The Utility of a 15-Lead Electrocardiogram in Determining the Laterality of an Accessory Pathway in Pediatric Patients with Wolff–Parkinson–White Syndrome

DOI: 10.19102/icrm.2012.030909

¹PETER F. AZIZ, MD, ²JAMIE GANLEY, RN, ²TAMMY S. WIEAND, MS and ²MAULLY J. SHAH, MBBS

¹The Cleveland Clinic Foundation, Department of Pediatric Cardiology, Cleveland Clinic Lerner College of Medicine, Cleveland, OH
²The Children’s Hospital of Philadelphia Division of Cardiology and the University of Pennsylvania School of Medicine, Philadelphia, PA

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ABSTRACT. Introduction: Several algorithms have been developed to describe the location of accessory pathways (APs) in Wolff–Parkinson–White (WPW). Standard 12-lead electrocardiogram (ECG) assessments have been utilized to predict AP location in published algorithms. In ECGs showing submaximal ventricular pre-excitation, conventional AP algorithms may not be applicable. The objective of this study is to validate a simple algorithm for determining AP laterality (right versus left) using the addition of right precordial leads (V3R, V4R) to the standard ECG. Methods: A retrospective study of patients with structurally normal hearts who had undergone successful catheter ablation (CA) for WPW from January 2002 to January 2008 was performed. Patients with multiple APs or patients with congenital heart disease were eliminated from the study. Pre-ablation 15-lead ECGs of all patients were assessed. Delta wave polarity (first 40 ms of QRS), QRS duration, PR duration, and QRS polarity in leads V3R and V4R were specifically evaluated by two readers. Readers were blinded to the electronic ECG read and to AP location. An algorithm was then tested using positive QRS polarity in leads V3R and V4R as predictive of a left-sided pathway and a negative QRS polarity in leads V3R and V4R as predictive of a right-sided pathway. Results: 185 patients fulfilled criteria for study. During CA, 107 patients (58%) had right-sided AP and 78 patients (42%) had left-sided AP. Using our algorithm, the positive predictive value of a right-sided AP was 88% (105/119) and 89% (105/118) for each ECG reader (p = NS). The positive predictive value of a left-sided AP was 97% (60/62) and 98% (60/61) for each reader (p = NS). Conclusions: A simple algorithm for determining laterality of an AP in WPW can be obtained by adding right precordial leads to a standard ECG prior to CA. This information may help plan mapping and ablation strategies as well as counsel families regarding procedural outcome and risk.

KEYWORDS. 15-lead electrocardiogram, accessory pathway, laterality, Wolff–Parkinson–White.

The authors report no conflicts of interest for the published content.
Manuscript received June 4, 2012, final version accepted July 18, 2012.
Address correspondence to: Peter F. Aziz, MD, The Cleveland Clinic Foundation, Department of Pediatric Cardiology, 9500 Euclid Avenue, M30b, Cleveland, OH 44195. E-mail: azizp@ccf.org

Introduction

Wolff, Parkinson, and White described a syndrome among healthy young patients with paroxysmal tachycardia in 1930. These patients had characteristic electrocardiogram (ECG) findings of “functional bundle branch block” and a shortened PR interval.¹ Although the pathophysiology of this condition was not known at that time, we now know that accessory atrioventricular connections cause ventricular pre-excitation, as manifested by a delta wave on ECG. The prevalence of Wolff–Parkinson–White (WPW) syndrome is 0.15%, although this may be an underestimate, as many asymptomatic patients are undiagnosed.² Owing to the risk of sudden cardiac death in patients with this syndrome, radiofrequency ablation of the accessory pathway (AP) is often recommended.^3–5

Several predictive algorithms have been devised to locate APs based on ECG findings.^6–9 Many of these algorithms use delta-wave polarity when predicting pathway location. From a practical standpoint, not all ECG leads will demonstrate pre-excitation in patients with WPW. Approximately 47% of patients with WPW have left-sided pathways according to a recent study by Bar Cohen et al.¹⁰ Catheter ablation (CA) of left-sided pathways utilizes a transseptal or retrograde transaortic approach, which increases the procedural risk of CA.¹¹ When counseling families regarding the risks of this procedure, distinguishing pathway sidedness (right versus left) is useful.

To date, all predictive algorithms published have used 12-lead ECGs.^6–9 A 15-lead ECG provides right-sided electrograms (V3R and V4R) and further detail regarding the location of an AP (Figure 1). Although 15-lead ECGs are not the standard at most institutions, they present no change in cost when compared with a 12-lead ECG, and offer valuable information regarding AP laterality. The aim of our study was to examine an algorithm using right precordial leads as predictors of AP laterality.

Methods

A retrospective chart review was performed on patients (less than 18 years of age) who had undergone successful CA for WPW from January 2002 to January 2008 at the Children’s Hospital of Philadelphia. Institutional Review Board approval was obtained prior to data collection. Patients excluded were the following: 1) patients with multiple APs as determined by electrophysiology study, 2) patients with congenital heart disease as diagnosed per routine pre-ablation echocardiogram; 3) patients with no obvious pre-excitation on pre-ablation ECG; 4) patients presenting for repeat radiofrequency ablation; and 5) patients without a pre-ablation 15-lead ECG. All ECGs were performed utilizing a GE Marquette MAC 5000 or 5500 ECG Machine (GE Healthcare, Wauwatosa, WI) at a paper speed of 25 mm/s. Pre-ablation 15-lead ECGs of all patients were assessed. QRS polarity in leads V3R and V4R were specifically evaluated by two experienced readers. Readers were blinded to the electronic ECG interpretation and to AP location.

An algorithm was then tested using positive QRS polarity in leads V3R and V4R as predictive of a left-sided pathway, and negative QRS polarity in leads V3R and V4R as predictive of a right-sided pathway. The results of both readers were then compared to assess interobserver variability.

Results

During the study period described, 265 pediatric patients underwent RF ablation for WPW. Of these, 185 patients met the inclusion criteria for this study. Eighty patients were excluded because of 1) congenital heart disease (13 patients, 5%); 2) multiple pathways (23 patients, 9%); and 3) lack of pre-ablation ECG (19 patients, 7%).

Of the 185 study patients, 107 (58%) had right-sided pathways and 78 (42%) had left-sided pathways. We used an algorithm, stating that a positive QRS polarity in leads V3R and V4R (Figure 2) is predictive of a right-sided pathway, and a negative QRS polarity in leads V3R and V4R (Figure 3) is predictive of a left-sided pathway, and determined predictive value. Ten patients (5.4%) had isoelectric polarity in the right precordial leads and were excluded from predictive value calculations (Table 1). The positive predictive value of a right-sided AP was 89% (105/118) for reader 1 and 88% (105/119) for reader 2 (Table 2), p = NS. The positive predictive value of a left-sided AP was 98% (60/61) for reader 1 and 97% (60/62) for reader 2 (Table 3), p = NS.

The predictive value of delta-wave polarity in the right precordial leads (first 40 ms of QRS complex) was also determined. Postulating that a positive delta wave is predictive of a left-sided pathway and a negative delta wave is predictive of a right-sided pathway, the positive predictive value was calculated. Using leads V3R and V4R, the positive predictive value of a right-sided pathway was 89% (54/61) for reader 1 and 88% (53/60) for reader 2, p = NS. The positive predictive value of a left-sided pathway was 60% (71/119) for reader 1 and 60% (71/118) for reader 2, p = NS. Comparing leads V3R and V4R, discrepant polarity (differing polarity in leads V3R and V4R) was found in five patients according to reader 1 and seven patients according to reader 2. These patients were excluded from predictive value calculations respectively.

Discussion

To date, 15-lead ECGs have not been utilized in algorithms to determine AP location. This is the first study, to our knowledge, that employs a 15-lead ECG for this purpose. Our study did not aim to identify the exact location of the AP on the atrioventricular valve annulus. From a practical standpoint, the most important aspect of pathway localization is determining laterality as the decision to perform a transseptal puncture or obtain arterial access for a retroaortic approach hinges on this key factor. With the increasing use of additional technologies such as cryothermal ablation and three-dimensional mapping equipment, it is possible to improve efficacy and safety of CA once the laterality of the AP has been determined.^12,13

Determining pathway laterality, though a much less vigorous investigation, has been shown to be inaccurate in children. For instance, when applying the Arruda or Fitzpatrick algorithms for prediction of pathway laterality, similar diagnostic inaccuracies are noted (84% and 74% respectively).^7,9 Although Boersma et al⁶ devised a specific algorithm for pathway location in the pediatric patient, the predictive value of this algorithm for pathway laterality was only 79%, highlighting the shortcomings of these approaches. Our algorithm utilizes right precordial leads and has the best published accuracy for determining pathway laterality in pediatric patients. Moreover, the positive value of predicting a left-sided pathway using our algorithm is nearly perfect at 97%. Given the relative simplicity of this algorithm, the pediatrician or the pediatric cardiologist can utilize this strategy for laterality purposes.

Explaining these limitations of ECG algorithms in the pediatric population may be in part due to robust AV node conduction causing partial concealment of AP conduction.⁶ Most of the previously described algorithms employ the delta wave (first 40 ms of the QRS) as a pivotal determining factor in pathway location.^6–9 Our algorithm instead uses QRS polarity alone, which can be applied to patients with subtle pre-excitation as often occurs in the pediatric population.

The study has several limitations. It is retrospective study; however, two-blinded readers arrived at very similar predictive values using a large patient population. Additionally, some patients in this study were found to have a negative QRS morphology in one right precordial lead and a positive precordial morphology in the other. We were unable to find patterns among these patients with regard to predicting pathway laterality. This finding occurred in a small subset of patients studied. We chose to exclude the congenital heart disease patients, as abnormal cardiac anatomy often complicates ECG interpretation. Unfortunately, no data exist regarding pathway localization in this complex, heterogeneous population.

Conclusion

Adult ECG localization algorithms may have poor diagnostic accuracy in young patients with WPW. Our study demonstrates that incorporating right-sided surface precordial leads in the ECG of pediatric patients with WPW is helpful in determining right vs. left laterality of APs.

References

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