Myocardial Infarction

26 Jun 2020 | Skedoc

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What Is Myocardial Infarction?

Myocardial Infarction is a condition that occurs due to the death of heart muscle tissue due to a lack of supply of blood and oxygen. It is usually seen as a consequence of fat build-up, and blockage of the arteries that supply blood to the heart.

Alternate names

  • Heart Attack / MI

Is this condition a medical emergency?

Myocardial infarction is a medical emergency and immediate medical attention is required.

Types of this condition

Myocardial infarction is categorized as:

  • ST-elevation MI (STEMI): The ST segment is elevated in the ECG readings, and the area of the heart muscle that is damaged is more, as the blockage may be significant or may have occurred for a longer time.
  • Non-ST elevation MI (NSTEMI): There is no elevation of the ST segment in the ECG readings and a small area of the heart muscle is damaged as the blockage may be small or may have occurred for a brief period.

Another form of classification of myocardial infarction is as follows:

  • Type 1: Myocardial infarction occurring due to plaque formation or rupture, fissuring, or dissection.
  • Type 2: Myocardial infarction related to increased oxygen demand or reduced oxygen supply such as seen in anemia, coronary artery spasm, coronary embolism, high or low blood pressure, irregular heart rhythms.
  • Type 3: Sudden cardiac death that includes signs and symptoms of heart muscle ischemia such as ECG changes, but death occurs before blood samples can be taken, or in the lag period before cardiac markers appear.
  • Type 4: Associated with coronary angioplasty and stents.
  • Type 5: Associated with coronary artery bypass grafting (CABG).

Causes of myocardial infarction

The most significant cause of myocardial infarction is the formation of a clot after atheromatous plaques or fatty deposits break or rupture inside the coronary arteries, the blood vessels that supply oxygen and nutrient-rich blood to the heart muscle. The blockage or reduction of blood supply due to the presence of the clot causes damage and death of the cells of the heart muscle leading to a heart attack.

Risk factors for myocardial infarction

Some of the major risk factors for myocardial infarction include:

  • Family history of heart disease
  • Aging
  • Lack of exercise
  • Smoking
  • Unhealthy eating habits
  • Bad oral hygiene
  • Metabolic syndrome
  • Being overweight or obese
  • High blood cholesterol levels
  • High blood pressure, or a history of high blood pressure
  • Diabetes
  • High sugar levels and high blood pressure (preeclampsia) during pregnancy
  • Peripheral vascular disease
  • Stress
  • Hyperthyroidism
  • Severe anemia
  • Recreational drugs such as cocaine, amphetamines
  • Some autoimmune conditions such as rheumatoid arthritis, lupus
  • Respiratory infections

Triggering factors

Although myocardial infarction can occur at any time or even at rest, it usually occurs in the morning hours. Some of the triggers for MI include:

  • Vigorous activity
  • Anger
  • Emotional stress
  • Sexual activity
  • Cocaine, amphetamines

Symptoms & signs of myocardial infarction

The primary symptom of myocardial infarction is severe chest pain that is felt behind the sternum (breast bone) and one that may extend to the neck, lower jaw, shoulders, and the left arm. The pain is described as pressure, tightness, stabbing, squeezing, or burning. It can be continuous and lasts as long as 30-60 minutes. It may or may not be preceded by prodromal symptoms of discomfort or general weakness a few days in advance. Some of the other symptoms that may be present include:

  • Sweating
  • Indigestion, a feeling of fullness
  • Nausea and vomiting
  • Shortness of breath
  • Cough
  • Wheezing
  • Fainting or light-headedness
  • Generalized weakness
  • Anxiety

The symptoms may be slightly different in women, and they may not always complain of severe chest pain, but the symptoms may be more generalized such as back pain, lightheadedness, heartburn, nausea and vomiting, fatigue, shortness of breath, neck pain radiating to the jaw, etc.

Investigations

Preliminary Investigations include:

  • ECG: it is the primary investigation that is done to establish a preliminary differentiation between a heart attack and unstable angina.
  • Blood Tests: are done to measure the levels of cardiac markers such as Troponin I or T, and the presence of these markers helps to differentiate between a heart attack and unstable angina. Other blood tests such as CBP to evaluate for anemia, and metabolic panel to monitor potassium and magnesium levels are also done.

Based on the results of the ECG and the cardiac markers, further tests may also be done and these include:

  • Coronary Angiogram: a minimally invasive diagnostic imaging procedure that is used to visualize the coronary arteries and locate the site and size of the blockage.
  • Echocardiogram: an imaging test that utilizes ultrasound waves to assess the functioning of the heart.
  • Myocardial Perfusion Imaging: It is not done if serial ECGs are negative and there are no cardiac markers. It is a procedure done using radioactive isotopes on a PET scan or SPECT scan to study the blood flow to the heart muscle during stress or increased activity.
  • CT Angiogram: a CT scan study of the coronary arteries done after injecting a high contrast dye containing iodine.

Diagnosis of myocardial infarction

Diagnosis of myocardial infarction and its cause is based on the interpretation of the results of the investigations. A diagnosis of myocardial infarction is confirmed if there are the presence of cardiac markers along with at least one of the following:

  • Symptoms related to ischemia.
  • Changes on the ECG such as ST-segment changes, new left bundle branch block, Q waves.
  • Changes in the motion of the heart wall on imaging tests.
  • Demonstration of a clot on angiogram.

Myocardial infarction is further diagnosed as:

  • STEMI: Changes in the ECG that show an elevation of the ST segment along with the presence of cardiac markers.
  • NSTEMI: the presence of cardiac markers and the absence of ST-segment elevation in the ECG.

Myocardial infarction treatment options

The treatment is aimed at relieving pain, restoring the blood flow to the heart at the earliest, and preventing further tissue damage. Treatment for myocardial infarction is based on whether it is:

  • STEMI: which indicates there are a significant blockage and heart tissue damage
  • NSTEMI: which indicates there is a partial or a temporary blockage with heart tissue damage

The treatment is also based on the level of risk for immediate future complications in the case of NSTEMI.

A. Medical management

Medical management of myocardial infarction may include the following:

  • Aspirin: To help reduce the clotting of the blood.
  • Thrombolytics: To help dissolve the clot and restore the blood flow. It is advisable to administer via injection within 30 minutes of the onset of symptoms.
  • Nitroglycerin: To improve the blood flow through the arteries.
  • Antiplatelet drugs: To prevent the formation of clots within the arteries.
  • Angiotensin: Converting Enzyme (ACE) Inhibitors: to increase the blood flow and decrease the blood pressure, thereby decreasing the workload of the heart.
  • Angiotensin Receptor Blockers: To reduce the blood pressure and the workload of the heart.
  • Beta-Blockers: To reduce the blood pressure and the workload of the heart.
  • Statins: To reduce the amount of cholesterol in the blood and to stabilize existing plaques and preventing them from rupturing.
  • Analgesics: To help in pain relief during a heart attack.
  • PCSK9 Inhibitors: Such as Evolocumab destroy low-density lipoproteins by binding to them and reduce the risk of future heart attacks.

B. Interventional including surgery and indications for surgery

Surgical intervention may be required in some cases of myocardial infarction, especially when the diagnosis of STEMI has been established. The surgical treatment may include:

  • Percutaneous Coronary Intervention (PCI) Angioplasty and Stenting: Which is a minimally invasive interventional cardiology procedure in which a balloon is guided through a catheter to unblock or widen the arteries and also, a tiny tubular metal mesh called a stent is placed inside the artery to act as a support and keep the artery open. It is advisable to perform this procedure within 90 minutes from the onset of symptoms.
  • Coronary Bypass Surgery or Coronary Artery Bypass Grafting: It is a procedure that is done when the blockage is significant and in which an arterial graft is used to bypass the blocked artery and restore the blood supply to the heart.

C. Role of diet/exercise/lifestyle changes/preventive measures

Maintaining a healthy lifestyle and habits is essential in the prevention of acute coronary syndrome specifically and heart disease in general. Some of the measures that need to be taken include:

  • Quitting smoking
  • Eating a healthy diet that includes fruits, vegetable, lean meats, and low-fat dairy
  • Getting regular exercise and staying physically fit
  • Maintaining proper body weight
  • Monitoring and keeping blood cholesterol levels under control
  • Monitoring and controlling blood pressure levels
  • Reducing mental and emotional stress
  • Keeping a check on alcohol consumption

Complications

The complication of myocardial infarction may include:

  • Hypotension, heart failure, and shock
  • Pericarditis
  • Post-myocardial infarction syndrome (Dressler's syndrome)
  • Myocardial rupture
  • Ventricular aneurysms
  • Abnormal heart rhythms such as atrial fibrillation, ventricular tachycardia, ventricular fibrillation leading to cardiac arrest

Prognosis

The prognosis of myocardial infarction depends on the location and extent of the heart muscle that is affected, on how early the blood flow was restored, and the presence or absence of other complications. Prognosis is poorer with:

  • Increasing age
  • Diabetes
  • Another coexisting vascular disease
  • Delay in restoring blood flow after a heart attack
  • Anterior infarcts - Damage on the anterior (front) side of the heart
  • Poor left ventricle function
  • Presence of ventricular tachycardia or fibrillation

Without treatment, a majority of the individuals will not survive for more than a month while a few will die within a few minutes after a heart attack.

When to contact the doctor or hospital/How to identify the emergency or complications?

Myocardial infarction is a medical emergency, and it is advisable to get immediate medical attention by contacting a doctor in the event of chest pain with or without the other accompanying symptoms. Early investigations and intervention will reduce the likelihood of further complications and death.

Indications for hospitalization if required

In the event of myocardial infarction, hospitalization would be required until all the investigations are completed and the individual is stabilized. Further hospitalization may be required if surgical interventions are needed.

Screening methods

Cardiovascular screening for both symptomatic and asymptomatic high-risk individuals can help to prevent future complications and morbidity. Screening tests may include blood tests for cholesterol, C reactive protein, blood sugar, and hypertension, and imaging tests such as echocardiography, coronary CT scans, and coronary calcium uptake.

Suggested clinical specialist/Departments to consult for this condition

Myocardial infarction would be attended to by the Emergency Department and subsequently by the Department of Cardiology.

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