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
