What is a myocardial infarction?
A myocardial infarction occurs when a portion of the heart muscle is starved of blood and oxygen and dies.
Myocardial infarction literally means “death of heart muscle”, and is also known as a heart attack.
What causes a myocardial infarction?
In addition to pumping blood around our body, our heart is a muscle that requires a constant supply of oxygen and nutrients.
The coronary arteries branch off the aorta (the main vessel that supplies oxygenated blood to the body) and there are four main coronary arteries: the right and left coronary artery, the left anterior descending artery, and the left circumflex artery.
If one of these arteries or its branches become blocked it is unable to supply a portion of the heart muscle with blood and oxygen and the tissue becomes starved of oxygen (this is known as cardiac ischemia). If the lack of oxygen persists, the heart muscle will die. This is known as a myocardial infarction or heart attack.
Blockages in the arteries are usually caused by a buildup of fat, cholesterol, and other substances (called a plaque) which narrows the blood vessel. The plaque can break away and form a clot that can block one of the smaller arteries.
Risk factors for a myocardial infarction include:
- Age: men over the age of 45 or women over the age of 55 are at increased risk
- Autoimmune conditions, such as rheumatoid arthritis
- Family history of a myocardial infarction
- High blood pressure
- High cholesterol or triglyceride levels
- Lack of physical activity
- Metabolic syndrome
- Preeclampsia during pregnancy
- Smoking or long-term exposure to second-hand smoke
- Substance misuse
What are the symptoms of a myocardial infarction?
Most myocardial infarctions produce some chest pain, although occasionally there are no symptoms at all. In some people, the symptoms may come and go, last over several hours, but may be subtle, especially in women.
Symptoms may include:
- Aching sensation in the chest or arms
- Sense of fullness in the chest
- Squeezing of the heart, like a giant fist has enveloped it
- Pain in the arm, neck, back, or jaw
- Cold sweat
- Dizziness or lightheadedness
- Shortness of breath
Symptoms of a myocardial infarction can often be mistaken for heartburn.
Many myocardial infarctions are preceded by symptoms of angina, which is chest pain that is caused by a low supply of oxygen to the heart muscle, usually caused by a partially blocked coronary artery. Unlike a myocardial infarction, however, the tissue does not die, and the heart is not permanently damaged. Rather the blood is restored and the pain resolves within minutes.
How is a myocardial infarction diagnosed?
See your doctor if you are having symptoms of angina. If you have already been diagnosed with angina, take nitroglycerin if prescribed. Call for emergency assistance if the nitroglycerin fails to resolve your symptoms.
Seek emergency assistance (immediately call 911) if you are having symptoms of a myocardial infarction or you suspect somebody is having a myocardial infarction. Take aspirin is recommended.
Your doctor will conduct some blood tests and perform an ECG (electrocardiogram) testing. Other tests may also be conducted, such as a chest x-ray or angiogram.
About a quarter of all myocardial infarctions occur without warning signs and are often associated with a condition called “silent ischemia”, where interruptions to the blood supply of the heart muscle occur but these are pain-free although they still result in damage. The condition is often discovered during routine ECG testing. People with diabetes are more at risk of silent ischemia.
How is a myocardial infarction treated?
Restoring blood flow quickly is important to minimize damage to heart tissue.
Treatments for a myocardial infarction include:
- Thrombolytics, to dissolve the clot
- Antiplatelet agents
- Analgesics, such as morphine for pain relief
- Other medications, such as beta-blockers, ACE inhibitors, and statins
- Cardiac rehabilitation