3. • Wolff-parkinson-white pattern, or WPW, is a type of
heart arrhythmia caused by an accessory pathway, or
an “extra” electrical conduction pathway connecting
the atria and ventricles, or upper and lower chambers
of the heart.
• Normally, an electrical signal starts at the sinoatrial or
SA node in the right atrium, it then propagates out
through both atria, including bachmann’s bundle in the
left atrium, and contracts both atria, it’s then is
delayed just a little bit as it goes through the
atrioventricular or AV node, before it passes through
the Bundle of His and to the Purkinje fibers of the left
and right ventricles, causing them to contract as well.
4. • The WPW pattern is a distinctive and important ECG
abnormality caused by preexcitation of the ventricles.
Normally the electrical stimulus travels to the
ventricles from the atria via the atrioventricular (AV)
junction. The physiologic lag of conduction through the
AV junction results in the normal PR interval of 0.12 to
0.2 sec. Consider the consequences of having an extra
pathway between the atria and ventricles that would
bypass the AV junction and preexcite the ventricles.
This situation is exactly what occurs with the WPW
pattern: an atrioventricular bypass tract connects the
atria and ventricles, circumventing the AV junction
5. • Bypass tracts (also called accessory pathways)
represent persistent abnormal connections
that form and fail to disappear during fetal
development of the heart in certain
individuals. These abnormal conduction
pathways, composed of bands of heart muscle
tissue, are located in the area around the
mitral or tricuspid valves (AV rings) or
interventricular septum. An AV bypass tract is
sometimes referred to as a bundle of Kent.
6.
7.
8.
9. Preexcitation of the ventricles with the classic WPW pattern produces the
following characteristic triad of findings on the ECG
• 1. The QRS complex is widened, giving the
superficial appearance of a bundle branch
block pattern. However, the wide QRS is
caused not by a delay in ventricular
depolarization but by early stimulation of the
ventricles. The T wave is also usually opposite
in polarity to the wide QRS in any lead, similar
to what is seen with bundle branch blocks
(“secondary T wave inversions”).
10. • The PR interval is shortened (often but not
always to less than 0.12 sec) because of the
ventricular preexcitation.
• The upstroke of the QRS complex is slurred or
notched. This is called a delta wave.
11. Differential diagnosis of Wide QRS
Complex
The major ECG patterns that produce a widened QRS complex
can be divided into four major categories.
1. Bundle branch blocks (intrinsic conduction delays)
including the classic RBBB and LBBB patterns
2. “Toxic” conduction delays caused by some extrinsic factor,
such as hyperkalemia or drugs (e.g., quinidine,
propafenone, flecainide and other related
antiarrhythmics, as well as phenothiazines, and tricyclic
antidepressants)
3. Beats arising in the ventricles, which may be ventricular
escape beats or ventricular premature beats (Chapter 16),
or electronic ventricular pacemaker beats
4. WPW-type preexcitation patterns
12. • The only normal electrical connection between
the atria and ventricles is the His bundle.
• Some people, however, have an extra or
‘accessory’ conducting bundle, a condition known
as the Wolff–Parkinson–White syndrome. The
accessory bundles form a direct connection
between the atrium and the ventricle, usually on
the left side of the heart, and in these bundles
there is no AV node to delay conduction.
13.
14. Electrophysiology of ECG changes
The features of pre-excitation may be subtle, or present only intermittently. Pre-excitation may be more pronounced with
increased vagal tone e.g. during Valsalva manoeuvres, or with AV blockade e.g. drug therapy.
15. The features of pre-excitation may be subtle, or
present only intermittently. The W-P-W
syndrome has been divided into two types (A
and B) on the basis of the direction of the
dominant QRS deflection in lead V1.
WPW may be described as type A or B.
Type A: positive delta wave
Type B: negative delta wave
16. Type A the delta wave and the remainder of the QRS complex are
primarily upright in lead V1, which shows R, RS, Rs, RSr', and Rsr'
patterns. A negative delta wave is seen in lead I.
17. Type B the delta wave and the QRS complex
are usually negative in lead V1, which shows
QS or rS patterns. Lead I shows a positive delta
wave.
18. Treatment
Patients with WPW who have symptomatic
tachycardias can usually be cured by an
ablation procedure during which the bypass
tract is ablated using radiofrequency (RF)
current. This highly successful treatment
requires a cardiac electrophysiologic
(EP) procedure in which special catheters are
inserted into the heart through peripheral
veins and
the bypass tract is located by means of ECG
recordings
(cardiac electrograms) made inside the heart.
