After explaining the purpose and how the study will be conducted, participants were recruited in training centers in Bamako and included footballer based on following criteria:

- Age between 14 and 35 years without distinction of sex;

- At least 10 hours regularly weekly training since one year;

- Consent to participate in the study.

All participants underwent the same procedure:

- They were first asked for cardiac symptoms, family history of known cardiac disease followed by cardiovascular examination in the athlete’s training sites;

- After that a rest ECG and two-dimensional transthoracic Echocardiography (TTE) were performed in medical facilities.

The ECG and echocardiographies were recorded respectively with a 12-lead CONTEC and an ATL 5000 echocardiographic machines.

Each ECG record was analyzed by a cardiologist in accordance with the Seattle 2013 criteria and those pathological reviewed by a second cardiologist according to the same criteria and definitively classified as normal (physiological) or abnormal ECG (requiring complementary explorations). A third cardiologist was associated in case of discordance of the first results.

For echocardiography, following values were considered as normal.

- Interventricular septum (IVS) : thickness less than 11 mm;

- Posterior wall (PW): thickness between 9 mm and 10 mm;

- Indexed LV: less than 28 mm in women and less than 30 mm in men;

- LVEF: greater than or equal to 55 mm in men as well as in women.

A survey formulary was used to collect data on socio-demographic, physical examination including data on cardiovascular auscultation, blood pressure, ECG and echocardiography records.

The collected data were inserted in a Microsoft Excel sheet and analyzed with SPSS version 20. Chi Square and Fisher statistical tests were used to compare our results. The significance level was set at 0.05.

We conducted a study among volunteering footballers, which mean that there is some degree of selection bias and we had only ECG and Echocardiography to perform cardiac evaluation. But this was to the best our knowledge the first study to systematically record ECG and Echocardiography for evaluation among athletes in our case footballers.

In our study we found more male footballer as reported in previous studies by Lahady et al. [9] , Tiéla [10] and Mounkoro [11] , the 2 latter authors using only ECG. This weak proportion could be explained by the fact that professional football is still widely practiced by men and consideration that football is more a male activity. There is since few years some changes leading to more football practice by girls.

Mean age in our study was 22.18 ± 4.37 years which was similar to those reported by Lahady et al. [9] and Rawlins [12] with respectively 25 and 21.

- Heart Rhythm

All the subjects were in sinus rhythm contrary to the results of Papadakis et al. [13] , Sheikh et al. [14] where some premature beats (PB) were observed. These PB can occur on a healthy heart as on a pathological heart, but disappear in the athlete with the effort.

- Heart Rate

Sinus bradycardia was frequently found in men and women with no significant difference (p = 0.168). Bradycardia is a common finding among athletes as reported by other authors with 33.9% for Grosjean [15] and up to 80% for Sharma et al. [16] . The higher proportion of bradycardia found by Sharma [16] could be due to his population with a longer duration of training as bradycardia is due to an increase in vagal tone secondary to training [15] .

- PR Duration

In sports, AV block (AVB) I is common and a priori benign. He is an indicator for a decrease in sympathetic tone and an increase in parasympathetic tone at rest. It could exist before the sport practice according to Brion [17] .

Our study found a prolongation of the PR duration type AVB I in footballers of both sexes without significant difference (p = 0.199). The same phenomenon of PR prolongation was observed by other authors in black and white athletes [1] - [14] with a significant difference [16] (p < 0.001).

- QRS Duration

We found an incomplete bundle branch block frequency comparable to that reported by Papadakis et al. [13] in 2011. In sport, incomplete right bundle block (RBBB) does not seem to be related to a real conductive disorder of the right branch but to a particular activation of the hypertrophied right ventricle or a vagal mechanism. On the other hand, the complete right branch block, the left branch blocks and hemiblocks are not part of the particularities of the athlete’s heart. Their discovery still requires a cardiological assessment [16] .

The enlarged QRS was observed more in men than in women without a significant difference.

- Sokolov’s Index:

The electrical left ventricular hypertrophy (LVH) based on Sokolov Lyon index is more common among athletes.

LVH was significantly found in men than in women with p < 0.0001. This result is similar to that of Rawlins et al. [12] where LVH was present in 9.2% + 1.2% among male against 8.6% + 1.2% among female (p < 0.0001). Constitution (shape and size of the thorax) are also factors that could increase the amplitude of the QRS according to the literature [15] which probably also explain the difference between both sexes.

- Corrected QT Using Bazett Formula: QTc

Bradycardia which is common in athletes leads to a significant lengthening of the QT interval [18] .

We found a high frequency of long QTc compared to a similar study done in Bamako by Mounkoro [9] (4.6%) among footballers under 15 years old. This difference could be related to age, the duration of sports practice leading to more bradycardia in older athletes like in our study. This QTc prolongation not exceeding 500 ms is usually attributed either to a delay in repolarization due to an increase in left ventricular mass in athletes or to a maladaptation of Bazett’s formula to low heart rates [15] .

- ST Elevation

It should be noted often, in the high-level athlete, an elevation of the J point followed by an elevation of the ST segment, most often concave upward, horizontal or ascending, and generally followed by a large positive T wave. This aspect has been called by some authors “early repolarization syndrome”.

ST segment elevation was present in more than half of our footballers with a significantly higher frequency in men than in women with p < 0.0001. Similar results were reported by Rawlins et al. [12] where ST + was present in 11% in men versus 1% in women with p < 0.001.

- Negative T Wave

The negative T wave was frequently found in our footballers with a higher incidence in men than in women with p = 0.013. Rawlins et al. [12] found 14% in men versus 2% in women with p < 0.001.

- Interventricular Septum (IVS)

IVS dimensions ranged from 7 to 16 mm with an average of 10.65 mm, with hypertrophy in 22 all males, 10.7%. Lahady et al. [9] reported 46 cases of septal hypertrophy between 11.5 to 16.5 mm whereas an average of 9.0 + −1.3, 9.0 + 1.3 mm in female black athletes were reported respectively by Sheikh [14] and Rawlins et al. [12] .

- Posterior Wall (PW)

The posterior wall was not very thick in our study (0.5%), unlike the result of Lahady et al. [9] who found a higher number of PW hypertrophy. This hypertrophy was significantly correlated with age above 30 years (p = 0.003).

- Indexed Left Ventricle Diameter (LVi)

The LVi was higher for female footballers than for boys, with a statistically significant difference (p = 0.001). Sheikh et al. [14] found no significant difference between the black athlete and the white athlete in the size of the left ventricle.

- The Ejection Fraction (EF)

The average left ventricular EF was similar to that found by Rawlins et al. [12] (67.4% + 6.7%). We also recorded low ejection fractions as reported by Lahady et al. [9] .

Summarizing sinus bradycardia, first degree AVB, RBBB, LVH, prolonged QT, ST segment elevation, repolarization disorders, increased LV mass, and increased left ventricle size were the different abnormalities found in our study population.

The frequency of these affections in athletes is due to a phenomenon of adaptation of the heart to intense and regular physical activities called athlete’s heart [13] . This adaptation concerns the four cavities with morphological and functional changes that are balanced, homogeneous and proportional.

It concerns aerobic disciplines with high training level (>8 - 10 hours/week, intensity > 60% VO₂ max) with hypertrophy-dilation. Anaerobic training (weightlifting) induces a very predominant concentric hypertrophy of the left ventricle.