Histopathology of the Mitral Valve Residual Leaflet in Obstructive Hypertrophic Cardiomyopathy

Mitral regurgitation in patients with hypertrophic cardiomyopathy: a case series

Background

Mitral regurgitation (MR) is a frequent occurrence in hypertrophic cardiomyopathy (HCM), often explained by valvular or sub-valvular abnormalities as part of a broad HCM phenotype spectrum.

Case summary

In this case series, we present two HCM cases diagnosed with systolic anterior motion of the anterior mitral valve (MV) leaflet and left ventricular outflow tract (LVOT) obstruction. Both cases had abnormal sub-valvular abnormalities that led to deterioration of LVOT obstruction and MR. The series highlights the need for close collaboration within a multidisciplinary team, with a special emphasis on the need for a personalized treatment strategy when considering septal reduction therapy and/or MV surgery.

Discussion

Mitral regurgitation is linked to adverse cardiac outcomes, often contributing towards symptoms, poor functional capacity, hospitalization, and advanced therapies. Complex and interlinked biomechanical factors lead to MR, often co-existing with LVOT obstruction. Multimodality imaging with echocardiography (transthoracic and transoesophageal) and cardiac magnetic resonance imaging plays a key role in determining the aetiology of MR in HCM. This case series highlights the role of this comprehensive assessment, paving the way for a personalized treatment pathway for patients.

The molecular and cellular landscape of hypertrophic cardiomyopathy phenotypes: transition from obstructive to end-stage heart failure

Hypertrophic cardiomyopathy (HCM) is a myocardial disorder which commonly presents as an obstructive or end-stage disease. This study aims to investigate the transcriptomic changes related to cardiac cell-specific expression profiles that underpin the molecular transition between the HCM phenotypes. This study utilizes bioinformatics meta-analysis to integrate independent datasets to generate a comprehensive gene expression profile of obstructive HCM and end-stage HCM phenotypes compared to donor hearts. Gene set enrichment and cellular deconvolution were applied to identify ontologies and pathways related to each phenotype and to enumerate cell abundances. The intersection between cell lineage genes and meta-genes was identified to explore the cellular contribution to the phenotypic molecular signatures. Meta-analysis revealed, enhanced muscle function and myocardial remodeling, alongside impaired immune and inflammatory processes in obstructive HCM. In contrast, enriched tissue matrix remodeling pathways and altered metabolic and signaling cascades were identified in end-stage HCM, indicating a shift towards cellular dysfunction and loss of homeostasis. These molecular profiles were associated with an altered cellular landscape, with increased cardiomyocytes and lower immune cell populations in obstructive samples but increased fibroblasts and smooth muscle cells in end-stage HCM, implicating extensive tissue remodeling. This study provides novel insights into the cellular contributions of contractile, immune, homeostatic, and vascular alterations underpinning each of the HCM phenotypes. KEY MESSAGES: HCM phenotypes are characterized by distinct molecular and cellular profiles. Obstructive HCM has an enriched contractile profile underpinned by an expanded cardiomyocyte population. End-stage HCM shifts the cellular profile towards extracellular and vascular remodeling.

Mitral Leaflet Shortening as an Ancillary Procedure in Obstructive Hypertrophic Cardiomyopathy

BACKGROUND

Mitral leaflet elongation is common in hypertrophic cardiomyopathy (HCM), contributes to obstructive physiology, and presents a challenge to the dual surgical goals of abolition of outflow gradients and abolition of mitral regurgitation. Anterior leaflet shortening, performed as an ancillary surgical procedure during myectomy, is controversial.

METHODS

This was a retrospective study of all patients undergoing myectomy from January 2010 to March 2020, with analysis of survival and echocardiographic results. The study compared outcomes of patients treated with myectomy and concomitant mitral leaflet shortening with patients treated with myectomy alone. Over this time, the technique for mitral shortening evolved from anterior leaflet plication to residual leaflet excision (ReLex).

RESULTS

Myectomy was performed in 416 patients aged 57.5 ± 13.6 years, and 204 (49%) patients were female. Average follow-up was 5.4 ± 2.8 years. Survival follow-up was complete in 415 patients. Myectomy without valve replacement was performed in 332 patients, of whom 192 had mitral valve shortening (58%). Mitral leaflet plication was performed in 73 patients, ReLex in 151, and both procedures in 32. Hospital mortality for patients undergoing myectomy was 0.7%. At 8 years, cumulative survival was 95% for both the myectomy combined with leaflet shortening group and the myectomy alone group, with no difference in survival between the 2 groups. There was no difference in survival between the anterior leaflet plication and ReLex groups. Echocardiography 2.5 years after surgery showed a decrease in resting and provoked gradients, mitral regurgitation, and left atrial volume and no difference in key variables between patients who underwent ancillary leaflet shortening and patients who underwent myectomy alone.

CONCLUSIONS

These results affirm that mitral shortening may be an appropriate surgical judgment for selected patients.

Mitral Geometry on the Mechanism of Left Ventricular Outflow Tract Obstruction in Hypertrophic Cardiomyopathy

OBJECTIVE

The mechanism of left ventricular outflow tract obstruction (LVOTO) is complex in hypertrophic cardiomyopathy (HCM). We aimed to evaluate the impact of mitral valve geometry on LVOTO by echocardiography.

MATERIALS AND METHODS

The study population comprised 177 consecutive patients with HCM. Morphological findings of left ventricular hypertrophy and LVOTO-related abnormalities were assessed by comprehensive transthoracic echocardiography. Aortomitral angle, mitral leaflet length, and coaptation height were measured and analyzed at rest. Multivariable stepwise forward logistic regression analysis was performed to identify geometric predictors of LVOTO.

RESULTS

One hundred thirty-seven patients had an LVOT gradient ≥30 mm Hg. Multivariable logistic regression showed that aortomitral angle (odds ratio [OR], 0.89; 95% CI, 0.83-0.95, P < .001), coaptation height (OR, 1.96; 95% CI, 1.41-2.72, P < .001), and accessory mitral valve chordae tendineae (OR, 13.1; 95% CI, 4.32-39.95; P < .001) were independently associated with LVOTO. Receiver operating characteristic analysis showed that the area under the curve of mitral coaptation height was higher (area under the curve = 0.815) than the other 2 indicators (P < .05).

CONCLUSION

Mitral coaptation height, aortomitral angle, and accessory mitral valve chordae tendineae were important predictors of SAM and LVOTO in HCM independent of septal hypertrophy.

Retrofitting the Heart: Explaining the Enigmatic Septal Thickening in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is the most common genetic cardiac disease and is characterized by left ventricular hypertrophy. Although this hypertrophy often associates with sarcomeric gene mutations, nongenetic factors also contribute to the disease, leading to diastolic dysfunction. Notably, this dysfunction manifests before hypertrophy and is linked to hypercontractility, as well as nonuniform contraction and relaxation (myofibril asynchrony) of the myocardium. Although the distribution of hypertrophy in hypertrophic cardiomyopathy can vary both between and within individuals, in most cases, it is primarily confined to the interventricular septum. The reasons for septal thickening remain largely unknown. In this article, we propose that alterations in muscle fiber geometry, present from birth, dictate the septal shape. When combined with hypercontractility and exacerbated by left ventricular outflow tract obstruction, these factors predispose the septum to an isometric type of contraction during systole, consequently constraining its mobility. This contraction, or more accurately, this focal increase in biomechanical stress, prompts the septum to adapt and undergo remodeling. Drawing a parallel, this is reminiscent of how earthquake-resistant buildings are retrofitted with vibration dampers to absorb the majority of the shock motion and load. Similarly, the heart adapts by synthesizing viscoelastic elements such as microtubules, titin, desmin, collagen, and intercalated disc components. This pronounced remodeling in the cytoskeletal structure leads to noticeable septal hypertrophy. This structural adaptation acts as a protective measure against damage by attenuating myofibril shortening while reducing cavity tension according to Laplace Law. By examining these events, we provide a coherent explanation for the septum's predisposition toward hypertrophy.