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

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

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

• 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