Acute - sudden or recent onset (usually within minutes to hours), presenting typically <24 hrs.
Chest - thorax midaxillary to midaxillary line, xiphoid to suprasternal notch
Pain – noxious uncomfortable sensation
Ache or discomfort
Definition of Acute MI
Is myocardial cell death that occurs because of a prolonged mismatch between perfusion and demand.
In the case of ST-elevation myocardial infarction (STEMI), this is caused predominantly by complete atherothrombotic occlusion of a coronary artery.
Diagnosis of STEMI
STEMI is diagnosed clinically when there is new and persistent ST-segment elevation in at least two contiguous leads of ≥1 mm in all leads other than leads V2-V3 where the following cut-off points apply:
≥2.5 mm in men <40 years old
≥2 mm in men >40 years old
≥1.5 mm in women regardless of age
1 mm = 1 small square.
Basic ECG
NORMAL ECG
QRS Complex
R
P
PR Segment
PR Interval
QT Interval
T
ST Segment
Normal ECG
ECG Interpretation Guidelines
Heart Rate: 60 - 100 bpm.
The P waves in leads I and II must be upright (positive) if the rhythm is coming from the sinus node.
Each QRS complex is preceded by a normal P wave.
Normal P wave axis: P waves upright in leads I and II, inverted in aVR.
The PR interval remains constant.
In the normal ECG, the T wave is always upright in leads I, II, V3-6, and always inverted in lead aVR.
Work-up
CXR to look for signs of congestive heart failure
Cardiac enzymes:
CK (will begin to rise 6 hours after infarct and remain elevated for 24-48 hours)
Troponin (will begin to rise 12 hours after infarct and remain elevated for 2 weeks). Need to follow serially if first set negative.
Serum Troponin
A normal serum troponin level two to three hours after symptom onset means there is a low probability of myocardial infarction, although myocardial infarction cannot be completely excluded.
The criteria for myocardial infarction for high-sensitivity troponin T is ≥ 15 ng/L, with a rise and/or fall of ≥ 50% over three to six hours. Z
Differential Causes of Elevated Serum Troponin
Renal dysfunction
Atrial or ventricular tachycardia
Pulmonary emboli with right ventricular infarction
Chronic and severe congestive cardiac failure and myocarditis
