Dynamic right ventricular outflow tract obstruction due to straight back syndrome and funnel chest – A pediatric case

Abstract

Thoracic deformity affects circulatory dynamics, and postural changes may affect hemodynamics. We report on the case of a 10-year-old girl with straight back syndrome (SBS) and funnel chest in which a right ventricular outflow tract (RVOT) obstruction was demonstrated by dynamic echocardiography. The patient occasionally experienced chest discomfort in the standing and sitting positions. Chest radiography and computed tomography showed SBS and funnel chest as well as limited anteroposterior chest space. Although she had a grade 3 systolic ejection murmur due to RVOT obstruction, it disappeared in the supine position. The cardiothoracic ratio was 56 % in the supine position but increased to 67 % in the upright position. Echocardiography showed that the RVOT was maintained in the supine (1.0 m/s) but narrowed in the sitting (1.7 m/s) position. This is the first pediatric case showing RVOT obstruction during the upright position that has been shown by dynamic echocardiography. Dynamic echocardiography in both positions may be useful for evaluating RVOT stenosis.

Learning objective

Patients with straight back syndrome and funnel chest have limited anteroposterior chest space, which may cause posture-dependent right ventricular outflow tract (RVOT) obstruction. Dynamic echocardiography in the supine and sitting position is useful to detect posture-dependent RVOT obstruction, which can be also observed in the pediatric population.

Introduction

The anteroposterior chest space is limited in patients with thoracic deformities such as straight back syndrome (SBS) and funnel chest. SBS is characterized by a congenital loss of the normal, gentle kyphotic curve of the upper dorsal spine [1]. In such cases, a functional heart murmur may turn into an organic murmur by respiratory [2,3] or postural changes [4]. However, the detailed mechanisms accounting for heart murmur exacerbation have not been fully understood [5]. We report the case of a juvenile with SBS, funnel chest, and an organic heart murmur and occasional chest discomfort only during sitting/standing positions and provide insightful imaging to assess the pathogenesis of the signs and symptoms in those with an SBS and funnel chest.

Case report

A 10-year-old girl was referred to our outpatient clinic for the evaluation of a heart murmur that was detected at a routine school physical examination. She had an unremarkable perinatal and developmental history. She had been followed up for precocious puberty, but no treatment was required. For a few years, she experienced occasional chest discomfort in the standing and sitting positions that were ameliorated in the supine position. A grade 3 systolic ejection murmur was heard in the third intercostal space of the left margin of the sternum in the standing and sitting positions, but the murmur disappeared in the supine position. These observations did not change between the inspiratory and expiratory phases. The cardiothoracic ratio was as wide as 67 % in the standing position but 56 % in the supine position (Fig. 1). Lateral view chest radiography and the sagittal plane of chest computed tomography (CT) showed SBS and funnel chest (Fig. 2, Videos 1 and 2), revealing a so-called pancake appearance of the heart packed in a narrow anteroposterior thoracic space resulting from posteriorly depressed sternum and straight dorsal spine with the absence of normal thoracic kyphosis [6]. The changes in blood pressure and percutaneous blood oxygen saturation between the supine and standing position were unremarkable, although a marked tachycardia (from 56 to 109 bpm) was observed after a postural change from supine to standing.

Fig. 1.

Chest radiography in the supine and standing positions. (A) The cardiothoracic ratio (CTR) in the supine position was 56 %. (B) However, in the standing position, the heart was laterally dilated and the CTR was 67 %.

Fig. 2.

(A) Chest radiography, lateral view, in the standing position and (B) chest computed tomography, sagittal view, in the supine position. The diagnosis of funnel chest and straight back syndrome was made based on the sternal concavity and lack of thoracic curvature. The distance from the middle of the anterior border T8 to a vertical line connecting Th4 and Th12 was only 0.4 cm in this patient, and the cut-off value for diagnosing straight back syndrome is 1.2 cm [10].

Echocardiography did not indicate any congenital heart disease. However, in the long-axis view focusing on the right ventricular outflow tract (RVOT), the RVOT was widely maintained (laminar flow, 1.0 m/s) in the supine position (Fig. 3A, Video 3), although it narrowed (turbulent flow, 1.7 m/s) in the sitting position (Fig. 3B, Video 4). These also indicated a shorter distance between the chest wall and the dorsal epicardium in the sitting position than in the supine position (9 cm vs. 10.5 cm) in the RV ejection phase (Fig. 3).

Fig. 3.

Transthoracic echocardiography in the supine and sitting position. (A) In the supine position, the right ventricular outflow tract (RVOT) width was maintained and the flow across the RVOT was laminar with a velocity of 1.0 m/s. (B) In the sitting position, RVOT was narrowed and the flow across RVOT was turbulent with a velocity of 1.7 m/s.

Discussion

This first pediatric case of SBS and funnel chest was accompanied by a significant heart murmur and occasional chest discomfort only in the sitting/standing positions. Although the mechanisms of the SBS causing RVOT obstruction have not been clarified to date, at least two possible mechanisms may explain the posture-dependent hemodynamics in this patient.

First, venous return is reduced in the sitting/standing position compared with that in the supine position. Reduction in venous return increases heart rate. The rise in heart rate in our patient was remarkable, mimicking postural tachycardia syndrome [7]. The reduction in venous return and increase in heart rate in the sitting/standing position may contribute to the postural occurrence of dynamic RVOT obstruction. Valsalva maneuver or nitrate administration during supine echocardiography is sometimes used to induce dynamic left ventricular outflow tract obstruction by facilitating preload reduction [8] and may be useful to elucidate the mechanism underlying dynamic RVOT obstruction, although we did not perform these techniques in this patient. An increase in the heart rate caused by a postural change to standing/sitting position may have enhanced the contractility of both ventricles by force-frequency relationship, possibly contributing to RVOT.

Second, the anteroposterior space in this patient was narrowed, or at least not as wide in the upright position as in the supine position. This observation is consistent with the lateral widening of the heart size in the chest radiography in the upright position compared to the supine position (Fig. 1). This observation is in striking contrast to that in normal subjects in which the anteroposterior space is widened in the upright position [9]. We postulate that the further limited anteroposterior room for the heart in the upright position may be the central mechanism of the postural occurrence of RVOT obstruction in patients with SBS. Because the right ventricle (RV) is a low-pressure system, the RV is more susceptible to external compression than the LV. Of note, any pulmonary stenosis with a peak velocity of 1.7 m/s may be too low to induce clinical symptoms. We therefore speculate that her chest discomfort may have largely been due to circulatory and neurohormonal changes induced by postural changes to standing and sitting positions with an increased heart rate, and that RVOT may be only one contributing factor. Only one previous report of an adult case indicated that dynamic echocardiography was useful in detecting the postural occurrence of RVOT obstruction as in the current case [4].

As one limitation of this report, chest CT was performed only in the supine position. Future technology allowing chest CT in a standing position would clarify the detailed postural change of the chest cavity and heart structure. In addition, the dynamic echocardiography did not record a simultaneous electrocardiogram.

In conclusion, in addition to the comprehensive supine echocardiography, dynamic echocardiography was useful for accurately diagnosing as well as deepening the understanding of the mechanism of postural occurrence of hemodynamic disturbance in not only adult but also pediatric cases of SBS or funnel chest.

The following are the supplementary data related to this article.

Videos 1 and 2

Axial computed tomography images (Video 1) and 3D images (Video 2) demonstrated limited anteroposterior space, as well as a flattened right ventricular outflow tract (RVOT) between the limited anteroposterior chest space, even in the supine position.

Video 3

Long-axis views of the right ventricular outflow tract (RVOT) in the supine position are shown. In the supine position, the width of the RVOT is maintained, and the flow across the RVOT is laminar.

Video 4

Long-axis views of the right ventricular outflow tract (RVOT) in the sitting position are shown. In the sitting position, the width of the RVOT is narrowed, resembling a “kissing” motion, and the flow across the RVOT is turbulent.

Patient permission/consent statement

Informed consent was obtained from the parents of the patient for publication of this case report.

Declaration of competing interest

None.