Mandatory Electrocardiographic Screening of Athletes to Reduce Their Risk for Sudden Death

Proven Fact or Wishful Thinking?

Definitions

The Israel Sport Regulations on Athletes Medical Testing, enacted in 1997, calls for the mandatory medical screening of all athletes in Israel (6). By law, to be allowed participation in sporting activities, every athlete in Israel must undergo medical screening by specifically accredited physicians. The Israel Sport Law defines athletes requiring screening as “individuals who engage in sportive activity at any level of physical endurance” (6). Only certified physicians who have participated in a specialized accreditation course can perform this screening (6).

The obligatory screening, mandated for all athletes, includes a medical questionnaire, physical examination, resting ECG, and Bruce-protocol exercise testing. Medical assessment, including resting ECG, is repeated on a yearly basis. In addition, athletes 17 to 34 years of age must undergo exercise stress testing every 4 years, whereas yearly exercise tests are required for athletes who are 35 years of age older or for athletes of any age competing at the national level. Beginning in 1999, all exercise tests were required by law to be symptom-limited tests.

At the discretion of the certified screening physicians, athletes with abnormal screening test results are referred to expert cardiologists, cardiac electrophysiologists, or both for additional testing and consultation. The final decision regarding certification or disqualification is eventually made based on the expert consultants' opinions.

Estimation of the number of sudden cardiac death events in athletes

The sudden death of a competitive athlete is a dramatic event that generally is covered by the media. Therefore, we limited our analysis to sudden death events in competitive athletes. As in previous studies (1), we systematically screened the general media for reports of sudden death in athletes. For that purpose, we assigned 2 professional media researchers to perform a systematic day-by-day search of the 2 leading newspapers in Israel (Yediot Aharonot and Maariv) (7). Of note, Yediot Ahronot reached 70% of the daily newspaper readership in Israel during the study period, whereas Yediot Ahronot and Maariv combined covered 90% of the readership (8,9). Beginning in September 2009 (and ending in December 2009), the professional media researchers scrutinized the newspapers published daily between January 1985 and December 2009. This 24-year period was targeted because we wanted to compare 2 equally long periods. Consequently, because the law mandating pre-participation ECG screening of athletes became effective 12 years previously (on November 1997) (5), we compared the 12-year period of 1985 through 1997 with that of 1998 through 2009. All the reports of deaths or dramatic medical events in competitive athletes were brought to the consideration of 3 investigators to determine (by consensus) whether the report could be considered as an athlete's sudden cardiac death or cardiac arrest. Sudden death was defined as a witnessed instantaneous death with futile resuscitation. Cardiac arrest was defined as instantaneous collapse with successful resuscitation. Sudden deaths related to trauma were excluded. As in previous studies (4), annual incidence rates were calculated by counting the events in 2-year periods and halving the result.

Estimation of the population at risk

According to the Israeli Sports Authority, the official Israeli sports organization acting under the Israeli Ministry of Sports, the number of registered athletes who engaged in competitive sports during 2009 was 45,000. We extrapolated these data to the growth of the Israeli population who were 10 to 40 years of age during the last 24 years as available from the Israeli Central Bureau of Statistics (10). In addition, because some data suggest that the percentage of the adult population engaging in sportive activities has increased by 50% during the last decade (11), we repeated our calculations of the number of athletes at risk, assuming a gradual doubling of the percentage of athletes over the 24 years of our study.

Statistical analysis

The rate of event was calculated as the number of sudden cardiac deaths in a certain period divided by the estimated number of person-years at risk. We used the parametric bootstrap, assuming no difference between the periods, and Poisson distributions for the observed death counts to compute the p value.

Main findings

We found that the average yearly incidence for a sudden cardiac death event among Israeli competitive athletes was 2.6 events per 100,000 person-years or 1 event per 38,000 athletes per year. These numbers are within the range reported by others (see the following text). Importantly, we found that a mandatory screening strategy including, resting ECG and exercise ECG, had no apparent influence on the incidence of sudden death in athletes.

Impact of mandatory screening on the incidence of sudden death of athletes viewed in the context of previous studies

Figure 2 shows the annual mortality per 100,000 person-years in our study and in the only 2 previous studies—from Italy (4) and from the United States (19)—that evaluated the effects of screening on the mortality of athletes over time. The Italian study (4) (pink graph in Fig. 2) analyzed the effects of a screening strategy that includes baseline ECG recording of all athletes on the mortality rates of those 35 years of age or younger. In that Italian study, the sudden death rate among athletes in the prescreening period was 3.6 per 100,000 person-years, which is similar to the 2.6 per 100,000 person-years finding in our study. The Italian investigators reported that after the onset of screening, the annual rate of sudden death among athletes decreased dramatically. Indeed, the pink graph shows an impressive reduction in the incidence of sudden cardiac death from 3.6 per 100,000 person-years in the prescreening period to 0.4 per 100,000 person-years at the end of the study (from point B to point F in Fig. 2) (4). Note that, in the Italian study, the prescreening period used as a reference value was limited to the 2 years before the enforcement of pre-participation screening (point A to point B in Fig. 2).

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Figure 2

Annual Incidence of Sudden Cardiac Death Expressed per 100,000 Person-Years in the 3 Studies Evaluating the Effects of Screening on the Mortality of Athletes Over Time

The Italian study (4) (pink graph) concluded that electrocardiography (ECG) screening (started in 1982) significantly reduced the incidence of sudden cardiac death by comparing the sudden death in the 2-year pre-screening period (A to B) with the post-screening period (B to F). The present study is depicted by the green graph. We compared the 12 years before screening (C to E) with the 12 years after the onset of mandatory ECG screening (E to G). Had we limited our comparison of the postscreening period to the 2-year period preceding the enforcement of screening in Israel (D to E vs. E to G, as performed in the Italian study), we would have concluded erroneously that screening saved lives of athletes in Israel. The study from Minnesota (19) (yellow graph) shows a low mortality rate in a population of athletes not undergoing systematic ECG screening.

More recently, Maron et al. (19) reported that the sudden death rate among high school athletes over a 23-year period in Minnesota was 1 per 100,000 person-years. That study appears as a yellow graph in Figure 2. The Minnesota sudden death rate of athletes was lower than the rates reported in Italy and in our study, although the ECG examination was not part of the screening strategy used in the United States during that period.

Our study (green graph in Fig. 2) reports the effects of a screening strategy that includes resting ECG and exercise stress testing and started at the end of 1997. There is marked variation in the sudden cardiac death rates that peaks at 8.4 per 100,000 person-years 2 years before the enforcement of screening (point D in Fig. 2). Note that if one compares the sudden death rates during the 2 years preceding the enforcement of screening with the mortality at the end of the study—as was done in the Italian study—one would conclude that our screening strategy is extremely effective for preventing sudden death among athletes because the sudden death rate decreased from 8.4 to 1.1 per 100,000 person-years (p < 0.001) (D to G in Fig. 2). It is only when one reviews the entire study period and compares the 12-year period before screening with the 12-year period after screening (from point C to G in Fig. 2) that it becomes obvious that this apparent mortality reduction is most likely related to a large year-to-year variation.

What is the evidence that mandatory pre-participation ECG screening of athletes prevents sudden death in athletes?

The only evidence that a mandatory screening strategy that includes a resting ECG reduces the sudden cardiac death risk in athletes comes from Italy (4). This Italian study is the basis for current guidelines from the European Heart Society advocating mandatory ECG screening of athletes (2). It is important to note that the conclusions of the Italian study are based on the comparison of sudden death rates of athletes recorded during the 2 years preceding the enforcement of ECG screening with the mortality rates 2 decades later (point A to B vs. B to F in Fig. 2). Had we adopted a similar strategy, we would have reached similar conclusions simply because the sudden cardiac death rates during the 2-year period preceding the enforcement of screening in Israel were unusually high (point D in Fig. 2). In reality, it is likely that this unusually high sudden-death rate observed among Israeli athletes in 1995 and 1996—and the public outcry that followed—led to the legislation mandating ECG screening of athletes in Israel in 1997. Only when one extends the comparison of sudden death rates to include the decade that preceded the enforcement of screening in Israel (and not only the last 2 years) with the decade that followed it does one realize that this mortality reduction is the result of a large variation in mortality rates over longer periods of observation. A similar phenomenon could have occurred in Italy. In other words, it is possible that high mortality rates in Italy in 1980 and 1981 led to the Italian legislation in 1982 and allowed for subsequent mortality reduction. Furthermore, immortal-time bias (20), a methodology flaw frequently encountered in observational studies (21), probably skewed the findings of the Italian study toward concluding that screening improves survival. Studies with time-dependent outcomes in which the test of interest (ECG screening, in this case) and the outcome analyzed (in this case, sudden death) occur during the same period are susceptible to time-dependent bias, also termed immortality bias. All the athletes who died suddenly during the prescreening period never made it to the first screening; consequently, the population of athletes who made it alive to the first screening already represented a selected lower-risk population—and their lower-risk characteristics contributed to the lower mortality rates in the post-screening period.

Study limitations

Data on the effects of ECG screening on mortality rates among athletes are observational and retrospective. This is true for our study and for the Italian and Minnesota studies (4,19). Because of the small number of events, it is possible that the observed nonsignificant difference is the result of a beta-type error. Although the Israel Sport Law mandated ECG screening of competitive as well as noncompetitive athletes, we limited our analysis to competitive athletes because sudden death in the latter is a highly visible event reported in the lay press (the sole source of our study). Although unlikely, we cannot exclude the possibility that screening reduced the mortality rate of noncompetitive athletes. It is also possible that under-reporting of sudden deaths among competitive athletes in leading newspapers led to underestimation of the sudden death risk for athletes. However, there is no reason to believe that the degree of under-reporting varied significantly during the different years of the study period. Moreover, except for the peak observed in 1995 and 1996, the sudden death rates in Israel are within the range reported by others. In addition, the number of athletes was known for the end of the study period, but was estimated for the preceding years on the premise that the fraction of the population engaging in competitive sports remained constant. This assumption could have led to serious errors when estimating the population at risk. However, repeating our calculations after assuming that the fraction of inhabitants practicing sports actually doubled over the years led to similar results. Finally, because of possible inherent shortcomings of the screening process in Israel, our results cannot be extrapolated to other countries.