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Q1: What does the ecg show (see p 479)?
Alternate complexes in the ECG (1,3,5,7) show evidence of short PR segment and a delta wave. This is referred to as “intermittent pre-excitation” or “intermittent Wolff-Parkinson-White syndrome”.
Q2: What should be the next step in management?
This patient is symptomatic. Her palpitations are most likely due to supraventricular tachycardia—more specifically atrioventricular re-entrant tachycardia. This warrants an electrophysiology study to localise the accessory pathway and perform curative ablation. Care must also be taken when starting the patient on atrioventricular node blocking agents like calcium channel blockers for supraventricular tachycardia as this may facilitate conduction down the accessory pathway during tachycardia.
Q3: Is this patient at risk for sudden death? if yes, how will you evaluate her for this risk?
Sudden death in patients with accessory pathways can occur due to ventricular fibrillation following rapid conduction over the accessory pathway during atrial fibrillation. The present patient may not be at risk for sudden death. This is because the accessory pathway seems to have a long refractory period. However, this cannot be stated with certainty as conduction properties of the accessory pathway can change with sympathetic influences. Studying the ECG during exercise may help to determine the properties of the accessory pathway. The use of sympathomimetic agents such as isoprenaline during electrophysiology study also serves the same purpose.
Intermittent pre-excitation was present in 6.7% of men and 16% of women in a large French study.1 Pre-excitation results from an accessory pathway. It is seen when an impulse travels down both the normal atrioventricular node and the accessory pathway. The pathway in this patient has a long refractory period allowing it to conduct only during alternate impulses. Accessory pathways can be localised from the surface ECG.2 Asymptomatic patients with intermittent pre-excitation are not at increased risk for sudden death. Intermittent preexcitation may also disappear over time.3 Whether patients with asymptomatic Wolff-Parkinson-White syndrome should undergo electrophysiological or pharmacological testing to determine their “potential” to develop serious cardiac arrhythmias is controversial. There is paucity of data concerning the natural history of Wolff-Parkinson-White syndrome in asymptomatic patients. Long term prospective studies are necessary to clarify which asymptomatic patients with Wolff-Parkinson-White syndrome require treatment. However, sudden death has been reported in asymptomatic patients as well.4 The conduction properties of the accessory pathways may change, especially during exercise or sympathetic activity which may lead to rapid atrioventricular impulse transmission. The use of isoprenaline has been shown to facilitate anterograde and retrograde conduction in accessory pathways in patients with intermittent pre-excitation.5 In patients with Wolff-Parkinson-White syndrome, a pre-excited RR interval of less than 220 msec on the surface ECG also identifies candidates at risk for sudden death.
Intermittent pre-excitation (intermittent Wolff-Parkinson-White syndrome).