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Wolff-Parkinson-White Syndrome (WPW)

WPW is caused by abnormal connections or in the heart called accessory pathways (APs). These abnormal pathways are present since birth and result from incomplete septation of the atria from the ventricles (1). Initially the heart develops as a hollow muscular tube with the atrial myocardium in direct contact with the ventricular myocardium. As the fetus ages, the heart folds on itself and connective tissue grows separating the top from the bottom part of the heart completely except for the atrioventricular node (AV node). When this separation process is incomplete, an AP is present. This AP can conduct the heartbeat from the ventricle to the atrium only, from the atrium to the ventricle only, or in both directions. In the first case (ventricle to atrium only), the AP is said to be concealed and the arrhythmia resulting is called supraventricular tachycardia (SVT). This can occur when a PVC blocks in the AV node, conducts up the AP with sufficient slowing that it then finds the AV node able to return the reentrant beat to the ventricles producing SVT. Alternately, a PAC can conduction down the AV node with sufficient slowing that it finds the AP able to return it to the atrium setting up reentrant SVT.

When the AP can conduct from atrium to the ventricle only, SVT is impossible, but arrhythmias such as atrial fibrillation and flutter may conduct so rapidly to the ventricles that the patient experiences a cardiac arrest. If the AP is not that fast, then a cardiac arrest will not occur and the patient may feel just like the average patient with atrial fibrillation. If the pathway can conduct in both directions, then both types of arrhythmias are possible as well as reentry that uses the AP for antegrade conduction to the ventricles with the AV node or a second AP forming the retrograde limb of the reentry circuit. Although APs are present from birth, only about 1% are hereditary and run in families.

Symptoms of WPW

Most people with WPW have “spells” consisting of palpitations or out right heart racing with associated symptoms of chest pain, pulsations in the neck, shortness of breath, light-headedness, fatigue, sweating, passing out or even rarely a cardiac arrest. After a spell, the patient may have frequent urination (due to release of ANF from the atria that causes a diuresis) or feel fatigued for hours to days. Some patients with WPW, however, have no symptoms at all.

Diagnosis of WPW

Usually (but not always) WPW can be diagnosed by doing a routine ECG showing some slurring between the P wave and the QRS. This slurring is referred to as a “delta wave.” Sometimes it is difficult to tell for sure whether a delta wave is present or not. In these cases, infusion of adenosine through an IV with repeating of the ECG will almost always show definitively whether WPW is present or not. Some patients with WPW are at risk for a cardiac arrest. Sometimes it is possible to identify patients at low risk for this catastrophe if a routine ECG or a 24-hour holter monitor shows that the delta wave suddenly disappears. Occasionally, on a stress test, the same phenomenon is observed i.e. as the heart rate increases, the delta wave suddenly disappears. However, only a very small percentage of patients fall into this category. Another approach to identifying WPW patients at low risk for cardiac arrest is to administer 10 mg/kg of procainamide intravenously over 5-10 minutes and show that the delta wave suddenly disappears. However, this test sometimes predicts that a patient is at low risk when in fact this is not the case. Because of this, the procainamide test has fallen into disfavor.

Advice for people with WPW

People with WPW frequently ask what to do when they have an episode of heart racing. The most important factor is to use common sense. If the person feels very bad (severe chest pain, severe shortness of breath) then calling 911 is prudent. Lesser degrees of symptoms give the person the opportunity to try vagal maneuvers to see if they can get their heart rhythm back to normal. The only maneuvers that are safe to try at home are the Valsalva maneuver or the Muller maneuver. Other maneuvers are not recommended. Eyeball pressure has resulted in retinal injuries. Immersing the face in ice water has rarely caused cardiac arrest. Gagging seldom works to restore normal rhythm. Patients that tolerate their racing without significant symptoms may elect to wait at home or even try to fall asleep in hopes that the episode will resolve on its own. Most patients will eventually go to the emergency room after waiting at home for a while if the episode does not abate on its own.

Emergency care for WPW

Physicians after recording an ECG and assessing the person’s vital signs will decide whether the person is unstable (hypotension, severe chest pain/ shortness of breath) or not. If the patient is unstable, they will be sedated and undergo external cardioversion to restore sinus rhythm. If the patient is stable, the physician may ask them to perform vagal maneuvers to see if sinus rhythm can be restored. If these are ineffective and SVT exists, then IV medications can be given such as adenocard, verapamil, diltiazem or beta-blockers. If these are ineffective or if the rhythm is wide-complex, other medications such as ibutilide, lidocaine or procainamide can be tried. If nothing succeeds in restoring normal rhythm, then eventually external cardioversion is performed. Usually, once normal rhythm is restored, the person can be discharged rather than admitted to the hospital. The typical cost for such a visit to the emergency room here in the US is $2000 or more.

Workup of WPW

Patients with WPW should be seen by an electrophysiologist. The typical workup of patients with WPW involves having an echocardiogram done to exclude hypertrophic cardiomyopathy or Epstein’s anomaly of the tricuspid valve. Patients with prominent symptoms of angina, or risk factors for coronary artery disease, may need stress testing or even a coronary angiogram.

Prognosis of WPW

WPW can be serious, leading to a cardiac arrest. However, most persons with WPW are at low risk of this catastrophe. However, most electrophysiologists feel that the risk of death in WPW patients who are having heart racing is greater if nothing is done than if WPW is fixed by an ablation – hence ablation is recommended. The issue of what to do in WPW patients who have never had any symptoms from it is less sure. In general, patients with so-called high-risk occupations/pursuits such as policemen, athletes, firemen, pilots, steelworkers etc…are better off with ablation. Also rare persons with a family history of WPW are known to be at higher risk of cardiac arrest and should undergo ablation. The other people with WPW who don’t have any symptoms may make up their own minds about ablation. Taken together as a group, persons with WPW have about a .15% risk of dying each year from the WPW. In reputed centers, the chance of dying or suffering a heart attack or stroke during the ablation procedure is less than 0.5%. Some persons looking at these numbers are reassured about them; however, if a person incurs this risk for 20 years, it would be 3-5% which should be concerning. Other persons with WPW notice that the risk of the ablation is the same as a few years risk of just living with it and decide to go ahead with the ablation. Needless to say, a successful ablation will prevent also any heart racing such as SVT that might otherwise occur in the future from the WPW.

Treatment options for WPW

Treatment options for patients with WPW include either antiarrhythmic drugs or ablation. Antiarrhythmic drugs, if a good option, would work best in WPW patients who were at the highest risk for a cardiac arrest. Unfortunately, in these high-risk patients, drugs do not work well enough to eliminate the risk of a cardiac arrest. Therefore the mainstay of treatment for WPW has been ablation, not medications.

RF ablation for WPW

In the 1990s, RF ablation replaced open-heart surgery for WPW in the 1990s. In general, RF ablation is successful in curing WPW in over 95% of patients with a risk of about 3% (2). No large studies comparing RF ablation with cryoablation have been performed, and definitive comparisons are speculative. However based on other research, there are several risks that are potentially greater with RF ablation when compared with cryoablation including the following:

  • Higher risk of stroke with left-sided pathways
  • Higher risk of perforation with any pathway
  • Higher risk of accidental damage to important structures near the pathway
  • Lower chance of success for pathways located within heart veins

Cryoablation vs. RF ablation for WPW

A large study of cryoablation (3) that enrolled 166 patients scheduled for ablation included 51 patients with what essentially was WPW. 44 of this group underwent cryoablation using a catheter with a 4 mm tip electrode. Although cryoablation in these patients was found to be safe, in only 77% was the procedure successful. Many doctors have since given up on the 4 mm catheter believing that it makes too small of a lesion to be effective. Preliminary use of catheters with larger tips (6 or 8 mm) in our institution suggests better outcomes. In certain patients who have failed RF ablation, cryoablation affords advantages (4).

There are three AP locations (comprising nearly half of all pathways) that may be more suitable for CrA than RF ablation. First, the 10% of pathways close to the AV node called septal pathways are ideal for CrA. Care must be taken with septal APs to preserve the AV node or a permanent pacemaker could be required. The advantage of cryoablation for these APs is the added safety of cryomapping. When the electrophysiologist has placed the cryoablation catheter where she/he believes the septal pathway to be, gentle cooling is delivered through the catheter (cryomapping) (5). If the AV node starts to be affected, the cooling is immediately turned off and the AV node can recover fully. The catheter is then repositioned to a different location and cryomapping is repeated. Finally a site will be found where cooling causes the pathway to loose function without affecting the AV node. At this site, freezing the tissue will create a permanent lesion causing the septal AP to be destroyed without affecting the AV node. On the other hand if a septal AP is approached with RF ablation, the only option is to make the burn hoping to shut off power if an untoward effect is seen. Unfortunately, research with RF ablation has shown that lethal temperatures can persist for up to 12 seconds after power is turned off. (6). Therefore the lesion continues to enlarge during that 12 seconds increasing the chance of inadvertent damage to the AV node requiring a permanent pacemaker. This risk in a large series of RF ablation was 3% (2). There was also an 11% chance of recurrence of heart racing after RF ablation in this same study probably contributed to by the caution with which the physicians had to use Therefore including failure to ablate the AP, the total failure rate approached 25%. The initial use of RF ablation in patients with septal APs highlighted the risk of a pacemaker (7). The safety and efficacy of CrA for septal APs in case reports (8-10) and small series (11-13) was excellent making this the ablation modality of choice for these APs. A larger series of 35 adolescent patients showed acute success rates comparable to what would have been expected with RF ablation, but with slightly higher recurrence rates (14).

The second AP location where CrA has an advantage is the rare AP located inside the coronary sinus. Animal studies have suggested that if these APs are within 5 mm of a coronary artery, there is a high chance of RF ablation damaging the artery, which could cause a myocardial infarction (15). cryoablation delivered close to such arteries is much less likely to damage the artery. Also if such pathways are in very small veins, not enough power can be given with RF ablation to make a big enough lesion to kill the AP (16). There are also cases of getting the RF catheter getting stuck in the small vein when RF energy ‘welds’ the catheter to the vein. CrA in small vein locations with low blood flow allows the CrA catheter to make a bigger lesion than normal, and welding does not occur. Cryoablation is almost certainly safer in such locations (17).

Thirdly, APs on the right side of the heart cross the tricuspid valve, which tends to move vigorously during right ventricular contraction. It may be difficult for the electrophysiologist to get a RF ablation catheter to stay in contact with the AP long enough to kill it. With CrA, the catheter sticks to the heart tissue within 10 seconds or so and will not move after freezing starts to occur. In a large series using RF ablation for right-sided APs, the success at the end of the first procedure was only 84% with 7% of patients requiring a second procedure. 14% of patients had recurrence of their heart racing (2). These results with RF ablation are not encouraging. One study of CrA in 3 patients with right-sided APs has been published showing efficacy in all 3 patients (18), but larger series have not been undertaken.

Review Articles:

Chen S, and Tai C. Ablation of atrioventricular accessory pathways: current techniques – state of the art. PACE 2001; 24:1795-1809.
A good review article although not current with regards to cryoablation.

Thornton A, and Jordaens L. Advances in the approaches to ablation of complex arrhythmias. J Cardiovasc Electrophysiol 2007;18:S2-S10.
A good review of the latest techniques and technologies.

Insulander P, Andersson M, Bergfeldt L et.al. Ablation of AVNRT and AVRT. Current results in 1310 consecutive patients. Poster from Stockholm, Sweden
Cryoablation was more effective for paraseptal pathways than RF ablation.

References:

  1. Kolditz D, Wijffels M, Blom N. Persistence of functional atrioventricular accessory pathways in postseptated avian hearts. Circulation 2007; 115:17-26.
  2. Calkins H, Yong P, Miller J. etal. Catheter ablation of accessory pathways, atrioventricular nodal reentrant tachycardia, and the atrioventricular junction: final results of a prospective, multicenter clinical trial. Circulation. 1999; 99: 262-270
  3. Friedman P, Dubuc M, and Green M, etal. Catheter cryoablation of supraventricular tachycardia: Results of the multicenter prospective “frosty” trial. Heart Rhythm. 2004; 1: 129-138
  4. Sacher F, Wright M, Tedrow U et.al. How to succeed in WPW ablation after a prior failure? A 1999-2006 multicenter experience. Presented at HRS 2007 in Denver, Colorado
  5. Theuns D, Kimman G, Torok T et.al. Ice mapping during cryothermal ablation of accessory pathways in WPW: the role of the temperature time constant. Europace 2044; 6:116-122.
  6. Bunch T, Bruce K, Johnson S etal. Analysis of Catheter-Tip (8-mm) and Actual Tissue Temperatures Achieved During Radiofrequency Ablation at the Orifice of the Pulmonary Vein. Circulation. 2004; 110: 2988-2995
  7. Schulter M and Kuch K. Catheter ablation form right atrium of anteroseptal accessory pathways using radiofrequency current. Journal of the American College of Cardiology. 1992; 19: 663-67
  8. Kimman G, Szili-Torok T etal. Transvenous cryothermal catheter ablation of a right anteroseptal accessory pathway. Journal of Cardiovascular Electrophysiology. 2001; 12: 1415-1417
  9. Lanzotti M, DePonti R, Tritto M etal. Successful treatment of anteroseptal accessory pathways by transvenous cryomapping and cryoablation. Italian Heart Journal. 2002; 3: 128-132
  10. Idris F, Green M, Tang A, etal. A cool ablation. Journal of Cardiovascular Electrophysiology. 2002; 13: 299
  11. Atienza F, Arenal A, Torrecilla etal. Acute and long-term outcome of transvenous cryoablation of midseptal and parahissian accessory pathways in patients at high risk of atrioventricular block during radiofrequency ablation. American Journal of Cardiology. 2004; 93: 1302-1305
  12. Gaita F, Riccardi R, Hocini M et.al. Safety and efficacy of cryoablation of accessory pathways adjacent to the normal conduction system. Journal of Cardiovascular Electrophysiology. 2003; 14: 825-829
  13. Gaita F, Montefusco A, Riccardi R, etal. Cryoenergy catheter ablation: a new technique for treatment of permanent junctional reciprocating tachycardia in children. Journal of Cardiovascular Electrophysiology. 2004; 15: 263-268
  14. Bar-Cohen Y, Cecchin F, Alexander M etal. Cryoablation for accessory pathways located near normal conduction tissues or within the coronary venous system in children and young adults. Heart Rhythm. 2006; 3: 253-258
  15. Aoyama H, Nakagawa H, Pitha J etal. Comparison of cryothermia and radiofrequency current in safety and efficacy of catheter ablation within the canine coronary sinus. J Cardiovascular Electrophysiology. 2005; 16: 1218-1226
  16. Morady F. Catheter Ablation of Supraventricular Arrhythmias: State of the Art. Pacing and Clinical Electrophysiology. 2004; 27:125-142
  17. Collins K, Rhee K, Kirsh J et.al. Cryoablation of accessory pathways in the coronary sinus in young patients: a multicenter study from the pediatric and congenital electrophysiology society’s working group on cryoablation. J Cardiovasc Electrophysiol 2007;18:592-597.
  18. Rodriguez L, Geller J, Tse H etal. Acute results of transvenous cryoablation of supraventricular tachycardia (atrial fibrillation, atrial flutter, Wolff-Parkinson-White syndrome, atrioventricular nodal reentry tachycardia). Journal of Cardiovascular Electrophysiology. 2002; 13: 1082-1089.