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Congenital Heart Diseases of the Cat
Symposium on Feline Cardiology
Congenital Heart Diseases of the Cat Gary R. Bolton, D.V.M., *and Si-Kwang Liu, D.V.M., Ph.D. t
Congenital diseases of the feline heart play a role of lesser importance than the acquired diseases, accounting for only about 15 per cent of feline heart disease. 6•8 •11 This low incidence has led to a void in the clinical description of even the more common defects. To facilitate their recognition, this paper discusses the clinical presentation of the more common congenital heart diseases of the cat, stressing clinical signs, physical examination, electrocardiography, thoracic radiography, and angiocardiography. The largest study of congenital heart disease in the cat is given in the article on the Pathology of Feline Heart Disease in this volume, in which 107 cats were identified as having congenital abnormalities. Ventricular septal defect, aortic stenosis, atrioventricular valve dysplasia, patent ductus arteriosus, persistent common atrioventricular canal, and tetralogy of Fallot are the most common anomalies. A general summary of the literature indicates the consistent occurrence of other defects such as persistent right aor~ic arch, pulmonic stenosis, atrial septal defect, and neonatal fibrosis, although the etiology of the latter condition is uncertain.1 At present, there are no firmly established breed or sex predispositions. The incidence of the congenital heart diseases may be low, but their importance should not be minimized. Most cats with congenital heart disease die by one year of age. 8 In addition, the most important feline heart diseases, the cardiomyopathies, may occur in young cats. When they do, congenital heart disease is an important consideration in the differential diagnosis.
*Associate Professor of Small Animal Medicine and Cardiology, New York State College of Veterinary Medicine, Ithaca, New York. tSenior Staff, Department of Pathology, The Animal Medical Center, New York, New York
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VENTRICULAR SEPTAL DEFECT Ventricular septal defect occurs alone or may contribute to a more complex anomaly. It is usually located in the ventricular septum just below the aortic valve in the left ventricle, and just beneath the septal leaflet of the right atrioventricular valve in the right ventricle. It allows shunting of blood from the high pressure left ventricle to the low pressure right ventricle. The resultant overfilling of the right ventricle causes right ventricular enlargement. The right ventricle ejects the blood into the pulmonary artery, causing the pulmonary arteries to enlarge (pulmonary overcirculation). High volume flow through the lungs causes increased pulmonary venous return to the left atrium and left ventricle. This volume overload results in left heart enlargement. Severely affected cats die in the first few days or weeks oflife. If they survive initially, it is not known how long they may live, but most cats with ventricular septal defect will probably die by one year of age. The cat may be presented in heart failure, but often the murmur is auscultated during routine physical examination for vaccination. The murmur is loud, and although it may be heard on both sides of the chest, it tends to be loudest over the right 4th or 5th intercostal space near the sternal border. A B-B shot femoral pulse may be appreciated. The electrocardiogram is often normal, but may show signs of biventricular enlargement and biatrial enlargement (Fig. 1). Thoracic radiographs may also be unspectacular, but should be examined for signs of biventricular, left atrial, and pulmonary artery enlargement
Figure l. Electrocardiogram recorded from a cat with a ventricular septal defect. Right axis deviation ( -120°), and the presence of an S-wave in leads I, 11, and III indicate right ventricular hypertrophy. The tall R-waves in lead II mav indicate left ventricular hyp~rtrophy. Biatrial enlargement is indicated by the tall, wide P-waves. Paper speed = 50 mm/sec, l em= l rnv.
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Figure 2. thoracic radiographs from the cal with a ventricular septal defect in Figure 1. A, The lateral view demonstrates biventricular enlargement. Indentation of the tracheajust. crania l to the carina is caused by right atrial enlarge ment. The left atrium is not well visualized. Prominent pulmonary arteries suggest overcirculation and a left-to-right shunt. B , This dorsoventral view confi rms the p r esence of biventricular enlargement, a nd left a trial enlargement is now a pparent (arrows ).
(Fig. 2). Radiopaque dye injected into the left ventricle demonstrates the defect as the dye passes through it into the right ventricle (Fig. :3). Medical therapy for congestive heart f ailure may be temporarily helpful if clinical signs develop, but surgery is a more permanent cure. Open heart surgery is impractical, but pulmonary artery banding is feasible and has been reported to help. 10 Banding the pulmonary artery
Figure 3. Left ventricular angiocardiogram of the same cat with ventricular septal d efect. Th e cathe ter (C) passes into the left ventricle (L). Dye fiows across the ventricular septal defect (an·ow) , into the right ventricle , across the pulmonic valve, and in to the pulmonary artery (P ). This causes si multaneous filling of the aorta and pulmo nary artery, from the left ventricle . (From Tilley, L. 1'.: Feline Cardiology. V ET. CLTN. :--ioRTH AM., 6:4 3 1, 1976, with permission. )
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causes increased right ventricular pressure, which decreases the amount of left-to-right shunting. Asymptomatic cats require only watchful waitmg. Aortic Stenosis
Aortic stenosis implies resistance to left ventricular outflow. The stenosis may be below the valve (subvalvular), at the valve (valvular), or above the valve (supravalvular). The cat is unique in that the stenosis is often supravalvular, 6 as opposed to the subvalvular type that is usual for the dog. The supravalvular constriction shapes the aorta into an hourglass configuration, and is associated with a malformation of the aortic valve.r; Regardless of the site of the stenosis, left ventricular enlargement results, and eventually left atrial enlargement occurs. The affected cat develops acute heart failure at a young age and is often stunted by this defect. The aortic stenosis murmur is a harsh systolic murmur, heard best over the aortic-pulmonic area. It tends to radiate rightward, and may be even louder at the right 3rd or 4th intercostal space near the sternal border. It also tends to radiate to the neck and up the carotid arteries. The femoral pulse may be small, but this is difficult to appreciate in a cat. Electrocardiograms may be normal or may detect left ventricular enlargement. Most cases show left axis deviation (Fig. 4). Radiographically, left ventricular and left atrial enlargement, as well as a poststenotic dilatation of the aorta may be present (Fig. 5). Dye injected into the left ventricle clearly shows the area of stenosis (Fig. 6).
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Figure 4. Electrocardiogram recorded from an 18 month old female domestic short haired Gltwith sup! avalvular aortic stenosis. A marked left axis deviation to -80° indicates left ventricular hypertrophy and/or left anterior Fascicular block. The P waves in lead II are partially lost in the T waves or the preceding beats, but they appear to be too wide, an indication or left atrial enlargement. Paper speed = 50 mm/sec, 1 em = l mv.
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Figure 5. Thoracic radiograph s from the same cat seen in Figure 4 . A, Biventricular and left atrial enlargement is demonstrated in this lateral view. B, Dorsoventral view demonstrates genera lized cardiomegaly, but the left heart. is esp ecially prominent.
Figure 6. Left ventricu lar a ngioca rdiogram of the cat seen in Figures 4 and 5. The stricture occurs in the aorta, above the aortic valve (arr01v p oints to valve). T he aorta takes an h ourglass conhguratio n. The postste n otic dilatation of the aorta contributes a great deal to t he a rea that was thought to be right ventricu lar enlargement in Figure 5A. Opacification of the left a trium is ca used b y regurgitation of dye throu gh an insufficient lef t atrioventricular valve.
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Practically speaking, little can be done for these cats. Propranolol (Inderal) is a drug that is helpful in reducing the high left ventricular pressure and in decreasing the tendency toward tachycardia and arrhythmia (see the article in this symposium on therapy in feline cardiac disease). Patent Ductus Arteriosus
Failure of the ductus arteriosus to close within the first few days or weeks of life results in a patent ductus arteriosus. It is usually a solitary defect but may occur in concert with other defects. The patent ductus permits flow of blood from the high pressure aorta into the low pressure pulmonary artery. Aortic pressure remains higher than pulmonary artery pressure in both systole and diastole, and blood flow across the defect is continuous unless significant pulmonary hypertension develops. The resultant overload of the pulmonary arteries causes them to enlarge (pulmonary overcirculation), and pulmonary venous return to the left atrium is increased, causing a volume overload of the left heart. Eventually, biventricular, left atrial, and even biatrial enlargement occurs. The aorta and pulmonary artery tend to develop aneurysmal dilatation of their proximal portions. Cats may die soon after birth. If they survive the immediate postpartum period, most will develop signs of heart failure by one year of age. Clinical signs are lethargy, dyspnea, exercise intolerance, and stunting. If the cat is asymptomatic, the murmur may be discovered during routine physical examination at the time of vaccination. The murmur is usually loud and is continuous throughout systole and diastole. It is best heard over the aortic-pulmonic valve region on the left and tends to radiate rightward and toward the thoracic inlet on the base of the sternum. A B-B shot femoral pulse is characteristic of this defect. The most consistent electrocardiographic finding is that of left ventricular hypertrophy. Left atrial and right ventricular hypertrophy may also be seen (Fig. 7). Thoracic radiographs vary but should be examined for biventricular and left atrial enlargement, pulmonary overcirculation, and aortic or pulmonic aneurysmal dilatation (Fig. 8). Dye injection into the aorta demonstrates the patent ductus (Fig. 9). Surgery is the treatment of choice for patent ductus arteriosus. Closure of the defect is similar to that for the dog with the exception that entrance into the thorax is gained through the left 6th intercostal space rather than the 4th as in the dog. 4 Persistent Common Atrioventricular Canal
A large septal defect that involves both the atrial and ventricular septum creates communication of all four cardiac chambers through a single defect, and is the basis for a common atrioventricular canal. The defect is in the lowermost portion of the atrial septum and the uppermost portion of the ventricular septum. The atrioventricular valves form
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Figure 7. Electrocardiogram recorded from an 8 mon th old domestic shorthaired cat with patent ductus arteriosus. The tall R waves in lead 11 signify left ventricular h ypertrophy. The axis of+ 100°, despite left ventricular hypertrophy, suggests right ventr icular hypertrophy. The tall wide P waves in lead II indicate bia trial enlarge ment. Paper speed = 50 mm/sec, l em= l mv. (From Cohe n , J. S., Tilley, L. P ., Liu, S.-K. , and DeHoff, W. D.: Patent ductus arteriosus in five cats. J.A .A.H.A., 11 :Ja n/ Feb. 1975, with permi ssion.)
Figure 8. Thoracic radiograp h s from the cat seen in Figure 7. A, T he lateral view demonstrates right ventricu lar enlargement ( I ) and left atria l enlargement (clear arrow) . Prominen t pulmonary arteries suggest overcirculation due to a left-to-right shunt. B, The . dorsoventral view confirms biventricular and left atrial (solid arrow) enlargement. Aneurysmal aortic dilatation is outlined by the clear arrows. (From Cohen, J. S., Tilley, L. P., Liu, S.-K. , and De Hoff, W. D.: Patent ductus arteriosu s in five cats. JA.A.H.A., 11 :Jan./Feb. , 1975, with per mission.)
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Figure 9. Aortic angiogram of the cat seen in Figures 7 and 8. Dye injected through the catheter (C) into the aorta (A) crosses the pa tent ductus (D) in to the pulmonary arter y (P) causing simultaneous fi lling of both vessels. T he le ft atriu m (LA) and left ventricle (LV) are opacified by d ye from the lungs via the pulmonary veins. (FTOrn Cohen, ]. S., Tilley, L. P., Liu, S.-K. , and DeHoff, W. D.: Patent ductus arteriosus in five cats. J.A.A.H.A., 11 :Jan ./Feb., 1975, with permission.)
in this r egion, and valvular defects are usually present. Cats with this d efect tend to develop m assive generalized cardiomegaly. The r ight atrium a nd ventricle enlarge because of the left-to-right flow from the left atrium and ventricle. Large pulmonary blood flow causes pulmonary artery enlargement (pulmonary overcirculation) and increased pulmonary venous return causes volume overload of the left h eart with leftsided cardiomegaly. A potential for cyanosis exists if pulmonary h ypertension causes right heart pressures to approximate or exceed those of the left. Affected kittens ar e usually stunted if they su rvive the immediate postpartum period, and death by 6 or 7 months of age is usual. A loud, mixed frequency systolic murmur is h eard best over the left cranial ventral thorax presumably due to a · relative or functional pulmonic stenosis. 7 A murmur of mitral insufficiency caused by a d eformed mitral valve m ay be heard, and righ tward r adiation may result from the ven tricular septal d efect or a d eform ed tr icu spid valve. If right ventricular pressure rises, th e murmur will diminish in inten sity or even disappear as flow across the defect diminishes. T he electrocardiogram is characterized by axis deviations and by wide QRS complexes, since the large defect in the septum cau ses bundle branch blocks (Fig. 1 0). Generalized cardiomegaly as seen on thoracic radiograph s can be spectacular (Fig. 11). Dye injected into the left ventr icle fills all chambers simultaneously (Fig. 12) . H eart failure is sever e and intractable, requiring a grave prognosis.
Tetralogy of Fallot Ventricular septal d efect and pulmonic sten osis combine to produ ce the deadly anomaly, tetralogy of Fallot. O verriding aorta and righ t ven tricular hyp ertrophy ar e incidental abnormalities that comple te th e te tralogy. Pulmonic ste n osis elevates right ventricular pressure until it either approximates or exceeds left ventricular pressure, a nd unoxyge-
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I Figure l 0. Electrocardiogram recorded from a S year old male domestic shorthaired cat with a commo n atrioventricular canal. Right bundl e branch block is indicated by the large, wide , negative terminal deflections in leads I, II, III , aVF, V2 and V10 . Paper speed = 50 mm/sec, l em = l mv.
Figure 11. Lateral thoracic radiog raph of the same cat as in Figure 10. Generalized cardiomegaly is obvious.
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Figure 12. Angiocardiogram of th e same ca t as in Figures I 0 and 11. Dye injected into the area of the atrioventricular defect opacifies all ch ambers simultaneously. (LA = left atrium, LV = left ventricle , RA = right atrium, R V =righ t ventricle, A = aorta, P = pulmo n ary artery.)
nated venous blood begins to How from the right ventricle through the ventricular septal defect into the left ventricle and aorta, causing cyanosis of the systemic circulation. Stunting is the rule, and continuous or intermittent episodes of d yspnea and cyanosis occur, ultimately resulting in death, u su ally by seven months of age. Dyspnea, lethargy, cyanosis, and fatigue are aggravated by exercise. A systolic murmur is usually present due either to the pulmonic stenosis or the ventricular septal defect, or both. If the pulmonic stenosis is severe, and ventricular pressu res are equal, no murmur may be presen t. Polycyth emia due to the cyanosis may cause an abnormally high packed cell volume.
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Figure 13. Electrocardiogram d epicting right axis d eviation to - 120". This indicates right ventricular hypertrophy, typical of tetralogy o f Fallot, although this is not the same cat seen in Figures 14 and 15. Paper speed = 50 mm/scc, 1 em = 1 mv.
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The electrocardiogram classically demonstrates right axis deviation from right ventricular hypertrophy (Fig. 13), but bundle branch block may occur and cause bizarre axis deviation 2 if the. septal defect interrupts the bundle branches. Thoracic radiographs are examined to d etect right ventricular enlargement and pulmonary undercirculation (Fig. 14). Dye injected into the right ventricle fills the aorta and pulmonary artery simultaneously (Fig. 15).
Figure 14. Thoracic radiographs of an 18 month old male domestic shorthaired cat with te tralogy of Fallot. A, La ter al view with severe right ventricular e nlargem ent tipping the heart horizontally from increased sternal contact. Notice the r adiolucency o f th e lung fi elds due to pulmonar y undercirculatio n . B, Dorsoventral view in which the enlar ged r ight ventricle displaces the heart to the left, falsely giving th e impressio n o f left ventricular enlarge me n t.
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Figure 15. Right ventricular angiocardiogram of t.be same cat with tetralogy of Fall ot seen in Figure 1'1. D ye injected into tbc right ventricle fills the pulmonary artery a nd the aorta sinniltaneously.
Cyanotic episodes may be controlled by the use of propranolol. 5 Surgical correction is impractical, but palliative procedures to increase pulmonary artery flow have been attempted in the cat and may be helpful.3
Congenital Atrioventricular Valvular Insufficiency Dysplasia of the right atrioventricular valve has recently been described,9 and left atrioventricular valve dysplasia is described elsewhere in this volume. Dysplasia involves malformation or malposition of the valve and/or its attachments, a nd results in valvular insufficiency. Often the d ysplastic valve accompanies another defect such as p e rsistent common atrioventricular canal, ventricular septal defect, atrial septal defect, pulmonic ste nosis , or aortic stenosis. 9 It m ay be a single defect of one valve or both atrioventricular valves may be involved. Clinical signs are variable in the affected cat. The m
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REFERENCES l. Bolton, G. R.: Feline cardiology. Feline Pract., 5:42 (Sept./Oct.), 1975. 2. Bolton, G. R., Ettinger, S. J., and Liu, S. K.: Tetralogy of Fallot in three cats. J.A.V.M.A., 160:1622, 1972. 3. Bush, M., Pieroni, D. R., Goodman, D. G., et al.: Tetralogy of Fallot in a cat. J.A.V.M.A., 161:637, 1972. 4. Cohen, ]. S., Tilley, L. P., Liu, S. K., et al.: Patent ductus arteriosus in five cats. J.A.A.H.A., 11:95, 1975. 5. Eyster, G. E., Anderson, L. K., Sawyer, D. C., et al.: Beta adrenergic blockade for management of tetralogy of Fallot in a dog. J.A.V.M.A., 169:637, 1976. 6. Liu, S. K.: Pathology of feline heart disease. In Kirk, R. W. (ed.): Current Veterinary Therapy V. Philadelphia, W. B. Saunders Co., 1974, p. 341. 7. Liu, S. K., and Ettinger, S. J.: Persistent common atrioventricular canal in two cats. J.A.V.M.A., 153:556, 1968. 8. Liu, S. K., Tashjian, R. ]., and Patnaik, A. K.: Congestive heart failure in the cat. J.A.V.M.A., 156:1319, 1970. 9. Liu, S. K., and Tilley, L. P.: Dysplasia of the tricuspid valve in the dog and cat. J.A.V.M.A., 169:623, 1976. 10. Sheridan,]. P., Mann, P. G., and Stock,]. E.: Pulmonary artery banding in the cat: A case report.]. Small Anim. Pract., 12:45, 1971. 11. Tilley, L. P.: Feline cardiology. Scientific Presentations of the 43rd Annual Meeting of the American Animal Hospital Association, 1976, p. 79.
New York State College of Veterinary Medicine Small Animal Hospital Ithaca, New York 14853
Congenital Heart Diseases of the Cat Gary R. Bolton, D.V.M., *and Si-Kwang Liu, D.V.M., Ph.D. t
Congenital diseases of the feline heart play a role of lesser importance than the acquired diseases, accounting for only about 15 per cent of feline heart disease. 6•8 •11 This low incidence has led to a void in the clinical description of even the more common defects. To facilitate their recognition, this paper discusses the clinical presentation of the more common congenital heart diseases of the cat, stressing clinical signs, physical examination, electrocardiography, thoracic radiography, and angiocardiography. The largest study of congenital heart disease in the cat is given in the article on the Pathology of Feline Heart Disease in this volume, in which 107 cats were identified as having congenital abnormalities. Ventricular septal defect, aortic stenosis, atrioventricular valve dysplasia, patent ductus arteriosus, persistent common atrioventricular canal, and tetralogy of Fallot are the most common anomalies. A general summary of the literature indicates the consistent occurrence of other defects such as persistent right aor~ic arch, pulmonic stenosis, atrial septal defect, and neonatal fibrosis, although the etiology of the latter condition is uncertain.1 At present, there are no firmly established breed or sex predispositions. The incidence of the congenital heart diseases may be low, but their importance should not be minimized. Most cats with congenital heart disease die by one year of age. 8 In addition, the most important feline heart diseases, the cardiomyopathies, may occur in young cats. When they do, congenital heart disease is an important consideration in the differential diagnosis.
*Associate Professor of Small Animal Medicine and Cardiology, New York State College of Veterinary Medicine, Ithaca, New York. tSenior Staff, Department of Pathology, The Animal Medical Center, New York, New York
Veterinary Clinics
of North America-Vol.
7, No. 2, May 1977
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VENTRICULAR SEPTAL DEFECT Ventricular septal defect occurs alone or may contribute to a more complex anomaly. It is usually located in the ventricular septum just below the aortic valve in the left ventricle, and just beneath the septal leaflet of the right atrioventricular valve in the right ventricle. It allows shunting of blood from the high pressure left ventricle to the low pressure right ventricle. The resultant overfilling of the right ventricle causes right ventricular enlargement. The right ventricle ejects the blood into the pulmonary artery, causing the pulmonary arteries to enlarge (pulmonary overcirculation). High volume flow through the lungs causes increased pulmonary venous return to the left atrium and left ventricle. This volume overload results in left heart enlargement. Severely affected cats die in the first few days or weeks oflife. If they survive initially, it is not known how long they may live, but most cats with ventricular septal defect will probably die by one year of age. The cat may be presented in heart failure, but often the murmur is auscultated during routine physical examination for vaccination. The murmur is loud, and although it may be heard on both sides of the chest, it tends to be loudest over the right 4th or 5th intercostal space near the sternal border. A B-B shot femoral pulse may be appreciated. The electrocardiogram is often normal, but may show signs of biventricular enlargement and biatrial enlargement (Fig. 1). Thoracic radiographs may also be unspectacular, but should be examined for signs of biventricular, left atrial, and pulmonary artery enlargement
Figure l. Electrocardiogram recorded from a cat with a ventricular septal defect. Right axis deviation ( -120°), and the presence of an S-wave in leads I, 11, and III indicate right ventricular hypertrophy. The tall R-waves in lead II mav indicate left ventricular hyp~rtrophy. Biatrial enlargement is indicated by the tall, wide P-waves. Paper speed = 50 mm/sec, l em= l rnv.
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Figure 2. thoracic radiographs from the cal with a ventricular septal defect in Figure 1. A, The lateral view demonstrates biventricular enlargement. Indentation of the tracheajust. crania l to the carina is caused by right atrial enlarge ment. The left atrium is not well visualized. Prominent pulmonary arteries suggest overcirculation and a left-to-right shunt. B , This dorsoventral view confi rms the p r esence of biventricular enlargement, a nd left a trial enlargement is now a pparent (arrows ).
(Fig. 2). Radiopaque dye injected into the left ventricle demonstrates the defect as the dye passes through it into the right ventricle (Fig. :3). Medical therapy for congestive heart f ailure may be temporarily helpful if clinical signs develop, but surgery is a more permanent cure. Open heart surgery is impractical, but pulmonary artery banding is feasible and has been reported to help. 10 Banding the pulmonary artery
Figure 3. Left ventricular angiocardiogram of the same cat with ventricular septal d efect. Th e cathe ter (C) passes into the left ventricle (L). Dye fiows across the ventricular septal defect (an·ow) , into the right ventricle , across the pulmonic valve, and in to the pulmonary artery (P ). This causes si multaneous filling of the aorta and pulmo nary artery, from the left ventricle . (From Tilley, L. 1'.: Feline Cardiology. V ET. CLTN. :--ioRTH AM., 6:4 3 1, 1976, with permission. )
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causes increased right ventricular pressure, which decreases the amount of left-to-right shunting. Asymptomatic cats require only watchful waitmg. Aortic Stenosis
Aortic stenosis implies resistance to left ventricular outflow. The stenosis may be below the valve (subvalvular), at the valve (valvular), or above the valve (supravalvular). The cat is unique in that the stenosis is often supravalvular, 6 as opposed to the subvalvular type that is usual for the dog. The supravalvular constriction shapes the aorta into an hourglass configuration, and is associated with a malformation of the aortic valve.r; Regardless of the site of the stenosis, left ventricular enlargement results, and eventually left atrial enlargement occurs. The affected cat develops acute heart failure at a young age and is often stunted by this defect. The aortic stenosis murmur is a harsh systolic murmur, heard best over the aortic-pulmonic area. It tends to radiate rightward, and may be even louder at the right 3rd or 4th intercostal space near the sternal border. It also tends to radiate to the neck and up the carotid arteries. The femoral pulse may be small, but this is difficult to appreciate in a cat. Electrocardiograms may be normal or may detect left ventricular enlargement. Most cases show left axis deviation (Fig. 4). Radiographically, left ventricular and left atrial enlargement, as well as a poststenotic dilatation of the aorta may be present (Fig. 5). Dye injected into the left ventricle clearly shows the area of stenosis (Fig. 6).
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Figure 4. Electrocardiogram recorded from an 18 month old female domestic short haired Gltwith sup! avalvular aortic stenosis. A marked left axis deviation to -80° indicates left ventricular hypertrophy and/or left anterior Fascicular block. The P waves in lead II are partially lost in the T waves or the preceding beats, but they appear to be too wide, an indication or left atrial enlargement. Paper speed = 50 mm/sec, 1 em = l mv.
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Figure 5. Thoracic radiograph s from the same cat seen in Figure 4 . A, Biventricular and left atrial enlargement is demonstrated in this lateral view. B, Dorsoventral view demonstrates genera lized cardiomegaly, but the left heart. is esp ecially prominent.
Figure 6. Left ventricu lar a ngioca rdiogram of the cat seen in Figures 4 and 5. The stricture occurs in the aorta, above the aortic valve (arr01v p oints to valve). T he aorta takes an h ourglass conhguratio n. The postste n otic dilatation of the aorta contributes a great deal to t he a rea that was thought to be right ventricu lar enlargement in Figure 5A. Opacification of the left a trium is ca used b y regurgitation of dye throu gh an insufficient lef t atrioventricular valve.
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Practically speaking, little can be done for these cats. Propranolol (Inderal) is a drug that is helpful in reducing the high left ventricular pressure and in decreasing the tendency toward tachycardia and arrhythmia (see the article in this symposium on therapy in feline cardiac disease). Patent Ductus Arteriosus
Failure of the ductus arteriosus to close within the first few days or weeks of life results in a patent ductus arteriosus. It is usually a solitary defect but may occur in concert with other defects. The patent ductus permits flow of blood from the high pressure aorta into the low pressure pulmonary artery. Aortic pressure remains higher than pulmonary artery pressure in both systole and diastole, and blood flow across the defect is continuous unless significant pulmonary hypertension develops. The resultant overload of the pulmonary arteries causes them to enlarge (pulmonary overcirculation), and pulmonary venous return to the left atrium is increased, causing a volume overload of the left heart. Eventually, biventricular, left atrial, and even biatrial enlargement occurs. The aorta and pulmonary artery tend to develop aneurysmal dilatation of their proximal portions. Cats may die soon after birth. If they survive the immediate postpartum period, most will develop signs of heart failure by one year of age. Clinical signs are lethargy, dyspnea, exercise intolerance, and stunting. If the cat is asymptomatic, the murmur may be discovered during routine physical examination at the time of vaccination. The murmur is usually loud and is continuous throughout systole and diastole. It is best heard over the aortic-pulmonic valve region on the left and tends to radiate rightward and toward the thoracic inlet on the base of the sternum. A B-B shot femoral pulse is characteristic of this defect. The most consistent electrocardiographic finding is that of left ventricular hypertrophy. Left atrial and right ventricular hypertrophy may also be seen (Fig. 7). Thoracic radiographs vary but should be examined for biventricular and left atrial enlargement, pulmonary overcirculation, and aortic or pulmonic aneurysmal dilatation (Fig. 8). Dye injection into the aorta demonstrates the patent ductus (Fig. 9). Surgery is the treatment of choice for patent ductus arteriosus. Closure of the defect is similar to that for the dog with the exception that entrance into the thorax is gained through the left 6th intercostal space rather than the 4th as in the dog. 4 Persistent Common Atrioventricular Canal
A large septal defect that involves both the atrial and ventricular septum creates communication of all four cardiac chambers through a single defect, and is the basis for a common atrioventricular canal. The defect is in the lowermost portion of the atrial septum and the uppermost portion of the ventricular septum. The atrioventricular valves form
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Figure 7. Electrocardiogram recorded from an 8 mon th old domestic shorthaired cat with patent ductus arteriosus. The tall R waves in lead 11 signify left ventricular h ypertrophy. The axis of+ 100°, despite left ventricular hypertrophy, suggests right ventr icular hypertrophy. The tall wide P waves in lead II indicate bia trial enlarge ment. Paper speed = 50 mm/sec, l em= l mv. (From Cohe n , J. S., Tilley, L. P ., Liu, S.-K. , and DeHoff, W. D.: Patent ductus arteriosus in five cats. J.A .A.H.A., 11 :Ja n/ Feb. 1975, with permi ssion.)
Figure 8. Thoracic radiograp h s from the cat seen in Figure 7. A, T he lateral view demonstrates right ventricu lar enlargement ( I ) and left atria l enlargement (clear arrow) . Prominen t pulmonary arteries suggest overcirculation due to a left-to-right shunt. B, The . dorsoventral view confirms biventricular and left atrial (solid arrow) enlargement. Aneurysmal aortic dilatation is outlined by the clear arrows. (From Cohen, J. S., Tilley, L. P., Liu, S.-K. , and De Hoff, W. D.: Patent ductus arteriosu s in five cats. JA.A.H.A., 11 :Jan./Feb. , 1975, with per mission.)
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Figure 9. Aortic angiogram of the cat seen in Figures 7 and 8. Dye injected through the catheter (C) into the aorta (A) crosses the pa tent ductus (D) in to the pulmonary arter y (P) causing simultaneous fi lling of both vessels. T he le ft atriu m (LA) and left ventricle (LV) are opacified by d ye from the lungs via the pulmonary veins. (FTOrn Cohen, ]. S., Tilley, L. P., Liu, S.-K. , and DeHoff, W. D.: Patent ductus arteriosus in five cats. J.A.A.H.A., 11 :Jan ./Feb., 1975, with permission.)
in this r egion, and valvular defects are usually present. Cats with this d efect tend to develop m assive generalized cardiomegaly. The r ight atrium a nd ventricle enlarge because of the left-to-right flow from the left atrium and ventricle. Large pulmonary blood flow causes pulmonary artery enlargement (pulmonary overcirculation) and increased pulmonary venous return causes volume overload of the left h eart with leftsided cardiomegaly. A potential for cyanosis exists if pulmonary h ypertension causes right heart pressures to approximate or exceed those of the left. Affected kittens ar e usually stunted if they su rvive the immediate postpartum period, and death by 6 or 7 months of age is usual. A loud, mixed frequency systolic murmur is h eard best over the left cranial ventral thorax presumably due to a · relative or functional pulmonic stenosis. 7 A murmur of mitral insufficiency caused by a d eformed mitral valve m ay be heard, and righ tward r adiation may result from the ven tricular septal d efect or a d eform ed tr icu spid valve. If right ventricular pressure rises, th e murmur will diminish in inten sity or even disappear as flow across the defect diminishes. T he electrocardiogram is characterized by axis deviations and by wide QRS complexes, since the large defect in the septum cau ses bundle branch blocks (Fig. 1 0). Generalized cardiomegaly as seen on thoracic radiograph s can be spectacular (Fig. 11). Dye injected into the left ventr icle fills all chambers simultaneously (Fig. 12) . H eart failure is sever e and intractable, requiring a grave prognosis.
Tetralogy of Fallot Ventricular septal d efect and pulmonic sten osis combine to produ ce the deadly anomaly, tetralogy of Fallot. O verriding aorta and righ t ven tricular hyp ertrophy ar e incidental abnormalities that comple te th e te tralogy. Pulmonic ste n osis elevates right ventricular pressure until it either approximates or exceeds left ventricular pressure, a nd unoxyge-
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I Figure l 0. Electrocardiogram recorded from a S year old male domestic shorthaired cat with a commo n atrioventricular canal. Right bundl e branch block is indicated by the large, wide , negative terminal deflections in leads I, II, III , aVF, V2 and V10 . Paper speed = 50 mm/sec, l em = l mv.
Figure 11. Lateral thoracic radiog raph of the same cat as in Figure 10. Generalized cardiomegaly is obvious.
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Figure 12. Angiocardiogram of th e same ca t as in Figures I 0 and 11. Dye injected into the area of the atrioventricular defect opacifies all ch ambers simultaneously. (LA = left atrium, LV = left ventricle , RA = right atrium, R V =righ t ventricle, A = aorta, P = pulmo n ary artery.)
nated venous blood begins to How from the right ventricle through the ventricular septal defect into the left ventricle and aorta, causing cyanosis of the systemic circulation. Stunting is the rule, and continuous or intermittent episodes of d yspnea and cyanosis occur, ultimately resulting in death, u su ally by seven months of age. Dyspnea, lethargy, cyanosis, and fatigue are aggravated by exercise. A systolic murmur is usually present due either to the pulmonic stenosis or the ventricular septal defect, or both. If the pulmonic stenosis is severe, and ventricular pressu res are equal, no murmur may be presen t. Polycyth emia due to the cyanosis may cause an abnormally high packed cell volume.
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Figure 13. Electrocardiogram d epicting right axis d eviation to - 120". This indicates right ventricular hypertrophy, typical of tetralogy o f Fallot, although this is not the same cat seen in Figures 14 and 15. Paper speed = 50 mm/scc, 1 em = 1 mv.
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The electrocardiogram classically demonstrates right axis deviation from right ventricular hypertrophy (Fig. 13), but bundle branch block may occur and cause bizarre axis deviation 2 if the. septal defect interrupts the bundle branches. Thoracic radiographs are examined to d etect right ventricular enlargement and pulmonary undercirculation (Fig. 14). Dye injected into the right ventricle fills the aorta and pulmonary artery simultaneously (Fig. 15).
Figure 14. Thoracic radiographs of an 18 month old male domestic shorthaired cat with te tralogy of Fallot. A, La ter al view with severe right ventricular e nlargem ent tipping the heart horizontally from increased sternal contact. Notice the r adiolucency o f th e lung fi elds due to pulmonar y undercirculatio n . B, Dorsoventral view in which the enlar ged r ight ventricle displaces the heart to the left, falsely giving th e impressio n o f left ventricular enlarge me n t.
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Figure 15. Right ventricular angiocardiogram of t.be same cat with tetralogy of Fall ot seen in Figure 1'1. D ye injected into tbc right ventricle fills the pulmonary artery a nd the aorta sinniltaneously.
Cyanotic episodes may be controlled by the use of propranolol. 5 Surgical correction is impractical, but palliative procedures to increase pulmonary artery flow have been attempted in the cat and may be helpful.3
Congenital Atrioventricular Valvular Insufficiency Dysplasia of the right atrioventricular valve has recently been described,9 and left atrioventricular valve dysplasia is described elsewhere in this volume. Dysplasia involves malformation or malposition of the valve and/or its attachments, a nd results in valvular insufficiency. Often the d ysplastic valve accompanies another defect such as p e rsistent common atrioventricular canal, ventricular septal defect, atrial septal defect, pulmonic ste nosis , or aortic stenosis. 9 It m ay be a single defect of one valve or both atrioventricular valves may be involved. Clinical signs are variable in the affected cat. The m
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REFERENCES l. Bolton, G. R.: Feline cardiology. Feline Pract., 5:42 (Sept./Oct.), 1975. 2. Bolton, G. R., Ettinger, S. J., and Liu, S. K.: Tetralogy of Fallot in three cats. J.A.V.M.A., 160:1622, 1972. 3. Bush, M., Pieroni, D. R., Goodman, D. G., et al.: Tetralogy of Fallot in a cat. J.A.V.M.A., 161:637, 1972. 4. Cohen, ]. S., Tilley, L. P., Liu, S. K., et al.: Patent ductus arteriosus in five cats. J.A.A.H.A., 11:95, 1975. 5. Eyster, G. E., Anderson, L. K., Sawyer, D. C., et al.: Beta adrenergic blockade for management of tetralogy of Fallot in a dog. J.A.V.M.A., 169:637, 1976. 6. Liu, S. K.: Pathology of feline heart disease. In Kirk, R. W. (ed.): Current Veterinary Therapy V. Philadelphia, W. B. Saunders Co., 1974, p. 341. 7. Liu, S. K., and Ettinger, S. J.: Persistent common atrioventricular canal in two cats. J.A.V.M.A., 153:556, 1968. 8. Liu, S. K., Tashjian, R. ]., and Patnaik, A. K.: Congestive heart failure in the cat. J.A.V.M.A., 156:1319, 1970. 9. Liu, S. K., and Tilley, L. P.: Dysplasia of the tricuspid valve in the dog and cat. J.A.V.M.A., 169:623, 1976. 10. Sheridan,]. P., Mann, P. G., and Stock,]. E.: Pulmonary artery banding in the cat: A case report.]. Small Anim. Pract., 12:45, 1971. 11. Tilley, L. P.: Feline cardiology. Scientific Presentations of the 43rd Annual Meeting of the American Animal Hospital Association, 1976, p. 79.
New York State College of Veterinary Medicine Small Animal Hospital Ithaca, New York 14853