Congenial heart disease: TETRALOGY OF FALLOT- Ettinger

Question 1

The defining anatomic features of tetralogy of Fallot include

Answer 1

Right ventricular outflow obstruction (PS),
secondary right ventricular hypertrophy,
a subaortic VSD,
and a rightward-positioned aorta (Figure 249-43).

PS occurring in combination with an isolated VSD, produces similar findings but the infundibular septum is not malaligned, the aorta is normal sized, and infundibulum of the right ventricle is not narrowed. These distinctions are commonly ignored in veterinary patients because corrective surgery is rarely performed

Question 2

Figure 249-43 Gross pathology of tetralogy of Fallot. A and B, The left-side view of two dogs with tetralogy of Fallot shows a large nonresistive ventricular septal defect (VSD) located between the aorta (Ao) and left ventricle (LV). Note the close proximity to the root of the aorta and the possibility for prolapse of an aortic valve leaflet into the VSD. C, Right-side view of the dog from B showing the large VSD (black arrow), pulmonic stenosis (white arrow), and hypertrophy of the right ventricle (RV). PA, Pulmonary artery.

Answer 2

Figure 249-43 Gross pathology of tetralogy of Fallot. A and B, The left-side view of two dogs with tetralogy of Fallot shows a large nonresistive ventricular septal defect (VSD) located between the aorta (Ao) and left ventricle (LV). Note the close proximity to the root of the aorta and the possibility for prolapse of an aortic valve leaflet into the VSD. C, Right-side view of the dog from B showing the large VSD (black arrow), pulmonic stenosis (white arrow), and hypertrophy of the right ventricle (RV). PA, Pulmonary artery.

Question 3

PATHOGENESIS

Tetralogy of Fallot has been extensively studied in Keeshond breeding colonies and is likely oligogenic in etiology.[83] A spectrum of lesions, ranging from the subclinical to the clinically complicated has been identified.124a-127a,31b Patterson et al. graded the conotruncal defects as follows: grade 1—subclinical malformations involving persistence of the conus septum fusion line, aneurysm of the ventricular septum, and absence of the papillary muscle of the conus; grade 2—PS or VSD in addition to the grade 1 lesions; and grade 3—tetralogy of Fallot: PS, VSD, and dextropositioned aorta (with secondary right ventricular hypertrophy).124a

Answer 3

PATHOGENESIS

Tetralogy of Fallot has been extensively studied in Keeshond breeding colonies and is likely oligogenic in etiology.[83] A spectrum of lesions, ranging from the subclinical to the clinically complicated has been identified.124a-127a,31b Patterson et al. graded the conotruncal defects as follows: grade 1—subclinical malformations involving persistence of the conus septum fusion line, aneurysm of the ventricular septum, and absence of the papillary muscle of the conus; grade 2—PS or VSD in addition to the grade 1 lesions; and grade 3—tetralogy of Fallot: PS, VSD, and dextropositioned aorta (with secondary right ventricular hypertrophy).124a

Question 4

Additional abnormalities found in some dogs included a dilated and tortuous ascending aorta, pulmonary atresia, hypoplasia of the supraventricular crest, and anomalies of the aortic arch system. Based on extensive breeding studies and sophisticated genetic analysis, conotruncal defects have been shown to be an inherited autosomal recessive trait with variable expression.76c

Answer 4

Additional abnormalities found in some dogs included a dilated and tortuous ascending aorta, pulmonary atresia, hypoplasia of the supraventricular crest, and anomalies of the aortic arch system. Based on extensive breeding studies and sophisticated genetic analysis, conotruncal defects have been shown to be an inherited autosomal recessive trait with variable expression.76c

Question 5

PATHOPHYSIOLOGY

The essential components of tetralogy of Fallot are severe RVOT obstruction and a VSD. As a result of the outflow obstruction and elevated right ventricular pressure, desaturated blood shunts from the right heart through the septal defect to mix with oxygenated blood coming from the left ventricle. Pulmonary arterial blood flow and pulmonary venous return are …….., and the left atrium and left ventricle are …………………

Answer 5

PATHOPHYSIOLOGY

The essential components of tetralogy of Fallot are severe RVOT obstruction and a VSD. As a result of the outflow obstruction and elevated right ventricular pressure, desaturated blood shunts from the right heart through the septal defect to mix with oxygenated blood coming from the left ventricle.122a,123a Pulmonary arterial blood flow and pulmonary venous return are scant, and the left atrium and left ventricle are small (underdeveloped).

Question 6

The addition of unoxygenated blood from the right ventricle to the systemic side of the circulation causes arterial ………….., decreased ………… …………… saturation, …………., and secondary ……………………..

Answer 6

The addition of unoxygenated blood from the right ventricle to the systemic side of the circulation causes arterial hypoxemia, decreased hemoglobin oxygen saturation, cyanosis, and secondary polycythemia.

Question 7

Systemic ……… circulation to the lung increases via the bronchial …………. system. These vessels supply blood to the capillaries of the pulmonary parenchyma either directly or via anastomosing connections with a larger pulmonary artery. A substantial portion of this blood can participate in pulmonary gas exchange.

Answer 7

Systemic collateral circulation to the lung increases via the bronchial arterial system. These vessels supply blood to the capillaries of the pulmonary parenchyma either directly or via anastomosing connections with a larger pulmonary artery. A substantial portion of this blood can participate in pulmonary gas exchange.

Other aspects of clinical pathophysiology have been previously described (see Clinical Evaluation of the Patient with Cyanotic Heart Disease).

Question 8

CLINICAL FINDINGS

Tetralogy of Fallot is common in the Keeshond, English Bulldog, and in some families of other breeds. It has also been recognized in the cat. Presenting complaints and clinical signs are as previously described for cyanotic heart disease. In most cases, the murmur of tetralogy of Fallot is produced by blood flowing through the stenotic pulmonic valve. A right-sided murmur, resulting from blood flow through the VSD, may predominate when PS is ……..and ……-to-…….shunting occurs across a restrictive VSD (i.e., an acyanotic defect).

Answer 8

CLINICAL FINDINGS

Tetralogy of Fallot is common in the Keeshond, English Bulldog, and in some families of other breeds.[45] It has also been recognized in the cat.9a Presenting complaints and clinical signs are as previously described for cyanotic heart disease. In most cases, the murmur of tetralogy of Fallot is produced by blood flowing through the stenotic pulmonic valve.75c A right-sided murmur, resulting from blood flow through the VSD, may predominate when PS is mild and left-to-right shunting occurs across a restrictive VSD (i.e., an acyanotic defect).

Question 9

The absence of an obvious murmur suggests pulmonary …….. and/or p………… with ……………….. (which decreases blood flow turbulence) and ejection across a large, nonrestrictive VSD.

Exercise or excitement may induce or enhance detection of peripheral cyanosis by accentuating right-to-left shunting by mechanisms previously described.

Answer 9

The absence of an obvious murmur suggests pulmonary atresia and/or polycythemia with hyperviscosity (which decreases blood flow turbulence) and ejection across a large, nonrestrictive VSD.

Exercise or excitement may induce or enhance detection of peripheral cyanosis by accentuating right-to-left shunting by mechanisms previously described.

Question 10

Radiography usually reveals a small or normal-sized heart with rounding of the right ventricular border (Figure 249-44). The main pulmonary artery is not always visibly enlarged, in contrast to the usual case of PS with intact ventricular septum. The pulmonary vasculature is diminished and the left auricle may be inconspicuous as a consequence of decreased venous return.

Answer 10

Radiography usually reveals a small or normal-sized heart with rounding of the right ventricular border (Figure 249-44). The main pulmonary artery is not always visibly enlarged, in contrast to the usual case of PS with intact ventricular septum. The pulmonary vasculature is diminished and the left auricle may be inconspicuous as a consequence of decreased venous return.

Question 11

The ECG typically exhibits criteria for right heart enlargement including right axis deviation, although left or cranial directed vectors may be found in some cats.129a

Answer 11

The ECG typically exhibits criteria for right heart enlargement including right axis deviation, although left or cranial directed vectors may be found in some cats.129a

Question 12

Echocardiographic findings include right ventricular hypertrophy, increased right ventricular chamber dimensions, reduced LA and LV dimensions, a large subaortic VSD, and right ventricular outflow obstruction (Figure 249-45). Doppler or angiographic contrast studies can be employed to document right-to-left shunting at the ventricular outflow level

Answer 12

Echocardiographic findings include right ventricular hypertrophy, increased right ventricular chamber dimensions, reduced LA and LV dimensions, a large subaortic VSD, and right ventricular outflow obstruction (Figure 249-45). Doppler or angiographic contrast studies can be employed to document right-to-left shunting at the ventricular outflow level

Question 13

Cardiac catheterization demonstrates ……………….. of left and right ventricular systolic pressures, compatible with a large nonrestrictive VSD. Oximetry samples reveal a step-down at the ……………….. level and the ………. blood is relatively desaturated.
Angiocardiography reveals right ventricular hypertrophy, narrowing of the right ventricular infundibulum, PS with minimal poststenotic dilatation, varying degrees of pulmonary artery hypoplasia, a large subaortic VSD, a small, dorsally displaced left ventricle, an enlarged and rightward-positioned aorta, and prominent bronchial circulation (Figure 249-47).

Bidirectional shunting across the VSD is common in anesthetized animals. Anticoagulation therapy (e.g., heparin) should be considered to prevent cerebral embolization during and immediately after cardiac catheterization.

Answer 13

Cardiac catheterization demonstrates equilibration of left and right ventricular systolic pressures, compatible with a large nonrestrictive VSD. Oximetry samples reveal a step-down at the left ventricular outflow level and the aortic blood is relatively desaturated.
Angiocardiography reveals right ventricular hypertrophy, narrowing of the right ventricular infundibulum, PS with minimal poststenotic dilatation, varying degrees of pulmonary artery hypoplasia, a large subaortic VSD, a small, dorsally displaced left ventricle, an enlarged and rightward-positioned aorta, and prominent bronchial circulation (Figure 249-47).

Bidirectional shunting across the VSD is common in anesthetized animals. Anticoagulation therapy (e.g., heparin) should be considered to prevent cerebral embolization during and immediately after cardiac catheterization.

Question 14

CLINICAL MANAGEMENT

The natural history and survival times of dogs and cats with tetralogy of Fallot in dogs and cats are not well characterized. Like other cyanotic heart diseases, tetralogy of Fallot can be tolerated for years, provided pulmonary blood flow is maintained and hyperviscosity is controlled.[26] Most affected animals have severely limited exercise capacity.

Answer 14

The natural history and survival times of dogs and cats with tetralogy of Fallot in dogs and cats are not well characterized. Like other cyanotic heart diseases, tetralogy of Fallot can be tolerated for years, provided pulmonary blood flow is maintained and hyperviscosity is controlled.[26] Most affected animals have severely limited exercise capacity.

Question 15

In cases of pulmonary atresia, pulmonary blood flow must be derived from a PDA, the bronchial artery, or an elaborate network of systemic collaterals.

Answer 15

In cases of pulmonary atresia, pulmonary blood flow must be derived from a PDA, the bronchial artery, or an elaborate network of systemic collaterals.

Question 16

Sudden death is common because of the combined consequences of…………….,……………,or…………………

Unlike PS with intact ventricular septum, congestive heart failure is an ……………………………

Answer 16

Sudden death is common because of the combined consequences of hypoxia, hyperviscosity, or cardiac arrhythmia.

Unlike PS with intact ventricular septum, congestive heart failure is an unusual outcome.

Question 17

Options for treating animals with tetralogy of Fallot include medical and surgical approaches. Definitive correction of the defect (closing the VSD and removing or bypassing the stenosis) can be done under cardiopulmonary bypass, but such surgery is rarely performed in animals.[84],77c As a general rule, the stenosis should not be relieved if the VSD cannot be closed. Why not?

Answer 17

because the loss of right ventricular pressure results in marked left-to-right shunting with subsequent left-sided congestive heart failure.[85],128a

Question 18

As an alternative to definitive correction, surgical palliation through the creation of a systemic to pulmonary shunt can be quite rewarding.[86],128a,141a,78c Subclavian to pulmonary artery (Blalock-Taussig), ascending aorta to pulmonary artery (Potts), and aorta to right pulmonary artery (Waterston-Cooley) connections have been made in dogs and cats. By creating a left-to-right shunt distal to the cyanotic defect, pulmonary perfusion is increased and there is a greater contribution of oxygenated blood to the systemic circulation. The size of the accessory shunt must be controlled to prevent overloading of the diminutive left ventricle and subsequent pulmonary edema. The extent to which these shunts remain patent over long periods of time in veterinary patients has not been reported.

Answer 18

As an alternative to definitive correction, surgical palliation through the creation of a systemic to pulmonary shunt can be quite rewarding.[86],128a,141a,78c Subclavian to pulmonary artery (Blalock-Taussig), ascending aorta to pulmonary artery (Potts), and aorta to right pulmonary artery (Waterston-Cooley) connections have been made in dogs and cats. By creating a left-to-right shunt distal to the cyanotic defect, pulmonary perfusion is increased and there is a greater contribution of oxygenated blood to the systemic circulation. The size of the accessory shunt must be controlled to prevent overloading of the diminutive left ventricle and subsequent pulmonary edema. The extent to which these shunts remain patent over long periods of time in veterinary patients has not been reported.

Question 19

Periodic phlebotomy, performed to maintain the PCV between 62% and 68%, produces a satisfactory result in many cases.[26] Excessive bleeding should be avoided, and the blood that is withdrawn is replaced with crystalloid fluids to maintain cardiac output and tissue oxygen delivery.138a Some children with tetralogy of Fallot benefit from beta-blockade with propranolol; however, controlled studies of the clinical efficacy of this treatment in animals are lacking.139a,140a Severe hypoxic spells should be treated with cage rest, oxygen, and sodium bicarbonate (if metabolic acidosis is evident). Treatment with vasoconstrictive agents such as phenylephrine can also help reduce the amount of right-to-left shunting. Drugs with marked systemic vasodilating properties should be avoided.

Answer 19

Periodic phlebotomy, performed to maintain the PCV between 62% and 68%, produces a satisfactory result in many cases.[26] Excessive bleeding should be avoided, and the blood that is withdrawn is replaced with crystalloid fluids to maintain cardiac output and tissue oxygen delivery.138a Some children with tetralogy of Fallot benefit from beta-blockade with propranolol; however, controlled studies of the clinical efficacy of this treatment in animals are lacking.139a,140a Severe hypoxic spells should be treated with cage rest, oxygen, and sodium bicarbonate (if metabolic acidosis is evident). Treatment with vasoconstrictive agents such as phenylephrine can also help reduce the amount of right-to-left shunting. Drugs with marked systemic vasodilating properties should be avoided.

Question 20

OTHER CAUSES OF CYANOTIC CONGENITAL HEART DISEASE

Valvular Atresia

Pulmonary atresia with a VSD is essentially an exaggerated form of tetralogy of Fallot (see Figure 249-47). All of the blood ejected from the right heart is shunted right-to-left across a large VSD and into an enlarged aorta. The tricuspid valve is usually normal. The term “pseudotruncus arteriosus” has been used to describe this defect. It differs from a true truncus arteriosus because careful dissection reveals an imperforate pulmonic valve and a vestigial cord representing the main pulmonary trunk. On occasion, both the pulmonic and tricuspid valves are atretic (see Figure 249-47). The right ventricle is small or hypoplastic and blood returning to the right atrium shunts through a patent foramen ovale or ASD to produce cyanosis. The lungs are supplied via a PDA or an extensive bronchoesophageal collateral circulation.

Answer 20

OTHER CAUSES OF CYANOTIC CONGENITAL HEART DISEASE

Valvular Atresia

Pulmonary atresia with a VSD is essentially an exaggerated form of tetralogy of Fallot (see Figure 249-47). All of the blood ejected from the right heart is shunted right-to-left across a large VSD and into an enlarged aorta. The tricuspid valve is usually normal. The term “pseudotruncus arteriosus” has been used to describe this defect. It differs from a true truncus arteriosus because careful dissection reveals an imperforate pulmonic valve and a vestigial cord representing the main pulmonary trunk. On occasion, both the pulmonic and tricuspid valves are atretic (see Figure 249-47). The right ventricle is small or hypoplastic and blood returning to the right atrium shunts through a patent foramen ovale or ASD to produce cyanosis. The lungs are supplied via a PDA or an extensive bronchoesophageal collateral circulation.

Question 21

Aortic atresia with a hypoplastic left heart is a rare form of cyanotic heart disease in dogs. The aortic orifice is often imperforate and the ascending aorta is hypoplastic and the mitral valve is usually atretic or hypoplastic. In the absence of a VSD the left ventricle is very small; when a VSD is present the left ventricle is better developed. The right heart supplies the entire pulmonary and systemic circulations, resulting in profound cyanosis and, in most cases, early death.

Answer 21

Aortic atresia with a hypoplastic left heart is a rare form of cyanotic heart disease in dogs. The aortic orifice is often imperforate and the ascending aorta is hypoplastic and the mitral valve is usually atretic or hypoplastic. In the absence of a VSD the left ventricle is very small; when a VSD is present the left ventricle is better developed. The right heart supplies the entire pulmonary and systemic circulations, resulting in profound cyanosis and, in most cases, early death.

Question 22

Double Outlet Right Ventricle

Double outlet right ventricle (DORV), wherein both great vessels exit from the right ventricle, has been reported in dogs and cats (Figure 249-48).146a,147a A VSD provides the left ventricle an avenue for outflow into the great vessels. Depending on the location of the VSD in relation of the origin of the great vessels, DORV can manifest as either pulmonary overcirculation or cyanosis. Concurrent abnormalities such as PS, pulmonary hypertension, and coarctation of the aorta can also affect the development of clinical signs. Cyanosis is likely if the VSD lies under the pulmonary artery. Surgical correction of this condition in dogs has been reported.[48]

Answer 22

Double Outlet Right Ventricle

Double outlet right ventricle (DORV), wherein both great vessels exit from the right ventricle, has been reported in dogs and cats (Figure 249-48).146a,147a A VSD provides the left ventricle an avenue for outflow into the great vessels. Depending on the location of the VSD in relation of the origin of the great vessels, DORV can manifest as either pulmonary overcirculation or cyanosis. Concurrent abnormalities such as PS, pulmonary hypertension, and coarctation of the aorta can also affect the development of clinical signs. Cyanosis is likely if the VSD lies under the pulmonary artery. Surgical correction of this condition in dogs has been reported.[48]

Question 23

Transposition of the Great Arteries

In D-transposition of the great arteries, the aorta originates from the right ventricle and the pulmonary trunk from the left ventricle.15a,145a In the pure and fatal case, two independent circulations exist and the systemic arteries never receive oxygenated blood. Survival of an animal with D-transposition depends on the presence (or production) of shunts between the two circulations to allow for mixing of blood to prevent fatal hypoxemia. These defects are complex, generally lethal, and most likely underdiagnosed in animals, relative to children, since most animals probably die at a very young age undiagnosed.

Answer 23

Transposition of the Great Arteries

In D-transposition of the great arteries, the aorta originates from the right ventricle and the pulmonary trunk from the left ventricle.15a,145a In the pure and fatal case, two independent circulations exist and the systemic arteries never receive oxygenated blood. Survival of an animal with D-transposition depends on the presence (or production) of shunts between the two circulations to allow for mixing of blood to prevent fatal hypoxemia. These defects are complex, generally lethal, and most likely underdiagnosed in animals, relative to children, since most animals probably die at a very young age undiagnosed.

Question 24

MISCELLANEOUS CARDIAC DEFECTS

The potential for anatomic and physiologic variants of congenital heart disease is tremendous, and it is beyond the scope of this chapter to discuss the entire spectrum of malformations. The following section summarizes clinically relevant aspects of rarely encountered cardiac and pericardial defects.
Endocardial fibroelastosis has been reported in dogs[87],151a,154a,155a and cats and is probably familial in some lines of Burmese and Siamese cats.12a,151a-153a,79c The gross anatomic findings include left ventricular and left atrial dilatation, with severe endocardial thickening characterized grossly by diffuse, white, opaque thickening of the luminal surface (Figure 249-49). Histologic lesions in the cat include diffuse hypocellular, fibroelastic thickening of the endocardium with layering of thin, randomly organized collagen and elastic fibers.151a,153a Edema of the endocardium with dilation of lymphatics is prominent and there is no evidence of myocardial inflammation or necrosis.

Answer 24

The potential for anatomic and physiologic variants of congenital heart disease is tremendous, and it is beyond the scope of this chapter to discuss the entire spectrum of malformations. The following section summarizes clinically relevant aspects of rarely encountered cardiac and pericardial defects.
Endocardial fibroelastosis has been reported in dogs[87],151a,154a,155a and cats and is probably familial in some lines of Burmese and Siamese cats.12a,151a-153a,79c The gross anatomic findings include left ventricular and left atrial dilatation, with severe endocardial thickening characterized grossly by diffuse, white, opaque thickening of the luminal surface (Figure 249-49). Histologic lesions in the cat include diffuse hypocellular, fibroelastic thickening of the endocardium with layering of thin, randomly organized collagen and elastic fibers.151a,153a Edema of the endocardium with dilation of lymphatics is prominent and there is no evidence of myocardial inflammation or necrosis.

Question 25

The clinical features of endocardial fibroelastosis include early development of left or biventricular failure, generally before 6 months of age. Mitral regurgitation may be detected. Left ventricular and atrial dilation are evident on radiographs and on the ECG. Limited echocardiographic studies performed to this date suggest reduction of left ventricular myocardial function, as opposed to pure valvular disease in which shortening fraction tends to be normal or increased.155a The diagnosis of primary endocardial fibroelastosis is, at times, tenuous, inasmuch as chronic left ventricular dilatation may lead to similar changes, particularly in the setting of mitral dysplasia, aortic stenosis, restrictive and dilated cardiomyopathy, or myocarditis. Dogs with endocardial fibroelastosis often have thickening of the mitral valve leaflets and mitral regurgitation.154a,155a Affected animals fail to thrive. Medical treatment of congestive heart failure may be effective in prolonging life, but recovery is unlikely.

Answer 25

The clinical features of endocardial fibroelastosis include early development of left or biventricular failure, generally before 6 months of age. Mitral regurgitation may be detected. Left ventricular and atrial dilation are evident on radiographs and on the ECG. Limited echocardiographic studies performed to this date suggest reduction of left ventricular myocardial function, as opposed to pure valvular disease in which shortening fraction tends to be normal or increased.155a The diagnosis of primary endocardial fibroelastosis is, at times, tenuous, inasmuch as chronic left ventricular dilatation may lead to similar changes, particularly in the setting of mitral dysplasia, aortic stenosis, restrictive and dilated cardiomyopathy, or myocarditis. Dogs with endocardial fibroelastosis often have thickening of the mitral valve leaflets and mitral regurgitation.154a,155a Affected animals fail to thrive. Medical treatment of congestive heart failure may be effective in prolonging life, but recovery is unlikely.

Question 26

Peritoneopericardial diaphragmatic hernia (PPDH) is a relatively common developmental anomaly of dogs and cats.163a-170a This condition is not a true cardiac anomaly, but it can be confused with other congenital and acquired conditions. For further information, the reader is referred to Chapter 253.

Answer 26

Peritoneopericardial diaphragmatic hernia (PPDH) is a relatively common developmental anomaly of dogs and cats.163a-170a This condition is not a true cardiac anomaly, but it can be confused with other congenital and acquired conditions. For further information, the reader is referred to Chapter 253.

Question 27

VASCULAR ANOMALIES Vascular anomalies can be classified based on their location within the vascular system. A number of vascular malformations have been reported.[88-90],49a,50a,171a-196a PDA represents the most important of the vascular malformations, and has been previously discussed. Peripheral vascular disorders, including abnormal abdominal and hepatic venous drainage and arteriovenous fistulas,37b are detailed in their respective chapters. Unilateral atresia of a pulmonary artery has been described in a cat with respiratory difficulty.185a Coronary arteries can develop anomalously, but rarely cause documented clinical disease except when associated with PS.[50] Other major vascular defects center about the aorta and the systemic venous drainage, and the salient features of these disorders will be briefly addressed.

Answer 27

VASCULAR ANOMALIES Vascular anomalies can be classified based on their location within the vascular system. A number of vascular malformations have been reported.[88-90],49a,50a,171a-196a PDA represents the most important of the vascular malformations, and has been previously discussed. Peripheral vascular disorders, including abnormal abdominal and hepatic venous drainage and arteriovenous fistulas,37b are detailed in their respective chapters. Unilateral atresia of a pulmonary artery has been described in a cat with respiratory difficulty.185a Coronary arteries can develop anomalously, but rarely cause documented clinical disease except when associated with PS.[50] Other major vascular defects center about the aorta and the systemic venous drainage, and the salient features of these disorders will be briefly addressed.

Question 28

AORTIC ANOMALIES Persistence of the right aortic arch, as opposed to the left fourth aortic arch causes regurgitation in weanlings because of constriction of the esophagus.49a,50a,171a-183a Vascular ring anomalies include this common malformation, and other total or partial ring anomalies such as those formed by retroesophageal subclavian arteries, double aortic arch, or left aortic arch with right-sided ligamentum arteriosum.177a,179a,180a,184a The condition is quite common in German Shepherd Dogs and has been recognized in many other canine breeds including Irish Setters and Great Danes. The condition is uncommon in cats. Occasionally, other cardiac defects are present, including PDA (Figure 249-50). This condition is described more fully in Chapter 267.

Answer 28

AORTIC ANOMALIES Persistence of the right aortic arch, as opposed to the left fourth aortic arch causes regurgitation in weanlings because of constriction of the esophagus.49a,50a,171a-183a Vascular ring anomalies include this common malformation, and other total or partial ring anomalies such as those formed by retroesophageal subclavian arteries, double aortic arch, or left aortic arch with right-sided ligamentum arteriosum.177a,179a,180a,184a The condition is quite common in German Shepherd Dogs and has been recognized in many other canine breeds including Irish Setters and Great Danes. The condition is uncommon in cats. Occasionally, other cardiac defects are present, including PDA (Figure 249-50). This condition is described more fully in Chapter 267.

Question 29

Figure 249-50 Gross pathology from a dog with persistent right aortic arch, patent ductus arteriosus (D), anomalous origin of the left subclavian artery (LSC), and persistent left cranial vena cava (PLCVC). The left sided view of the heart, great vessels, and esophagus (Eso) shows the entrapment and cranial dilation of the esophagus by the patent ductus arteriosus. The origin of the left subclavian artery is moved distal from its usual location and is behind the esophagus. The persistent left cranial vena cava can be seen extending laterally along side of the esophagus and left heart base, and coursing around the caudal waist of the heart. Ao, Aorta; LV, left ventricle.

Answer 29

Figure 249-50 Gross pathology from a dog with persistent right aortic arch, patent ductus arteriosus (D), anomalous origin of the left subclavian artery (LSC), and persistent left cranial vena cava (PLCVC). The left sided view of the heart, great vessels, and esophagus (Eso) shows the entrapment and cranial dilation of the esophagus by the patent ductus arteriosus. The origin of the left subclavian artery is moved distal from its usual location and is behind the esophagus. The persistent left cranial vena cava can be seen extending laterally along side of the esophagus and left heart base, and coursing around the caudal waist of the heart. Ao, Aorta; LV, left ventricle.

Question 30

Aorticopulmonary septal defect (window) is caused by failure of the truncus arteriosus to differentiate, causing a common opening between the aorta and pulmonary artery, and shunting develops between the left and right sides of the circulation. While a clinical condition similar to that of PDA can develop, some reports suggest that in most cases, pulmonary hypertension develops during the first year of life and that clinical signs are similar to those in dogs that develop Eisenmenger's syndrome because of other defects.[90],188a-191a Management is similar to that for a reversed PDA. Surgery is difficult without cardiopulmonary bypass and should not be attempted if pulmonary vascular resistance is markedly elevated.

Answer 30

Aorticopulmonary septal defect (window) is caused by failure of the truncus arteriosus to differentiate, causing a common opening between the aorta and pulmonary artery, and shunting develops between the left and right sides of the circulation. While a clinical condition similar to that of PDA can develop, some reports suggest that in most cases, pulmonary hypertension develops during the first year of life and that clinical signs are similar to those in dogs that develop Eisenmenger's syndrome because of other defects.[90],188a-191a Management is similar to that for a reversed PDA. Surgery is difficult without cardiopulmonary bypass and should not be attempted if pulmonary vascular resistance is markedly elevated.

Question 31

Coarctation and interruption of the aorta is a rare defect in dogs that is characterized by narrowing of the aorta distal to the subclavian artery, adjacent to the ductus arteriosus. A case reported by Eyster demonstrated systolic and diastolic murmurs and left ventricular failure.193a The clinical features of coarctation in children are well described and in many ways are similar to this case.15a Aortic interruption has been reported in 2 dogs193a,80c and a case of tubular hypoplasia of the ascending aorta in a dog also has been described.194a While these lesions differ from coarctation, they are additional examples of malformation of the aorta in small animals. Definitive diagnosis usually requires angiography, though magnetic resonance imaging (MRI) and computed tomography (CT) scanning are effective methods for evaluating lesions of the aortic arch. Surgical correction has been successful in affected dogs.

Answer 31

Coarctation and interruption of the aorta is a rare defect in dogs that is characterized by narrowing of the aorta distal to the subclavian artery, adjacent to the ductus arteriosus. A case reported by Eyster demonstrated systolic and diastolic murmurs and left ventricular failure.193a The clinical features of coarctation in children are well described and in many ways are similar to this case.15a Aortic interruption has been reported in 2 dogs193a,80c and a case of tubular hypoplasia of the ascending aorta in a dog also has been described.194a While these lesions differ from coarctation, they are additional examples of malformation of the aorta in small animals. Definitive diagnosis usually requires angiography, though magnetic resonance imaging (MRI) and computed tomography (CT) scanning are effective methods for evaluating lesions of the aortic arch. Surgical correction has been successful in affected dogs.

Question 32

VENOUS ANOMALIES Thoracic venous anomalies rarely cause cardiac problems in small animals. Total or partial anomalous pulmonary venous return has been reported in a dog and behaves functionally as a left-to-right shunt at the atrial level.80a Abnormalities of abdominal venous drainage, such as patent ductus venosus, can induce hepatic encephalopathy. A relatively common venous abnormality of clinical significance during thoracic surgery or cardiac catheterization is the persistent left cranial vena cava (Figure 249-51).[91],195a,81c This structure, normally present in the fetus as part of the left cardinal venous system, may persist and drain into the embryologically related coronary sinus in the caudal aspect of the right atrium. Persistent left cranial vena cava may interfere with surgical exposure, particularly during surgical treatment of persistent right fourth aortic arch, or confound cardiac catheterization, but otherwise it is of no known functional significance (Figure 249-52). As with persistence of the right fourth aortic arch, this vascular anomaly is common in German Shepherd Dogs, and has been reported in other canine breeds as well as in cats.133a,195a Division of this vessel generally poses no clinical problem provided the normal right cranial vena cava is also present (see Figure 249-52). Venous aneurysms or related anomalies are extremely rare.38b

Answer 32

VENOUS ANOMALIES Thoracic venous anomalies rarely cause cardiac problems in small animals. Total or partial anomalous pulmonary venous return has been reported in a dog and behaves functionally as a left-to-right shunt at the atrial level.80a Abnormalities of abdominal venous drainage, such as patent ductus venosus, can induce hepatic encephalopathy. A relatively common venous abnormality of clinical significance during thoracic surgery or cardiac catheterization is the persistent left cranial vena cava (Figure 249-51).[91],195a,81c This structure, normally present in the fetus as part of the left cardinal venous system, may persist and drain into the embryologically related coronary sinus in the caudal aspect of the right atrium. Persistent left cranial vena cava may interfere with surgical exposure, particularly during surgical treatment of persistent right fourth aortic arch, or confound cardiac catheterization, but otherwise it is of no known functional significance (Figure 249-52). As with persistence of the right fourth aortic arch, this vascular anomaly is common in German Shepherd Dogs, and has been reported in other canine breeds as well as in cats.133a,195a Division of this vessel generally poses no clinical problem provided the normal right cranial vena cava is also present (see Figure 249-52). Venous aneurysms or related anomalies are extremely rare.38b

Question 33

Figure 249-52 A, Specimen from a dog with persistent left cranial vena cava (LCVC). Note that the LCVC wraps around the caudal waist of the heart and is distinct from the anatomically correct right cranial vena cava (RCVC). B, Nonselective angiogram from a dog. Contrast is injected into the right and left jugular veins. The normal right cranial vena cava (R) is evident, as is the persistent left cranial vena cava (L). Not that the left vena cava wraps around the caudal aspect of the heart and enters into the caudal portion of the right atrium. Ao, Aorta; LAu, left auricle; LV, left ventricle; RAu, right auricular appendage; RV, right ventricle.

Answer 33

Figure 249-52 A, Specimen from a dog with persistent left cranial vena cava (LCVC). Note that the LCVC wraps around the caudal waist of the heart and is distinct from the anatomically correct right cranial vena cava (RCVC). B, Nonselective angiogram from a dog. Contrast is injected into the right and left jugular veins. The normal right cranial vena cava (R) is evident, as is the persistent left cranial vena cava (L). Not that the left vena cava wraps around the caudal aspect of the heart and enters into the caudal portion of the right atrium. Ao, Aorta; LAu, left auricle; LV, left ventricle; RAu, right auricular appendage; RV, right ventricle.