myocardial%20infarction%20w_%20st-segment%20elevation
MYOCARDIAL INFARCTION W/ ST-SEGMENT ELEVATION
Myocardial infarction is death of cardiac myocytes (necrosis) caused by prolonged ischemia. The term acute "usually" refers to the time 6 hours to 7 days following pathologic appearance of the infarct.
The patient may experience ischemic-type chest discomfort with accompanying symptoms of nausea, vomiting, dyspnea, diaphoresis, lightheadedness, dizziness, syncope, fatigue and weakness.
Rapid diagnosis and risk stratification of chest pain in patients are important to identify acute myocardial infarction patients who will benefit from reperfusion therapy.

Myocardial%20infarction%20w_%20st-segment%20elevation Signs and Symptoms

Definition

Acute Myocardial Infarction (AMI)

  • Myocardial infarction is death of cardiac myocytes (necrosis) caused by prolonged ischemia
  • The term “acute” usually refers to the time 6 hours - 7 days following pathologic appearance of the infarct
  • A prior or unrecognized/silent MI is a condition that has the following criteria: 
    • Abnormal Q waves with or without symptoms in the absence of non-ischemic causes
    • Loss of viable myocardium on imaging consistent with an ischemic cause
    • Patho-anatomical findings of a previous MI 
  • A recurrent MI is an MI occurring 28 days after an incident MI while a re-infarction is an acute MI occurring within 28 days of an incident or recurrent MI

Signs and Symptoms

The patient may experience ischemic-type chest discomfort with the following characteristics:

  • Retrosternal/substernal chest pain lasting 10-20 minutes or longer
    • Pain is usually described as heaviness, pressure or burning in nature
    • Pain may occur at rest or during activity and does not respond fully to Glyceryl trinitrate (GTN)
  • The pain which is usually central or in the left chest may radiate to the jaw, neck, left arm, back or shoulder
  • Discomfort is diffuse, not localized, positional nor affected by movement of the region
  • Occasionally, symptoms are mistaken for indigestion or heartburn if pain occurs in the epigastric region
  • Accompanying symptoms may include nausea, vomiting, dyspnea, diaphoresis, lightheadedness, dizziness, syncope, fatigue and weakness
  • Atypical pattern may occur especially in females, diabetics and elderly patients; the pain develops in the arm, shoulder, wrist, jaw or back without occurring in the chest
  • MI should be suspected especially if the symptoms are severe and occur suddenly
  • MI may present with autonomic nervous system activation (eg pallor, sweating), hypotension or narrow pulse pressure, bradycardia or tachycardia, 3rd heart sound (S3), basal rales

Risk Stratification

  • Identifying patients who are at increased risk of further reinfarction or death is essential in order that it can be prevented or intervention can be done accordingly
    • Referral of high-risk patients to specialty centers should be made for early coronary angiography and revascularization 
  • Risk stratification of post-STEMI patients can be done clinically or by using the GRACE or the Thrombolysis in Myocardial Infarction (TIMI) risk scores 

High-Risk Patients

  • Left ventricular ejection fraction (LVEF) <35%, ischemia that affects >50% of viable myocardium, post-revascularization (percutaneous coronary intervention or coronary artery bypass graft surgery)
  • Clinical indicators include:
    • Advanced age
    • Hypotension and cardiogenic shock
    • Anterior infarction
    • Elevated initial serum creatinine
    • Malignant arrhythmias
    • Early angina on minimal exertion/post-infarct angina
    • Tachycardia
    • Killip class >1
    • Previous infarction
    • Heart failure history
    • Persistent chest pain
    • Peripheral arterial disease

Medium-Risk Patients

  • Patients not considered low risk or high risk based on imaging criteria should be treated based on symptomatic status

Low-Risk Patients

  • LVEF >50% or mild inducible ischemia that affects <20% of viable myocardium
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