Shock to the Heart

My younger brother Sam was diagnosed with Wolff-Parkinson-White (WPW) syndrome when he was 6 years old.  This syndrome is characterized by the presence of an extra electrical pathway in the heart that leads to an extremely rapid heart rate, or tachycardia, of over 100 beats per minute (BPM).  Sam would experience these very painful episodes of accelerated heart rate (his heart rate was near 200 BPM during one episode) for a few minutes at a time, several times a week.  At one point, the episodes would “cluster” together and occur only hours apart.

Normally, an action potential originates in the sinoatrial (SA) node in the right atrium, causing a wave of depolarization and concurrent contraction of both atria.  This electrical stimulus then travels to the atrioventricular (AV) node, where there is a delay before the signal continues through the bundle of His, right and left bundle branches, and Purkinje fibers, leading to ventricular depolarization and contraction.  This delay in signal transmission is important for maintaining a regular heart rate within the normal 60-100 BPM at rest.

The conduction pathway in a WPW patient can differ in several ways.  The most common (and what my brother had) is an accessory AV pathway called the bundle of Kent, found between one of the atria and ventricles.  This circuit bypasses the AV node and does not delay the electrical signal, causing premature depolarization of the ventricles.  This is responsible for the rapid heart rate, or more specifically, supraventricular tachycardia, found in these patients.  In WPW, the signal from the SA node travels through both pathways, the accessory pathway first and the normal pathway second, but because of the lack of signal delay in the accessory pathway, an irregular heartbeat is formed.  

	Normal electrical pathway (left) and abnormal bundle of Kent pathway in WPW patients (right).

 This syndrome can be easily diagnosed with an electrocardiogram (ECG), since WPW exhibits unique ECG activity.  These features include a shortened PR interval, a widened QRS interval, and the presence of a Delta wave, shown below.  

A typical ECG recording from a WPW patient.

The most common treatment and cure for WPW is a radiofrequency (RF) catheter ablation procedure, where a tube (catheter) is inserted through an artery in the groin region and brought to the heart, where the energy from the radiofrequency destroys the extra pathway (the bundle of Kent).  Sam underwent this procedure a couple of months after his diagnosis.  Besides a couple of complications during surgery (his heart had to be stopped twice; the procedure wasn’t as simple and refined as it is today), he has remained mostly symptom free.  Since this is a congenital condition, perhaps the simple measure of having routine ECGs at birth would prevent the painful and frightening symptoms that my brother had to experience before his treatment.

Fun Fact: Rock musicians Marilyn Manson and Meat Loaf both had WPW. 

 

References:

Bartlett, T., Friedman, P.  Current management of the Wolff-Parkinson-White syndrome.  Journal of Cardiac Surgery.  8(4), 503-515, 1993.

Fengler, B., Brady, W., Plautz, C.  Atrial fibrillation in the Wolff-Parkinson-White syndrome: ECG recognition and treatment in the ED. The American Journal of Emergency Medicine.  25(2), 576-583, 2007.

(2012, June 4).  Wolf-Parkinson-White Syndrome. Pub Med Health, Retrieved from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001206/.

Rosner, M., Brady Jr, W., Kefer, M., Martin, M.  Electrocardiography in the patient with the Wolff-Parkinson-White syndrome: diagnostic and initial therapeutic issues. The American Journal of Emergency Medicine.  17(7), 705-714, 1999.

Images: http://en.wikipedia.org/wiki/Wolff%E2%80%93Parkinson%E2%80%93White_syndrome#Diagnosis.

              http://www.sciencedirect.com.dml.regis.edu/science/article/pii/S0735675706004505.