Around a quarter of us – one in four – walk around with a gap in our hearts. Yes, a literal gap.
It is a remnant of our time in the womb, when when the fetal lung is not yet matured and functioning.
As consultant interventional cardiologist Datuk Dr Yap Yee Guan explains, this is because we received oxygenated blood straight from our mother’s uterus via the umbilical cord.
Therefore, there was no need for our foetal selves to pump blood to our lungs to get oxygenated. In any case, we cannot breathe in the womb as amniotic fluid surrounds us.
A gap in the incompletely-formed atrial septum, which forms the border between the left and right atriums of our heart, provided a natural shortcut to bypass the unneeded right ventricle.
The right ventricle serves to pump deoxygenated blood from the body to our lungs to get oxygenated again. Usually, this gap – called the foramen ovale – closes up at birth, due to certain biochemical and pressure changes in the heart that happen then.
The upper and lower septal portions fuse together to form a continuous wall – the septum, says Dr Yap.
However, he adds: “Even though that is what is suppose to happen, in a quarter of adults – 25% of the general population – this septum remains open.”
He notes that this situation, called a patent foramen ovale (PFO), is not the same as a hole in the heart, which is called an atrial septal defect.
With the latter, there is a literal hole in the heart as the two septal portions remain separate, whereas the former is more of a gap caused by overlapping sections of the atrial septum that flap apart when the atriums contract, because they have not fused together.
The good news is that most people with PFOs usually do not experience any problems due to this gap. However, it has been found that a high percentage of patients who have been hit by a cryptogenic stroke have a PFO.
Says Dr Yap: “Historically, we’ve found that young people with stroke or people with cryptogenic stroke, a large proportion of them – 40% – will have a PFO, as opposed to 25% of the general population.
“It has been suggested previously that perhaps there is an association between young people (roughly those less than 60 years of age) with stroke with no known cause and this condition (PFO).”
A cryptogenic stroke is a stroke for which no cause or origin can be identified.
About 20%-30% of ischaemic strokes, which are caused by a blood clot blocking an artery in the brain and which comprise about 80% of all strokes, are cryptogenic strokes. It tends to occur in younger people as they are less likely to have the known risk factors or medical conditions that can precipitate a stroke.
Having a PFO may increase the risk of having a stroke as a clot that comes from elsewhere in the body can slip through the gap in the atrial septum from the right atrium to the left atrium, and from there to the brain. (All veins eventually lead to the right atrium.)
Dr Yap notes that this association is probably not very surprising as there have been echocardiograms of patients with cryptogenic stroke where blood clots can be seen at the PFO, waiting to get across to the left atrium.
In addition, the increasing prevalence of deep vein thrombosis (DVT), where blood clots form in our veins, has also increased the chances of a younger person with a PFO being affected by stroke.
The clot in the right atrium is most likely to be from DVT, where blood clots form in our veins, then travel to the right side of the heart and lung, resulting in the increased chance of a younger person with a PFO being affected by stroke.
It is estimated that around 10% of general population have experienced DVT, as one of its risk factors is inactivity, e.g. prolonged sitting without moving, like during long-haul flights or at work or play in front of the computer – activities that are becoming increasingly common.
While there is not much one can do to prevent a cryptogenic stroke, there are ways to prevent a recurrent stroke – and all stroke patients have a higher risk of suffering from another stroke.
An effective device
Typically, cryptogenic stroke patients were treated with antiplatelet or anticoagulant therapy, colloquially known as blood-thinners.
However, Dr Yap shares that recent studies have shown that a device, known as a PFO closure device, can decrease the risk of a repeated stroke in cryptogenic stroke patients with a PFO significantly.
The results of three large clinical trials comparing the use of the device versus antiplatelet or anticoagulant therapy in such patients were published last year.
The Reduce trial showed that the risk of a recurrent stroke was decreased by 77% in the group with the device (1.4% absolute risk), compared to those on medication (5.4% absolute risk), after an average of 3.2 years follow-up.
The Close trial saw 6% of those on medication experiencing a second stroke, versus none with the device, after an average of 5.3 years.
And a sub-study of the earlier published Respect trial looking at patients after an average of 5.9 years, found a 45% decrease in risk of a recurrent stroke in the group with the device.
The PFO closure device comprises of two elastic discs made out of a mesh of nitinol (nickel titanium) and dacron cloth, connected with a tether. The two discs block off the gap on either side of the atrial septum.
Dr Yap explains that inserting and placing the device, though a relatively straightforward procedure, requires a highly-skilled interventional cardiologist who has a good understanding of anatomy and the technical challenges of performing the procedure.
It is done by inserting a catheter into the femoral vein of the leg, and passing it all the way up to the right atrium of the heart and through the PFO to the left atrium.
The device is then inserted and passed through the catheter, and deployed when in the right position.
“The procedure is very safe,” he says. “The only thing is that by closing the PFO, there is a slightly higher risk of a transient condition called paroxysmal atrial fibrillation, which is an irregular heartbeat. But most of the time, this is self-limiting – it will disappear by itself.”
While a PFO as the cause of a cryptogenic stroke is easily treatable, Dr Yap stresses that it is essential for someone with a stroke to receive a thorough evaluation from a neurologist – the medical specialist in stroke – to rule out all other more known causes of stroke first.
It is the neurologist who will refer the patient to the cardiologist to investigate the possibility of a previously-unknown PFO, after ruling out all other causes.
Dr Yap emphasises that younger stroke patients have a long life ahead of them, and every possible effort to reduce their risk of a second stroke should be made, especially with the availability of such an effective treatment.