A College Student With Palpitations
A 20-year-old college student presents with frequent heart palpitations. He has been in excellent health.
The patient had a normal echocardiogram at age 16 when his father was found to have a bicuspid aortic valve. At age 18, he began experiencing intermittent episodes of sudden tachycardia provoked by strenuous athletics. A formal treadmill exercise test failed to demonstrate any dysrhythmia or ischemia despite a peak heart rate of 199 beats per minute at 12:30 minutes of the standard Bruce protocol. By age 19, he was having episodes about monthly, with a heart rate he estimated to be about 220 beats per minute. He has learned to terminate episodes with the Valsalva maneuver.
The patient's blood pressure is 120/80 mm Hg. His resting heart rate is 58 beats per minute. His physical examination is entirely normal.
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 underlying structural heart disease that might form an “arrhythmic substrate.”
2. What is the likely diagnosis?
The most likely diagnosis, on the basis of the patient’s age, the structurally normal heart, and the symptoms, is a paroxysmal supraventricular tachycardia. In the absence of an ECG taken during the tachycardia, the precise mechanism cannot be determined. The differential diagnosis includes ectopic atrial tachycardia (based on either an automatic or reentrant mechanism), atrioventricular (AV) nodal reentrant tachycardia, paroxysmal atrial fibrillation or flutter, and AV reciprocating tachycardia dependent on a (concealed) bypass tract. Although paroxysmal ventricular tachycardia cannot be excluded, it is much less likely.
3. What should be done next to evaluate and/or treat him?
Because the patient tolerates his tachycardia well— that is, there are no symptoms to suggest hemodynamic compromise with the dysrhythmia—and there is a low index of suspicion for a ventricular origin, the first order of business is to document the rhythm disturbance and clarify its mechanism so that appropriate therapeutic options may be defined.
The patient was given an event recorder, but no tachyarrhythmia was detected over several weeks. He was reluctant to take medication, and no further workup was undertaken.
About a year and a half later, another ECG is obtained as part of a routine examination (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 ventricular pre-excitation. The PR interval is short, and there is slurring of the upstroke of the QRS complex (seen most clearly in leads V2 through V4), indicating transmission of the atrial impulse to the ventricle through both an accessory pathway and the AV node. The diagnosis is now clearly Wolff-Parkinson-White (WPW) syndrome, and the tachycardia is almost certainly a reciprocating tachycardia utilizing the accessory pathway. If, during the tachycardia, the electrical impulse travels antegrade (from atrium to ventricle) down normally through the AV node and then up the accessory pathway, the tachycardia is called orthodromic and would have a narrow complex on an ECG. If the impulse travels down the accessory pathway and then up the AV node, it is called antidromic and would have a wide complex. The intermittent nature of the pre-excitation, indicating variable antegrade electrical conduction down the accessory pathway, and demonstrated by the prior, normal ECG, is a common finding in WPW syndrome.
2. What should be done next to evaluate and/or treat the patient?
The patient should have an electrophysiologic (EP) study performed to assess the electrical properties of the accessory pathway. Pathways that support rapid antegrade conduction are associated with increased risk of sudden cardiac death, because they can potentiate very fast ventricular rates in the presence of an atrial arrhythmia such as atrial fibrillation. An EP study also sets the stage for a radiofrequency ablation of the accessory pathway, which is a curative procedure.