Wolff-Parkinson-White (WPW) syndrome is a heart condition with an extra electrical pathway. While an electrocardiogram (EKG) is a common diagnostic tool, it doesn’t always reveal the condition. A normal EKG doesn’t definitively rule out WPW. Understanding why this occurs and what other diagnostic options are available provides a clearer picture.
Understanding Wolff-Parkinson-White Syndrome
Wolff-Parkinson-White syndrome is a congenital heart condition, present from birth. It involves an abnormal electrical connection, an accessory pathway, between the heart’s upper chambers (atria) and lower chambers (ventricles). This extra pathway allows electrical impulses to bypass the atrioventricular (AV) node, which normally regulates signal timing. This “pre-excitation” can disrupt the heart’s normal rhythm, leading to rapid heartbeats (tachyarrhythmias) that can cause symptoms like palpitations, dizziness, or shortness of breath.
How WPW Presents on an EKG
When WPW syndrome is actively conducting, it produces distinct signs on a standard EKG. A primary indicator is a shortened PR interval (typically less than 120 milliseconds), reflecting the electrical impulse bypassing the normal AV node delay. Another characteristic finding is the “delta wave,” a slurring or slow rise at the beginning of the QRS complex, indicating premature ventricular activation. The QRS complex, representing ventricular depolarization, also appears widened (usually greater than 120 milliseconds) due to this early activation. These combined EKG features are characteristic of pre-excitation caused by the accessory pathway.
Reasons WPW Might Not Be Detected by EKG
Despite characteristic EKG findings, WPW syndrome may not always be detected on a standard EKG. One factor is intermittent pre-excitation, where the accessory pathway conducts signals only occasionally; an EKG taken when inactive will appear normal. Another scenario involves a “concealed pathway,” which conducts electrical impulses only from the ventricles back to the atria. Since it doesn’t conduct signals forward during normal heart rhythm, it doesn’t cause pre-excitation or a delta wave on a surface EKG. However, these pathways can still participate in abnormal heart rhythms, and their anatomical location can also influence EKG visibility.
Additional Diagnostic Approaches
When WPW syndrome is suspected but a standard EKG is inconclusive, further diagnostic steps are necessary. Ambulatory EKG monitoring, such as a Holter monitor or event recorder, captures the heart’s electrical activity over an extended period (typically 24 to 72 hours or longer). These devices detect intermittent pre-excitation or abnormal heart rhythms missed by a brief office EKG. An exercise stress test may also evaluate the heart’s electrical response during physical exertion. An electrophysiology (EP) study is the definitive diagnostic procedure for WPW, involving thin catheters to map electrical pathways, confirm diagnosis, and assess risk.