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Myocardial Infarction

Updated : August 24, 2023





Background

Myocardial infarction (MI), also known as a heart attack, occurs when blood flow to a part of the myocardium is reduced or completely blocked, leading to inadequate oxygen supply to the tissue. This lack of oxygen can cause damage to the heart muscle cells and eventually lead to their death, a process known as necrosis.

In most cases, MI is caused by underlying coronary artery disease, which is the leading cause of death in the United States, accounting for about 1 in every 4 deaths. MI can present in different states, ranging from silent to fatal. Some people may experience no symptoms, while others may have severe chest discomfort or pressure that can spread to the jaw, neck, shoulder, or arm.

Other possible symptoms include shortness of breath, sweating, nausea, and lightheadedness. In some cases, the first sign of MI may be sudden cardiac arrest, which can lead to death if not treated promptly. Early diagnosis and treatment of MI are crucial for preventing complications and improving outcomes.

Epidemiology

Myocardial infarction is a common condition, with millions worldwide experiencing a heart attack yearly. According to the World Health Organization, coronary heart disease (CHD), which includes MI, is the leading cause of death globally. The risk of myocardial infarction increases with age, with most heart attacks occurring in people over 45.

However, heart attacks can also occur in younger people, particularly those with underlying risk factors such as diabetes, high blood pressure, or a family history of heart disease. Men are more likely than women to have a heart attack, although the gap has been closing in recent years. Women are more likely to have atypical symptoms and may be misdiagnosed or have delayed diagnosis and treatment. Certain racial and ethnic groups have a higher risk of myocardial infarction than others.

For example, African Americans, Hispanic/Latino Americans, and Native Americans have a higher risk of CHD and MI than white Americans. Asian Americans have a lower incidence of MI than the other groups mentioned. Certain lifestyle factors can increase the risk of myocardial infarction, such as smoking, physical inactivity, poor diet, and excessive alcohol consumption. Certain medical conditions can increase the risk of myocardial infarction, including high blood pressure, high cholesterol, diabetes, and obesity.

Anatomy

Pathophysiology

Myocardial infarction occurs when one or more large epicardial coronary arteries become abruptly hindered for 20 to 40 minutes, typically due to a thrombotic occlusion caused by plaque rupture. The insufficient oxygen supply to the myocardium causes initial changes at the ultrastructural level, such as sarcolemmal disruption and myofibril relaxation, followed by mitochondrial alterations.

This ultimately leads to liquefactive necrosis of the myocardial tissue, which spreads from the sub-endocardium to the sub-epicardium. Although the subepicardium has an increased collateral circulation, its death is delayed. The extent of cardiac dysfunction depends on the region affected by the infarction.

Since the myocardium has minimal regenerative ability, scar tissue forms during the healing process, often resulting in heart remodeling characterized by segmental hypertrophy of remaining viable tissue, and cardiac dysfunction.

Etiology

Myocardial infarction is closely linked with coronary artery disease, and modifiable and non-modifiable risk factors contribute to the development of MI. The INTERHEART, multi-center case-control study identified several modifiable risk factors, including smoking, hypertension, abnormal lipid profile, diabetes mellitus, abdominal obesity, lack of daily consumption of fruits or vegetables, lack of physical activity, psychosocial factors, and alcohol consumption.

Of these, smoking and abnormal apolipoprotein ratio were strongly associated with MI. Moreover, moderately high plasma homocysteine levels, an independent risk factor, were identified as a modifiable risk factor for MI. On the other hand, non-modifiable risk factors include advanced age, genetics, male gender, and especially with a first-degree relative’s history of cardiovascular events before age 50.

Genetics

Prognostic Factors

Despite significant advances in its treatment, MI has a high mortality rate of 30%, with most deaths occurring before hospital arrival. Additionally, within the first year after an MI, there is an additional mortality rate of 12%.

The extent of cardiac muscle damage and ejection fraction play a crucial role in determining the overall prognosis, with patients with preserved left ventricular function tending to have better outcomes.

However, several factors can worsen the prognosis, including advanced age, diabetes, congestive heart failure, delayed reperfusion, elevated C-reactive protein and B-type natriuretic peptide levels, and depression.

Clinical History

Clinical History

The clinical history of myocardial infarction includes risk factors such as smoking, high blood pressure, cholesterol, diabetes, obesity, and a family history of heart disease.

Symptoms of a heart attack may include chest pain or discomfort, shortness of breath, sweating, nausea or vomiting, light-headedness or dizziness, and pain or discomfort in the arms, back, neck, jaw, or stomach.

A diagnosis of myocardial infarction is typically made based on a combination of clinical symptoms, electrocardiogram (ECG) results, and blood tests that measure levels of specific proteins released during a heart attack.

Physical Examination

Physical Examination

Myocardial ischemia can manifest in various forms, such as chest pain, mandibular discomfort, upper extremity pain, or epigastric discomfort. These symptoms may occur during physical activity or at rest. Dyspnea or fatigue can also occur, referred to as ischemic equivalents. Chest pain associated with myocardial ischemia is usually felt behind the sternum and is described as pressure or heaviness.

The pain may spread to the neck, left shoulder, or arms and may occur without any apparent triggers. It may come and go or persist for more than 20 minutes. The pain is generally not affected by changes in position or movement. Other symptoms, such as nausea, sweating, abdominal pain, dyspnea, and syncope, may also be present.

Myocardial infarction can also present in unusual ways, such as palpitations or, in extreme cases, cardiac arrest. In some instances, there may be no noticeable symptoms.

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Differential Diagnoses

Angina pectoris

Pneumothorax

Pulmonary Embolism

ST-segment elevation myocardial infarction (STEMI)

Non-ST segment elevation myocardial infarction (NSTEMI)

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

Pharmacological Treatment:

Thrombolytics: Thrombolytics can dissolve blood clots and restore blood flow to the heart. These drugs are most effective when given within the first few hours of an MI. Commonly used thrombolytics include alteplase, reteplase, and tenecteplase.

Antiplatelet agents: Antiplatelet agents, such as aspirin and clopidogrel, help to prevent blood clots from forming and can reduce the risk of further heart damage. These drugs are usually given in combination with thrombolytics.

Beta-blockers: Beta-blockers help to slow the heart rate and reduce the workload on the heart. This can help reduce the amount of oxygen the heart needs and prevent further damage. Commonly used beta-blockers include metoprolol and carvedilol.

ACE inhibitors: ACE inhibitors help widen blood vessels and reduce blood pressure, improving blood flow to the heart. These drugs are also effective in preventing further heart damage. Commonly used ACE inhibitors include enalapril and lisinopril.

Statins: High cholesterol levels can contribute to the development of heart disease, so statins are often prescribed to people who have had an MI to reduce the risk and prevent further attacks.

Lifestyle Changes: Making lifestyle changes such as quitting smoking, eating a healthy diet, and getting regular exercise can help to reduce the risk of further heart damage. In addition, stress reduction can help to reduce stress and improve overall heart health.

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Medication

 

metoprolol

Early Treatment
Initial dose::

5

mg

Intravenous (IV)

every 2 minutes as tolerated for three doses
tolerance dose: 50 mg orally every 6 hours; continued for two days
intolerance dose:25-50 mg orally every 6 hours depending on the rate of intolerance
Late Treatment:
Maintenance dose: 100 mg orally twice a day
Congestive Heart Failure:
25 mg orally once a day; double dose every two weeks up to 200 mg orally once a day



ramipril

2.5

mg

Orally 

daily 1 week, following 5 mg Daily for 3 weeks



lisinopril

5 mg orally (onset of symptoms of acute MI);
Subsequent dose of 5 mg orally after 24 hours, and 10 mg orally after 48 hours.
and increase 10 mg orally daily 6 weeks.



clopidogrel 

Indicated for Recent MI and Stroke:

75

mg

Tablet

Orally 

every day



veliflapon 


Indicated for Myocardial Infarction and Heart Attacks
Pending FDA approval for the therapy of heart attacks and myocardial infarction



dopamine 

Indicated for treating heart problems and imbalances in shock caused by infections, injuries, septicemia, surgery, kidney issues, or heart failure

Continuous infusion:
Initial dose: 2-10 mcg/kg/min intravenously (IV)

Maintenance dose: 2-50 mcg/kg/min intravenously (IV)



aspirin 

prophylaxis:

75 mg to 162 mg once a day orally



 

dopamine

continuous infusion:
2-10 mcg/kg/min IV
2-50 mcg/kg/min IV



dopamine

continuous infusion:
2-10 mcg/kg/min IV
2-50 mcg/kg/min IV



 

aspirin 

75 mg to 100 mg once a day orally



Media Gallary

References

https://www.ncbi.nlm.nih.gov/books/NBK537076/

Myocardial Infarction

Updated : August 24, 2023




Myocardial infarction (MI), also known as a heart attack, occurs when blood flow to a part of the myocardium is reduced or completely blocked, leading to inadequate oxygen supply to the tissue. This lack of oxygen can cause damage to the heart muscle cells and eventually lead to their death, a process known as necrosis.

In most cases, MI is caused by underlying coronary artery disease, which is the leading cause of death in the United States, accounting for about 1 in every 4 deaths. MI can present in different states, ranging from silent to fatal. Some people may experience no symptoms, while others may have severe chest discomfort or pressure that can spread to the jaw, neck, shoulder, or arm.

Other possible symptoms include shortness of breath, sweating, nausea, and lightheadedness. In some cases, the first sign of MI may be sudden cardiac arrest, which can lead to death if not treated promptly. Early diagnosis and treatment of MI are crucial for preventing complications and improving outcomes.

Myocardial infarction is a common condition, with millions worldwide experiencing a heart attack yearly. According to the World Health Organization, coronary heart disease (CHD), which includes MI, is the leading cause of death globally. The risk of myocardial infarction increases with age, with most heart attacks occurring in people over 45.

However, heart attacks can also occur in younger people, particularly those with underlying risk factors such as diabetes, high blood pressure, or a family history of heart disease. Men are more likely than women to have a heart attack, although the gap has been closing in recent years. Women are more likely to have atypical symptoms and may be misdiagnosed or have delayed diagnosis and treatment. Certain racial and ethnic groups have a higher risk of myocardial infarction than others.

For example, African Americans, Hispanic/Latino Americans, and Native Americans have a higher risk of CHD and MI than white Americans. Asian Americans have a lower incidence of MI than the other groups mentioned. Certain lifestyle factors can increase the risk of myocardial infarction, such as smoking, physical inactivity, poor diet, and excessive alcohol consumption. Certain medical conditions can increase the risk of myocardial infarction, including high blood pressure, high cholesterol, diabetes, and obesity.

Myocardial infarction occurs when one or more large epicardial coronary arteries become abruptly hindered for 20 to 40 minutes, typically due to a thrombotic occlusion caused by plaque rupture. The insufficient oxygen supply to the myocardium causes initial changes at the ultrastructural level, such as sarcolemmal disruption and myofibril relaxation, followed by mitochondrial alterations.

This ultimately leads to liquefactive necrosis of the myocardial tissue, which spreads from the sub-endocardium to the sub-epicardium. Although the subepicardium has an increased collateral circulation, its death is delayed. The extent of cardiac dysfunction depends on the region affected by the infarction.

Since the myocardium has minimal regenerative ability, scar tissue forms during the healing process, often resulting in heart remodeling characterized by segmental hypertrophy of remaining viable tissue, and cardiac dysfunction.

Myocardial infarction is closely linked with coronary artery disease, and modifiable and non-modifiable risk factors contribute to the development of MI. The INTERHEART, multi-center case-control study identified several modifiable risk factors, including smoking, hypertension, abnormal lipid profile, diabetes mellitus, abdominal obesity, lack of daily consumption of fruits or vegetables, lack of physical activity, psychosocial factors, and alcohol consumption.

Of these, smoking and abnormal apolipoprotein ratio were strongly associated with MI. Moreover, moderately high plasma homocysteine levels, an independent risk factor, were identified as a modifiable risk factor for MI. On the other hand, non-modifiable risk factors include advanced age, genetics, male gender, and especially with a first-degree relative’s history of cardiovascular events before age 50.

Despite significant advances in its treatment, MI has a high mortality rate of 30%, with most deaths occurring before hospital arrival. Additionally, within the first year after an MI, there is an additional mortality rate of 12%.

The extent of cardiac muscle damage and ejection fraction play a crucial role in determining the overall prognosis, with patients with preserved left ventricular function tending to have better outcomes.

However, several factors can worsen the prognosis, including advanced age, diabetes, congestive heart failure, delayed reperfusion, elevated C-reactive protein and B-type natriuretic peptide levels, and depression.

Clinical History

The clinical history of myocardial infarction includes risk factors such as smoking, high blood pressure, cholesterol, diabetes, obesity, and a family history of heart disease.

Symptoms of a heart attack may include chest pain or discomfort, shortness of breath, sweating, nausea or vomiting, light-headedness or dizziness, and pain or discomfort in the arms, back, neck, jaw, or stomach.

A diagnosis of myocardial infarction is typically made based on a combination of clinical symptoms, electrocardiogram (ECG) results, and blood tests that measure levels of specific proteins released during a heart attack.

Physical Examination

Myocardial ischemia can manifest in various forms, such as chest pain, mandibular discomfort, upper extremity pain, or epigastric discomfort. These symptoms may occur during physical activity or at rest. Dyspnea or fatigue can also occur, referred to as ischemic equivalents. Chest pain associated with myocardial ischemia is usually felt behind the sternum and is described as pressure or heaviness.

The pain may spread to the neck, left shoulder, or arms and may occur without any apparent triggers. It may come and go or persist for more than 20 minutes. The pain is generally not affected by changes in position or movement. Other symptoms, such as nausea, sweating, abdominal pain, dyspnea, and syncope, may also be present.

Myocardial infarction can also present in unusual ways, such as palpitations or, in extreme cases, cardiac arrest. In some instances, there may be no noticeable symptoms.

Differential Diagnoses

Angina pectoris

Pneumothorax

Pulmonary Embolism

ST-segment elevation myocardial infarction (STEMI)

Non-ST segment elevation myocardial infarction (NSTEMI)

Pharmacological Treatment:

Thrombolytics: Thrombolytics can dissolve blood clots and restore blood flow to the heart. These drugs are most effective when given within the first few hours of an MI. Commonly used thrombolytics include alteplase, reteplase, and tenecteplase.

Antiplatelet agents: Antiplatelet agents, such as aspirin and clopidogrel, help to prevent blood clots from forming and can reduce the risk of further heart damage. These drugs are usually given in combination with thrombolytics.

Beta-blockers: Beta-blockers help to slow the heart rate and reduce the workload on the heart. This can help reduce the amount of oxygen the heart needs and prevent further damage. Commonly used beta-blockers include metoprolol and carvedilol.

ACE inhibitors: ACE inhibitors help widen blood vessels and reduce blood pressure, improving blood flow to the heart. These drugs are also effective in preventing further heart damage. Commonly used ACE inhibitors include enalapril and lisinopril.

Statins: High cholesterol levels can contribute to the development of heart disease, so statins are often prescribed to people who have had an MI to reduce the risk and prevent further attacks.

Lifestyle Changes: Making lifestyle changes such as quitting smoking, eating a healthy diet, and getting regular exercise can help to reduce the risk of further heart damage. In addition, stress reduction can help to reduce stress and improve overall heart health.

metoprolol

Early Treatment
Initial dose::

5

mg

Intravenous (IV)

every 2 minutes as tolerated for three doses
tolerance dose: 50 mg orally every 6 hours; continued for two days
intolerance dose:25-50 mg orally every 6 hours depending on the rate of intolerance
Late Treatment:
Maintenance dose: 100 mg orally twice a day
Congestive Heart Failure:
25 mg orally once a day; double dose every two weeks up to 200 mg orally once a day



ramipril

2.5

mg

Orally 

daily 1 week, following 5 mg Daily for 3 weeks



lisinopril

5 mg orally (onset of symptoms of acute MI);
Subsequent dose of 5 mg orally after 24 hours, and 10 mg orally after 48 hours.
and increase 10 mg orally daily 6 weeks.



clopidogrel 

Indicated for Recent MI and Stroke:

75

mg

Tablet

Orally 

every day



veliflapon 


Indicated for Myocardial Infarction and Heart Attacks
Pending FDA approval for the therapy of heart attacks and myocardial infarction



dopamine 

Indicated for treating heart problems and imbalances in shock caused by infections, injuries, septicemia, surgery, kidney issues, or heart failure

Continuous infusion:
Initial dose: 2-10 mcg/kg/min intravenously (IV)

Maintenance dose: 2-50 mcg/kg/min intravenously (IV)



aspirin 

prophylaxis:

75 mg to 162 mg once a day orally



dopamine

continuous infusion:
2-10 mcg/kg/min IV
2-50 mcg/kg/min IV



dopamine

continuous infusion:
2-10 mcg/kg/min IV
2-50 mcg/kg/min IV



aspirin 

75 mg to 100 mg once a day orally



https://www.ncbi.nlm.nih.gov/books/NBK537076/