Cardiorespiratory effects of hemic versus nonhemic prime during and immediately following mitral valve replacement in dogs.

In order to limit the hemodilution effect during cardiopulmonary bypass (CPB) in low weight animal patients, blood is often used as a component of the prime solution. This study was undertaken to evaluate the effects of the addition of blood to the prime solution on the hemodynamic and respiratory parameters during and following mitral valve replacement in dogs. Ten dogs were randomly assigned to receive either a hemic (HP), 75% blood component, or a nonhemic prime (NP) solution. The hemodilution was 5 +/- 4% and 25 +/- 10% for the HP and NP groups, respectively. Cardiopulmonary measurements were taken 20 minutes before initiating CPB, during CPB, and 20 min after termination. The hematocrit level, the hemoglobin concentration, and the arterial oxygen content were significantly lower in the NP group during and following CPB. However, the systemic oxygen transport index was not significantly different between the NP group (355 +/- 87 mL/min/m2) and the HP group (546 +/- 155 mL/min/m2) following CPB. Our study indicates that, in normal dogs undergoing hemodilution from a nonhemic prime solution, the cardiovascular function is able to maintain the systemic oxygen transport in the period immediately following mitral valve replacement.     

Beating heart mitral valve replacement with a bovine pericardial bioprosthesis for treatment of mitral valve dysplasia in a Bull Terrier

OBJECTIVES: To describe an open, beating heart surgical technique and use of a bovine pericardial prosthetic valve for mitral valve replacement (MVR) in the dog. STUDY DESIGN: Clinical case report. ANIMALS: Male Bull Terrier (17-month-old, 26 kg) with mitral valve dysplasia and severe regurgitation. METHODS: A bovine pericardial bioprosthesis was used to replace the mitral valve using an open beating heart surgical technique and cardiopulmonary bypass. RESULTS: Successful MVR was achieved using a beating heart technique. Mitral regurgitation resolved and cardiac performances improved (left ventricular end-diastolic diameter decreased from 57.6 to 48.7 mm, and left atrium/aorta ratio returned to almost normal, from 1.62 to 1.19). Cardiopulmonary by-pass time and total surgical duration were decreased compared with standard cardioplegic techniques. Surgical recovery was uneventful and on echocardiography 6 months later valve function was excellent. CONCLUSION: Considering the technique advantages (no cardiac arrest, ischemic reperfusion injury, and hypothermia, or the need for aortic dissection and cannulation for administration of cardioplegic solution), short-term mortality and morbidity may be reduced compared with standard cardioplegic techniques. CLINICAL RELEVANCE: Based on experience in this dog, beating heart mitral valvular replacement is a seemingly safe and viable option for the dog and bovine pericardial prosthesis may provide better long-term survival than mechanical prostheses.     

Open Heart Surgery with Deep Hypothermia and Cardiopulmonary Bypass in Small and Toy Dogs

Objective: To evaluate open heart surgery with deep surface‐induced hypothermia (sHT) and low‐flow cardiopulmonary bypass (CPB) in small and toy‐breed dogs. Study Design: Case series. Animals: Small breed dogs (n=8) weighing <5.5 kg with naturally occurring cardiac disease. Methods: Deep sHT under isoflurane anesthesia and low‐flow rate CPB with a small‐volume prime circuit were used. Ventricular septal defect was closed directly in 2 dogs and severe mitral regurgitation was corrected with mitral valvuloplasty (MVP) in 5 dogs and mitral valve replacement in 1 dog. Results: All dogs survived surgery; 1 dog died 6 days and 1 died 2 months after MVP. The other 6 dogs lived (mean follow‐up, 32.8 months; range, 12–65 months). Mean body weight at surgery was 3.6 kg (range, 2–5.3 kg). Mean lowest esophageal temperature was 21.4°C (range, 19.8–23.8°C). Mean lowest pump flow volume was 29.2 mL/kg/min (range, 9.4–57.7 mL/kg/min) during aortic cross‐clamping (mean, 53.5 minutes; range, 25–79 minutes). Mean hematocrit before CPB was 38.6% (range, 33–47%) and 20.3% (range, 13–24%) during CPB with a small circuit priming volume of 225–260 mL. Conclusion: Deep sHT with low‐flow rate CPB may be used for open heart surgery in small dogs weighing <5.5 kg. Clinical Relevance: Open heart surgery for selected congenital defects and acquired defects in small and toy‐breed dogs may be successfully performed using deep sHT and CPB.     

Long‐term outcome in dogs undergoing mitral valve repair with suture annuloplasty and chordae tendinae replacement

Mitral valve repair under cardiopulmonary bypass was performed in three dogs with clinical signs associated with mitral regurgitation that were not controlled by medication. Mitral valve repair comprised circumferential annuloplasty and chordal replacement with expanded polytetrafluoroethylene. One dog died 2 years after surgery because of severe mitral regurgitation resulting from partial circumferential suture detachment. The others survived for over 5 years, but mild mitral valve stenosis persisted in one. The replaced chordae did not rupture in any dog. Mitral valve repair appears to be an effective treatment for mitral regurgitation in dogs. Chordal replacement with expanded polytetrafluoroethylene is a feasible technique, demonstrating long‐term durability in dogs. However, mitral annuloplasty techniques need improvement.     

Short-term performance of mitral valve replacement with porcine bioprosthetic valves in dogs

Porcine bioprosthetic valves cross-linked with glutaraldehyde and polyepoxy compound were newly developed for mitral valve replacement (MVR) in dogs. Five beagle dogs were performed a left thoracotomy and underwent MVR using the porcine bioprosthetic valves during cardiopulmonary bypass (CPB). A vein catheter inserted into right atrium and a vent catheter inserted into the right ventricle to drain. The hemodynamic conditions of CPB were excellent during surgery. The left atrial pressure was measured before and after MVR; there was no significant difference and it was normal. Thrombosis and the prosthetic valve regurgitation were not observed one week after MVR. Pressure half time (PHT) prolonged significantly (P<0.05) from 31.40 +/- 4.0 msec presurgery to 99.20 +/- 19.4 msec at seven days after MVR, although it indicated the normal range as the bioprosthetic valve. The symptom of the prosthetic valve failure was not observed. This study indicated that the MVR using porcine bioprosthetic valves under CPB might have been effective in dogs as a short-term evaluation.     

Successful surgical treatment of mitral valve stenosis in a dog

OBJECTIVE: To report the successful surgical management (open mitral commissurotomy, OMC) of mitral stenosis (MS), incorporating heart-beating cardiopulmonary bypass (CPB), in a 1-year-old dog. STUDY DESIGN: Clinical case. ANIMALS: One-year-old Cairn Terrier with MS. MATERIALS AND METHODS: Diagnosis of MS was confirmed by means of 2-dimensional, continuous-wave and color-flow Doppler echocardiography. Surgery was performed through a left intercostal thoracotomy. CPB was initiated and the heart was kept beating. The fused commissures of the mitral valve were incised to free the cusps of the valve. RESULTS: Left intercostal thoracotomy allowed easy observation of the mitral orifice during heart-beating OMC. Persistent bleeding from the atriotomy site required a second surgical procedure after which the dog had an uneventful recovery. Echocardiography at 2 weeks and 1 year postoperatively indicated substantial improvement in left ventricular filling (pressure half-time=187 ms before surgery, 105 ms [2 weeks] and 110 ms [1 year] after surgery). Enlargement of the left atrium resolved; however, moderate mitral valve regurgitation was still present. CONCLUSIONS: MS can be successfully treated by OMC, facilitated by use of CPB. Substantial improvement in cardiac function was evident by ultrasound and Doppler examination postoperatively. CLINICAL RELEVANCE: OMC under heart-beating CPB should be considered for the treatment of MS in the dog.     

Effect of modified ultrafiltration on cytokines and hemoconcentration in dogs undergoing cardiopulmonary bypass

Cardiac surgery using cardiopulmonary bypass (CPB) generates severe inflammatory reactions secondary to hemodilution and surgical stress. This study was conducted to evaluate whether modified ultrafiltration (MUF) could be performed safely and to clarify its effects during mitral valve repair in dogs in terms of hemodilution and the status of inflammatory cytokines. We retrospectively studied 38 dogs with mitral valve disease who underwent MUF immediately after mitral valve repair under CPB. To determine the effect of MUF, we measured the pre- and post-MUF blood dilution and blood cytokine levels. The levels of red blood cells, hematocrit (HCT), and albumin were significantly increased after MUF, whereas interleukin (IL)-6 levels were significantly increased from 24.3 (range 9.6–54.6) to 32.3 (15.9–65.1) pg/ml. The levels of IL-8 and IL-10 declined significantly after MUF, from 368.2 (246.1–669.4) and 45.4 (28.6–76.1) to 272.2 (174.1–414.4) and 28.8 (18.8–44.5) pg/ml, respectively. Our results demonstrated that MUF can be applied in dogs undergoing CPB and is effective in achieving hemoconcentration. Moreover, MUF may be useful for the removal of cytokines. Further studies are needed to validate these findings and clarify the effects of inflammatory cytokines after CPB.     

Mitral valve replacement for the treatment of congenital mitral dysplasia in a bull terrier

A 10-month-old entire male bull terrier was presented with a history of collapse on exercise. Clinical examination, electrocardiography, radiography and echocardiography all supported a diagnosis of mitral valve dysplasia. There was no evidence of congestive heart failure. Surgical intervention consisted of open resection of the dysplastic mitral valve and its replacement with a bioprosthetic valve. The procedure was performed through a median sternotomy and the dog was placed on to full cardiopulmonary bypass. Total cardiopulmonary bypass time was 70 minutes. A full recovery was made and at the time of writing (17 months postoperatively) the dog is clinically normal requiring no medication.     

OBSERVER VARIATION IN THE TWO-DIMENSIONAL ECHOCARDIOGRAPHIC EVALUATION OF MITRAL VALVE PROLAPSE IN DOGS

In this study, the observer variation and the influence of observer experience in diagnosing mitral valve prolapse in dogs was assessed by having three observers with different degrees of echocardiographic experience (10 years, 4 years, and no prior experience) analyze 303 mitral valve video recordings from 253 dogs, both with and without mitral regurgitation. To assess intraobserver variation, 16 recordings were analyzed twice, and 34 dogs were scanned twice at intervals of a few days. By consensus, 90 dogs had no mitral valve prolapse, 130 had mild and 33 had severe mitral valve prolapse. Intraobserver repeatabilities ranged from 88% to 100% and interobserver repeatabilities from 70% to 78%. In 79% to 94% of the dogs that were scanned twice, the observers diagnosed both recordings identically. All repeatabilities were reduced by approximately 10% when mitral valve prolapse was graded into mild and severe. The three observers differed significantly in diagnosing mitral valve prolapse when compared with each other in pairs (all p-values < 0.01). The unexperienced observer had the highest and most unsystematic occurrence of false diagnoses. It is possible that the interobserver repeatabilities would have been lower had each sonographer obtained his own echocardiograms. We conclude, that mitral valve prolapse in dogs can be diagnosed using two-dimensional echocardiography with the same degree of observer variation as reported in human studies, and that education and training of staff is mandatory to ensure proper ultrasonographic evaluation.     

Surgical repair of a complete endocardial cushion defect in a dog

Objective: To describe surgical repair of a complete endocardial cushion defect (ECD) in a dog. Study Design: Clinical report. Animal: A 5‐month‐old, 9.2 kg male Shetland sheepdog. Methods: Echocardiographic examination revealed an ostium primum atrial septal defect (ASD), an inlet ventricular septal defect (VSD), mitral regurgitation (MR) and tricuspid regurgitation (TR), and a complete ECD was diagnosed. Surgical correction was performed using cardiopulmonary bypass (CPB) via right atriotomy. A polytetrafluoroethylene (PTFE) patch was secured along the margin of the inlet VSD using simple continuous suture, then the cleft in the septal mitral leaflet was sutured. Similarly, the cleft in the septal tricuspid leaflets was sutured. To complete inlet VSD closure, the VSD patch was secured to these sutured leaflets by simple continuous suture. Another PTFE patch was used to close the ostium primum ASD. Result: After surgery, MR, TR, and interventricular shunting were decreased. The dog was alive 6 years and 5 months after the surgery with no evidence of an interventricular shunt, TR, or other clinical signs. Conclusions: Complete ECD in a dog was corrected using a 2‐patch technique under CPB.     

The mechanobiology of mitral valve function,degeneration, and repair

In degenerative valve disease, the highly organized mitral valve leaflet matrix stratification is progressively destroyed and replaced with proteoglycan rich, mechanically inadequate tissue. This is driven by the actions of originally quiescent valve interstitial cells that become active contractile and migratory myofibroblasts. While treatment for myxomatous mitral valve disease in humans ranges from repair to total replacement, therapies in dogs focus on treating the consequences of the resulting mitral regurgitation. The fundamental gap in our understanding is how the resident valve cells respond to altered mechanical signals to drive tissue remodeling. Despite the pathological similarities and high clinical occurrence, surprisingly little mechanistic insight has been gleaned from the dog. This review presents what is known about mitral valve mechanobiology from clinical, in vivo, and in vitro data. There are a number of experimental strategies already available to pursue this significant opportunity, but success requires the collaboration between veterinary clinicians, scientists, and engineers.     

Technique and postoperative management for successful cardiopulmonary bypass and open-heart surgery in dogs

Twenty-six healthy mixed-breed dogs (25 to 35 kg) underwent hypothermic (27 C) cardiopulmonary bypass. The heart was arrested with cold (4 C) cardioplegic solution, and left ventriculostomy performed. Postoperative mortality was 11.5% (3/26). Two deaths were attributable to ventricular fibrillation the night after surgery, and one death 2 weeks later was the result of pulmonary embolization. All other dogs recovered promptly and were well at follow-up evaluation 6 weeks later. The most important considerations were (1) the surgical approach, ie, combining left lateral thoracotomy with cannulation of the right atrium and left femoral artery for cardiopulmonary bypass (CPB) (avoiding median sternotomy and aortic arch perfusion), (2) the adherence to strict criteria for CPB perfusion, consisting of blood flow of at least 2.2 L/m2/min, PCV no less than 25%, gas flow through the oxygenator (97% O2, 3% CO2) of at least 3.5 L/min, maintenance of a mean arterial blood pressure greater than 60 mm of Hg, and heparinization to maintain activated clotting time over 480 seconds, (3) the use of dipyridamole infusion to preserve platelets during CPB, resulting in decreased postoperative blood loss and (4) the monitoring of cardiac, respiratory, renal, and neurologic functions before, during, and after the operation, with particular emphasis on fluid balance and electrolytes. We concluded that a high success rate is possible for open-heart surgery in the dog requiring cardiopulmonary bypass, but only through meticulous surgical technique and the combined application of many monitoring techniques, with timely intervention to correct serious departures from homeostasis.     

ECHOCARDIOGRAPHIC ASSESSMENT OF 537 DOGS WITH MITRAL VALVE PROLAPSE AND LEAFLET INVOLVEMENT

In this work we investigated which mitral valve leaflet was most often involved in mitral valve prolapse with degenerative mitral valve disease and whether there was an association with breed, age, gender, or weight. Five hundred and thirty-seven dogs with mitral valve prolapse-degenerative mitral valve disease were assessed; the cross-breed dog was the most represented breed (248 dogs, 46.2%). Mitral valve prolapse was more common in male dogs, and the average age was 11.3±2.8 years. Prolapse of the anterior leaflet was present in 48.4% of dogs, prolapse of the the posterior leaflet in 7.1%, and bileaflet prolapse was present in 44.5%; this distribution is different than that typically found in humans. There was a significant correlation between severity of mitral regurgitation and severity of mitral valve prolapse or ISACHC class, and between severity of mitral valve prolapse and ISACHC class. There was no relationship between the particular affected leaflet(s) and severity of mitral regurgitation, severity of mitral valve prolapse, or ISACHC class. Our findings suggest that the susceptibility to the mitral valve prolapse-degenerative mitral valve disease is not confined to a specific breeds and that the specific leaflet prolapsing is different in dogs compared with humans.     

Direct measurements of nitric oxide release in relation to expression of endothelial nitric oxide synthase in isolated porcine mitral valves

The aim of this study was to measure the direct release of nitric oxide (NO) from the porcine mitral valve using a NO microelectrode. Furthermore, the expression and localization of endothelial nitric oxide synthase (eNOS) in the mitral valve was studied using immunohistochemistry, Western blotting and RT-PCR. Results show that bradykinin increases NO release from mitral valves (DeltaBradykinin: 33.71 +/- 10.41 nm NO, P < 0.001, n = 10), whereas N-nitro-l-arginine methyl esther (l-NAME) decreases NO release when compared with basal level (Deltal-NAME: 82.69 +/- 15.66 nm NO, P < 0.005, n = 4). Both protein and mRNA expression of eNOS in mitral valves and in isolated valvular endothelial cells suggest that the NO release is mainly associated with the mitral valve endothelium. It is concluded that direct NO release from porcine mitral valves coincides with eNOS expression. This study documents useful techniques for investigations into the role of local NO release in mitral valve diseases.     

Isolation of methicillin-resistant Staphylococcus lugdunensis in a dog with endocarditis

A 4-year-old male castrated Borzoi dog presented on referral for evaluation of pleural effusion, ventricular arrhythmias, and suspected dilated cardiomyopathy. Echocardiogram identified several masses along the chordae tendineae, as well as a long the annulus of the mitral valve. A blood culture was positive for methicillin resistant Staphylococcus lugdunensis. The dog was also positive for Bartonella DNA on PCR testing. Aggressive antibiotic therapy was instituted. However, the dog continued to have recurrent pleural effusion and progressive azotemia. The dog was euthanized 39 days after diagnosis. Necropsy confirmed the presence of intracardiac abscesses, thrombosis and endocarditis. S. lugdunensis is a recently identified rare cause of endocarditis in humans characterized by intracardiac abscess formation, highly destructive valvular lesions preferentially affecting the mitral valve and a high mortality rate. This is the first reported case of S. lugdunensis isolation in a dog with endocarditis.     

Challenges of Cardiopulmonary Bypass—A Review of the Veterinary Literature

Cardiopulmonary bypass (CPB) has been used in veterinary medicine in experimental surgery and to address congenital and acquired diseases. We review the veterinary literature and expose common challenges of CPB in dogs and cats. Specifically, we describe the most specific elements of this technique in veterinary patients. The variety in animal size has made it difficult to standardize cannulation techniques, oxygenators, and priming volumes and solutions. The fact that one of the most common cardiovascular disorders, mitral valve disease, occurs predominantly in small dogs has limited the use of bypass in these patients because of the need for small, low prime oxygenators and pumps that have been unavailable until recently. Coagulation, hemostasis, and blood product availability have also represented important factors in the way CPB has developed over the years. The cost and the challenges in operating the bypass machine have represented substantial limitations in its broader use.     

An update on treatment and prognostic indicators in canine myxomatous mitral valve disease

Mitral regurgitation caused by myxomatous mitral valve disease is the most common cause for congestive heart failure and cardiac-related mortality in dogs. Typically, it takes several years for the disease to progress from mild, clinically silent myxomatous mitral valve disease to severe disease with signs of congestive heart failure. A proportion of dogs will never progress into congestive heart failure before they die from other causes or old age. Some variables have been shown to be predictive of onset of congestive heart failure and they might be useful to identify dogs that need more frequent monitoring and eventually treatment. Results from several controlled clinical trials are available concerning medical treatment of dogs with myxomatous mitral valve disease with or without congestive heart failure. These trials provide estimates of treatment effects and also allow identification of other variables with prognostic value for the outcome after the onset of congestive heart failure. Use of prognostic variables together with qualitative and quantitative results from clinical drug trials may aid the clinician and owner to plan and decide on optimal management of the myxomatous mitral valve disease dog. The purpose of this article is to review the current knowledge of prognostic variables and therapy for this common condition in dogs.     

Echoguided closed commissurotomy for mitral valve stenosis in a dog

Surgical treatment of mitral stenosis (MS) usually consists of open mitral commissurotomy (MC) or percutaneous balloon MC, which require a cardiopulmonary bypass or transseptal approach, respectively. We describe here the first surgical management of congenital MS in a dog using a less invasive procedure, a surgical closed MC under direct echo guidance. A 5-year-old female Cairn terrier was referred for ascites, weakness, and marked exercise intolerance for 2 months, which was refractory to medical treatment. Diagnosis of severe MS associated with atrial fibrillation (AF) was confirmed by echo-Doppler examination and electrocardiography. Poor response to medical treatment suggested a corrective procedure on the valve was indicated. However, due to the cost and high mortality rate associated with cardiopulmonary bypass, a hybrid MC was recommended. A standard left intercostal thoracotomy was performed and three balloon valvuloplasty catheters of differing diameters were sequentially inserted through the left atrium under direct echo guidance. Transesophageal echocardiography revealed a 62% reduction in the pressure half-time compared to the pre-procedure. Thirteen months after surgery the dog is still doing well with resolution of ascites and a marked improvement of most echo-Doppler variables.     

Left ventricular outflow tract to left atrial fistula associated with endocarditis in a dog

A one-year-old, intact male, 28-kg, mixed-breed dog developed neurological episodes consistent with emboli. An acquired III/VI holosystolic heart murmur was ausculted in the mitral area, and valvular endocarditis with pulmonic and aortic insufficiency were noted at echocardiographic examination. An abnormal communication (i.e., fistula) between the left ventricular outflow tract (LVOT) and the left atrium adjacent to the mitral valve annulus was noted with Doppler imaging and confirmed with angiography. Infective valvular endocarditis was confirmed based on two of three blood cultures being positive for Staphylococcus intermedius. In humans, a sequela to infective endocarditis of the aortic or mitral valve, or both, is rupture of the mitral-aortic intervalvular fibrosa, resulting in a communication between the LVOT and the left atrium. This is the first report of this sequela in the dog.     

Surgical management of subvalvular aortic stenosis and mitral dysplasia in a golden retriever

A 12monthoid neutered male golden retriever was presented with a history of lethargy and exercise intolerance. Clinical examination, electrocardiography, radiography and echocardiography supported a diagnosis of fixed subvalvular aortic stenosis with a Doppler pressure gradient of 77.5 mmHg. Surgical inspection also revealed gross structural abnormalities of the mitral valve consistent with mitral dyspiasia. intervention consisted of resection of the dysplastic mitral valve and the subvalvular aortic stenosis. The mitral valve was replaced with a bioprosthetic valve. Total cardiopulmonary bypass time was 65 minutes and aortic crossclamp time was 55 minutes. A full recovery was made and 11 months postoperatively the aortic transvalvular gradient was 30 mmHg. At the time of writing, 12 months after surgery, the dog was clinically normal and requires no medication.