Sudden cardiac arrest: tracking a silent killer
Sudden deaths from cardiac arrest areon the rise, even among athletes, and doctors are struggling towork out why, writesElaine Yau
The unfortunate demise of Hong Kong resident Andy Naylor at a triathlon race two weekends ago has brought attention to sudden death, cases of which are rising in this city, figures indicate.
The 43-year-old, a top local runner and Hong Kong police superintendent, "experienced distress" near the end of the 3.8-kilometre swim leg in the Hudson River during the Ironman US Championship in New York, according to race organisers. The results of an autopsy are pending.
Naylor's death comes a year after two athletes died of sudden cardiac arrest in the 1.5-kilometre swimming portion of the New York City Triathlon, also in the Hudson River.
Minneapolis Heart Institute cardiologist Kevin Harris published a study in 2010 in
The Journal of the American Medical Association analysing the results of 2,971 USA Triathlon-sanctioned events held between January 2006 and September 2008, involving nearly 960,000 participants.
During that period, 14 participants died. Thirteen of them, aged between 28 and 65, died while swimming and another while cycling. Autopsies identified cardiovascular abnormalities as factors behind seven of nine swimming deaths.
Harris' study found a sudden-death rate of 1.5 per 100,000 competitors in triathlons, while the rate in marathons over a 30-year period was 0.8 per 100,000.
Evidence suggests that exercise seems to trigger or cause sudden cardiac death in athletes with underlying heart disease, says Dr Timothy Noakes, a sports science professor at the University of Cape Town in South Africa.
A consultant cardiologist with Yan Chai Hospital in Tsuen Wan, Dr Stephen Tam Kin-ming, says about 20 per cent of sudden-death cases are caused by heart conditions that have existed since birth, such as coronary artery anomalies and hypertrophic cardiomyopathy, where a portion of the heart muscle becomes thicker without any obvious cause.
These are widely believed to be the leading causes of death, particularly in young athletes.
Other victims have structurally normal hearts, but die of heart rhythm disorders. Ventricular tachycardia (fast heart rhythm) and ventricular fibrillation (irregular heart rhythm) can trigger acute coronary syndrome, where blood supply to the heart is suddenly blocked, causing sudden death.
"[These victims] haven't had any ultrasound tests and the heart problem remains hidden. Sports veterans who are susceptible to sudden cardiac death usually suffer from hidden heart disease," says Tam, who is also the chairman of the Hong Kong Public Hospitals Cardiologist Association.
Recent studies shed light on the role of genetics in underlying heart conditions. An
American Journal of Cardiology study published online last month confirmed the link between the sickle-cell trait - a genetic condition behind a blood disorder - and cardiac death among young African-American male athletes, especially football players.
The sickle-cell trait affects about 8 per cent of the American population.
A large and comprehensive investigation by an international team of researchers, published last year in
PLoS Genetics, discovered a variation in the human DNA sequence that was linked to a significant increase in the risk of sudden cardiac death.
"Our analysis suggests if you have one copy of this variant, your increased risk is double that of someone who doesn't," wrote lead author Dan Arking of Johns Hopkins University. "If you have two copies, having inherited one from each parent, you have almost a fourfold increased risk of sudden cardiac death."
Not all cardiac arrests are caused by underlying or genetic heart disease. In Hong Kong, cardiologists say, lifestyle factors, such as fast-food diets and the lack of physical activity are greater culprits. Because sudden cardiac arrest is so often linked to coronary artery disease, the risk factors are similar.
The rising number of sudden deaths in Hong Kong is mirrored in the spike in deaths caused by coronary heart disease - the narrowing of small blood vessels - which has gone up by some 50 per cent from a decade ago. Department of Health figures show that 6,400 people died of heart disease in 2009, accounting for 15.6 per cent of all deaths in Hong Kong. One-third of these fatalities were sudden.
And cardiologist Tam says the victims are getting younger and younger. "While people aged 50 got it in the past, sufferers are just 30 or 40 [years old] now. The rising incidence among young people has to do with poor lifestyle."
A recent report by the cardiologist association cited taxi and commercial drivers as among those in high-risk occupations where workers are predisposed to die suddenly.
Figures retrieved from local newspaper reports showed that a total of 24 local drivers aged between 29 and 81 - half of whom were cabbies - died abruptly in the 12 months to May this year.
"Many drivers are living high-risk lifestyles with irregular mealtimes, a diet heavy in salt, sugar and fat, and a sedentary lifestyle," Tam says.
"Eighty per cent of sudden-death cases [are caused by] coronary heart disease, [which in turn is] caused by smoking, stress, poor diet, obesity and lack of exercise … Besides, [heart attacks] may occur in coronary-heart-disease sufferers during strenuous exercise such as a marathon," he adds.
Professor Yu Cheuk-man, head of Prince of Wales Hospital's cardiology unit, says the symptoms are unnoticed in most sudden-death cases. "Those with [irregular heartbeats] will feel heart palpitations and pass out gradually. Some die on the first attack."
Heart attack symptoms include intense chest pain, heart palpitations, cold sweat, dizziness and shortness of breath. But Duncan Ho Hung-kwong, a cardiology specialist with the Hong Kong Sanatorium and Hospital, says victims rarely show these signs.
"The symptom of chest pain extending to the upper jaw and arms - always mentioned by people and the media - is only seen in very few people. Any kind of [discomfort] can be a sign of heart attack, like shoulder pain and back pain.
"It's likely that sufferers misinterpret it as only muscle pain. The symptoms can be mild, like those for a cold," Ho warns.
One of his recent patients felt nauseous while walking, after eating breakfast. The patient went home, vomited and felt better. Still, he went to hospital as a precaution.
"We did an electrocardiogram [which records the heart's electrical signals] and it turned out he had just suffered a heart attack," says Ho.
He says everyone should get at a check-up as a precaution, especially those who have a family history of heart disease.
The tests include an ultrasound for the heart-thickening condition, a scan of the coronary arteries' size as well as a stress test where patients run on a treadmill while connected to an electrocardiogram, which tracks how the heart responds to stress and exercise.
Chinese University researchers have been studying Hongkongers who have suffered sudden heart attacks since 2007, with more than 2,000 people having been analysed so far. Yu, from Prince of Wales, says the study aims to explore the effects of high-risk factors on coronary heart disease.
To their surprise, the researchers found that half of the Hongkongers had only one or zero high-risk factors before they were stricken. In contrast, it takes two or three high-risk factors for a foreigner to have a heart attack.
"We do not know the reason for the discrepancy … Maybe it has to do with our rice-based diet which is heavy in carbohydrates," Yu says. "We are still recruiting patients for the study and will study what predisposes them to heart attacks."