**3. Morphological variants of hypertrophic cardiomyopathy**

HCM is characterized by varying degree of septal hypertrophy and this led to the emergence of several morphological variants of HCM. These variants include basal septal hypertrophy, apical, midventricular or combination of any [5]. A key feature in the basal variant is the presence of SAM of the anterior mitral valve leaflet, while a key feature in the apical variant is the presence of small left ventricular cavity and absence of SAM.

Recognition of these variants is critical especially when considering patients for septal reduction therapy to ensure delivering the right modality and decrease the chance of persistence or recurrence of the LVOT obstruction.

#### **4. Current indications for septal myectomy**

Surgical septal myectomy should be considered for those symptomatic patients who failed medical treatment or for those who are intolerant to medical therapy. Morphological variants may play a role in proceeding with surgery as well. Variants like apical and midventricular level of obstruction are difficult to manage medically and do not respond to Alcohol septal ablation.

#### **5. Surgical approaches for septal myectomy**

Understanding the different morphological variants of HCM is critical in selecting the right surgical approach for the patient. This ensures elimination of the LVOT obstruction and minimizes if not prevents any residual/recurrent significant gradient/obstruction.

The procedure is done through a standard median sternotomy with central aortic and single venous (right atrial) cannulation. Although septal myectomy has been reported via a minimally invasive approaches such as endoscopic [6] and robotic [7], we do believe median sternotomy should be considered the gold standard for these cases as it provides adequate exposure to the heart and mediastinal structures and facilitates performing all maneuvers that are needed to facilitate exposure to the interventricular septum and performance of an adequate septal myectomy.

Prior to venous cannulation, we measure the gradient across the LVOT directly by placing a needle in the distal ascending aorta and another one in the left ventricular cavity (via the right ventricle free wall) simultaneously (**Figure 1A** and **B**).

#### **Figure 1.**

 *Intraoperative photos showing the technique of direct pressure measurement of the left ventricular outflow tract gradient prior to initiation of cardiopulmonary bypass. In (A), a needle is placed in the distal ascending aorta, and in (B) the second needle is placed into the left ventricular cavity indirectly via the free wall of the right ventricle (RV) and the interventricular septum. PA: Pulmonary artery; RV: Right ventricle.* 

This measures the resting LVOT gradient ( **Figure 2** ) and then provocative maneuvers are performed. These maneuvers are important to evaluate the LVOT gradient as it occurs with exercise. A variant of HCM is known as "Latent obstruction" will be discussed later but patients with this variant do not have any significant gradient at rest but they do with exercise. These provocative maneuvers can be either an induction of a premature ventricular contraction (Brockenbrough-Braunwald-Morrow) ( **Figure 3** ) or administration of isoproterenol.

 This will be repeated after coming off cardiopulmonary bypass to document elimination of any significant gradient across the LVOT. Based on the variant of septal hypertrophy and the level of obstruction, the technique of myectomy may differ or be a combination of the following:

#### **5.1 Trans-aortic myectomy**

 This is the most common approach and is used for the most common variant which is basal or subaortic obstruction. The technical details have been described

#### **Figure 2.**

 *Intraoperative pressure tracing showing the resting left ventricular outflow tract gradient by direct needle pressures. The left ventricular pressure is in white, while the aortic pressure is in light blue colors. LVOT: Left ventricular outflow tract.* 

#### **Figure 3.**

 *Intraoperative pressure tracing from the same patient showing positive Brockenbrough-Braunwald-Morrow maneuver by induction of premature ventricular contraction. The left ventricular pressure (white color) increased, while the aortic pressure (light blue) decreased, resulting in significant left ventricular outflow tract gradient.* 

before [ 8 ]. Once the heart is arrested with antegrade cardioplegia, a hockey-stick aortotomy is performed down to the base of the non-coronary sinus of Valsalva. The aortotomy in these cases has to be a bit lower than standard aortotomy for aortic valve replacement to provide adequate exposure to the LVOT.

 Stay sutures are then applied and the LVOT is assessed. This is a 360-degree visual assessment of the LVOT and the mitral apparatus prior to performing any resection ( **Figure 4** ). The result of this assessment determines the degree of septal bulge, how far down in the left ventricular cavity the resection has to extend, the abnormalities that may coexist in the mitral subvalvular apparatus such as anomalous chordae ( **Figure 5** ) and/or papillary muscles. These all can lead to persistent or recurrent LVOT gradient. A variety of instruments – seen in **Figure 6** - are needed to perform the myectomy.

 The resection then starts below the nadir of the right coronary cusp ( **Figure 7** ) and extends in an anti-clockwise direction towards the commissure between the left and non-coronary cusps. Scissors are then used to complete the resection. This is the initial resection which serves to widen the subaortic area and facilitates further access to the left ventricular cavity. Further resection has to be performed along the interventricular septum and towards the left ventricular apex to ensure complete elimination of any residual gradient. Some maneuvers can help with exposing that part of the septum such as placing a sponge stick on the free wall of the right ventricle that helps bringing the interventricular septum in view ( **Figure 8** ). The area of resection is further widened as we go deeper into the ventricular cavity which what makes this "extended" in comparison to the initial "Morrow" operation.

 A proper septal myectomy is a 3-dimensional operation in regards to the extent of resection [ 9 ], and all other potential causes of recurrent/residual LVOT obstruction have to be addressed such as resection of anomalous papillary muscles and/or chordae ( **Figure 9** ). The aortotomy is then closed in two-layers and the heart is de-aired and the aortic cross clamp is removed.

*Hypertrophic Cardiomyopathy: Surgical Perspectives DOI: http://dx.doi.org/10.5772/intechopen.109568*

#### **Figure 4.**

 *The anatomic landmarks of the left ventricular outflow tract after performing the aortotomy and prior to the myectomy. The area of the interventricular septum (IVS) is visualized, as well as the membranous septum (\*) where resection should be avoided. The mitral valve (MV) is visualized deep in the left ventricle. RCA: Right coronary artery ostium; RCC: Right coronary cusp; LCA: Left coronary artery ostium; LCC: Left coronary cusp; NCC: Non-coronary cusp; MV: Mitral valve; IVS: Interventricular septum.* 

#### **Figure 5.**

 *An intraoperative view through the aortotomy showing an anomalous mitral valve chord in the left ventricular outflow tract. These chordae can result in persistent or recurrence of gradient after an initial myectomy as it limits the mobility of the anterior mitral valve leaflet and can result in persistence of systolic anterior motion (SAM).* 

#### **5.2 Trans-apical myectomy**

 Trans-apical approach can be done for one of three main indications: (1) midventricular variant, where the transaortic approach may not be adequate, (2) apical

#### **Figure 6.**

 *The variety of surgical instruments that are useful during the myectomy procedure. Different types of surgical blades, aortic cusp retractors, pituitary Rongeurs to help with removal of the muscle pieces.* 

#### **Figure 7.**

 *The resection starts below the nadir of the right coronary cusp (RCC) and goes into anti-clockwise direction towards the anterior mitral valve leaflet and chordal structures (\*). RCC: Right coronary cusp; LCC: Left coronary cusp; NCC: Non-coronary cusp.* 

#### **Figure 8.**

 *One of the helpful maneuvers to facilitate exposure of the lower part of the interventricular septum is using a sponge stick (\*) to depress the free wall of the right ventricular and rotate the septum, thus bringing it in view to the surgeon.* 

#### **Figure 9.**

 *The completed myectomy specimen with two anomalous chordae. Notice the contact lesion (white scar) on the resected specimen. This occurs as a result of the anterior mitral vale leaflet hitting the septum during systole (systolic anterior motion).* 

variant, and (3) in those patients who do not have adequate left ventricular cavity and non-obstructive variant of HCM where left ventricular enlargement can be performed to improve their left ventricular end-diastolic volume.

 We have described the technique previously [ 10 ], but briefly, after the cardioplegic arrest, the left ventricular apex is delivered into the field and the left anterior descending (LAD) coronary artery is identified. An apical incision is done 1 cm to the left and parallel of the LAD ( **Figure 10** ). In the apical variant, the left ventricular apex is quite obliterated with muscles and it is critical to stay on the interventricular septum side ( **Figure 11** ) to avoid risk of injury of the mitral valve papillary muscles

#### **Figure 10.**

 *An apical incision is made in the left ventricular apex which facilitates myectomy in patients with midventricular and apical hypertrophic cardiomyopathy.* 

#### **Figure 11.**

 *A view through the opened left ventricular apex showing the resected muscle specimen-in progress- and the interventricular septum (IVS). It is important for the surgeon to stay on the IVS side during resection till he/she able to visualize the papillary muscles of the mitral valve to avoid inadvertent injury to the mitral subvalvular structures. IVS: Interventricular septum.* 

#### **Figure 12.**

 *After the resection, the left ventricular cavity now is widened and the mitral valve subvalvular structures can be easily visualized.* 

which are usually apical displaced and hypertrophied in these cases ( **Figure 12** ). Once the left ventricular cavity is entered, further resection is performed and the cavity is further widened. The apex is then closed in two layers and suture line is supported with Teflon felt.

#### **5.3 Trans-mitral myectomy**

 This is a left atrial approach to the interventricular septum through the mitral valve. It has been used by some authors as an alternative to the transaortic approach but it requires detachment of the anterior leaflet of the mitral valve followed most likely by patch augmentation after completing the resection [ 11 ]. One has to be familiar with this approach as the anatomy of the interventricular septum differs through this approach compared to the trans-aortic exposure.

 We believe this may be more of value in children and those with small aortic root where the trans-aortic approach may not be adequate. Another potential advantage is that it helps addressing the mitral valve pathology and performing the myectomy through one incision.

#### **6. Adjuncts to septal myectomy**

#### **6.1 Abnormalities of the mitral subvalvular apparatus**

#### *6.1.1 Papillary muscle abnormalities*

 Detection of papillary muscle abnormalities on preoperative echocardiogram can be challenging, therefore, it is important for the surgeon to evaluate the mitral subvalvular apparatus as part of the overall thorough evaluation of the LVOT. Anomalous papillary muscle can be a cause of persistent/recurrent gradient after an initial-what it seems like- a complete myectomy [12].

It is critical to differentiate these anomalous muscles from the true papillary muscles of the mitral valve. A key difference is the insertion of the anomalous papillary muscle into the body of the leaflet, rather than the free edge and therefore, it can be excised safely.

#### *6.1.2 Anomalous chordae*

These anomalous chordae are attached to the body of the anterior mitral valve leaflets and not to the free edge which helps differentiating these chordae from primary chordal structures of the mitral valve. These can limit the mobility of the anterior mitral leaflet and result in SAM as well.

Some anomalous chordae can cause adherence of the papillary muscles to the septum and cutting this helps mobilizing these papillary muscles and minimize the gradient and the chance of SAM after septal myectomy. In general, there should be no chordal attachment between the mitral valve apparatus and the interventricular septum.

#### **6.2 Management of concomitant atrial fibrillation**

Due to the elevated left ventricular end-diastolic pressure and subsequently left atrial pressure secondary to the significant LVOTO, it is not uncommon for patients with HCM to present with atrial fibrillation (AFib). Losing the atrial kick in those with HCM and diastolic dysfunction results in significant drop in their cardiac output and symptoms, therefore, it is important to maintain normal sinus rhythm in these patients [13].

Our strategy is to offer biatrial Cox-maze IV procedure using a combination of radiofrequency and cryoablation for those with chronic persistent AFib, while in those with paroxysmal AFib, bilateral pulmonary vein isolation is sufficient. Routine excision or exclusion of the left atrial appendage is part of either procedures.

#### **6.3 Mitral valve surgery**

Historically, mitral valve replacement was one of the proposed solutions to LVOTO in patients with HCM, however this is not currently the case. With adequate extended left ventricular septal myectomy, all SAM is eliminated and the mitral regurgitationeven if severe- is significantly improved if not completely eliminated.

Our approach is to perform mitral valve surgery in the settings of septal myectomy only in the presence of intrinsic mitral valve pathology and mitral regurgitation that is not the result of SAM and the dynamic nature of the LVOTO in HCM. Repair is preferred over replacement in all cases due to the long-term survival benefit of mitral repair that is documented across multiple studies in the literature. Mitral valve repair techniques may also need to be modified in these cases to avoid recreating SAM after the repair such as if a ring to be used, a one size larger may be preferred.

In some cases, when there is a question about the need for mitral valve repair or if the mechanism of regurgitation is unclear, we will perform a complete myectomy, and then come off cardiopulmonary bypass and re-evaluate the mitral valve and make the decision if interventions on the mitral valve is necessary at this stage.

If mitral valve replacement is necessary, then it is important to choose a mechanical or a low profile bioprosthesis that does not project into the LVOT and results in LVOT gradient.
