Age

In general, the qualitative changes that occur in adolescent athletes are similar to those observed in more mature adults. However, voltage criteria for left and right ventricular hypertrophy may be more commonly present in adolescent athletes because of their thin chest walls.⁸ T-wave inversions in the right ventricular leads (V1 to V3) may be observed in up to 5% of adolescent athletes and usually regress by the age of 16 years and are representative of the juvenile ECG pattern rather than cardiac pathology (Figure 51-2).²³ In contrast, T-wave inversions in the anterior leads beyond V1 are identified in only 0.1% of adult athletes and warrant further investigations to exclude a cardiac disorder.²³

FIGURE 51-2 A 12-lead electrocardiogram taken from a 15-year-old male junior elite tennis player demonstrating T-wave inversions in the anterior leads (V1 to V3), consistent with the juvenile electrocardiogram pattern.

Few studies pertain specifically to ECG appearances in elite athletes (those aged ≥40 years); however, some data indicate that among athletes who participate in endurance sporting disciplines such as long-distance running, cycling, and cross-country skiing, a higher prevalence of atrial arrhythmias and heart block is seen compared with the general population.

Gender

The majority of studies assessing cardiac adaptation in athletes have evaluated predominantly white male subjects. In our experience, females exhibit ECG patterns similar to those of males but have a significantly lower prevalence of voltage criteria for cardiac hypertrophy, early repolarization changes, and T-wave inversions.

Ethnicity

The concept that an athlete’s ethnic background may alter the appearance of the resting 12-lead ECG has been examined by a number of recent reports comparing ECG patterns between white athletes and those with African or Afro-Caribbean ancestry (referred to as black athletes). Racial differences in ECG appearance have been recognized historically, with the observation in the 1950s that J-point and ST-segment elevation may be part of the normal ECG in young black men.^24,25

Recent studies have demonstrated that black male athletes demonstrate a higher prevalence of voltage criteria for left ventricular hypertrophy as well as bizarre repolarization anomalies that may simulate myocardial infarction (MI), Brugada syndrome, or phenotypic manifestations of both hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy (Figure 51-3). In one study of nearly 2000 American football players (67% black), 5.8% of black players had an ECG appearance that was deemed “markedly abnormal” by the investigators, compared with only 1.8% of white players.²⁶ Only a small proportion underwent subsequent echocardiographic evaluation, but the investigators concluded that in the majority of cases, the changes observed represented a normal ethnic variation.

FIGURE 51-3 A 12-lead electrocardiogram taken from a male African endurance athlete, a medalist at the 2008 Beijing Olympics. Note the deep T-wave inversions and convex ST-segment elevation in the anterior precordial leads (V1 to V3). He subsequently underwent further evaluation, which did not reveal any underlying cardiac abnormalities.

Our experience of evaluating large numbers of adolescent and adult male athletes of Afro-Caribbean origin has revealed that 25% exhibit marked repolarization changes comprising convex ST-segment elevation and deep (≥0.2 mV) T-wave inversions in leads V1 to V4 (Figure 51-4).²⁷ Such anomalies do not correlate with cardiac hypertrophy, chamber enlargement, or cardiac arrhythmias during exercise testing and on 24-hour ambulatory Holter recordings. Published data pertaining to female black athletes indicate that 14% of adult black female athletes exhibit minor T-wave inversions in the anterior precordial leads compared with less than 1% of white female athletes in the absence of structural heart disease (Figure 51-5).²⁸ The precise mechanism and significance of such anomalies remains to be elucidated and requires longitudinal assessment.

FIGURE 51-4 A 12-lead electrocardiogram taken from a black British premier soccer player exhibiting large QRS complexes, convex ST-segment elevation in leads V1 to V4, and deep T-wave inversions in leads V1 to V3.

FIGURE 51-5 A 12-lead electrocardiogram taken from a female African endurance runner during routine pre-participation screening demonstrating T-wave inversions in the anterior precordial leads (V1 and V2), accompanied by characteristic convex ST-segment elevation.

Sporting Discipline

Sporting discipline affects cardiac adaptation. In general, athletes participating in purely endurance sports such as cycling, rowing, and long-distance running exhibit larger left ventricular cavities and a greater magnitude of left ventricular hypertrophy compared with athletes involved in purely isometric sports, such as wrestling and judo. Athletes participating in long-distance endurance sports are more likely to exhibit sinus bradycardia, voltage criteria for cardiac chamber enlargement, and repolarization changes.²⁹ We advise caution against such generalizations because the training programs involved in most sports, particularly for athletes participating at the regional or national level, are arduous, physically intensive, and involve a combination of isotonic and isometric exercises. In our experience, an enormous overlap in ECG patterns exists among athletes participating in a large range of ball, racket, endurance, and power sports.

T-Wave Inversions

Repolarization changes consisting of ST-segment depression and T-wave inversions are much less frequent than ST-segment elevation and high-voltage T waves, being present in 3% to 4% of white adolescent and adult athletes.^11,23 The prevalence of T-wave inversions is significantly lower in white female athletes and considerably higher in male and female black athletes. These electrical anomalies overlap with the phenotypic manifestations of cardiomyopathy, ion channel disorders, and anabolic steroid abuse (Table 51-3) and warrant thorough evaluation before being attributed to physiological adaptation.^30–33 In a longitudinal study of 123 adult male white athletes with deep T-wave inversions, 39 (32%) had echocardiographic and clinical evidence of cardiac disease and were treated appropriately for their respective conditions.³⁴ Of the 84 remaining athletes without demonstrable cardiac disease, 81 were followed up for a mean of 9 years (±7; range, 1 to 27 years). Of these, 5 athletes (6%) subsequently developed a cardiomyopathy, with one death and one aborted cardiac arrest as a consequence of ventricular fibrillation (VF) caused by arrhythmogenic right ventricular cardiomyopathy and hypertrophic cardiomyopathy, respectively. The remaining 70 athletes did not develop any pathologic cardiac conditions during the period of follow-up. These data suggest that the presence of deep T-wave inversions in an athlete may be a harbinger of subtle cardiomyopathies and the risk of fatal ventricular arrhythmias and that such athletes should remain under periodic surveillance. T-wave inversion patterns in the anterior precordial leads (V1 to V3/V4) may be acceptable in adolescent athletes and in those of Afro-Caribbean origin; however, T-wave inversions in the lateral leads in adolescent athletes or black athletes warrant further evaluation for cardiac disease.²⁷

Table 51-3 ECG Changes in a Number of Cardiac Diseases That May Be Observed During Pre-participation Screening

Prolonged Q-T Interval

A long Q-T interval (>440 ms in males and >450 ms in females) is identified in 0.4% to 0.69% of athletes and is an indication for disqualification from competitive sport to minimize the risk of SCD, according to the European Society of Sports Cardiology guidelines.^13,35 However, the prevalence of a long Q-T interval in athletes is significantly higher than the actual prevalence of congenital long QT syndrome (LQTS) (0.04%), possibly because the Q-T interval may be overestimated by Bazzet’s formula at heart rates below 40 beats/min and measurements may also be influenced by sinus arrhythmia and slightly wider QRS complexes observed in athletes compared with the general population.³⁶ The positive predictive value (PPV) of an isolated corrected Q-T interval in the 440- to 470-ms range is not precisely known but is likely to be low, probably less than 10%. On the basis of these considerations, the Bethesda guidelines recommend an upper QTc limit of 470 ms in males and 480 ms in females.¹⁴ Our experience of athletes with long Q-T intervals suggests that a QTc 500 ms or greater is highly suggestive of LQTS, even in the absence of symptoms or an overt family history, and is usually associated with the other features of the disorder on exercise stress testing, such as paradoxical prolongation of the Q-T interval with increasing heart rate (up to 120 beats/min) and a long Q-T interval in other first-degree relatives.³⁵

Hypertrophic Cardiomyopathy

Cardiac adaptation to exercise is associated with modest increases in cardiac chamber wall thickness and cavity size. Typically, the left ventricular wall thickness in increased by 15% to 20%, and left ventricular cavity size may be increased by 10%.¹⁶ Occasionally, some male athletes (1.5% to 3% of white and 18% black athletes) (Figure 51-6) exhibit substantial increases in left ventricular wall thickness ranging from 13 mm to 16 mm, which fall within values observed in individuals with morphologically mild hypertrophic cardiomyopathy, which is the commonest cause of death in the young (age <35 years) worldwide (see Table 51-1).^37–40 The distinction between the athlete’s heart and hypertrophic cardiomyopathy is vital because an erroneous diagnosis has the potential for serious consequences (see Table 51-3). The differentiation between the two entities is possible with the assessment of cardiac chamber size and indices of systolic and diastolic functions using echocardiography and cardiac magnetic resonance imaging (MRI); abnormalities on the 12-lead ECG may provide crucial information to unravel the clinical dilemma, which may prove challenging.^41–43 The presence of deep T-wave inversions in any lead other than V1 in white athletes and in leads other than V1 to V4 in black athletes, pathologic Q waves, ST-segment depression, and left bundle branch block (LBBB) indicates pathologic left ventricular hypertrophy (Figure 51-7). Conversely, identification of the Sokolow-Lyon voltage criterion for left ventricular hypertrophy in isolation (without other associated features of left ventricular hypertrophy, including ST-segment depression, T-wave inversions, leftward axis, and voltage criterion for left atrial enlargement) is highly suggestive of physiological left ventricular hypertrophy (Figure 51-8).

FIGURE 51-6 Distribution of left ventricular wall thickness in 300 highly trained black male athletes and 300 white male athletes of similar age, size, and sporting caliber demonstrating that a significantly higher proportion of black athletes exhibit a wall thickness >12 mm compared with white athletes (18% vs. 3% as indicated by A and B, respectively).

(From Basavarajaiah S, Boraita A, Whyte G, et al: Ethnic differences in left ventricular remodeling in highly-trained athletes relevance to differentiating physiologic left ventricular hypertrophy from hypertrophic cardiomyopathy, J Am Coll Cardiol 51[23]:2256–2262, 2008.)

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