MEDizzy - Ms. Milsap is an 18-year-old high school volleyball star

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Disorders of the cardiovascular system 2

Ms. Milsap is an 18-year-old high school volleyball star with a sports scholarship to the local university. As part of her admission process, she is required to undergo a full medical assessment prior to taking part in collegiate sports. Physical examination reveals no abnormalities, although she reports a rare episode of palpitations and light-headedness. ECG reveals a PR interval of 0.06 msec, a QRS duration of 140 msec, and a slurred upstroke or delta wave in the initial part of the QRS. You correctly diagnose this as a Wolf-Parkinson-White pattern. Which of the following findings is reassuring that Ms. Milsap will suffer no ill effects or need catheter ablation due to this abnormality?

ExplanationWolf-Parkinson-White (WPW) pattern is almost always due to accessory pathway conduction whereby electrical signals are able to propagate from atria to ventricles without first going through the AV node. As opposed to the AV node, many accessory pathways fail to exhibit decremental conduction (a slowing of conduction at increasing rates of excitation) and thus are able to rapidly conduct fast atrial rhythms to the ventricles. At exceedingly fast rates (as might be present in atrial fibrillation), this can lead to cardiovascular collapse. The observation that Ms. Milsap’s delta wave disappears and QRS complex normalizes at a relatively high heart rate is reassuring. In that case, the accessory pathway cannot conduct antegrade at a rate >120 bpm and is unlikely to cause serious tachyarrhythmia. The ability to augment a rapid sinus rhythm is normal for her age and does not carry any particular prognosis. The location of the accessory pathway in a septal position makes is it somewhat more difficult to ablate with catheters, and the operator must take care to avoid the native AV node and His-Purkinje system. The ability of the accessory pathway to conduct both antegrade and retrograde makes it a substrate for atrioventricular reentrant tachycardia (AVRT).