Tiffaney is worried about her newborn son. Ever since she brought Caleb home fro

Question

Tiffaney is worried about her newborn son. Ever since she brought Caleb home from the hospital it has been so hard to get him to eat and he seems to be breathing too hard all the time. She stopped feeding and tried every bottle and formula on the market, but nothing has worked. So, at his one month check-up, her stomach is in knots as they place Caleb on the scale. The nurse says, “9 pounds, 7 ounces.” Tiffaney realizes Caleb has only gained one pound since he was born and she breaks into tears. Dr. Baker checks over Caleb in the check up room, taking extra time feeling and listening to his chest. During the check up, Tiffaney explains her struggle with trying to get her son to eat and how he cries almost the entire day. After the check up Dr. Baker says, “When I listen to Caleb’s heart I hear an extra sound called a murmur. I want to use an echocardiogram and an ECG to get a good picture of all the parts of his heart.” After a full day of tests, Tiffaney meets with Dr. Baker in his office. He explains, “After a careful review of all the information, I have discovered that Caleb has a hole in the heart muscle wall between his right and left ventricles. We call it a ventricular septal defect. That is probably why he has been so irritable and hard to feed. The hole is not very big, but he will still need to have surgery to repair it.” Although the thought of her tiny son having surgery is terrifying, Tiffaney is relieved to know why things have been so tough at home.

Questions: 1. The defect in Caleb’s heart allows blood to mix between the two ventricular chambers. Due to this defect would you expect the blood to move from left-to-right ventricle or right-to-left ventricle during systole? Explain your answer based on your understanding of blood pressure and resistance in the heart and great vessels.

5. Caleb’s heart allows oxygenated and deoxygenated blood to mix. Based on your knowledge of the heart and the great vessels, describe other anatomical abnormalities that cause the mixing of oxygenated and deoxygenated blood.

a. What happens to Caleb’s systemic cardiac output as a result of his ventricular septal defect (VSD)? Explain your answer.

6.One of the problems that worried Tiffaney was that Caleb seemed to be breathing too hard all the time. Let’s consider how this symptom is related to his heart defect.

a. Describe what would happen to the blood volume and pressure entering the pulmonary circuit as a result of his VSD.

b. Describe what would happen to the myocardium of Caleb’s right ventricle as a result of his VSD.

c. Based on the location of Caleb’s defect, what part of the conduction system might be at risk for abnormalities?

Explanation / Answer

Answer:

1. a. Caleb's defect causes blood to move from the left ventricle to the right ventricle during systole.

b. Blood moves into an open space where there is the least amount of resistance (pressure) or down its resistance (pressure) gradient. The blood pressure in the right ventricle is lower than the pressure in the left ventricle. This phenomenon occurs because the afterload in the right ventricle is lower than the afterload of the right ventricle. The difference between these afterloads is due to the pulmonary blood vessels generating less resistance when compared to the systemic blood vessels.

5. Patent ductus arteriosus:

Normally the ductus arteriosus, which connects the fetal pulmonary trunk to the aorta, closes very soon after birth. However, if it fails to close then it remains open, or patent. A patent ductus arteriosus allows a portion of the oxygenated blood from the aorta to flow back to the pulmonary trunk, where it mixes with deoxygenated blood that is sent to the lungs. Because of this, there is a significant increase in the volume of blood that goes to the lungs.

Atrial Septal Defect (ASD):

A hole in the wall between the two upper chambers is called an atrial septal defect, or ASD. Normally, systemic deoxygenated blood is carried by the superior and inferior vena cavae to the right atrium, and the left atrium receives oxygen-rich blood from the pulmonary veins. When a defect is present between the atria, some oxygen-rich blood leaks back to the right side of the heart. It then goes back to the lungs even though it is already rich in oxygen. Because of this, there is a significant increase in the volume of blood that goes to the lungs.

a. Due to a left-to-right blood shunt, the left ventricular volume falls during systole prior to the opening of the aortic valve. This shunt decreases stroke volume and cardiac output from the left ventricle into the aorta.

6. a. There is an increase in the total amount of blood pumped to the pulmonary trunk during each systole. Thus, the total pressure in these vessels also increases.

(This excessive volume/pressure, or pulmonary hypertension, causes pulmonary edema indicated by Caleb's increased work of breathing.)

b. Due to the left-to-right shunt, the blood volume within the right ventricle increases. Due the volume overload, the right ventricle cannot effectively pump out blood, causing an increase in end systolic volume and stretching of the myocardium. The end result is an overall enlargement of the wall of the right ventricle called hypertrophy.

c. The bundle of His (atrioventricular bundle) and the bundle branches are along the interventricular septum. So, if the defect included a large portion of the septum, all of these areas could be at risk for abnormalities. This would show up as a bundle branch block on an ECG rhythm strip.

(One way VSDs are classified is if they include the contractile myocardium, the conduction system, or both.)

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