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Chapter 2: Cardiac arrhythmias 53

Prophylaxis involves identification and avoidance palpitations sometimes accompanied by chest pain and

of trigger factors where possible. Pharmacological dyspnoea, which may last minutes, hours or days.
prophylaxis may be achieved using anti-arrhythmic
drugs (e.g. flecainide). Radiofrequency ablation of
Investigations
the AV node or accessory pathway is being increas- During sinus rhythm the rapid conduction through
ingly used as an effective method to prevent recur-
the accessory pathway causes a short PR interval
rence.
(<0.12 seconds) and a wide QRS complex beginning
with a slurred part known as a δ wave (see Fig. 2.8).
Wolff–Parkinson–White syndrome During a tachycardic episode, the conduction enters
the ventricle through the AV node thus the PR interval
Definition and QRS morphology return to normal. Retrograde
Congenital predisposition to recurrent supraventricular excitation of the atria causes abnormal P waves fol-
tachycardia due to the presence of an extra accessory lowing the QRS complex.
pathway between the atria and the ventricles.
Complications
Aetiology
Sudden cardiac death may rarely occur if atrial fibrilla-
Abnormalconnectionbetweenatriumandventricle(e.g.
tion occurs. This leads to ventricular fibrillation because
bundle of Kent) that allows quick conduction from the
the accessory pathway can conduct rapid impulses with-
atria to the ventricles bypassing the AV node. Half of
out the usual blocking effect of the AV node, leading to
patientshaveatachycardiaeitherduetore-entryoratrial
sudden death.
fibrillation.
Pathophysiology Management
NormallythefastconductionthroughthebundleofKent Re-entrant tachycardias are treated with drugs that
allows the adjacent area of ventricle to be rapidly depo- block retrograde conduction through the accessory
larised (preexcitation), whilst the remainder of the ven- pathway, e.g. disopyramide, propanolol or amio-
tricle is depolarised by the normal route. However, the darone. Verapamil and digoxin are contraindicated as
two pathways may form a re-entry circuit with the fast they accelerate anterograde conduction through the
accessory pathway causing a retrograde stimulation of accessory pathway.
the atria and hence the AV node. The result is a form of Symptomatic patients should be offered a specialist
paroxysmal supraventricular tachycardia. evaluation for radioablation of the accessory pathway.

Clinical features Prognosis
In sinus rhythm Wolff–Parkinson–White syndrome is With age the pathway may fibrose and so some patients
asymptomatic. Patients may experience paroxysms of ‘growout of’ the condition.

δ Wave

Rhythm strip Short PR interval
(II)

Figure 2.8 Resting ECG in Wolff–Parkinson–White syndrome.