Wed3November0903PM 1

A 42-year-old woman presents to the Emergency department with an episode of collapse. She was apparently sitting in local coffee shop when she felt the onset of very rapid palpitations and then fell to the floor.

She has a history of asthma for which she takes a regular Seretide inhaler and has just been prescribed a course of erythromycin for a lower respiratory tract infection. It appears that she also purchased an over-the-counter fluconazole tablet for an episode of vulval candida infection that morning.

Examination reveals a BP of 122/72 mmHg, pulse is 75 and regular. There are no murmurs and her chest appears clear. As you are about to walk away from the bedside you notice a paroxysm of 10-12 sec of torsades de pointes VT on the monitor.

Investigations reveal:

Hb 128 g/L (135-180)

WCC 6.2 ×109/L (4.5-10)

PLT 230 ×109/L (150-450)

Na 136 mmol/L (135-145)

K 4.1 mmol/L (3.5-5.5)

Cr 82 µmol/L (70-110)

Magnesium 0.9 mmol/L (>0.7)

ECG shows sinus rhythm with a QT interval of 610 ms.

Which of the following is the most appropriate intervention?

(Please select 1 option)

Isoprenaline

Amiodarone

Overdrive pacing

Magnesium Correct

Bisoprolol

Explanation

Even though the magnesium level is above the lower limit of normal, studies still indicate that magnesium infusion increases the chances of maintaining sinus rhythm in patients presenting with torsades. It can be given as a bolus of 1-2 g/IV initially over 30-60 seconds, or as an infusion at a rate of 3-10 mg/min.

Close monitoring is required because of the risk of inducing depression of neuromuscular function via hypermagnesaemia.

Amiodarone and bisoprolol can potentiate the risk of torsades via further QT prolongation and must therefore be avoided in this situation.

Isoprenaline can be used to increase the ventricular rate in sinus rhythm to above 90 bpm, reducing the risk of further episodes of torsades. In the event that isoprenaline is ineffective, overdrive pacing to increase the ventricular rate can be considered.

In this situation it is likely that washout of the fluconazole and macrolide will lead to cessation of the episodes of torsades.

Answer Statistics

1

1%

2

3%

3

4%

4

92%

5

2%

Times answered: 281