Monday, 11 June 2012

The case for ECG screening

By Andy Ho, The Straits Times, 9 Jun 2012

IN THE first four months of this year alone, four cases of sudden cardiac death (SCD) among the young were reported in the media.

They included a 21-year-old full-time national serviceman (NSF), two 18-year-olds and a 10-year-old schoolboy.

Such tragedies have also been seen elsewhere. Exertion can trigger heart rhythm problems and cardiac arrest even in the young who are apparently fit but have an undetected heart condition. So the circumstances in which SCD occurs are usually those where physical exertion is involved. Thus, SCD appears to be more common in athletes or NSFs.

But without a mandatory registry of SCD, no one knows its real prevalence. Different expert estimates vary widely. For example, in Italy, the SCD rate in the Veneto region fell from 3.6 per 100,000 athlete-years in 1979, before electrocardiogram (ECG) screening was mandated, to 0.4 per 100,000 athlete-years in 2004 with ECG screening (which was mandated from 1982).

The huge drop pointed to the utility of ECG screening in Italy rather than a real drop in SCD rates, which would depend mostly on genetic and familial factors.

However, recent data suggests a rate of 0.4 per 100,000 athlete-years in Minnesota high school athletes who had not been ECG-screened. This means they were at nine times less risk than Italian athletes who had no ECG screening in 1979, but the same risk as Italian athletes who were ECG screened in 2004.

One reason may be that their genetic causes differ. In the Italian case, the main cause was 'arrhythmogenic right ventricular cardiomyopathy' (a hereditary electrical fault in the heart). This was rare in Minnesota, where 'hypertrophic cardiomyopathy' (a hereditary structural fault in the heart) was the main cause of SCD.

Also, in Italy, the age group studied ranged from 12 to 35 years while the US data covered only 13- to 19-year-olds. Such population differences must be kept in mind if used to estimate rates here.

Most victims did not have a history of heart symptoms and had passed physical examinations by a physician whenever these were performed.

A clinical examination will identify only 2 to 6 per cent of those at risk, according to one study. Adding an ECG test - with the patient at rest, without a treadmill run to stress the heart - raises the detection rate to 50 per cent.

Right now, the pre-enlistment medical exam for NS routinely includes the ECG at rest, and further investigations if abnormalities are detected. So the question is whether ECGs should be mandated before participation in competitive sports in Singapore.

The Italian experience would seem to suggest so. Yet a study in Israel found a drop in SCD cases - from 4.27 per 100,000 before ECG screening was mandated down to 3.13 per 100,000 athlete-years after ECGs (with a treadmill test) were mandated - for athletes from 1997.

This was not a statistically significant drop. Nevertheless, the European Society of Cardiology recommends including ECGs.

However, the American Heart Association recommends against mandating ECGs. But the US debate is largely one about the cost-effectiveness of mandatory ECGs for a rare condition within a huge US population of athletes.

Moreover, ECG screening does give rise to lots of false positives. That is, it says you have the problem when you actually don't.

Then, there are also false negatives, where you do have the problem but the test fails to pick it up because the heart problem doesn't cause abnormal ECG readings.

A 2008 meta-analysis showed that at-rest ECGs have a 40 per cent false-positive rate and a 4per cent false-negative rate, considered a failing grade for a screening test. The problem with a false positive is that it leads to further testing - which may be non-invasive like ECG, but occasionally also risky and invasive, like cardiac catheterisation.

In terms of cost-effectiveness, economists measure the cost per year of life saved by a test. Since the young are involved, many years of life may be potentially saved. A 2010 estimate puts it at US$50,000 (S$64,000) to US$100,000 per year of life saved by ECGs conducted on young athletes. This is comparable to flu shots for children at US$112,000 per year of life saved.

But if ECG screening is applied to a small group at higher risk of SCD because of more frequent and greater physical exertion, such cost considerations disappear. Any higher-risk group is likely to benefit from ECG screening because of logically higher SCD rates within such a sub-group.

For this reason, top-flight professional US athletes in football, basketball and others are all ECG-screened, along with treadmill tests. This component tests the heart's behaviour under physical exertion, thus increasing the likelihood of bringing out ECG abnormalities, especially if there were none at rest.

And in these highly conditioned professional athletes at high levels of competition, there is a slow but sure rise in SCD rates with age. Thus older participants in marathons and triathlons here should be screened too, with not just the ECG at rest but also with exertion on a treadmill.

If your teen is seriously involved in sports or your middle-aged husband is bitten by the marathon bug, consider paying for ECG screening that includes the treadmill stress test as well.

Meanwhile, the reporting of all SCD cases should be mandated. Such a registry will, over time, give experts a better picture of the SCD rate and causes, which will help in its prevention here.

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