• Acute Coronary Syndrome (ACS)
• Angina Pectoris
• ECG and ACS Without ST Elevation
• ST Depression and ACS Without ST Elevation
• Flat Ascending ST Depression and ACS Without ST Elevation
• Negative T Waves and ACS Without ST Elevation
• ECG and Subendocardial Ischemia
• ECG Dynamics in ACS without ST Elevation
• ECG Diagnostics in ACS without ST Elevation
• ST Depression - Differential Diagnosis

Acute Coronary Syndrome (ACS)

• Acute Coronary Syndrome (ACS) is an acute ischemic injury to the myocardium
• Most commonly results from a ruptured atheroma (fibrous "cap")
• A thrombus forms at the site of rupture, leading to acute
• stenosis (progression of narrowing)
• occlusion (blockage)

Acute Coronary Syndrome

• In acute coronary syndrome, the following can occur:
• ST elevations, ST depressions (rarely is the ST segment normal)
• ST Elevations
• Occur within minutes of occlusion
• On ECG is an STEMI infarct (ST Elevation Myocardial Infarction)
• Occlusion causes subepicardial ischemia
• In 20 minutes, subepicardial necrosis occurs
• In 4-9 hours, transmural necrosis occurs
• In 3-8 hours, troponin starts to be released from necrotic cardiomyocytes
• In 9 hours, a pathologic Q wave forms
• Rarely does a pathologic Q wave not form
• ST Depressions
• Occur within minutes of stenosis
• Stenosis causes subendocardial ischemia
• On ECG, ST depressions are observed
• Rarely is the ST segment normal in subendocardial ischemia
• The only difference between unstable angina pectoris and NSTEMI infarction is:
• NSTEMI has subendocardial necrosis (troponin is released)
• Unstable angina pectoris does not have necrosis (troponin is not released)
• NSTEMI Infarction (Non-ST Elevation Myocardial Infarction)
• In 20 minutes, subendocardial necrosis occurs
• Transmural necrosis does not occur
• Therefore, no pathologic Q wave forms
• Rarely, transmural necrosis and a pathologic Q wave may occur
• In 3-8 hours, troponin starts to be released from necrotic cardiomyocytes
• Unstable Angina Pectoris
• Occurs with stenosis
• But ischemia is less severe compared to NSTEMI
• No necrosis occurs
• Therefore, troponin is not released

ECG and ACS Without ST Elevation

• Acute Coronary Syndrome without ST elevation
• Results from acute progression of stenosis
• Causes subendocardial ischemia
• ACS without ST elevation is classified into:
• Unstable Angina Pectoris (UAP) (causes subendocardial ischemia)
• NSTEMI Infarction (causes subendocardial necrosis)
• UAP and NSTEMI cannot be differentiated by ECG
• They produce similar ECG changes
• However, ECG changes in ACS are dynamic
• If ACS without ST elevation is suspected, the patient should have repeated ECG recordings

Acute Coronary Syndrome Without ST Elevation

• ACS without ST elevation can present with the following ECG findings:
• ST depressions (70%)
• Negative T waves (20%)
• Both ST depressions and Negative T waves
• Normal ECG
• NSTEMI and UAP cannot be differentiated by ECG
• The only difference is that NSTEMI has elevated troponin in laboratory tests

Flat Ascending ST Depression and ACS Without ST Elevation

• Flat Ascending ST Segment (Slow upsloping ST segment)
• Has an ascending rate of < 1.5mV/1s
• Steep Ascending ST Segment (Rapid upsloping ST segment)
• Has an ascending rate of > 1.5mV/1s

Flat Ascending ST Depression

• Flat ascending ST segment < 1.5mV/1s
• Ascending ST depression of 1.5mm
• ST depression is measured 80ms after the J point
• This ST depression is ischemic

Steep Ascending ST Depression

• Steep ascending ST segment > 1.5mV/1s
• Ascending ST depression of 1.5mm
• ST depression is measured 80ms after the J point
• Steep ST depression is never ischemic

ECG and Subendocardial Ischemia

• Subendocardial ischemia
• May not show ECG changes
• ECG can be normal
• Will not be visible on ECG if the following is present:
• Left ventricular hypertrophy
• Left bundle branch block
• Cannot localize the ischemic area
• Unlike STEMI
• NAP and NSTEMI have the same ECG changes
• In NSTEMI, necrosis occurs (troponin is released)
  
  
  
• Prinzmetal Angina
• Is subepicardial ischemia
• Due to temporary occlusion from spasm of the coronary artery
• On ECG, it mimics acute STEMI
• However, ECG normalizes within about 30 minutes
• No necrosis (no infarction)

ECG Diagnostics in ACS without ST Elevation

ST Depression

• ST depression must be present in at least 2 adjacent leads
• Horizontal (Descending) ST depression ≥ 0.5mm
• Flat ascending ST depression ≥ 1.5mm

Negative T Waves

• Do not have to be present during ischemia
• Discordant (T wave has the opposite direction to the QRS complex)
• Symmetric
• Deep ≥ 2mm (at least in 2 adjacent leads)

Unstable Angina Pectoris

• Sinus Rhythm
• Inverted T Waves (I, aVL, V2-V6)
• The patient had approximately 10 minutes of angina and troponin was normal later
• The inverted T waves were not present in older ECG recordings
• Indicates unstable angina pectoris
• If the patient had elevated troponin without ST elevation later
• It would indicate an NSTEMI infarction

Ischemia Post-Ergometry

• The patient had an ECG recorded immediately after bicycle ergometry
• Sinus Tachycardia
• Inverted T waves and ST depressions (I, aVL, V2-V6)
• ST Elevation in aVR can indicate severe ischemic damage
• In this case, it represents a reciprocal change
• Tachycardia later resolved and the ECG normalized
• The patient has stable angina pectoris
• This is not an acute coronary syndrome

Unstable Angina Pectoris

• Sinus Rhythm
• Inverted T Waves (V1-V5, aVL)
• The patient experienced minimal subjective discomfort
• The patient had a chronic stenosis of the proximal LAD
• This is unstable angina pectoris
• See the following ECG