Mon25October0757PM 16

A 52-year-old man is admitted to the Emergency department in atrial fibrillation with a ventricular rate of 210 beats per minute. Shortly after receiving pharmacotherapy to treat his arrhythmia, the patient develops ventricular fibrillation from which he is successfully resuscitated.

On review of an ECG from a previous admission it is noted that he has a PR interval of 40 ms, a prominent delta wave in lead I and a QRS duration of 120 ms.

Which of the following drugs is most likely be to implicated in the development of ventricular fibrillation in this patient?

(Please select 1 option)

Procainamide

Disopyramide

Amiodarone

Digoxin Correct

Ibutilide

Explanation

Wolff-Parkinson-White syndrome (WPWS) is associated with an accessory pathway of electrical conduction between the atria and the ventricles. Unlike the atrioventricular (AV) node, this accessory pathway (bundle of Kent) does not have the capability of slowing down a rapid rate of atrial depolarisation. The AV node is, in other words, bypassed by a short circuit. Patients are prone to atrial fibrillation or flutter with a rapid ventricular response or narrow complex AV re-entry tachycardia.

If a patient with WPWS develops atrial fibrillation, digoxin can promote transmission of impulses through this accessory pathway as its action is by blocking the AV node. This may result in an extremely rapid ventricular rate, and even ventricular fibrillation. It is therefore contraindicated.

Other drugs that interfere with AV nodal conduction, such as adenosine, beta blockers and calcium channel blockers, are also relatively contraindicated.

Drugs of choice are the class III antiarrhythmic drugs amiodarone and ibutilide (K+ channel block) and procainamide (Na+ channel block).

Answer Statistics

1

15%

2

8%

3

22%

4

56%

5

2%

Times answered: 273