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