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Title: Quantification of right atrial end-systolic volume and ejection fraction in children undergoing cardiac surgery with two dimensional transesophageal echocardiography
Authors: Molli kiran
Issue Date: Dec-2019
Publisher: SCTIMST
Abstract: Left atrial (LA) end-systolic volume reflects the burden of left ventricular (LV) diastolic dysfunction. LA end-systolic volume index of > 34 ml/m2 is associated with adverse outcomes in patients, including a higher incidence of stroke, heart failure and death.1-4 Recently, right atrial (RA) end-systolic volumes and RA ejection fraction (EF) were quantified in healthy adult volunteers.5, 6 These data have now been incorporated in the 2015 update on quantification of cardiac chambers and volumes.7 Children undergoing cardiac surgery may have right ventricular (RV) diastolic dysfunction secondary to the effects of lesions causing either volume overload (atrial septal defects [ASD]) or pressure overload (Tetralogy of Fallot [TOF]).8-10 RV diastolic dysfunction may similarly affect the RA end-systolic volumes and RA EF. Therefore, it would be useful to know the “normal” values of RA end-systolic volume and RA EF in children. But such values may be difficult to obtain either in healthy children or in children undergoing non-cardiac surgery (i.e., those without cardiovascular disease); this would require additional imaging of the heart (often difficult without general Anaesthesiaesia) and would be both unwarranted and unethical. Furthermore, values obtained in adults may vary considerably from those in children. Children with ventricular septal defect (VSD) may have similar RA/RV chamber dimensions as compared to children without cardiovascular disease, since VSDs usually lead to LA/ LV volume overload without affecting the right heart. 9 Technically, the blood transits across the VSD into the pulmonary artery (PA). However, as both ventricles contract simultaneously, the RV does not realize a volume overload in this situation. 3 Similarly, volume overload of the RA does not occur. 9 2-dimensional (2D) echocardiography is now the standard monitoring of care for patients undergoing cardiac surgery.11 Therefore, the primary aim of the study was to establish “normal” RA end-systolic volume (indexed to body surface area) and RA EF in children using 2D echocardiography; these values were obtained from the cohort of children undergoing VSD repairs. The secondary aim of the study was to obtain the RA end-systolic volume and RA EF in children with RA/RV volume overload (ASD) and RV pressure overload (TOF) to determine if baseline differences existed between the three lesions. Apart from abnormal hemodynamics, body size is the most powerful determinant of the size of cardiovascular structures: all cardiovascular structures increase in size parallel to somatic growth, a phenomenon known as cardiovascular allometry. Expressing measurements in relation to body size allows a meaningful distinction between normal and abnormal values in children.12 RA anatomy The RA is the cardiac chamber that typically receives deoxygenated blood from the systemic venous and coronary sinus return. Blood is then directed into the RV through the tricuspid valve. During embryogenesis and development, after the right horn of the sinus venosus incorporates into the RA, the valve of the sinus venosus divides the RA into two chambers. A posterior smooth portion forms from the sinus venosus, and an anterior muscular portion forms from the embryologic RA. The valve of the sinus venosus usually regresses during weeks 9–15 of gestation, with the cranial portion forming the 4 crista terminalis and the caudal portion forming the valves of the inferior vena cava (eustachian valve) and coronary sinus (thebesian valve). Looking at the three dimensional (3D) images of the heart, the RA is positioned to the right and anteriorly, while the LA is situated to the left and posteriorly 13 The RA comprises of three components: appendage, the venous part (sinus venarum) and the vestibule. The crista terminalis is a muscular ridge in the RA wall that separates the smooth and muscular portions of the atrium. The eustachian valve primarily serves to direct blood toward the fossa ovalis in fetal life. The thebesian valve prevents reflux of RA blood into the coronary sinus. The normal RA is a thin, complex 3D structure that serves as a passive conduit to RV filling in early diastole and by active contraction during late diastole. When the tricuspid valve is closed, it acts as a reservoir for systemic venous return. RA enlargement has been considered as an early sign of RV diastolic dysfunction, where its increased reservoir capacity compensates for diminished RV compliance. 14 Echocardiographic evaluation of the RA The evaluation of the RA is less standardized than for the left heart, especially because of different echocardiographic evaluation techniques and more complex spatial anatomy of the right heart. The RA size and function measurement have been described from the trans-thoracic apical four-chamber or subcostal views. Briefly, RA long-axis is measured from the center of the tricuspid annulus to the center of the superior RA wall, parallel to the interatrial septum. The RA minor axis is measured between the mid-RA free wall to the interatrial septum, perpendicular to the long-axis. 5 RA area is traced at the end of ventricular systole, from the lateral aspect of the tricuspid annulus to the interatrial septum following the atrial endocardium. The area between the leaflets and annulus of the tricuspid valve, together with the superior and inferior vena cava and RA appendage are excluded from RA area. From apical four-chamber view, visual comparison of a RA that appears larger than LA is qualitative evidence of chamber enlargement.
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