A College Student With Palpitations

A 20-year-old college student presents with frequent heart palpitations. Hehas been in excellent health.

The patient had a normal echocardiogram at age 16 when his father wasfound to have a bicuspid aortic valve. At age 18, he began experiencing intermittentepisodes of sudden tachycardia provoked by strenuous athletics. A formaltreadmill exercise test failed to demonstrate any dysrhythmia or ischemiadespite a peak heart rate of 199 beats per minute at 12:30 minutes of the standardBruce protocol. By age 19, he was having episodes about monthly, witha heart rate he estimated to be about 220 beats per minute. He has learned toterminate episodes with the Valsalva maneuver.

The patient's blood pressure is 120/80 mm Hg. His resting heart rate is58 beats per minute. His physical examination is entirely normal. His ECG isshown here.

1. What does this ECG show?
2. What is the likely diagnosis?
3. What should be done next to evaluate and/or treat this patient?

WHAT'S WRONG:1. What does the ECG on the previous page show?
The tracing is normal. There is no evidence of underlyingstructural heart disease that might form an"arrhythmic substrate."

2. What is the likely diagnosis?
The most likely diagnosis, on the basis of the patient'sage, the structurally normal heart, and the symptoms,is a paroxysmal supraventricular tachycardia. Inthe absence of an ECG taken during the tachycardia,the precise mechanism cannot be determined. The differentialdiagnosis includes ectopic atrial tachycardia(based on either an automatic or reentrant mechanism),atrioventricular (AV) nodal reentrant tachycardia, paroxysmalatrial fibrillation or flutter, and AV reciprocatingtachycardia dependent on a (concealed) bypass tract.Although paroxysmal ventricular tachycardia cannot beexcluded, it is much less likely.

3. What should be done next to evaluate and/ortreat him?
Because the patient tolerates his tachycardia well--that is, there are no symptoms to suggest hemodynamiccompromise with the dysrhythmia--and there is a lowindex of suspicion for a ventricular origin, the first orderof business is to document the rhythm disturbance andclarify its mechanism so that appropriate therapeutic optionsmay be defined.

The patient was given an event recorder, but no tachyarrhythmia was detectedover several weeks. He was reluctant to take medication, and no furtherworkup was undertaken.

About a year and a half later, another ECG is obtained as part of a routineexamination (Figure).

1. What is the diagnosis now?
2. What should be done next to evaluate and/or treat the patient?

WHAT'S WRONG:1. What is the diagnosis now?
The tracing now shows evidence of ventricularpre-excitation. The PR interval is short, and there isslurring of the upstroke of the QRS complex (seenmost clearly in leads V₂ through V₄), indicating transmissionof the atrial impulse to the ventricle throughboth an accessory pathway and the AV node. The diagnosisis now clearly Wolff-Parkinson-White (WPW)syndrome, and the tachycardia is almost certainly areciprocating tachycardia utilizing the accessory pathway.If, during the tachycardia, the electrical impulsetravels antegrade (from atrium to ventricle) down normallythrough the AV node and then up the accessorypathway, the tachycardia is called orthodromic andwould have a narrow complex on an ECG. If the impulsetravels down the accessory pathway and then upthe AV node, it is called antidromic and would have awide complex. The intermittent nature of the pre-excitation,indicating variable antegrade electrical conductiondown the accessory pathway, and demonstratedby the prior, normal ECG, is a common finding inWPW syndrome.

2. What should be done next to evaluate and/ortreat the patient?
The patient should have an electrophysiologic (EP)study performed to assess the electrical properties ofthe accessory pathway. Pathways that support rapidantegrade conduction are associated with increased riskof sudden cardiac death, because they can potentiatevery fast ventricular rates in the presence of an atrial arrhythmiasuch as atrial fibrillation. An EP study also setsthe stage for a radiofrequency ablation of the accessorypathway, which is a curative procedure.