Thaibinh P. Nguyenba, DVM, DACVIM (Cardiology); Anthony H. Tobias, BVSc, PhD, DACVIM (Cardiology)
The ductus arteriosus is a normal vascular connection between the aorta and main pulmonary artery in the fetus that permits blood to bypass the nonfunctional fetal lungs. Increased blood oxygen content and decreased circulating prostaglandin levels induce muscular closure of the ductus at birth, thereby allowing blood to flow through the functional lungs of the neonate. Complete closure is achieved in the following weeks via autolysis of ductal musculature, which converts the ductus into the ligamentum arteriosum.
Patent ductus arteriosus (PDA) refers to the failure of the ductus arteriosus to close and is caused by hypoplasia and asymmetry of the ductal muscle mass. This histologic abnormality results in a greater proportion of aorta-like elastic tissue in the ductus that weakens its ability to constrict. PDA is one of the most common congenital cardiovascular defects in dogs, accounting for 25 to 30% of such defects.1 PDA allows left to right shunting of blood from the higher pressure aorta, through the PDA, into the main pulmonary artery. Sequelae can include volume overload of the left side of the heart, mitral valve regurgitation, arrhythmias, left-sided congestive heart failure, pulmonary hypertension, and death. One report suggested that at least 64% of dogs with untreated PDA will die of related complications within 1 year of diagnosis.2 Clinical recognition is vital and facilitated by the presence of a loud continuous heart murmur and hyperdynamic pulses in young dogs and predisposed breeds, such as Miniature and Toy Poodles, Collies, English Springer Spaniels, Keeshonds, Maltese, Pomeranians, Shetland Sheepdogs, and Yorkshire Terriers.1
Surgical Ligation of Patent Ductus Arteriosus
Surgical ligation via thoracotomy had long been the standard for PDA therapy in human medicine. Since the first successful procedure performed in 1938,3 surgical ligation has been proven to have low complication and mortality rates in people.4 Similarly, surgical ligation has been the standard for PDA therapy in dogs with demonstrated success and relatively low mortality rates.2,5,6 Although major surgical complications are relatively uncommon, they are often due to severe hemorrhage and can be associated with high mortality rates when present (42% mortality associated with severe hemorrhage).5 Widespread use of Doppler echocardiography has also shown relatively high rates of post-operative residual flow (35 to 45%)7,8 as well as some instances of recannalization.9
Minimally Invasive Per-Catheter Occlusion of Patent Ductus Arteriosus
The Human Experience
Minimally invasive PDA therapy involves per-catheter placement of occlusion devices within the ductus arteriosus and has superseded surgical ligation in people because of a desire to decrease morbidity associated with PDA therapy.10 Per-catheter PDA occlusion in people began in the 1960s using various devices and became commonplace in the 1990s with the use of embolization coils. Although popular for this purpose, PDA occlusion with coils was often associated with residual flow and aberrant embolization.11 Recently, AGA Medical Corporation (Plymouth, MN) revolutionized PDA therapy with the introduction of the Amplatzer® Duct Occluder. This device, which utilizes a nitinol alloy shape-memory technology combined with occlusive fabric, has proven significantly more effective in PDA closure than embolization coils12 and is the current treatment of choice and the only FDA approved device for PDA occlusion in people.
The Veterinary Experience
Veterinary cardiology has long relied upon devices intended for humans as options for minimally invasive PDA therapy in dogs. Embolization coil use was first reported in 199513,14 but has been associated with significant technical difficulties and high rates of procedure abandonment (11%), aberrant embolization of pulmonary or systemic arteries (22%), and residual flow (66% at 1 day post-procedure).15 These complications are often due to coil instability, large PDA sizes, and difficult PDA shapes. Although use of the Amplatzer® Duct Occluder has lessened some of these complications, the delivery procedure is more complicated, and significant rates of residual flow persist (25% at 1 day post-procedure).16 Use of the Amplatzer® Vascular Plug, a device intended for occluding arteriovenous malformations in the peripheral vasculature in people, also yielded relatively high rates of residual flow in dogs (26% at 1 day post-procedure).17
Since 2005, we have had the opportunity to collaborate with AGA Medical Corporation in the development and clinical evaluation of the first cardiovascular device designed specifically for the dog, the Amplatz® Canine Duct Occluder (ACDO), as well as an accompanying deployment procedure.18 The ACDO proved highly effective in occluding a wide variety of PDA shapes and sizes. Specifically, proper ACDO selection confers remarkably low incidences of device migration and residual ductal flow (6% at 1 day post-procedure).19 In addition, the unique deployment procedure was straightforward, user-friendly, and feasible in a wide range of dog somatotypes and body weights (3.0 to 32.3 kg).18,19 Since its market release in January 2007 by Infiniti Medical, Llc. (Haverford, PA), the ACDO has become the treatment of choice for dogs with PDA in numerous universities and private practices globally. Furthermore, the ACDO employs a novel multi-layer nitinol technology that precludes the need for occlusive fabric. This novel approach in device design has proved so effective in its clinical debut with the ACDO that the technology is beginning to appear in cardiovascular devices intended for use in people.
PDA is a common and important congenital cardiovascular defect in dogs, and definitive therapy is crucial for a positive clinical outcome. Surgical ligation of PDAs is an established method for therapy, but this procedure has been superseded as the standard of care in people by minimally invasive per-catheter occlusion. The veterinary profession may be held to the same standard by an increasingly aware and informed clientele. The ACDO represents a reliable and highly efficacious minimally invasive method for PDA therapy. Although research is ongoing, the ACDO has significantly altered the approach to PDA therapy in dogs as well as cardiovascular device design for humans.
1. Buchanan J. J Vet Cardiol 2001;3(1):7.
2. Eyster G, et al. J Am Vet Med Assoc 1976;168(5):435.
3. Kaemmerer H, et al. Am J Cardiol 2004;94(9):1153.
4. Mavroudis C, et al. Ann Surg 1994;220(3):402.
5. Birchard S, et al. J Am Vet Med Assoc 1990;196(12):2011.
6. Goodrich K, et al. Vet Surg 2007;36(1):43.
7. Van Israel N, et al. J Small Anim Pract 2002;43(9):395.
8. Stanley B, et al. Vet Surg 2003;32(3):231.
9. Van Israel N, et al. J Small Anim Pract 2003;44(11):480.
10. Moore J, et al. Catheter Cardiovasc Interv 2005;64(1):91.
11. Galal M. J Interv Cardiol 2003;16(2):157.
12. Pass R, et al. J Am Coll Cardiol 2004;44(3):513.
13. Miller M, et al. Proc 13th ACVIM Forum 1995:308.
14. Snaps F, et al. J Am Vet Med Assoc 1995;207(6):724.
15. Campbell F, et al. J Vet Intern Med 2006;20(1):83.
16. Sisson D. J Am Vet Med Assoc 2003;223(7):999.
17. Achen S, et al. J Vet Intern Med 2007;21(3):611 (abstract).
18. Nguyenba T, et al. J Vet Cardiol 2007;9(2):109.
19. Nguyenba T, et al. J Vet Intern Med (in press).