Right-to-left shunt detection in patent foramen ovale: The value of synchronized contrast transcranial Doppler and contrast transthoracic echocardiography

Abstract

Patent foramen ovale (PFO) is a common congenital heart disorder associated with stroke, decompression sickness and migraine. Combining synchronized contrast transcranial Doppler with contrast transthoracic echocardiography has important clinical significance and can improve the accuracy of detecting right-left shunts (RLSs) in patients with PFO. In this letter, regarding an original study presented by Yao et al, we present our insights and discuss how to better help clinicians evaluate changes in PFO-related RLS.

Key Words: Contrast transcranial Doppler; Contrast transthoracic echocardiography; Combined multimodal ultrasound; Patent foramen ovale; Right-to-left shunt

Core Tip: Combining synchronized contrast transcranial Doppler with contrast transthoracic echocardiography enhances the accuracy of detecting right-left shunt (RLS) detection in patients with patent foramen ovale (PFO), who exhibit symptoms such as cryptogenic stroke, migraine, and dizziness. Nonetheless, this study has several limitations, such as the lack of reliability of the results and the low resolution of ultrasound technology. In addition, four-dimensional blood flow magnetic resonance imaging (MRI) is a new technology that has emerged in recent years and can be used to comprehensively evaluate cardiac blood flow patterns by quantifying hemodynamic parameters. It may help detect abnormal right atrial blood flow patterns in PFO and provide visualization of right-to-left shunting. Future studies should include a larger sample size with the gold standard and combine ultrasound and MRI to evaluate RLS alterations associated with PFO completely, thereby offering valuable information for precise diagnosis and treatment.

TO THE EDITOR

We read with great interest a recent paper titled "Right-to-left shunt detection via synchronized contrast transcranial Doppler combined with contrast transthoracic echocardiography: A preliminary study". In this study, Yao et al[1] evaluated the clinical utility of combining synchronized contrast transcranial Doppler (cTCD) with contrast transthoracic echocardiography (cTTE) for the detection of detecting right-left shunt (RLS). As a noninvasive examination method, it has important clinical significance to support better diagnosis and treatment decisions, especially for patients with cryptogenic stroke, migraine, and dizziness[2,3].

SYNCHRONIZED CTCD AND CTTE FOR PATENT FORAMEN OVALE

Patent foramen ovale (PFO) involves a small hole between two chambers at the top of the heart, which may occur in one-fifth of the population[4]. This leads to a RLS of unsaturated blood from the right atrium, potentially allowing venous thrombosis to enter the arterial circulation and subsequently causing embolism. This could lead to a series of diseases, including cryptogenic stroke, migraine, and acute limb ischemia, that occur secondarily from embolism[5]. Currently, noninvasive examinations for PFO with RLS include two ultrasound examination methods. One is cTCD, which is renowned for its high sensitivity. However, the false-positive rate of cTCD is very high. For example, the presence of an extracardiac shunt can also lead to cTCD positivity[6]. The other is traditional cTTE, which has a low cost and low sensitivity[7]. In this study, the authors diagnosed four PFO patients by synchronously applying cTCD and cTTE and followed them for 24 months. The results of this study provide a particularly deep impression. They reported that using cTTE or cTCD alone may underestimate the risk of RLS. Combining cTCD with cTTE could improve diagnostic accuracy and support better diagnosis and treatment decisions. The microembolic signals in the cerebral circulation could be detected by cTCD, and the cardiac structure and shunt pathways could be visualized by cTTE. Complete information on cardiac structure and blood flow could promote diagnostic accuracy and subsequent treatment decisions.

However, we identified several potential shortcomings in this study. First, not all patients in this study received gold standard confirmation at the time of inclusion. In future research, the use of contrast-enhanced transesophageal echocardiography as the gold standard and a larger sample size are recommended to further validate the conclusions of this study[8]. Second, ultrasound itself has technical limitations, such as insufficient resolution and differences between operators. Cardiac magnetic resonance imaging (MRI) has potential advantages in the diagnosis of PFO, and we recommend it as a supplementary tool. Conventional sequences can provide high-resolution information on the cardiac anatomy and function of PFO patients, with sensitivity and specificity exceeding 90%[9]. Four-dimensional blood flow MRI is an emerging technology that can comprehensively evaluate intracardiac hemodynamics[10-13]. However, there is currently a lack of reports related to sensitivity and specificity, which are worthy of further research.

CONCLUSION

In summary, the combination of cTCD with cTTE is highly important for detecting the RLS of PFO. It has the potential to improve patient diagnosis and subsequent treatment management, especially for patients with cryptogenic stroke and migraine. In future research, including a larger-scale validation with the gold standard and combining ultrasound and MRI to fully evaluate the cardiac structure and hemodynamic changes associated with PFO are recommended. These efforts will help refine diagnostic strategies and optimize clinical decision-making for PFO.