Advanced EKGs - Wolff-Parkinson-White (WPW) Syndrome

Summary

This video explores Wolf-Parkinson-White (WPW) syndrome and pre-excitation in electrocardiography (EKG). It explains how an accessory pathway bypasses the normal conduction system, leading to a short PR interval, Delta waves, and a wide QRS complex. The video distinguishes between WPW pattern (asymptomatic) and WPW syndrome (symptomatic with arrhythmias), focusing on the arrhythmias, particularly atrioventricular reentrant tachycardia (AVRT). It also covers the mechanisms of orthodromic and antidromic AVRT, as well as other arrhythmias in WPW. The localization of accessory pathways is demonstrated using EKG features, and the video concludes with a discussion on concealed WPW and intermittent pre-excitation.

Takeaways

• 😀 Pre-excitation is the rapid propagation of a depolarization wavefront due to an accessory conductive pathway that bypasses the normal conduction system.
• 😀 Wolf-Parkinson-White (WPW) syndrome refers to the presence of pre-excitation and symptoms like palpitations, light-headedness, chest pain, and even sudden cardiac arrest.
• 😀 Key EKG features of pre-excitation include a short PR interval, a Delta wave, and a wide QRS complex.
• 😀 The term 'bundle of Kent' should be avoided when referring to accessory pathways, as it implies a specific pathway that may not be accurate for all cases.
• 😀 Accessory pathways are typically remnants of connections between the atria and ventricles during embryological development and can be located at various anatomical sites in the heart.
• 😀 WPW syndrome can lead to arrhythmias like atrioventricular re-entrant tachycardia (AVRT), which can be classified into orthodromic and antidromic types.
• 😀 Orthodromic AVRT features narrow QRS complexes, while antidromic AVRT results in wide QRS complexes due to depolarization through the accessory pathway.
• 😀 Permanent junctional reciprocating tachycardia (PJRT) is a form of orthodromic AVRT that is incessant, often due to concealed accessory pathways.
• 😀 Non-AVRT arrhythmias in WPW patients can include sinus tachycardia, atrial fibrillation, atrial flutter, and AVNRT, all of which may present with wide QRS complexes.
• 😀 Concealed WPW occurs when the accessory pathway is only capable of retrograde conduction, making it undetectable on EKG in sinus rhythm.
• 😀 Intermittent pre-excitation is a rare condition where some QRS complexes show pre-excitation while others do not, leading to an alternating pattern of normal and wide QRS complexes.

Q & A

What is preexcitation, and how does it affect the heart's conduction system?

Preexcitation refers to the presence of an accessory pathway in the heart, bypassing the normal AV node delay. This leads to early depolarization of the ventricles, which results in a shortened PR interval and a widened QRS complex on the EKG.

What are the key features of a normal conduction system in the heart?

The normal conduction system of the heart involves the SA node, AV node, His bundle, bundle branches, and Purkinje fibers. Impulses travel through these structures with a brief delay at the AV node, leading to a normal PR interval (120–200 ms) and a sharp QRS complex (less than 120 ms).

How can preexcitation be identified on an EKG?

Preexcitation can be identified on an EKG by a short PR interval, a Delta wave (slurred upstroke of the QRS), and a prolonged QRS duration. These features result from early ventricular depolarization due to an accessory pathway.

What is the difference between WPW pattern and WPW syndrome?

WPW pattern refers to the presence of preexcitation on the EKG without any symptoms. WPW syndrome, however, involves the same EKG features but also presents with symptoms such as palpitations, lightheadedness, and even sudden cardiac arrest.

What are the two main types of atrioventricular reentrant tachycardia (AVRT) seen in WPW?

The two main types of AVRT in WPW are orthodromic and antidromic. In orthodromic AVRT, the impulse moves through the normal conduction system and retrogrades up the accessory pathway, resulting in narrow QRS complexes. In antidromic AVRT, the impulse moves through the accessory pathway first, leading to wide QRS complexes.

What causes the wide QRS complexes in antidromic AVRT?

In antidromic AVRT, the impulse moves through the accessory pathway first, bypassing the normal conduction system. This results in a wide QRS complex on the EKG due to abnormal ventricular depolarization.

Can a patient with WPW have arrhythmias without delta waves present on their EKG?

Yes, some patients with WPW have a condition called concealed WPW, where the accessory pathway exists but no delta waves are visible on the EKG. These patients may still experience arrhythmias that can only be diagnosed through an electrophysiological (EP) study.

What is the significance of intermittent preexcitation in patients with WPW?

In intermittent preexcitation, patients may show alternating EKG patterns of preexcited and normal complexes. This rare condition can present as intermittent episodes of arrhythmias or normal sinus rhythms and requires careful monitoring for diagnosis.

What is the mechanism behind the arrhythmias seen in WPW syndrome?

The arrhythmias in WPW syndrome occur because of the presence of an accessory pathway that can allow electrical impulses to travel abnormally. This can lead to reentrant circuits and tachycardias, such as AVRT or other forms of abnormal atrial and ventricular conduction.

Why is the PR interval shorter in patients with preexcitation or WPW?

The PR interval is shorter in patients with preexcitation because the impulse bypasses the normal AV node delay, allowing the ventricles to be depolarized earlier than usual, resulting in a shortened interval.