Atrial fibrillation/flutter in pre-excitation

Overview

• Atrial fibrillation (AF) occurs in 20% of patients with Wolff-Parkinson-White (WPW) pattern, and atrial flutter in 7%
• The presence of an accessory pathway (AP) allows for rapid conduction directly to the ventricles, bypassing the AV node
• Ensuing rapid ventricular rates may result in degeneration to ventricular tachycardia (VT) or ventricular fibrillation (VF)
• The administration of AV nodal blocking drugs preferences conduction via the AP, and may precipitate ventricular arrhythmias and cardiac arrest

ECG features of atrial fibrillation in WPW:

Atrial Flutter results in the same features as AF in WPW except the rhythm is regular and may be mistaken for VT.

Management of AF with WPW

In patients that are unstable due to AF, urgent synchronised DC cardioversion is required.

However, it is in the more stable patient that we must be cautioned with the presence of an AP. Treatment with AV nodal blocking drugs (e.g. adenosine, calcium channel blockers, beta blockers) should be avoided for two reasons:

• Most APs have a shorter refractory period than the AV node, hence the ventricular rate can be more rapid if AV conduction occurs preferentially via the AP
• Normally, anterograde conduction occurs via both the AP and AV node, and these wavefronts fuse in the ventricles. Conduction through the AV node is actually a brake on AP conduction, ceasing its propagation path in the ventricle

AV nodal blockade can thus be catastrophic, preferencing conduction via the AP and leading to uninhibited propagation through the ventricles. The result is an increase in ventricular rate and possible degeneration into VT or VF.

The most widely available medical management option in the stable patient is procainamide.

The preferred long-term approach for patients with an AP and recurrent tachyarrhythmias is ablation.

ECG Examples

Example 1

Atrial fibrillation in a patient with WPW:

• Rapid, irregular, broad complex tachycardia (overall rate ~ 200 bpm) with a LBBB morphology (dominant S wave in V1)
• This could easily be mistaken for AF with LBBB
• However, the morphology is not typical of LBBB, the rate is too rapid (up to 300 bpm in places, i.e. too rapid to be conducted via the AV node), and there is a subtle beat-to-beat variation in the QRS width which is more typical of WPW (LBBB usually has fixed width QRS complexes)

Example 2

• Another example of AF with WPW resulting in a very rapid (up to 300 bpm in places), irregular broad-complex tachycardia with varying QRS width
• There are two narrow complexes (in V1-3), where the atrial impulses are presumably conducted via the AV node instead of via the AP
• This rhythm is extremely difficult to differentiate from polymorphic VT; however it does not demonstrate the twisting morphology characteristic of torsades de pointes

NB: Regardless of the aetiology, the most appropriate treatment for this rhythm (if sustained) would be immediate electrical cardioversion

Intermittent WPW

Example 3

AF with WPW showing intermittent pre-excitation:

• Some of the impulses are transmitted via the AP (= pre-excited beats), producing characteristic delta waves
• Other impulses are transmitted via the AV node, producing narrow QRS complexes

Example 4

• Another example of AF with WPW with intermittent pre-excitation — characteristic delta waves are best seen in V2

Clinical Cases

• Top 100 ECG – Case 002
• Top 100 ECG – Case 038
• Top 100 ECG – Case 073
• Top 100 ECG – Case 092
• Top 100 ECG – Case 136

Related Topics

• Pre-excitation syndromes
• Pre-excitation with atrial fibrillation/flutter
• Atrioventricular Re-entry Tachycardia (AVRT)
• Supraventricular tachycardia
• VT versus SVT with aberrancy
• ECG Medical Training – WPW Syndrome Part 1
• ECG Medical Training – WPW Syndrome Part 2

Clinical Cases

• Top 100 ECG – Case 002
• Top 100 ECG – Case 038
• Top 100 ECG – Case 073
• Top 100 ECG – Case 092
• Top 100 ECG – Case 136

Related Topics

• Atrial fibrillation
• Atrial flutter
• Pre-excitation syndromes
• Atrioventricular Re-entry Tachycardia (AVRT)
• Supraventricular tachycardia
• VT versus SVT with aberrancy
• Wiesbauer F. Atrial Fibrillation Management Essentials. Medmastery
• ECG Medical Training – WPW Syndrome Part 1
• ECG Medical Training – WPW Syndrome Part 2

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest