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Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Print version ISSN 0102-0935On-line version ISSN 1678-4162

Arq. Bras. Med. Vet. Zootec. vol.52 n.5 Belo Horizonte Oct. 2000

http://dx.doi.org/10.1590/S0102-09352000000500003 

Clinical diagnosis and alternative surgical treatment of tetralogy of Fallot in a dog.
A case report

[Diagnóstico clínico e tratamento cirúrgico alternativo da tetralogia de Fallot em cão. Relato de caso]

 

M.H.M.A Larsson1, L. Pereira2, F.B. Jatene3, R.F. Freitas1;L.O.D. Barbusci1, S.M. de Oliveira4, M.C.D. Abduch4

1Faculdade de Medicina Veterinária e Zootecnia -USP
Av. Prof. Dr. Orlando Marques de Paiva, 87
05508-000-São Paulo, SP
2Faculdade de Medicina Veterinária da Universidade do Grande ABC
3Instituto do Coração da FM-USP
4Núcleo Diagnóstico Veterinário, SP

 

Recebido para publicação, após modificações, em 14 de abril de 2000.
E-mail: akaolar@usp.br

 

 

ABSTRACT

Tetralogy of Fallot was diagnosed in a 30 month-old Cocker Spaniel female, through physical, radiographic, electrocardiographic, and echocardiographic exams. The animal was submitted to a palliative surgical correction, the Blalock-Taussig technique, and 46 months after the surgery, no signs of cardiopulmonary decompensation were observed.

Keywords: Dog, tetralogy of Fallot, diagnosis, surgical correction

 

RESUMO

Tetralogia de Fallot foi diagnosticada em uma fêmea Cocker Spaniel, de 30 meses de idade, por meio de exames físico, radiográfico, eletrocardiográfico e ecocardiográfico. A paciente foi submetida à correção cirúrgica paliativa, técnica de Blalock-Taussig, e em avaliação recente, 46 meses após a cirurgia, apresentava-se sem qualquer manifestação sintomática de descompensação cardiopulmonar.

Palavras-Chave: Cão, tetralogia de Fallot, diagnóstico, correção cirúrgica

 

 

INTRODUCTION

The prevalence of congenital heart diseases has recently increased and that may be due to better diagnostic techniques, increased diseases incidence and there are, clearly, national and regional differences in the recognition of cardiac specific malformations within certain breeds (Buchanan, 1992).

According to some authors (Olivier, 1988; Buchanan, 1992; Bonagura & Darke, 1995; Goodwin, 1995) the tetralogy of Fallot (TF) is one of the most frequently diagnosed congenital cardiac defects in dogs. It is characterized by right ventricular outflow obstruction (pulmonic stenosis), secondary right hypertrophy, subaortic ventricular septal defect, and overriding aorta, and is the cardiac heart disease (CHD) that most commonly determines cyanosis.

Breed predisposition to tetralogy of Fallot is observed in Keeshond, English Bulldog, Miniature Poodle, Miniatura Schnauzer and wirehaired Fox Terrier (Patterson, 1989; Buchanan, 1992; Goodwin, 1995).

Approximately 80% of affected dogs become symptomatic during the first year of life. The life expectancy for untreated symptomatic dogs is significantly reduced, with death occuring about two years of age. Occasionaly, mildly symptomatic dogs will survive well into adult life (Olivier, 1988).

Clinically, the tetralogy of Fallot is characterized by poor growth, exertional respiratory difficulty, cyanosis, generalized weakness, syncope, murmur, polycytemia and hyperviscosity of the blood (Stepien & Miller, 1994; Goodwin, 1995). Exercise and excitement may induce or worsen the cyanosis because of the left to right shunt aggravation (Stepien & Miller, 1994).

Radiographic exam may reveal a normal or mildly enlarged cardiac silhouette with right ventricular enlargment, and pulmonary vessels are visible but smaller than normal. The main pulmonary artery varies in size; a poststenotic dilation may be observed secondary to valvular pulmonic stenosis. The left atrium may be small if pulmonary flow is reduced (Olivier, 1988; Bonagura & Darke, 1995; Goodwin, 1995).

While the electrocardiogram shows only a right deviation of the cardiac axis, the definitive diagnosis is made echocardiographically by the presence of right ventricular hypertrophy, pulmonic stenosis and interventricular communication (Kaplan, 1991; Stepien & Miller, 1994; Goodwin, 1995). Animals with tetralogy of Fallot survive while the pulmonary blood flow is maintained and the blood viscosity is controlled. Sudden death is common in consequence of hypoxia, blood hyperviscosity or cardiac arrhythmia (Stepien & Miller, 1994).

The prognosis, even with treatment, is fair to poor (Eyster & DeYoung, 1985; Ringwald & Bonagura, 1988). Some patients with tetralogy of Fallot will respond to medical therapy, but for those that do not, surgery should de considered. Cardiopulmonary bypass surgery permits definitive repair of the defects, but mortality exceeds 75%. Palliative surgical techniques, such as Blalock-Taussig and Potts, increase pulmonary blood flow and also increase oxigen content of systemic circulation, alleviating the clinical signs (Cooper et al., 1992).

This report presents a case of tetralogy of Fallot in a 30 month-old, Cocker Spaniel female dog which was submitted to the Blalock modified technique and that 46 months after the surgery the animal was in good condition, without any sign of decompensation.

 

CASE REPORT

A 30 month-old Cocker Spaniel female was referred for examination to the Veterinary Hospital of the Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, in June 1993, presenting cough, exercise intolerance, pale and slightly cyanotic mucous membranes, and cardiac murmur at the left base. The electrocardiogram revealed cardiac rate of 240bpm, wandering sinus pacemaker, and right electrical axis deviation.

During the following 27 months the animal presented many alternated periods of clinical improvement and worsening, the latter always controlled by medical therapy. In September 1995, the bitch presented a worsening of the clinical condition with severe cyanosis, dyspnea, pulmonary crackles, systolic ejection murmur (IV/VI) heard best at left base, and hematocrit of 62%. Chest radiography revealed right heart enlargment, and pulmonary vessels smaller than normal. Echocardiography confirmed the diagnosis of tetralogy of Fallot showing pulmonic stenosis, overriding aorta, ventricular septal defect, and right ventricular hypertrophy.

In October 1995, after stabilization of the clinical picture, in order to increase pulmonary blood flow, the patient was submitted to the Blalock-Taussig technique, and the left subclavian artery was anastomosed with pulmonary artery. The surgery was performed at Setor de Cirurgia Experimental do Instituto do Coração (INCOR) da Universidade de São Paulo. The patient was continuously evaluated during the first 72 hours after surgery, and one week later it presented an evident improvement of clinical picture, specially the cyanosis, and the hematocrit was 52%.

Posterior clinical evaluations at 6, 12, 24, 38 and 46 months after the surgery revealed a stable and compensated patient with hematocrit under 50%, although the thoracic radiographies showed rounded right ventricular border, enlarged ascending aorta, and diminished pulmonary circulation. The echocardiographic examination performed 38 months after surgery showed malposition of the aortic root and ventricular septal defect (Fig.1), and hypertrophy and flattening of the ventricular septum as well as hypertrophy of right ventricular wall with evident pappilar muscles (Fig. 2).

 

Figure 1. Two dimensional exhocardiogram recorded from right parasternal position, long-axis view. Ventricular septal defect overriding of aorta and hypertrophy of left and right ventricles

 

 

Two dimensional exhocardiogram recorded from right parasternal position, short-axis view. Hypertrophy and flattening of the ventricular septum due to elevated right ventricular pressure. Hypertrophy of right ventricular wall with evident pappilar muscle.

 

DISCUSSION

Tetralogy of Fallot is a complex conotruncal anomaly and is the most common cause of cyanotic heart disease in dogs (Eyster & DeYoung, 1985; Ringwald & Bonagura, 1988; Kaplan, 1991; Sisson, 1991). The malformation (anterior rightward displacement) of the enlarged aorta overriding the interventricular septum leads to unoxygenated blood from the right ventricle entering the systemic circulation and causing cyanosis (Kaplan, 1991).

According to many authors the mode of inheritance of tetralogy of Fallot appears to be a polygenic trait (Olivier, 1988; Patterson, 1989; Bonagura & Darke, 1995), but Stepien & Miller (1994) believe that this defect is transmitted by a penetrant authonomic charater.

As referred by Olivier (1988), Ringwald & Bonagura (1988), Sisson (1991), Cooper et al. (1992), Bonagura & Darke (1995), and Goodwin (1995), the patient of this report presented, initially, cough, exercise intolerance, mild cyanosis, and cardiac murmur at left base. During two years, approximately, it presented many periods of clinical state worsening, with severe dispnea and cyanosis, pulmonary crackles, and high hematocrit, always managed with drugs (Furosemide, Digoxin, and Propanolol) and homemade hyposodic diet.

Severity of clinical signs is determined principally by degree of obstruction to pulmonary blood flow (Kirklin et al., 1977). The greater the right ventricular outflow tract obstruction the more dramatic the reduction of the pulmonary blood flow is, causing right-to-left shunting of unsaturated blood across the ventricular septal defect and into the systemic circulation (Ringwald & Bonagura, 1988). Pulmonary arterial flow and venous return are scant; the left atrium and left ventricle remain small, and the significant contribution of right ventricle blood to systemic blood flow causes hypoxemia, decreased hemoglobin oxygen saturation, cyanosis, and secondary polycythemia (Bonagura & Darke, 1995).

The murmur of tetralogy of Fallot is tipically a systolic ejection murmur heard best at the left base of the heart, and it is not uncommon to identify a soft sternal border murmur that may indicate radiation of the pulmonic stenosis or shunting into the septal defect (Bonagura & Darke, 1995).

Due to the shunting of the venous blood into the aorta and consequent hypoxia, the kidneys are stimulated to release erythropoietin. Chronic elevations of erithropoietin result in polycythemia. The increased blood viscosity related to polycythemia can produce significant hemodynamic effects as sludding of blood and poor capillary perfusion. Patients with severe polycythemia may present seizures (Goodwin, 1995) and exercise or excitement may induce or worsen cyanosis by accentuating right-to-left shunting (Bonagura & Darke, 1995).

Both medical and surgical therapies can be employed in the management of tetralogy of Fallot. Under cardiopulmonary bypass, definitive correction of the defect (closing ventricular septal defect and removing or bypassing the pulmonic stenosis) can be done, but such procedures are rarely performed in animals because of the attendant mortality and expense (Cooper et al., 1992; Bonagura & Darke, 1995; Goodwin, 1995).

Medical management is of some value but usually provides only temporary palliation of disease (Ettinger & Sutter, 1970). According to Goodwin (1995), b -adrenergic blocade may be used to reduce the dynamic component of right ventricular flow obstruction, and to attenuate b -adrenergic-mediated decreases in systemic vascular resistance, once the enhancement in systemic vascular resistance will lower the magnitude of right-to-left shunting.

Palliative surgical options include Blalock anastomosis and Potts anastomosis. In the former, the left subclavian artery is anastomosed with the pulmonary artery in order to increase pulmonary blood flow. The Potts anastomosis consists of a side-to-side anastomosis of the aorta and pulmonary artery. These techniques are generally effective in reducing signs of pulmonary hypoperfusion and systemic hypoxia (Goodwin, 1995). By increasing pulmonary venous return through these palliative surgical options, left heart size increases, and there is a greater contribution of oxygenated blood to the systemic circulation. However, the size of the shunt must be controlled to prevent overloading of the diminutive left ventricle and subsequent pulmonary edema.

In children with tetralogy of Fallot in which total correction is not indicated, palliative extracardiac systemic-to-pulmonary artery shunts have been responsible for significant improvement in clinical signs for duration over 10 years (Ringwald & Bonagura, 1988).

There are few reports in veterinary medicine in which a systemic-pulmonary artery shunt has been performed to palliate signs of tetralogy of Fallot (Arciniegas et al., 1979; Arciniegas et al., 1982; Ringwald & Bonagura, 1988) and the longest period to which these shunts remain patent postoperatively is approximately 24 months, employing Potts technique (Ringwald & Bonagura, 1988).

The present case is believed to be the first report of tetralogy of Fallot with surgical palliative correction in a dog in Brazil. After clinical (physical, radiographic, electrocardiographic and echocardiographic) diagnosis, the patient was submitted to Blalock-Taussig technique, when it was 30 month-old and, in a recent evaluation, 46 months after the surgery, it is doing well without any sign of cardiopulmonary decompensation. Probably the successfulness of this case is related to the fact that the surgical correction was made in an adult animal, and because the created shunt was of an adequate size, that is, nor too small to cause an inadequate pulmonary flow, neither too large, which overload the left side of the heart and lead to subsequent pulmonary edema.

 

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