Straight back syndrome was first 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 findings 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 outflow tract, and palpitations occur when it presses the left ventricular outflow 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 . 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 outflow tract is squeezed and the aortic root is squeezed. Turbulence or vibration occurs when blood passes through the squeezed site , or related to the dislocation of the main pulmonary artery and the murmur is a functional murmur due to increased valvular flow, high output, tachycardia, increased venous reflux, or decreased systemic vascular resistance , usually confined 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.
The results of echocardiography showed that the inner diameter of right ventricular outflow tract in upright position was 10.00 ±6.68mm, while that in supine position was 15.45 ±6.06mm. There was a significant difference in the difference of right ventricular outflow tract diameter in upright position P= 0.011, indicating that the right ventricular compression was more obvious in upright position, which was more consistent with the murmur in sitting position of the 3 male patients we observed. Combined with the internal diameter of left ventricular outflow tract in upright position 20.50 ±1.91 mm, and in supine position 18.75 ±0.96 mm, the difference of internal diameter of left ventricular outflow tract in supine position was significantly different P=0.035 the left ventricular outflow 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 films, it is known that the most significant and consistent X-ray manifestation of straight back syndrome is the loss of normal kyphosis of the thoracic vertebrae seen on lateral chest films 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 . In addition, patients with straight back syndrome can cause cardiac compression due to the decrease of chest volume, such as acute myocardial infarction , chest tightness, palpitation , tachycardia and so on. ECG can show left axis deviation and incomplete right bundle branch block .
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 find 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 films directly through physical examination to exclude the disease.