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Acyanotic congenital heart defects: Pathology review

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Cardiovascular system

Vascular disorders
Congenital heart defects
Cardiac arrhythmias
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Acyanotic congenital heart defects: Pathology review

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USMLE® Step 1 style questions USMLE

9 questions
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A 15-year-old girl is brought to the pediatrician for evaluation of leg pain that is exacerbated by exercise. The patient reports having difficulty keeping up with her classmates while playing soccer at school. She has not started having menses. Her mother had menarche at the age of 12. The patient’s temperature is 37.2°C (99.0°F), pulse is 80/min, respirations are 14/min. Upper extremity blood pressure is 140/81 mmHg, and lower extremity blood pressure is 118/70 mmHg. Physical examination reveals a low posterior hairline, Tanner stage I breasts and webbed neck.  Which of the following additional examination findings will most likely be seen in this patient? 

Transcript

Content Reviewers:

Antonia Syrnioti, MD

In a pediatric cardiology clinic, 4-year-old Tara is brought in by her parents because she has not been acting herself over the past month. The mother also mentioned that she can’t keep up with the other children when playing and often gets fatigued or short of breath. Vital signs include a temperature of 37.0 degrees Celsius or 98.6 degrees Fahrenheit, a heart rate of 100 beats per minute, a blood pressure of 110 over 70 mmHg, and a respiratory rate of 18 breaths per minute. On examination, her skin is pink, and auscultation of the heart reveals a holosystolic murmur over the left sternal border.

Ok, so Tara has some sort of congenital heart defect. Congenital heart diseases are defects in the embryological development of the heart or its major blood vessels. When the defect causes blood to move from the right to the left side, it’s called a right-to-left shunt. This is because deoxygenated blood from the right side goes to the left side, and then enters the systemic circulation. A large amount of deoxygenated blood in the systemic circulation gives the physical appearance of cyanosis, which is a bluish discoloration of the skin. Therefore, right-to-left defects are called cyanotic heart diseases. Conversely, left-to-right shunts are called acyanotic heart defects, because there is no cyanosis. In general, individuals with acyanotic congenital heart diseases could be asymptomatic or present with signs of heart failure, such as exercise intolerance, shortness of breath, and in the case of infants and young children; poor feeding and failure to thrive.

Okay, of the acyanotic congenital heart diseases, ventricular septal defect, or VSD, is the most common. The ventricular septum normally separates the left and right ventricles, and is made of a membranous component, which is the upper one-third, and a muscular component, which is the lower two-thirds. The defect most commonly occurs in the membranous portion of the septum. Ventricular septal defects are usually small and they often end up closing on their own. Individuals are asymptomatic at birth, and if symptoms develop, they usually occur a couple of weeks later or even later in life. This is a helpful clue on exams. On auscultation, a systolic murmur can be heard along the left sternal border. Bear in mind though that the smaller the defect, the more audible the murmur. That’s because when blood rushes through a more narrow opening, it produces more turbulence and therefore, more noise. In addition, because the defect allows oxygenated blood to move from the left to the right side of the heart, the oxygen saturation will be higher than normal in the right ventricle and the pulmonary artery.

Okay, now let’s move up the heart and look at atrial septal defects, or ASD. Remember that an atrial septal defect is different from a patent foramen ovale. Normally, when the heart is first developing, a strip of tissue called the septum primum between the left and right atria grows downward, slowly creating two separate chambers by closing a gap or opening known as ostium primum. The septum primum then fuses with the endocardial cushion and closes the gap completely. Meanwhile, a hole appears in the upper area, called the ostium secundum. Now, we also have the septum secundum which grows downward, just to the right of the septum primum, and covers the ostium secundum, leaving a small opening called the foramen ovale, which allows blood to go from the right atrium to the left atrium. At birth, the septum secundum and septum primum slap shut, and then fuse and close off the foramen ovale. However, for your exams, it’s important to know that the foramen ovale remains patent in approximately 25% of normal adults. A high yield fact is that the most common atrial septal defect is a problem with the formation of the septum secundum, and it’s specifically called an ostium secundum defect. Ostium secundum atrial septal defects are usually isolated, whereas the less common ostium primum defects typically occur in association with other congenital cardiac anomalies. A high yield association of ostium primum defects is with Down syndrome, or Trisomy 21. Similar to ventricular septal defects, individuals are usually asymptomatic.

On auscultation, the most characteristic feature of an atrial septal defect is the fixed split S2. Normally, during inspiration, the S2 heart sound actually splits into two separate sounds. That’s because during inspiration, there’s negative pressure in the chest to bring in air. That negative pressure also brings a bit more venous blood back to the right atrium and right ventricle, so it takes a little bit more time for the right ventricle to squeeze this extra blood into the pulmonary artery, and it takes a little bit more time for the pulmonary valve to close. This can be heard as a physiologic splitting of the S2 during inspiration where the pulmonary valve closes a bit later than the aortic valve.

Now, with an atrial septal defect, there’s extra blood that gets shunted from the left atrium to the right atrium and right ventricle, which passes by the pulmonic valve and causes a delay in the closure of the pulmonic valve relative to the aortic valve closure, producing a split S2. But since the atria communicate via the defect, inspiration produces no net pressure difference between them, and has no effect on the splitting of S2. So, S2 is fixed, meaning that it’s split to the same degree during inspiration and expiration. Now, similar to ventricular septal defects, the oxygen saturation will be increased in the right ventricle and pulmonary artery. Saturation will also be increased in the right atrium and this is what distinguishes atrial from ventricular septal defects.

An important complication of both a patent foramen ovale and an atrial septal defect is the development of paradoxical emboli from the venous circulation. Say someone develops a deep vein thrombosis in their legs, from which an embolus breaks off and travels up to the right heart, but instead of going from the right atrium t