Patients who have been diagnosed with a cryptogenic stroke (i.e. no usual cause of the stroke, especially for sufferers aged under 60) may benefit from this test. The culprit for the stroke may be a small hole in their heart.
As foetuses in the womb, almost all of us have a foramen ovale, an opening between the right and left upper chambers of the heart. The majority of them close soon after birth. However, a quarter of the population may be left with a tiny defect (hole) which is called a patent foramen ovale (PFO).
An ordinary transthoracic echocardiogram (TTE) on its own may not pick up this defect.
A blood clot from the leg or veins in the abdomen could travel into the right side of the heart and cross through the small hole into the left side of the heart. From there the clot can migrate to the brain, giving rise to a stroke.
Microbubble testing involves mixing a patient’s blood with a small quantity of air and saline (salt water) in a syringe, and injected it into an arm vein.
The microscopic bubbles, smaller than a red blood cell, generated by this are acoustic, allowing doctors to get an accurate ultrasound picture.
As they pass through the body and enter into the right side of the heart, a TTE can clearly identify microbubbles that cross the intra-atrial septum (where a PFO is usually found).
Depending on the number of bubbles crossing, it is described as a small or large "shunt".
Patients with a PFO registering a large "shunt" will benefit from sealing their PFO with a cardiac closure device. This device is delivered through a vein in the groin into the heart. Patients will be referred to a specialist unit such as Bristol Heart Institute for this procedure, at the decision of their treating stroke physician or neurologist. The operation can be done under heavy sedation or general anaesthetic and usually involves an overnight stay in hospital.
There are virtually no risks to having a microbubble test.