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
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