From the Guidelines
Locating an accessory pathway based on ECG involves analyzing specific patterns during normal sinus rhythm and any tachyarrhythmias, with the most recent guidelines from 2016 providing the foundation for diagnosis and management 1. To locate an accessory pathway, first look for a short PR interval (<120 ms) and delta wave (slurred upstroke of the QRS complex), which are classic findings of ventricular pre-excitation in Wolff-Parkinson-White syndrome.
- The polarity and morphology of the delta wave across different leads can help determine the pathway location.
- For left-sided pathways, the delta wave is typically positive in leads I and aVL, and negative in V1.
- Right-sided pathways often show negative delta waves in leads I and aVL, with positive delta waves in V1.
- Posteroseptal pathways typically show negative delta waves in leads II, III, and aVF. During tachycardia episodes,
- a narrow complex tachycardia with retrograde P waves suggests orthodromic atrioventricular reentrant tachycardia (AVRT),
- while a wide complex tachycardia resembling ventricular tachycardia may indicate antidromic AVRT. The RP interval during tachycardia can also provide clues about the pathway location. These ECG findings help localize the accessory pathway, which is crucial for planning ablation procedures, though definitive localization often requires electrophysiology studies for confirmation 1. It's also important to consider the clinical presentation and differential diagnosis based on symptoms, as outlined in the guidelines 1. In cases where the diagnosis is unclear or the patient is symptomatic, further evaluation and management may be necessary, as recommended by the guidelines 1.
From the Research
Locating Accessory Pathway based on ECG
To locate an accessory pathway based on an ECG, several key features must be identified:
- A short PR interval (less than 0.12 seconds) 2, 3, 4
- A slurring of the initial segment of the QRS complex, known as a delta wave 2, 3, 4, 5
- A QRS complex widening with a total duration greater than 0.12 seconds 2, 4
- Secondary repolarization changes reflected in ST segment-T wave changes that are generally directed opposite (discordant) to the major delta wave and QRS complex changes 2
Diagnostic Considerations
The presence of these features can indicate the Wolff-Parkinson-White (WPW) syndrome, a form of ventricular preexcitation involving an accessory conduction pathway 2, 3, 4, 6. The accessory pathway bypasses the atrioventricular (AV) node, creating a direct electrical connection between the atria and ventricles 2, 3.
ECG Analysis for Accessory Pathway Localization
ECG analysis can help in the detection of the delta wave, which is an important indicator for diagnosing WPW syndrome 5. The use of continuous wavelet transform can aid in detecting the P wave, QRS complex, and T wave, and computing their durations after determining the boundary location (onsets and offsets of the P, QRS, and T waves) 5. The PR duration, QRS duration, and upstroke of the QRS complex can then be used to determine the presence or absence of the delta wave 5.
Clinical Implications
Patients with WPW syndrome may present with a wide spectrum of symptoms, ranging from mild palpitations to unstable tachydysrhythmias and sudden cardiac death 2, 3, 4, 6. The importance of recognizing this syndrome lies in the potential risk of developing supraventricular tachyarrhythmias, which can cause disabling symptoms and, in extreme cases, sudden cardiac death 2, 3, 6. Electrophysiologic studies are recommended to characterize and localize the accessory pathway 3, 4, 6.