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Acute Myocardial Infarction

What is Acute Myocardial Infarction (AMI)?

Myocardial infarction commonly known as a heart attack is a pathological irreversible damage to the heart muscles caused by an imbalance between oxygen supply and demand to the heart muscle. This occurs due to buildup of fat or cholesterol in the blood vessel lining leading to plaque formation. This plaque cause narrowing of the coronary arteries in a process called atherosclerosis. The plaque eventually breaks away and the blood clot forms around it resulting in partial or total occlusion of blood flow to the heart muscle. Most AMIs are caused by atherosclerosis, but the other medical conditions can be the culprit as well. These include coronary artery spasm, cocaine abuse, congenital heart diseases, collagen vascular disease, and hypercoagulable state. AMI is categorized into 2 categories based on ECG findings, namely non-ST-segment elevation MI (NSTEMI) and ST-segment elevation MI (STEMI).

What is the epidemiology of Acute Myocardial Infarction?

Approximately three million people worldwide suffer from acute myocardial infarction, with more than one million deaths in the United States annually. According to the American Heart Association (AHA), someone in the United States has a heart attack about every 40 seconds. Also, in a typical adult Emergency department population with acute chest pain, about 15% of patients will have acute coronary syndrome (ACS).

What are the risk factors of Acute Myocardial Infarction?

There are both modifiable and non-modifiable risk factors of AMI. Modifiable risk factors include:

  • High level of blood cholesterol and LDL
  • Low level of HDL called “good cholesterol”
  • Hypertension
  • Diabetes
  • Family history of coronary artery disease at an early age
  • Cigarette smoking
  • Obesity
  • Physical inactivity 

In contrast, age, sex, and family history are non-modifiable risk factors for AMI.

What are the symptoms of Acute Myocardial Infarction?

The main symptom of AMI is chest discomfort or pain often described as heaviness, crushing, pressing, tightness, or squeezing and tends to spread to the lower jaw, neck, shoulder, and upper abdomen.

Other symptoms are shortness of breath, nausea, vomiting, or belching, sudden weakness, sweating, or lightheadedness.

Some patient population such as elderly, women and diabetes present with atypical symptoms such as abdominal pain or dizziness or no specific symptoms and this are known as “silent” MI and these can be challenging for patients, family members, and healthcare practitioners.

How to Diagnosis Acute Myocardial Infarction?

History and physical examination are very important in the diagnosis of AMI and should focus on the onset, quality, and associated symptoms. Rapid testing with ECG is indicated for all patients presenting with chest pain. Laboratory tests such as Cardiac biomarker (troponins), CBC, lipid profile, renal function, and the comprehensive metabolic panel should also be ordered. An echocardiogram can be useful as well to assess wall motion and to detect the presence of cardiac tamponade.

What are the differential diagnoses of Acute Myocardial Infarction?

  • Pulmonary embolism
  • Aortic dissection
  • Pneumothorax
  • Pericarditis

What are the treatments of Acute Myocardial Infarction?

Treatment will depend on the type of AMI on ECG findings. Treatment of all MI patients includes, oxygen therapy, IV nitroglycerin or sublingual for pain relief, morphine can also be given to ease patient’s anxiety and aspirin to prevent platelet aggregation at the rupture site and stop new blood clots from forming

Immediate reperfusion is the most important treatment therapy for a patient with STEMI. The preferred method is percutaneous coronary intervention (PCI) and should be performed within 90 minutes of the diagnosis of STEMI. The procedure is done using a threaded catheter through a large blood vessel toward the heart and a dye is injected to locate the blockage in the heart blood vessel. Thrombolytics agents known as clot-buster can also be used as a reperfusion agent if PCI is not visible within 90 minutes and should be administered if no contraindication within 30 minutes of patient presentation. 

Patient with NSTEMI is treated with medications including aspirin to prevent new blood clot, beta-blockers to slow heart rate and a statin to lower cholesterol in the blood. An urgent cardiac catheterization to open the clogged coronary arteries or intensive medical therapy will be determined based on patient presentation and diagnostic test findings.

How to prevent Acute Myocardial Infarction?

  • Blood pressure control
  • Regular exercise
  • Eating healthy
  • Lowering LDL and Cholesterol

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