Risky Rhythyms

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.

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.

• 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.

• 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).

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

• 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!

• 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

• 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.

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

• 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.