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Myocardial infarction (MI), commonly referred to as a heart attack, is caused by a decrease or complete blockage of blood flow to the heart muscle (myocardium). This can lead to irreversible death of myocardial cells, resulting in MI and potentially causing a change in colour of the cardiac muscle. MI can be caused by ischemia, which is when there is a lack of oxygen delivery to the myocardial tissue due to reduced blood flow. This can be a result of coronary artery disease, with plaques made up of cholesterol building up and blocking arteries. MI can lead to various complications, including arrhythmias, ventricular aneurysms, and heart failure, which can impact the colour of the cardiac muscle.
| Characteristics | Values |
|---|---|
| Definition | Myocardial infarction (MI), commonly known as a heart attack, is defined as the irreversible death of myocardial cells caused by ischemia. |
| Causes | Myocardial infarction is caused by a decreased or complete cessation of blood flow to a portion of the myocardium. This is often due to plaque rupture with thrombus formation in an epicardial coronary artery. |
| Symptoms | Chest pain is the hallmark symptom of myocardial infarction, but it can also cause breathlessness and mimic heartburn. Other symptoms include chest discomfort or pressure radiating to the neck, jaw, shoulder, or arm. |
| Complications | Complications of myocardial infarction include disturbances in heart rhythm (arrhythmias), ventricular septal defect (VSD), papillary muscle rupture or dysfunction, cardiac free wall rupture, ventricular aneurysm, dynamic left ventricular outflow tract obstruction, and right ventricular failure. |
| Treatment | Treatment for myocardial infarction involves improving blood flow to the heart muscle and may include medications, angioplasty to open blocked arteries, or bypass surgery. In the case of papillary muscle rupture, emergency surgical intervention is required, which may involve mitral valve repair or replacement. |
| Prevention | Leading a heart-healthy lifestyle can help prevent myocardial infarction by keeping arteries strong, elastic, and smooth, allowing for maximum blood flow. |
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What You'll Learn
Myocardial infarction (MI) causes
Myocardial infarction (MI), commonly referred to as a heart attack, is caused by a decrease or complete cessation of blood flow to the myocardium, which is part of the heart muscle. This deprivation of oxygen-rich blood can lead to myocardial cell death and necrosis, resulting in tissue death or infarction.
The most common cause of MI is atherosclerosis, where plaques made up of cholesterol and other substances build up on the walls of the coronary arteries, restricting blood flow. If these plaques rupture, a blood clot can form, blocking an artery and leading to a sudden, severe MI. This process of artery blockage is known as myocardial ischemia, which can develop slowly over time or occur rapidly. Myocardial ischemia can cause serious complications, including irregular heart rhythms (arrhythmias) and heart failure.
Other causes of MI include coronary artery spasms, where severe squeezing of a blood vessel, often narrowed by cholesterol plaques, results in reduced blood flow. Certain infections, such as COVID-19, can also cause damage to the heart muscle, and spontaneous coronary artery dissection (SCAD) is a rare but life-threatening condition where a tear occurs inside a heart artery.
MI can lead to various complications, including disturbances in heart rhythms, such as atrial fibrillation and ventricular tachycardia. Stroke is also a risk, which can occur due to clots transmitted from the heart or bleeding following anticoagulation treatment. Cardiogenic shock, resulting from the heart's inability to pump blood effectively, is the leading cause of in-hospital mortality following MI.
The treatment of MI includes the use of aspirin to prevent blood clotting, and nitro-glycerin to manage chest pain and improve oxygen supply to the heart. Early recognition of symptoms and immediate medical attention are crucial for improving the chances of survival during an MI.
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Cardiac muscle necrosis
Myocardial infarction (MI), commonly known as a heart attack, is caused by a decreased or completely blocked blood flow to a part of the myocardium. This results in a lack of oxygen in the myocardium, which can lead to myocardial cell death and liquefactive necrosis of the myocardial tissue. This process is known as cardiac muscle necrosis or heart muscle necrosis.
Coagulation necrosis is characterised by intramitochondrial flocculent precipitates, margination of nuclear chromatin, small holes in the plasma membrane, and relaxed myofibrils. After necrosis occurs, cardiac muscle cells are typically invaded by leukocytes, which phagocytose the sarcoplasmic debris. This results in the persistence of sarcolemmal "tubes" surrounded by condensed interstitial stroma and vessels. In cases of severe myocardial disruption, fibroblastic proliferation and collagen deposition can lead to the formation of scar tissue.
The extent of necrosis after MI is influenced by the duration of ischemia and the size of the area at risk (AAR), which is the region of tissue affected by the arterial blockage. The location of the blockage also impacts the infarct size, with proximal LAD occlusions in humans associated with a greater extent of necrosis and a worse prognosis. Additionally, necrosis is influenced by genetic and cellular factors that control cell-death susceptibility and modulate infarct expansion within the AAR.
Biological markers, such as enzymes and isoforms, are used to diagnose and monitor myocardial necrosis. These include total creatine kinase (CK), its cardiac isoenzyme (CK-MB), and isoforms of CK-MM and CK-MB. Cardiac troponins T and I (cTnT and cTnI) are also used as markers of myocardial injury and necrosis. These biomarkers help assess the severity and time course of myocardial injury and guide patient management.
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Myocardial ischemia
Myocardial infarction is characterised by the lack of oxygen delivery to myocardial tissue, resulting in tissue death or infarction. It is considered a type of acute coronary syndrome, which describes a sudden or short-term change in symptoms related to blood flow to the heart. Myocardial infarction can lead to cardiac arrest, where the heart stops contracting, causing all vital organs to cease functioning and potentially leading to death.
The treatment for myocardial ischemia focuses on improving blood flow to the heart muscle. This may include medications, procedures such as angioplasty to open blocked arteries, or bypass surgery. Leading a heart-healthy lifestyle is crucial in treating and preventing myocardial ischemia, as it helps keep arteries strong, elastic, and smooth, allowing for maximum blood flow.
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MI complications
Myocardial infarction (MI), commonly known as a heart attack, occurs when there is decreased or no blood flow to a part of the heart muscle (myocardium). This deprives the myocardium of oxygen, leading to tissue death (infarction) and causing permanent damage to the heart muscle. MI can lead to various complications, some of which may manifest up to a week after the initial event.
Complications of MI can be broadly categorized into arrhythmic, mechanical, and inflammatory sequelae. Arrhythmic complications include disturbances in heart rhythms, such as atrial fibrillation, ventricular tachycardia, and fibrillation. These irregularities can weaken the heart and may even be life-threatening. Mechanical complications include ventricular septal defect (VSD), papillary muscle rupture or dysfunction, cardiac free wall rupture, ventricular aneurysm, and dynamic left ventricular (LV) outflow tract (OT) obstruction. Inflammatory complications include early pericarditis and post-MI syndrome.
Additionally, MI can lead to cardiogenic shock, which is the leading cause of in-hospital mortality. Cardiogenic shock occurs when the heart is unable to pump blood adequately, typically within the days following an acute MI. The risk of cardiogenic shock is influenced by factors such as infarct size and age. MI can also cause Dressler's syndrome, a reaction to larger infarcts that can lead to pericarditis.
In the long term, MI can result in heart failure due to impaired heart muscle function, scarring, and increased muscle size. About 10% of MI cases develop an aneurysm of the left ventricle myocardium, which is a risk factor for heart failure, ventricular arrhythmia, and clot formation. Stroke is another potential complication of MI, as clots can form in the heart and travel to the brain.
The prognosis and outcomes following MI depend on factors such as ejection fraction, age, and comorbidities, and the success of reperfusion and revascularization procedures. Early diagnosis, prompt treatment, and surgical intervention are crucial for improving survival rates and patient outcomes. Cardiac rehabilitation also plays a vital role in the recovery process, offering benefits such as improved quality of life and reduced disability.
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MI diagnosis and treatment
Myocardial infarction (MI), commonly known as a heart attack, occurs when there is decreased or completely blocked blood flow to a part of the heart muscle (myocardium). This can be caused by a partial or complete blockage of a coronary artery due to a buildup of plaques (atherosclerosis). MI can lead to serious complications, including disturbances in heart rhythm, stroke, and heart failure. Therefore, prompt diagnosis and treatment are crucial.
Diagnosis of MI
MI diagnosis involves a combination of patient history, physical examination, and diagnostic tests. During a physical examination, a healthcare provider will check vital signs, including pulse, blood oxygen levels, and blood pressure, and listen to heart and lung sounds. They will also inquire about the patient's symptoms and may request a description of the event from someone who was present.
Diagnostic tests play a crucial role in confirming MI. These include:
- Blood tests: Measuring cardiac troponin levels in the blood is considered one of the most reliable ways to diagnose MI. Troponins are highly sensitive biomarkers for detecting injury to the heart muscle, with levels rising within 2-3 hours of injury and peaking within 1-2 days. Other blood tests, such as creatine kinase MB (CK-MB) and myoglobin, are less specific but may still be used in conjunction with troponin tests.
- Electrocardiogram (ECG): ECG is often one of the first tests performed in an emergency setting and involves measuring the electrical activity of the heart. It can detect abnormalities associated with MI, such as ST-segment elevation (indicative of STEMI) or depression, T-wave changes, new Q waves, and left bundle branch block. Repeated ECGs may be necessary to monitor changes over time.
- Non-invasive imaging: While not routinely recommended, chest X-rays, echocardiography, and myocardial perfusion imaging can be used to explore alternative causes of symptoms or confirm suspicions of coronary artery disease.
Treatment of MI
The treatment of MI is time-critical, and immediate medical attention is essential. The primary goal is to restore blood flow to the heart and prevent further damage. Treatment options include:
- Pharmacological interventions: Dual antiplatelet therapy, including intravenous heparin infusion and adenosine diphosphate inhibitor receptor (P2Y12 inhibitor), is often administered before reperfusion. Other medications, such as glycoprotein IIb/IIIa inhibitors or direct thrombin inhibitors, may be given during reperfusion procedures. Long-term medications, such as aspirin, high-dose statins, beta-blockers, and ACE inhibitors, may be prescribed following an acute MI to prevent recurrent events.
- Reperfusion strategies: The preferred method for STEMI is emergent PCI (percutaneous coronary intervention), ideally performed within 12 hours of symptom onset. If PCI is unavailable within 90 minutes, intravenous thrombolytic agents should be used to dissolve blood clots and restore blood flow. For NSTEMI, the initial approach typically involves medical management with antiplatelet agents and other medications, with PCI considered within 48 hours if necessary.
- Cardiac rehabilitation: Following the initial treatment, patients may undergo cardiac rehabilitation, including follow-up monitoring, stress testing, and lifestyle modifications, to prevent future cardiac events.
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Frequently asked questions
Myocardial infarction (MI), commonly referred to as a "heart attack", is the irreversible death of myocardial cells caused by ischemia, or lack of oxygen delivery to the myocardial tissue.
MI leads to ultrastructural changes in the heart muscle, including sarcolemmal disruption, myofibril relaxation, and mitochondrial alterations. The infarcted area heals by scar formation, and the remodelled heart is characterised by dilation and segmental hypertrophy of the remaining viable tissue.
MI is often associated with chest pain or discomfort that can radiate to the neck, jaw, shoulder, or arm. Other symptoms may include shortness of breath, nausea, sweating, and irregular heart rhythms.
MI can lead to various complications, including disturbances in heart rhythms (arrhythmias), ventricular septal defect (VSD), papillary muscle rupture, cardiac free wall rupture, ventricular aneurysm, cardiogenic shock, and heart failure.
