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© 2003 European Association of Cardio-Thoracic Surgery
Left ventricular sub-valvar mitral aneurysms
a Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
* Corresponding author. Tel.: +44-29-2074-2944; Fax: +44-29-2074-5439 Received October 24, 2002; received in revised form June 20, 2003; accepted July 2, 2003
We retrospectively reviewed the surgical treatment of 12 patients (nine female, mean age 16.1±8.7 years) with sub-mitral aneurysms managed in our institution between 1991 and 2002. We identified three groups of patients in accordance with the degree of posterior mitral annular involvement by the aneurysm. A single aneurysm neck was found in seven patients, multiple necks in two and involvement of the entire posterior mitral annulus in three patients. Involvement of the entire posterior annulus by the aneurysmal process has not been previously described. The mean age of this latter group 29±5.1 years was significantly older than the former (  ), suggesting a possible progressive nature of sub-mitral aneurysms. An intracardiac surgical approach was used in six patients and a combined intra and extracardiac approach in the remainder. There was no operative mortality. The mitral valve was initially repaired in eight patients. Failure of closure of the aneurysm necessitating reoperation occurred in four patients (33.3%). An understanding of the inter-relationship between the aneurysm and mitral valve is essential for successful surgical repair. Histology of the aneurysm tissue showed rheumatic heart disease in two patients and tuberculosis in two patients. Hence, although sub-valvar aneurysms are thought to be congenital, a third of our patients had evidence of co-existent rheumatic heart disease or tuberculosis.
Key Words: Heart valve; Mitral valve; Ventricular aneurysm; Submitral aneurysm; Surgical repair
Sub-aortic and sub-mitral left ventricular (LV) aneurysms have been collectively referred to as sub-valvar aneurysms, and were first described by Corvisart in 1812 [1]. Sub-valvar aneurysms have been described predominantly in the indigenous African populations of the world, although it has been reported in mixed races and Caucasians [2]. A number of etiologies have been proposed for the development of the anatomical and pathophysiological processes associated with this condition, and the current consensus is that sub-valvar aneurysms are most likely due to a congenital weakness of the fibrous annulus of the valve [2,3]. Sub-aortic aneurysms usually occur in relation to the left coronary cusp of the aortic valve and the more common sub-mitral aneurysms in relation to the posterior annulus of the mitral valve (Fig. 1). Pathophysiologically, sub-mitral aneurysms involve the fibrous mitral annulus and with enlargement displace the posterior mitral annulus and sub-valvar supporting apparatus apart, resulting in restriction of the posterior mitral leaflet and failure of leaflet coaptation with secondary mitral regurgitation. Clinical symptoms arise as a result of valvar regurgitation or occasionally from compression of cardiac structures [4,5].
We reviewed our experience, surgical approach and complications experienced with the repair of sub-mitral aneurysms.
We conducted a retrospective review of 12 patients referred to Groote Schuur and Red Cross Children's Hospitals for surgical correction of sub-mitral LV aneurysms between 1991 and 2002. Patients were divided into three groups according to the extent of posterior mitral annulus involvement by the aneurysm neck: Type I, single localized neck (Fig. 1); Type II, multiple necks (separate distinct openings, and not a large neck with pseudo division by the sub-mitral chordal apparatus into separate openings); and Type III, involvement of the entire posterior mitral annulus (Fig. 2). Complete involvement of the posterior annulus has not previously been described in the literature.
Cardiopulmonary bypass with bicaval atrial cannulation and moderate hypothermia (28–32 °C) was used. Myocardial protection, after aortic cross-clamping, was provided with cold St. Thomas No. 2 crystalloid cardioplegic solution with added lignocaine (20 mg/l) and intermittent multidose cold 1:1 St. Thomas/blood cardioplegia reinfusions. Tissue samples from the aneurysm sac were sent for histological study from ten patients. Intraoperative transesophageal echocardiography was not available for the majority of patients. 2.1. Surgical approach to sub-mitral aneurysm Two techniques to approach and repair sub-mitral aneurysms have been described. The technique described by Antunes used an exclusive intracardiac approach, via the left atrium through the inter-atrial groove [4]. The neck of the sub-mitral aneurysm is identified by retracting the edge of the posterior mitral leaflet, and examining the sub-valvar area between the mitral valve annulus and papillary muscles. A ‘right-angled’ instrument is then inserted into the aneurysm to determine the relationship between the aneurysm and the posterior left atrial wall. An incision is then made in the floor of the left atrium/posterior mitral leaflet parallel to the posterior mitral annulus to allow access to the aneurysm neck (Fig. 3). The mitral leaflets are usually normal and the area/height of the posterior mitral leaflet height needs to be preserved. The advantage of this ‘intracardiac’ approach is that the mitral valve can be assessed and tested for competence following repair of the sub-mitral aneurysm. This approach is however difficult in large complicated aneurysms, especially if the aneurysm has not expanded below the floor of the left atrium, and in these cases either an extracardiac or a combination of an intracardiac and extracardiac approach can be used [4,6,7].
In the extracardiac approach, the aneurysm is opened from the epicardial side through the aneurysm wall, which is usually very thin and friable, by retracting and rotating the heart anticlockwise to expose the aneurysm anterior to the atrio-ventricular groove in the vicinity of the left atrial appendage. The relationship of the circumflex coronary artery to the edge of the aneurysm may be difficult to determine; however, the circumflex coronary artery is usually displaced away from the atrio-ventricular groove towards the left ventricular free wall. 2.2. Surgical closure of sub-mitral aneurysm The posterior mitral leaflet chordae (especially the tertiary chordae) can obscure the full extent of the neck and occasionally divide the aneurysm neck into ‘pseudo multiple necks’. Traction sutures placed at the edges of the neck of the aneurysm or at the corners of each opening in the case of multiple aneurysm necks are helpful in defining the extent of the defect.The ‘neck’ of the aneurysm was closed with pledgeted interrupted 2-0 or 3-0 multifilament polyester horizontal mattress sutures placed through the edge of the aneurysm neck on the left ventricular edge and then through the posterior mitral annulus, or alternatively with a patch of synthetic material, bovine or autologous pericardium. A mitral annuloplasty was then performed, usually with an annuloplasty ring, either the Carpentier Edwards Classic D ring or flexible Physio annuloplasty ring (Edwards Life Sciences, Santa Ana, CA, USA).
3.1. Demographics The mean age was 16.1±8.7 years (range 8–33 years), all presented with some degree of mitral regurgitation, and the majority of patients were female (  , Table 1). All patients were from African ancestry or of mixed racial group. Patients were referred to our unit as a result of asymptomatic incidental findings of mitral regurgitation found during routine examination at primary and secondary health facilities to symptoms of congestive cardiac failure secondary to severe mitral regurgitation, and were in New York Heart Association (NYHA) Class I to IV (Table 1). The sub-valvar aneurysms were diagnosed pre operatively by means of transthoracic echocardiography and left ventricular angiography.
3.2. Surgical findings The sub-mitral aneurysms were repaired using either an exclusive intracardiac approach in six patients or in combination with an epicardial approach in the remaining six patients, and there was no operative mortality. The most common primary technique used to close the LV aneurysm was by direct suture (Table 1). There were seven patients with a Type I defect (exclusive intracardiac approach used in four patients), and two patients with Type II (combined approach used in both patients, both of whom had initially been thought to be Type I defects and multiple necks were not initially seen at the first operation). Mean age of Type I defects was 12.2±4.4 years, and Type II defects 10.3±0.4 years. Direct suture closure was used initially in all but one of the patients with Type I and II defects, and the mitral valve was repaired in seven patients (five Type I, both Type II). Failure of closure of the sub-mitral LV aneurysm, necessitating a repeat surgical procedure occurred in four patients (one third of all patients) – two with Type I defects, both of the two with Type II defects. Echocardiographic examination had revealed recurrent enlargement of the LV aneurysm. The initial surgical approach had been a combined approach in three of the four patients needing repeat procedures, more probably reflecting the complexity initially faced as opposed to the approach per se. In three patients the initial closure technique had been by direct suture versus one patient in whom a patch had been initially used. Re-repair was done 1–17 months after the initial surgery (average of 6.3±7.5 months). The sub-mitral aneurysm involved the entire posterior mitral annulus extending from the antero-lateral to the postero-medial commissure in the three patients with Type III defects (Fig. 2). This extensive annular involvement has not been previously described. An exclusive intracardiac approach was used in two patients, and a direct suture repair was used in both. The mitral valve required replacement in two patients (two thirds of patients); a mitral valve repair was initially attempted in one patient but abandoned intraoperatively because of distortion of the sub-valvar mitral apparatus following closure of the sub-valvar aneurysm. The mean age of patients with Type III defects 29.0±5.1 years, was older than the other groups. 3.3. Follow up Follow up data was obtained in seven of the patients discharged (71%) with follow-up of 1–48 months. The low percentage of follow-up happened as a result of poor socio-economic and demographic factors, with many of our patients returning to rural areas with no mechanism of follow-up. Of the seven patients followed (three had mitral valve repairs and four valve replacements), no mitral regurgitation or recurrence was demonstrated.3.4. Histology findings Two patients had lesions suggestive of associated active rheumatic carditis and two patients had histological evidence suggestive of tuberculosis (Table 1). In the remainder of patients no specific etiology could be identified and the diagnosis of congenital sub-mitral aneurysm was made.
The true incidence of sub-valvar aneurysms is certainly underestimated, especially in the early stages when there are no clinical symptoms. In our institution sub-valvar mitral aneurysms constituted less than 1% of cases of isolated mitral valve disease, as reported by Antunes [4]. The etiology of sub-valvar aneurysms is mostly thought to be a congenital weakness of the fibrous annulus of the valve, which is further supported by the predominant single race group involved, as well as the anatomy and embryology of the affected area [2,3]. We identified co-existent pathology (rheumatic carditis or tuberculosis) on histology in a third of our patients, which may though merely reflect the endemic incidence of these conditions in this population and not necessarily a causal mechanism. Complete involvement of the entire posterior mitral annulus has not been previously described, and implies that there is a spectrum in this condition of single or multiple defects involving the posterior mitral annulus to complete annular involvement. However, our observation that patients with complete annular involvement comprised an older group would support a hypothesis that involvement of the sub-mitral annulus may be progressive. Surgical intervention is the only method of treatment of sub-mitral LV aneurysms and was first reported in 1963 by Shrire and Barnard; the aneurysm was approached via an extracardiac approach [6–8]. Inherent difficulties associated with the extracardiac approach included inadequate exposure of the mitral annulus, residual mitral regurgitation, and technical difficulties in approaching the aneurysm due to adhesions. Antunes described the transatrial approach in 1987 [4]. In our experience sub-mitral aneurysms could not always be approached exclusively by one technique, because of the extent of involvement of the posterior mitral annulus, aneurysm size and degree of mitral valve incompetence. Surgical failure was not related to the surgical approach, but rather to failure to identify additional aneurysm necks (50% of failures) or inadequate closure of the aneurysm. Successful repair is dependent on the appropriate understanding of the relationship between the aneurysm, the mitral valve and the annulus.
Complete involvement of the posterior mitral annulus has not been previously documented, and our observation that this occurred in an older patient cohort is suggestive of a progressive nature of this condition. Acquired factors may play a role in the etiology of sub-mitral aneurysms, although ethnic congenital factors currently appear to be the predominant factor. Failure to identify multiple aneurysm necks was a factor in failure of the primary procedure, and surgical success is dependent on an appropriate understanding of the relationship of the sub-mitral aneurysm and mitral valve. Patients with involvement of the entire posterior mitral valve annulus were more likely to require mitral valve replacement. doi:10.1016/S1569-9293(03)00141-5
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Abstract
1. Introduction
