Hypertrophic obstructive cardiomyopathy (HOCM) predisposes to left ventricular outflow tract obstruction (LVOTO), which can significantly reduce quality of life and is associated with sudden cardiac death. It is important to note that the LVOTO in HOCM patients is not solely caused by the hypertrophied interventricular septum (IVS), but rather is multifactorial. Therefore, a thorough understanding of LVOT anatomy and left ventricular (LV) geometry is crucial in addressing all these factors (1, 2).
IVS hypertrophy decreases the diameter of the LVOT, which not only increases the pressure gradient, but causes higher blood flow velocity and turbulence across the LVOT. As a result, the turbulent high-velocity jet pulls the anterior mitral valve leaflet (AMVL), which is one of the boundaries of the outflow tract, toward the muscular IVS during systole. This phenomenon is known as systolic anterior motion of the mitral valve (SAM). SAM contributes to the dynamic obstruction and hinders the coaptation of the mitral valve (MV) leading to functional mitral regurgitation (MR). Addressing the primary pathology often improves MR (1, 2).
In addition, the fibrotic proliferation of the fibrous trigones affects the systolic excursion of the AMVL away from the IVS increasing the incidence of SAM (3). Furthermore, it is not uncommon to find accessory MV chords attaching the papillary muscles to the IVS or even fusion of the papillary muscles to the IVS. Both contribute to the dynamic obstruction of blood flow.
Therefore, it is crucial to have a comprehensive surgical strategy that addresses all factors contributing to LVOTO to achieve adequate relief of obstruction. This video presents the surgical technique of the extended septal myectomy operation, as well as the mobilization of the fibrous trigones and resection of accessory MV chords.
Preoperatively, the surgeons measured the IVS using TEE and MRI. A cardiac CT was preformed to exclude the presence of coronary myocardial bridges. If a coronary myocardial bridge is present, a coronary angiography with fractional flow reserve (FFR) is performed to assess the significance of coronary compression and the need for coronary unroofing (1).
The surgical approach is undertaken via a full median sternotomy. Cardiopulmonary bypass is initiated with mild hypothermia, and LV venting is performed. Cardioplegia is then administered through the aortic root.
The aorta is incised obliquely and retracted to provide better visualization. After identifying the subvalvular components, the trigones are mobilized bluntly from the AMVL (3). Next, the septal myectomy is started 0.5 cm below the nadir of the right coronary cusp and extended toward both trigones. The level of resection is displaced slightly apically below the membranous septum to avoid the conduction pathway. Apical extension of the resection is carried out until reaching the base of the papillary muscles. Accessory chords between the papillary muscles and IVS are divided.
The goal is to resect the hypertrophied segment in one piece to avoid fragmenting the IVS. However, if exposure is difficult, the specimen can be divided into two longitudinal halves. Finally, irrigation of the LV is performed followed by deairing and closure of the aortotomy.
References
- Yacoub MH, Afifi A, Saad H, Aguib H, Elguindy A. Current state of the art and future of myectomy. 2017;6(7):307-317. doi:10.21037/acs.2017.06.04
- Affronti A, Pruna-guillen R, Quintana E, et al. Surgery for Hypertrophic Obstructive Cardiomyopathy : Comprehensive LVOT Management beyond Septal Myectomy. Published online 2021.
- Yacoub M, Onuzo O, Riedel B, Radley-Smith R, Hanley FL. Mobilization of the left and right fibrous trigones for relief of severe left ventricular outflow obstruction. J Thorac Cardiovasc Surg. 1999;117(1):126-133. doi:10.1016/S0022-5223(99)70477-0
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