CHAPTER 7: Ventricular Preexcitation
157
However, the PR interval is not always abnormally short and the QRS complex is not
always abnormally prolonged. Figure 7.7A illustrates an abnormally slow onset of the
QRS complex following a normal PR interval (0.16 second). Figure 7.7B illustrates an
abnormally short PR interval preceding a QRS complex of normal duration (0.08 second).
Conduction through the bundle of Kent may be relatively slow, or the bundle of Kent may
directly enter the His bundle. Among almost 600 patients with documented ventricular
preexcitation, 25% had PR intervals of 0.12 second and 25% had a QRS complex dura-
tion of 0.10 second.
5
When ventricular preexcitation is suspected in a patient with tachyarrhythmia but no
ECG evidence of preexcitation, the following diagnostic procedures may be helpful:
1. Pace the atria electronically at increasingly rapid rates to induce conduction via
any existing accessory pathway.
2. Produce vagal nerve stimulation to impair normal conduction through the AV
node so as to induce conduction via any existing accessory pathway.
3. Infuse digoxin intravenously for the same purpose as in procedure 2.
A
I
V1
II
V2
III
V3
B
I
V1
II
V2
III
V3
F I G U R E 7 . 7 .
A.
Slow onset of the QRS complex following a normal PR interval (
arrows
).
B.
Short
PR interval preceding a normal QRS complex duration (
arrows
).
