CLINICAL PATHOPHYSIOLOGY made ridiculously simple™ / Клинична патофизиология направена изключително лесна: CHAPTER 1. THE CARDIOVASCULAR SYSTEM

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away from heart), but do not be fooled: the umbilical vein is carrying oxygenated blood to the baby.4 The umbilical vein connects to the fetal venous system, which eventually returns blood to the fetal right atrium via the inferior vena cava (IV C). If this blood enters the fetal venous system, it will be mixed with deoxygenated blood that is on its way back to the heart. However, this inferior vena cava blood genated blood from the umbilical vein is still+ moreoxy­ oxygenated than blood coming from the superior vena cava (SVC).

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Notice that both the relatively more oxygenated blood from the IVC and the less oxygenated blood from the SVC both mix in the right heart. However, the IVC enters at an angle such that the blood is di­ rected towards the fo ramen ovale, a passageway in the intra-atrial septum that allows communication between the atria. Thus, the more oxygenated blood from the IVC makes it across to the left heart (which can then pump it to the body). What about the re­ maining blood from the SVC and IVC that returns to the right atrium and passes to the right ventricle? It would not be of much use to have it travel through the lungs since they cannot yet oxygenate blood (in fact, the developing lungs use oxygen from the very little blood they do get for their own development). Most of the blood from the right heart ej ected through the pulmonary artery passes through a shunt called the ductus arteriosus, which connects the pulmonary artery to the aorta. Thus, the lungs are almost en­ tirely bypassed either by direct passage from the IVC to the right atrium through the foramen ovale to the left atrium or from the right ventricle through the pulmonary artery through the ductus arteriosus to the aorta.

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When the baby takes its first breath after birth, the newly expanded lungs offer far less resistance than they did while they were collapsed. This favors flow from the right heart/pulmonary artery to the lungs, as opposed to the ductus arteriosus. The decrease in flow through the ductus arteriosus along with a decrease in prostaglandin levels causes the ductus arteriosus to

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close. 5 The changes in pressure also result in closure of the foramen ovale. These shunt closures lead to the

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establishment of the adult circulation as described in Fig. 1-1.

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Classification of Congenital Heart Disease

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Congenital heart disease is divided into pathologies that cause cyanosis ("blue babies") and those that do not cause cyanosis. For cyanosis to occur, deoxy­ genated blood must somehow bypass the lungs and make it into the systemic circulation. What would Though your first guess might be some kind ofintrac­ allowsystem/rightdeoxygenatedheart tobloodthe toleftgetsidefromof thethe venousbody? ardiac shunt (e.g., atrial septal defect (ASD), or ven­ tricular septal defect (VSD)), realize that due to relatively higher pressure in the left heart vs. the right, ASDNSD should not normally lead to cya­ nosis. The only situation in which a septal defect could lead to cyanosis would be if there is a VSD and right heart pressures are abnormally elevated so as to overcome left heart pressures. Tetralogy of Fal­ lot is an example ofthis. Normally, however, any com­ munication between the 2 circulations should not lead to cyanosis.

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5 Prostaglandin levels are high during gestation, which also

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helps keep the ductus open. One can take advantage of this fact in the treatment of some congenital heart disease by keeping

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the ductus open after birth by prostaglandin administration, or by closing it with anti-inflammatories (e.g., indomethacin) if it remains open.

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Cyanotic Heart Disease

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Tetralogy of Fallot

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Fig. 1-26. Tetralogy of Fallot. Te tra means four, and

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there are four components of the pathology here: a VSD, an overriding aorta (i.e., one which spans the middle portions ofboth ventricles), and right ventricular hyper­ trophy (leading to a boot-shaped heart on a chest X-ray) secondary to pulmonic stenosis. The stenotic pulmonary artery causes the deoxygenated blood from the right ventricle to flow through the VSD instead of the pul­ monary artery. This blood then flows from the left ven­ tricle into the aorta. This mixes the venous and oxygenated blood supplying the systemic circulation, which causes cyanosis. If a baby feeds or exerts

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her/himself, s/he will need increased blood flow to vari­

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ous parts of the systemic circulation. The arteries in

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these areas will dilate, thus decreasing the resistance in the systemic circulation, which encourages blood to go from right to left (by making the path ofleast resist­ ance even less resistant). This leads to increasing cyanosis, and these episodes are known as "Tet spells" ("tet" is short for tetralogy). If the decrease in systemic resistance increases right-to-left flow, how do you think a patient could try to relieve these symptoms? If there were a way to increase systemic resistance, this would raise left-sided pressure. Increased left-sided pressure will shunt a little more blood back to the right so it can go through the pulmonary system and get oxygenated. Children do this by squatting, which increases resist­ ance in the arterial system, and thus decreases right­ to-left shunting. Treatment is surgical: patching shut the VSD and widening the pulmonary outflow tract.

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Transposition of the Great Arteries

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Fig. 1-27. Transposition of the great arteries. In this

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condition, the aorta and pulmonary artery connect to

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the wrong ventricles: the pulmonary artery to the left ventricle and the aorta to the right ventricle. Thus, de­ oxygenated venous blood returns to the right heart and then is ejected into the aorta to the systemic circulation, which then returns to the right heart, etc. The left heart receives blood from the lungs and then ej ects into the lungs, and then the blood comes back to the left heart and then is returned to the lungs, etc. The result is two parallel loops instead of a continuous progression. In utero, the communications between the two circula­ tions via the fo ramen ovale and ductus arteriosus allow for enough mixing to maintain oxygenation of tissues. However, when these close at birth, there is no way of getting oxygenated blood to the tissues, which can be deadly. If diagnosed in utero, efforts are made to keep the ductus arteriosus open after birth (by administer­ ing prostaglandins) until surgery can be performed to attach the great vessels to their appropriate ventricles.

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Other Causes of Cyanotic Heart Disease

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There are other less common cardiac anomalies that can lead to cyanosis, such as a single ventricle, hy­ poplastic left heart, totally anomalous pulmonary ve­ nous return, and many others. The main point to keep in mind is that for a cardiac lesion to cause cyanosis, there must either be a right-to-left shunt (e.g., tetral­ ogy of Fallot) or the blood must somehow be bypassing the lungs (e.g., transposition of the great arteries). Non-cardiac causes of cyanosis in the newborn are dis­ cussed in case #3 in Chapter 10.

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Noncyanotic Congenital Heart Disease

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Atrial Septal Defect (ASD) and Ventricular Septal Defect (VSD)

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Since left heart pressure normally exceeds right heart pressure (with a few exceptions e.g., tetralogy of Fallot), blood flows through ASDs and VSDs from left to right. This results in an increased amount of blood handled by the right heart.

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Fig. 1-28. Catheterization findings in ASD and VSD. Although these defects can be detected by murmur on physical exam and then visualized by echocardi­ ography, sometimes catheterization is performed. Catheterization will demonstrate increased oxygena­ tion ofthe blood in the right side of the heart compared to normal patients. If there is an ASD or VSD, blood in the right heart will be a mixture of venous return from the right side of the body (deoxygenated) and oxy­ genated blood that has traversed the defect from the left heart. If there is only a VSD, only the right ventri­ cle will have this elevated 02. Since the leak is from the left ventricle to the right ventricle, the blood in the right atrium should still be purely venous deoxy­ genated blood. This is in contrast to ASD where both the right atrium and the right ventricle have in­ creased 02 (since oxygenated blood passes from the left atrium to the right atrium via the ASD and then from the right atrium to the right ventricle).

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Atrial Septal Defect (A SD) . A small ASD can be asymptomatic, but a large ASD can lead to significant overload of the right ventricle, which can result in its enlargement. In such cases, surgical repair of the ASD is necessary. Since there is not really a sub­ stantial amount of pressure across the ASD, the blood flow across the ASD itself does not create a murmur. However, due to the volume overload of the right heart, increased flow across both tricuspid and pul­ monic valves can produce murmurs during diastole and systole, respectively. Additionally since the amount of blood ej ected by the right heart becomes greater than that ej ected by the left, pulmonic valve closure occurs later than aortic valve closure. This causes a fixed split of S2. Diagnosis is made by echocardiography or MRI.

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Ve ntricular Septal Defect (VSD) . The murmur of VSD occurs when the ventricle contracts, i.e., a holosys­ tolic murmur. A VSD causes increased flow to the lungs, which can eventually cause such severe pulmonary hy­ pertension that the pressure in the right heart over­ comes the pressure in the left heart, reversing the shunt. This is Eisenmenger syndrome (Fig. 1-29).

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Fig. 1-29. Eisenmenger syndrome. The left ventricle normally has a harder job than the right ventricle, ejecting to the entire systemic vasculature instead of the low-pressure pulmonary system. Thus, the left ventricle is stronger than the right ventricle. So when the heart squeezes, if there is a hole, the stronger left ventricle wins and pushes blood over to the right side. Now the flow through the lungs is increased since the right heart is pumping extra blood (i.e., it is pumping both the venous return from the body and the oxygenated blood from the left ventricle that passes through the defect). This causes the pressure to be so high in the lungs that the right-sided system eventually starts to be under higher pressure than the left. At that point, the right side starts to win, pushing blood through the VSD to the left side. The blood in the right heart has not yet been oxygenated by the lungs, and so when it passes to the left side, the body gets some blood without oxygen, leading to cyanosis. This is Eisenmenger syndrome: a left-to­ right shunt causing pulmonary and right heart pres­ sures to increase so that the shunt reverses, resulting in blood flow from right to left through the defect, causing cyanosis.

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Patent Ductus Arteriosus (PDA)

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The ductus arteriosus serves as an in utero connec­

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tion between the pulmonary artery and the aorta. In the fetal circulation, this allows blood ej ected by the right heart (which contains oxygenated blood from the mother) to pass from the pulmonary artery to the aorta, bypassing the lungs since they would not be oxygenating this blood anyway. At birth, the ductus arteriosus closes. What would happen if the ductus arteriosus did not close at birth? As with all other shunts we have described, the left-sided pressure is higher than right-sided pressure, so flow across the PDA will be from aorta to pulmonary artery, the op ­ posite of in utero. The result is that oxygenated blood from the aorta passes to the pulmonary artery, and then goes for another trip to the lungs and back to the left heart and round and round again. This in­ creases the work of the left heart since it is now re­ sponsible for the normal pulmonary venous return and the extra blood that comes through the shunt. This extra work can lead to heart failure. Also, as with other left-to-right shunts, pulmonary blood flow increases, which can lead to elevated pulmonary ar­ terial pressure. This elevated pulmonary arterial pressure can subsequently result in right heart fail­ ure and/or sufficiently elevated pulmonary artery pressure so as to reverse flow through the PDA (anal­ ogous to Eisenmenger syndrome). This would allow deoxygenated blood from the pulmonary artery to pass to the aorta, causing cyanosis.

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If there is a patent ductus arteriosus, blood flows through it constantly throughout the cardiac cycle, re­ sulting in a continuous machine-like murmur.

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Since prostaglandins keep the ductus open, anti-in­ flammatories (i.e., indomethacin) can be used to
close the ductus. If this treatment fails, surgical liga­ tion can be performed.

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Pulmonic Stenosis

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Pulmonic stenosis can occur in adults, but it occurs more commonly as a congenital lesion. Similar to the effect of aortic stenosis on the left ventricle, pulmonic stenosis causes the right ventricle to hypertrophy. If severe, this can cause right heart failure. The murmur is systolic. Pulmonic stenosis can occur as part of tetralogy of Fallot or independently.

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Congenital Aortic Stenosis

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Congenital aortic stenosis is similar in pathophysiology to adult aortic stenosis: a congenitally stenotic valve in­ creases the workload on the left ventricle, leading to hy­ pertrophy. Hypertrophy can result in fatigue, dyspnea, syncope, and eventual congestive heart failure, depend­ ing on the severity. What kind of murmur occurs in aor­ tic stenosis? Systolic ejection m
urmur.

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Coarctation of the Aorta

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Coarctation of the aorta is a congenital narrowing of the aorta that can occur anywhere along its length. Most commonly it occurs near the ductus arteriosus. A severe coarctation increases the resistance facing the left ven­ tricle, and can thus lead to congestive heart failure.

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Clinical manifestations of coarctation of the aorta. How does the heart respond to increased re­ sistance in adult aortic stenosis? Hypertrophy. Left

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ventricular hypertrophy is also one potential conse­ quence of aortic coarctation. Additionally, in a neo­ nate, the body will take advantage of collateral vessels along the undersurface of the ribs to supply the lower portion of the body. One manifestation of this is the radiologic finding of rib notching: the enlarged collateral vessels under the ribs actually wear away at the rib surface over time due to their increased blood flow, and these notches can be seen on chest X-ray.

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What type of murmur would coarctation of the aorta cause? When is blood passing through the murmur­ producing area? Blood flows through the aorta during systolic ej ection, and thus aortic coarctation produces a systolic ejection murmur.

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Coarctation of the aorta can also result in higher blood pressure in the upper extremities than in the lower extremities. Why? If the coarctation occurs dis­ tal to the brachiocephalic, common carotid, and left subclavian arteries, these vessels will all get normal flow, while the circulation distal to the coarct will get diminished flow. If the coarct occurs distal to the bra­ chiocephalic take-off but proximal to the left subcla­ vian take-off, there will be higher blood pressure in the right arm than in the left.

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Fig. 1-30. Aortic coarctation. Depending on whether the coarctation occurs proximal or distal to the ductus arteriosus, different manifestations can occur. The ductus arteriosus is distal to the brachiocephalic ar­ tery (which gives rise to the right common carotid ar­ tery and right subclavian artery), the left common carotid artery, and the left subclavian artery. If the narrowing occurs proximal to the ductus (preductal coarctation), but still distal to the three vessels men­ tioned above, what happens in utero? The three ves­ sels of the arch are proximal to the obstruction, and so blood from the left ventricle easily goes through these to the head and upper extremities. While the ductus is open in utero, blood from the pulmonary artery flows through the ductus arteriosus to the aorta distal to the obstruction to supply the lower body, and all is well.

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What happens when the ductus closes at birth? The head and upper extremities receive normal blood flow since they occur proximal to the obstruction. The lower half of the body, however, has reduced blood flow, due to the narrowing of the aorta and the loss of the "detour" via the ductus arteriosus. What would be the consequence of this? Blood pressure would be much higher in the upper extremities than the lower extrem­ ities. What if the ductus failed to close in preductal coarctation? Again, the upper body will be normally supplied by the left ventricle, but the lower body will be supplied by the pulmonary artery through the ductus arteriosus to the aorta. This results in the delivery of a mixture of deoxygenated and oxygenated blood to the lower half of the body. This can lead to differential cyanosis, in which the upper half of the body appears normal while the lower part of the body is cyanotic.

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In post-ductal coarctation, the clinical consequences depend on the severity. As mentioned above, a very se­ vere coarctation can lead to heart failure.

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Review of Congenital Heart Disease

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Congenital heart disease can be divided into diseases that cause cyanosis and those that do not. In heart dis­ eases that cause cyanosis, blood must have some way of bypassing the lungs. This can occur either via trans-

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