Question 30.1

The following ECG (ECG 1) was recorded in a 25-year-old patient in ICU who was alert and conscious with a blood pressure of 100/50 mmHg.

What rhythm is demonstrated?

Give the reasons for your answer.

(40% marks)

(the college has not released their ECGs; the image above was appropriated from LITFL without any explicit permission but in the spirit of FOAM)

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College Answer

The ECG is consistent with a diagnosis of SVT with aberrant conduction for the following reasons:

There are no capture or fusion beats
There is no concordance in the chest leads
The QRS complexes are relatively narrow (under 160ms)
The patient’s age makes the diagnosis of an atrial origin more likely


This image comes from the LITFL page on distinguishing VT from SVT with aberrancy. As such, it is well suited to this SAQ. The reason for wanting to know the difference is that potentially a patient in VT will become very unstable if AV-nodal blockers like adenosine are given.

Is this VT or SVT with Aberrant Conduction? How do I know?

Supraventricular tachycardia

Historical features

  • Young age
  • Previous SVTs terminated with adenosine

ECG changes

  • Same RBBB or LBBB pattern as the patient's normal ECG
  • WPW on pre-tachycardia ECG
  • Responds to vagal manoeuvres

Ventricular tachycardia

Historical features

  • Old age
  • Ischaemic heart disease, MI
  • HOCM, long QT, Brugada

ECG changes

  • No typical RBBB or LBBB morphology
  • Bizarre axis deviation
  • Very broad complexes (>160ms)
  • AV dissociation (P rate is different to QRS rate)
  • Capture beats — occasional normal QRS complexes
  • Fusion beats — a normal and a wide QRS superimposed on top of one another
  • Concordance:         all the chest lead QRSs point in the same direction
  • Brugada’s sign –  From onset of QRS complex to nadir of S-wave is > 100ms
  • Josephson’s sign – Notching near the nadir of the S-wave
  • Left ear of RSR complex is higher than right


From "the ECG made easy", by Hampton (2003), and ECGs shamelessly stolen from Life in The Fastlane without any sort of permission, but in the non-commercial spirit of free education

One may turn to the ARC guidelines for management of supraventricular tachycardias (guideline 11.9), which suggests (Class A evidence) that in a stable patient, vagal manoeuvres ought to be tried and then adenosine may be used unless contraindications exist. An unstable patient may also have a trial of adenosine while a defibrillator is being acquired, or while the chest is being shaved etc.....

As their reference for this set of guidelines, the ARC quote the ACC's statement.