The Relationship Between Weight and Ablation Outcomes in Pediatric WPW

Weighing less than 30 kg is associated with a small but increased risk for major adverse events in pediatric patients with Wolff Parkinson White syndrome (WPW syndrome), according to results recently published in JACC: Clinical Electrophysiology.

The retrospective multicenter cohort study used data from the Improving Pediatric and Adult Congenital Treatment (IMPACT) registry of pediatric and congenital catheterization and electrophysiology study procedures to assess whether patient weight was associated with acute ablation outcomes.

The participants were aged 1 to 21 years who were receiving elective, first-time electrophysiology study for WPW from April 1, 2016, through December 1, 2019. The patients were categorized into those weighing less than 30 kg (n=624) and those 30 kg or more (n=3832).

The primary outcome was 1 or more major adverse event, including death, cardiac arrest, tamponade, embolic stroke, heart block requiring permanent pacing, unplanned cardiac surgery, or unplanned vascular surgery.

A total of 4456 patients with WPW (57% male; mean age, 13.1±3.7 years) were included. Their mean (SD) weight was 56 kg (24 kg), and the less than 30-kg group represented the lowest 14th percentile among the participants.

The patients who weighed less than 30 kg were more likely to have documented supraventricular tachycardia and to have received beta blockers or other antiarrhythmic drugs (all, P <.001). Significant differences in accessory pathway (AP) location were found between the 2 groups, with a greater frequency of left-sided nonseptal pathways and lower frequency of right-sided septal pathways occurring in the less than 30-kg group (P <.001).

Weight less than 30 kg was associated with an increased likelihood of composite major adverse events (0.3% vs 0.05% in the ≥30 kg group; P =.04). No significant association was observed between the participants’ weight and risk for an adverse event (P =.10).

Ablation was deferred in 9% of participants in the less than 30-kg group and in 12% of those in the 30-kg or more group, although it was not statistically significant (P =.07). The use of cryoablation only (11% vs 11%; P =.70) and combined use of radiofrequency plus cryoablation (7% vs 7%; P =.70) was comparable in the 2 groups.

Among participants with attempted ablation, the less than 30-kg group had significantly greater acute success (95% vs 92%; P =.009). Patients who weighed 30 kg or more had an increased rate of the composite outcome of deferred or failed ablation (19% vs 14% in the <30 kg cohort; P =.001).

In multivariable modeling that adjusted for AP type, location, and ablation energy source, weight of less than 30 kg was a predictor of ablation success (odds ratio [OR], 1.6; 95% CI, 1.01-2.7; P =.046). Radiofrequency plus cryoablation (OR, 0.3; 95% CI, 0.2-0.4; P <.001) and non-left-free wall pathway locations were predictors for ablation failure.

Similar findings were observed in unadjusted analysis with use of a weight threshold of 15 kg, although the less than 15-kg group had 26 participants. Patients in the less than 15-kg group had a success rate of 95%, with cryoablation only used in 8% and irrigated radiofrequency in no participants. No adverse events were observed in the less than 15 kg group.

Among several limitations, the study could be biased toward larger and more organized electrophysiology programs, details such as unplanned cardiac or vascular surgeries are not known, and outcomes cannot be described at the individual case level. Furthermore, the analysis is limited to patients with a single ablation target and those without congenital heart disease or cardiomyopathy, and outcomes such as postdischarge complications and arrhythmia recurrence are not assessed.

“There are likely anatomic factors that promote acute success in smaller patients,” wrote the investigators. “However, higher success comes at the cost of higher rates of MAEs [major adverse events]. Operator and center experience are critical factors that cannot be accounted for in this analysis. As such, these data should not be interpreted to broadly support earlier ablation in pediatric WPW.”