Although an isolated CMVL is an uncommon congenital cardiac diagnosis, it is a well-recognized cause of congenital MR. Isolated CMVL should be distinguished from cleft mitral valves that are associated with atrioventricular septal defects or other forms of congenital heart disease. It is rare to find an isolated CMVL in either the anterior or posterior leaflet, with one study using transthoracic echocardiography reporting a prevalence of isolated posterior CMVL with moderate or severe MR of 0.07% (4). A retrospective, unpublished review of the echocardiogram reports from 2011 through 2020 at our institution showed a total of 24 patients with documented cleft mitral valve. Of these cases, 91.7% (22 out of 24 patients) had some form of associated atrioventricular septal defects, often completely repaired earlier in life. Anterior clefts were much more common than posterior clefts, 21 and 3 clefts, respectively. Another study reviewed 19 consecutive patients with cleft mitral valve on echocardiography and found that 15 of the patients had an associated congenital heart lesion (atrial septal defect, ventricular septal defect, patent ductus arteriosus or tetralogy of Fallot) (1). Of the 4 patients with isolated CMVL in this study, only 1 patient had a posterior CMVL. CMVL can sometimes be associated with additional mitral valve abnormalities including generalized thickening of leaflets, prolapse of anterior leaflet, papillary muscle anomalies, and anomalous insertion of the anterior leaflet chordae (usually towards the LV outflow tract sometimes causing the obstruction) (5). Functional consequences of CMVL can include significant MR and less commonly LV outflow tract obstruction in the presence of abnormal chordal attachments (6).
The diagnosis of CMVL is commonly made my echocardiography, particularly TEE with 3-D acquisition (7). While an isolated CMVL is rare, it must be acknowledged that the diagnosis of CMVL using transthoracic echocardiography is particularly challenging and often leads to under recognition. As such, the increasing use of 3-D TEE has resulted in better understanding of the mechanisms of hemodynamically significant MR (including CMVL) before surgical or percutaneous intervention (7-9). When patients with significant MR due to unrecognized CMVL are referred for surgical intervention, the likelihood of its diagnosis in a non-beating, flaccid heart at the time of surgery is low. A pre-operative TEE, as was performed in our patient’s case, can be very helpful with establishing a diagnosis as well as planning and assessing the feasibility of repair.
Surgical repair of a mitral cleft is usually the treatment of choice. Surgical repair is most often completed by suturing opposed edges of the cleft coupled with annuloplasty. When there is a lack of substance due to fibrous shrinkage of the valvular tissue, resection of the cleft edges together with partial tissue replacement using an autologous pericardial tissue can accomplish a stable valve reconstruction (5,10).
Percutaneous intervention with Mitraclip has also been used to successfully treat CMVL when the valvular anatomy appears favorable (11). Willemsen et. al. described the first use of MitraClip in a patient with severe MR and dilated cardiomyopathy who also had an isolated posterior CMVL (12). In this case, a MitraClip was placed posteromedial right along the cleft, which reduced the MR in the cleft. However, there remained a new MR jet in the more anterolateral side, so a second MitraClip was placed on the anterolateral side in symmetric fashion with a significant reduction in MR. Furthermore, MitraClip may be a safer option for high surgical risk patients or those with previously repaired atrioventricular septal defects who experience progressive MR later in life (11,13).
Another interesting feature of this case is the dynamic nature of severe MR, which was likely a major contributor to the refractory CS. Completely undiagnosed and not causing any symptoms prior to the AMI, the MR became severe in the setting of anterior wall stunning and increased afterload from high-dose vasopressors. This prompted an urgent evaluation of the mitral valve for potential surgical repair. The severity of MR dramatically decreased after several days of support, but then increased again as left ventricular remodeling progressed over following months. Only the durable LVAD eventually stabilized the patient and resulted in a marked reduction of the MR which typically occurs with mechanical left ventricular unloading, especially in HeartMate 3(14).
In retrospect, the patient in our case may have missed a window of opportunity for repair of his CMVL (with associated MR), prior to developing progressive LV dilation and end-stage heart failure. The severe, refractory CS experienced by our patient was disproportionate to the degree of LV systolic dysfunction immediately post LAD revascularization. This suggests poor cardiac reserve as a result of longstanding MR caused by the underlying, isolated posterior CMVL. Given the ultimate hemodynamic consequences of his CMVL and MR, one can argue that this patient’s long-term course may have been more favorably altered if this were corrected prior to discharge. Because of the massively dilated LA, evaluation with only transthoracic echocardiography might significantly underestimate the true functional severity of MR. In this case, full hemodynamic assessment in the cardiac catheterization laboratory prior to hospital discharge would provide better clinical data upon which to base therapeutic decision making, especially regarding invasive MV corrective therapies.