Patent ductus arteriosus

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Patent ductus arteriosus (PDA) is a rare genetic heart disease of dogs characterized by a 'machine murmur' and progressive congestive heart failure.

The ductus arteriosus is a blood vessel that connects the two main arteries of the body - the aorta and the pulmonary artery. This blood vessel is normal in the fetus, but shortly after birth, it should close. When the ductus arteriosus remains open or patent after birth, this abnormal communication between the aorta and pulmonary artery passes extra volumes of blood into the lungs. Blood shunting from the descending aorta to the pulmonary artery results in a volume load on the pulmonary vasculature and left heart.

A fairly characteristic type of heart murmur is usually present, but to confirm the diagnosis and to make sure that there are no other heart defects, an ultrasound examination of the heart (echocardiography) is highly recommended.

The preferred treatment is surgical closure of the patent vessel. If surgery is performed early enough, a normal lifespan can be expected. Transvenous coil embolisation has been reported in cats, representing an additional method of definitive treatment[1].

Without surgery, the prognosis is poor; death due to congestive heart failure generally occurs anywhere from one month to five years of age.

Patent ductus arteriosus is genetically determined in almost every case, and this fact impacts the value of purebred cats used for breeding.

Reverse patent ductus arteriosus

PDA defects that ultimately reverse (rPDA) and shunt right to left usually are very large defects in cats. The shunting can result in acute death owing to massive volume overload and left-sided congestive heart failure[2].

Cats with rPDA present with signs of respiratory difficulty, lethargy and weakness, especially in the hindlegs. Cyanosis in the caudal extremities is also common, with pink cranial mucous membranes (differential cyanosis).

Signs of respiratory difficulty may occur, especially with exercise. Physical examination usually reveals an absence of heart murmurs, and a split second heart sound secondary to presence of pulmonary hypertension. Additionally, the right apical precordial impulse may be accentuated because of right heart enlargement. The hematocrit is often >65%.

Thoracic X-Rays usually reveals a ductal aneurysm (dilation of the descending aorta. Color and spectral Doppler echocardiography may reveal right-to-left shunting laminar blood flow across the ductus.

Treatment of rPDA involves periodic phlebotomy to decrease the hematocrit, and avoid strenuous exercise. Sildenafil (Viagra) may be administered in an attempt to decrease the clinical signs associated with pulmonary hypertension.

Surgical ligation or interventional closure of a rPDA is contraindicated[3].

References

  1. Schneider, M & Hildebrandt, N (2003) Transvenous embolisation of the patent ductus arteriosus with detachable coils in 2 cats. J Vet Intern Med 17:349
  2. Kittleson, MD (1998) Patent ductus arteriosus. In Kittleson, MD, Kienle, RD (Eds): Small animal cardiovascular medicine. Mosby, St Louis. pp:218
  3. Roland, RM (2010) Congenital heart disease. In August, JR (Ed): Consultations in feline internal medicine. Vol 6. Elsevier Saunders, Philadelphia. pp:420