After a perfect myectomy for obstructive hypertrophic cardiomyopathy, which patients should need more? That is the question

Mitral abnormalities are often associated with hypertrophic obstructive cardiomyopathy (HCM), and, in large published cohorts, combined strategies involving mitral valve intervention are performed in up to a third of all HCM surgical cases [1]. A broad array of combined strategies have been proposed [2, 3].

In this issue of the Journal, Ram et al. proposes to assess the benefits of the Secondary Chordal Resection strategy in addition to the conventional Septal Myectomy performed in 65 patients in comparison to a cohort of 105 patients with isolated conventional Septal Myectomy. This technique was first described in 2015 by Ferrazzi et al. [4] in a cohort of 23 patients operated on at the Sheba Medical Center (Tel Aviv—Israel). The combined technique is really appealing, fast and easily accessible through the same aortotomy. Ram et al. confirms the short operative time, low postoperative morbidity, and mortality. Compared with myotomy alone, the combined technique is associated with lower left ventricular outflow track (LVOT) gradients and wider aorto-mitral angle. In addition, mid-term outcomes are comparable for both strategies, with lower gradient and fewer mitral regurgitation (MR) grades throughout a mean 32-month echocardiographic follow-up with the combined technique.

The treatment of both cohort populations did not occur synchronously: 40% of patients who were treated with the combined technique being treated after 2019. This difference in timing introduces 2 biases: first, in terms of surgeon’s learning curve with probably a growing confidence and expertise of the surgeon with the combined technique leading to its wider use over time and, second, in terms of the interpretation of the numbers, the echocardiographic follow-up in the combined group is limited. When comparing freedom from ≥3+ MR grade, only 1 patient reached the 5 years echocardiographic follow-up in the chordal resection group versus 62 in the control group. This finding should be kept in mind when considering the long-term consequences of the secondary chordal cutting on the mitral function.

Despite the apparent similarity of both populations and the described ‘eyeballing choice’ strategy, 2 obvious patient profiles arise from Table 4 who were more likely to be treated with the combined strategy: patients who benefit from the combined strategy had a thinner preoperative septum and a narrower aorto-mitral angle, both responsible for a high-degree of LVOT obstruction. On the other hand, patients who finally were treated with an isolated myectomy had lower LVOT obstruction degrees despite a septum almost 20% thicker. Thus, in the absence of comparable preoperative patient profiles, the results presented can only serve as exploratory conclusions and as the basis for further more robust prospective comparative studies.

The question of the long-term consequences of the secondary chordae cutting on the mitral valve structure and function remains to be explored with a longer follow-up period. The role of secondary chordae (i.e. strut chordae) in maintaining the left ventricular architecture has been largely described previously [5]. The secondary chordal resection technique previously was utilized for the surgical treatment of secondary MR [6], and it is also used in conjunction with ‘modern’ posterior quadrangular resection for the surgical treatment of primary MR to avoid asymmetrical traction of the leaflet base after a sliding plasty [7]. These techniques have shown good short- and mid-term outcomes but the long-term consequences of the secondary chordae resection still should be investigated.

Interestingly, the edge-to-edge strategy and the secondary cord cutting technique, both in conjunction with a myectomy, were compared in a small randomized study of the Novosibirsk centre [8]. The authors reported good outcomes in terms of  Systolic Anterior Motion SAM-induced MR and LVOT obstructions with no evidence of statistical differences between both strategies. Thus, for surgeons with less expertise with HCM, secondary chordae resection is probably easier to perform.

The secondary chordal resection is a promising additional technique, in particular for a subset of HCM patients with mild septum thickness and a predominating ‘mitral component’ (narrower aorto-mitral angle, thick secondary chordae). The long-term consequences of this technique, which could render the mitral apparatus more fragile over time, must be investigated with a long-term follow-up before being largely adopted. The use of these strategies should not, however, lead to surgeons losing sight of the central role of the septal myectomy that remains the gold standard and main component of the surgical treatment of HCM. This study finally advocates for a scrupulous and dedicated preoperative echocardiographic assessment, including a precise aorto-mitral curtain and LVOT characterization, and a careful analysis of the mitral valve (leaflets length) and its subvalvular apparatus.

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