Acute myocardial infarction
Acute myocardial infarction (AMI) or heart attack is a medical emergency that arises when a part of the heart muscle is deprived of oxygen and nutrients due to a lack of blood supply, resulting in tissue death and potentially fatal complications. It belongs to a spectrum of the acute coronary syndrome (ACS) which is a sudden blockage of blood flow to the heart. AMI is divided into 2 types based on the findings of the electrocardiogram:
ST-elevation myocardial infarction (STEMI)
Non-ST-elevation myocardial infarction (NSTEMI)
The characteristic symptom of AMI is persistent chest pain which varies in intensity, ranging from discomfort to intense, excruciating pain. The feeling itself is often described as crushing, squeezing, stabbing, or burning and is accompanied by pressure or fullness in the chest. In some people, it radiates to the arms, neck, jaw, back, or stomach. Not only in the intensity and pattern, but it also differs in the rate of onset; developing suddenly and without any warning in some people while gradually increasing over several minutes to hours in others.
Despite chest pain being the characteristic symptom, around 20% of the patients only experience mild discomfort in the chest and are known to have an atypical onset of AMI. Atypical onset is more commonly seen in females, diabetics, the elderly, or postoperative individuals.
Along with chest pain, patients may exhibit:
Shortness of breath
The diagnostic protocol for AMI begins with an assessment of the patient's clinical symptoms, medical history, and physical examination.
The electrocardiogram (ECG) is the initial and foremost investigation for AMI. It should be performed within 5 to 10 minutes of arrival at an emergency department. ECG maps out the electrical signals of the heart using electrodes that are placed on the patient's chest, arms, and legs. Irregularities in the heart's rhythm and electrical signals indicate AMI. Particularly, it is important to distinguish STEMI and NSTEMI which defines the direction of further investigation and management.
Next, a blood sample is taken to evaluate the level of certain biomarkers such as troponins T and I, MB isoforms of creatine (CK-MB), creatine kinase (CK), and myoglobin. Most important among these biomarkers are troponins which are typically found in the heart muscles and their higher levels in the blood indicate damage to the heart muscle. Troponin levels peak during the first 48 hours of the heart damage and then remain constant during the next 24 hours. A steep rise or fall in troponin levels indicates an acute injury whereas stable values in serial measurements indicate chronic myocardial injury.
Finally, an echocardiography is performed which shows wall motion abnormalities and helps aid immediate management decisions as well as detect long-term complications.
The goal of AMI management is to relieve pain, restore blood flow to the affected area of the heart as quickly as possible, reduce the damage to the heart muscle, and prevent long-term complications including the risk of future heart attacks. These goals are achieved by a combination of the following interventions:
Medications: Commonly used medications include painkillers such as non-steroidal anti-inflammatory drugs (NSAIDs) which include aspirin and ibuprofen and sometimes opioids such as morphine. A very important drug given in emergency settings is nitroglycerin which relaxes the blood vessels supplying the heart and improves blood flow to the heart. Beta-blockers, such as metoprolol, reduce the workload of the heart. And blood thinners, such as heparin, prevent the formation of blood clots.
Reperfusion therapy: In STEMI, reperfusion therapy, preferably percutaneous coronary intervention (PCI), is required in less than 60 minutes of arrival at the hospital. A PCI involves inserting a thin, flexible tube into an artery, usually in the groin or wrist, and threading up to the heart to place a catheter balloon that inflates to unblock the blood vessel. Sometimes a stent (a small mesh) is also placed to prevent it from narrowing again. If PCI is not available, thrombolytic medications are given to achieve the same purpose; however, they are not as effective as PCI.
Coronary artery bypass surgery: In cases where the initial therapy has not produced optimal results and the blood vessels leading to the heart muscles are still not properly unclogged, a coronary artery bypass surgery (CABG) is done to unblock the remaining blood vessels. In this surgical procedure, a blood vessel taken from another region of the body of the patient is grafted onto the heart to bypass the blocked blood vessel.
Cardiac rehabilitation: To reduce the long-term complications of AMI and improve the quality of life of the patients, cardiac rehabilitation is often recommended. Patients go through a tailored program of exercise, education, and counseling designed to help them recover and return to their everyday life activities.
Lifestyle changes: Lifestyle modifications are at the core of achieving positive long-term outcomes of AMI therapy. Such modifications include quitting smoking, adopting a heart-healthy diet, and engaging in regular physical activity.
In conclusion, AMI is a medical emergency that requires prompt diagnosis and management to prevent potentially life-threatening complications. Chest pain is the cardinal symptom but its intensity and pattern of onset vary among individuals. Diagnosis involves an ECG, blood tests, and echocardiography, while management includes medications, reperfusion therapy, bypass surgery, cardiac rehabilitation, and lifestyle changes. Early recognition and appropriate intervention are crucial to improve patient outcomes and reduce the risk of future heart attacks.