Prenatal diagnosis of coronary artery to right ventricle fistula: a case description

Introduction

Left coronary artery to right ventricle fistula (LCARVF) is an extremely rare congenital cardiovascular malformation and a subtype of coronary artery fistula (CAF) (1). It is characterized by an abnormal channel directly connecting the left coronary artery to the right ventricle, creating an atypical blood flow pathway between the coronary arteries and the heart chambers. This abnormal connection results in a high-pressure blood shunt from the coronary artery to the low-pressure right ventricle, forming a left-to-right shunt. This shunt can lead to an insufficient blood supply to the coronary arteries—causing myocardial ischemia—and to an increase in the volume load on the right ventricle, potentially resulting in serious consequences, such as cardiac insufficiency. A prenatal diagnosis of LCARVF is extremely rare. Here, we report a case of right ventricular fistula diagnosed by fetal cardiac ultrasound midpregnancy that was confirmed postnatally.

Case presentation

A 28-year-old pregnant woman underwent a midtrimester anomaly scan at 23+⁶ weeks of gestation. The fetal growth parameters were as follows: biparietal diameter, 60.8 mm; head circumference, 213.6 mm; abdominal circumference, 200.9 mm; femur length, 41.4 mm; and humerus length, 38.3 mm. Fetal heart scanning indicated a widened left coronary artery, measuring approximately 2.1 mm in diameter (Figure 1A). Blood flow was observed within the right ventricle, with a jet extending from the apex toward the tricuspid valve, showing a continuous shunt (Figure 1B) and a peak flow velocity of 89 cm/s (Figure 1C). Further examination of the fetal heart and other systems revealed no significant abnormalities, and the abnormal shunt was considered to be a LCARVF.

Figure 1 Two-dimensional and Doppler ultrasound imaging was conducted for critical assessment of the fetal coronary artery and abnormal shunt hemodynamics in the fetal heart. (A) Fetal heart two-dimensional ultrasound was used to measure the diameter of the coronary artery. (B) Color Doppler indicated a continuous blood flow signal from the apex toward the tricuspid valve (arrow). (C) Measurement of blood flow velocity. AO, aorta; LV, left ventricle; RV, right ventricle.

Prenatal diagnostic amniocentesis indicated no chromosomal aneuploidy or known pathogenic genomic copy number variations over 100 kb in the amniotic fluid sample. Postnatal echocardiography revealed a dilated left coronary artery with a main stem diameter of approximately 2.59 mm (Figure 2A) and a right coronary artery diameter of 1.57 mm (Figure 2B). The left anterior descending artery reached the apex and then looped along the posterior interventricular septum to the posterior atrioventricular groove, where it connected with the right ventricle at the apical and atrioventricular groove regions (Figure 2C). The diameters of the shunt openings were 2.0 and 2.2 mm, respectively, and continuous wave Doppler indicated a continuous shunt with a flow velocity of approximately 300 cm/s (Figure 2D). The diagnosis was confirmed as LCARVF with continuous coronary-to-ventricular shunting. After cardiac surgical evaluation, dynamic observation was recommended. At the time of writing, the infant is 9 months old and is in good general condition. All procedures performed in this study were in accordance with the ethical standards of the ethics committee of Gansu Provincial Maternity and Child-care Hospital with the approval No. 2023GSFY[98] and with the Helsinki Declaration (as revised in 2013). Publication of this article and accompanying images was waived from patient consent according to the ethics committee of Gansu Provincial Maternity and Child-care Hospital.

Figure 2 Postnatal two-dimensional and color Doppler echocardiographic images of the infant provided key measurements of the coronary arteries and demonstrated abnormal shunt flow. (A) Inner diameter of the left coronary artery. (B) Inner diameter of the left coronary artery fistula into the right ventricular fistula opening (arrow). (C) Color Doppler indicated that the left anterior descending artery reached the apex and then looped along the posterior interventricular septum to the posterior atrioventricular groove, showing bright turbulent flow at the connection sites with the right ventricle at the apical and atrioventricular groove regions. (D) The continuous shunt flow velocity was approximately 300 cm/s. IVS, interventricular septum; LCA, left coronary artery; LDA, left descending artery; RA, right atrium; RV, right ventricle.

Discussion

CAF is a rare but relatively common type of coronary artery anomaly, typically affecting the right side of the heart, and it may exist independently or co-occur with congenital heart disease (CHD) (2). The prevalence of CAF in the general population is only 0.002%, accounting for 0.2% to 0.4% of all congenital cardiovascular diseases (3). The incidence of congenital solitary CAF is approximately 1 in 50,000 live births (4). Embryologically, its etiology is attributed to the persistence of intracardiac trabecular connections formed by endothelial cells and blood lacunae. In these cases, the right coronary artery is more frequently involved, accounting for approximately 50% to 60% of all cases of CAF (5). A study indicates that while the right ventricle is a common drainage site for CAF, the pulmonary artery is the most common, accounting for around 76% of such sites. Generally, low-pressure chambers are the most frequent drainage sites for congenital CAFs (6). Left CAFs that drain directly into the right ventricle are particularly rare, representing approximately 10% of CAF cases. Due to the extreme rarity of this pathology, specific incidence data are not yet available.

Prenatal echocardiography is the primary method for diagnosing LCARVF during the fetal period. Two-dimensional echocardiography allows for an initial assessment of the cardiac anatomy, including the size of the heart chambers and the thickness of the heart walls. Color Doppler echocardiography is essential for diagnosis, as it can detect an abnormal, high-velocity, continuous, low-resistance blood flow signal originating from the left coronary artery and directly entering the right ventricle, which may indicate the presence of a fistula.

Based on our experience, we summarized the key features relevant to diagnosing LCARVF during the fetal period.

• Signs similar to ventricular septal defect (VSD): although abnormal shunting observed during fetal echocardiography may resemble that of VSD, a key distinction is that CAF typically does not involve bidirectional flow across the interventricular septum. The blood flow in CAF is usually unidirectional, flowing from the left coronary artery directly into the right ventricle or other chambers.
• Abnormal blood flow direction: continuous tracking and observation of blood flow direction is a crucial method for tracing and identifying abnormal blood flow patterns, which is key in diagnosing CAF. In cases of CAF, the blood flow direction in the coronary arteries often deviates from normal circulation, for example, to the right ventricle. By continuously tracing the origin and course of the abnormal blood flow, the presence of an abnormal shunt can be effectively identified.
• Coronary artery enlargement: in most cases of CAF, coronary artery enlargement is also observed. This dilation is a hallmark feature, as the fistula leads to abnormal blood flow and volume, resulting in an enlargement of the coronary artery. Such changes are detectable through high-resolution fetal echocardiography.
• Occasional retrograde flow in the aorta: in certain phases of the fetal cycle, retrograde blood flow in the aorta can also be observed, particularly in cases with large shunt volumes. This reverse flow can serve as an additional diagnostic indicator, suggesting the presence of CAF.

Diagnosing LCARVF during the fetal period presents significant challenges. First, the fetal heart has a complex structure and is small in size, while the coronary arteries are exceedingly narrow during fetal development, with fistulas usually having an even smaller diameter. The related literature suggests that abnormal shunting observed during fetal echocardiography may lead to right ventricular dilation and slight cardiac dysfunction. If the shunt volume is substantial, signs such as enlarged heart chambers and increased right ventricular pressure load may appear, potentially indicating early signs of fetal cardiac insufficiency. Some fetuses may also present with mild pericardial effusion or asymmetry in the heart chambers. In our case, the fetus did not exhibit any changes in cardiac function. Overall, fetal CAFs generally lack specific clinical symptoms or signs, suggesting that the actual prevalence of LCARVF during the fetal period may be underestimated.

Postnatal echocardiography is a valuable tool for further evaluating LCARVF, offering high accuracy (7). In the neonatal period, echocardiography can reveal the fistula’s anatomical structure and hemodynamic characteristics in detail. Postnatal echocardiography can often identify left coronary artery dilation and clearly display the fistula, with color Doppler frequently showing the flow pathway and velocity directly from the left coronary artery to the right ventricle. Continuous wave Doppler imaging can measure the blood flow velocity and volume within the fistula, assess the shunt size, and evaluate its impact on right ventricular pressure. If the fistula flow is substantial and the shunt volume is significant, the newborn may develop symptoms of cardiac insufficiency or even congestive heart failure, in which case, early intervention is required.

In addition to conventional echocardiography, speckle tracking echocardiography (STE) holds great promise in assessing myocardial function, particularly in cases of CHD such as LCARVF. This innovative technique allows for the measurement of global longitudinal strain (GLS) and global longitudinal strain rate (GLSR), reflecting myocardial deformation during the cardiac cycle, and can reveal the subtle functional abnormalities that may not be visible on traditional echocardiography. Studies have shown that STE is effective in detecting subclinical myocardial dysfunction, especially in cases with abnormal shunting such as LCARVF, for which conventional echocardiography might miss early signs of right ventricular strain (8,9).

STE has already demonstrated prognostic value in the assessment of CHD. Research has confirmed its ability to identify reduced right ventricular GLS, which can indicate early signs of myocardial impairment even before overt structural or functional abnormalities appear. Additionally, the application of STE in assessing right ventricular function in newborns with LCARVF could provide more detailed insights, helping clinicians determine if early intervention is required.

Conclusions

Although LCARVF is rare, its potential risks make prenatal diagnosis particularly critical. Detecting LCARVF during the fetal period offers the opportunity for early intervention and provides key insights into improving the child’s prognosis.

Given that this case was encountered during the midgestation period, the actual conditions of the fetal heart (such as its small size and high heart rate) prohibited the application of STE. We look forward to its future integration into clinical practice as technology advances.

Acknowledgments

None.

Footnote

Funding: This study was supported by Lanzhou Talent Innovation and Entrepreneurship Project (No. 2023-RC-23 to L.Y.).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-2420/coif). L.Y. reports receiving funding from the Lanzhou Talent Innovation and Entrepreneurship Project (No. 2023-RC-23). The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the ethics committee of Gansu Provincial Maternity and Child-care Hospital with the approval No. 2023GSFY[98] and with the Helsinki Declaration (as revised in 2013). Publication of this article and accompanying images was waived from patient consent according to the ethics committee of Gansu Provincial Maternity and Child-care Hospital.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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