Steven J. Kalbfleisch, MD
A 31-year-old man with no prior medical history was brought to the emergency department (ED) after suffering an out-of-hospital cardiac arrest. He reported the onset of a rapid heart rate to a friend after completing a 10-mile run. He began to feel progressively worse and suddenly collapsed. Bystander CPR was initiated, and the EMS was called. Upon arrival, the EMS personal found the patient to be in ventricular fibrillation (Figure 13-1), and he was converted to sinus rhythm with an external shock. The 12-lead ECG obtained upon arrival in the ED (Figure 13-2) demonstrated evidence of ventricular preexcitation with a probable left lateral accessory pathway. A cardiac catheterization and echocardiogram were performed and revealed no evidence of structural heart disease. An electrophysiology study confirmed the presence of a single left lateral accessory pathway. The accessory pathway had an antegrade block cycle length and refractory period of 280 ms and 260 ms, respectively, in the baseline state. Orthodromic reciprocating tachycardia with a cycle length of 400 ms (heart rate of 150 bpm) was easily induced and was hemodynamically stable. After the addition of intravenous isoproterenol at 8 μg/min, the accessory pathway block cycle length and refractory period decreased to <200 ms and <210 ms, respectively (Figure 13-3). The patient had successful radiofrequency ablation of the accessory pathway performed. At follow-up there was no further arrhythmia symptoms or recurrence of preexcitation on the ECG.
FIGURE 13-1 Initial rhythm recorded on the external defibrillator by the emergency squad. Coarse ventricular fibrillation is demonstrated on the ECG strip, which was converted to sinus rhythm by an external 200J shock.
FIGURE 13-2 The12-lead ECG recorded in the emergency department. The WPW pattern is clearly seen on the ECG. The positive delta wave in lead V1 and negative delta wave in lead aVL are indicative of a left lateral accessory pathway location.
FIGURE 13-3 Tracings from the electrophysiologic study during atrial pacing with an infusion of isoproterenol at 8 μg/min. Shown are recordings from surface leads I, II, and V1 and intracardiac recordings from the high right atrium (HRA), His bundle proximal, mid, and distal locations (HB p, HB m, and HB d), coronary sinus proximal to distal locations (CS p to CS d), and right ventricular apex (RV). Atrial pacing stimuli (S) are delivered throughout the tracing at a cycle length of 200 ms (300 bpm). A His bundle recording (H) is detected at the beginning of the tracing indicating that initially there was conduction down both the normal AV conduction system and accessory pathway. The HV interval measured from the onset of the first complete QRS complex (dotted line) is –70 ms. There is 1:1 conduction from the atrium to the ventricle across the accessory pathway at 300 bpm during the isoproterenol infusion. This confirms that this is a high-risk accessory pathway and can account for the episode of aborted sudden death.
The prevalence of the Wolff-Parkinson-White (WPW) ECG pattern, which indicates the presence of an accessory pathway causing ventricular preexcitation, is estimated to be on the order of 0.1% to 0.3%.1,2
Although there is a clear association between the presence of ventricular preexcitation and sudden cardiac death (SCD), the overall risk of sudden death in this patient population is relatively small.
The incidence of SCD in asymptomatic patients with a WPW ECG pattern is low and estimated to be <0.5% per patient-year.3
However, the prevalence of aborted SCD in large series of patients with WPW syndrome referred to an electrophysiology center for treatment of symptomatic arrhythmias is on the order of 1% to 2%, and in approximately 50% of these patients the aborted SCD event was their first arrhythmia symptom.4,5
ETIOLOGY AND PATHOPHYSIOLOGY
The mechanism of SCD in WPW patients is most often due to the presence of atrial fibrillation, which conducts rapidly across an accessory pathway and triggers ventricular fibrillation (Figure 13-4).
FIGURE 13-4 Atrial fibrillation degenerating to ventricular fibrillation. The initial portion of the image shows atrial fibrillation conducting across and accessory pathway at rates of over 300 bpm. The arrow points to where the rhythm degenerates to ventricular fibrillation.
In the majority of patients with an accessory pathway, the occurrence of atrial fibrillation is triggered by an episode of paroxysmal supraventricular tachycardia (PSVT) due to AV reentrant tachycardia.
Like patients without WPW, patients with WPW can have atrial fibrillation triggered for reasons other than an episode of PSVT. Regardless of the cause of atrial fibrillation, as long as there is rapid conduction across the accessory pathway, the arrhythmia can degenerate into ventricular fibrillation and result in a cardiac arrest.
A number of clinical predictors for the occurrence of SCD in patients with WPW have been described and include male gender, young age, older age, septal accessory pathway location, left lateral accessory pathway location, presence of multiple accessory pathways, history of syncope, and the presence of symptomatic tachycardia. These clinical predictors are very weak and nonspecific, and due to the small numbers of patients in most series the studies often have conflicting data.4,5
Patients with baseline intermittent preexcitation on their ECG or telemetry monitors are felt to be at low risk for SCD since this generally indicates that their accessory pathway cannot conduct at rapid rates.
The use of noninvasive testing with stress testing and pharmacologic agents has been advocated for risk stratification of patients with persistent WPW pattern on their ECG. Patients with abrupt loss of preexcitation during stress testing or intravenous procainamide are considered at low risk for sudden death since this indicates the presence of a pathway with relatively poor antegrade conduction characteristics.6
The diagnosis of WPW after an episode of aborted SCD is reliant on seeing ventricular preexcitation on the ECG or detecting an antegrade accessory pathway during invasive electrophysiologic testing. It is important to realize that the WPW pattern on the ECG may be subtle and difficult to detect especially if the pathway is located far from the AV node (ie, left lateral accessory pathways) or if AV node conduction is rapid. It is also important to understand that the degree of preexcitation on the baseline ECG is not predicative of whether the pathway is a high risk pathway or not.
Although there are a number of clinical and noninvasive predicators for risk stratifying patients with WPW, the most consistent data for determining whether a pathway is of high risk is with invasive electrophysiologic testing.4,5,7,8
If a patient suffers a cardiac arrest and is found to have preexcitation on an ECG, the next step is to determine if the pathway is capable of rapid conduction to cause hemodynamic collapse during atrial fibrillation or trigger ventricular fibrillation. Electrophysiologic testing of patients with WPW who have suffered an aborted cardiac arrest have consistently shown that these patients have very rapid conduction across the pathway as measured by the shortest RR interval during induced atrial fibrillation (<250 ms), atrial effective refractory period (<240 ms), and maximal rate of conduction across the accessory pathway (>250 bpm).5
If the pathway does not have very rapid conduction in the baseline state, it is important to retest the patient on isoproterenol. Many pathways will have marked enhancement of conduction during adrenergic stimulation, and it has been noted that a significant percentage of patients with WPW suffer a cardiac arrest during exercise or other periods of high adrenergic tone.5,9
If a patient survives an episode of aborted sudden death and is found to have a WPW pattern on an ECG, it should not be assumed that the accessory pathway is the etiology, although this is highly likely especially in younger patients without a prior history of cardiac disease.
The WPW ECG pattern can be associated with other forms of organic heart disease, such as Ebstein anomaly and hypertrophic cardiomyopathy, so an evaluation for structural heart disease with some form of cardiac imaging needs to be done prior to electrophysiologic testing.
If the patient does not have structural heart disease and at electrophysiologic testing the patient’s accessory pathway is not found to be a high-risk, rapidly conducting pathway, then consideration of other arrhythmic causes of cardiac arrest such as long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, or primary ventricular fibrillation needs to be considered.
For patients presenting with atrial fibrillation and rapid conduction across an accessory pathway, either external cardioversion or intravenous procainamide should be considered, depending upon their hemodynamic status (Figure 13-5). Procainamide slows conduction across the accessory pathway and may convert atrial fibrillation.
FIGURE 13-5 (A) The presenting 12-lead ECG demonstrates atrial fibrillation with rapid conduction across a left-sided accessory pathway. The shortest RR intervals during atrial fibrillation were <200 ms. (B) The patient was converted to sinus rhythm after an external shock, and the 12-lead ECG in sinus rhythm is also shown. Ventricular preexcitation is best seen in leads V3 and V4 but is fairly subtle in many of the ECG leads. This case helps demonstrate that the degree of preexcitation on the 12-lead ECG is not a reliable indicator if an accessory pathway is a high-risk pathway.
Agents that slow AV nodal conduction such as verapamil, diltiazem, or β-blockers should be avoided during the acute episode of atrial fibrillation since they may increase conduction over the accessory pathway and hasten cardiovascular collapse. By blocking AV nodal conduction, these agents decrease the number of impulses that conduct across the AV node, penetrate the accessory pathway in the retrograde direction, and modulate antegrade conduction.
The cornerstone of therapy for patients with symptomatic WPW is radiofrequency catheter ablation. This procedure is highly effective (>95% acute success) and safe (<2% serious complication risk), and it provides a durable long-term cure in high-risk WPW patients with a prior history of cardiovascular collapse.10
In patients who are not able to be ablated using percutaneous techniques, consideration for either surgical ablation or long-term medical therapy should be entertained. If antiarrhythmic therapy is chosen, a drug that slows or blocks antegrade accessory pathway conduction needs to be included to minimize the risk of rapid conduction during atrial fibrillation.
Patients with a history of aborted sudden cardiac death or hemodynamic compromise and WPW need to understand that if their condition is left untreated the recurrence rate is high and that the efficacy and cost-effectiveness of catheter ablation is superior to other treatment strategies.11
Patients with an asymptomatic WPW ECG pattern should be counseled that the risk of SCD is low, but not zero, and that if arrhythmia symptoms begin to occur, further evaluation with either telemetry monitoring or invasive electrophysiologic testing is generally recommended.
In asymptomatic patients who have high-risk professions or are competitive athletes, consideration can be given to perform electrophysiologic testing for risk stratification with a goal of ablating a high-risk pathway, if one is present. Because of the risk of triggering life-threatening arrhythmias during competitive athletics, the European Society of Cardiology mandates that all athletes with WPW undergo risk stratification with electrophysiologic testing. The Bethesda Conference on sports eligibility requires electrophysiologic testing in symptomatic WPW patients and considers it advisable for asymptomatic athletes with WPW who are engaged in moderate or high-level competitive sports. Both of these bodies recommend radiofrequency ablation of the WPW if a high-risk pathway is found at electrophysiologic testing to retain athletic eligibility.12
1. Averill KH, Fosmoe RJ, Lamb LE. Electrocardiographic findings in 67,375 asymptomatic subjects, IV: Wolff-Parkinson-White syndrome. Am J Cardiol. 1960;6:108-129.
2. Sears GA, Manning GW. The Wolff-Parkinson-White pattern in routine electrocardiography. Can Med Assoc J. 1962;87:1213-1217.
3. Munger TM, Packer DL, Hammill SC, et al. A population study of the natural history of Wolff-Parkinson-White syndrome in Olmsted County, Minnesota, 1953-1989. Circulation. 1993;87:866-873.
4. Timmermans C, Smeets J, Rodriguez LM, Vrouchos G, Dool V, Wellens HJ. Aborted sudden death in the Wolff-Parkinson-White syndrome. Am J Cardiol. 1995;76:492-494.
5. Brembilla-Perrot B, Tatar C, Suty-Selton C. Risk factors of adverse presentation as the first arrhythmia in Wolff-Parkinson-White syndrome. Pacing Clin Electrophysiol. 2010;33:1074-1081.
6. Gaita F, Giustetto C, Riccardi R, Mangiardi L, Brusca A. Stress and pharmacologic tests as methods to identify patients with Wolff-Parkinson-White syndrome at risk for sudden death. Am J Cardiol. 1989;64:487-490.
7. Pappone C, Santinelli V, Rosanio S, et al. Usefulness of invasive electrophysiologic testing to stratify the risk of arrhythmic events in asymptomatic patients with Wolff-Parkinson-White pattern. J Am Coll Cardiol. 2003;41:239-244.
8. Santinelli V, Radinovic A, Manguso F, et al. The natural history of asymptomatic ventricular pre-excitation. J Am Coll Cardiol. 2009;53:275-280.
9. Szabo TS, Klein GJ, Sharma AD, Yee R, Milstein S. Usefulness of isoproterenol during atrial fibrillation in evaluation of asymptomatic Wolff-Parkinson-White pattern. Am J Cardiol. 1989;63:187-192.
10. Antz M, Weib C, Volkmer M, et al. Risk of sudden death after successful accessory atrioventricular pathway ablation in resuscitated patients with Wolff-Parkinson-White syndrome. J Cardiovasc Electrophysiol. 2002;13:231-236.
11. Hogenhuis W, Stevens SK, Wang P, et al. Cost-effectiveness of radiofrequency ablation compared with other strategies in Wolff-Parkinson-White syndrome. Circulation. 1993;88:II 437-446.
12. Pelliccia A, Zipes DP, Maron BJ. Bethesda conference #36 and the European Society of Cardiology consensus recommendations revisited. J Am Coll Cardiol. 2008;52:1990-1996.