ECGs

ECGs are frequently presented to candidates sitting the OSCE element of the exam, a systematic approach is essential.

• Name, date, calibration (1mv=1cm, 0.2s=1cm [small square 40 msec])
• Rate = 300/number of big squares between Q-Q
• Rhythm AF, tachy (>100), brady (<60), sinus, heart block
• Axis normal = -30° to +110°

P              peaked, tall Dright atrial hypertrophy

notched, broad Dleft atrial hypertrophy

P-R          >5 small squares

I degree block: prolonged PR interval

                II degree block:

                                Wekeneback: sequential ­ of PR interval

Mobitz typ II: fixed PR, dropped QRS (2:1, 3:1…)

                III degree block: disassociation of P and QRS

QRS        wide (<2.5 small squares)

MarroW Dright bundle branch block

WilliM Dleft bundle branch block

Q             1mm wide, 2mm/25% of R-wave

D old MI

Normal in lead I, aVL V₆

ST           raised: 1mm 2xconsangious limb-leads, 2mm chest-leads

Depression: myocardial ischemia

Reverse tick: digoxin effect

Saddle shaped elevation: acute constrictive pericarditis

T              peaked hyperkalaemia

Flat, prolonged, hypokalaemia

Ischemia, infarction

Normal in III, V_1-2 (and V₃ in Negroes)

U             Normal/Hypokalaemia

 

MI: Hyperacute T-waves, ST-elevation T-wave inversion, Q-waves. Inf. (II, III, aVF) Ant. (V_1-4), Lat. (I, aVL,V_5-6) Post. look at V_1-2. New LBBB.

PE: S-I (deep S-waves in I), Q-III (Q-waves in III), T-III (inverted T-waves in III). More generally a sign of R-heart strain.

Hyperkalaemia: tall tented T, wide QRS

Hypokalaemia: flattened T, prominent U, (muscle weakness, cramps, tetany)

 

Resources

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ECG Wave-Maven – is a resource with many “barn-door” ECGs, presented in a quiz format; large database, expert explanations.