Patent ductus arteriosus (PDA) is one of the three most common congenital cardiac abnormalities in dogs, found in both pedigreed and mixed breed dogs, but is very uncommon in cats. Evaluation of medical records from three major veterinary referral centers collected over a period of 21 years yielded only 28 reports of client-owned cats with congenital PDA diagnosed by means of echocardiography.
The ductus arteriosus is a natural fetal vascular structure connecting the pulmonary artery to the aorta, which shunts blood away from the pulmonary circulation in the nonaerated fetal lung to the systemic circulation via the aorta. As the fetal lung is collapsed and requires very minimal blood flow, the pulmonary vascular resistance in the fetus is very high, much higher than systemic vascular resistance. At birth, when the lungs expand and become aerated, the situation is reversed, and pulmonary vascular resistance decreases significantly compared to systemic vascular resistance. In the normal neonate, the muscles of the ductus arteriosus constrict and close this structure down within a few minutes to a few hours after birth, and by one month after birth, the ductus arteriosus is anatomically closed, leaving just a remnant elastic ligament, the ligamentum arteriosum. In hereditary PDA, the ductal smooth muscle is hypoplastic so it does not constrict shortly after birth and then blood flow is abnormally shunted from left to right in most cases, causing pulmonary overcirculation, left atrial and left ventricular volume overload, and eccentric hypertrophy of the left side of the heart.
Little has been published regarding treatment and outcome of feline PDA. In dogs, untreated PDA usually leads to the development of congestive heart failure within the first year of life. The best outcomes in canine PDA are obtained when treatment with surgical occlusion of the PDA is performed as soon as possible after diagnosis. Surgical occlusion of the PDA can be accomplished by extravascular ligation of the ductus arteriosus or intravascular occlusion with a device such as a coil or other catheter-delivered device designed to stimulate thrombosis. Intravascular occlusion procedures are becoming more frequently used, as they are less invasive than open surgical attenuation and are associated with fewer complications. Intravascular attenuation of a PDA has been performed in cats, but obtaining adequate vascular access through which to pass the catheter delivery device is challenging in very small patients.
Feline patients with PDA included in this retrospective study were mostly mixed breeds (22/28); fifteen were female and 13 were males. The median body weight of these patients was 2.1 kg (range 0.6 to 5.7 kg). Most of these patients initially presented to the referring veterinarian for reasons such as vaccinations or neutering, rather than historical clinical signs of heart disease. Clinical signs of potential cardiac disease noted by referring veterinarians or clinicians at the referral hospitals included tachypnea (9/28), bradycardia (4/28), bounding femoral pulses (4/28), small body size for age (3/28), increased respiratory effort (3/28), and a heart murmur (28/28). The heart murmur was the reason for referral of all 28 cats to a specialty center, and all but one patient’s record documented the grade of the heart murmur. Grade 6/6 heart murmurs were noted in 5/27 patients, grade 5/6 in 12/27, grade 4/6 in 4/27, grade 3/6 in 3/27, grade 2/6 in 2/27, and grade 1/6 in 1/27. In dogs with PDA, the murmur almost always is a continuous one with a point of maximum intensity (PMI) in the left axillary area; in cats with PDA, this finding is less consistent. Only 9/28 of the cats with PDA were described as having continuous murmurs. In the 20/28 cats where a PMI of the murmur was recorded, 7/20 had a PMI on the right side of the thorax, while in 13/20 the PMI was identified on the left side of the thorax.
Radiographic findings were available for 21 of the 28 cats. Generalized cardiomegaly was found in 19/21 of the cases, the pulmonary vasculature was distended in 18/21, and aortic bulging was identified in 5/21. Pulmonary infiltrates were found in 11/21 of the cats for whom radiographs were available. In the 16/28 cats for whom electrocardiographic studies were available, only 2/16 had normal QRS complexes, and 12/16 demonstrated tall R waves suggestive of left ventricular enlargement.
Cardiac abnormalities in addition to the PDA were identified in 23/28 cats using echocardiography performed by a board-certified veterinary cardiologist. These included right ventricular hypertrophy (5/23), left ventricular hypertrophy (14/23), left atrial hypertrophy (10/23), enlarged pulmonary arteries (5/23), pulmonary hypertension (2/23), and aortic insufficiency (4/23). In a number of the patients, congenital abnormalities in addition to the PDA were found, including ventricular septal defects (3/23), aortic stenosis (3/23), pulmonary atresia-ventricular septal defect (1/23; previously known as tetralogy of Fallot), pseudotruncus arteriosus (1/23), and mitral valve dysplasia (1/23), among others.
Seventeen of the 28 cats diagnosed with PDA underwent vascular attenuation, and 11 did not. Of the 11 cats that did not undergo a vascular attenuation procedure, only 2 received any medical management; the rest (9/11) received no pharmacological treatment at all. Surgical attenuation was declined by the owners of the two cats who were treated with medical management. One of these cats received furosemide but was lost to follow-up; the other received enalapril for 16 years and was reported to be very healthy until it was euthanized. None of the cats who underwent vascular attenuation received any medication following the attenuation procedure.
One of the 17 cats receiving vascular attenuation underwent a single coil embolization procedure. A single surgical procedure for ligation of the PDA was performed in 14/17 cats; 1/17 underwent 2 open surgical ligations, and 1/17 underwent multiple vascular attenuation procedures including both surgery and coil embolization. The median age at the time of surgical attenuation was 5 months (range 1.5 to 10 months). Four of the 15 cats who underwent open surgical ligation experienced complications related to hemorrhage, which is also the most common complication in dogs undergoing surgical ligation of a PDA. Two of these hemorrhage cases resulted in death or euthanasia. Postoperative complications in 6/13 surviving patients included left-sided laryngeal paralysis (2/6), dysphagia and a voice change (1/6), fever (1/6), chylous effusion (1/6), and incomplete occlusion of the PDA (1/6) requiring additional procedures for complete attenuation.
Of the 16/28 cats for whom follow-up information was available, 11/16 that underwent vascular attenuation lived from < 1 day to 191 months after the procedure. Five of the cats receiving no treatment or medical treatment only had a median survival time of 45 months (range 15-96 months). Of the 15 cats receiving vascular attenuation that survived to discharge from the hospital, 7 were still alive at the time of study follow-up, 2 had died for reasons unrelated to their PDA, and 6 were lost to follow-up at a median of 7 weeks after discharge.
Results of the study demonstrated that there was no significant difference in the survival time of cats that underwent vascular attenuation (n = 15) versus those that received medical or no management (n = 11); however, the study population was quite small. In those cats that did receive a vascular attenuation procedure, both open surgical ligation and coil embolization proved to be effective methods for the treatment of PDA in cats. All of the patients studied had a heart murmur detected prior to one year of age, whereas in dogs PDAs are not always diagnosed until the dog is an adult (> 1 year of age).
For the primary care clinician who is evaluating the health of newly adopted kittens, this study presents several important messages: (1) the cardiac auscultation abnormalities associated with feline PDA may not be as consistent or clear-cut as they are in dogs, in which PDA is almost always associated with a grade 4/6 or above continuous machinery-like murmur with a PMI at the left cranial thorax; (2) bounding femoral pulses, reported in 75% of dogs with PDA, appear to be uncommon in cats with PDA; (3) cats with PDA are likely to be presented for routine wellness or pre-gonadectomy examinations with no history of clinical signs associated with cardiac or pulmonary disease reported by owners; (4) while PDA is considered to be a rare condition in cats and significantly less prevalent than in dogs, it may be underdiagnosed due to subtler or unobserved historical signs and more diverse, less pathognomonic clinical and auscultatory findings than in dogs; (5) PDA closure by vascular attenuation is recommended in feline patients with this abnormality, as such procedures confer a significant survival benefit in dogs, and cats are likely to be similar to dogs in the progression of pathophysiologic changes that untreated PDA engenders; (6) body weight of feline PDA patients, as with canine PDA patients, was not significantly associated with procedural success or survival time with respect to vascular attenuation; (7) iatrogenic damage to the left recurrent laryngeal nerve could be more likely in cats undergoing open surgical ligation of the PDA than in dogs due to the smaller surgical field in cats, and these patients should therefore be evaluated for laryngeal dysfunction with a postoperative laryngeal examination under sedation. [PJS]