Introduction

Interventional cardiology is a branch of cardiology that deals specifically with the catheter based treatment of structural heart diseases. A large number of procedures can be performed on the heart by catheterization. This most commonly involves the insertion of a sheath into a large blood vessel and cannulating the heart under X-ray visualization (most commonly fluoroscopy). This approach offers several advantages, including the accessibility of the vessels in most patients, the short period of in-hospitalization following the procedure, and the minimal complications. The main advantages of using the interventional cardiologic approach are the avoidance of the scars and pain, and long post-operative recovery. Major cardiac interventional cardiac therapies in veterinary fields are balloon valvuloplasty for stenotic aortic or pulmonic diseases⁷, coil embolization for patent ductus arteriosus¹, Amplatz septal or ductal occlusion for atrial septal and ventricular septal defects and closure of a patent ductus arteriosus^2,3, and percutaneous permanent pacemaker implantation for refractory dysrhythmias. In this lecture, the talk will be focused on the ductal occlusion methods for patent ductus arteriosus and the balloon valvuloplasty for pulmonic stenosis, which are most commonly performed in small animal practice.

Transcatheter Ductal Occlusion for Patent Ductus Arteriosus

For many years, the most common device used for patent ductus arteriosus occlusion has been embolization coils (i.e., Gianturco spring occluding coil). With proper techniques and proper patient selection, this has become a procedure associated with high success and low morbidity.^1,4 Coil occlusion is best suited to close a patent ductus arteriosus with a minimal internal diameter of less than 5 mm. Success is usual with a patent ductus arteriosus diameter of 3–5 mm, but a larger patent ductus arteriosus is probably best served by alternate techniques. More recently, the Amplatzer canine ductal occluder (ACDO) device has expanded the ability to close patent ductus arteriosus at cardiac catheterization.^2,3 This device is more reliable and easier to implant in a large patent ductus arteriosus than embolization coils. Other occlusion devices remain under investigation. Most patients with an isolated patent ductus arteriosus can have successful treatment by catheterization after the first few months of life.

Typically, complete occlusion is achieved at catheterization. Occasionally, a tiny residual left-to-right shunt remains at the end of the procedure, which closes by thrombus formation over the following days or weeks. Left-to-right shunt rarely persists through a partially occluded patent ductus arteriosus. Usually, the magnitude of the shunt is significantly smaller than prior to occlusion. If there is residual ductal flow after coil embolization, a close follow up is needed to look for hemolysis, which manifests by hemoglobinuria and anemia. If this occurs, the residual duct has to be closed either by additional coil delivery or other occlusion method, if necessary.⁴ In humans, there are concerns about the hemolysis from long-term risk of endocarditis. Rare reports describe association of a persistently patent ductus after occlusion attempts with hemolysis or endocarditis.

Procedural risks of patent ductus arteriosus occlusion by catheter are few and largely influenced by the experience of the physician performing the procedure. With coil embolization, dislodgement of the coil with embolization of the pulmonary arterial tree or the systemic tree can occur. Although pulmonary arterial embolization has been described in literature^3,4, this condition could never result in any long-term sequelae. There will be no difference in perfusion of either lung after several years of pulmonary embolization. Arterial embolization has been rarely encountered but it necessitated coil extraction using a snare retrieval device.⁵ Hemolysis and recanalization have been reported but it has never caused clinical illness.

These risks include embolization of the device being used to occlude the patent ductus arteriosus, blood vessel injury, and stroke. In the case of device embolization, the device can usually be retrieved by transcatheter techniques, and a second device can be successfully placed in the patent ductus arteriosus.

Balloon Valvuloplasty for Pulmonic Stenosis

Balloon valvuloplasty is designed to relieve pulmonary valve obstruction by using the radial forces of balloon inflation of a balloon catheter positioned across the pulmonic valve.⁷ This static balloon-dilation technique is currently performed worldwide to relieve pulmonary valve obstruction. The general consensus based on current data is that balloon valvuloplasty is the treatment of choice for managing isolated pulmonary valve stenosis. In general, indications for balloon pulmonary valvuloplasty are similar to those used in surgical pulmonary valvotomy, that is, moderate pulmonary valve stenosis with a peak-to-peak gradient > 60 mm Hg with a normal cardiac index (~ 4 m/s peak velocity). The technique of balloon pulmonary valvuloplasty involves positioning a balloon catheter across the stenotic valve, usually over an extra-stiff exchange-length guide wire and inflating the balloon with diluted contrast material to accomplish valvotomy. For larger pulmonic orifice, double balloon procedure (two balloons introduced via each femoral vein) is often necessary. Although the short-term success rate was high, data on long-term results are scarce.^7,9 Published studies reveal generally low residual peak instantaneous Doppler gradients with minimal late recurrence of pulmonary stenosis.^7,9

Balloon valvuloplasty can cause trauma to the tricuspid valve, although it is a rare complication for this procedure. Some brachycephalic dogs (e.g., English bulldogs and boxers) have an aberrant single right coronary artery (type R2A) causing the left coronary to encircle the base of the MPA at the level of the pulmonic annulus.⁸ Surgical valvulotomy (i.e., Patch Graft surgery) and balloon dilation have both had fatal results if this anomaly is present at the time of correction of the pulmonic stenosis.^8,9

References

1.  Henrich E, Hildebrandt N, Schneider C, Hassdenteufel E, Schneider M. Transvenous coil embolization of patent ductus arteriosus in small (≤ 3.0 kg) dogs. J Vet Intern Med. 2011;25(1):65–70.

2.  Falcini R, Gaspari M, Polveroni G. Transthoracic echocardiographic guidance of patent ductus arteriosus occlusion with an Amplatz® canine duct occluder. Res Vet Sci. 2011;90(3):359–62.

3.  Gordon SG, Saunders AB, Achen SE, Roland RM, Drourr LT, Hariu C, Miller MW. Transarterial ductal occlusion using the Amplatz Canine Duct Occluder in 40 dogs. J Vet Cardiol. 2010;12(2):85–92.

4.  Hildebrandt N, Schneider C, Schweigl T, Schneider M. Long-term follow-up after transvenous single coil embolization of patent ductus arteriosus in dogs. J Vet Intern Med. 2010; 24(6):1400–6.

5.  Lee SG, Hyun C. Retrieval of an embolization coil accidentally dislodged in the descending aorta of a dog with a patent ductus arteriosus. J Vet Sci. 2007;8(2):205–7.

6.  Locatelli C, Domenech O, Silva J, Oliveira P, Sala E, Brambilla PG, Bussadori C. Independent predictors of immediate and long-term results after pulmonary balloon valvuloplasty in dogs. J Vet Cardiol. 2011;13(1):21–30.

7.  Tobias AH, Stauthammer CD. Minimally invasive per-catheter occlusion and dilation procedures for congenital cardiovascular abnormalities in dogs. Vet Clin North Am Small Anim Pract. 2010;40(4):581–603.

8.  Fonfara S, Martinez Pereira Y, Swift S, Copeland H, Lopez-Alvarez J, Summerfield N, Cripps P, Dukes-McEwan J. Balloon valvuloplasty for treatment of pulmonic stenosis in English Bulldogs with an aberrant coronary artery. J Vet Intern Med. 2010;24(2):354–9.

9.  Schrope DP. Balloon valvuloplasty of valvular pulmonic stenosis in the dog. Clin Tech Small Anim Pract. 2005;20(3):182–95.