Risky Rhythyms

aka ECG Exigency 003

5 risky rhythms. Each tells a story. Can you work out what is happening before its too late? What can you do to save the day?

Rhythm strip 1

ECG Rhythm strip Exigency 003 1
Q1.1 What rhythm is shown?

This is a classic example of sick sinus with the “tachy-brady” syndrome

  • Runs of tachycardia interspersed with long sinus pauses (up to 6 seconds).
  • The sinus rate is extremely slow, varying from 40 bpm down to around 10 bpm in places.
  • Sinus beats are followed by paroxysms of junctional tachycardia at around 140 bpm.

Q 1.2 What will you do next?

This patient needs a pacemaker, stat!

  • Admit to a monitored bed on a coronary care unit.
  • Commence temporary pacing via external pads or pacing wire until a permanent pacemaker can be arranged.

Rhythm strip 2

ECG Rhythm strip Exigency 003 2
Q 2.1 What rhythm is shown?
  • Six beats of sinus rhythm at 90 bpm.
  • The 7th beat is a premature atrial complex (PAC) with different morphology P, QRS and T waves, which initiates a run of a supraventricular tachycardia at 150bpm.
  • The onset of the SVT is typical of an AV-nodal re-entry tachycardia (AVNRT), although with the rate of 150bpm, atrial flutter with a 2:1 block is also a possibility.

Q 2.2 What will you do next?
  • Scrutinise the 12-lead ECG for flutter waves.
  • Try some adenosine (or vagal stimuli such as a Valsalva manoeuvre or carotid massage); this should unmask any flutter waves and may convert AVNRT to sinus rhythm.
  • Flutter may require DC cardioversion or treatment with anti-arrhythmics (e.g. amiodarone).

Rhythm Strip 3

ECG Rhythm strip Exigency 003 3
Q 3.1 What rhythm is shown?

narrow complex tachycardia is interrupted by a run of polymorphic VT, which rapidly deteriorates into ventricular fibrillation.

Q 3.2 What will you do next?
  • Precordial thump!
  • Start charging the defibrillator!
  • Shock at 200 J (biphasic) or 360 J (monophasic). Three stacked shocks if the arrest is witnessed and monitored.
  • Start CPR!

Rhythm Strip 4

ECG Rhythm strip Exigency 003 4
Q 4.1 What rhythm is shown?
  • Sinus rhythm, or possibly ectopic atrial rhythm (biphasic / inverted P waves in lead II)
  • Rate of 90 bpm
  • Prolonged QTc interval of 540 ms (greater than half the R-R interval)
  • Ventricular ectopics with ‘R-on-T’ phenomenon
  • The second ventricular ectopic initiates a run of torsades de pointes

Q 4.2 What will you do next?
  • DC cardioversion if unstable.
  • Load with magnesium (e.g. 2 g over 1-2 minutes) and start a magnesium infusion.
  • Correct hypokalemia.
  • Consider: Overdrive pacing to achieve a ventricular rate of 90-120 bpm.
  • Consider: Isoprenaline infusion.

Rhythm Strip 5

ECG Rhythm strip Exigency 003 5
Q 5.1 What rhythm is shown?

This is a typical ECG recording of a patient receiving a bolus of adenosine for AVNRT.

  • AV-nodal re-entry tachycardia (AVNRT) at 140 bpm
  • A pause in the middle of the strip with several ventricular escape complexes
  • Cardioversion to sinus rhythm at 90 bpm at the end of the strip

Q 5.2 What will you do next?
  • Get a 12-lead ECG to confirm return to sinus rhythm.
  • If the patient is well and remains in sinus rhythm they can be discharged.
  • Consider electrophysiology follow up for recurrent AVNRT.


Cardiovascular curveball 700





Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.