Myocardial infarction (Heart Attack)

       Heart muscle is the hardest working muscle of the body which pumps approximately 4-5 litre of blood ever minute during rest. Only coronary arteries supply blood to heart muscle. Blood flowing through the chambers of the heart is not useful for the heart muscle.

Heart attack or Myocardial infarction (MI) is the irreversible necrosis (death) of heart muscle secondary to prolonged ischemia (lack of oxygen supply). This usually is the result of a blockage in one or more of the coronary arteries. During last 30 years, large decline of MI incidence in developed countries and alarming increase in developing countries like India.

Etiology

Atherosclerosis: Atherosclerosis is a condition in which there is gradual plaque build-up within artery walls, resulting in narrowing of artery. Atherosclerosis is the disease primarily responsible for most acute coronary syndrome (ACS) cases.

Coronary artery disease (CAD) or Coronary heart disease (CHD): when atherosclerosis occurs in coronary arteries, heart does not get sufficient blood, the condition called coronary artery disease or coronary heart disease.

Non-modifiable risk factors:

Ø  Age: Men are at a higher risk of heart attack after age 45 and women after age 55.

Ø  Family history: A positive family history of MI in first-degree male relative aged 45 years or younger and first-degree female relative aged 55 years or younger.

Ø  Male-pattern baldness.

Modifiable risk factors:

Ø  Smoking or other tobacco use.

Ø  Bad cholesterol (LDL), is one of the leading causes of a blockage in the arteries.

Ø  Saturated fats may also contribute to the build-up of plaque in the coronary arteries. Saturated fats are found mostly in meat and dairy products, including beef, butter, and cheese.

Ø  Trans fat contributes to clogging of arteries. Trans fat is usually artificially produced and can be found in a variety of processed foods.

Ø  Diabetes mellitus: High blood sugar levels can damage blood vessels and eventually lead to coronary artery disease.

Ø  Hypertension: High blood pressure damages arteries and accelerates the build-up of plaque.

Ø  Obesity (abdominal obesity)

Ø  Psychosocial stress

Ø  Sedentary lifestyle and/or lack of exercise

Ø  Reduced consumption of fruits and vegetables

Ø  Poor oral hygiene

Ø  Type A personality

Ø  Elevated homocysteine levels

Symptoms

Ø  Chest pain: The typical chest pain of acute MI usually is intense and unremitting for 30-60 minutes. It is retrosternal and often radiates up to the neck, shoulder, and jaws, and down to the left arm. The chest pain is also perceived as squeezing, aching, burning, or even sharp.

Ø  There may have prodromal symptoms of fatigue, chest discomfort, or malaise in the days preceding the event; alternatively, typical ST-elevation MI (STEMI) may occur suddenly without warning.

Ø  Profuse sweating.

Ø  Shortness of breath.

Ø  Anxiety, commonly described as a sense of impending doom.

Ø  Light headedness, with or without syncope.

Ø  Coughing, wheezing, and the production of frothy sputum may occur.

Ø  Nausea, with or without vomiting.

Ø  In some patients, the symptom is epigastric, with a feeling of indigestion or of fullness and gas.

Ø  Many Myocardial infarctions are either "silent" or are not clinically recognized by patients, families, and health care providers.

Signs

Ø  Tachycardia: The patient’s heart rate is often increased.

Ø  Irregular Pulse.

Ø  Blood Pressure: BP initially elevated because of peripheral arterial vasoconstriction. Later, with right ventricular MI or severe left ventricular dysfunction, there is hypotension (fall in BP) and cardiogenic shock can be seen.

Ø  Tachypnoea: The respiratory rate may be increased in response to pulmonary congestion or anxiety.

Investigations

Ø  Electrocardiography (ECG):

o   ECG is most important tool in the initial evaluation. ST-segment elevation greater than 1 mm in two anatomically contiguous leads or presence of new Q waves.

o   Intermediate-probability: ST-segment depression or T-wave inversion.

o   Low-probability: Normal ECG findings or nonspecific findings on ECGs do not exclude the possibility of MI.

Ø  Cardiac biomarkers/enzymes:

o   Cardiac troponin should be measured at presentation in suspected MI.

o   Troponin is a contractile protein that is not normally found in serum; it is released only when myocardial necrosis occurs.

o   Serum levels increase within 3-12 hours from the onset of chest pain, peak at 24-48 hours, and return to baseline over 5-14 days.

o   Serial measurement of cardiac troponins after the initial level is normal at presentation, 3 to 6 hours after symptom onset, is recommended.

Ø  Cardiac imaging:

o   Coronary angiography in individual with highly probable or confirmed acute MI can be used to definitively diagnose or rule out coronary artery disease.

o   Multi-detector computed tomography (MDCT) coronary angiography may be considered as an alternative to invasive angiography to exclude ACS when cardiac troponin and/or ECG results are inconclusive.

Prognosis

Ø  Acute myocardial infarction is associated with a 30% mortality rate; about 50% of the deaths occur prior to arrival at the hospital.

Ø  Approximately half of all patients with an MI are re-hospitalized within 1 year of their index event.

Ø  Better prognosis is associated with:

o   Successful early reperfusion (ST-elevation MI goals: patient arrival to fibrinolysis infusion within 30 minutes or percutaneous coronary intervention within 90 minutes.

o   Preserved left ventricular function.

o   Short-term and long-term treatment with beta-blockers, aspirin, and ACE inhibitors.

Ø  Poorer prognosis is associated with the following factors:

o   Advanced age.

o   Diabetes mellitus.

o   Previous cerebrovascular disease or peripheral vascular disease.

o   Delayed or unsuccessful reperfusion.

o   Poorly preserved left ventricular function.

o   Evidence of congestive heart failure.

o   Involvement of electrocardiograph (ECG) lead aVR.

o   Depression.

Management

Prehospital care

Ø  Intravenous access,

Ø  Supplemental oxygen if SaO₂ is less than 90% on pulse oximetry.

Ø  Aspirin: Aspirin preferably chewable should be given in a dose of at least 162 to 325 mg for fibrinolytic therapy, unless there is a clear history of aspirin allergy.

Ø  Nitroglycerin: Nitroglycerin 0.4 mg tablet sublingually or by spray should be given as it relaxes venous system reducing workload of the heart thereby help in chest pain. If relief is experienced within 5 minutes of the first Nitroglycerin dose, repeated doses can be given every 5 minutes for a maximum of 3 doses total.

Ø  Nitroglycerin should be avoided in hypotension or bradycardia.

Ø  Telemetry and prehospital ECG, if available

Ø  Adequate analgesia: Morphine in initial dose of morphine of 2 to 4 mg as an IV bolus can be given, repeated every 5 to 10 minutes until the pain is relieved.

Ø  The use of NSAIDs should be avoided as these are associated with adverse cardiovascular events.

Emergency department and inpatient care:

Ø  The first goal for healthcare professionals in management of acute myocardial infarction (MI) is to diagnose the condition in a very rapid manner.

Ø  Resuscitation of the patient.

Ø  Initial therapy is directed toward restoration of perfusion as soon as possible to salvage as much of the jeopardized myocardium as possible. This may be accomplished through medical or mechanical means, such as percutaneous coronary intervention (PCI), or coronary artery bypass graft (CABG) surgery.

Ø  Angioplasty (Percutaneous coronary intervention): A thin, flexible tube with a balloon on the end is threaded through a blood vessel to the blocked coronary artery. Then, the balloon is inflated to push the plaque against the wall of the artery. This widens the inside of the artery, restoring blood flow. Also a stent may be put in the artery to help keep it open.

Ø  Coronary artery bypass grafting (CABG): It is a surgery in which arteries or veins are taken from other areas of body and sewn in place to go around the blocked coronary arteries. This provides a new route for blood flow to the heart muscle.

Lifestyle modifications

Ø  Dietary changes: A low-fat and low-salt diet with dietary counseling,

Ø  Quit Smoking

Ø  Regular exercise: The recommended frequency of regular exercise training is three or more times a week, for at least 30 minutes per session.

Ø  Possible goal numbers for your risk factors include:

o   Blood pressure lower than 140/90 mm Hg

o   Waist circumference lower than 35” for women and 40” for men

o   Body mass index (BMI) between 18.5 and 24.9

o   Blood cholesterol under 180 mg/dL

o   Fasting Blood glucose under 100 mg/dl