Myocardial infarction

A myocardial infarction (MI) is the medical term for what is commonly called a heart attack.

This condition is a dangerous type of acute coronary syndrome. Acute coronary syndrome describes sudden changes in blood flow to the heart. An MI occurs when blood flow decreases or stops in a coronary artery. This lack of oxygen delivery to the heart muscle is called ischemia. When the muscle cells do not receive oxygen, they die. This tissue death is known as an infarction.

The most common cause of an MI is coronary artery disease. In this condition, buildup forms inside the arteries. A common mechanism involves the rupture of an atherosclerotic plaque. This plaque is a buildup of material in the artery wall. When the plaque ruptures, it can cause a complete blockage of the artery. Less commonly, a coronary artery spasm can cause an MI. A spasm is a sudden squeezing of the artery. These spasms can be triggered by extreme cold or significant emotional stress. This specific stress-related condition is sometimes called Takotsubo syndrome, or broken heart syndrome.

Doctors classify MIs into different types based on an electrocardiogram (ECG). An ECG is a test that records the electrical activity of the heart. One type is called an ST elevation myocardial infarction, or STEMI. This is identified when specific changes appear on the ECG. Another type is the non-ST elevation myocardial infarction, or NSTEMI. The distinction is important for how doctors treat the patient. While both involve heart muscle damage, the electrical patterns differ.

Symptoms of an MI can vary greatly between people. The most common sign is retrosternal chest pain. This pain often feels like tightness, pressure, or squeezing. It can radiate to the left shoulder, arm, or jaw. Some people describe the sensation as heartburn or anxiety. About 30% of people experience atypical symptoms. Women are more likely to have these unusual symptoms. They may feel nausea, fatigue, or pain in the neck and back. Some people experience a "silent" MI. This means they have little or no history of symptoms.

Medical professionals use several tools to diagnose an MI. They use blood tests to look for specific biomarkers. One important protein is called troponin. The presence of troponin in the blood indicates that heart cells have died. Doctors also look for creatine kinase MB. Once an MI is confirmed, treatment must be time-critical. For a STEMI, doctors try to restore blood flow quickly. They may use percutaneous coronary intervention (PCI). This involves pushing the arteries open, sometimes using a stent. A stent is a tiny tube that holds the artery open.

Other treatments include thrombolysis. This is the use of medication to remove a blockage. For an NSTEMI, doctors might use the blood thinner heparin. If a patient has diabetes or multiple blockages, they may need surgery. This is called coronary artery bypass surgery, or CABG. After the event, patients often take long-term medications. These include aspirin, beta blockers, and statins. Lifestyle changes are also a standard part of recovery.

Myocardial infarctions are a major global health issue. In 2015, approximately 15.9 million MIs occurred worldwide. This included over 3 million STEMIs and 4 million NSTEMIs. In the United States, about one million people have an MI every year. In the developed world, the risk of death from a STEMI is about 10%. In 2011, MIs were one of the five most expensive conditions for hospital stays in the US. The cost was about $11.5 billion for 612,000 stays.

Many factors can increase the risk of an MI. These include high blood pressure, smoking, and diabetes. Obesity, poor diet, and lack of exercise also play roles. Smoking is a major cause, contributing to about 36% of coronary artery disease cases. Genetics also matter. Scientists have found 27 genetic variants associated with an increased risk. Some of these involve genes like PCSK9 and SORT1. Family history is a significant factor for many people.