Fig. 7.1
Mitral annuloplasty. The size and shape of the annuloplasty ring restores normal mitral annular size and geometry resulting in improved mitral leaflet coaptation and competence (Adapted from Chan et al. [4]. With permission from Elsevier)
Fig. 7.2
Sizing the annuloplasty ring. The annuloplasty ring is sized by measurement of the distance between the fibrous trigones and the size of the anterior mitral valve leaflet (Adapted from Chan et al. [4]. With permission from Elsevier)
Good long-term results following undersized mitral annuloplasty for functional ischaemic mitral regurgitation have been associated with: (i) complete coronary artery revascularisation, (ii) use of a complete rigid or semi-rigid ring, (iii) achieving a surface of mitral leaflet coaptation of 8 mm or greater, and (iii) leaving minimal residual mitral regurgitation [5, 8]. Braun et al., for example, reported that at 5 years following mitral annuloplasty combined with CABG in patients with functional ischaemic mitral regurgitation, mean mitral regurgitation grade improved from 3.1 ± 0.6 to 0.8 ± 0.7 (p < 0.001) [5, 9]. 84 % had less than moderate mitral regurgitation, 14.6 % had moderate mitral regurgitation, and 1.4 % had moderate-severe mitral regurgitation at 5 years. The mitral leaflet coaptation length was maintained at 8 mm.
However, significant recurrence of mitral regurgitation has been reported in several studies following mitral annuloplasty [10–16]. This has been associated with the following factors:
- (i)
Flexible rings or bands [6, 11, 13–17]. The mitral annulus is dilated both at the anterior annulus and the posterior annulus in functional ischaemic mitral regurgitation with the greatest increase being in the septolateral diameter [1, 3, 18, 19]. The use of a complete rigid or semi-rigid ring, rather than a flexible ring or band, may, therefore, be important to restore mitral annular size and geometry. Moreover, continued left ventricular remodelling has been associated with recurrent mitral regurgitation and the use of a complete rigid or semi-rigid ring may be important to overcome this [12, 20].
- (ii)
Failure to undersize [11–15]. The use of an undersized ring has been recommended to decrease the septolateral dilatation present in functional ischaemic mitral regurgitation and, hence, increase the surface of mitral leaflet coaptation. Studies which have reported good results in functional ischaemic mitral regurgitation have generally used this approach [5, 8].
- (iii)
- (iv)
Incomplete coronary artery revascularisation. The primary cause of functional ischaemic mitral regurgitation is left ventricular dysfunction and dilatation secondary to myocardial ischemia or infarction. Complete coronary artery revascularisation, particularly of viable ischaemic left ventricular segments is, therefore, important to restore left ventricular contractility [21]. Progression of mitral regurgitation has been reported following incomplete coronary artery revascularisation [22].
- (v)
Leaving greater than trace mitral regurgitation [13, 23]. The presence of greater than trace mitral regurgitation at the end of the operation may mean greater severity of the mitral regurgitation during physical activity and, hence, continued left ventricular volume overload and impairment of left ventricular reverse remodelling [24, 25].
- (vi)
Excessive dilatation of the left ventricle. Greater recurrence of mitral regurgitation has been reported with significantly dilated left ventricles (e.g., left ventricular end systolic diameter greater than 51 mm or left ventricular end diastolic diameter greater than 65 mm) [5, 9, 26]. In such patients, it has been suggested that undersized mitral annuloplasty should be combined with additional surgical procedures on the left ventricle such as left ventricular restoration surgery [27], left ventricular infarct plication [28] or external left ventricular constraining devices such as the Coapsys [29].
- (vii)
Excessive leaflet tethering. There are some reports that excessive leaflet tethering is a risk factor for the development of significant recurrent mitral regurgitation (tethering distance greater than 1.1 cm, tethering area greater than 1.6 cm2) [30, 31]. Such cases may benefit from additional surgical adjuncts to mitral annuloplasty such as papillary muscle relocation [32], papillary muscle sling [33], and secondary chordal cutting [34]. These techniques are discussed in separate chapters. Long-term results of these techniques are currently awaited.
Surgical Operative Technique
Intra-operative trans-oesophageal echocardiographic assessment of the mitral valve is essential to confirm the findings of the pre-operative transthoracic echocardiography. This is usually performed after the induction of general anaesthesia and before the commencement of cardiopulmonary bypass. It is important to ensure that there is no associated structural valve lesions as other etiologies of mitral regurgitation can co-exist with functional ischaemic mitral regurgitation.
As in all mitral valve surgery, optimal setup is very important in ischaemic mitral valve surgery to maximise exposure and visualisation of the mitral valve. This is particularly so in functional ischaemic mitral regurgitation as the left atrium is typically not very enlarged, unlike in degenerative or rheumatic mitral regurgitation. To maximize exposure of the mitral valve, the pericardium should be lifted up on the right side and left free on the left side. This has the effect of rotating the heart upwards and towards the left, bringing the mitral valve into view when the left atrium is opened. A Cosgrove mitral retractor is used. Further visualisation of the mitral valve is enabled by incising the pericardium on top of the superior vena cava (SVC) and perpendicular to it; this allows retraction of the heart upwards when the retractors are placed [35].
The aorta, SVC and IVC are cannulated. An antegrade cardioplegia and a retrograde cardioplegia cannula are inserted. Tapes may be passed around the SVC and IVC. Cardiopulmonary bypass is commenced. A cross clamp is applied. Cardioplegia is delivered antegradely to start with and then every 20 min retrogradely while suction is applied to the aortic root. The venous cannulation lines are placed over on the left side supported by the mitral retractor.
The mitral valve can be approached either through a left atriotomy or a right atriotomy via a trans-septal approach. With a left atriotomy approach, the fat within Sondergaard’s grove is dissected with diathermy so as to approach the left atrium more medially and nearer to the mitral valve. Alternatively, an incision is made midway between the inter-atrial septum and the origin of the right superior pulmonary vein, and extended inferiorly along the left atrium towards the left inferior pulmonary vein, ending a few mm inferior to it. The incision is then extended superiorly a few mm beyond the end of the right superior pulmonary vein onto the roof of the left atrium. One or two small mitral retractors are then inserted and lifted up together and towards the left side, opening up the left atrium and exposing the mitral valve. To improve visualisation of the mitral valve further, the incision can be extended superiorly and medially, underneath the SVC and onto the roof of the left atrium [35].
A systematic analysis of the mitral valve is performed. The mitral valve is first inspected. Note is made of any excessive leaflet tissue, leaflet perforations, ruptured chordae or ruptured papillary muscles. The lesion is then determined using a pair of nerve hooks. A reference point, such as P1 or the commissures, is chosen. Each part of the mitral valve leaflet is lifted up in turn and compared to the reference point to determine if there is leaflet prolapse or restriction. Leaflet restriction in functional ischaemic mitral regurgitation is typically difficult to assess in the arrested flaccid heart and is often not apparent. It is important to ensure that there are no associated lesions as these would need to be addressed.
In the absence of any other lesions, an undersized mitral annuloplasty is performed. The mitral annulus is first sized by pulling on the marginal chordae supporting the anterior leaflet with two nerve hooks or a right angled clamp. The ring sizer is then placed over the unfurled anterior leaflet and a sizer is chosen which matches the surface area of the anterior leaflet. If the leaflet restriction is asymmetric and mainly in the P3 area as identified by echocardiography, the Carpentier-McCarthy-Adams IMR ETlogix Annuloplasty Ring (Edwards LifeSciences) is a suitable ring. A ring of the same size as the sizer is used as this ring is already downsized in the P2-P3 area. However, if the leaflet restriction is more symmetrical, as in a more global dilatation of the LV, a symmetrical complete rigid or semi-rigid ring, such as the Carpentier-Edwards Physio or Classic Rings (Edwards LifeSciences), or equivalent, are used, downsized by 2 sizes. For example, if the annulus is sized as 30 mm, a 26 mm ring is used. Under-sizing of the annuloplasty ring compensates for the loss of mitral annular function in functional ischaemic mitral regurgitation as discussed in Chap. 2 and increases the coaptation surface area between the anterior and posterior leaflets.
Interrupted non-pledgeted 2/0 ethibond horizontal mattress sutures are placed around the mitral annulus. Unlike in degenerative and rheumatic mitral regurgitation where under-sizing of the annuloplasty ring is not used, the use of an undersized annuloplasty ring in functional ischaemic mitral regurgitation results in increased tension in the annuloplasty ring and care must therefore be taken to ensure that adequate sutures are placed around the mitral annulus, and which are of sufficient length and depth, to avoid ring dehiscence. The sutures can be overlapped if necessary to provide added strength. If the IMR ring is used, this is broader in the P3 region to permit a double row of sutures to be placed. However, care must be taken when using this ring to ensure that the annuloplasty suture positioned at the middle of the P2 scallop is placed in the middle of this ring posteriorly so as not to distort the mitral annulus.
The competency of the mitral valve is tested by injecting water or saline through the valve into the left ventricle. The mitral valve should be able to hold a reasonable pressure of water with no more than trace mitral regurgitation. The final test of the repair is performed using transoesophageal echocardiography when the patient is off cardiopulmonary bypass with a systolic blood pressure above 100 mmHg. There should be no more than trace mitral regurgitation. The left atrium is closed by a single continuous layer of 4/0 polypropylene starting at either end of the incision.
Results of Treatment
Hospital Mortality
The hospital mortality of patients with functional ischaemic mitral regurgitation undergoing mitral annuloplasty combined with CABG in recent series varies from 1.5 to 21 % and may be related to differences in the baseline characteristics of the patients [5, 7, 8, 10, 11, 13, 15, 16, 20, 23, 36–41]. In one study which reported an operative mortality of 21 %, 93 % of patients either had a myocardial infarction within 2 weeks or had unstable angina requiring intravenous heparin and nitrates [10]. Higher operative mortality is also reported for patients with a poor left ventricular ejection fraction (less than 30–40 %) [23, 36–38, 40]. The hospital mortality in the 3 most recent randomised controlled trials of functional ischemic mitral regurgitation was less than 3 % [41–43].
Left Ventricular Reverse Remodelling
Observational studies have long reported significant left ventricular reverse remodelling, improvement in cardiac function and NYHA functional class following concomitant CABG plus mitral valve annuloplasty in functional ischaemic mitral regurgitation. However, most of these studies did not have a control group of patients who only had CABG and so it was not possible to determine how much of these improvements could be attributed to the mitral valve repair and how much was a result of successful coronary artery revascularisation. These findings have now been confirmed in several randomised controlled trials which have recently reported (Table 7.1) [41–43].
Table 7.1
Comparison of left ventricular end systolic volume index (LVESVI) and mitral regurgitation (MR) severity at follow-up in the RIME Trial and the CTSN ischemic mitral regurgitation trials
LVESVI (ml/m2)a | MR ≥ 2+ (%) | |
|---|---|---|
RIME Trial – 1 year results | ||
CABG | 67.4 (−6 %) | 50 |
CABG + MV repair | 56.2 (−28 %) | 4 |
p-value | 0.002 | <0.001 |
CTSN Moderate MR Trial – 1 year results | ||
CABG | 46.1 (−17 %) | 30 |
CABG + MV repair | 49.6 (−16 %) | 11 |
p-value | NS | <0.001 |
CTSN Severe MR Trial – 1 year results | ||
CABG + MV repair | 54.6 (−11 %) | 33 |
CABG + MV replacement | 60.7 (−10 %) | 2 |
p-value | 0.18 | <0.001 |
CABG + MV repair (if no recurrent MR) | 47.3 (−22 %) | 0 |
CABG + MV repair (if recurrent MR) | 64.1 (+5 %) | 100 |
CTSN Severe MR Trial – 2 year results | ||
CABG + MV repair | 52.6 (−15 %) | 59 |
CABG + MV replacement | 60.6 (−10 %) | 4 |
p-value | 0.19 | <0.001 |
CABG + MV repair (if no recurrent MR) | 42.7 (−31 %)b | 0 |
CABG + MV repair (if recurrent MR) | 62.6 (+2 %) | 100 |
Mean regression of left ventricular volumes and dimensions by up to 28 % have been reported 1–2 years following CABG combined with mitral annuloplasty, provided a durable mitral valve repair is achieved [8, 36, 41, 42]. The reduction in left ventricular volumes appears to be dependent on the success of eliminating the mitral regurgitation. In the Randomised Ischemic Mitral Evaluation (RIME) Trial, left ventricular end systolic volumes decreased by 28 % at 1 year following CABG plus mitral annuloplasty compared to a reduction in 6 % in those undergoing isolated CABG [41]. Of note, the freedom from moderate or more mitral regurgitation at 1 year following CABG plus mitral annuloplasty in this study was 96 % compared to 50 % in those undergoing isolated CABG. Greater reductions in left ventricular dimensions following combined CABG plus mitral valve annuloplasty compared to isolated CABG were also reported in an Italian randomised controlled trial [44]. In the Cardiothoracic Surgical Network (CTSN) moderate ischemic mitral regurgitation trial, left ventricular volumes decreased by 16 % at 1 year following CABG plus mitral annuloplasty compared to 17 % in those undergoing isolated CABG. The freedom from moderate or more mitral regurgitation following combined CABG plus mitral annuloplasty in this trial was 89 % compared to 70 % in those undergoing isolated CABG [42]. In the CTSN severe ischemic mitral regurgitation trial, left ventricular volumes decreased by only 11 % at 1 year following CABG plus mitral annuloplasty. However, the freedom from moderate or more mitral regurgitation in this trial was only 67 % [43]. Of note, in patients who had no recurrent mitral regurgitation at 1 year in this study, left ventricular volumes decreased by 22 %, a result similar to that reported in the RIME Trial [41, 43]. Similar results at 2 years were recently reported by the CTSN severe ischemic mitral regurgitation trial. Left ventricular volumes decreased by 15 % 2 years after CABG plus mitral valve repair; the freedom from moderate or more mitral regurgitation was only 41 %. However, in those with no recurrent mitral regurgitation, left ventricular volumes decreased by 31 % at 2 years, as compared to an increase of 2 % in those with recurrent mitral regurgitation [45]. A consistent finding in these randomised studies is that significant left ventricular reverse remodelling can be expected if a successful and durable mitral valve repair is achieved at the time of CABG (Table 7.1). However, left ventricular reverse remodelling will not occur if recurrent or persistent mitral regurgitation is present.
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