EKG Interpretation Cheat Sheet
1) Rate
- Regular - Count-Off
- Irregular - Count number of QRS in 10s x 6
2) Rhythm
3) Axis
4) Alphabet - Width? Height? Shape? (Up/Down, Contour)
P Waves:
• Inverted P Waves (in inferior leads)?
• PR interval < 120 ms = AV junction origin (e.g. accelerated junctional rhythm)
• PR interval ≥ 120 ms, origin within the atria (e.g. ectopic atrial rhythm)
• Variable P-Wave Morphology = multifocal atrial rhythm
• No P Waves/Fibrillary = afib
• Saw-Tooth = Atrial Flutter
PR Interval:
• 1° Block - PR >200ms
• 2° Block Type I - PR ↑ incrementally before loss of P
• 2° Block Type II - Suddenly Lose P
• 3° Complete Block (nothing getting through)
QRS Complex:
• Pathological Q waves:
> 40 ms (1 mm) wide > 2 mm deep or > 25% of depth of QRS complex
Seen in leads V1-3 (Right sided leads)
• R wave abnormalities:
Dominant R wave in V1
Dominant R wave in aVR Poor R wave progression
ST Segment:
• Septal (V1-2)
• Anterior (V3-4)
• Lateral (I + aVL, V5-6)
• Inferior (II, III, aVF)
• Right ventricular (V1, V4R)
• Posterior (V7-9)
T Waves:
• Normal: Upright in all leads except aVR and V1 (Invert III normal variant), Amplitude < 5mm in limb leads, < 15mm in precordial leads
• Hyperacute T waves Inverted T waves, Biphasic T waves, ‘Camel Hump’ T waves, Flattened T waves
QT/QTC Interval:
• QT interval is inversely proportional to heart rate
• Bazett formula: QTC = QT / √ RR - Note: there are multiple QTc correction formulas
• Prolonged QTc > 440ms in men, > 460ms in women
• QTc > 500 is associated with increased risk of torsades de pointes
• Short QTc < 350ms
• Rule of thumb: a normal QT is less than half the preceding RR interval
Other:
• U waves = severe hypokalaemia or bradycardia
• J /Osborn wave (between QRS and ST) = hypothermia
• Delta Wave (before QRS) = WolffParkinson-White syndrome
• Epsilon Wave (blip QRS) = Arrhythmogenic right ventricular dysplasia (ARVD)
- Amy Chung, MD, MSc @AmyChung
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