Hypertrophic cardiomyopathy is a genetically transmitted cardiovascular disease, predominantly inherited in an autosomal dominant manner. Its prevalence, approximately 0.5%, makes it a relatively common condition in the general population.
The initial diagnosis is based on the presence of significant left ventricular hypertrophy not explained by other underlying cardiac or systemic diseases. However, additional associated abnormalities, such as mitral regurgitation (MR), should be systematically evaluated using echocardiography due to their implications for symptomatology and prognosis in these patients.
In patients with both left ventricular outflow tract obstruction (LVOTO) and MR, it is crucial to assess the pathophysiological mechanism, particularly in those being considered for invasive procedures aimed at reducing LVOTO. The indication for each surgical technique will differ based on the primary mechanism of the valvular disease.
This article presents a review of the evaluation and etiological characterization of mitral regurgitation in patients with hypertrophic obstructive cardiomyopathy (HOCM). Currently, septal myectomy is the invasive procedure of choice for patients with an obstructive outflow gradient or persistent symptoms despite optimal medical therapy. However, the available evidence regarding the optimal surgical approach for managing MR remains controversial.
Mitral regurgitation is a frequent finding in patients with HOCM. In a large proportion of cases, MR is secondary to the presence of systolic anterior motion (SAM) of the anterior mitral leaflet in relation to dynamic outflow tract obstruction. Nevertheless, other factors, such as mitral leaflet elongation, anterior displacement of the subvalvular mitral apparatus, or anomalies in the disposition of the papillary muscles, may also contribute to the presence of MR. In cases of SAM-mediated MR, significant improvement has been observed with the use of novel therapies such as the selective cardiac myosin inhibitor mavacamten, while septal myectomy remains the treatment of choice in cases refractory to medical therapy due to its effectiveness in reducing both the gradient and MR.
The objective of this review is to reassess the different surgical techniques available for managing MR in patients with HOCM and to define the necessary preoperative evaluation to determine the most appropriate technique for each case.
Preoperative evaluation
A detailed assessment of each patient’s anatomical abnormalities is essential, with transthoracic echocardiography (TTE) being the primary diagnostic tool. The anatomical determinants commonly involved in LVOTO include a hypertrophic interventricular septum, a narrow outflow tract, and abnormal mitral valve and subvalvular structures.
Various theories have been proposed to explain the hemodynamic mechanisms leading to SAM, but it is likely a multifactorial phenomenon. The presence and severity of SAM correlate with the degree of LVOTO and can be quantified based on the distance between the mitral leaflet and the septum, as well as the duration of their contact during systole.
Next, LVOTO should be assessed by estimating the peak gradient using Doppler techniques, considering it significant when ≥30 mmHg. SAM-mediated MR typically presents as a jet directed inferolaterally and worsens with an increase in dynamic obstruction. For this reason, stress echocardiography can be useful in its assessment. It is also important to consider the limitations of existing quantification methods, with regurgitant volume being the most accurate measurement.
Mitral leaflet length and papillary muscle characteristics should also be examined, as abnormalities in both structures play a role in MR. In 10–20% of patients with non-SAM-mediated MR, evaluating the underlying valvular mechanism is recommended to guide therapeutic management. Finally, atrial fibrillation is significantly more common in this population and exacerbates MR.
Surgical management of mitral regurgitation in hypertrophic obstructive cardiomyopathy
Due to its effectiveness and low complication rate, septal myectomy is the surgical procedure of choice for symptomatic HOCM patients with a persistent gradient ≥50 mmHg despite medical treatment. Alcohol septal ablation is considered an alternative for patients with prohibitive surgical risk.
The Mayo Clinic group has reported a reduction of more than 50% (p<.0001) in the proportion of patients with MR grade ≥3+ following an extended myectomy beyond the septal contact point of the mitral valve.
On the other hand, Wang et al. describe the development of a novel transapical approach guided by transesophageal echocardiography that does not require cardiopulmonary bypass. In their series of 47 patients with different obstruction mechanisms, the percentage of patients with MR grade ≥3+ and the left ventricular outflow tract gradient was significantly reduced (p<.0001).
Other groups, such as Balaram et al., have described additional techniques, including leaflet plication, as in the “resection-fold-release” technique, aimed at patients with septal hypertrophy, redundant mitral valve tissue, and hypertrophic papillary muscles. This approach has also demonstrated a significant reduction in both the gradient (by 50%) and MR (p<.01).
Additionally, different mitral valve repair techniques have been proposed, such as “AMLE” (anterior mitral leaflet extension) by Kofflard et al. This technique, which involves suturing a pericardial patch to the anterior mitral leaflet, has been shown to significantly reduce LVOTO, MR, and SAM (p<.001). Other surgical options, such as anterior mitral leaflet retention plasty, limit leaflet mobility toward the septum and have been described in pediatric patients. However, these procedures often lead to mitral stenosis.
Various techniques, including realignment, resection, or reorientation of the papillary muscles, can also be useful in reducing LVOTO.
Combined approach to LVOTO and the mitral valve
A recent European study compared isolated septal myectomy with myectomy combined with mitral valve repair or replacement. The intervention on the mitral valve was associated with higher mortality and an increased incidence of atrioventricular block requiring pacemaker implantation.
Other studies have compared the 10-year survival rates of mitral repair versus replacement, showing a significantly higher survival rate in the repair group (p = .002). For this reason, combined mitral valve intervention should be avoided whenever possible, maintaining the primary objective of reducing LVOTO and preventing SAM.
Additionally, there is ongoing debate regarding the benefit of isolated septal myectomy in patients with a septal thickness <18 mm. Lapenna et al. analyzed the outcomes of 76 patients with HOCM and septal thickness <18 mm. Patients undergoing mitral valve replacement in combination with septal myectomy had thinner septa and more severe MR than those who underwent isolated myectomy (p = .02). At discharge, patients who received combined myectomy and valve replacement had lower residual MR and SAM (p < .001). This significant difference also extended to the cumulative incidence of MR recurrence over nine years (p = .005).
Regarding edge-to-edge repair techniques, Sorajja et al. described a sustained reduction in LVOTO and MR at more than 15 months in their cohort. However, experience with this approach remains limited, and it should be reserved for patients with favorable anatomy and high surgical risk.
COMMENTARY:
The first key takeaway from this review is the importance of characterizing the mechanism of MR in patients with HOCM. Not all cases of MR are SAM-mediated, meaning that not all patients will benefit from the same therapeutic strategy.
Currently, pharmacological treatments can significantly reduce the dynamic obstructive gradient and MR. Patients whose MR is primarily mediated by SAM are likely to benefit the most from these therapies. This underscores the importance of identifying patients with intrinsic mitral valve abnormalities.
First, this subgroup of patients may be the ones who benefit most from a combined approach involving both septal reduction and mitral valve repair or replacement. Second, identifying these patients can help avoid performing invasive procedures aimed solely at reducing LVOTO, which may not be effective in improving symptoms in cases where intrinsic valve disease is present.
A precise echocardiographic assessment will facilitate surgical decision-making, allowing for the consideration of additional interventions such as mitral leaflet plication or papillary muscle reorientation along with septal myectomy. This decision should be carefully evaluated, as interventions on the mitral valve are associated with higher morbidity and mortality compared to isolated septal myectomy—especially mitral valve replacement, which increases the risk of bleeding and thromboembolism. For this reason, mitral valve replacement should be reserved for cases where the valve is non-repairable and significant MR persists despite complete resolution of obstruction and SAM.
Another relevant concept is the development of new surgical approaches that allow for septal intervention without requiring sternotomy or cardiopulmonary bypass, thereby reducing potential complications. The use of transesophageal echocardiography during surgery is particularly valuable for guiding the procedure and confirming gradient resolution at the end of the intervention.
Additionally, the successful use of edge-to-edge repair devices in patients with favorable anatomy and high surgical risk broadens the therapeutic options, especially for patients who are not candidates for surgery.
In conclusion, MR is frequently observed in patients with HOCM. However, a thorough echocardiographic evaluation of each patient’s structural abnormalities is essential to determine the most appropriate therapeutic strategy.
Reducing the gradient via septal myectomy should be a primary goal, particularly in patients with SAM-mediated MR, but it is not the definitive solution for all cases involving intrinsic mitral valve abnormalities. The introduction of combined procedures may improve patient outcomes, and when necessary, mitral valve repair should be prioritized over replacement due to its lower morbidity and mortality.
The development of surgical techniques that do not require cardiopulmonary bypass, along with the implementation of edge-to-edge repair devices, expands the range of therapeutic possibilities for this patient population.
REFERENCE:
Wang H, Zhu Y, Quintana E, Ibáñez C, Deng Y, Wei X, et al. Systolic anterior motion-mediated mitral regurgitation and surgical management in hypertrophic obstructive cardiomyopathy. Eur J Cardiothorac Surg [Internet]. 2024;66(5). doi:10.1093/ejcts/ezae376.
