Using the ‘ECG in 20 Seconds’ approach
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
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.