feelings like acid indigestion
  • Nervousness.

Diagnosis

The initial tests to diagnose a heart attack are performed in the emergency room. Once a positive diagnosis is made, follow-up tests allow further evaluation of the heart.

  • Electrocardiogram. An electrocardiogram (EKG) is a noninvasive test that measures the electrical activity of the heart. Abnormalities in the resulting data reveal a past or ongoing heart attack.
  • Blood tests. Elevated levels of specific cardiac enzymes known as troponins may be indicative of muscle damage from a heart attack.
  • Imaging. The size, detailed anatomy, and condition of the heart are visualized using techniques such as chest X-ray, computed tomography (CT) scan, and cardiac magnetic resonance imaging (MRI). An echocardiogram also produces an image of the heart by recording and processing sound waves that bounce back from the heart.
  • Stress test. Following a heart attack, this test evaluates the heart rate and rhythm under stress either in the form of exercise (treadmill or stationary bicycle) or induced with medication.
  • Angiography. This procedure uses X-ray imaging to visualize the flow of a contrast dye that is injected into the arteries, and detects blockages.

Treatment

The following lifestyle and medical interventions are used to treat a heart attack:

  • Lifestyle changes. Individuals who suffer a heart attack can improve their cardiovascular health and prevent future heart attacks by exercising regularly; maintaining a healthy weight; and sticking to a nutritious diet of foods that are rich in fruits and vegetables, but low in cholesterol, fat, and salt. Avoiding tobacco and limiting stress also helps maintain healthy arteries.
  • Medication. Aspirin and drugs like it minimize damage to the heart by preventing clot formation. Similarly, thrombolytic drugs dissolve existing clots, while blood thinners make the blood less sticky, hence less likely to clot. Beta blockers and angiotensin-converting enzyme (ACE) inhibitors reduce burden on the heart by lowering blood pressure. Excessive chest pain is treated with pain relievers and nitroglycerine. Statin drugs that lower cholesterol can also enhance outcomes following a heart attack.
  • Surgery. Surgical procedures that treat the cause of a heart attack include angioplasty and coronary bypass surgery. During an angioplasty, an existing plaque is compressed outward by inflating a balloon at the site. Then, a mesh tube (stent) is installed to prevent future plaque buildup at that site. Coronary artery bypass grafting restores blood flow to the heart by redirecting an existing upstream vein passed the blocked site.

Prevention

Individuals with a high risk of having a heart attack may be advised to take aspirin and other blood-thinning medications. Blood pressure and cholesterol lowering drugs may also be prescribed to help prevent plaque formation. At-home measures for maintaining healthy cardiovascular health include regular exercise, a healthy body weight, and a diet low in cholesterol, fat and salt. At-risk individuals should also avoid smoking, limit alcohol, and eliminate high-stress activities.

Sources

  • “About Heart Attacks”. American Heart Association. Jun 2014. Retrieved Jun 24, 2014. http://www.heart.org/HEARTORG/Conditions/HeartAttack/AboutHeartAttacks/About-Heart-Attacks_UCM_002038_Article.jsp.
  • "Heart attack ". Mayo Clinic. Mayo Foundation for Medical Education and Research. May 2014. Retrieved Jun 24, 2014. http://www.mayoclinic.org/diseases-conditions/heart-attack/basics/definition/con-20019520.
  • “What is a Heart Attack”. National Heart, Lung, and Blood Institute. NIH. Dec 2013. Retrieved Jun 24, 2014 https://www.nhlbi.nih.gov/health/health-topics/topics/heartattack/diagnosis.html.
  • “Heart Disease Facts”. Centers for Disease Control. Feb 2014. Retrieved Jun 24, 2014. http://www.nlm.nih.gov/medlineplus/ency/article/007089.htm.
  • Heidt, T, Sager, H.B., Courties, G., Dutta, P., Iwamoto, Y., Zaltsman, A., von Zur Muhlen, C., Bode, C., Fricchione, G.L., Denninger, J., Lin, C.P., Vinegoni, C., Libby, P., Swirski, F.K., Weissleder, R., Nahrendorf, M. “Chronic variable stress activates hematopoietic stem cells.” Nat Med. Published online 22 June 2014.