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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