One November morning in 2016, Mr Ng Kok Seng's heart stopped beating for six seconds but the retiree, then 62, did not notice and carried on with his daily activities.
He found out only later in the day after a tiny device implanted in his chest, known as an Insertable Cardiac Monitor (ICM), alerted a team at the National University Health System (NUHS), which called him and told him to go for an emergency consultation.
Mr Ng learnt he had atrial fibrillation, a common heart rhythm disorder, which causes the organ to beat much faster than usual - over 300 beats per minute, up from the usual 60 to 80. It is also responsible for about one-quarter of all strokes.
The device was inserted into Mr Ng after he had a stroke in October 2016.
Dr Seow Swee Chong, a senior consultant at the National University Heart Centre's Department of Cardiology who treated Mr Ng, said his experience is common among patients with atrial fibrillation. "Around 80 per cent to 90 per cent of our patients who have atrial fibrillation don't have any symptoms," he said.
Typically, atrial fibrillation is diagnosed using an electrocardiogram (ECG).
Dr Pipin Kojodjojo, another senior consultant at the Department of Cardiology, said, however, that this method has problems. As a majority of patients with the disorder do not have symptoms, they are unaware of their condition and do not get checked. The ECG will appear abnormal only if atrial fibrillation occurs during the test.
What is atrial fibrillation?
Dr Pipin Kojodjojo, senior consultant at the National University Heart Centre's Department of Cardiology, estimated that 50,000 Singaporeans have atrial fibrillation, although the actual figure could be higher.
It is a chronic and progressive condition, which means that with time, it will recur more frequently until the heart is unable to beat regularly again. It affects around 15 to 20 per cent of those over the age of 80.
Those who have certain conditions including obesity, hypertension and obstructive sleep apnoea are also at higher risk of atrial fibrillation, which is responsible for about one-quarter of all strokes. Atrial fibrillation-related strokes are also typically more disabling, said Dr Pipin.
He added that Singapore has seen a significant increase in the proportion of stroke patients with atrial fibrillation - 20.6 per cent in 2016, up from 16 per cent in 2007. Citing the growing number of patients requiring treatment for the condition here, he said: "It's really a major healthcare issue for us, and even more so in future."
"Atrial fibrillation can come and go... if you just had a check-up yesterday, it doesn't mean you can't have the condition today," said Dr Pipin.
So in 2015, the Heart Rhythm and Stroke teams at the National University Hospital and National University Heart Centre did a study to find a better way to detect atrial fibrillation.
A total of 205 patients like Mr Ng, who had strokes with no known cause, were implanted with ICMs.
The device, which is roughly the length of an AAA battery but flatter, takes around three minutes to be inserted into a patient under local anaesthesia via injection.
ICMs have a battery life of about three years and can record and analyse patients' heart rhythms throughout the day.
In the event of a heart rhythm disturbance, a team at NUHS is alerted. Once the condition is detected, appropriate treatment can be done to reduce the risk of stroke.
Atrial fibrillation was detected in about 12 per cent of the patients who had ICMs inserted, whose condition might have otherwise been missed.
The study also found that ICMs are more than seven times more effective than traditional methods in detecting atrial fibrillation with no symptoms.
Dr Seow said accurate diagnosis is important as without a diagnosis of atrial fibrillation, stroke patients are typically discharged on weaker blood thinners such as aspirin.
However, such medication is ineffective to prevent strokes caused by atrial fibrillation, which requires specific blood thinners called oral anticoagulants.
Atrial fibrillation can come and go... if you just had a check-up yesterday, it doesn't mean you can't have the condition today.
DR PIPIN KOJODJOJO, senior consultant at the National University Heart Centre's Department of Cardiology
A patient whose atrial fibrillation is undetected is thus at higher risk of getting a second stroke.
Dr Seow noted that all the patients in the study who had their condition detected were given such medication and have not been hit by a second stroke.
In Mr Ng's case, after his ICM alerted Dr Seow that he had an abnormal heart rhythm, he had a pacemaker inserted and was given anticoagulants.
The retiree said: "Because of the ICM, the atrial fibrillation was detected... It saved me."
Given its success, Ng Teng Fong General Hospital will also be introducing ICMs to detect atrial fibrillation in patients with unexplained stroke. This will start in December.
NUHS will also be expanding the operating hours of its nurse-led clinic for atrial fibrillation at Bukit Batok Polyclinic to better facilitate management of the condition.