Cardiac catheterization is performed on a 7-year-old boy. The image below shows the pattern of oxygen saturation in the patient's cardiac chambers and outflow tracts (structural abnormalities are not shown). This patient most likely has which of the following findings on physical examination?

Question

Cardiac catheterization is performed on a 7-year-old boy.  The image below shows the pattern of oxygen saturation in the patient's cardiac chambers and outflow tracts (structural abnormalities are not shown).  This patient most likely has which of the following findings on physical examination?

Quizplus · Accepted Answer

11ec160b_3a87_27a9_9249_f305e4831f2f_MD0001_00 This patient has an abnormal increase in oxygen saturation (SpO₂) between the right atrium and the right ventricle (see normal oxygenation pattern), indicating the presence of a left-to-right shunt that is most likely the result of a ventricular septal defect (VSD). With smaller VSDs, blood is shunted mainly from left to right due to the high pressure differential between the ventricles. As a result, right ventricular SpO₂ increases but left ventricular SpO₂ remains relatively normal. Larger VSDs allow equalization of chamber pressures, which results in more bidirectional mixing and decreased left ventricular SpO₂. Right atrial SpO₂ remains normal with VSDs of any size, unless tricuspid regurgitation is also present. Turbulent blood flow across a small VSD produces a loud holosystolic murmur best heard over the lower left sternal border. This murmur may be absent in larger (nonrestrictive) VSDs due to decreased resistance across the VSD and a lower trans-septal pressure gradient. (Choice A) A bifid carotid pulse with brisk upstroke ("spike-and-dome") is characteristic of hypertrophic cardiomyopathy, a condition with dynamic left ventricular outflow tract obstruction during systole. SpO₂ in the cardiac chambers remains normal. (Choice B) A precordial continuous, machine-like murmur indicates patent ductus arteriosus, which produces isolated pulmonary artery SpO₂ elevation. (Choice C) A decreased femoral-to-brachial blood pressure ratio is found in coarctation of the aorta, which does not alter right ventricular SpO₂. (Choice D) Fixed splitting of S2 occurs with an atrial septal defect (ASD), which causes increased SpO₂ in the right atrium compared with the vena cava but identical right atrial and ventricular SpO₂. VSD may result in wide splitting of S2 due to increased right ventricular volume causing delayed closure of the pulmonary valve; however, fixed splitting of S2 is more indicative of an ASD, as equalization of left and right atrial pressures minimizes the respiratory variation in ventricular blood flow. (Choice F) Mucosal cyanosis and fingernail clubbing may be observed in cyanotic congenital heart disease or as late features of ASDs or VSDs (eg, Eisenmenger syndrome). Blood flow across the VSD in Eisenmenger syndrome is right to left due to elevated pulmonary vascular resistance, resulting in decreased SpO₂ in the left ventricle. Educational objective: Increased blood oxygen saturation between 2 right-sided vessels or chambers indicates the presence of a left-to-right shunt. If the abnormal oxygen increase occurs between the right atrium and the right ventricle, a ventricular septal defect (VSD) is likely present. Small VSDs produce a holosystolic murmur that is loudest over the lower left sternal border. __________ References: Shunt lesions. (http://www.ncbi.nlm.nih.gov/pubmed/26471816)

Cardiac Catheterization Is Performed on a 7-Year-Old Boy