Journal of Veterinary Cardiology (2011) 13, 197e201
Partial external mitral annuloplasty in dogs with myxomatous mitral valve degeneration and congestive heart failure: Outcome in 9 cases James N.B.M. de Andrade, DVM, MSc, PhD a,*, E. Christopher Orton, DVM, MSc, PhD b, June Boon, MSc b, Celina T.D. Nishimori, DVM, MSc PhD a, Claudio Olivaes, MSc a, Aparecido A. Camacho, DVM, MSc, PhD c a
Programa de Pos-Graduacao em Medicina Veterinaria de Pequenos Animais, Hospital Veterinario, Universidade de Franca, Rua Armando Sales Oliveira 201, 14404-600 Franca, Sao Paulo, Brazil b Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, James L. Voss Veterinary Teaching Hospital, Colorado State University, Fort Collins, CO 80523-1620, USA c Departamento de Clinica e Cirurgia, Faculdade de Ciencias Agrarias e Veterinarias, Universidade Estadual Paulista, Campus de Jaboticabal, Via de acesso Prof. Paulo Donato Castellane s/n, Jaboticabal, Sao Paulo 14884-900, Brazil Received 5 May 2010; received in revised form 3 May 2011; accepted 6 May 2011
KEYWORDS Mitral valve disease; Surgery; Annuloplasty; Dogs
Abstract Objective: To report the outcome of partial external mitral annuloplasty in dogs with congestive heart failure (CHF) due to mitral regurgitation caused by myxomatous mitral valve degeneration (MMVD). Animals, materials and methods: Nine client-owned dogs with CHF due to mitral regurgitation caused by MMVD. Surgery consisted of a double row of pledgetbutressed continuous suture lines placed into the left ventricle parallel and just ventral to the atrioventricular groove between the subsinuosal branch of the left circumflex coronary artery and the paraconal branch of the left coronary artery. Results: Two dogs died during surgery because of severe hemorrhage. Two dogs died 12 and 36 h after surgery because of acute myocardial infarction. Three dogs were euthanized 2 and 4 weeks after surgery because of progression of CHF, 1 was euthanized 30 days after surgery for non-cardiac disease, and 1 survived for 48
* Corresponding author. E-mail address: [email protected]
(J.N.B.M. de Andrade). 1760-2734/$ - see front matter ª 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jvc.2011.05.002
J.N.B.M. de Andrade et al. months. In the 5 dogs that survived to discharge there was no significant change in the left atrium to aortic ratio with surgery (3.6 0.56 before surgery; 3.1 0.4 after surgery; p ¼ 0.182), and no significant change in mitral regurgitant fraction in 4 dogs in which this measurement was made (78.7 2.0% before surgery; 68.7 7.5% after surgery; p ¼ 0.09). Conclusions: Partial external mitral annuloplasty in dogs with CHF due to MMVD was associated with high perioperative mortality and most dogs that survived to discharge failed to show clinically relevant palliation from this procedure. Consequently, partial external mitral annuloplasty is not a viable option for dogs with mitral regurgitation due to MMVD that has progressed to the stage of CHF. ª 2011 Elsevier B.V. All rights reserved.
Introduction Myxomatous mitral valve degeneration (MMVD) is the most common cardiac disease of dogs.1 Pathologic alterations include thickening, billowing and prolapse of the leaflets; lengthening, thickening, or rupture of chordae tendineae; and dilation of the valve annulus.2 These changes lead to progressive mitral regurgitation and congestive heart failure (CHF) in some cases. Medical management of MMVD is directed at palliation of CHF and does not address the underlying structural alterations of the valve apparatus. Valve repair or replacement with MMVD via open-heart surgery in dogs on cardiopulmonary bypass has been reported. However this treatment is expensive, not widely available, and has limitations with regards to patient size.3 Surgical interventions aimed at reducing the circumference of the mitral annulus in the beating heart may decrease mitral regurgitation and slow progression of MMVD. Buchanan and Sammarco4 described complete external circumferential mitral annuloplasty in dogs with MMVD. The authors reported reduction of mitral regurgitation with this procedure, but perioperative mortality was prohibitively high. The principal complication was hemorrhage associated with passage of the suture behind the left atrium and in the atrioventricular groove. Recently, Kolla ´r et al5 proposed a method for partial external subannular plication and demonstrated a 17% reduction in mitral annulus circumference in normal dogs. The technique consists of a double row of pledgeted running sutures inserted into the left ventricular free wall parallel and ventral to the atrioventricular groove. Using this method, Belerenian et al6 reported a reduction in mitral regurgitation in dogs with MMVD prior to the onset of CHF.
In this study, we report the outcome of partial external mitral annuloplasty in dogs with MMVD that has progressed to the stage of CHF.
Animals, materials and methods Animals Nine client-owned dogs (5 male, 4 female) were recruited for the study at the Veterinary Teaching Hospital, Colorado State University, Colorado, USA (n ¼ 5) and Programa de Pos-Graduacao em Clinica de Pequenos Animais, Universidade de Franca, Franca, Sao Paulo, Brazil (n ¼ 4). The dogs were all small breeds with a weight range of 4.1e16.3 kg and an age range of 7e15 years. Evaluations included physical examination and echocardiography on the day before and after the surgery.
Echocardiography Two-dimensional, M-mode and Doppler echocardiography was performed using right short-axis and long-axis, and left cranial and apical views. Appearance and motion of the mitral valve was evaluated. M-mode measurements were made in accordance with the American Society of Echocardiography guidelines.7 Left atrium to aortic ratio (LA:Ao) was measured in the two-dimensional short-axis view.8 Regurgitant area was measured by color flow Doppler from the left apical 4-chamber view and compared with the area of the left atrium. Severity of mitral regurgitation was classified as mild (<20% of left atrium), moderate (20e50% of left atrium) or severe (>50% of the left atrium).9 In 4 dogs, mitral regurgitant fraction was calculated as total stroke volume minus forward stroke volume divided by total stroke volume. Total stroke volume was determined by Simpson’s
Partial external mitral annuloplasty in dogs with myxomatous mitral valve degeneration
rule. Forward stroke volume was measured as aortic cross sectional area multiplied by aortic velocity-time integral.10
Technique Dogs were premedicated with midazolamd (0.1 mg/kg SQ) and hydromorphonee (0.1 mg/kg SQ). General anesthesia was induced by etomidatef (0.5 mg/kg IV) or propofolg (5 mg/kg IV) and maintained with isoflurane.h Thoracotomy was performed by median sternotomy (n ¼ 5) or via the left 6th intercostal space (n ¼ 4). The pericardium was opened ventral to the phrenic nerve. A double row of pledgeted PTFEi (n ¼ 5) or polyesterj (n ¼ 4) running suture was inserted into the left ventricular free wall ventral and parallel to the atrioventricular groove. Branches of the coronary vessels were excluded from the running suture by passing the suture into the ventricular muscle beneath the vessels. The suture was placed between the subsinuosal branch of the left circumflex coronary artery and the paraconal branch of the left coronary artery (Fig. 1). A clamp was applied to the end of the suture, which was gradually tightened while myocardial color and the T wave of the ECG were observed for evidence of myocardial ischemia. In 5 dogs, intraoperative transesophageal echocardiography was performed to assess mitral annulus size, leaflet apposition, and mitral regurgitation by color flow Doppler. The ends of the suture were then tied. The pericardium and thorax were routinely closed. Analgesia was provided with intravenous fentanylk (0.2 mg/kg/min) and intercostal nerve block or intrapleural bupivacainel (2 mg/kg).
Statistical analyses Echocardiographic data (mean standard deviation) before and after surgery were compared by
d Midazolam, Baxter Healthcare Corporation, Deerfield, IL 60015, USA. e Hydromorphone, Baxter Healthcare Corporation, Deerfield, IL 60015, USA. f Amidate, Hospira, Inc. Lake Forest, IL 60045, USA. g Propovan, Crista ´lia Prod. Quı´m. Farm. Ltda, Itapira, SP 13970-000, Brazil. h Attane, Minrad Inc., 3950 Bethlehem PA, 18017 USA; Buffalo, NY 14202, USA. i Gore-Tex, W.L. Gore & Associates Inc., Flagstaff, Arizona 86004, USA. j Ethibond-Ethicon, Johnson & Johnson Produtos Profissionais Ltda, Rod. Pres. Dutra, KM 154 Sa ˜o Jose dos Campos, SP, Brazil. k Fentanyl citrate, Hospira, Inc., Lake Forest, IL 60045, USA. l Bupivacaine (0.75%), Hospira, Inc., Lake Forest, IL 60045, USA.
Figure 1 Double-row pledget-buttressed sutures ventral to the atrioventricular groove, from cranial to the subsinuosal branch of the left circumflex coronary artery to caudal to the paraconal branch of the left coronary artery. Coronary branches were avoided by passing the suture beneath the vessels into the ventricular muscle.
paired t-test using commercial software (Graphpad Prism V 5.02) with p < 0.05 considered significant.
Results All dogs had MMVD based on echocardiographic appearance (nodularity) and motion (leaflet prolapse) of the mitral valve and severe mitral regurgitation (regurgitant area > 50% LA area). Fractional shortening was 41 6.5% and LA:Ao was >1.7. All of the dogs were in stage C or D heart failure.11 Two dogs died during surgery because of severe hemorrhage caused by rupture of the ventricular wall during suture placement. Two dogs died 12 and 36 h after surgery from acute myocardial infarction. Five dogs survived to discharge. In these 5 dogs, there was no significant LA:Ao change with surgery (3.6 0.56 before surgery; 3.1 0.4 after surgery; p ¼ 0.182). There was also no significant change in mitral regurgitant fraction in the 4 dogs in which this measurement was made (78.7 2.0% before surgery; 68.7 7.5% after surgery; p ¼ 0.09). Three of the 5 surviving dogs were euthanized between 2 and 4 weeks after surgery due to progressive CHF. One dog was euthanized 30 days after surgery for reasons unrelated to cardiac disease (intervertebral disc disease). One dog survived for 48 months after surgery. Medical therapy for CHF (furosemide, enalapril and spironolactone) was continued in all dogs that survived to discharge.
Discussion Myxomatous mitral valve degeneration has a variable course with many dogs never progressing to CHF. However once dogs develop CHF, the clinical course is more predictable and the prognosis is guarded to poor. Borgarelli et al.12 showed that the presence of CHF and LA:Ao > 1.7 are significantly associated with decreased survival time. The dogs in our study were all in CHF (Stage C) with LA:Ao > 1.7. Partial external mitral annuloplasty, however, was associated with very high perioperative mortality. Further, most of the dogs that survived to discharge showed no significant clinical improvement and had short survival times. The results of our study are consistent with the previously reported results of circumferential external annuloplasty.4,13 A decrease in the circumference of the mitral annulus can be achieved by external annuloplasty, and this in turn can reduce the severity of mitral regurgitation in dogs with MMVD. However, the procedure is associated with a high incidence of fatal hemorrhage that occurs when placing the suture directly into the atrioventricular groove and passing the suture behind the left atrium. In our study, partial mitral external annuloplasty was performed in an attempt to avoid fatal hemorrhage by placing the suture ventral to the atrioventricular groove and avoiding passage of the suture behind the left atrium. Fatal hemorrhage still occurred in 2 dogs due to tearing of the left ventricle. Two other dogs in the study died from acute myocardial infarction, presumably the result of occlusion of coronary arteries by overtightening the suture. This occurred despite awareness of and an attempt to minimize this complication by observing the response of the myocardium for any evidence of ischemia during surgery. Belerenian et al6 reported the results of partial external mitral annuloplasty in five dogs with MMVD and one with congenital mitral dysplasia. The procedure in these six dogs was performed prior to the onset of CHF. They demonstrated partial or total correction of mitral regurgitation based on perioperative transesophageal echocardiography. One dog in that report died 48 h after surgery due to ventricular arrhythmias. That study, however, did not report a survival benefit or prolongation of the CHF-free interval. In our study, we performed partial external mitral annuloplasty in nine dogs with MMVD that had progressed to CHF. Of the 5 dogs that survived to discharge, 3 failed to achieve any significant palliation and were euthanized within weeks after
J.N.B.M. de Andrade et al. surgery. One dog survived for a period of 48 months after the procedure. Consequently, our data suggest that significant palliation with partial external mitral annuloplasty in dogs with MMVD after the onset of CHF will likely be difficult to achieve.
Conclusions In our study, partial external mitral annuloplasty in dogs with CHF due to MMVD was associated with high perioperative mortality. Further, most dogs that survived to discharge following surgery failed to show clinically relevant palliation from this procedure. Consequently, we conclude that partial external mitral annuloplasty is not a viable option for dogs with MMVD that has progressed to CHF (Stage C).
Conflict of interest The authors report no conflict of interest.
Acknowledgments The authors are grateful to Fundacao de Amparo a Pesquisa no Estado de Sao Paulo, FAPESP, for financial support.
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