Root of the study and selection of the patient group

The starting point of this study was the reality that paediatric patients may continue to experience palpitations even after a supraventricular tachycardia ablation, which was reported to have success rate of up to 98%, and there is a gap in the literature to define the best diagnostic tool to distinguish between true recurrent cases and clinically insignificant complaints, especially for paediatric population, who describe and perceive palpitations in a manner that is more ambiguous compared to adults. ^{Reference Kafalı, Özgür and Şahin1–Reference Van Hare, Carmelli and Smith3} Since there is rarely a correlation between the severity of symptoms and the diagnosis of arrhythmias in children, ambulatory cardiac monitoring holds significant diagnostic importance. Furthermore, we specifically selected our patient population from those over the age of 10, as this age group can better recognise symptoms, and we excluded patients with Wolff-Parkinson-White and Mahaim pathways, whose recurrences can be detected on surface electrocardiogram. Additionally, to avoid confounding factors from other arrhythmias such as atrial and ventricular premature contractions that might mimic supraventricular tachycardia recurrences, we excluded patients with CHD from the study.

Speculations for possible mechanism of palpitation after supraventricular tachycardia ablation

The reason for persistent palpitations despite the absence of recurrence is still seeking for an answer. One possible explanation is that patients with arrhythmias have an increased awareness of their heart rhythms. Consequently, benign irregularities like premature atrial and ventricular contractions, or paroxysmal sinus tachycardia, may be felt as palpitations. Li and colleagues conducted a study comparing patients under 19 years who underwent tachyarrhythmia ablation and later presented with palpitations to a control group. They found that 56% of the patients experienced palpitations after the first month post-ablation, with a recurrence rate of 7.2% in this group. Although there was no difference in the frequency of palpitations between the groups, the need for medical attention was four times higher in the post-ablation group. ^{Reference Li, Kallas and LePoidevin4} Carbery and colleagues also found that 35% of children and young adults with structurally normal hearts who underwent atrioventricular nodal reentrant tachycardia ablation experienced palpitations post-procedure. ^{Reference Carberry, Balmert and Stanley5} Mann et al. investigated the relationship between post-procedure palpitations and recurrence in patients over the age of 10, with a mean age of 37, who underwent supraventricular tachycardia ablation for accessory pathway and/or atrioventricular nodal reentrant tachycardia. They reported that 58% of 77 patients continued to experience palpitations despite successful ablation. Additionally, 70% of the patients underwent repeated electrophysiology study, and a recurrence rate of 10% was found in the patient group. The study postulated that assessing the return of pathway conduction based on symptoms can be misleading. ^{Reference Mann, Kelly and Adler6}

Inappropriate sinus tachycardia has also been reported after catheter modification of atrioventricular nodal conduction, potentially due to the ablation damaging cardiac autonomic nerves, which might contribute to presence of symptoms in some patients. ^{Reference Ehlert, Goldberger and Brooks7,Reference Ptaszynski, Kaczmarek and Ruta8} Effect of radiofrequency ablation of accessory pathways on autonomic tone in children was investigated by Sehra and colleagues in their study, which depicted exemplary data with a prospective design in paediatric population. They conducted non-invasive testing, tilt testing, and 24-hour Holter monitoring less than 72 hours before the electrophysiological study and again within 24 hours after the ablation procedure, comparing these results with those of a normal control group. The findings demonstrated that acute changes occurred in both non-invasive and invasive measures, consistent with increased sympathetic tone or decreased parasympathetic tone. Similarly, in an adult population, Ehlert et al. published persistent inappropriate sinus tachycardia in 3 out of 8 patients following radiofrequency catheter ablation of the atrioventricular node’s fast pathway. They attributed this increase in heart rate to vagal withdrawal, potentially due to the destruction or damage of autonomic fibres in the atrioventricular junction. Additionally, the rise in sinus rate was correlated with the number of energy applications. ^{Reference Ehlert, Goldberger and Brooks7} Considering that 9 (53%) of the arrhythmias in 17 out of 73 event recordings from patients in our study group were identified as sinus tachycardia, especially in patients with atrioventricular nodal reentrant tachycardia, it should be noted that, even though the statistical difference among diagnostic subgroups post-ablation has not been demonstrated, the aforementioned phenomenon might particularly influence patients who underwent atrioventricular nodal reentrant tachycardia ablation, which involves the area around the atrioventricular node. The number of patients with inappropriate sinus tachycardia after atrioventricular nodal reentrant tachycardia ablation was limited in our study, and in fact, cryoablation had been applied to all except one patient. Therefore, the impact of lesions being delivered to the parasympathetic ganglia around the atrioventricular node during procedure may pose a larger role in the probable mechanism of inappropriate sinus tachycardia rather than solely the type of ablation. Similarly, cases of postural orthostatic tachycardia syndrome have also been reported for awareness, particularly when orthostatic symptoms non-existent before the procedure become pronounced following ablation. Atrioventricular nodal disturbance and/or neuropathy were possibly addressed, though the mechanism is not being fully elucidated. ^{Reference Kanjwal9} Along with the potential changes in the autonomic system, it is beneficial to remind clinicians of the other differential diagnoses, such as hypoxia, anaemia, hypovolemia, shock, myocardial ischaemia, pulmonary oedema, hyperthyroidism, medication, hypocalcaemia, and illicit drug use, which could substantially improve the patient’s quality of life when properly identified.

Another contributor to the perception of palpitation may claimed to be age and age-related dynamic changes in diagnoses. In a study of Brembilla-Perrot and colleagues, investigating symptom recurrences following atrioventricular nodal reentrant tachycardia ablation in adults with 6% of recurrence rate and 16% of post-ablation palpitation rates, which is in alignment with our results, it was noted that there was a higher frequency of inappropriate sinus tachycardia, especially among young and female patients, particularly during the initial 6-month period until reinnervation expected to be established. ^{Reference Brembilla-Perrot, Sellal and Olivier10} We did not identify any associations between age, gender, diagnostic subset, or weight and odds of post-ablation palpitations. Neither demographics nor procedural details influenced the risk of post-ablation palpitations. Although age was not found to have a significant impact on palpitations, given the relative homogeneity of our patient cohort in terms of age, we cannot entirely exclude the possibility that in a broader population, younger individuals may exhibit a lower correlation between palpitations and arrhythmias.

Why external event recorders?

Among the available monitoring systems, we aimed to investigate the usability of external event recorders, as these devices provide much longer recording durations compared to electrocardiogram and 24-hour Holter monitoring, thereby covering a broader symptom interval. Despite the existence of various loop recorders, including implantable ones, the literature supports the higher effectiveness of implantable loop recorders in conditions such as syncope and presyncope, where patient cooperation is limited during the event, compared to palpitation as the presenting symptom. Consequently, we believe that external event recorders can be less invasive alternatives for children experiencing palpitations, thereby avoiding the requirement of surgical implantation and subsequent device removal. Even though activating the device at the moment of the event may be accepted as a factor disrupting symptom-arrhythmia correlation in the young patient group, based on the results of highly specific patient group of ours, all patients were able to record at least one episode demonstrating that children over the age of 10 can effectively cooperate with the use of event recorders.

Numerous studies have demonstrated the superiority of event recorders over 24-hour Holter monitoring in capturing intermittent and short-duration palpitations. ^{Reference Scalvini, Zanelli and Martinelli11–Reference Hoch, Rockx and Krahn14} External loop recorders are reported to increase the successful diagnosis rate up to 87% from 20% compared with the usual diagnostic strategies, providing another aspect with shorter duration of definitive diagnosis and cost effectiveness of reduction up to 70%. ^{Reference Francisco-Pascual, Santos-Ortega and Roca-Luque15} Available technologies for external event recording can be subgrouped as follows: External event recorders without a loop provide non-continuous ambulatory recordings. When activated by the patient, an electrocardiogram is recorded and transmitted to a receiving centrer. Event recorders with looping memory continuously record a single-lead electrocardiogram, but the rhythm strip is only saved when the patient activates the device. Most devices can be programmed to save both before and after activation. These devices come in various designs, including chest-attached electrodes, wrist-worn devices, and handheld credit card-sized devices. Auto-triggered event monitors with looping memory automatically detect pre-specified high or low heart rates. Patients can also manually trigger recordings if they experience symptoms, with both functions operating simultaneously.

Decision on the ideal monitoring length in paediatric patients, especially since symptom frequency can vary widely, is challenging, yet the difficulty in documenting electrocardiograms during symptoms in our 36 patients with recurrent episodes indicates that capturing such events is challenging for patients with infrequent symptoms. Once patient compliance with the device and recording is established, obtaining recordings for at least 2 weeks in patients who report frequent palpitations can facilitate the detection of symptomatic arrhythmias.

How this study helps?

In our study, palpitations following supraventricular tachycardia ablation in the paediatric age group were observed in approximately 15% of cases, indicating that this could be a significant concern during patient follow-up. Given the frequency of patient complaints, we recommend using external event recorder monitoring for at least two weeks approach, especially when the major complaint is palpitation, is a non-invasive and, as demonstrated in our study, achieved a symptom-arrhythmia detection rate of 23%, making it a reliable tool for the adolescent age group.

In the data previously published by our institution in 2016, arrhythmia was detected in 131 out of 336 external event recordings obtained from 460 symptomatic paediatric patients (73% of whom presented with palpitations). The symptom-rhythm correlation was reported to be 39%. ^{Reference Saygi, Ergul and Ozyilmaz16} Coherently, Akca and colleagues reported a symptom-rhythm correlation of 30.2% for their “palpitation” subgroup with the results of external event recordings from 172 symptomatic patients under the age of 18, among which 56.9% of the requested recordings were indicated for the complaint of palpitations. ^{Reference Akca, Uysal and Bostan17} It is noteworthy that in those studies which are notable for being conducted in large paediatric groups with various symptoms, sinus tachycardia was reported in 25% and 47.1% of the external event recordings, respectively. In our study (super specific population with specific complaint), of the 73 event recordings, 17 were arrhythmia-positive, and nine of these were identified as inappropriate sinus tachycardia, which indicates its significance as a cause of palpitations in paediatric age group. Another aspect we noticed is that although statistically insignificant, the positivity rate among those experiencing palpitations (3 out of 8 event recordings were supraventricular tachycardia positive, 37%) and the frequency of palpitations in those with recurrences were observed more frequently in the focal atrial tachycardia subgroup compared to atrioventricular nodal reentrant tachycardia and concealed accessory pathway, at rates of 33% vs. 21% and 19%, respectively. These results can be interpreted as palpitations in patients with focal atrial tachycardia may be more accurately indicative of recurrences.

As a matter of fact, we believe this study is important due to the specific patient group involved and the scarcity of publications investigating validation of palpitations in children who have undergone supraventricular tachycardia ablation. Based on current knowledge, though the underlying mechanism is not fully understood, it is important to inform families that they should be aware of such possible persistency of post-ablation palpitations and are not necessarily indicative of recurrence.

We postulate that selecting appropriate ambulatory monitoring can help clinicians avoid unnecessary electrophysiological studies and accurately identify true recurrent cases. At this point, external event recorders can be reliably used to validate recurrences in the adolescents, considering the frequency of palpitations in patients who have undergone supraventricular tachycardia ablation.