The Clinical Manifestation of Straight Back Syndrome in Echocardiogram Performance


 Background: There were no studies on the mechanism of clinical manifestations of straight back syndrome. Our aim was to explore the mechanism of clinical symptoms of straight back syndrome.Methods: From February 2018 to February 2021, we included 4 patients (3 males and 1 female) with straight back syndrome as the experimental group, and 4 normal people matched with sex and BMI as the normal control group. Basic information of patients, laboratory examination, echocardiography in supine and standing position, chest film in positive and lateral position, basic information of control group and echocardiography in supine and standing position were collected. The differences of clinical data between the two groups were compared and analyzed. Results: There were significant differences in left ventricular outflow tract diameter, right ventricular outflow tract diameter and right ventricular outflow tract velocity in the experimental group (their P values were 0.035, 0.011 and 0.015, respectively), but there was no significant difference in left ventricular outflow tract velocity in the standing and supine position (P=0.638). The left ventricular outflow tract diameter, the right ventricular outflow tract diameter and the right ventricular outflow tract velocity in the experimental group were significantly different (P<0.05). The internal diameters of left ventricular outflow tract in upright position, supine position, right ventricular outflow tract, supine position, right ventricular outflow tract were20.50±1.91mm, 18.75±0.96mm;10.00±6.68mm, 15.45±6.06mm;124.25±40.29cm/s and 91.00±28.93cm/s, respectively, in standing position, recumbent position, right ventricular outflow tract, right ventricular outflow tract, supine position, right ventricular outflow tract, supine position, supine position. The velocity of left ventricular outflow tract in upright position was 82.50±2.01 cm/s, and that in supine position was 83.25±2.06 cm/s. There was no significant difference in left ventricular outflow tract velocity in standing and supine position, which may be related to the compression of right ventricular outflow tract.Conclusions: In this study, we got the clinical manifestations of direct-back syndrome patients through comparison of straight back syndrome.


Introduction
Due to the congenital abnormal development of the thoracic vertebrae and the lack of physiological curvature, straight back syndrome leads to the shortening of the anterior and posterior diameter of the chest, the compression or displacement of the heart and large vessels and a series of clinical syndromes similar to organic heart disease. However, there are no studies on the mechanism of clinical manifestations of straight back syndrome. This study mainly discussed the mechanism of clinical manifestations in patients with straight back syndrome.

Materials And Methods
Material From February 2018 to February 2021, we studied four patients-three men and one woman. Each patient had at least one standard 12-lead ECG, and all subjects received echocardiography. Each patient has one or more sets of positive and lateral chest radiographs ( Figure 1). Echocardiographic evaluation included left ventricular out ow tract diameter in supine position, left ventricular out ow tract velocity in supine position, right ventricular out ow tract diameter in supine position and right ventricular out ow tract velocity in supine position. We adopted the following methods: 1. Collect 4 such patients as the experimental group, obtain the case data, sign the relevant informed consent form, and select 4 normal people with matched age, sex and BMI as the control group, and also sign the relevant informed consent form. 2. Collect the basic information of the patients, the electrogram of the laboratory examination, the color Doppler ultrasound of the recumbent standing heart, the chest lm of the anterior and lateral position, collect the basic information of the control group, and the color Doppler ultrasound of the recumbent standing heart. The results of supine echocardiography and orthostatic echocardiography of all subjects were collected, and the results of supine and standing echocardiography of the same subjects were compared and statistically analyzed.

Statistical analysis:
Discrete variables are reported as counts and percentages. Continuous variables in accordance with normal distribution were expressed as mean ±standard deviation. Single factor analysis of variance was used for inter-group comparison, and the least signi cant difference method was used for intra-group comparison. The classi cation variable is expressed as an example (%), and the chi-square or Fisher exact test is applied. All statistical analyses were performed using SPSS software, version 23.0. P 0.05 indicated statistical signi cance.

Results
In the 4 experimental groups included in this study, 3 male patients had clinical manifestations of 2nd-3rd intercostal murmur at the left edge of the sternum and grade 3 systolic ejection murmur at the left edge of the sternum. One female presented with palpitation, as shown in Table 2. The physiological curvature of the spine and thoracic vertebrae disappeared in both positive and lateral chest DR ( Figure 1). The age was 22.50 ±1.30 years old, and the systolic blood pressure difference in standing and recumbent position was 4.00 ±9.93 mmHg. The difference of diastolic blood pressure, heart rate and BMI in standing and lying position were 18.00 ±17.96 and 17.91 ±2.47 kg/m², respectively. See Table   There were 4 normal controls, whose age was 25.50±1.00 years old. The difference of systolic blood pressure, diastolic blood pressure and heart rate in standing and supine position was (7.00±2.58), (5.50±2.52) and (3.50±3.00), respectively, and that in standing and supine position was (25.50±1.00) years, 7.00±2.58mmHg and 3.50±3.00, respectively. BMI was 17.67±2.38 kg/m ². We found that there was a difference in age between the test group and the control group (P<0.01), but there was no signi cant difference in gender (P=1.000), baseline systolic blood pressure difference in sitting position (P=0.595), baseline diastolic blood pressure difference in sitting position (P=0.708), baseline heart rate difference in sitting position (P=0.162), and BMI (P=0.893). Among them, the average value and standard deviation of baseline heart rate difference in sitting position in the test group were signi cantly larger than those in the control group.
There were signi cant differences in left ventricular out ow tract diameter, right ventricular out ow tract diameter and right ventricular out ow tract velocity in the experimental group (their P values were 0.035, 0.011 and 0.015, respectively), but there was no signi cant difference in left ventricular out ow tract By comparing left ventricular out ow tract diameter difference, right ventricular out ow tract diameter difference, left ventricular out ow tract velocity difference and right ventricular out ow tract velocity difference between the experimental group and the control group, we found that there were signi cant differences in the right ventricular out ow tract inner diameter difference and the right ventricular out ow tract velocity difference between the experimental group and the control group (their P values were 0.012 and 0.003, respectively). This further indicates that the compression of the right ventricle is more signi cant in patients with straight back syndrome than in normal subjects.

Discussion
Straight back syndrome was rst reported by Rawling in 1960. It is rarely seen clinically, and it usually occurs in young, thin individuals. At present, the etiology of straight back syndrome is not clear, which may be mainly related to the anatomical structure of human chest, and it is easy to be misdiagnosed as organic heart disease, of which atrial septal defect is the most common. At present, the reports on straight back syndrome have not discussed the mechanism of its symptoms. In this study, the mechanism of straight back syndrome symptoms was discussed through the results of lying and standing blood pressure and color Doppler echocardiography, and normal people matched with sex and BMI were included as controls.
In this study, we found that the patients with straight back syndrome were mainly compressed by the right ventricle, and the sitting position oppressed the right ventricle more obviously. the second intercostal heart complex at the left edge of the sternum could be heard during auscultation in 3 male patients and palpitation in 1 female patient. There was no obvious abnormality in their laboratory examination, only that the chest radiographs lost the normal posterior curvature of the thoracic vertebrae ( Figure 1). These ndings suggest that the pathogenesis of straight back syndrome is caused by the reduction of the anterior and posterior diameter of the chest, which oppresses the heart, and its clinical manifestations are different due to different parts of the heart. Heart murmur occurs when it compresses the right ventricular out ow tract, and palpitations occur when it presses the left ventricular out ow tract.
Previous studies have suggested that the mechanism of murmur in patients with straight back syndrome is, on the one hand, due to a decrease in deep inhalation and an increase in deep exhalation [4]. On the other hand, it may be related to the mechanism of the murmur that the spine and sternum lose the normal physiological Radian so that the heart is close to the sternum, the right ventricular out ow tract is squeezed and the aortic root is squeezed. Turbulence or vibration occurs when blood passes through the squeezed site [5], or related to the dislocation of the main pulmonary artery and the murmur is a functional murmur due to increased valvular ow, high output, tachycardia, increased venous re ux, or decreased systemic vascular resistance [6], usually con ned to the base [7,8,9]. However, our study shows that patients with straight back syndrome oppress both the right ventricle and the left ventricle, mainly the right ventricle. position was signi cantly different P=0.035 the left ventricular out ow tract of patients on the surface was also oppressed, while the female patients we observed only showed palpitation without cardiac murmur, which may be related to the fact that her right ventricle was not compressed obviously and mainly oppressed the left ventricle. According to the anterior and lateral X-ray lms, it is known that the most signi cant and consistent X-ray manifestation of straight back syndrome is the loss of normal kyphosis of the thoracic vertebrae seen on lateral chest lms Figure 1. Compared with the normal chest, this change in thoracic shape is obvious, which is also the reason for the narrow distance between the spine and the sternum [10]. In addition, patients with straight back syndrome can cause cardiac compression due to the decrease of chest volume, such as acute myocardial infarction [11], chest tightness, palpitation [12], tachycardia and so on. ECG can show left axis deviation and incomplete right bundle branch block [8].

Limitations
Our study has the following limitations. 1. Our analysis is a study of a relatively small sample size. We can't rule out the possibility that after enlarging the sample, we will nd that it is inconsistent with the current results. 2. There is no genetic exploration of the patient. 3. No intervention-related follow-up results were performed. Prospect: for young patients in the future, we can do positive and lateral chest lms directly through physical examination to exclude the disease.

Conclusion
In this study, by comparing the changes of echocardiography in patients with straight back syndrome in standing and recumbent position, we concluded that the clinical manifestations of patients with straight back syndrome were related to the site of cardiac compression.   Figure 1 Anteroposterior view of the chest x-ray in Case 1. Lateral view shows a straight dorsal spine and narrow anteroposterior diameter.