For the first time, the present study assessed myocardial performance in a pool of children with WPW by using non-invasive Myocardial Work analysis. Our findings suggested that children with WPW may have subtle impairment of myocardial performance even in presence of normal ventricular function by standard echocardiographic parameters. We found GWI predicted by GLS, sBP and age, GCW predicted by GLS and sBP, and GWW and GWE predicted only by QRS interval.
Several studies have previously described left ventricle dysfunction in young15–17 and adult18,19 patients with WPW with different imaging modalities, even in absence of tachycardia. Recently, Nagai et al.19 used speckle tracking echocardiography to demonstrate an impairment of LV GLS, global circumferential strain, as well as LV EF, in a population of adult patients with WPW (mean age 40 ± 12 years). In a younger population (mean age 14.1 years – range 6.9–21.6 years), Akimoto et al.20 demonstrated, instead, a reduction in mid-basal circumferential strain, but not in LV EF. The same authors20 also demonstrated a reduction in GLS in WPW patients with right-sided AP, however, patients with left-sided AP presented normal GLS. In agreement with Akimoto et al., in our study, children with WPW had normal values of LV EF compared with controls. Similarly, in our very young cohort of WPW patients (mean age 8.7 ± 3.5 years), GLS did not differ significantly from controls. As previously hypothesized17, indeed myocardial dysfunction may appear with longer exposure to AP and be more frequently found with advancing age. However, we found an impairment of all myocardial work indices in WPW patients, compared to controls. We hypothesized, in presence of normal LV EF and GLS, myocardial work indices may represent a more sensitive method to study myocardial performance in pediatric patients with WPW. GLS indeed may detect subtle myocardial impairment even in presence of normal LV EF21, but it still carries load-dependency limitation22. Myocardial work has been shown to have an added value, taking into account deformation as well as afterload, and being less affected by load-dependence23,24.
In accordance with previous studies, we found low MWI and MCW associated with low GLS and sBP8; moreover, low MWI was found associated with younger age25,26.
In a study by Maréchaux27, in WPW patients with interventricular septum accessory pathway, as well as in patients with left bundle branch block (LBBB), a specific LV longitudinal strain pattern was described, which, interestingly, was more frequently found in patients with prolonged QRS duration. In normal conditions, myocardial segments contract all together during systole, with very little or no waste of energy. It is observed that the presence of myocardial dyssynchrony reduces myocardial performance because work performed by one segment is wasted by stretching other segments28.
In line with these observations, we found a correlation between impaired MWE and MWW and prolonged QRS duration.
We speculated these observations may be related to the higher dyssynchrony carried by a prolonged QRS observed in children with WPW. An impairment of MWE and MWW has been previously demonstrated in patients with cardiomyopathy and LBBB28,29. Similarly, in our patients with WPW, the presence of pre-excited myocardial segments shortening against a closed aortic valve may be responsible for the observed reduced work. As a consequence, the work done by the pre-excited segments does not contribute to LV EF but may represent a measure of contractile reserve after AP ablation, similar to patients with LBBB who undergo cardiac resynchronization therapy28.
Interestingly, in our study, the impairment of myocardial work was not independently related to a diagnosis of WPW per se. It means that not all patients with WPW would benefit from AP ablation, but rather only patients with wider QRS and worse values of myocardial work. In particular, we found children with WPW and QRS > 110 msec at higher risk for impairment of myocardial performance (worse IQR of MWE and MWW).
As demonstrated previously, evaluation of segmental work in ventricles with asynchronous contraction may contribute to the understanding mechanism underlying remodelling and developing LV dysfunction28,30. In accordance, myocardial work analysis should be regularly performed during follow-up of patients with WPW, and in presence of QRS interval > 110 msec, a closer follow-up should be considered in order to detect asymptomatic children with reduced values of myocardial work indices who may benefit from an early AP ablation.
4.1 Limitations
This study has some limitations. The lack of outcome information after the electrophysiological study represented the main one. As a result, we did not have data on myocardial work trends after AP catheter ablation. Moreover, considering the relatively small population of WPW patients, we did not perform a subgroup analysis to investigate peculiarities between different AP locations.
Finally, considering the study was conducted on children, we did not have data on the use of myocardial work on adults with longer exposure to the AP.