Mitral regurgitation (MR) associated with secondary to degenerative mitral valve disease (DMVD) is an acquired cardiac disease that most commonly occurs in dogs. Severity of DMVD is related to age, the degree of MR (murmur or countercurrent jet), and the degree of valvular degeneration. Deterioration of clinical signs and worsening prognosis of DMVD occurs because of advancing mitral valve degeneration, development of mitral valve prolapse, and progressive thickening and eventual rupture of the chordae tendineae. When compensatory functions of the pulmonary vasculature for MR fail, cough and dyspnea due to pulmonary congestion and pulmonary edema occur. Dyspnea due to severe pulmonary edema is treated with diuretics, oxygen inhalation, nitrates, cardiotonics, and vasodilators. Recently, pimobendan has been shown to have beneficial response to MR dogs with improvements in quality of life and survival. However, survival following DMVD and/or rupture of the chordae tendineae is no longer than 2 years. Because medical treatment of MR with cardiovascular drugs is palliative, MR generally progresses to severe disease. Therefore, a more radical cure to reduce MR requires surgical intervention.

Mitral valve repair was developed as an alternative treatment option for mitral regurgitation and has demonstrated results superior to mitral valve replacement in humans. Valve replacement and long term survival have been reported in dogs. However, the primary issue associated with mitral valve replacement is the subsequent need for life-long antithrombotic treatment, which is not required following mitral valve repair. At present, the long-term outcome in dogs after mitral valve repair is poorly documented. We present the long-term outcome of small-breed dogs after mitral valve repair. We evaluated cardiac reverse remodeling after mitral valve repair under cardiopulmonary bypass (CPB) for mitral regurgitation in small breed dogs.

Three hundred seventy dogs with mitral regurgitation were treated between 2006 and 2014. The cardiac murmur was grade 4/6–6/6. The preoperative thoracic radiographs showed cardiac enlargement (vertebral heart scale [VHS] 11.0–13.1). Echocardiography showed severe mitral regurgitation and left atrial enlargement (LA/AO 2.0–4.2). After inducing anesthesia, a thoracotomy was performed through the fifth intercostal space. CPB was initiated by use of a CPB circuit connected to carotid artery and jugular vein catheters. After inducing cardiac arrest, the left atrium was sectioned and chordae tendineae rupture was confirmed. The chordae tendineae were replaced with expanded polytetrafluoroethylene. A mitral annulus plasty was performed, and the left atrium was closed. After aortic declamping and appropriate restarting of the heart was confirmed, the chest was closed. After MVR, the heart rate significantly decreased from 118–164 bpm to 75–138 bpm. The grade of cardiac murmur was significantly reduced to 0/6–3/6, three months postoperatively, and the cardiac silhouette was reduced (VHS 9.8–11.5) in the chest X-rays. Echocardiography confirmed the marked reduction in both the mitral regurgitant ratio (62–87% to 4–64%, p < 0.05) and the left atrial dimensions (LA/AO 1.2–2.2). Mitral valve repair reduced cardiac size by reduction of the regurgitant rate.

After surgery, clinical signs improved and patients were discharged within 12 days postoperatively. Several dogs died within 10 days after surgery as a result of bleeding or pancreatitis. In the postoperative physical examination, cough was no longer present, and the animal's appetite had improved. In addition, with the improvement in general condition, body weight increased. The clinical signs had essentially disappeared by 1 month after surgery. In addition, cardiac reverse remodelling was also observed at 1 month postoperatively. Based on the reduction in class of The International Small Animal Cardiac Health Council classification, the clinical signs had improved after MVR. In addition, the number of medications used decreased by 1 month post operatively. By 3 months after the surgery, many dogs did not require medication.

Properly performed mitral valve repair for DMVD confers excellent durability and long-term clinical outcomes in humans. Surgical repair of DMVD normally incorporates 2 components: leaflet or chordal repair to correct prolapse and annuloplasty to restore normal annular geometry, increase leaflet coaptation, reduce tension on suture lines, and prevent future annular dilation. Artificial chordal replacement with expanded polytetrafluoroethylene (ePTFE) is an established technique for mitral valve repair with good long-term results, which is usually used for prolapse of the anterior and/or posterior mitral leaflet.

Open heart surgery using CPB can be performed safely in small breed dogs. Mitral valve repair is an effective therapy for DMVD with severe MR. Postoperative complications include pancreatitis and thrombosis, which may be reduced by future advancement in techniques.

For mitral valve repair to be more widely available there are likely two options: increasing the number of facilities capable of supporting a team of traveling surgeons and to increase the number of facilities capable of successfully performing this procedure. The requirements of an open heart surgery team comprises of well-trained cardiovascular surgeons, perfusionist, anesthesiologist, cardiologist, internist, criticalist and support staff. A team leader is essential and should delegate roles to each member to prevent unnecessary mishaps pre-, peri- and postoperatively. The team leader should be able to direct the members if a complication should arise. Therefore, good communication is imperative. The key to becoming comfortable with managing an open heart surgical procedure is experience. Therefore, an abundant caseload, proper facility and well-trained support staff is necessary for a successful program.

As the field of veterinary medicine continues to advance, clients are also more willing to take extraordinary measures for treatments for their pets. There is a large demand and necessity of mitral valve repair, and it is necessary to increase the availability of this procedure. Simultaneously training veterinary surgeons while developing facilities capable of supporting a traveling team should be the next steps for the future of mitral valve repair in veterinary medicine.

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