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Benefits and limitations of electrocardiographic and echocardiographic screening in top level endurance athletes

The study was designed to assess the usefulness of routine electrocardiography (ECG) as well as transthoracic echocardiography (TTE) in screening top level endurance athletes. An additional goal was to attempt to identify factors determining occurrence of adaptive and abnormal changes in ECG and TTE. The retrospective analysis included basic medical data, ECG and TTE results of 262 athletes (123 rowers, 32 canoeists and 107 cyclists), members of the Polish National Team. The athletes were divided into two age groups: young (≤ 18 years; n = 177) and elite (> 18 years; n = 85). ECG and TTE measurements were analysed according to the International Recommendations from 2017 and 2015, respectively. Adaptive ECG changes were found in 165 (63%) athletes. Abnormal ECG changes were identified in 10 (3.8%) athletes. 98% of athletes exceeded TTE norms for the general population and 26% exceeded norms for athletes. The occurrence of both adaptive ECG findings and abnormalities in the TTE (in norms for athletes) was strongly associated with the years of training, hours of training per week and the age of the athlete. Male gender and the years of training were independent predictors of the ECG and TTE findings. Abnormal ECG changes were not related to the time of sport. Among 10 athletes with ECG changes, only 3 had changes in TTE and no relationship was found between abnormal finding in ECG and TTE (p = 0.45). ECG and TTE screening complement each other in identifying endurance athletes requiring treatment or verification. Unlike abnormal ECG changes, adaptive ECG changes and TTE abnormalities are strongly related to the training duration, which reflects physiological adaptation of the heart to physical exertion in high endurance athletes.


INTRODUCTION
them had any family history of sudden cardiac death. Median age in the young group was 17 (2) years and in the elite group was 23 (4) years.

Normal ECG findings in athletes
Training-related (normal) changes were observed in 165 (63%) athletes. In the young group of athletes such changes were observed in 56% and in the elite 77% of competitors. The most common findings were early repolarization syndrome (39%), isolated left ventricular hypertrophy (32%) and sinus bradycardia (13%). The incidence of normal ECG findings is shown in Table 1.

Abnormal ECG findings in athletes
Non-training related (abnormal) changes were identified in 10 (3.8%) athletes. Particular parameters evaluated in the criteria along with their definitions and the number of athletes who met the given parameter are presented in Table 2.

Predictive factors for the occurrence of normal and abnormal findings in the ECG
The logistic regression analysis demonstrated that predictors that statistically significantly affected the occurrence of adaptive changes were the age of the athletes, training duration (in years), and male gender. The group of elite athletes had a 2.5 times higher odds for having a normal ECG finding. Each year of training increased the likelihood of these changes by 14%. Male gender and years of training were found to be independent predictors of normal ECG findings.
No relationship was found between abnormal ECG findings and the time of sport.

Group characteristics
The retrospective study was based on data from a medical examination, anthropometric results, electrocardiograms and echocardiographic examinations of rowers, canoeists and cyclists who were members of the Polish National Team. They were competing in national and international sports competitions. The results arose from periodic check-ups carried out in the Institute of Sport -National Research Institute in Warsaw, in 2014 and 2015. The athletes were divided into two age groups of ≤ 18 years (young) and > 18 years (elite).

Electrocardiographic examination
A standard resting 12-lead ECG was performed using a Marquette-Hellige, Cardio-Soft V6.73/2 device from General Electric USA. All ECGs were recorded at 25 mm/s and 10 mm/mV. Each ECG was analysed according to the standards of the International Recommendations for ECG Interpretation in Athletes from 2017 (ESC 2017) [3]. The abnormalities were divided into adaptive, borderline and pathological changes.

Echocardiographic examination
A 2D TTE was performed using the Vivid 7 device (GE Vingmed Ultrasound AS, USA) and M4S probe (1.5-4.0 MHz) with simultaneous ECG (single-lead) recording. The results were analysed on an external computer (offline) using dedicated software (Echo PAC version 112; GE Healthcare, Wauwatosa, WI, USA). All measurements were made in accordance with the echocardiographic international recommendations from 2015 [4,5]. Echocardiographic norms for the general population and also for athletes are presented in Table 4.
The analysis of ECG and TTE was performed by one doctor (AJ). In case of doubt, ECG tracings were reviewed again with another doctor (MK) and mutual agreement was obtained.

Statistic analysis
The results were analysed in Statistica version 13.1 with a medical add-on. Distribution of variables was checked with Shapiro-Wilk test. Data are presented as mean ± standard deviation (M ± SD) or median (interquartile range) (Md (IQR)). Comparison of groups was performed using Student's t-test or the Mann-Whitney U test for quantitative variables and a 2 x 2 table and chi² test for qualitative features. The multifactorial models were based on backward stepwise regression to determine independent predictive factors.
Analysis of variance (ANOVA) was used to assess the differences in the grouped results. Statistical significance was determined by a value of p < 0.05.

Echocardiographic analysis
All athletes who underwent ECG also underwent TTE. A total of 219 out of 262 echocardiographic images were interpreted. Detailed results broken down by age groups are presented in Table 3.
Elite athletes were characterized by much thicker muscle, greater left ventricle mass and larger dimensions of heart chambers - Table 3.

Average left ventricular mass index (LVMI) values increased in
successive years of training sports. Reduced values were observed in the athletes who trained 18 and 19 years, which resulted from the predominance of women in these groups - Figure 1.

Left ventricle remodelling
The type of left ventricular remodelling was assessed according to the work of Ganau et al. [6]. The group of elite athletes was characterized by significantly more frequent concentric hypertrophy than the group of young athletes (48.1% compared to 22.9%, p < 0.001).
On the other hand, the group of young athletes significantly more

Abnormal TTE result according to reference values for the general population and for athletes
As many as 98.2% of the examined athletes exceeded echocardiographic norms for the general population. Moreover, about a quarter of them (i.e. 26%) exceeded even norms for athletes, mainly a dimension of the ventricular septum over 12 mm (24.2%) - Table 4.
The occurrence of abnormalities in echocardiography, namely exceeding the reference values for athletes in the measurements, was strongly associated with belonging to specific age groups, elite athletes much more frequently presented deviations than young ones, respectively 46% compared to 15%, p < 0.001. In the logistic regression it was found that 1 year of training increased the odds of the occurrence of norms for athletes being exceeded by 24% [OR = 1.24], p < 0.001 - Table 5.
As in the case of normal ECG findings, the occurrence of abnormalities in the TTE examination was strongly associated with the years of training, hours of training per week and the age of the athlete.
Moreover, the group of elite athletes had over 4.5 times greater chance of abnormalities being revealed in the TTE examination than the young ones. The strongest independent predictors of exceeding the echocardiographic norms for athletes were male gender and the years of training - Table 5.

Abnormal ECG findings and abnormal result of TTE examination according to reference values for athletes
In the group of 10 athletes who presented an abnormal ECG (according to the ESC 2017 criteria) 8 also underwent TTE and among them 3 presented an abnormal TTE result according to norms for athletes. There was no relationship between the occurrence of abnormal ECG findings and exceeding echocardiographic norms for athletes (chi-square test: abnormal ECG findings vs abnormal TTE according to athletes norms, p = 0.45).

DISCUSSION
The study showed that high-performance athletes practising endurance disciplines manifest significant changes in the heart. Almost all the assessed athletes (98.3%) exceeded at least one echocardiographic norm used for the general population and most of them (63%) had normal findings in the ECG.
In analyses aimed at identifying predictive factors for ECG and echocardiographic changes, it was found that both normal ECG findings and exceeded echocardiographic norms depended on identical variables related to the time of training such as belonging to the group of elite athletes, training duration (in years), age and training intensity.
It was also found that the group of elite athletes had a 2.5 times higher odds for having normal findings in the ECG and over 4.5 times greater odds for exceeding norms in TTE, and each year of training increased the likelihood of these changes by 14% and 24%, respectively. In addition, it was found that among normal ECG changes bradycardia and early repolarization (ER) were more common in the elite athletes, probably due to increased vagal tone/parasympathetic activity in this age group. Similarly, Brosnan et al. observed that competitive athletes more often present normal, training-related ECG changes than non-competitive athletes, which might confirm the relationship of these changes with physical effort [8]. At the same time, pathological ECG changes have not been shown to be related to the duration of training.

Utility of ECG or TTE screening in a group of the highest endurance athletes
As can be seen from the presented data, enlarged heart chambers and left ventricle hypertrophy were not uncommon. Every fourth athlete showed significant deviations, which mostly concerned the size of the ventricular septum. Interventricular septum hypertrophy (IVS thickness ≥ 13 mm) was found in 8.7% of the competitors, which significantly differed from the average dimensions observed in competitors of other disciplines, where septal hypertrophy usually affected 2% of athletes [2,9,10].
The explanation for the differences can be found in the study of Pelliccia et al. In 1991 he examined a large group of highly trained  However, the theory of concentric hypertrophy in healthy athletes is controversial. There are opinions that, as there are no sports disciplines characterized by only one type of heart load, the four left ventricular geometry patterns seem to be artificial and the term concentric hypertrophy in the context of the adaptation of the athlete's heart should be used with caution because it closely suggests hypertrophic cardiomyopathy (HCM) [15,16].
One of the aims of the study was the parallel assessment of the usefulness of the two diagnostic methods in the evaluation of sportdependent heart remodelling. As part of electrocardiographic screening, 10 athletes with significant pathology were examined, including four with Wolff-Parkinson-White Syndrome (WPW) and long QT (LQT) who had a potential threat to life and health. They were covered by specialist care. Others presented intraventricular conduction disturbances, T wave inversion, and ST segment depression. According to experts, such changes suggest congenital or acquired heart disease [3].
The above-mentioned athletes were evaluated with TTE examination -three had interventricular septum hypertrophy (IVS > 12 mm), including one with a dimension over 15 mm (Figure 2). Nevertheless, in a group of highly trained endurance athletes, changes imitating cardiomyopathies may result from advanced remodelling [17].

Sharma et al. noted that physiology and pathology interpenetrate
and can be difficult to distinguish especially in cases where there is athletes and only 1.7% of them presented a septum size over 13 mm.
However, in a detailed analysis of the subgroups in the aforementioned study it emerged that rowers, canoeists, cyclists, i.e. high endurance athletes, had similar results (7%) to those obtained in the present study [11,12].
This confirms the thesis about the more frequent occurrence of deviations in the group of athletes exposed to the largest static and dynamic loads and significant differences even compared to athletes of other high endurance disciplines.
The that despite the expected athletes' heart geometry driven towards eccentric hypertrophy, concentric hypertrophy occurred in most cases and mostly concerned male athletes [14]. Another limitation is the lack of long-term follow-up that would help assess the clinical significance of changes found in the ECG and TTE. The prospective assessment is ongoing, but this was not the purpose of the present study.
Due to the lack of a standardized measurement of blood pressure, the study did not take into account its effect on the mass and type of left ventricular hypertrophy.

CONCLUSIONS
1. Athletes practising disciplines affecting the cardiovascular system most require individualized assessment because 25% of them exceed the standards set for athletes.

Electrocardiographic and echocardiographic diagnostics comple-
ment each other in identifying endurance athletes requiring treatment (further verification) or special supervision. This confirms the need to perform both tests in competitive athletes.
3. Gender and training duration (in years) are the strongest independent predictors associated with the physiological adaptation of the heart to physical exertion in high-performance athletes.
advanced adaptation in response to the highest efforts, because even with heart diseases such as HCM, the disease may have a different expression and might run smoothly without affecting life expectancy [18][19][20]. The analysis carried out seems to confirm this thesis, and the final diagnosis would require among other things genetic testing.
Heart imaging methods such as echocardiography form an integral part of the assessment of athletes suspected of having heart disease based on medical history, physical examination or resting 12-lead ECG [4,21]. The routine TTE at the first stage of sports screening is objectionable to many researchers, primarily for economic reasons.
A number of screening protocols have been created to try to optimize the use of mass-scale TTE while minimizing time and costs [22,23].
Wyman et al. suggested using a 5-minute TTE 2D test as a useful and relatively easily accessible screening method [24]. Other authors recommend the limited use of echocardiography for screening only in selected groups of athletes. Kinoshita et al. speculate that the inclusion of echocardiographic screening should be considered only in very tall athletes due to the more frequent occurrence of aortic dilatation in this group [25]. Until now, only a small proportion of international sports organizations have decided to use echocardiography on a wide scale. These include FIFA and its subordinate federations, as well as organizations related to motor sports, cycling and basketball (NBA) [21].
In the conducted study, it was found that performing echocardiography in all competitors allowed us to capture several significant deviations requiring further observation, which we would not have found at earlier stages of screening. One was an 18-year-old rower with a bicuspid aortic valve (BAV), without abnormal ECG findings.
The next was a 28-year-old canoeist, who was characterized by an It has also been shown that TTE and ECG in most cases fail to detect the same abnormalities. In the group of 57 competitors who exceeded the echocardiographic norms for athletes, as many as 52 were not selected in the ECG screening.
Based on the presented data, it seems reasonable to use echocardiography not only in pre-screening, but also in understanding heart remodelling in endurance sports.

Limitations
One of the limitations of this study is the lack of a control group composed of people who do not practise sport. However, the aim of the study was to compare the ECG and morphological parameters of the heart in two age groups of athletes subjected to the same