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A 50 year old man presents with shortness of breath and sharp central chest pain of 24 hours duration.

  • He has no past medical history and is on no medication.
  • Describe and interpret his ECG

Using the ‘ECG in 20 Seconds’ approach

Rate: 198
Rhythm: difficult to see P waves, however the rate is regular
QRS: is it wide or narrow?:narrow complex
is it tall or small? : there are alternating tall and shorter complexes: electrical alternans
is morphology normal?: no delta seen
ST-T: normal
PR/QT: difficult to see P waves, QT appears prolonged, due to T wave location in RR interval.

The diagnosis is narrow complex tachycardia with electrical alternans.

QRS alternates may be:

1 Conduction alternans: It can occur in MI, WPW, PE. When associated with a narrow complex tachycardia as above, it may indicate orthodromic atrioventricular re-entry tachycardia, with accessory pathway.

2 Motion alternans: This is a motion artefact related to the movement of the heart. It is associated with an enlarged pericardial sac and with hypertrophic cardiomyopathy.

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