Efforts to reduce the incidence of sudden cardiac arrest and death (SCA/D) in young athletes has led the European Society of Cardiology (1) to recommend electrocardiogram (ECG) screening as part of a pre-participation examination (PPE) of young competitive athletes prior to participation in 2005. Professional bodies around the world have followed this recommendation with statements of their own. With some in agreement including the International Olympic Committee (2); some agreeing but with limitations, such as the Australasian Society for Sports Physicians (3) ; while organizations in the United States have resisted calls for blanket screening (4, 5) . The evidence-base to support inclusion of ECG screening for reducing incidence of SCA and SCD in young athletes has not undergone systematic review. A previous systematic review assessed the effectiveness of ECG screening to detect potentially lethal cardiac disorders, but did not address the impact on SCA, SCD and the potential negative effects of ECG screening (6) .
The provision of a systematic summary of existing data on the outcomes of ECG screening will provide both the public, health care practitioners, and policy makers with vital information about the health effects of ECG screening in these populations when compared with history and physical examination alone.
The aim of this study was to review all available evidence assessing the effect of the addition of ECG screening as part of PPE in young athletic, and military populations on incidence of SCA/D, . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint
The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09. 13.20193706 doi: medRxiv preprint and to synthesize available research to evaluate the effect of the addition of ECG on the occurrence of SCA/D.
This review is part of a project with two objectives: identifying the global incidence of SCA/D in athletes and military members, and evaluating the effect of screening ECG on SCA/D in the same population. It was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)(7) guidelines, and was registered at PROSPERO March 18 th 2019 under CRD42019125560 (8) .
The search strategy was designed in conjunction with a medical librarian experienced in systematic reviews (MS), and the search strategy used combined the dual objectives into a single search. The search strategy is included in the supplementary appendix. We searched MEDLINE, Embase, Cochrane CENTRAL, Web of Science, BIOSIS, Scopus, SPORT discus, PEDro, between 2/22/19 and 3/1/19 and Clinicaltrials.gov on 7/29/19. Review articles and position statements were reviewed for eligible articles (9) (10) (11) . There was no limitation on language or date of publication.
Studies eligible for inclusion were randomized and non-randomized controlled trials, where pre-participation examination including ECG was the primary intervention used to screen . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint
The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint athletes or military 40 years of age or younger. Accepted controls were no screening, usual care, or pre-participation examination without ECG. Age 40 was selected due to the increased incidence of coronary artery disease as cause of SCA/D with increasing age, and the desire to focus on etiologies other than coronary artery disease (10, 12) .
The pre-specified primary outcome was the difference in SCA/D in athletes and military populations screened with ECG compared to control groups not screened with ECG. Secondary outcomes to assess the impact of ECG screening included the rate of screened participants removed from sport/activity for cardiac conditions; rate of participants with abnormal cardiac findings and treated as a result of screening; the proportion of those removed from sport for cardiac conditions, treated and returned to sport. Pre-planned subgroup analysis were considered based on age, gender, race, and by type and level (i.e. elite, scholastic, recreational) of sport played or military role.
Independent dual-investigator article screening, selection, risk of bias (ROB) assessments, and extraction was performed with Covidence (Covidence.org, Veritas Health Innovation, Melbourne, Australia 2018). The primary author (AL) screened all titles, and the second reviewer was from a team of three (CM, NP, VL). Google Translate (translate.google.com, Google LLC, Mountain View, CA) was used for articles in foreign languages when technically possible. When not technically possible, physician translators were used. The Cochrane risk of . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint
The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint bias tool (13) , native to Covidence was used for ROB assessment. Disagreements were resolved by discussion with primary author (AL), and the second reviewer.
Meta-analysis was performed with the statistical package native to Review Manager (Cochrane Collaboration, London, UK) using the random-effects Mantel-Haenszel method based on the clinical heterogeneity within the included studies(14). Data are presented as relative risk with 95% confidence interval in those screened with ECG compared with those not screened with ECG where possible. Heterogeneity is reported with summary statistics I 2 and Chi 2 , with prespecified values of <30% considered low; 30-70% considered moderate; and >70% considered high. A p-value of 0.10 or lower for Chi 2 statistic was indicated statistical heterogeneity.
Sensitivity analysis and publication bias assessment (e.g. funnel plot asymmetry) were planned but not performed due the small number of included studies.
No funding was received for the completion of this project.
After removal of 10,780 duplicates, and addition of a further 11 titles after hand search, 20,059 titles and abstracts were screened from database searches, and additions from review of recent review articles. Full text screening was carried out on 322 articles, four of these met criteria for inclusion ( Figure 1 ).
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All included studies were non-randomized controlled studies. Three were on athletes (15) (16) (17) and included a total of 6,431,380 subjects, and 1 was in military males only(18) including 5,257,792 subjects. Three studies included a historical control group, comparing the rate of SCD in a control cohort prior to the implementation of ECG screening, to an intervention cohort after ECG screening began (15, 17, 18) . No studies were identified which reported an outcome of SCA. Two studies were included in meta-analysis, both on athletes , and in both it was unclear if the historical control group received a screening PPE, or no examination (15, 16) . In the two studies not included in meta-analysis, one including only military males (18) , and one in athletes(16) compared the rate of SCD in a cohort who had been screened with PPE including ECG, with the rate in a cohort that received a PPE without ECG. Full descriptions and characteristics of these four studies are presented in the supplementary appendix.
We found no studies reporting data on our secondary objectives. Corrado, et. al., (2006) do report observational data on a subgroup of their intervention cohort which received further testing after initially abnormal ECG screening. Subgrouping by level of athlete, age, sex, race was not possible based on the reported data in any of the included studies.
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The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint All included studies were found to have either unknown, or high risk of bias in the large majority of categories evaluated (Table 1) . No included studies reported funding which was determined to increase their risk of bias. Further details on the risk of bias determination is included in the characteristics of included studies table in the supplementary appendix. Table 1 : Risk of bias in included non-randomized trials in objective 2; based on Cochrane risk of bias tool • Signifies low risk of bias; •signifies unclear risk of bias; •signifies high risk of bias Effectiveness of ECG screening Corrado, et. al. (2006) reports an analysis on SCD in athletes in the Veneto region of Italy. The authors report a primary outcome of an 89% decrease in incidence of SCD after the implementation of ECG screening program for athletes in 1982. This is done by comparing a two-year time period prior to the initiation of screening (1979-80), to the final two years of the screening period (2003-04). In our analysis, data from 23 years of athletes screened with ECG compared with the three years of athletes not screened with ECG showed a 63% decreased risk in the ECG screened group (RR 0.37; 95%CI 0.20 to 0.69). 
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The copyright holder for this this version posted September 14, 2020. [16] [17] [18] [19] was found to be 0.89, and 25-29 was found to 1.04. These were described as nonsignificant, with only the point estimates, and no confidence intervals reported. The abstract is unclear as to whether the statistical method used was relative risk or odds ratio, making interpretation of the findings difficult. No extractable data were present. We were unable to find a published article based on the abstract by Abacherli, et. al. and attempts to obtain additional data from the lead author were unsuccessful. Maron, et. al. (2009) , in comparing a cohort of U.S. athletes in the state of Minnesota who have undergone PPE without ECG screening, with a proportion of ECG screened athletes from the . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint
The copyright holder for this this version posted September 14, 2020. Two studies (15, 17) including athlete participants were included in meta-analysis ( Figure 2) .
The results show a relative decrease risk of 42% for SCD in athletes screened by ECG but uncertainty was high, with a potential 77% relative decrease to a 45% relative increase in those The authors did not describe the treatment rendered to athletes with positive screening ECG beyond the further diagnostic studies used and did not report on athletes returning to sport after treatment.
For the primary outcome of SCD we judged the evidence to be of very low certainty due mainly to high risk of bias, serious inconsistency, and serious imprecision.
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The copyright holder for this this version posted September 14, 2020. Very Low *Summary of decisions on quality of the evidence: Study design: Non-randomized historically controlled trials at high risk of bias Risk of bias: Very serious concern. Downgraded for significant risk of bias in these historically controlled trials, including in categories of randomization, allocation, blinding and sequence generation, as well as risk of significant confounding due to the historical nature of the studies. Inconsistency: Serious concern. Based on the differences in the estimate of effect and the high heterogeneity with I 2 of 71%, and significant Chi 2 p value of 0.06. Indirectness: No concern. The studies included evaluate the event of interest, in the population of interest. Imprecision: Serious concern. Downgraded for wide confidence intervals despite meeting the optimal information size. With the calculated event rates in these combined studies, a power analysis with p=0.05, and Beta=0.80, a total of 3,177,808 [1,548,556 per group] is suggested for a randomized trial. Publication Bias: not evaluated due to small number of studies. Other factors: There is likely significant confounding which has occurred in these trials. The confounding present is likely to have increased the effect estimate.
Our systematic, pre-registered, comprehensive, and up-to-date review found very low-quality evidence that ECG screening decreases risk of sudden cardiac death in young athletes and . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint military members. However, caution is needed when considering this finding. Firstly, we were able to perform meta-analysis only with two studies. The absolute risk reduction from pooling these studies was 0.00157%. Using a single year assessment (19) , this would result in a number needed to screen to prevent one death in one year of 63,694. Secondly, only one of the four studies included reached statistical significance when evaluated the effect of ECG screening on SCD, and the remaining studies report confidence intervals which include both considerable decreased and increased risk with ECG screening. Thirdly, the findings of one study are based on unpublished data (18) . And fourth, due to high risk of bias, high heterogeneity and poor precision of effect estimates, the overall certainty of evidence on the effectiveness of ECG screening was judged to be very low. Taken together, we have very low confidence that our findings would not change substantially with further high-quality research.
The existing evidence base to support the use of ECG screening to prevent SCD in athletes is largely confined to the data presented in the Corrado, et. al. (2006) article included in the review. There are significant methodologic concerns about this article, including the inherent bias, and likely confounding present, when comparing a small historical control group to a much larger intervention group some 20 years later. There have also been concerns raised about the transparency of the data reported, and further follow up data on the Italian screening program (20) . While there have been no recent controlled studies published, two recently published cohort studies may call into question the ability of screening athletes to prevent SCA/D. Both report on cohorts of mostly male, professional soccer players who underwent ECG screening as part of pre-participation examinations (21, 22) . Both reported results with . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. for history alone, 2% with physical exam alone, and 3.4% with ECG alone. Sensitivity with ECG was reported as 100% compared to 15.4% for history, and 7.7% for physical exam.
As demonstrated in this review, there remains little trial data to compare information on how ECG screening affects athlete's removal from sport, follow up treatment, and potential return to sport. There is cohort data on some of these outcomes, the most notable again being from the included Corrado, et. al. (2006) article which reports on a subgroup of the screened athletes . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint
The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint included, with 9% found to be abnormal and receiving further testing, ultimately resulting in 2% excluded from sport. A 2014 scientific statement from the American Heart Association (27) details a selection of published articles on ECG screening cohort studies, with no control groups and community ECG screening projects in athletes 12-25 years old. Articles reviewed report abnormal ECG rates from 2.5-25%, further testing of 2.5-24%, and disqualification from sport rates 0f 0.2-2% of those screening. More modern cohort studies referenced above (26, 28) comparing history and physical exam to additional ECG screening in the same cohort of patients have shown lower levels of initially positive results in ECG screened athletes to those completing the American Heart Association(29) history questionnaire, and physical exam alone.
It is difficult to compare how these findings affected further testing and treatment, as all subjects received history, physical, and ECG screening interventions. Drezner, et. al. (2016) report the identification of 0.25% of athletes with a serious cardiac condition after full evaluation in collegiate athletes in the United States (26) . Drezner, et. al. (2016) also report an average of 2.6 days out of sport to evaluate those with ECG abnormalities on screening. It is also notable, that within studies using ECG screening and reporting the cardiac abnormalities identified, that Wolff-Parkinson-White syndrome is often far and away the most frequent finding, often making up the majority of identifiable cardiac conditions considered serious (26, 28, 30) , which is of questionable significance when attempting to prevent SCA/D (31) .
Over the past decade, refinement of the ECG criteria for diagnosing these potentially lethal cardiac conditions has continued to improve the sensitivity, and decrease the false positive rates (32) . While these advancements in the diagnostic capability of ECG screening have . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint
The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint occurred, there have been no controlled trials published on independent cohorts of patients comparing the ability of ECG to PPE with history and physical alone to prevent SCA/D. There is great need for a prospective study which tests the utility of screening ECG to prevent SCA/D in athletes. Carrying out a prospective study on this topic would be a daunting task, and with the rarity of the condition may not be possible. To undertake such a project, one could consider randomizing clusters of high school and collegiate athletes to ECG screening with PPE compared to PPE. A model such as this may be even more feasible in the military, where large numbers of recruits enter into service every year. It would be possible to randomize subjects in this setting, which could lead to the data needed. Short of these two trials, it should be possible to compare the rates of SCA/D in a cohort study in the U.S. Many universities have transitioned to testing their athletes, and comparing the rates of SCA/D in these universities, to comparable universities who do not screen, would be technically feasible.
We believe the strength of this review lies in the breadth of the search for controlled trials of any kind which report on the ability of screening ECG in athletes or military members to prevent SCA/D. The primary limitation of our review is the low quality of evidence provided by the included studies leading to uncertainty for decision making. The limitations lie in both the paucity of, and the poor quality of the identified research reporting outcomes on SCA/D in our population.
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The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint There is very low-quality evidence ECG screening decreases risk of sudden cardiac death in young athletes and military members. Decisions regarding the use of screening ECG need to consider evidence here that ECG screening could also increase risk of sudden cardiac death. We have very low confidence that our findings would not change substantially with further highquality research.
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The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint Acknowledgements: This work was previously presented in abstract form at the AMSSM annual meeting 2020, and as a master's dissertation at Oxford University.
Competing Interests: No authors report competing interests with this work Funding: No funding was received for this work What is already known:
• Multiple cardiology and sports medicine professional organizations have made differing recommendations on the use of the electrocardiogram (ECG) in screening in young athletes. • ECG screening of athletes has been shown to be more effective than history and physical examination alone to diagnose conditions which put the athlete at risk for sudden cardiac arrest or death (SCA/D). • Few data are available to answer the question of the effectiveness of ECG screening in preventing SCA/D in young athletes.
What are the new findings:
• We identified only four published accounts (3 full papers and one conference abstract) of non-randomized trials reporting on the effectiveness of ECG screening to prevent SCA/D in young athletes and military members. • The quality of the published evidence is judged to be of very low quality to answer the question of whether ECG screening prevents episodes of SCA/D. • No difference was identified between screened and non-screened athletes in data synthesis of two of the published articles eligible for meta-analysis (RR 0.58; 95%CI 0.23, 1.45).
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. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Studies included in quantitative synthesis (meta-analysis) Screening ECG = 2 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint
The copyright holder for this this version posted September 14, 2020. . https://doi.org/10.1101/2020.09.13.20193706 doi: medRxiv preprint Figure 2 : Meta-analysis of studies reporting data on outcomes of sudden cardiac death in athletes screened with ECG (experimental), compared to athletes not screened with ECG (control)
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