Wolff-Parkinson-White syndrome

0.1-0.3% of general population
can be intermittent

Classical WPW triad:

Short PR interval
- < 120ms
- Not universal
  - may be a bit longer depending on distance from sinus node to accessory pathway
  - 120-140ms PR intervals do not necessarily r/o WPW
Delta waves
- slurring and slow rise of the initial upstroke of the QRS
- May be very subtle or seen in only 1-2 leads
  - Beware “pseudo-deltas” that may mimic WPW but do not have other triad findings to avoid misdiagnosis
Widened QRS interval
- 120ms
- Modified conduction through the accessory pathway will cause abnormal ventricular depolarization and result in secondary ST segment and T wave abnormalities

WPW + SVT

Narrow complex regular rhythm
- orthodromic AVRT
- looks like other types of paroxysmal SVT, treat like usual SVT with AV nodal blockers
Wide complex regular rhythm
- antidromic AVRT
- looks like VT → treat like VT
  Possibility of adenosine induced AF

Pre-excited AF

Very rapid irregularly irregular tachycardia
- rates may approach 250-300 beats/min
- changing morphology
  - some narrow (via AVN)
  - some wide (via accessory pathway)
  - some fusion
Often misdiagnosed as SVT, VT, or atrial fibrillation with BBB
- Misdiagnosis and treatment with AVN blockers can be deadly!
Treat with procainamide, flecainide, or preferably electrical cardioversion
Avoid all AV Nodal blockers
- adenosine
- Beta-blockers
- Calcium channel blockers
- Digoxin
- Amiodarone
  very rarely for AF (w/o accessory pathway) to reach HR >200bpm
∵ blocked by AV node
if HR >250bpm & irregular → pre-excited AF until proven otherwise
procainamide preferably block accessory pathways

DDx

Ashman phenomenon: stable
TdP: changing axis

doesn't matter just DC cardioversion ∵ patient couldn't be stable for long

References

Writing Committee Members. 2014 AHA/ACC/HRS Guideline for the Management of Patients with Atrial Fibrillation: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. JAC 2014;64(21):2246–80. PMID: 24682347