Which of the following disorders can lead to cyanosis, tachycardia, and systemic desaturation that is caused by the mixing of deoxygenated and oxygenated blood in the left side of the heart?


• Tricuspid atresia occurs when the tricuspid valve fails to develop. Without the tricuspid valve, there is an undersized or absent right ventricle. Tricuspid atresia allows no blood to flow from the right atrium to the right ventricle and to the lungs. Instead, deoxygenated blood crosses from the right atrium through an atrial septal defect into an enlarged left atrium.

• This oxygen-poor blood in the enlarged left ventricle reaches the lungs for oxygenation by being shunted back through a ventricular septal defect into the pulmonary artery, and some of it instead goes out into systemic circulation through the aorta.

• These structural abnormalities result in deoxygenated blood in the systemic circulation, causing cyanosis and tachycardia.

• Tetralogy of Fallot also includes a ventricular septal defect as well as pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta that sits above both ventricles and allows blood from both sides of the heart to be pumped out to the body. This means some of the blood meant to go to the lungs "skips" this step and then this deoxygenated blood goes into circulation instead.

• A patent foramen ovale (PFO) refers to a hole in the atrial septum that is present in utero. It normally closes by birth. If it does not close properly, it is called a patent foramen ovale. This defect works like a flap valve, opening only during conditions when there is increased pressure inside the chest. This increased pressure occurs when people strain while having a bowel movement, coughing, or sneezing. If the pressure is great enough, blood may travel from the right atrium to the left atrium. If there is a clot, it also may cross the PFO, enter the left atrium, and travel out of the heart and to the brain (causing a stroke) or into a coronary artery (causing a heart attack). Symptoms of a PFO are evident only when the flap valve is open, and so these symptoms may be transient or even asymptomatic in some cases.

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