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12-07: PSVT Due to Accessory AV Pathways (Preexcitation Syndromes)

Kevin P. Jackson

ESSENTIALS OF DIAGNOSIS

ESSENTIALS OF DIAGNOSIS

  • Two classic features of Wolff-Parkinson-White (WPW) pattern on ECG are short PR interval and wide, slurred QRS complex due to manifest preexcitation (delta wave).

  • Most patients with WPW pattern do not have clinical history of arrhythmia but have a higher risk of SCD due to the possibility of rapidly conducted atrial fibrillation through the accessory pathway.

  • Risk factors for SCD with WPW include age younger than 20, history of tachycardia, and rapid conduction properties at electrophysiologic testing.

GENERAL CONSIDERATIONS

Accessory pathways or bypass tracts between the atrium and the ventricle bypass the compact AV node and can predispose to reentrant arrhythmias, such as AVRT and atrial fibrillation. These may be wholly or partly within the node (eg, Mahaim fibers), yielding a short PR interval and normal QRS morphology (eFigure 12–6). More commonly, they make direct connections between the atrium and ventricle through Kent bundles (eFigure 12–7). When direct AV connections conduct antegrade (manifest preexcitation) they produce a classic WPW pattern on the baseline ECG consisting of a short PR interval and a wide, slurred QRS complex (delta wave) owing to early ventricular depolarization of the region adjacent to the pathway. Although the morphology and polarity of the delta wave can suggest the location of the pathway, mapping by intracardiac recordings is required for precise anatomic localization.

eFigure 12–6.

Short PR. Normal P wave with PR interval < 0.12 sec. A 31-year-old woman came to the emergency department following an episode of syncope consistent with vasovagal type. She has no history of palpitation or documented tachycardia. Her previous ECG had similar pattern. The possible etiologies of short PR interval are rapid conduction in an anatomically normal AV node, conduction through fast pathway, paranodal fiber, conduction bypasses most or all of the AV node, and small, underdeveloped AV node. Lown-Ganong-Levine syndrome includes (1) PR interval < 0.12 second, (2) normal P wave, (3) normal QRS duration, and (4) documented paroxysmal supraventricular tachycardia.

A 12 lead electrocardiograph shows a rhythmic tracing with a short P R interval in lead 2.
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eFigure 12–7.

A: ECG at initial preparticipation physical evaluation (preablation) demonstrates a WPW pattern. Red arrows identify the characteristic delta wave and short PR interval. B: Postablation ECG. WPW pattern has been extinguished. Note the absence of a delta wave and normalization of the PR interval. New T wave inversion in the inferior leads is a result of the ablation therapy that typically resolves over time. WPW, Wolff-Parkinson-White. (Reproduced with permission from Rao AL, Salerno JC, Asif IM et al. Evaluation and management of Wolff-Parkinson-White in athletes. Sports Health. 2014;06(04):326–332.)

A 12 lead electrocardiograph shows a rhythmic tracing with a classic W P W pattern. A 12 lead electrocardiograph shows the rhythmic tracing observed post ablation.
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A 12 lead electrocardiograph shows a rhythmic tracing with a classic W P W pattern. A 12 lead electrocardiograph shows the rhythmic tracing observed post ablation.
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Accessory pathways occur in 0.1–0.3% of the population and facilitate reentrant arrhythmias owing to the disparity in refractory periods of the AV node and ...

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