The arrhythmic risk in Kearns–Sayre syndrome: still many questions unanswered—Authors’ reply

We thank Dr Del Monte et al. for their interest¹ and are pleased to answer their questions.

As stated in the aims,² we specifically focused on the long-term detection, by standard and dynamic electrocardiogram (ECG) assessment, of the involvement of the cardiac conduction system and on the progression of its disorders in childhood Kearns–Sayre syndrome (KSS).

The electrophysiological study (EPS), with the H-V interval measurement, may have diagnostic and prognostic utility in these patients, even if it is not universally considered the gold standard for the indication and timing of pacemaker implantation.³ Moreover, as recently reported by Joosten et al.⁴ on the arrhythmic risk in myotonic dystrophy (DM) type 1, considering the etiopathogenesis of rhythm disorders in DM superimposed on that of KSS: ‘the presence of specific conduction anomalies ECG (long PR and/or intraventricular conduction defects) are independent predictors of having an HV interval ≥ 70 ms on an EPS; combining individual ECG parameters, the positive predictive value for abnormal infrahissian conduction on EPS is 78% in these patients’. Finally, EPS cannot be routinely performed in paediatric patients with poor compliance, whereas a routine ECG can significantly predict the arrhythmic risk and the occurrence of catastrophic events, even in centres without paediatric electrophysiologists.

We are aware that ventricular arrhythmias (VAS) can be triggered by early or delayed post-depolarization or can be favoured by structural anomalies. Even considering that the stratification of tachyarrhythmias was not our goal, we collected data on VAS (patient 10 in Table 1, original paper).² Furthermore, the limited literature suggests that VAS may be an expression of the progression of the disease and, therefore, may have a limited incidence in paediatric patients.⁵

Cardiac magnetic resonance (CMR) imaging is essential in the structural and tissue characterization of myocardial tissue. We collected only some CMR data because some patients were not compliant due to their young age and comorbidities (i.e. psychiatric disorders).

The implantable loop recorder (ILR) could be a valid alternative for detecting arrhythmic events. However, the ILR provides a single non-standard lead, and it does not allow the complete analysis of the ECG. In our patients, the ECG was performed step-by-step permitting the accurate description of a progressive deterioration of conduction system in KSS. Moreover, ILR implantation is only recommended in patients with unknown cardiovascular symptoms and without abnormal non-invasive cardiac tests.⁶

We concluded the article recommending our approach to diagnostic and therapeutic management of children with KSS: we reported an optimal follow-up for these patients proposing pacemaker implantation in bifascicular block or advanced/complete atrioventricular block. This deduction was based on the extent of our cohort of paediatric patients and on the analysis of the literature,³ not only on case reports.

Actually, multicentre studies are needed to better understand the cardiac involvement of KSS and to write cardiac treatment consensus for paediatric patients with KSS or other mitochondrial diseases. However, this was not our purpose. We aimed to explain and describe the cardiac involvement and ECG characteristics of a large cohort of children with KSS.

Conflict of interest: none declared.

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