As advancements in medical cardiology progress, so too do the techniques in surgical interventional procedures. This allows for more treatment options, hopefully leading to better overall outcomes for patients and clients.
Traditionally, interventional procedures are performed alongside fluoroscopy; however, trials in the use of concurrent transoesophageal echocardiography have been performed (Caivano et al., 2012). Percutaneous vascular access allows for minimally invasive surgical techniques, improving patient recovery time and reducing the length of hospitalisation.
The three most common cardiology interventions currently performed in veterinary practice include balloon valvuloplasty of the pulmonic valve, patent ductus arteriosus closure and transvenous pacing (Scansen, 2017). This article will focus on new techniques that can be used for a variety of cardiac conditions.
Pulmonic stenosis and pulmonic artery stenting
Pulmonic stenosis has been reported as one of the most common canine congenital heart defects (Oliveira et al., 2011) and one that is routinely treated by cardiologists in referral centres. This disease leads to an increased pressure load on the right ventricle, thus causing hypertrophy and cardiac remodelling. Clinical signs can range from being asymptomatic to syncope and death.
Pulmonic stenosis has classically been categorised into two subtypes – A and B – but there is often a mixture of abnormalities. Type A is characterised by a pulmonic annulus with normal dimensions; however, the pulmonic valves’ leaflets are fused, forming a “diaphragm-like” structure. Type B involves a hypoplastic pulmonic annulus, wherein the pulmonic leaflets are often thickened and dysplastic, and may or may not be fused (Madron, 2016).
Balloon valvuloplasty (BVP), a technique whereby a balloon catheter is inflated in the right ventricular outflow tract at the level of the pulmonic valve, is used to open fused leaflets in order to reduce the degree of stenosis. Previously, it has been the only treatment of choice. Multiple studies have shown that patients with type B morphology have a much poorer prognosis than their type A counterparts (Bussadori et al., 2001) and a poorer response to BVP (Scansen, 2018).
Treatment options for dogs with type B pulmonic stenosis and those that respond poorly to standard BVP are becoming more readily available
Treatment options for dogs with type B pulmonic stenosis and those that respond poorly to standard BVP are becoming more readily available. Techniques used include high-pressure balloon dilation catheters to provide more force on the narrowed pulmonic valve and cutting balloon catheters to widen the stenosis (Scansen, 2017). Currently, high-pressure balloons are preferred over cutting.
Pulmonic stent implantation may be considered when these procedures are unsuccessful, if a dog is deemed unlikely to respond to high-pressure BVP or if there is an aberrant coronary artery. This technique involves placing a stent across the narrowed valve to reduce the pressure gradient across it. Studies in children have shown that successful stent placement provides optimal outcomes for patients with pulmonic stenosis (Abqari, 2022). In dogs, studies regarding stent placement in the right heart have shown positive results, improving clinical signs and the degree of stenosis for patients with annulus hypoplasia (Borgeat et al., 2021).
Patents ductus arteriosus and Amplatzer Vascular Plug II
The presence of a patent ductus arteriosus (PDA) is a fairly common congenital condition in dogs, whereby blood shunts from the aorta into the pulmonary artery. This disease may lead to pulmonary over-circulation, resulting in left atrial and ventricular volume overload. When the left heart is unable to compensate for the increased blood volume, pulmonary oedema and signs of congestive heart failure may be observed.
Fortunately, most PDAs can be cured via closure in a number of ways. Without closure, studies show that prognosis is poor as most patients develop congestive heart failure and are euthanised on humane grounds within one year (Saunders et al., 2013). PDA occlusion should only be attempted in cases of left-to-right shunting (ie blood shunting from the aorta to the pulmonary artery), as the closure of a reverse PDA (right-to-left shunt) would exacerbate pulmonary hypertension, which is usually acutely fatal.
Previously, closure was limited to open thoracic surgery and duct ligation, as well as the placement of transarterial/transvenous coils for ductal closure (Blossom et al., 2010). However, modern devices have recently been developed for minimally invasive techniques to close PDAs. These devices have lower complication rates than thoracic surgery, which has higher rates of haemorrhage, residual ductal flow and increased recovery time.
Minimally invasive techniques include Amplatz canine duct occluders (ACDOs) and vascular plugs – in particular, the Amplatzer Vascular Plug II (AVP II). The advantages of these devices are:
- They are easier to deploy
- They can be repositioned during surgery
- The approach is via a 2cm inguinal or jugular groove incision.
In the hands of an experienced cardiologist, patients can recover quickly from the procedure, and most will go home the next day. The specific benefit of the AVP II is that it can be used in very small dogs (even around 2kg) because it is placed via the venous route. This reduces the need for invasive thoracic surgery, even in the tiniest of patients.
Left atrial decompression
Increased pressure in the left atrium resulting in left-sided congestive heart failure is a common sequela to multiple cardiac conditions in dogs, with the most common being myxomatous mitral valve disease (Keene et al., 2019).
Previously, the only option for patients suffering from this condition was medical management with a combination of positive inotropes, balanced arteriodilators, diuretics and angiotensin-converting enzyme inhibitors. More recently, left atrial decompression has been developed as a palliative method to reduce pressures in the left heart, thereby temporarily alleviating the signs of left-sided congestive heart failure. The procedure involves accessing the heart percutaneously via the venous route before incising the interatrial septum, creating an artificial atrial septal defect. This allows blood from the left atrium (high pressure) to enter the right atrium (low pressure), reducing the afterload of the left atrium and, thus, pulmonary venous congestion. This defect can be widened by balloon valvuloplasty or even stented in some cases (O’Brien et al., 2017).
Left arterial decompression […] can be performed without the need for cardiac bypass, the equipment is readily available in most cardiology referral centres and it can be repeated
Left arterial decompression is appealing for multiple reasons: it can be performed without the need for cardiac bypass, the equipment is readily available in most cardiology referral centres and it can be repeated, if necessary. Studies have shown that left atrial decompression leads to an immediate and significant reduction in left atrial pressures. Median survival time post-surgery is 195 days (Allen et al., 2021). This procedure not only improves clinical signs but may also extend the lives of patients suffering from congestive heart failure who would otherwise be euthanised.
Mitral valve repair
Unfortunately, dogs with mitral valve disease, especially those in the advanced stages, have a poor prognosis as there is no cure. On top of this, the medical therapies aimed to stave off the disease involve a multitude of daily drugs which owners may find difficult to administer correctly.
Previously, no surgical options were available for dogs suffering from this disease; however, techniques stemming from human medicine have recently been developed. The most commonly used techniques include circumferential mitral annuloplasty, which involves tightening and reinforcing the ring of cartilage around the mitral valve, and chordae tendineae repair (Buchanan and Sammarco, 1998).
Studies have shown that successful repair reduces the clinical signs of mitral valve disease and, therefore, the need for daily medical therapies, and extends the survival time of dogs versus medical therapy alone (Griffiths et al., 2004). However, cardiopulmonary bypass is required to facilitate these surgeries. Historically, this was only achievable on larger-breed dogs but as advancements in technique have been made, smaller patients can now successfully undergo the procedure (Uechi et al., 2012).
Another new, minimally invasive technique called transcatheter edge-to-edge mitral valve repair (TEER) is being undertaken in a small number of cardiology centres worldwide. This new approach gains access to the heart through a small incision in the thoracic wall followed by a needle puncture at the apex of the heart. Performed alongside fluoroscopy and transoesophageal echocardiography, a device called a “V-clamp” is positioned across the mitral valve to reduce regurgitation, thus reducing left atrial volume overload.
Although limited, early data suggests that survival rates in dogs undergoing surgery are up to 91 percent within the first nine months after the procedure (Kadotani and Fries, 2023). As mitral valve disease is the most common cardiac condition affecting canines, this shows huge promise for increasing the potential surgical options and, therefore, outcomes for patients.
Conclusion
It is clear that advancements in interventional cardiology procedures can have a positive impact on the quality of life for both pets and owners alike
It is clear that advancements in interventional cardiology procedures can have a positive impact on the quality of life for both pets and owners alike. As more and more techniques develop, so too do the options for clients and patients with a multitude of cardiac conditions. Previously “untreatable” diseases are now being managed with innovative techniques that advance our knowledge of what is possible in the field of veterinary cardiology.
