The aim of the present study was to indagate whether the presence of the fQRSV1 ECG pattern might be associated with physiological or pathological heart adaptations, focusing specifically on young athletes.

The main results of this study can be summarised as follows:

1.

fQRSV1 is a frequent and training-related ECG pattern also in apparently healthy young athletes.

2.

fQRSV1 pattern is associated with training-induced right and left ventricular remodelling.

3.

Subjects with fQRSV1 do not present higher onset of arrhythmias at maximal exercise testing compared with subjects with no fQRSV1.

Different fQRS morphologies have been described in the past with a heterogeneous prevalence in subjects with and without cardiac disease, strictly depending on the definition and localisation used for the fQRS determination [11, 20, 21]. Moreover, a recent study analysing the prevalence of fQRSV1 in adult athletes showed an association with training-induced RV remodelling, proposing to investigate this phenomenon also in younger athletes and evaluate the related arrhythmic risk [8]. For this reason, only fQRSV1 having an rSr’s’ with a quadriphasic or higher-phasic pattern in lead V1 was considered for this study, in order to eliminate possible confounding with the typical conduction delay in the iRBBB and RBBB. The QRS complex in lead V1 was recently detailed for young athletes, distinguishing iRBBB from the crista supraventricularis pattern (defined as an rSr´ pattern in lead V1 together with a QRS ≤ 100 ms and S wave < 40 ms in I or V6), with the latter often misdiagnosed for an iRBBB [22]. The prevalence of the crista pattern in young athletes appears to exceed that of iRBBB and does not appear to be associated with RV dilation [22]. Moreover, a recent algorithm for ECG interpretation in children practicing sport was proposed [23], reducing the time cut-off to classify the iRBBB to less than 100 ms, not mentioning the presence of fQRS as borderline or abnormal finding. In addition, iRBBB was classified as borderline ECG finding in children, thus requiring further investigation when associated with right or left axis deviation. The classification for iRBBB used in our study and the consequent need for further investigations followed that adopted in the adult athlete population.

fQRS has been traditionally described as a marker of conduction delay that may represent an abnormal area of the myocardium, thus predisposing to a greater arrhythmic risk in patients with heart disease [21]. Indeed, the underlying substrate of the fQRS could be linked to the presence of a myocardial scar, reflecting the inhomogeneous activation of the ventricles [24, 25]. Some authors described the fQRS as a sign of myocardial perfusion deficit [26], linking this pattern to specific heart diseases like sarcoidosis [27]. Furthermore, it has been shown that a baseline fQRS was associated with an up to three-fold increased risk for major arrhythmic events in patients with Brugada syndrome [28].

However, in recent years, fQRSV1 has been described as a frequent ECG pattern in young and healthy athletes, frequently associated with training-induced ventricular remodelling [8, 9]. Given the high demand related to the athletes’ cardiovascular workload, many structural and electrical adaptations can occur, thus explaining common features of the athlete’s heart considered uncommon in the general population [29,30,31]. Our study’s results align with this physiological interpretation, showing how fQRSV1 could be a marker of sport-related ventricular adaptation; indeed, subjects with fQRSV1 had higher index RV EDD and TAPSE values, while this pattern was independently associated with the global RV function. Despite no difference in weekly training hours has been detected, athletes with the fQRSV1 demonstrated higher exercise capacity and tolerance, indices of improved training adaptations, suggesting that fQRSV1 is probably more related to the training intensity rather than the training volume. On the other hand, sports classification did not seem to be a significant modifier in this sporty population of children and adolescents, as also previously demonstrated by Orlandi et al. [9].

Moreover, a subgroup analysis was performed, identifying 111 young athletes with at least 8 h of training per week, defined as “highly trained” athletes, using the most recent definition of athletes and considering current studies on this topic [8, 32]. In this “highly trained” subgroup, athletes with fQRSV1 presented markers of RV and LV remodelling, and the pattern resulted independently associated with RV and LV function and adaptation. Current evidence explaining adaptations to high training load in the paediatric heart is few and sometimes with conflicting outcomes [33]. Indeed, if D’Ascenzi et al. described a paediatric physiological training-induced remodelling, especially in RV parameters [5], Rodriguez-Lopez et al. affirmed that cardiac remodelling in young athletes is mainly focused on the left chambers [6]. Thus, considering only studies analyzing fQRS in athletes, Orlandi et al. recently showed how the fQRS pattern was independently associated with LV cardiac mass indices, while a study by Ollitreaut et al. demonstrated that fQRSV1 was associated with training-induced RV remodeling [8].

One possible explanation for these conflicting results may be the connection between age and training load. Indeed, it is well known that training volume and intensity increase progressively with the development of children and adolescents [34]. The fQRSV1 pattern is associated with structural and functional changes typical of the athlete's heart, specifically evident in the right sections. As training volume increases, cardiac adaptations may amplify, and this is also reflected in surface ECG patterns associated with cardiac remodeling. It is possible that with larger training volumes and loads, the fQRSV1 pattern, although always strictly linked to the electrical activity of right sections, is more affected by ventricular adaptations of the left chambers that proportionally exceed the growth of the right chambers.

The presence of a fQRS pattern could complicate the decision-making process regarding eligibility for participation in competitive sports as no sufficient data are yet available providing evidence on the clinical relevance of this ECG characteristic in athletes. Indeed, the relationship between fQRSV1 and arrhythmias has never been investigated in healthy young athletes. It is known that fQRS may indicate potentially higher risk in patients with well-established structural heart disease or channelopathy but the relationship between fQRS and major arrhythmias is not fully understood [35]. In our study subjects with fQRSV1 presented a similar arrhythmic burden during maximal exercise testing compared to the rest of the subjects, both in terms of the origin (supraventricular or ventricular), morphology, or complexity (isolated or repetitive). fQRSV1 does not appear to be a pattern that might predispose to greater arrhythmic risk, supporting its para-physiological relevance. The electrical delay that might be hypothesised from the ECG pattern does not seem to enhance the common mechanisms of the onset of ventricular arrhythmias, not even for those originating from the RVOT [8].

Therefore, fQRSV1 appears to be a benign marker of cardiac remodelling, more common in highly trained subjects, and the associated morpho-functional adaptations do not affect the arrhythmic burden, particularly regarding ventricular arrhythmias. For this reason and for the absence of reported major adverse events during the follow-up period, fQRSV1 should currently be considered a common unremarkable sign in the athlete’s ECG [36].

Limitation and Perspectives

To the best of our knowledge, this is the largest study on the fQRS ECG pattern in a population of young athletes and the first to specifically address some open questions in sports cardiology regarding the associated risk of exercise-induced arrhythmias. Nevertheless, there are some limitations to be reported. Our study included only young athletes who underwent echocardiography as second-line investigation during the pre-participation screening for sports eligibility. The indications to perform echocardiography were related to minor diagnostic findings detected during the first-line examination as murmur or ≥ two premature ventricular beats. Nevertheless, to minimize this possible selection bias, athletes with previously known cardiopathies, ECG abnormalities or symptoms were excluded from the study. Moreover, after the second-line investigations, including 24 h Holter ECG (with an exercise session, none of the included athletes was found to be not eligible for competitive sports. Furthermore, our study focused only on standard systolic parameters, while other evaluations such as global longitudinal strain, Doppler tissue imaging, or speckle tracking should be added in future investigations. Newer techniques of RV segmentation could help in the evaluation of the relationship between the fQRSV1 pattern and RV remodeling, such as RV strain [37].