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Mitral valve repair in dogs
Journal of Veterinary Cardiology (2012) 14, 185e192
www.elsevier.com/locate/jvc
Mitral valve repair in dogs* Masami Uechi, DVM, PhD Veterinary Cardiovascular Medicine and Surgery, Laboratory of Veterinary Internal Medicine, Department of Veterinary Medicine, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-8510, Japan Received 26 August 2011; received in revised form 1 December 2011; accepted 12 January 2012
KEYWORDS Cardiopulmonary bypass; Mitral annuloplasty; Mitral chordal replacement; Mitral regurgitation; Canine
Abstract Prognosis for dogs with severe mitral regurgitation is poor with medical therapy alone. Open surgical mitral valve repair consisting of circumferential mitral annuloplasty and artificial chordal replacement confers durability and improved long-term clinical outcome without a need for long-term antithrombotic therapies. This approach has been successfully used in canine patients, including small-breed dogs. Methods for mitral valve repair applicable to small dogs are described. ª 2012 Elsevier B.V. All rights reserved.
Introduction
* “A unique aspect of the Journal of Veterinary Cardiology is the emphasis of additional web-based images permitting the detailing of procedures and diagnostics. These images can be viewed (by those readers with subscription access) by going to http://www.sciencedirect.com/science/journal/17602734. The issue to be viewed is clicked and the available PDF and image downloading is available via the Summary Plus link. The supplementary material for a given article appears at the end of the page. Downloading the videos may take several minutes. Readers will require at least Quicktime 7 (available free at http://www.apple.com/quicktime/download/) to enjoy the content. Another means to view the material is to go to http:// www.doi.org and enter the doi number unique to this paper which is indicated at the end of the manuscript.” E-mail addresses: [email protected], uechi. [email protected].
Dogs with severe mitral regurgitation have a poor prognosis despite recent medical advances for the management of heart failure.1 While pimobendan improves the clinical condition and prognosis in affected dogs, 80% of these patients are likely to worsen or die within 2 years of diagnosis.2 Because medical management of secondary heart failure is incapable of correcting disorders of the mitral valve complex, surgical intervention is required to improve clinical condition and prognosis. Surgical treatments for mitral regurgitation include valve replacement and valve repair. While these are standard therapies in humans,3e6 mitral valve surgery has been reported in comparatively few veterinary patients.7e18 Open heart surgery is
1760-2734/$ - see front matter ª 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jvc.2012.01.004
186 Abbreviations CPB cardiopulmonary bypass ePTFE expanded-polytetrafluoroethylene
more commonly attempted in larger breeds, as it is difficult to perform cardiopulmonary bypass (CPB) in small dogs using traditional methods.14 Recent improvements in CPB techniques have facilitated its effective use in small-breed dogs18e20 and even in a cat.21 These advances have enabled successful mitral valve surgery in a wider range of dog sizes. Faulty mitral valves can be replaced with a mechanical valve16 or a bioprosthetic valve.10,12,17 In the case of prosthetic valves, longterm survival is promoted by carefully matching the size of a prosthetic heart valve to the dog and strong efforts to avoid thrombosis.16 One advantage of bioprosthetic valves is that they are less thrombogenic than mechanical valves.10,12,17,22 Bioprosthetic valve replacement may be particularly useful in cases of mitral valve dysplasia, in which the original mitral valve is difficult to repair.10,12,17 One potential drawback of bioprosthetic valves is their tendency to calcify or degenerate over time, thus reducing long-term survival.23 Dogs receiving bioprosthetic valves have been known to survive >17 months,10,12,17 with no reports to date of calcification bioprosthetic heart valves in dogs. In both human4,5 and veterinary medicine,13,14,18 properly performed mitral valve repair, including both circumferential mitral annuloplasty and artificial chordal replacement, confers excellent durability and improved longterm clinical outcomes without the need for long-term antithrombotic therapy. Thus, mitral valve repair may become an important treatment for mitral regurgitation in dogs. This report describes methods for mitral valve repair in dogs.
M. Uechi to avoid excess hemodilution. Induction of hypothermia during CPB reduces demand for O2 and preserves peripheral tissues. This is achieved by combination of body-surface cooling and use of a heat exchanger within the CPB circuit. Use of both techniques simultaneously maximizes control of the body temperature. When used in conjunction with anesthesia, hypothermia limits damage during CPB by maintaining low blood circulation.18,24
Cannulation for CPB In preparation for CPB, the left carotid artery and the jugular vein are surgically isolated and the thoracic cavity is opened at the left 4th or 5th intercostal space. Heparin (400 U/kg) is administered intravenously. Once the activated clotting time has exceeded 300 s, an arterial cannula is inserted into the carotid artery.25 In dogs weighing <5 kg, arterial cannulation to the carotid artery requires a 6-Fr cannula, whereas an 8-Fr cannula is needed for dogs weighing 5e10 kg. A single venous cannula is inserted into the left jugular vein. An 8 to 10-Fr cannula in dogs weighing <5 kg or a 10 to 14-Fr cannula in dogs weighing 5e10 kg is appropriate. Cannulation of peripheral vessels is preferred over direct cannulation of aorta and right atrium in small dogs in order to avoid obstructing visualization of the surgical field by the cannulae. The CPB circuit is connected to both the arterial and venous cannulae. Air is carefully removed from the arterial side of the circuit. The artery and vein lines are de-clamped and CPB is commenced at a flow rate of 90e120 mL/kg/min. The body temperature is held between 25 and 30 C. The pump flow is carefully monitored to match venous return (Fig. 1). During CPB, anesthesia is switched from inhalation of isoflurane to intravenous fentanyl and propofol infusion. During CPB, arterial and central venous blood pressure, oxygen saturation and blood gases are monitored.
Cardiopulmonary bypass
Induction of cardiac arrest
Mitral valve surgery requires stopping the heart and support of cardiac and pulmonary function by CPB. This is accomplished by a heart-lung machine with an extracorporeal circuit, oxygenator, and heat exchanger. The CPB circuit is filled with a priming solution consisting of 20% Dmannitol, 7% sodium bicarbonate, and heparin sodium in acetate Ringer’s solution. In dogs weighing <4 kg, priming solution should be replaced with 20e50 mL of whole blood in order
Mitral valve repair requires a bloodless and motionless field of vision. This is achieved by infusing a cardioplegia solution into the coronary arteries via the aortic root. A catheter is inserted through a purse-string suture on the left lateral side of the ascending aorta. The aorta is occluded using a vascular clamp placed distal to the cardioplegia cannula and proximal to the brachiocephalic artery. Cardioplegic solution is immediately infused into root of the aorta to induce cardiac
Mitral valve repair in dogs
187
Figure 1 Cardiopulmonary bypass. An arterial cannula is placed in a carotid artery and a venous cannula is inserted into the jugular vein. Both cannulae were connected to the CPB circuit. Venous blood was withdrawn from the jugular cannula and sent from the blood reservoir to the artificial lung by the CPB pump; the blood was then returned to the carotid artery. Shed blood is returned to the blood reservoir via suction lines.
arrest (Video 1). Administration of cardioplegia solution is repeated every 20 min. Although this is the standard protocol for intracardiac procedures, it is also possible to utilize an on-beat cardiac surgery technique,17,21 which diminishes the risk of ischemia-reperfusion injury.26 However, this may cause blood to leak from the aorta obscuring the surgical field. Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Discontinuing CPB The patient is re-warmed to >36 C prior to weaning from CPB. After the left atrium has been closed, the aortic clamp is removed. As coronary circulation restored, cardiac rhythm may return spontaneously (Video 3). Use of a defibrillator at 10e30 J may be required if ventricular fibrillation is observed. The flow rate is decreased in a stepwise fashion until CPB is terminated. Once the cannulae have been removed, it is generally necessary to administer protamine (1.0e1.5 mg of protamine per 100 units of heparin) to reverse the effects of heparin. Protamine activates the complement cascade through the classic pathway and occasionally provokes temporary severe bronchospasm, elevation of pulmonary vascular resistance, and hypotension. These reactions can cause severe hypotension and hypoventilation. These adverse reactions are reduced by slow stepwise administration of protamine (0.1e3.2 mg/kg per 5e20 min).
Mitral valve repair Our team employs a left atriotomy approach to perform mitral valve repair. This enables visualization of ruptured mitral chordae tendineae through the opened left atrium (Video 2). Several methods of mitral repair have been reported in humans.3e6,27e29 The Carpentier technique, which uses leaflet resection and rigid or semi-rigid annuloplasty rings, has been widelyused in humans.27 However, this technique substantially disrupts important functions of the mitral valve complex, and as a result, most centers have found it difficult to repair more than 50e60% of insufficient valves.28,29 An alternative is the technique reported by Lawrie,28 who used artificial chords and a flexible annuloplasty ring sutured in place with a running technique without leaflet resection. This method can be correlated with the normally functioning mitral valve in the beating heart. Resection of the mitral leaflet would be a particularly difficult procedure in small-breed dogs because of their small size. These results suggest that mitral valve repair in dogs is best achieved with artificial chordal replacement and mitral annuloplasty without mitral resection.
Mitral chordal replacement Replacement of chordae tendineae has been established as the most effective technique in repair of mitral chordal rupture; supplanting
188 partial leaflet resection, chordal transfer, and chordal shortening.6,30e35 The main challenge in chordal replacement is the difficulty of adjusting artificial chordae to the appropriate length. Ideally artificial chordae length should match that of the opposing chordae to ensure proper coaptation of the opposing leaflets. Several methods, including application of a caliper, transesophageal echocardiography, and multiple knots6,30,36,37 have been reported to ensure that artificial chordae are of the optimal length. However, these techniques may be difficult to apply to the hearts of smallbreed dogs. Instead, a temporary Alfieri (edge-toedge) stitch can be used to maintain the visual field and ensure proper coaptation of the leaflets.38 After observing a tendency toward overshortening of artificial chordae, we have successfully employed a temporary Alfieri stitch to place artificial chordae in the septal and mural mitral leaflets. Placement of artificial chordae is accomplished by passing a double-armed expanded-polytetrafluoroethylene (ePTFE) suture (CV-6) through lateral portion of the septal leaflet and then though the craniolateral papillary muscle. The double-armed suture is then passed back through the septal leaflet. We now prefer to use a pledget in the papillary muscle as we have observed papillary muscle rupture in one patient. We then place a second ePTFE chordae tendineae between the medial portion of the septal leaflet and the caudomedial papillary muscle (Fig. 2, Video 2). A third ePTFE suture is placed between the mid-portion of the mural mitral leaflet and the caudomedial papillary. After all the artificial chordae are placed, a temporary Alfieri stitch is placed and the artificial chordae are adjusted for length and tied. Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Mitral annuloplasty Mitral annuloplasty plays an important role in maintaining long-term durability after mitral valve repair.39 The saddle-shaped mitral annulus is higher at the cranial and caudal segments and lower at the commissures.40e42 The mitral area is reduced from mid-diastole to late systole, such that the mitral annulus exhibits translational motion during systole.40,43 This sphincter mechanism increases the depth of leaflet coaptation during systole, and increases the annular orifice area during diastole.40e42 These physiological motions of the annulus should be maintained during mitral annuloplasty. Annular stabilization with prosthetic
M. Uechi
Figure 2 Placement of artificial chordae. The septal mitral leaflet is shown with ruptured caudal chordae tendineae and papillary muscles (A). The double-armed ePTFE suture is passed through the mitral valve, into the caudomedial papillary muscle, and then back through the mitral leaflet (B). Another suture was made on the other side in the same manner and both were tied. This procedure was repeated on the mural leaflet.
materials enhances durability by increasing leaflet coaptation and preventing future annular dilatation.39 Saddle-shaped annuloplasty rings provide superior uniform annular force distribution compared to flat rings, and appear to minimize outof-plane forces that could be transmitted to leaflets and chords.44 Prosthetic rings designed for humans are not of a suitable size for small-breed dogs. Use of a mitral plication suture instead of an annuloplasty ring may preserve the natural shape and hemodynamic performance of the annulus.45,46 However this method is not as durable as ring
Mitral valve repair in dogs annuloplasty due to detachment of the suture from the annulus.47e50 By contrast, prosthetic soft ring annuloplasty provides reproducible and long-term results in dogs. The best alternative for small dogs is a soft prosthetic ring made of ePTFE material that can be trimmed to an appropriate size at surgery. The size of the mitral annulus can be determined by a sizer that matches the mitral annulus and the root of the aorta. We frequently observe annular dilatation at the cranial and caudal mitral commissures. This prevents us from achieving proper coaptation, thereby leading to nontrivial mitral regurgitation. This may be rectified by use of a plication stitch between the mural and septal leaflets at the commissures.51 Our preferred approach for mitral annuloplasty is placement of plication sutures with pledgets at the cranial and caudal commissures of the mitral annulus to reduce the size of both commissure regions. Then 5-0 sutures are preplaced in the mitral annulus and passed through a strip of ePTFE material approximately 1.5 mm wide and 40e55 mm in length (Fig. 3, Video 3). The sutures are then tied to seat the annuloplasty ring. Antithrombotic therapy with dalteparin sodium should be started when the volume of drainage from the thoracic cavity is less than 3 mL/h and continued for 1 week. Administration of an anti-
189 platelet agent is necessary for 1e3 months after surgery. Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Surgical outcomes Mitral valve repair improves clinical signs, such as cough, dyspnea, and anorexia. Improved appetite can lead to gains in body weight and improved cardiac cachexia (Fig. 4). Auscultation should reveal significant reductions in the grade of the cardiac murmur. Chest X-rays should reveal significant decreases in vertebral heart size and tracheal elevation (Fig. 5). Echocardiography should show decreases in the left atrial and left ventricular end-diastolic diameters, with marked reductions in mitral regurgitation (Video 4). Mitral valve repair improves clinical signs and reverses cardiac remodeling. These outcomes reduce the need for cardiovascular drug therapy. Cumulatively, the improved clinical condition of surgically treated dogs indicates that mitral regurgitation can be effectively treated with mitral valve repair. If left untreated, severe mitral regurgitation has a poor prognosis in canine patients.1 In most cases, dogs are not expected to survive for >1 year, even
Figure 3 Mitral annuloplasty techniques. Mattress sutures with pledgets are placed in the cranial and caudal commissure of the mitral annulus to reduce the size of both commissure regions (A). Interrupted sutures are placed in the mitral annulus and passed through strips of ePTFE material (B). Annuloplasty is completed by tying the sutures and seating the annuloplasty rings (C). Intraoperative mitral annuloplasty is shown (D).
190
M. Uechi mitral valve repair.51 Other surgeons have reported long-term survival (>3 years) after mitral valve repair.14 Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Conclusion
Figure 4 Dog with severe mitral regurgitation before and after mitral valve repair. Prior to surgery, the dog was thin, had a poor hair coat and abdominal distension (A). Six months after surgery, the dog had gained weight, its coat condition had improved, and the abdomen distension had resolved (B).
if given medical treatment.1,2 Mitral valve repair and replacement, however, both improve prognosis in dogs with mitral regurgitation.10,12,13,16,17 We observed 93% survival at 38 months after
Mitral valve repair in dogs using cardiopulmonary bypass is an effective treatment for severe mitral regurgitation in small dogs. Reestablishment of coaptation by annuloplasty and chordal replacements using ePTFE are the most appropriate repair methods for small dogs. Successful mitral repair offers the probably of decreased clinical signs, reduced need for cardiac medical therapies, and improved survival in dogs with severe mitral regurgitation.
Conflict of interest The author has no conflicts of interest to declare.
Acknowledgments The author acknowledges surgical team members. This study was supported in part by a Grant-in-Aid for General Scientific Research (C-22580369) from the Ministry of Education, Culture, Sports, Science and Technology, Japan; a grant from the Ministry of Health, Labour and Welfare, Japan; and a NUBS Research Grant in both 2009 and 2011.
References
Figure 5 Thoracic radiographs before (A) and after (B) mitral valve repair demonstrating significant decrease in cardiac size.
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Available online at www.sciencedirect.com
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Mitral valve repair in dogs* Masami Uechi, DVM, PhD Veterinary Cardiovascular Medicine and Surgery, Laboratory of Veterinary Internal Medicine, Department of Veterinary Medicine, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-8510, Japan Received 26 August 2011; received in revised form 1 December 2011; accepted 12 January 2012
KEYWORDS Cardiopulmonary bypass; Mitral annuloplasty; Mitral chordal replacement; Mitral regurgitation; Canine
Abstract Prognosis for dogs with severe mitral regurgitation is poor with medical therapy alone. Open surgical mitral valve repair consisting of circumferential mitral annuloplasty and artificial chordal replacement confers durability and improved long-term clinical outcome without a need for long-term antithrombotic therapies. This approach has been successfully used in canine patients, including small-breed dogs. Methods for mitral valve repair applicable to small dogs are described. ª 2012 Elsevier B.V. All rights reserved.
Introduction
* “A unique aspect of the Journal of Veterinary Cardiology is the emphasis of additional web-based images permitting the detailing of procedures and diagnostics. These images can be viewed (by those readers with subscription access) by going to http://www.sciencedirect.com/science/journal/17602734. The issue to be viewed is clicked and the available PDF and image downloading is available via the Summary Plus link. The supplementary material for a given article appears at the end of the page. Downloading the videos may take several minutes. Readers will require at least Quicktime 7 (available free at http://www.apple.com/quicktime/download/) to enjoy the content. Another means to view the material is to go to http:// www.doi.org and enter the doi number unique to this paper which is indicated at the end of the manuscript.” E-mail addresses: [email protected], uechi. [email protected].
Dogs with severe mitral regurgitation have a poor prognosis despite recent medical advances for the management of heart failure.1 While pimobendan improves the clinical condition and prognosis in affected dogs, 80% of these patients are likely to worsen or die within 2 years of diagnosis.2 Because medical management of secondary heart failure is incapable of correcting disorders of the mitral valve complex, surgical intervention is required to improve clinical condition and prognosis. Surgical treatments for mitral regurgitation include valve replacement and valve repair. While these are standard therapies in humans,3e6 mitral valve surgery has been reported in comparatively few veterinary patients.7e18 Open heart surgery is
1760-2734/$ - see front matter ª 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jvc.2012.01.004
186 Abbreviations CPB cardiopulmonary bypass ePTFE expanded-polytetrafluoroethylene
more commonly attempted in larger breeds, as it is difficult to perform cardiopulmonary bypass (CPB) in small dogs using traditional methods.14 Recent improvements in CPB techniques have facilitated its effective use in small-breed dogs18e20 and even in a cat.21 These advances have enabled successful mitral valve surgery in a wider range of dog sizes. Faulty mitral valves can be replaced with a mechanical valve16 or a bioprosthetic valve.10,12,17 In the case of prosthetic valves, longterm survival is promoted by carefully matching the size of a prosthetic heart valve to the dog and strong efforts to avoid thrombosis.16 One advantage of bioprosthetic valves is that they are less thrombogenic than mechanical valves.10,12,17,22 Bioprosthetic valve replacement may be particularly useful in cases of mitral valve dysplasia, in which the original mitral valve is difficult to repair.10,12,17 One potential drawback of bioprosthetic valves is their tendency to calcify or degenerate over time, thus reducing long-term survival.23 Dogs receiving bioprosthetic valves have been known to survive >17 months,10,12,17 with no reports to date of calcification bioprosthetic heart valves in dogs. In both human4,5 and veterinary medicine,13,14,18 properly performed mitral valve repair, including both circumferential mitral annuloplasty and artificial chordal replacement, confers excellent durability and improved longterm clinical outcomes without the need for long-term antithrombotic therapy. Thus, mitral valve repair may become an important treatment for mitral regurgitation in dogs. This report describes methods for mitral valve repair in dogs.
M. Uechi to avoid excess hemodilution. Induction of hypothermia during CPB reduces demand for O2 and preserves peripheral tissues. This is achieved by combination of body-surface cooling and use of a heat exchanger within the CPB circuit. Use of both techniques simultaneously maximizes control of the body temperature. When used in conjunction with anesthesia, hypothermia limits damage during CPB by maintaining low blood circulation.18,24
Cannulation for CPB In preparation for CPB, the left carotid artery and the jugular vein are surgically isolated and the thoracic cavity is opened at the left 4th or 5th intercostal space. Heparin (400 U/kg) is administered intravenously. Once the activated clotting time has exceeded 300 s, an arterial cannula is inserted into the carotid artery.25 In dogs weighing <5 kg, arterial cannulation to the carotid artery requires a 6-Fr cannula, whereas an 8-Fr cannula is needed for dogs weighing 5e10 kg. A single venous cannula is inserted into the left jugular vein. An 8 to 10-Fr cannula in dogs weighing <5 kg or a 10 to 14-Fr cannula in dogs weighing 5e10 kg is appropriate. Cannulation of peripheral vessels is preferred over direct cannulation of aorta and right atrium in small dogs in order to avoid obstructing visualization of the surgical field by the cannulae. The CPB circuit is connected to both the arterial and venous cannulae. Air is carefully removed from the arterial side of the circuit. The artery and vein lines are de-clamped and CPB is commenced at a flow rate of 90e120 mL/kg/min. The body temperature is held between 25 and 30 C. The pump flow is carefully monitored to match venous return (Fig. 1). During CPB, anesthesia is switched from inhalation of isoflurane to intravenous fentanyl and propofol infusion. During CPB, arterial and central venous blood pressure, oxygen saturation and blood gases are monitored.
Cardiopulmonary bypass
Induction of cardiac arrest
Mitral valve surgery requires stopping the heart and support of cardiac and pulmonary function by CPB. This is accomplished by a heart-lung machine with an extracorporeal circuit, oxygenator, and heat exchanger. The CPB circuit is filled with a priming solution consisting of 20% Dmannitol, 7% sodium bicarbonate, and heparin sodium in acetate Ringer’s solution. In dogs weighing <4 kg, priming solution should be replaced with 20e50 mL of whole blood in order
Mitral valve repair requires a bloodless and motionless field of vision. This is achieved by infusing a cardioplegia solution into the coronary arteries via the aortic root. A catheter is inserted through a purse-string suture on the left lateral side of the ascending aorta. The aorta is occluded using a vascular clamp placed distal to the cardioplegia cannula and proximal to the brachiocephalic artery. Cardioplegic solution is immediately infused into root of the aorta to induce cardiac
Mitral valve repair in dogs
187
Figure 1 Cardiopulmonary bypass. An arterial cannula is placed in a carotid artery and a venous cannula is inserted into the jugular vein. Both cannulae were connected to the CPB circuit. Venous blood was withdrawn from the jugular cannula and sent from the blood reservoir to the artificial lung by the CPB pump; the blood was then returned to the carotid artery. Shed blood is returned to the blood reservoir via suction lines.
arrest (Video 1). Administration of cardioplegia solution is repeated every 20 min. Although this is the standard protocol for intracardiac procedures, it is also possible to utilize an on-beat cardiac surgery technique,17,21 which diminishes the risk of ischemia-reperfusion injury.26 However, this may cause blood to leak from the aorta obscuring the surgical field. Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Discontinuing CPB The patient is re-warmed to >36 C prior to weaning from CPB. After the left atrium has been closed, the aortic clamp is removed. As coronary circulation restored, cardiac rhythm may return spontaneously (Video 3). Use of a defibrillator at 10e30 J may be required if ventricular fibrillation is observed. The flow rate is decreased in a stepwise fashion until CPB is terminated. Once the cannulae have been removed, it is generally necessary to administer protamine (1.0e1.5 mg of protamine per 100 units of heparin) to reverse the effects of heparin. Protamine activates the complement cascade through the classic pathway and occasionally provokes temporary severe bronchospasm, elevation of pulmonary vascular resistance, and hypotension. These reactions can cause severe hypotension and hypoventilation. These adverse reactions are reduced by slow stepwise administration of protamine (0.1e3.2 mg/kg per 5e20 min).
Mitral valve repair Our team employs a left atriotomy approach to perform mitral valve repair. This enables visualization of ruptured mitral chordae tendineae through the opened left atrium (Video 2). Several methods of mitral repair have been reported in humans.3e6,27e29 The Carpentier technique, which uses leaflet resection and rigid or semi-rigid annuloplasty rings, has been widelyused in humans.27 However, this technique substantially disrupts important functions of the mitral valve complex, and as a result, most centers have found it difficult to repair more than 50e60% of insufficient valves.28,29 An alternative is the technique reported by Lawrie,28 who used artificial chords and a flexible annuloplasty ring sutured in place with a running technique without leaflet resection. This method can be correlated with the normally functioning mitral valve in the beating heart. Resection of the mitral leaflet would be a particularly difficult procedure in small-breed dogs because of their small size. These results suggest that mitral valve repair in dogs is best achieved with artificial chordal replacement and mitral annuloplasty without mitral resection.
Mitral chordal replacement Replacement of chordae tendineae has been established as the most effective technique in repair of mitral chordal rupture; supplanting
188 partial leaflet resection, chordal transfer, and chordal shortening.6,30e35 The main challenge in chordal replacement is the difficulty of adjusting artificial chordae to the appropriate length. Ideally artificial chordae length should match that of the opposing chordae to ensure proper coaptation of the opposing leaflets. Several methods, including application of a caliper, transesophageal echocardiography, and multiple knots6,30,36,37 have been reported to ensure that artificial chordae are of the optimal length. However, these techniques may be difficult to apply to the hearts of smallbreed dogs. Instead, a temporary Alfieri (edge-toedge) stitch can be used to maintain the visual field and ensure proper coaptation of the leaflets.38 After observing a tendency toward overshortening of artificial chordae, we have successfully employed a temporary Alfieri stitch to place artificial chordae in the septal and mural mitral leaflets. Placement of artificial chordae is accomplished by passing a double-armed expanded-polytetrafluoroethylene (ePTFE) suture (CV-6) through lateral portion of the septal leaflet and then though the craniolateral papillary muscle. The double-armed suture is then passed back through the septal leaflet. We now prefer to use a pledget in the papillary muscle as we have observed papillary muscle rupture in one patient. We then place a second ePTFE chordae tendineae between the medial portion of the septal leaflet and the caudomedial papillary muscle (Fig. 2, Video 2). A third ePTFE suture is placed between the mid-portion of the mural mitral leaflet and the caudomedial papillary. After all the artificial chordae are placed, a temporary Alfieri stitch is placed and the artificial chordae are adjusted for length and tied. Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Mitral annuloplasty Mitral annuloplasty plays an important role in maintaining long-term durability after mitral valve repair.39 The saddle-shaped mitral annulus is higher at the cranial and caudal segments and lower at the commissures.40e42 The mitral area is reduced from mid-diastole to late systole, such that the mitral annulus exhibits translational motion during systole.40,43 This sphincter mechanism increases the depth of leaflet coaptation during systole, and increases the annular orifice area during diastole.40e42 These physiological motions of the annulus should be maintained during mitral annuloplasty. Annular stabilization with prosthetic
M. Uechi
Figure 2 Placement of artificial chordae. The septal mitral leaflet is shown with ruptured caudal chordae tendineae and papillary muscles (A). The double-armed ePTFE suture is passed through the mitral valve, into the caudomedial papillary muscle, and then back through the mitral leaflet (B). Another suture was made on the other side in the same manner and both were tied. This procedure was repeated on the mural leaflet.
materials enhances durability by increasing leaflet coaptation and preventing future annular dilatation.39 Saddle-shaped annuloplasty rings provide superior uniform annular force distribution compared to flat rings, and appear to minimize outof-plane forces that could be transmitted to leaflets and chords.44 Prosthetic rings designed for humans are not of a suitable size for small-breed dogs. Use of a mitral plication suture instead of an annuloplasty ring may preserve the natural shape and hemodynamic performance of the annulus.45,46 However this method is not as durable as ring
Mitral valve repair in dogs annuloplasty due to detachment of the suture from the annulus.47e50 By contrast, prosthetic soft ring annuloplasty provides reproducible and long-term results in dogs. The best alternative for small dogs is a soft prosthetic ring made of ePTFE material that can be trimmed to an appropriate size at surgery. The size of the mitral annulus can be determined by a sizer that matches the mitral annulus and the root of the aorta. We frequently observe annular dilatation at the cranial and caudal mitral commissures. This prevents us from achieving proper coaptation, thereby leading to nontrivial mitral regurgitation. This may be rectified by use of a plication stitch between the mural and septal leaflets at the commissures.51 Our preferred approach for mitral annuloplasty is placement of plication sutures with pledgets at the cranial and caudal commissures of the mitral annulus to reduce the size of both commissure regions. Then 5-0 sutures are preplaced in the mitral annulus and passed through a strip of ePTFE material approximately 1.5 mm wide and 40e55 mm in length (Fig. 3, Video 3). The sutures are then tied to seat the annuloplasty ring. Antithrombotic therapy with dalteparin sodium should be started when the volume of drainage from the thoracic cavity is less than 3 mL/h and continued for 1 week. Administration of an anti-
189 platelet agent is necessary for 1e3 months after surgery. Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Surgical outcomes Mitral valve repair improves clinical signs, such as cough, dyspnea, and anorexia. Improved appetite can lead to gains in body weight and improved cardiac cachexia (Fig. 4). Auscultation should reveal significant reductions in the grade of the cardiac murmur. Chest X-rays should reveal significant decreases in vertebral heart size and tracheal elevation (Fig. 5). Echocardiography should show decreases in the left atrial and left ventricular end-diastolic diameters, with marked reductions in mitral regurgitation (Video 4). Mitral valve repair improves clinical signs and reverses cardiac remodeling. These outcomes reduce the need for cardiovascular drug therapy. Cumulatively, the improved clinical condition of surgically treated dogs indicates that mitral regurgitation can be effectively treated with mitral valve repair. If left untreated, severe mitral regurgitation has a poor prognosis in canine patients.1 In most cases, dogs are not expected to survive for >1 year, even
Figure 3 Mitral annuloplasty techniques. Mattress sutures with pledgets are placed in the cranial and caudal commissure of the mitral annulus to reduce the size of both commissure regions (A). Interrupted sutures are placed in the mitral annulus and passed through strips of ePTFE material (B). Annuloplasty is completed by tying the sutures and seating the annuloplasty rings (C). Intraoperative mitral annuloplasty is shown (D).
190
M. Uechi mitral valve repair.51 Other surgeons have reported long-term survival (>3 years) after mitral valve repair.14 Supplementary data related to this article can be found online at doi:10.1016/j.jvc.2012.01.004.
Conclusion
Figure 4 Dog with severe mitral regurgitation before and after mitral valve repair. Prior to surgery, the dog was thin, had a poor hair coat and abdominal distension (A). Six months after surgery, the dog had gained weight, its coat condition had improved, and the abdomen distension had resolved (B).
if given medical treatment.1,2 Mitral valve repair and replacement, however, both improve prognosis in dogs with mitral regurgitation.10,12,13,16,17 We observed 93% survival at 38 months after
Mitral valve repair in dogs using cardiopulmonary bypass is an effective treatment for severe mitral regurgitation in small dogs. Reestablishment of coaptation by annuloplasty and chordal replacements using ePTFE are the most appropriate repair methods for small dogs. Successful mitral repair offers the probably of decreased clinical signs, reduced need for cardiac medical therapies, and improved survival in dogs with severe mitral regurgitation.
Conflict of interest The author has no conflicts of interest to declare.
Acknowledgments The author acknowledges surgical team members. This study was supported in part by a Grant-in-Aid for General Scientific Research (C-22580369) from the Ministry of Education, Culture, Sports, Science and Technology, Japan; a grant from the Ministry of Health, Labour and Welfare, Japan; and a NUBS Research Grant in both 2009 and 2011.
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Figure 5 Thoracic radiographs before (A) and after (B) mitral valve repair demonstrating significant decrease in cardiac size.
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