Question 14.1

Created on Thu, 12/17/2015 - 07:51
Last updated on Sun, 01/21/2018 - 18:17
Pass rate: 75%
Highest mark: 8.8

Topic

Other SAQs in this paper

Other SAQs on this topic

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)

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College Answer

a)
Wolf-Parkinson-White syndrome

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

b)

IV procainamide or amiodarone is preferred, but any class Ia, class Ic, or class III antiarrhythmic can be used (Digoxin, Verapamil contraindicated)

Discussion

the ECG features of WPS are:

  • The PR interval is short (less than 0.12 seconds)
  • There is a delta wave (a slurred upstroke of the QRS complex)
  • Wide QRS (because the delta wave widens it)
  • ST Segment and T wave discordant changes: T waves point in the opposite direction to the QRS.
  • Pseudo-Q waves: negatively deflected delta waves in the inferior / anterior leads
  • prominent R wave in V1-3 (mimicking posterior infarction).

The model answer to Question 3.1 from the first paper of 2009 lists digoxin and verapamil. Digoxin decreases the refractory period of the accessory pathway and verapamil tends to accelerate the ventricular response to AF by a similar mechanism. 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

Pharmacological Peculiarities of WPW
Arrhythmia Drugs contraindicated Drugs Recommended
Orthodromic AVRT -
  • Adenosine
  • Verapamil
  • Diltiazem
  • Procainamide
  • Amiodarone
Antidromic AVRT
  • Adenosine
  • Verapamil
  • Diltiazem
  • β-blockers
  • Digoxin
  • Procainamide
  • Flacainide
  • Propafenone
  • Amiodarone
AF
  • Adenosine
  • Verapamil
  • Diltiazem
  • ß-blockers
  • Digoxin
  • Procainamide
  • Ibutilide
  • Dofelitide
  • Flecainide
  • Amiodarone


     

References

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.