Introduction


Wolff-Parkinson-White syndrome (WPW) is a syndrome, first described in 1930, in which certain abnormalities of the ECG are accompanied by episodes of symptomatic tachycardia. The tachycardias (fast heart rhythms) may cause palpitations. Sometimes the term WPW is used even if there are no symptoms, though this is strictly-speaking incorrect. A small proportion of cases are at risk of sudden cardiac death.

Epidemiology


The ECG changes of WPW are present in 2-3 per thousand individuals; most have no symptoms, so the true frequency is lower. This is a congenital disorder: it may be diagnosed at any age, though usually in childhood or as a young adult. It is commoner in males (2:1 sex ratio).

Pathophysiology


Normally, the upper chambers of the heart (the atria) are electrically isolated from the lower chambers (the ventricles) by the fibrous atrioventricular ring (AV ring) which acts as an electrical insulator. Electrical signals can normally only pass between the atria and ventricles through specialised conducting tissue known as the atrioventricular node (AV node) and Bundle of His. The AV node has special properties, most notably a built in time delay, and some intrinsic pacemaker ability, which together protect the important ventricles (doing nearly all the pumping of the heart) from the worst effects of any arrhythmia in the atria.

In WPW, there are one or more so-called accessory pathways between the atria and ventricles, in which a strand (or larger piece) of myocardium (heart muscle) forms an abnormal electrical connection between these two halves of the heart. The properties of an accessory pathway may vary: some may be able to conduct electrical impulses from the atria to the ventricles (antegrade conduction), some may conduct in the other direction (retrograde), and some may conduct in both directions. A strict use of the term WPW requires that the accessory pathway may conduct (at least) antegradely, though it is sometimes incorrectly applied to cases in which the pathway only conducts retrogradely. Other important properties of the accessory pathway include its position in the AV ring and its refractory period (period of time during which it cannot be activated electrically).

The antegradely-conducting accessory pathway allows electrical signals from the atria to reach part of the ventricles before any signals passing through the AV node can do so. This is almost never a significant problem of itself, but the pathway may be associated with a couple of different types of arrhythmia. Firstly, an atrioventricular reentrant tachycardia (AVRT) may occur, in which a circular electrical activation may be set up in which signals pass up one (normal or abnormal) pathway and down the other; more commonly this would be down the AV node/His bundle, and up the accessory pathway. This causes the heart to beat fast for a period of time; it is a nuisance but not life-threatening. The other important arrhythmia is "pre-exited atrial fibrillation" in which a chaotic rhythm (atrial fibrillation) occurs in the atria. This is generally a benign rhythm (in the short term), except that in WPW, IF the accessory pathway is able to conduct impulses to the ventricles from the atria at a high rate (often NOT the case), there is a risk of causing ventricular tachycardia or ventricular fibrillation; the latter causes sudden death unless immediately treated. In people without WPW, the AV node completely protects against the possibility of atrial fibrillation causing the fatal ventricular fibrillation.

WPW may be associated with a variety of congenital structural abnormalities of the heart; these are more likely to be present if the diagnosis is made in early childhood. If the diagnosis is made in the teens or later, structural abnormalities are rare. Most people with WPW do not have any other abnormality of the heart. A small number of cases are inherited, with autosomal dominant inheritance, but most are not inherited.

Symptoms


By definition, people with WPW have symptoms, which could include palpitations, syncope or sudden cardiac death. As explained above, the latter is rare. Palpitations are due to one of the fast heart rhythms described above, and people will notice the heart suddenly beating fast for a period of minutes or hours. The frequency of palpitations varies considerably, from one episode in a lifetime, to daily episodes; one or two episodes a year would be a common pattern. Unusually there could be episodes of syncope (blackout), with or without preceding palpitations.

ECG changes


The characteristic feature of the ECG is the "delta wave", in which there is a slurred upstroke (or downstroke) of the QRS complex. This is due to the early activation ("pre-excitation") of part of the ventricular myocardium through an accessory pathway. It is slurred because the activation is through the relatively slowly conducting ventricular muscle rather than the rapidly-conducting specialised tissue (the His-Purkinje system). The delta wave may cause the QRS complex to be wider than usual, and may cause the PR interval to be shorter, but these latter features are neither necessary nor sufficient to make the diagnosis on ECG. The pattern of the delta waves (in what leads they are positive or negative on a 12-lead electrocardiogram) allows the position of the accessory pathway to be worked out in most cases. In some people the accessory pathway's properties fluctuate enough from day to day to cause the presence of delta wave to be variable. In other patients, the delta wave may usually not be visible ("latent" WPW, a misnomer) - this occurs typically in a proportion of people with a so-called far left lateral pathway. The delta wave may sometimes become visible at fast heart rates or in atrial premature beats in these cases. To complicate matters, multiple pathways are present in a minority of cases.

Diagnosis


A characteristic ECG in conjunction with symptoms is enough to make a firm diagnosis. An electrophysiology study (EPS), in which electrodes are maniplated through blood vessels (often from the groin) up into the heart, may be used. This is used if there is diagnostic doubt (for instance if the ECG is borderline) or to assess for the risk of rapid pre-excitation of the ventricles (and hence the dangerous ventricular fibrillation). An EPS is the first stage of radiofrequency catheter ablation treatment, where required.

Treatment

  • No specific treatment. In many cases no specific treatment is required.
  • Drugs. The "class 1C" anti-arrhythmic drugs such as flecainide or propafenone are the most useful. To have any effect, these drugs must be taken regularly. Certain groups of drugs given for some arrhythmias are generally contraindicated in WPW; these include beta blockers, calcium antagonists and digoxin. These latter groups of drugs may occasionally be used by cardiac electrophysiologists (the doctors specialising in heart rhythm problems), but be wary if any other doctor initiates them, if you have WPW. I am not advising you to disregard your doctor's advice, though.
  • Radiofrequency catheter ablation. Initial successful attempts (early 1980s) to physically remove the accessory pathway used open heart surgery. This is still occasionally used, but only generally if surgery is needed for some other reason at the same time. The next development involved placing catheters (special wires or tubes) within the heart, guided from blood vessels in the groin or elsewhere, into the heart using X rays. At first the accessory pathways were destroyed using DC shocks. It was later found that better, more consistent and safer results could be obtained by applying a high frequency (radiofrequency) AC current to the region of the pathway. This last technique is known as radiofrequency catheter ablation. In the right hands, this has become an entirely routine and extremely safe procedure, with success rates of 90-95% on one sitting (of a procedure lasting 1-3 hours, sometimes more). There is the proviso that if the pathway is very near the AV node (an anteroseptal pathway) there will be an increased reluctance of all concerned to have the procedure done, as if the AV node is damaged, a permanent pacemaker may be required; this is occasionally required wherever the pathway is located. There are other rare complications. Other catheter ablation techniques are under development, including the using of very low temperatures applied to the accessory pathway (cryoablation). If successful, any of the "ablation" techniques described in this paragraph cause a complete cure.

Prognosis


Prognosis is excellent. A small proportion of cases have a risk of sudden cardiac death, which can be accurately predicted by electrophysiological testing. Almost all cases can be cured by radiofrequency ablation if necessary, with the provisos given above.

Sources


The author of this node has professional experience and knowledge in this field, and apart from checking a couple of small details, was written without reference to any other text. You should see a doctor if you think anything here applies to you however.

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