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Review Question - QID 218523

QID 218523 (Type "218523" in App Search)
A 2-year-old boy is brought to a pediatric cardiologist for an ablation procedure. He has been experiencing intermittent supraventricular tachycardia for about 6 months and was identified to have an aberrant electrical node in the left atrium. He was born at term to a healthy G1P1 mother and has no significant structural cardiac abnormalities on ultrasound. His temperature is 98.6°F (37°C), 98/59 mmHg, pulse is 119/min, and respirations are 18/min. A physical exam reveals a cheerful boy with no obvious anatomical abnormalities. Cardiac auscultation reveals no murmurs, rubs, or gallops. After induction of anesthesia, a catheter is introduced in the right femoral vein. Which of the following structures will need to be traversed in order to reach the ectopic foci in the left atrium?

Ductus arteriosus

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Ductus venosus

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Interatrial septum

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Interventricular septum

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Pulmonary vein

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This patient who undergoes cannulation of the right femoral vein in order to ablate a foci in the left atrium will need to have the catheter cross the interatrial septum from the right to the left side of the heart.

The primitive atrium starts embryologically as a single structure that pumps blood to both ventricles. Over the course of development, this structure is divided into left and right halves by the septum primum, which grows downward from the superior part of the primitive atrium. As the septum primum nears the atrioventricular cushions, new openings form at the center creating the foramen secundum. This opening is then closed by the septum secundum, which grows downwards in order to form the definitive interatrial septum. During normal development, these structures fuse to prevent communication between the left and right sides of the heart. Failure of this septation results in a patent foramen ovale. In patients without this defect, an intravenous catheter needs to penetrate the interatrial septum in order to access the left side of the heart.

Kharbanda et al. studied the properties of the interatrial septum in patients with atrial fibrillation. They find that this structure can result in re-entrant circuits leading to the failure of ablation therapies. They recommend more detailed anatomical studies of this structure in order to better facilitate the treatment of atrial fibrillation.

Incorrect Answers:
Answer 1: The ductus arteriosus is a connection between the pulmonary artery and the aorta that exists during embryological development and allows for shunting of blood from the right to the left side of the heart, bypassing the pulmonary vasculature. In normally developing children, this connection closes soon after birth so it could not be used as a connection in this patient. Failure of closure results in a patent ductus arteriosus with a continuous machine-like murmur on exam.

Answer 2: The ductus venosus is a connection between the umbilical vein and the inferior vena cava that allows for oxygenated blood to bypass the liver during embryological development. This connection does not allow for right to left shunting of blood in the heart.

Answer 4: The interventricular septum also separates the left and right sides of the heart and can be penetrated in order to access the left side of the heart. This would only be performed in patients with an existing ventricular septal defect; however, there is no evidence (for example, a harsh holosystolic murmur) of a defect in this patient.

Answer 5: The pulmonary vein brings oxygenated blood from the pulmonary circuit back to the left side of the heart. A catheter is not able to traverse the pulmonary circuit directly from the right to the left sides of the heart because the pulmonary capillaries are too small to allow for catheter passage.

Bullet Summary:
The interatrial septum separates the right and left sides of the heart and can be penetrated to allow for catheter passage from the venous system to the left atrium for cardiac procedures.

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