Wolff-Parkinson-White (WPW) syndrome is a congenital cardiac abnormality that manifests itself as a conduction irregularity found between the sinoatrial (SA) and atrioventricular (AV) nodes. In an otherwise healthy heart, electrical conduction begins at the SA node, which is located in the right atrium. An electrical pulse is then sent downward causing the atrium to contract and subsequently reaching the AV node, which acts as the connecting catalyst to allow the electrical pulse to reach the ventricles causing them to contract.1 This pathway is controlled as electrical conduction is regulated by the SA and AV node. However, in a patient with Wolff-Parkinson-White syndrome, there is an extra pathway—also known as the accessory pathway—that allows conduction to occur directly between the atrium and ventricles, bypassing the AV node, thus leading to preexcitation of the ventricles. This preexcitation allows conduction to occur with higher and uncontrolled rates resulting in tachycardias.2 The electrocardiogram (ECG) shows a shortened PR interval and the characteristic “delta wave” which resembles a slurring slow rise of the initial portion of the QRS interval.
Pathophysiology and Treatment:
In the long-term preventative setting, WPW is managed surgically through catheter ablation.3 However, in the emergent setting treatment is dictated by specific manifestations of WPW associated arrhythmias. There is WPW with orthodromic tachycardia, WPW with antidromic tachycardia, and WPW with atrial fibrillation.4
1. WPW with orthodromic tachycardia
A. Orthodromic tachycardia occurs when the electrical circuit travels normally from the SA node to the AV node and down the Purkinje fibers; however, the circuit reenters the atrium via the accessory pathway causing the tachycardia as represented in Figure 1.
a. This rhythm resembles a supraventricular tachycardia (SVT) even though etiology is slightly different; however, treatment is identical.5
B. Diagnosis is made through electrocardiogram (ECG).
a. ECG will show a regular narrow QRS complex tachycardia resembling a SVT as seen in Figure 1.6
a. Due to its similar mechanism as SVT, orthodromic tachycardia can be treated the same method as a SVT with an AV node blocker (AVNB).5
- Adenosine7, 8
- Verapamil8, 9
- Beta blockers10
2. WPW with antidromic tachycardia
A. Antidromic tachycardia occurs when the electrical circuit travels from the SA node through the accessory pathway first, then up the Purkinje fibers, and through the AV node all through a retrograde or opposite direction than the orthodromic tachycardia as seen in Figure 1.
a. This rhythm resembles a ventricular tachycardia (VT), even though etiology is slightly different; however, treatment is identical.6
B. Diagnosis is also made through ECG.
a. ECG will show a regular wide QRS complex tachycardia resembling a ventricular tachycardia as seen in Figure 1.6
a. It is necessary to treat with agents that selectively target the accessory pathway.
- Loading dose: 20 to 50 mg/min IV infusion until arrhythmia suppressed, hypotension ensues, QRS prolonged by 50%, or total cumulative dose of 17 mg/kg12
- Alternative loading dose: 100 mg every 5 minutes until arrhythmia is controlled or any condition described above is met.12
- Follow with a continuous infusion of 1 to 4 mg/min (must reduce maintenance dose in patients with renal impairment).12
c. Amiodarone 150 mg IV over 10 minutes, then 1 mg/minute for 6 hours, then 0.5 mg/minute for 18 hours or change to oral dosing.13
Figure 1. Diagrams of orthodromic and antidromic electrical pathways and associated ECG rhythms. Available at: https://umem.org/files/uploads/content/MattuECG%20Tumblr/OrthoAnti.jpg. Accessed August 4, 2014.
3. WPW with Atrial Fibrillation
A. This is the most dangerous etiology of the WPW manifestations due to its high risk of iatrogenic error and deadly ventricular arrhythmias.2
B. In WPW with atrial fibrillation, electrical conduction in the heart travels down two paths, the normal pathway through the AV node AND from the atrium to the ventricles through the accessory pathway as seen in Figure 2.14
C. Diagnosis is made through ECG.
a. The two electrical pathways manifest themselves on ECG as irregularly irregular rhythms.
- While pulses that pass through the AV node have some rate regulation due to the AV node, impulses traveling through the accessory pathway have no rate regulation, leading to measured ventricular rates on ECG above 200 beats per minute (bpm).2
> This lack of regulation through the accessory pathway causes the irregular wave morphologies with no consistencies in the QRS waves as seen in Figure 3.
> In contrast, Figure 4 depicts a more typical atrial fibrillation without WPW where the QRS waves are seen to be more regular and ventricular rate does not exceed 150-200 bpm (due to the rate regulation caused by the AV node).
b. Atrial fibrillation with WPW is often misdiagnosed as a SVT, VT, or atrial fibrillation with a bundle branch block.
- If misdiagnosed, treatment with an AVNB will preferentially block the AV node and consequently divert all electrical impulses down the accessory pathway.15
> This shunting of electrical impulses to the accessory pathway causes ventricular fibrillation and high risk of death.
> Therefore, AVOID ALL AVNBs (i.e. adenosine, non-dihydropyridine calcium channel blockers, beta blockers, digoxin, and amiodarone) in patients with WPW with atrial fibrillation.
a. Immediate cardioversion is the recommended first line treatment for hemodynamically unstable patients when WPW with atrial fibrillation presents.16
b. In a hemodynamically stable patient, procainamide can be used, as it selectively targets the accessory pathway.12
- Per 2010 ACLS guidelines, procainamide dosing is as follows:
> Loading dose: 20 to 50 mg/min IV infusion until arrhythmia suppressed, hypotension ensues, QRS prolonged by 50%, or total cumulative dose of 17 mg/kg12
> Alternative loading dose: 100 mg every 5 minutes until arrhythmia is controlled or any condition described above is met. 12
> Follow with a continuous infusion of 1 to 4 mg/min (must reduce maintenance dose for renal impairment).12
Figure 2. Diagram of WPW with atrial fibrillation with associated ECG. Available at: http://www.rjmatthewsmd.com/Definitions/supraventricular_tachyarrhythmias.htm. Accessed August 9, 2014.
Figure 3. ECG of atrial fibrillation with WPW.
Available at: http://osuemed.wordpress.com/2011/05/26/nightmare-ekg/. Accessed August 4, 2014.
Figure 4. ECG of atrial fibrillation without WPW.
Available at: http://www.emedu.org/ecg/af.htm. Accessed August 4, 2014.
A. WPW orthodromic tachycardias are treated as SVT with an AVNB (i.e. adenosine, verapamil, beta blockers).
B. WPW antidromic tachycardias are treated as VT with procainamide or amiodarone.
C. WPW with atrial fibrillation is treated with immediate cardioversion if hemodynamically unstable. Procainamide is a reasonable choice in hemodynamically stable patients.
Edwin Lim, PharmD Class of 2015
Thomas Jefferson University
Jefferson School of Pharmacy, Philadelphia, PA
Robert Pugliese, PharmD, BCPS (@theEDpharmacist)
Clinical Specialist, Emergency Medicine
Thomas Jefferson University Hospital, Philadelphia, PA
Reviewed by: Craig Cocchio, PharmD, BCPS and Nadia Awad, PharmD, BCPS
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