The following ECG (ECG 1) is from a 35-year-old male who presents with paroxysmal tachycardia.
a) Describe this ECG. (30% marks)
b) What would be the possible pharmacological options if his tachycardia were to recur? (20% marks)
short PR interval, less than 3 small squares (120 ms)
slurred upstroke to the QRS indicating pre-excitation (delta wave) broad QRS
secondary ST and T wave changes
IV procainamide or amiodarone is preferred, but any class Ia, class Ic, or class III antiarrhythmic can be used (Digoxin, Verapamil contraindicated)
the ECG features of WPS are:
What can we say about the safety of AV nodal blockers in WPW?
On this basis, the authorities tend to recommend the use of Class I or Class III agents instead of AV nodal blockers. The model answer to Question 3.1 from the first paper of 2009 lists procainamide and amiodarone as first-line agents, whereas digoxin and verapamil are contraindicated. Digoxin decreases the refractory period of the accessory pathway and verapimil tends to accelerate the ventricular response to AF by a similar mechanism. Since 2009, public opinion has also drifted away from amiodarone. As an acute infusion it is basically a beta-blocker with some AV nodal specificity. It is therefore the wrong drug for acute management of WPW SVT; or rather, it will probably be safe in the narrow-complex-obviously-orthodromic population, with the aforementioned caveats. In the long term, it becomes more useful, as its Class III and Class I effects begin to develop, slowing conduction down the accessory pathway.
Thus, generally speaking many of the AV node blockers are at least relatively contraindicated in WPW with AF, and in AVRT unless it is confidently known to be orthodromic AVRT. The table below has been compiled with the use of the belowlisted references and the UpToDate article on this topic
|Arrhythmia||Drugs contraindicated||Drugs Recommended|
Redfearn, D. P., et al. "Use of medications in Wolff-Parkinson-White syndrome." Expert opinion on pharmacotherapy 6.6 (2005): 955-963.
Winter, C., R. Nagappan, and S. Arora. "Potential dangers of the Valsalva manoeuvre and adenosine in paroxysmal supraventricular tachycardia-beware preexcitation." Critical Care and Resuscitation 4.2 (2002): 107.