Sudden cardiac death (SCD) is a leading cause of sports- and exercise-related mortality, with one study of U.S. competitive athletes showing that 56% of sudden deaths over a 27-year span were related to cardiovascular disease.1 Many of the conditions that predispose individuals to this tragic outcome can be picked up on a resting 12-lead athlete ECG. Trained athletes already have cardiac adaptations from routine, long-term physical activity, which underscores the importance of a careful ECG assessment as part of a larger evaluation. This can help ensure a safe return to sports after a period of illness for those with conditions that place them at high risk for SCD.
ECG Changes in the Athletic Heart
Because regular physical activity and training can cause changes to the heart itself, various professional groups have issued guidance on interpreting an athlete's heart ECG. In 2017, an international group of experts published criteria for ECG interpretation in athletes in the British Journal of Sports Medicine (BJSM),2 and professional societies around the world have since endorsed it. The group called attention to a critical need for "physician education in modern ECG interpretation that distinguishes normal physiological adaptations in athletes from distinctly abnormal findings suggestive of underlying pathology."
They also noted that various hereditary, structural, and electrical disorders have been tied to risk of SCD in athletes, and that most of these conditions can be uncovered by using a resting 12-lead ECG. Guidance from the group divides ECG findings for athletes into three categories: normal, abnormal, and borderline ECG findings.
Normal ECG Findings
The BJSM criteria classify these as training-related changes that represent physiological adaptations to regular exercise. Over time, regular training will induce electrical changes reflective of increases in cardiac chamber size and increased vagal tone. In athletes, the following ECG findings are considered normal:
- Increased QRS voltage for left ventricular or right ventricular hypertrophy
- Incomplete right bundle branch block (RBBB)
- Early repolarization
- ST-segment elevation
- Sinus bradycardia or arrhythmia
- Ectopic atrial or junctional rhythm
Abnormal ECG Findings
Abnormal ECG findings in athletes are not related to training or an expected adaptation to exercise, the BJSM document notes. These findings include:
- T-wave inversion
- ST-segment depression
- Prolonged QT interval
- Pathologic Q waves
- Complete left bundle branch block
- QRS duration of 140 ms or more
- Type 1 Brugada pattern
Borderline ECG Findings
The authors of the BJSM criteria list the following as borderline ECG findings in athletes:
- Left or right axis deviation
- Left or right atrial enlargement
- Complete RBBB
Any one of these findings alone is unlikely to signal pathological cardiovascular disease in an athlete, the authors say, but the presence of at least two may be an indication to dig deeper.
Interpreting an Athlete ECG
Any one of the findings described on its own would not warrant further evaluation as long as the athlete is asymptomatic and has no family history of inherited cardiac disease or SCD, according to the BJSM guidance. However, if at least two are present, physicians should investigate further to search for pathologic cardiovascular disorders.
Keep in mind that ECG alone may not be sufficient to capture all of the conditions that place athletes at risk for sudden death. "Specifically, ECG can suggest or detect cardiomyopathies, ion channelopathies, myocarditis, and ventricular pre-excitation, yet other causes of SCD in young athletes, such as anomalous coronary arteries, premature coronary atherosclerosis, and aortopathies, are not readily detected by ECG," the guidance states. "Thus, even if correctly interpreted, an ECG will not detect all conditions predisposing to SCD, and evaluation of cardiovascular symptoms, a concerning family history, or abnormal physical examination requires a more comprehensive investigation."
Resting vs. Ambulatory ECG
Although most of the conditions that place individuals at risk for SCD can be picked up on a resting 12-lead ECG, some situations may warrant ambulatory monitoring, according to the BJSM guidance. They listed the possibility of such monitoring in athletes with the following abnormal ECG findings:
- Profound sinus bradycardia (resting heart rate ≤30 bpm or a sinus pause ≥3 s)
- High-grade atrioventricular block
- Ventricular arrhythmias
- Atrial tachyarrhythmias
- Profound first-degree heart block (in certain clinical situations)
- Multiple premature ventricular contractions
The authors note that multiple premature ventricular contractions are rare, found in less than 1% of athlete ECGs, and that how far physicians should go in evaluating them "is controversial and excluding pathology may be difficult."
"At a minimum, an ambulatory Holter monitor, echocardiogram, and exercise stress test should be performed," they advise. "The availability of modern small, leadless ambulatory recorders allows for longer ECG monitoring, including during training and competition, to exclude complex ventricular arrhythmias."
Return to Play for Those with High-Risk Conditions
Providers may advise individuals who have underlying conditions that place them at high risk for SCD to forgo exercise and athletic competition. But this precludes them from deriving the myriad benefits that come with exercising, and some studies suggest that a return to sports is possible if done carefully. For instance, as reported by TCTMD, two studies presented at the 2023 annual meeting of the American College of Cardiology (ACC), suggest that patients with genetic heart conditions like hypertrophic cardiomyopathy and long QT syndrome can—with expert guidance—participate in sports or vigorous physical activity with a low rate of adverse events.3
Professional societies have provided some guidance around this issue as well, with ECG playing a key role. In 2015, the American Heart Association and the ACC issued eligibility and disqualification recommendations for competitive athletes with cardiovascular abnormalities, and of note, provide advice on returning athletes who have developed myocarditis back to their sports.4 Before resuming physical activity, these individuals should undergo a resting echocardiogram, 24-hour Holter monitoring, and an exercise ECG at least three to six months after the initial event.
More recently, in 2020, the European Society of Cardiology (ESC) released guidelines on sports cardiology and exercise in patients with cardiovascular disease, addressing a return to physical activity in several scenarios.5 For competitive athletes who develop an acute coronary syndrome, for example, the authors recommend an echocardiogram, an exercise test with 12-lead ECG, or a cardiopulmonary exercise test before resuming sports participation.
For patients with myocarditis, the ESC recommends a comprehensive evaluation that encompasses imaging studies, an exercise stress test, and a Holter monitor to provide information on risk stratification. A return to sports could be considered, the authors say, if there are no symptoms and no abnormalities on the various tests.
Remaining Vigilant When Resuming Activity
Even when athletes with high-risk features have undergone a thorough evaluation that includes a resting or ambulatory 12-lead ECG, the potential for SCD remains. Athletes in these situations and their care providers should have plans in place to ensure a quick response should they experience problems during competitions.
This issue took on greater importance during the COVID-19 pandemic once it became apparent that SARS-CoV-2 infection was leaving signs of damage in the heart. Several groups issued guidance on how to safely return athletes to competition in the wake of infection, with ECG serving as an integral part of cardiac screening.
In October 2020, leadership from the ACC's sports and exercise cardiology section provided guidance that includes tailored algorithms for competitive high school athletes, recreational masters-level athletes, and adult competitive athletes, with testing recommendations dependent on COVID-19 symptom severity.6
Despite the key role of diagnostic ECG in helping athletes at all levels safely return to sports, regardless of prior history of COVID-19, some serious cardiac issues may slip through, underscoring the need to remain vigilant and prepared should an athlete suffer a cardiac event.
The ACC group provides a message that resonates beyond the context of the pandemic. "It is of paramount importance that we do not lose sight of the value of thoroughly rehearsed emergency action planning that ensures timely response to the athlete who has collapsed with immediately available automated external defibrillation therapy," they say, adding that these efforts "represent our best strategy to save lives."
1. Maron BJ, Doerer JJ, Haas TS, et al. Sudden deaths in young competitive athletes: analysis of the 1,866 deaths in the United States, 1980-2006. Circulation. February 2009;119(8):1085-1092. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.108.804617
2. Drezner JA, Sharma S, Baggish A, et al. International criteria for electrocardiographic interpretation in athletes: consensus statement. British Journal of Sports Medicine. April 2017;51:704-731. https://bjsm.bmj.com/content/51/9/704
3. O'Riordan M. Studies support (careful) return to sport for athletes with genetic conditions. TCTMD.com. https://www.tctmd.com/news/studies-support-careful-return-sport-athletes-genetic-conditions. Accessed June 2, 2023.
4. Maron BJ, Udelson JE, Bonow RO, et al. Eligibility and disqualification recommendations for competitive athletes with cardiovascular abnormalities: task force 3: hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy and other cardiomyopathies, and myocarditis: a scientific statement from the American Heart Association and American College of Cardiology. Circulation. November 2015;132(22):e273-e280. https://www.ahajournals.org/doi/full/10.1161/CIR.0000000000000239
5. Pelliccia A, Sharma S, Gati S, et al. 2020 ESC guidelines on sports cardiology and exercise in patients with cardiovascular disease: the task force on sports cardiology and exercise in patients with cardiovascular disease of the European Society of Cardiology (ESC). European Heart Journal. January 2021;42(1):17-96. https://academic.oup.com/eurheartj/article/42/1/17/5898937
6. Kim JH, Levine BD, Phelan D, et al. Coronavirus disease 2019 and the athletic heart: emerging perspectives on pathology, risks, and return to play. JAMA Cardiology. October 2020;6(2):219-227. https://jamanetwork.com/journals/jamacardiology/fullarticle/2772399