0071643192.pdf

PATHOPHYSIOLOGY

■ Bundle of Kent connects atrium directly to ventricle.

■ “Normal” conduction

■ Impulses travel down both the accessory pathway AND the AV node to

the ventricle →slurred QRS complex on the resting ECG.

■ In some, bypass tract is completely hiddenduring normal conduction.

■ AFib or a-flutter

■ If short refractory period in accessory pathway →manyimpulses reach

ventricle→very high ventricular rates (wide complexes).

■ Orthodromic reentry tachycardia

■ Reentry circuit with impulse traveling down the AV node and up the

accessory pathway →narrow complexes.

■ Rate controlled by AV node (good)

■ Antidromic reentry tachycardia

■ Reentry circuit with impulse traveling down the accessory pathway and

up the AV node →wide complexes.

■ Rate controlled by accessory pathway (bad)

ECG FINDINGS

■ Resting ECG = preexcitation (see Figure 1.13)

■ Short PR interval

■ Slurred R wave (the delta wave) →wide QRS.

■ Orthodromic reentry tachycardia

■ Narrow QRS complexes

■ No P waves

■ Rates> 200 bpm

■ Antidromic reentry tachycardia

■ Wide QRS complexes

■ No P waves

■ Rates often > 200 bpm

RESUSCITATION

A bypass tract may be

completely hidden on the

resting ECG.

The orthodromic circuit travels

down the AV node (good).

The antidromic circuit travels

down the accessory pathway

(bad).

I

II

III

aVR

aVL

aVF

V1

V2

V3

V4

V5

V6

FIGURE 1.13. Delta wave on resting ECG.