Ran into Wolff-Parkinson-White syndrome during a call the other day (also known as WPW or pre-excitation syndrome in the medical field). I remember hearing about it briefly in class, but not much more than it has a really cool name. It is a relatively rare syndrome, but tricky in that the patient can range from having no symptoms to fatal consequences. By the way, it can affect any age (my patient was early 20’s). It is one of the conditions that causes healthy young athletes to drop dead on the sports field each year. So you guessed it, review time.
To the Medical Dictionary…
Wolff-Parkinson-White syndrome is a specific type of abnormality of the electrical system of the heart.
“Normally, electrical impulses in the heart pass through the atrioventricular (AV) node on their way to depolarize the ventricles. The AV node acts as a moderator, slowing the impulse before it reaches the ventricles to allow for proper coordination between the upper and lower heart chambers. This brief pause lets blood travel through the AV valves into the ventricles before ventricular contraction occurs.
The AV node also limits the number of electrical impulses that reach the ventricles. In some arrhythmias, the atria can deliver more than 200 impulses to the AV node every minute. The AV node doesn’t let them all pass because at that rate, the ventricles have no time to fill and limited time to contract, resulting in a precipitous drop in cardiac output and blood pressure.
However, in a patient with a preexcitation syndrome, the electrical impulses bypass the AV node. Instead, they travel on an alternative pathway (also called a bypass tract or accessory pathway) that has no delays or rate limits. Consequently, the atrial impulse reaches the ventricles sooner than if it had gone via the AV node. Under certain circumstances, these bypass tracts can allow dangerously fast rhythms to occur.
A bypass tract can occur in any area of the heart that permits the depolarization wave to reach the ventricles prematurely. Bypass tracts-connections made up of strands of atrial-like muscle-can occur in any number of combinations involving the atria, ventricles, AV node, bundle of His, or fascicles and can occur on either side of the heart. Each anomalous connection produces specific changes on the 12-lead electrocardiogram (ECG) that will provide clues to the location and type of bypass tract.
In WPW, the most common preexcitation syndrome, the bypass tract is the bundle of Kent, a direct connection between an atrium and ventricle. This congenital condition was first described in otherwise-healthy young people with recurrent paroxysmal supraventricular tachycardia (PSVT) whose baseline ECG rhythm showed a short PR interval and a bundle-branch block pattern (findings common in many preexcitation syndromes). However, WPW syndrome has these distinct hallmarks:
* a short PR interval (less than 0.12 second). The absence of the normal AV nodal delay causes the QRS to occur earlier and therefore closer to the P wave. Remember that the PR interval also shortens with an increased heart rate and in some atrial and junctional rhythms.
* a delta wave. This small segment of the QRS, which is frequently referred to as an abnormal “slurring of the QRS” (see Conduction in Wolff-Parkinson-White Syndrome), represents early, abnormal depolarization of the ventricles. Negative delta waves in lead V^sub 1^ indicate a right-sided bypass tract and can mimic the pathologic Q-waves of myocardial infarction.
* a wide QRS complex. The QRS complex is [>0.12s] because the electrical impulse depolarizes the ventricles earlier than usual. A small amount of ventricular tissue begins to depolarize near the bypass tract, activating before the rest of the ventricle, but because it doesn’t use the fast bundle-branch pathway, the QRS complex is wider than normal.”2
(Image 1 is an example of a normal electrical pathway, Image 2 shows pre-excitation pathways)
How a medic will know…
As mentioned, this syndrome causes a specific pattern on an electrocardiogram. It is most identifiable by a delta wave in multiple leads (Wolff-Parkinson-White pattern). The delta wave may occur on intermittent beats. In case of type A pre-excitation (left atrioventricular connections), a positive R wave will be seen in V1 (“positive delta”) on the precordial leads of the electrocardiogram, while in type B pre-excitation (right atrioventricular connections), a predominantly negative delta wave will be seen in lead V1 (“negative delta”). 4 WPW is also linked to episodes of rapid heart rates, such as supraventricular tachycardia (SVT) or atrial fibrillation. 5 The rapid heart rate is caused by successful electrical bypass. This can lead to that drop in cardiac output we talked about (the ventricles do not have time to fill), and potentially fatal arrhythmias.
Signs and Symptoms…
Individuals affected by Wolff-Parkinson-White syndrome can experience palpitations, rapid heart rates, difficulty breathing, dizziness and lightheadedness as well as near loss of consciousness and complete loss of consciousness. For the most part, these symptoms occur all of a sudden and are not associated with warning signs. Usually, there are no dramatic triggers, however, caffeine, alcohol, and exercise can cause the heart to start racing.7
Ebstein’s anomaly, a congenital heart defect that involves displacement of the tricuspid valve, located on the right side of the heart, is one known cause of Wolff-Parkinson-White syndrome. This anomaly allows blood to flow via the small hole to the other side of the heart. Often, there is no known cause for Wolff-Parkinson-White syndrome. 8
A patient’s doctor may have instructed them to try a vagal maneuver during an episode of a fast heartbeat. Vagal maneuvers affect the vagus nerve, which helps regulate your heartbeat. The maneuvers include coughing, bearing down as if you are having a bowel movement, and putting an ice pack on your face.
Various drugs may be used to treat Wolff-Parkinson-White syndrome. The purpose of these drugs is to slow the electrical signals and excitation of heart muscles. A patient may also prescribe a pill version of an anti-arrhythmic drug, such as flecainide (Tambocor) or propafenone (Rythmol, Rythmol SR), to take if you have an episode of a fast heartbeat that doesn’t respond to vagal maneuvers.
A more permanent solution is ablative therapies. This may be accomplished with radiofrequency or cardiac catheters to cut through or destroy the tissue which is causing the abnormal electrical signals.
During more serious episodes the patient may require an injection of an anti-arrhythmic medication, such as adenosine, to restore a normal heart rate (which would be administered by a higher level Paramedic, or in hospital). During a lethal episode the patient may require cardioversion. 9
Why is it called Wolff-Parkinson-White syndrome?
(1) (anatomical heart on print) http://www.etsy.com/ca/listing/62337811/anatomical-heart-print-vintage-french?ref=exp_listing
- Most frequent arrhythmia in WPW syndrome (cardiophile.org)
- missed heart problems in young (drgleesonlaw.wordpress.com)
- Delta wave on ECG (cardiophile.org)