Chambers and pre-excitation
Wolff–Parkinson–White pattern
Short PR, delta wave and a broad QRS — an accessory pathway with a direct line to the ventricle.
70 bpmSinus with pre-excitation
What you see
- PR interval under 120 ms.
- Delta wave — a slurred upstroke at the start of the QRS.
- QRS over 110 ms as a consequence of that slurred beginning.
- Secondary ST and T changes discordant with the delta wave, which can mimic infarction.
Why it looks like that
An accessory pathway bypasses the AV node and inserts directly into ventricular muscle. Part of the ventricle is therefore depolarised early and slowly, cell to cell — that early, slow activation is the delta wave, and it fuses with the normally conducted beat.
What to do
- Asymptomatic pre-excitation found incidentally: risk-stratify, and consider ablation in those in high-risk occupations.
- Symptomatic pathways (WPW syndrome) are treated with catheter ablation, which is curative in over 95%.
- For orthodromic AVRT with a narrow complex, vagal manoeuvres and adenosine are appropriate.
The trap
In atrial fibrillation with pre-excitation, AV nodal blockade removes the only brake on the accessory pathway. Adenosine, verapamil, diltiazem, digoxin and beta-blockers can all precipitate VF. The answer is DC cardioversion, or procainamide if stable.
delta waveaccessory pathwayAVRTablation