SAN DIEGO—Transcranial Doppler is superior to transesophageal echocardiography (TEE) for the detection of patent foramen ovale (PFO), according to the results of a research study presented at the 2014 International Stroke Conference. Transcranial Doppler also is superior to TEE for stratifying patients with PFO who are at risk of ischemic stroke resulting from paradoxical embolism.
“This [finding] does not mean that everybody can go and pack up their TEE machine,” said J. David Spence, MD, Professor of Neurology and Clinical Pharmacology at the University of Western Ontario in London, Canada. “We still need transesophageal echo to find other causes of stroke from the heart. These techniques are complementary.”
Approximately 25% of the general population has PFO, and the condition is responsible for approximately 5.5% of stroke. The question of whether PFO should be closed is controversial because the finding is incidental in about 80% of patients with stroke. In addition, PFO patches can cause complications such as blockage of the aortic valve or femoral artery. “We need to identify, among patients with PFO, which are the ones that are more likely to have a stroke, and therefore more likely to respond to treatments like patching the hole,” said Dr. Spence.
TEE Did Not Identify Several Large Shunts
Research has found that transcranial Doppler is a more sensitive detector of emboli than TEE, which has been regarded as the gold standard in this application. To compare the techniques, Dr. Spence and colleagues examined 334 patients referred to an urgent transient ischemic attack (TIA) clinic between 2000 and 2013. All patients had cryptogenic stroke and were suspected of having paradoxical embolism, and all had a right-left shunt on transcranial Doppler saline studies. A total of 284 patients had TEE data available.
Approximately 70% of patients were female, and the mean age was 53. Patients were followed up for a median of 420 days, and 85 participants had a recurrent ischemic stroke or TIA.
TEE failed to detect right-to-left shunt in 43 (15.4%) patients. Approximately 46% of undetected shunts were grade one, and about 32% of undetected shunts were grade two. TEE also failed to detect grades three, four, and five shunts, albeit to lesser degrees.
Approximately 25% of the shunts that TEE missed were high-grade shunts. “They were the shunts that were associated with prediction of risk,” said Dr. Spence. “Patients with a shunt grade greater than three were significantly more likely to have a stroke or TIA during the follow-up of almost 40 years than the ones who had smaller shunts.”
Transcranial Doppler Could Reduce Medical Costs
Researchers should perform transcranial Doppler in a clinical trial to determine whether closure of a shunt prevents stroke, said Dr. Spence. “It is too early to say that we should be patching PFOs in clinical practice. I do suspect, however, that there are many cardiologists out there putting patches in people just because they have a PFO and a stroke. If they’re going to do that, they ought to be looking at the size of the shunt. But … we need evidence that treating these people with the high-risk shunts is going to be beneficial.”
If transcranial Doppler replaces TEE for the detection of PFO, it could result in significant cost savings. A transcranial Doppler machine costs approximately one-eighth the cost of a TEE machine, and training is much shorter for transcranial Doppler than for TEE.
In addition, the cost of the test is less for transcranial Doppler than for TEE. “If we can identify the smaller fraction of people who are going to have an event and only patch them, that would also save a lot of money in the medical care system,” concluded Dr. Spence.
—Erik Greb