Electrocardiogram

Aka: Electrocardiogram, EKG, ECG

1. See Also
   1. Electrocardiogram in Myocardial Infarction
   2. Electrocardiogram in Pulmonary Embolism
   3. Electrocardiogram in Pericarditis
   4. Electrocardiogram in Atrial Fibrillation
2. Background
   1. Interpretation requires patient age, EKG indication
3. Precautions
   1. Standard EKG speed and amplitude is nearly always the best setting
      1. Although EKG gain can be increased and EKG speed can be slowed, the result is often more difficult to interpret
   2. Do not rely on computerized EKG Interpretation (aside from interval measurement)
      1. There is no standardization for software quality across EKG manufacturers and accuracy varies widely
      2. Computer interpretations miss STEMIs in up to 23-41% of cases
      3. Atrial Fibrillation is a frequent false positive on computer interpretations
      4. Pacemaker rhythms are frequently misinterpreted by computers (STEMI false positives and false negatives)
      5. References
         1. Orman and Mattu in Herbert (2018) EM:Rap 18(3): 1-2
         2. Schlapfer (2017) J Am Coll Cardiol 70(9): 1183-92 [PubMed]
         3. Willems (1991) N Engl J Med 325(25):1767-73 +PMID:1834940 [PubMed]
4. Components: EKG Paper
   1. Record speed: 25 mm/sec
   2. Small square (1 mm): 0.04 seconds
   3. Large square (5 mm): 0.20 seconds
5. Components: Leads
   1. Limb leads (bipolar)
      1. Lead I: Left arm - Right arm (0 degrees)
      2. Lead II: Left leg - Right arm (60 degrees)
      3. Lead III: Left leg - Left arm (120 degrees)
   2. Augmented Limb Leads (unipolar)
      1. Lead aVR: (-150 degrees)
      2. Lead aVL: (-30 degrees)
      3. Lead aVF: (90 degrees)
   3. Precordial Leads (unipolar chest)
      1. Lead V1: Right sternal border (Right Ventricle)
      2. Lead V2: Left sternal border
      3. Lead V3: Medial Breast (Septum)
      4. Lead V4: Nipple
      5. Lead V5: Lateral Breast
      6. Lead V6: Lateral chest wall (Left Ventricle)
6. Evaluation: Approach
   1. Assess EKG Validity
   2. Rate and Rhythm: "Watch your P's and Q's and the 3R's"
      1. Lead II P Waves upright? Otherwise not sinus rhythm
      2. QRS wide or narrow?
      3. Rate?
      4. Regularity of Rhythm?
      5. Relationship between P Waves and QRS Complex
   3. EKG Axis
   4. Intervals (prolonged?)
      1. PR interval
      2. QRS Complex
      3. QT Interval
   5. Hypertrophy?
      1. Left Ventricular Hypertrophy
      2. Right Ventricular Hypertrophy
      3. Right Atrial Enlargement
      4. Left Atrial Enlargement
   6. Infarction?
      1. Q Waves
      2. R Wave Progression
      3. ST Segments
      4. T Waves
   7. Reference
      1. Grauer (2001) 12 Lead EKGs, KG/EKG Press, Gainesville
7. Interpretation: Specific Circumstances
   1. See Electrocardiogram in Myocardial Infarction
   2. See EKG Changes in Syncope due to Arrhythmia
   3. See Electrocardiogram in Atrial Fibrillation
   4. Ventricular Tachycardia
      1. Northwest axis (opposite Nl axis)
      2. V1-V6 positive QRS Complex
      3. See AV dissociation
   5. Pericarditis
      1. See Electrocardiogram in Pericarditis
      2. Stage I: Diffuse ST inc all leads except aVR, V1
      3. Stage II: ST segments temporarily normalize
      4. Stage III: Diffuse ST depress +/- T inversion
      5. Stage IV: Gradual normalization of ST and T Waves
   6. Pulmonary Embolism
      1. See Electrocardiogram in Pulmonary Embolism
      2. Right Strain Pattern (Classic PE, but rarely seen)
         1. S1 (deep S wave in lead I)
         2. Q3 (Q wave in lead III)
         3. T3 (inverted T Wave in lead III)