Congenital heart disease: VALVULAR REGURGITATION and cyanotic heart disease- Ettinger Flashcards

Question

Administration of beta-blockers, calcium channel blockers, and/or digoxin is helpful in some cases for the management of atrial fibrillation or other supraventricular tachyarrhythmias. Some patients tolerate serious defects surprisingly well for many years. In other cases there is rapid progression to heart failure and death.

Answer 1

Administration of beta-blockers, calcium channel blockers, and/or digoxin is helpful in some cases for the management of atrial fibrillation or other supraventricular tachyarrhythmias. Some patients tolerate serious defects surprisingly well for many years. In other cases there is rapid progression to heart failure and death.

Answer 2

Pulmonic stenosis (PS) is the third most common congenital heart defect occurring in dogs, and is occasionally recognized in cats. PS occurs in the majority of cases as an isolated heart defect, but it is also frequently accompanied by additional cardiac anomalies, such as tricuspid dysplasia. Congenital outflow tract obstructions of the right heart can develop in the subvalvular and supravalvular regions, but primary malformation of the pulmonary valve (dysplasia) is the most frequently observed defect in dogs.

Answer 3

Patterson and associates, who studied the heritability and pathology of pulmonic valve dysplasia in the Beagle, initially suggested a polygenic mode of transmission for this defect. These breeding studies did not, however, exclude the possibility of a single gene mechanism with variable penetrance. The pattern of inheritance of PS has not been studied in other predisposed dog breeds or in cats.

Answer 4

PATHOLOGY Valvular lesions consist of varying degrees of valve thickening, leaflet fusion, and/or hypoplasia of the valve annulus. While some dogs manifest a thin dome-shaped valve with a central orifice (Figure 249-27), many dogs have more complicated lesions resembling atypical PS in children.15a,86a,88a The valve leaflets are often thickened, misshapen, and/or fused (see Figure 249-27). The annulus of the pulmonic valve is hypoplastic in some dogs, further narrowing the area available for right ventricular ejection.

Answer 5

Histologic abnormalities include thickening of the valve spongiosa and the presence of bands of fusiform cells in a dense collagen network. These changes are thought to represent overproduction of normal valve elements or a failure of conversion of the cushionlike embryonic valve primordia.

Answer 6

Some dogs with valve dysplasia also have a fibrous ring just below the valve leaflets accompanying the valvular changes. In other dogs and cats[46] the obstructive lesion occurs in the infundibular region of the RVOT. On occasion the RVOT is partitioned from the body (inflow region) of the right ventricle by a well-developed, fibromuscular ridge, resulting in an anomaly referred to as double- or dual-chambered right ventricle.[48

Answer 7

Supravalvular PS is uncommon, and in the authors’ experience, is most often observed in Giant Schnauzers.

Answer 8

A unique form of subvalvular PS caused by anomalous development of the coronary arteries has been described in English Bulldogs and Boxers.[49],[50] In this condition, the left and right coronary arteries branch from a single large coronary artery, which originates from the right aortic sinus of Valsalva (Figure 249-28). From this location, the anomalous left coronary artery encircles the RVOT just below the pulmonary valve, thereby contributing to the subvalvular component of this complex malformation (see Figure 249-28).

Answer 9

Figure 249-28 Coronary artery anomaly seen in some English Bulldogs with pulmonic stenosis. A, Left and right coronary arteries are seen to branch from a single large coronary artery that originates from the right aortic sinus of Valsalva. From this location, the left coronary artery encircles the right ventricular outflow tract just below the level of the pulmonary valve. B, Anterior wall of the pulmonary artery and right ventricle (RV) has been removed to show the hypoplastic annulus, the diminutive proximal pulmonary artery (PA), and the crowded and thickened pulmonary valve leaflets. Ao, Aorta; LV, left ventricle.

Answer 10

Increased resistance to systolic ejection results in concentric right ventricular hypertrophy, which generally develops in proportion to the severity of the obstructing defect. While this compensatory response serves to normalize wall stress, it can have deleterious consequences. In some dogs with PS, secondary hypertrophy of the infundibular region of the RVOT contributes to outflow tract obstruction, particularly during exercise or stress. The existence of this additional mechanism of obstruction can complicate the clinical outcome of surgical valvotomy or interventional balloon valvuloplasty.

Answer 11

Other cardiac defects can complicate the physiology and alter the clinical presentation and prognosis of patients with PS. PS and tricuspid valve dysplasia can be a particularly injurious combination. Insofar as the volume of tricuspid regurgitation is a function of the size of the regurgitant orifice (severity of dysplasia) and the systolic pressure gradient (severity of PS), severe tricuspid regurgitation tends to develop in affected dogs, leading to intractable right-sided heart failure.

Answer 12

Meticulous ultrasonic examination, often using contrast echocardiography, will reveal that patent connections between the right and left heart occur in a substantial percentage of dogs with PS, and some dogs with severe PS become cyanotic as a result of right-to-left shunting through an ASD, patent foramen ovale, or VSD. Many of these abnormalities have a common origin in the maldevelopment of the embryonic conotruncal septum. These types of defects are discussed more thoroughly under the heading of tetralogy of Fallot.

Answer 13

PATHOPHYSIOLOGY Obstruction to right ventricular outflow increases resistance to ejection, causing a proportional increase in ventricular systolic pressure. Concentric hypertrophy of the right ventricle develops in an attempt to normalize wall stress. During systole, blood ejected from the right ventricle accelerates as it traverses the obstructive orifice. Blood flow velocity increases and becomes turbulent distal to the obstruction. A poststenotic dilation develops in the main pulmonary artery as the turbulent jet of blood decelerates and expends some of its kinetic energy against the vessel wall.

Answer 14

Concentric hypertrophy reduces right ventricular diastolic compliance, impairs ventricular filling, and often results in elevated right atrial pressure. Tricuspid regurgitation from progressive ventricular dilation, valvular dysplasia, or a combination of these factors, can contribute to further increases in atrial pressure. As right atrial pressure approaches 15 mm Hg, jugular distension, ascites, pleural effusion, and other signs of right-sided congestive heart failure develop.

Answer 15

Syncope and sudden death are uncommon in dogs with PS the physiologic mechanisms responsible have not been elucidated. Hypotension is presumed to develop as a consequence of reduced cardiac output (secondary to bradycardia or worsening of a dynamic infundibular obstruction) and in combination with peripheral arteriolar vasodilation (with or in anticipation of exercise). Stimulation of mechanoreceptors in the pressure overloaded right ventricle may trigger the reflex bradycardia and vasodilation.

Answer 16

Reduced right coronary blood flow has been documented in some dogs with PS and may contribute to the development of syncope, exercise intolerance, and myocardial failure. On rare occasion, severe septal hypertrophy caused by PS results in dynamic LV outflow tract obstruction.

Answer 17

PS is common in certain breeds including Beagles, Samoyeds, Chihuahuas, English Bulldogs, Miniature Schnauzers, Cocker Spaniels, Boykin Spaniels, Labrador Retrievers, Mastiffs, Chow Chows, Newfoundlands, Basset Hounds, and other terrier and spaniel breeds.8a,9a, 9b,19b Miniature Doberman Pinschers also seem predisposed.

Answer 18

Most dogs with PS are asymptomatic during the first year of life when the condition is usually discovered via detection of a heart murmur. Approximately 35% of dogs with severe disease demonstrate clinical signs, which can include exertional fatigue, syncope, or ascites.[51] Signs of congestive right heart failure, such as ascites, are most often reported in dogs that are older.88a In cats with severe PS, exertional dyspnea and lethargy may be present.[47] Cyanosis may be noted when PS is complicated by right-to-left shunting across a patent foramen ovale or coexisting atrial or ventricular septal defect.

Answer 19

The most prominent physical examination finding is a systolic ejection murmur that is best heard over the left heart base and that often radiates dorsally. In some cases the murmur is heard equally well on the right cranial thorax. In dogs with concurrent severe pulmonic valvular insufficiency, the systolic ejection murmur is accompanied by a soft decrescendo diastolic murmur heard best just ventral to the pulmonic valve region. A holosystolic murmur of tricuspid regurgitation may be noted over the right hemithorax as well. Large amplitude jugular pulses may result either from a giant a wave caused by atrial contraction into the stiff right ventricle or from cv waves indicating significant tricuspid regurgitation. Jugular venous distension and prominent jugular pulses are evident in most dogs with right heart failure and ascites. Peripheral arterial pulses are usually normal.

Answer 20

Right ventricular enlargement is usually present on the electrocardiogram unless the lesion is very mild.31a,32a,90a Right axis deviation, and deep S waves in leads I, II, III, and the left precordial chest leads (V2, V4) are common indicators of right heart enlargement (Figure 249-29).

Answer 21

Thoracic radiographs typically show a prominent right heart and poststenotic dilation of the main pulmonary artery (Figure 249-30).8a,22a-24a,88a These changes are usually most evident on the dorsoventral view. Additional and more variable findings include dilation of the proximal left pulmonary artery, diminished size of the pulmonary vasculature, and enlargement of the caudal vena cava

Answer 22

Echocardiography is the most commonly used method for confirming a diagnosis of PS. M-mode and 2D imaging typically show concentric hypertrophy of the right ventricle, increased prominence of the papillary muscles, deformity in the region of the obstruction(s), narrowing of the RVOT, varying degrees of right atrial enlargement, and poststenotic dilation of the main pulmonary artery (Figure 249-31).[3],[52] Of the four cardiac valves, the pulmonic valve is often the most difficult to visualize clearly by transthoracic echocardiography. Thus, it is impossible to visualize the exact location and nature of the obstruction in some dogs. It is often particularly difficult to identify a discrete subvalvular obstruction in close proximity to the pulmonary valve. The pulmonic valve leaflets are typically thickened, often fused, and appear to dome upwards into the pulmonary artery during systole (see Figure 249-31). Hypoplasia of the pulmonic valve annulus further obscures the valve anatomy and confounds consideration of treatment. Color flow Doppler echocardiography is useful in establishing the anatomic location of the obstruction, as the turbulent, high-velocity jet can usually be seen emerging just distal to the obstructive orifice (see Figure 249-31). Mild to moderate pulmonic valve insufficiency is also apparent in many dogs affected with valvular PS.

Answer 23

To accurately quantify the severity of the obstruction, the peak velocity of the blood flow jet must be recorded on a spectral Doppler tracing acquired with the continuous-wave Doppler beam in parallel alignment with the direction of flow (see Figure 249-31). This is usually accomplished from either the right or left cranial parasternal windows. The modified Bernoulli equation, ΔP = 4V2, is applied to relate the instantaneous pressure gradient across an obstruction (ΔP, in mm Hg) to the peak velocity of jet distal to the obstruction (V, in meters/second). As a general rule, Doppler-derived gradients are 40% to 50% higher than the gradient measured during cardiac catheterization in an individual dog.20b Such discrepancies are attributed in part to the fact that Doppler studies are performed in awake animals, and transvalvular flow is considerably higher in these circumstances than in dogs that have been anesthetized for cardiac catheterization. In addition, hemodynamic studies typically indicate the severity of obstruction as a peak-to-peak pressure gradient, and such measures are almost always lower than the instantaneous peak pressure gradient calculated from Doppler measures of peak flow velocity.[53]

Answer 24

Doppler interrogation of the right heart is also particularly helpful for identifying and assessing the severity of coexisting tricuspid valve insufficiency. Measuring the velocity of this regurgitant jet is particularly helpful for assessing the severity of the PS obstruction when it is not possible to attain proper alignment with flow through the outflow tract. In dogs with both dynamic (infundibular) and fixed (valvular) stenosis, Doppler interrogation of the outflow tract and pulmonary artery can produce a tracing that displays the temporal and velocity relationship between the two components of the stenosis.

Answer 25

Angiocardiography is often performed just before balloon valvuloplasty or to clarify right heart anatomy in anticipation of surgery. Such studies clearly demonstrate the anatomic location of the obstruction(s), the degree of right ventricular hypertrophy, presence of tricuspid regurgitation, and the poststenotic dilation of the pulmonary artery. The angiographic features of valvular stenosis consist of any combination of the following: narrowing at the immediate base of the valve sinuses, asymmetrical valve sinuses, hypoplasia of the annulus or a valve sinus, thickening of individual valve leaflets producing a lucent filling defect, narrowing of the dye column with a central or asymmetric jet of contrast observed within a narrowed valve orifice, or systolic doming of the valve (indicating fusion of the commissures) (Figure 249-32).86a,88a Dynamic muscular obstruction of the right ventricular infundibulum is often visible in dogs with PS (Figure 249-33). The term double-chambered right ventricle is applied when the right ventricle is divided into a low-pressure region (the infundibulum) and a region of high pressure (the apex and inlet portion of the RV) by a muscular or fibromuscular ridge deep in the infundibulum (Figure 249-34). Left ventricular angiography or coronary arteriography should be performed when abnormalities of the left heart or coronary circulation are suspected. Such studies must be performed whenever surgery or balloon valvuloplasty is contemplated in an English Bulldog or Boxer dog. Enlargement of the right coronary artery is an expected finding in all dogs with PS and well-developed right ventricular hypertrophy.

Answer 26

Hemodynamic confirmation of outflow tract obstruction is accomplished by measuring a systolic pressure gradient across the lesion (see Figure 249-1). The severity of the obstruction is usually defined as the difference in peak systolic pressures measured above and below the obstruction (peak-to-peak pressure gradient). Inasmuch as the recorded gradient varies with the rate of flow across the obstruction, this measurement is greatly affected by myocardial contractility and the anesthetic regimen selected. Despite these limitations, the systolic pressure gradient has been used to divide patients with PS into mild (80 mm Hg) categories.87a,88a,93a A more accurate approach requires the measurement of cardiac output and calculation of the functional area of the constricted orifice.

Answer 27

Precise criteria for establishing an accurate prognosis have not been developed for dogs and cats with PS. Clinical experience indicates that most dogs with mild and even moderate PS (Doppler derived gradient

Answer 28

CLINICAL MANAGEMENT Patients with uncomplicated PS of mild or moderate severity usually do not require treatment. Serial echocardiographic examinations can be performed to monitor the degree of ventricular hypertrophy, development of secondary infundibular stenosis, and development of tricuspid regurgitation. Exercise restriction is usually unnecessary. Some dogs will develop more severe obstruction over time.

Answer 29

Dogs with severe or symptomatic disease are candidates for surgery or balloon valvuloplasty. The exact pressure gradient warranting intervention cannot be stated with certainty. Dogs with a Doppler gradient exceeding 100 to 125 mm Hg should be considered candidates for balloon valvuloplasty or surgery. Dogs with lesser gradients are also candidates for these procedures if they are symptomatic or have a large amount of tricuspid regurgitation. Intervention at a young age should be encouraged as the development of overt congestive heart failure substantially lessens the chance for a successful outcome, regardless of the method of repair. Because of a high likelihood of heritability, even mildly affected dogs should not be bred.

Answer 30

The goals of intervention in dogs with severe PS are to abolish or reduce the systolic pressure gradient to the mild range and to provide symptomatic relief in dogs experiencing clinical signs. For many years, surgery was the only available option for treating PS, and a number of surgical techniques have been advocated, including valve dilation, patch grafting, or the placement of a conduit from the RV to the pulmonary artery.* The open patch-graft technique is a particularly versatile and cost-effective method for treating dogs with PS, particularly when there is a substantial subvalvular obstruction.22b,34c,35c This technique is well-suited to the treatment of some defects not amenable to balloon valvuloplasty (e.g., dogs with muscular RVOT obstructions, double-chambered right ventricle, or severe hypoplasia of the pulmonic annulus). The patch-graft technique should not be performed in dogs with subvalvular PS caused by anomalous coronary artery development as severing of the artery and death will result.

Answer 31

Catheter-based percutaneous balloon valvuloplasty is a preferred alternative to surgery in many dogs with valvular PS.[†] A dilation catheter tipped with an inflatable balloon is placed across the obstructing orifice and repeatedly inflated (Figure 249-35). Successful reduction of the obstructive gradient by 50% or more has been reported in 75% to 80% of the dogs treated with this technique.[51,55-57] Retrospective analysis of 40 dogs that underwent balloon valvuloplasty indicated a 53% reduction in mortality as compared with 41 dogs that did not undergo the procedure.[58]

Answer 32

Improvements in balloon catheter design and refinements in technique have expanded the application of this procedure to dogs weighing as little as four pounds40c and in cats.[46] Balloon valvuloplasty is most successful when the pulmonary annulus is normally developed and the valves are relatively thin and fused. More variable results are obtained in dogs with complex lesions and hypoplasia of the pulmonary annulus.38c,41c Thus, careful evaluation of the pulmonary valve, annulus, and RVOT is important in predicting short-term outcome of the valvuloplasty procedure, and may be of greater importance than selection of balloon size.[59] In the authors experience, balloon dilation is of dubious value in dogs with severe muscular RVOT obstructions or double-chambered type defects. While balloon valvuloplasty is generally regarded as a safe procedure with a low complication rate, life-threatening problems such as hemorrhage, cardiac puncture, and arrhythmias do occur. Dogs with hypoplasia of the pulmonary annulus or anomalous development of the coronary arteries are at particular risk for serious complications, including avulsion of the coronary artery or rupture of the pulmonary annulus.36c Delayed re-stenosis can occur, but this is not thought to be an important problem.[56] When congestive heart failure or atrial fibrillation develops secondary to PS, the prognosis is poor. If medical stabilization can be achieved, balloon valvuloplasty or surgery can be attempted.

Answer 33

Subvalvular aortic stenosis (SAS) is the most common congenital cardiac malformation in large breed dogs.97a-109a,1c-5c,42c Most cases of SAS result from a fixed ridge or ring of fibrous tissue located in the LVOT, just below the aortic valve. SAS is a problematic disorder for several reasons. It is very difficult to diagnose in mildly affected dogs and it is difficult to treat when it is severe.

Answer 34

The phenomenon of dynamic SAS is also being recognized with increasing frequency in dogs and cats with a variety of cardiac disorders, including fixed SAS, mitral valve dysplasia, hypertrophic cardiomyopathy, and other conditions causing hypertrophy of the interventricular septum (i.e., PS, tetralogy of Fallot)

Answer 35

Bull Terriers are predisposed to valvular aortic stenosis wherein the leaflets are thickened and the aortic valve annulus is mildly hypoplastic. Boxers also demonstrate aortic annulus diameters that are smaller than other breeds of dogs, and this confounds diagnosis of mild disease in this breed.[60] Mild AS caused by a bicuspid valve occurs on rare occasion. Fixed aortic stenosis has been described in a small number of cats,12a,13a,36a,25b including one case of supravalvular stenosis.101a

Answer 36

PATHOLOGY AND PATHOGENESIS SAS has been extensively studied in the Newfoundland dog. Breeding studies in this breed have established a genetic basis for the perpetuation of SAS.4a,100a The pattern of inheritance is most compatible with an autosomal dominant mode of transmission with modifying genes; however, a polygenic mechanism can not be excluded. The breeding colony studies of Pyle and Patterson further indicate that the obstruction may not be present at birth, but instead develops during the first 4 to 8 weeks of life.4a,99a,100a,103a,104a This progression has particular significance relative to the identification of cardiac murmurs in pups of breeds known to be at risk for SAS.

Answer 37

The lesions of SAS in Newfoundlands have been described in postmortem studies as mild (grade 1), consisting of “small, whitish, slightly raised nodules on the endocardial surface of the ventricular septum immediately below the aortic valve”; moderate (grade 2), consisting of a “narrow ridge of whitish, thickened endocardium” extending partially about the LVOT; and severe (grade 3), consisting of “a fibrous band, ridge, or collar completely encircling the LVOT just below the aortic valve.”4a,100a This ring is raised above the endocardium, extends to, and may involve the cranioventral leaflet of the mitral valve and the base of the aortic valves (Figure 249-36). The stenotic ring consists of loosely arranged reticular fibers, mucopolysaccharide ground substance, and elastic fibers. Discrete bundles of collagen and even cartilage are found in advanced lesions.100a Cardiac catheterization of dogs with grade 1 lesions failed to reliably detect the postmortem lesion, whereas grade 2 lesions often were associated with soft cardiac murmurs and minimal systolic pressure gradients. As evidenced by these studies, clinical detection of mild SAS may be quite difficult, and that genetic counseling may be fraught with error. A variety of cardiac abnormalities can accompany SAS, most notably mitral valve dysplasia, PDA, and a host of aortic arch abnormalities. The valvular lesions seen in Bull Terrier dogs, including myxomatous degeneration and cartilaginous metaplasia of the valve leaflets, resemble those in humans with calcific valvular stenosis.[61]

Answer 38

In some affected dogs, the pathologic findings diverge from the classical description. The anterior mitral valve leaflet is thickened in apposition to a septal plaque of endocardial fibrosis where the mitral leaflets impacts the interventricular septum as a consequence of dynamic obstruction.[62] Instead of a fibrous collar, the septum is uniformly hypertrophied or a broad fibromuscular ridge, arising from the base of the interventricular septum, protrudes into the LVOT. Malformed, malpositioned, or malaligned papillary muscles, thickened chordae tendineae, and elongated or distorted mitral leaflets contribute to the development of obstruction.[63]

Answer 39

Concentric hypertrophy of the left ventricle develops in dogs with valvular, fixed or dynamic SAS more or less in proportion to the severity of the outflow obstruction, albeit that the correlation between wall thickness and the magnitude of the measured gradient is often poor.[64] Structural and functional abnormalities of the left ventricle[65] and coronary circulation are well documented in dogs with SAS.103a, 104a Abnormal coronary flow has also been measured in the larger, extramural arteries with diminished baseline diastolic flow and reversal of coronary flow during systole.8a,104a

Answer 40

Focal areas of myocardial infarction and fibrosis are commonly observed in the papillary muscles and subendocardium of dogs with severe SAS, often in association with abnormal intramural coronary arteries. Histologic changes of the intramural coronary arteries in these locations include intimal proliferation of connective tissue and smooth muscle, and medial degeneration. These changes are presumably related to the high wall tension found in this condition, and their genesis may be related to the elaboration of angiotensin II or other biochemical mediators of hypertrophy and remodeling.[66-68] Moreover, these arterial lesions may be important in the genesis of malignant ventricular arrhythmias and sudden death.

Answer 41

PATHOPHYSIOLOGY Obstruction to left ventricular outflow causes an increase in left ventricular systolic pressure and concentric hypertrophy. Consequent to fixed obstruction, left ventricular ejection is delayed causing a diminished and late rising arterial pulse (parvus et tardus). High velocity and turbulent flow across the stenotic area produces the systolic ejection murmur and results in poststenotic dilation of the ascending aorta, aortic arch, and brachiocephalic trunk.

Answer 42

Left atrial hypertrophy develops as a consequence of the reduced compliance of the hypertrophied left ventricle. Mild aortic regurgitation is commonly present, presumably because of thickening of the valve leaflets or dilation of the ascending aorta. Damage to the aortic valvular endothelium (jet lesions) predisposes dogs with SAS to bacterial endocarditis.

Answer 43

Dogs with severe SAS can develop left-sided congestive heart failure from myocardial failure, diastolic pump failure caused by increased ventricular stiffness, mitral regurgitation, atrial fibrillation, or a combination of these factors. More often, exertional syncope or sudden death is reported, presumably as a result of myocardial ischemia and the development of malignant ventricular arrhythmias.

Answer 44

In some dogs, exertional collapse may be caused by hypotension precipitated by exercise-induced increases in left ventricular pressure, activation of ventricular mechanoreceptors, and inappropriate bradycardia or vasodilation.

Answer 45

Congenital SAS is most common in Newfoundlands, Boxers, Rottweilers, Golden Retrievers, and German Shepherd Dogs.[45],[70] Valvular AS is common only in Bull Terriers. The clinical findings of SAS vary with the severity of the obstruction and the presence of concurrent cardiac defects. Clinical findings in pups with mild SAS are often subtle and easily overlooked.5a-9a,98a-100a Asymptomatic dogs have a soft to moderately intense ejection murmur that can easily be confused with an innocent or functional heart murmur.[71] More sophisticated time-frequency analysis of soft murmurs may provide clues as to which murmurs are associated with mild disease.[72] Insofar as the lesions of SAS can develop during the postnatal period, the murmur may become increasingly prominent during the first 6 months of life. Severely affected dogs may present with exertional fatigue, syncope, or left-sided congestive heart failure, but the vast majority of dogs are asymptomatic. In dogs with severe disease, a common client observation is that the affected dog is smaller than its healthy littermates. Sudden death, without premonitory signs, is common in dogs aged 1 to 3 years of age.50c

Answer 46

Recognition of severe SAS is not difficult, as the murmur generally becomes louder and longer when the obstruction is more severe.46c The murmur of severe SAS is usually best heard at the left heart base, recognizing that in some dogs, the systolic murmur is equally loud or louder at the right cardiac base, presumably from radiation into the ascending aorta. The murmur of aortic stenosis often radiates up the carotid arteries and can be auscultated over the ventral cervical region. In some affected dogs, a soft diastolic murmur secondary to aortic valve insufficiency is also detected. A substantial percentage of dogs with SAS have mitral regurgitation, but these murmurs are usually difficult to separate given their similar timing and overlapping areas of maximal intensity. Other physical abnormalities detected in moderate to severely affected dogs include a diminished and late rising arterial pulse and a prominent left ventricular heave arising from the hypertrophied left ventricle.

Answer 47

The electrocardiogram is often normal, but may, in severe cases, indicate left ventricular hypertrophy (increased R wave amplitude in leads II, III, aVF, V2, V4). Depression of the ST segment and T wave changes suggest myocardial ischemia, particularly when these alterations are precipitated by exercise or occur in the company of ventricular ectopia (Figure 249-37). Compared with the resting electrocardiogram, 24-hour ambulatory (Holter) ECG recordings offer a more sensitive method of detecting ventricular arrhythmia and ST segment changes, particularly when such changes are only precipitated by exercise. The severity of arrhythmias detected in this fashion often corresponds to the severity of disease.[73]

Answer 48

Thoracic radiographs can be normal or may indicate left ventricular hypertrophy.8a,22a-24a Poststenotic dilation of the horizontally inclined ascending aorta causes loss of the cranial waist on the lateral radiograph and widening of the mediastinum on the dorsoventral radiograph (Figure 249-38). Mild left atrial enlargement is common in dogs with moderate or severe SAS but marked left atrial enlargement suggests concurrent mitral regurgitation.

Answer 49

Angiocardiography is useful for delineating the site and geometry of obstruction, which is usually most evident in the ventral aspect of the outflow tract when viewed on the lateral projection (Figure 249-39). Other angiographic findings include poststenotic dilation of the ascending aorta, enlargement of the left coronary artery and its extramural branches, a small left ventricular cavity, hypertrophy of the papillary muscles and left ventricular wall. Supravalvular aortic injections can be performed to identify insufficiency of the aortic valve, but Doppler echocardiography is a more sensitive technique. Hemodynamic recordings are made to document the presence of a systolic pressure gradient across the obstruction and to document its severity (Figure 249-40). Such recordings are also useful for detecting elevated left ventricular end-diastolic pressure and impending congestive heart failure.8a,105a As a result of diminished flow (cardiac output), pressure gradients recorded from dogs with SAS are depressed by general anesthesia to approximately 40% to 50% of those measured in the unanesthetized state.47c

Answer 50

Moderate to severe SAS is easily confirmed by 2D and Doppler echocardiography. Typical findings include concentric left ventricular hypertrophy, a subvalvular obstructing lesion, and poststenotic dilation of the aorta (Figure 249-41).[3],[52],27a,106a The papillary muscles and endocardial surface of the ventricular myocardium often appear hyperechoic, presumably as a result of myocardial ischemia and replacement fibrosis or calcification. Structural changes in the mitral valve can often be appreciated and abnormal motion of the mitral valve (systolic anterior motion) can be detected in those dogs with coexisting mitral valve dysplasia and dynamic obstruction.[62]

Answer 51

Spectral Doppler interrogation of the LVOT is used to assess disease severity by measuring the peak velocity of flow in the LVOT.48c Such measures show excellent correlation with invasive measures (see Figure 249-41).49c Doppler measurements can be made from a variety of parasternal or subcostal imaging windows although velocities obtained from the subcostal position generally display the highest values.27b While Doppler-estimated pressure gradients between 80 and 100 mm Hg (peak flow velocities ranging from 4.5 to 5.0 m/s) are used to indicate moderate LVOT obstruction, and higher velocities used to indicate severe obstructions, these designations are somewhat arbitrary. Doppler-derived pressure gradients are affected by the amount of flow (cardiac output) through the obstructive orifice, and may either overestimate the severity of obstruction if cardiac output is high (e.g., in dogs that are stressed or excited), or underestimate severity if flow is subnormal (e.g., in dogs with concurrent myocardial failure). In these cases, indexing the gradient to stroke volume or some related measure or simple estimation of the two-dimensional orifice area may provide a better estimate of disease severity.[64],[74] Color flow Doppler recordings are valuable for detecting and estimating the severity of coexisting aortic or mitral valve insufficiency.

Answer 52

Antemortem detection of the mildest forms of SAS by echocardiography is often not achievable. Dogs with subtle abnormalities (i.e., grade 1 lesions as described previously), escape detection by even the most accomplished examiners. Even in dogs with grade 2 lesions, segregation from normal dogs on the basis of left ventricular velocities is problematic. An upper limit for aortic velocity in normal dogs has been reported but is not well established for differing breeds and examination conditions.[75] The maximum normal aortic velocity in the authors’ laboratory is 1.7m/s (upper limit of the 95% confidence interval); however, velocities in excess of this value are sometimes recorded in completely normal dogs or dogs with no evidence of a discrete outflow obstruction but slightly diminished outflow tract dimensions (Boxers, Bull Terriers, Golden Retrievers). A diagnosis of mild SAS is more secure when mildly elevated velocity measures are accompanied by disturbed flow, an anatomic lesion is visible, and when velocity flow suddenly accelerates over a discrete region in the LVOT. The inability to reliably detect mild SAS is a great source of frustration when attempting to provide genetic counseling to breeders, who are interested in reducing the incidence of disease.

Answer 53

NATURAL HISTORY Severe SAS is a discouraging condition, since many affected dogs die prematurely. In a retrospective survey of 96 dogs with SAS, 21 died suddenly, most often during the first 3 years of life.50c Eleven dogs developed endocarditis (6 dogs) and/or heart failure (7 dogs), and 32 dogs evidenced exercise intolerance or syncope. Dogs with minimal ventricular hypertrophy, mild ventricular outflow obstruction, and a maximal Doppler pressure gradient of less than 50 mm Hg are more likely to live normal lives, whereas dogs with pressure gradients in excess of 125 mm Hg are very likely to develop serious complications or to experience sudden death. Complicating factors that contribute to an adverse outcome include: mitral regurgitation, aortic regurgitation, aortic valve endocarditis, and atrial fibrillation.51c-53c Sudden death is most likely to occur during or shortly after vigorous activity.

Answer 54

CLINICAL MANAGEMENT Dogs with mild SAS are not treated other than administration of prophylactic antibiotics during periods of anticipated bacteremia, such as during dental procedures, surgery, or whenever a concurrent infectious disease is suspected. This practice remains common despite the fact that the efficacy of prophylactic antibiotics for reducing the risk of bacterial endocarditis in dogs with SAS has not been definitively established.53c A number of treatment options can be considered for dogs with moderate to severe SAS, but most are of uncertain value.

Answer 55

Open resection of the obstructing lesion during cardiopulmonary bypass clearly offers the best opportunity to substantially and permanently and reduce the systolic pressure gradient;54c,55c however, an otherwise successful procedure does appear to substantially alter the prevalence of sudden death.55c Other surgical procedures employed to dilate or bypass the obstruction have either failed to achieve a sustained reduction of the systolic pressure gradient or they entail an unacceptable risk of complications.56c,57c Moreover, these remedies are usually limited in their availability and prohibitively expensive to be considered practical options.

Answer 56

Balloon dilation of SAS has been attempted in dogs as an alternative to surgery or lifelong medical therapy. On average, catheter-based balloon dilation is able to reduce the severity of SAS obstruction in dogs by 50%29b; however, this short-term benefit is attenuated in some (and perhaps a majority) of dogs over time48c, and balloon valvuloplasty has not been shown to improve survival versus medical therapy with atenolol.[76] Balloon dilation of SAS is more challenging than balloon valvuloplasty of PS. Life-threatening complications of SAS include fatal arrhythmia, development of aortic valve endocarditis, rupture of the aortic annulus, and avulsion of the brachiocephalic artery during balloon withdrawal. Moreover, the inability of surgical resection to prevent sudden death suggests that effective treatment requires more than reduction of the pressure gradient.

Answer 57

The authors typically recommend avoidance of prolonged vigorous exercise, recognizing that in young and otherwise healthy dogs, even this conservative recommendation is not always practical. Based on clinical and pathologic evidence of myocardial ischemia, the authors also advise administration of beta-adrenergic receptor blockers to dogs with high gradients or a history of syncope. Beta-blockers (such as atenolol) reduce maximal heart rate, decrease myocardial oxygen consumption, and improve diastolic coronary artery flow, thereby offering a protective effect to the myocardium against ischemia and the development of arrhythmias. Moreover, dogs on high doses of beta-blockers seem less willing (or are less able) to indulge in prolonged vigorous exercise. In theory, treatment with calcium channel blockers or angiotensin converting-enzyme inhibitors may also be of value in dogs with SAS; however, none of the medical strategies have been evaluated in placebo-controlled clinical trials.

Answer 58

ANOMALOUS DEVELOPMENT OF THE ATRIA AND COR TRIATRIATUM Cor triatriatum (sinister and/or dexter) has been reported in both cats and dogs.156a-158a,33b,69c-72c With these defects, the atrium is partitioned into an accessory atrial chamber, which receives venous return, and is separated from the true atrium by a perforate membrane. The suffix, sinister or dexter, is used to indicate whether the left or right atrium is abnormally partitioned; however, the term cor triatriatum alone usually refers to a left-sided lesion. If the partitioning membrane causes obstruction, dilation of the venous chamber and the entering veins is evident and congestion develops. In contrast to mitral or tricuspid valve stenosis, blood flows through the stenotic orifice during both systole and diastole; however, the functional consequences of these defects are very similar.

Answer 59

From a clinical perspective, supravalvular mitral stenosis (SMS) often closely resembles cor triatriatum (sinister); however, SMS is frequently accompanied by additional mitral valve abnormalities. The primary distinction between SMS and cor triatriatum (sinister) relates to the location of the obstructing membrane. In animals with SMS, the obstructing membrane is located ventral (distal) to the foramen ovale and the left auricle is functionally part of the proximal chamber and dilates as pressure in this chamber rises (Figure 249-42).[55] In animals with true cor triatriatum (sinister) the obstructing membrane is located dorsal (proximal) to the foramen ovale; the left auricle lies downstream from the obstruction and is not enlarged. If the foramen ovale is closed, there is little difference between these defects. Affected cats typically present with signs of pulmonary congestion, but pulmonary hypertension and right heart failure are also seen.

Answer 60

Cor triatriatum dexter results from persistence of the embryological right sinus venosus valve. In dogs with this malformation, the right atrium is partitioned by a diaphragm located caudal to the tricuspid valve and foramen ovale. Affected dogs usually evidence congestion in the caudal half of the body (ascites) but fail to demonstrate jugular distension or an audible murmur. Other clinical findings include prominence of the cutaneous abdominal veins, hepatomegaly, and diarrhea from malabsorption. Dogs with congenital or acquired obstruction of the caudal vena cava (Budd-Chiari syndrome) present with similar clinical findings.

Answer 61

In most affected dogs, the electrocardiogram and thoracic radiographs, with the notable exception of caudal vena cava enlargement, are unremarkable. Diagnosis can be accomplished by echocardiography or angiography.[77] Treatment for cor triatriatum generally requires surgical resection or bypass of the obstruction,[78],73c,74c balloon dilation of the obstructing membrane can also be attempted.[79-81]

Answer 62

LESIONS CAUSING RIGHT-TO-LEFT SHUNTING: CYANOTIC HEART DISEASE The term “cyanotic congenital heart disease” is used to categorize those congenital defects causing admixture of venous and arterial blood, such as tetralogy of Fallot. Since the pathophysiology and clinical signs of these conditions are similar, they will be considered as a group. Only the most important defects are discussed to illustrate the clinical syndrome common to these conditions.

Answer 63

PATHOPHYSIOLOGY Mechanisms of Right-to-Left Shunting In order for desaturated blood to shunt into the systemic arteries there must be a defect that allows admixture of unsaturated and saturated blood, as occurs with transposition of the great vessels; or a communicating defect connecting the two sides of the circulation and some mechanism elevating pressures on the right.

Answer 64

PDA, aorticopulmonary window, VSD, and ASD

Answer 65

The factors underlying the development Eisenmenger's syndrome are incompletely understood but are most likely related to shear stresses caused by the high flow rates in the pulmonary vasculature and proliferative changes within the vessel wall.

Answer 66

Eisenmenger's syndrome usually develops rapidly in small animals and almost always before 6 months of age. Intimal thickening, medial hypertrophy, and plexiform lesions of dogs and cats with Eisenmenger's physiology are similar to those of humans as described by Edwards and Heath and amended by Roberts.

Answer 67

These plexiform lesions are considered irreversible; consequently, neither medical therapy nor closure of the shunt will effectively improve the condition once these changes have developed. In fact, surgical closure of the shunt pathway forces the right ventricle to work solely against a tremendous resistance, resulting in right ventricular failure, circulatory collapse, and death.

Answer 68

Effects of Hypoxemia Systemic responses to arterial hypoxemia include an increase in red blood cell mass in an attempt to improve systemic oxygen transport. Hypoxia of the renal tissue incites erythropoietin release and induces secondary polycythemia.

Answer 69

When the PCV exceeds the 65% to 68% range, the high viscosity of the blood predisposes patients to thrombosis and microvascular complications. This hyperviscosity syndrome is the primary cause of morbidity and mortality in affected animals. Clinical manifestations include weakness, hemostatic deficiencies, renal dysfunction, metabolic acidosis, iron deficiency, cerebrovascular events, syncope, and seizures.

Answer 70

Ratio of Systemic to Pulmonary Resistance The magnitude of right-to-left shunting fluctuates with the relative resistances of the systemic and pulmonary circulations. Exercise promotes systemic arteriolar vasodilation and decreases systemic resistance, thereby increasing the magnitude of right-to-left shunting.

Answer 71

In cases of right ventricular hypertrophy and VSD, tachycardia or elevated sympathetic tone can increase the magnitude of right-to-left shunting by exacerbation of dynamic infundibular obstruction and increased resistance to right ventricular ejection. Beta-adrenergic blocking drugs are sometimes used to blunt or prevent this phenomenon, particularly in patients with tetralogy of Fallot. Beta-blockers also tend to limit exercise, offering another explanation for their efficacy in some patients.

Answer 72

Anemia, absolute or relative, reduces the ratio of systemic to pulmonary resistance when pulmonary resistance is fixed. By this mechanism, overzealous phlebotomy can increase the severity of arterial hypoxemia as it decreases the oxygen carrying capacity of blood.

Answer 73

Additional Circulatory Factors Right-to-left shunting leads to compensatory increases in nutritive blood flow to the lung via the bronchial arteries. These systemic collateral vessels are easily recognized at angiography. While uncommon, it is possible for these vessels to rupture, leading to hemoptysis.

Answer 74

Paradoxical embolization is another potential complication of right-to-left shunting defects. Normally, the pulmonary vasculature filters systemic venous emboli before they can reach the left side of the circulation. With reversed shunting, the possibility of a venous embolus reaching the coronary, cerebral, or other systemic arteries must be considered, particularly when intravenous catheters are used. By this mechanism, a thrombus, infectious agents, or air may gain access to vital systemic organs.

Answer 75

Animals with cyanotic heart disease sometimes experience adverse reactions (particularly bradycardia) to sedatives and tranquilizers.

Answer 76

Septal defects in association with tricuspid valve disease (ASD + TVD) or PS (ASD or VSD + PS); and PDA or septal defects complicated by pulmonary hypertension (PHT + ASD or VSD or PDA).

Answer 77

Failure to grow, shortness of breath, exertional fatigue, weakness, syncope, and seizures. Affected animals evidence dyspnea when stressed.

Answer 78

It is important to realize that providing 100% oxygen does not significantly improve the hypoxemia caused by right-to-left shunting. Administering 100% oxygen raises the concentration of dissolved oxygen, but does not substantially raise the amount of oxygen bound to hemoglobin which represents primary reservoir of oxygen in the blood.

Answer 79

Animals with cyanotic heart disease are usually polycythemic. This phenomenon is most obvious when the hemoglobin concentration of young animals with cyanotic heart disease is compared with age-matched normal animals.

Answer 80

Cardiac auscultation of cyanotic patients varies in accordance with the underlying defects. Dogs and cats with tetralogy of Fallot usually evidence the typical systolic murmur of PS. In contrast, most animals with Eisenmenger's physiology lack a prominent murmur but often display a loud or split-second heart sound caused by pulmonary hypertension and asynchronous semilunar valve closure. On occasion, an ejection sound with a soft, short, systolic murmur may be evident at the left heart base.

Answer 81

Cyanotic heart disease, with rare exception (tricuspid atresia and anomalous systemic venous return) is characterized by right ventricular hypertrophy, which is usually evident on ECG recordings, thoracic radiographs, and echocardiograms. As a general rule, the pulmonary arteries and veins are diminished in size and the lungs appear underperfused (hyperlucent) on survey chest films. The main pulmonary artery and proximal lobar arteries are usually visibly dilated when Eisenmenger's syndrome is the basis for reversed shunting, but these structures are not enlarged with pulmonary or tricuspid atresia. In dogs with classic tetralogy of Fallot with a muscular infundibular obstruction, the pulmonary artery is hypoplastic and poststenotic dilatation of the main pulmonary artery is not prominent on the dorsoventral radiograph. Dogs and cats with valvular PS and a restrictive VSD demonstrate more prominent enlargement of the pulmonary artery segment and proximal lobar arteries. These seemingly trivial distinctions often become important when surgical repair is contemplated.

Answer 82

Echocardiography The echocardiogram is particularly helpful assessing the cyanotic patient since most defects can be easily visualized. Careful evaluation the right ventricular inflow and outflow tracts usually reveals the site of shunting; and the direction of blood flow can be easily ascertained by Doppler or contrast imaging.[3] Detailed ultrasound studies often renders cardiac catheterization unnecessary unless surgery is contemplated and pulmonary hypertension (as opposed to PS) cannot be otherwise ruled out. Estimation of pulmonary vascular and right ventricular pressures can often be estimated noninvasively by measuring the peak velocity of even a small jet of pulmonic or tricuspid valve insufficiency, and applying the Bernoulli equation (see Cardiac Imaging). Echocardiographic contrast agents can be used to amplify weak signals from small jets, permitting more accurate assessment of jet peak velocity and cardiac pressures.

Answer 83

Cardiac Catheterization Cardiac catheterization and angiocardiography of is advisable whenever uncommon or complex defects are suspected or when surgical repair is contemplated. In addition to showing the location and severity of the shunt, angiography outlines the anatomy of the defect (e.g., pulmonic, tricuspid dysplasia), and permits visualization of the pulmonary vasculature. Direct measurements of intravascular pressure are useful to assess the severity of pulmonary hypertension and to confirm the presence of unusual or easily overlooked defects such as tricuspid valve stenosis. The measurement of pulmonary artery pressure is essential when cardiac or vascular surgery is contemplated in a patient with cyanotic heart disease. If pulmonary vascular resistance is normal, pulmonary flow can be augmented and systemic hypoxemia improved by creation of an artificial left-to-right shunt between a systemic and a pulmonary artery distal to the site of the cyanotic defect (e.g., Blalock-Taussig shunt).

Congenital heart disease: VALVULAR REGURGITATION and cyanotic heart disease- Ettinger Flashcards

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