A 37-year-old woman with a history of anxiety disorder presents to the emergency department (ED) with concern for panic attack. She describes a sensation of chest-pounding palpitations, racing heart rate, severe dyspnea, and lightheadedness. She is beginning to feel some chest heaviness. She has a several-year history of these intermittent symptoms, which she ascribes to her "panic attacks." These paroxysms often last for 10-15 minutes and spontaneously subside before her arrival to the ED. In the past, she had an extensive but essentially normal cardiac work-up, which included electrocardiography, exercise treadmill test, 24-hour Holter monitor, and echocardiography. She notes that she was asymptomatic at the time that the studies were being conducted. Her primary care provider diagnosed her with anxiety disorder with panic attacks and prescribed a selective serotonin reuptake inhibitor (SSRI). Despite treatment, she has had several episodes per year. They do not appear to be associated with anything in particular. Her current episode began while she was playing water polo with her community league team and, to her surprise, it did not spontaneously subside. She began to feel drained of her usual energy and stamina and thought that she would pass out. She immediately got out of the pool and was quickly rushed to the ED by her friends.

On initial physical examination, the patient is a young woman in athletic condition who appears pale and diaphoretic. In general, she is somewhat lethargic and in mild respiratory distress. Her heart rate is irregular and tachycardic, ranging from 170 to 300 bpm. Her blood pressure is 80/46 mm Hg. Her respiratory rate is 18 breaths/min, with an oxygen saturation of 99% on 2 L. Her heart sounds include an S1 and S2, with an irregular tachycardic rhythm. The patient's lung sounds are clear to auscultation bilaterally. Her extremities are free of edema, but they are cool and with faint distal pulses.

The initial electrocardiogram (ECG, see Figure 1) reveals an irregular, wide complex tachycardia at a rate of 224 bpm. Because of her altered mentation and significant hypotension, the American Heart Association's (AHA's) Advanced Cardiac Life Support (ACLS) algorithm[1] is initiated by the ED staff, and a synchronized cardioversion is performed. The patient converts to a normal sinus rhythm at a heart rate of 58 bpm. A repeat 12-lead ECG is obtained (see Figure 2).

On the basis of the clinical presentation and the first ECG, what is the diagnosis?

Hint: The key to diagnosis is combining the rate and morphology of the QRS complex with an understanding of whether the rhythm is regular, irregular, or irregularly irregular. The ECG in Figure 1 is unique and considered pathognomonic.

a. Monomorphic ventricular tachycardiab. Atrial fibrillation with aberrancyc. Polymorphic ventricular tachycardiad. Wolff-Parkinson-White syndrome with atrial fibrillatione. Right ventricular outflow tract tachycardia

DiscussionThe diagnosis of Wolff-Parkinson-White (WPW) syndrome with atrial fibrillation was made on the basis of the patient's history in conjunction with the classic ECG findings in both figures. The history of previously undiagnosed paroxysms of palpitations, lightheadedness, and shortness of breath is common in cases of supraventricular tachycardia. The subtle findings on the baseline ECG are often overlooked, and young patients can be diagnosed with other disorders, such as anxiety. This patient's baseline ECG (see Figure 2) contains a short (<120 msec) P-R interval. There is subtle widening of the QRS complex to >120 msec. The initial portion of the QRS complex is slurred, with a slow upward slope immediately before the sharp upstroke. This initial slur is known as a delta wave. The arrhythmia (see Figure 1) is irregularly irregular; this is an important fact in recognizing atrial fibrillation. The wide complex tachycardia represents activation of the ventricles through a pathway outside of the normal conduction system. The heart rates of 170-300 bpm are consistent with the cycle of atrial fibrillation, with almost 1:1 activation of the ventricles through this accessory pathway. It is important to remember that because these rapid heart rates lack the decremental conduction (an intrinsic protective mechanism) from the atrioventricular node, the ventricular rhythm can degrade into ventricular fibrillation, resulting in sudden cardiac death. This is a life-threatening event and requires immediate intervention, even if the patient appears hemodynamically stable. In this case, the ED staff made use of the AHA's ACLS algorithms because of the patient's hemodynamic instability.[1] Synchronized cardioversion is a reasonable option for treatment of this rhythm. Alternatively, if the patient is a bit more stable, a bolus of amiodarone, which is also part of the ACLS algorithm, could selectively decrease conduction through the bypass tract relative to the atrioventricular node, resulting in a break in the rhythm. This can help avoid cardioversion, though there may be concerns over transient hypotension. If the rhythm is recognized immediately, procainamide is another, more effective option for stopping the arrhythmia. After cardioversion, the patient was started on procainamide in consultation with the cardiovascular medicine service.

Preexcitation, or WPW syndrome, is an abnormality recognized on the surface ECG that represents an early activation of the ventricle outside the normal conduction pathway.[2] As normal atrial conduction occurs, there is inherent delay in the atrioventricular node prior to activation of the ventricles. With preexcitation, a communication or "accessory pathway" exists between the atria and ventricle that bypasses normal atrioventricular node conduction delay and activates some portion of the ventricle. The resultant beat is a fusion of early and normal ventricular activation. The bundle of Kent, a communicating tract between the left atrial appendage and left ventricle, is a classic example of a preexcitation pathway. Localization of the various types of accessory pathways can often be achieved through the baseline ECG.[3] For example, in Figure 2, the delta wave is

positive in V1 (moves toward V1) and negative in aVL (moves away from aVL), suggesting that this pathway is located in the left ventricle along the lateral wall.

Atrioventricular accessory pathways are not the only mechanism of early ventricular activation. There are rare reports of atrio-Hisian (from atria to bundle of His) pathways, a condition known as Lown-Ganong-Levine (LGL) syndrome.[2] In LGL syndrome, the ECG demonstrates a short P-R interval (usually <0.12 sec) without a delta wave and with a normal QRS complex.

Preexcitation is believed to have an estimated prevalence of 0.1-0.3% in the general population. As in the original descriptions, preexcitation syndromes predispose patients (often otherwise young and healthy) to paroxysmal tachydysrhythmias, specifically atrioventricular reentrant tachycardias. Initially, these syndromes were thought to be benign until the recognition that atrial fibrillation in these patients can precipitate ventricular fibrillation.[4,5] Luckily, this patient presented prior to having such a lethal event. As many as 80% of patients with WPW syndrome have reentrant tachycardia, 15-30% have atrial fibrillation, and 5% have atrial flutter.[2] Ventricular fibrillation is estimated to occur in patients with recurrent tachycardia at about 0.1% of the time.

The initial treatment for acute tachycardia is as described in the AHA's ACLS protocol.[1] In many cases of narrow complex tachycardia, adenosine can be helpful in both the diagnosis and, depending on the underlying arrhythmia, the treatment to stop the cycle of the arrhythmia; however, patients who have the typical narrow-complex atrioventricular reentrant tachycardia associated with WPW can theoretically be at risk for harm. This is not just because adenosine can prolong conduction and refractory time in the atrioventricular node, promoting conduction down the accessory pathway, but also because there is a small risk of precipitating atrial fibrillation with adenosine. Digoxin is absolutely contraindicated when there is atrial fibrillation because it may shorten the refractory period and enhance conduction over the bypass tract, resulting in even faster conduction to the ventricles and increasing the risk for ventricular fibrillation. If the diagnosis is made early, the American College of Cardiology (ACC)/AHA guidelines for the management of atrial fibrillation in WPW syndromes list direct-current (DC) cardioversion, ibutilide to break the atrial fibrillation, and procainamide as class I treatment options.[6] Amiodarone has a class IIb indication. Digoxin and nondihydropyridine calcium channel blockers are listed as class III agents because of the potential harm that they can cause.

As mentioned above, some patients with WPW syndrome are at risk for sudden death. In these patients, a cardiac electrophysiology study and radiofrequency catheter ablation

may be definitive and curative. ACC/AHA guidelines for radiofrequency ablation (RFA) list symptomatic patients with drug-resistant accessory pathway arrhythmias or atrial fibrillation in preexcitation syndromes as class I indications for RFA.[7] A family history of sudden cardiac death in patients with accessory pathways has a class IIa indication. Because of the association with family history, there is a great deal of active research in identifying the underlying molecular and genetic mechanisms that result in the development of such accessory pathways.[8,9] It is therefore important to review family history in patients who present with these syndromes. The patient in this case did not have an immediate family history of sudden cardiac death. There is also data to support radiofrequency ablation in asymptomatic patients who may be at high risk for atrial arrhythmia as recognized by electrophysiology studies.[10] ACC/AHA guidelines include a class IIa recommendation for asymptomatic patients whose jobs, livelihood, or safety may be adversely affected by arrhythmia.[7]

Given this patient's history of severe symptoms and her presentation with atrial fibrillation, the cardiovascular electrophysiology service recommended radiofrequency ablation. She underwent the procedure during her admission and had no complications. At 3-month follow-up, she was free of any need for antiarrhythmic medication. In addition, she noted that she did not have any further "panic attacks" in that timeframe, and her primary care provider was planning to wean her off of the SSRI.

Which of the following is NOT a reasonable treatment option for a symptomatic patient with atrial fibrillation conducting through a WPW accessory pathway?

a. Immediate direct-current (DC) cardioversionb. Ibutilidec. Procainamided. Digoxine. Amiodarone

With the exception of digoxin, all of these are reasonable treatment options for a symptomatic patient presenting with atrial fibrillation conducting down a preexcitation pathway. Because digoxin prolongs refractoriness preferentially in the atrioventricular node, it will increase conduction down the accessory pathway. This will increase ventricular rates to match atrial fibrillation rates, resulting in ventricular fibrillation and sudden cardiac death. Digoxin is absolutely contraindicated in such patients.

A 22-year-old man presents to the ED after a sudden episode of palpitations, lightheadedness, and dyspnea. Symptoms resolve before the patient arrives in the ED; however, you recognize that his ECG reveals a short P-R interval and a delta wave. During the interview, he tells you that he had a similar episode once before while driving a bus at his college campus and that the doctors did an extensive cardiac work-up, which he was told was negative. He had an uncle who died of sudden cardiac death at a similar age, so naturally he is concerned. What would be the most appropriate next step?

a. Discharge the patient to home on a beta-blocker for presumed supraventricular tachycardia.

b. Reassure the patient that his symptoms are likely related to anxiety, given the negative cardiac work-up, and offer to prescribe an SSRI.

c. Explain your suspicions based on the baseline ECG and arrange electrophysiology testing and possible radiofrequency ablation with the cardiology service.

d. Arrange an outpatient Holter monitor to confirm the arrhythmia of concern.e. Initiate oral amiodarone treatment and arrange outpatient follow-up with a

cardiologist.