The left ventricular outflow in hypertrophic cardiomyopathy: from structure to function

Anatomy of the Ventricular Outflow Tracts: An Electrophysiology Perspective

Outflow tract ventricular arrhythmias are the most common type of idiopathic ventricular arrhythmia. A systematic understanding of the outflow tract anatomy improves procedural efficacy and enables electrophysiologists to anticipate and prevent complications. This review emphasizes the three-dimensional spatial relationships between the ventricular outflow tracts using seven anatomical principles. In turn, each principle is elaborated on from a clinical perspective relevant for the practicing electrophysiologist. The developmental anatomy of the outflow tracts is also discussed and reinforced with a clinical case.

Does a standard myectomy exist for obstructive hypertrophic cardiomyopathy? From the Morrow variations to precision surgery

OBJECTIVES

The purpose of this work is to revisit the history of surgical treatment for obstructive hypertrophic cardiomyopathy (oHCM) over the last 60 years, in the light of advancing knowledge of the pathophysiology of obstruction.

METHODS

In this narrative review the contribution of the different surgical approaches to the field will be assessed in our personal experience in Florence.

RESULTS

Septal myectomy is the treatment of choice in patients with obstructive hypertrophic cardiomyopathy who remain symptomatic despite optimal medical treatment. Over the decades, numerous "theme variations" of the Morrow operation have been proposed, each of them targeting a specific pathophysiological determinant of left ventricular outflow tract obstruction.

CONCLUSIONS

Precision surgery in oHCM patients today depends on the ability of the surgeon to combine and master these variations, with the bird's eye view allowed by climbing on the shoulders of giants.

Emerging Medical Treatment for Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common myocardial disease characterized by otherwise unexplained left ventricular hypertrophy. The main cause of disabling symptoms in patients with HCM is left ventricular outflow tract (LVOT) obstruction. This phenomenon is multifactorial, determined both by anatomical and functional abnormalities: myocardial hypercontractility is believed to represent one of its major determinants. The anatomical anomalies are targeted by surgical interventions, whereas attenuating hypercontractility is the objective of old and new drugs including the novel class of allosteric myosin inhibitors. This review summarizes the current treatment modalities and discusses the emerging therapeutical opportunities focusing on the recently developed cardiac myosin ATPase inhibitors Mavacamten and CK-274. Novel surgical and interventional approaches are also discussed.

Surgical myectomy: Rationale and personalized technique

Septal myectomy is currently the gold standard treatment for symptomatic patients with hypertrophic cardiomyopathy. The procedure needs to be tailored and performed in a personalized fashion, taking into consideration the anatomical spectrum of this disease. The procedure needs to address the various components that contribute to the clinical and pathological picture of this disease including, the fibrous trigones, accessory tissues, papillary muscles, mitral valve and myocardial bridges. The operation can be performed with very low mortality and morbidity in high-volume experienced centers with predictable excellent short and long-term outcomes. There is a need for broadening the experience of this procedure to the rest of the world and for future development of new enhanced precision imaging and surgical tools.

Current state of the art and future of myectomy

Surgical relief of left ventricular outflow tract obstruction (LVOTO) in hypertrophic cardiomyopathy (HCM) requires more than septal myectomy. The procedure is currently the gold standard for all symptomatic HCM patients except those with comorbidities. The operation requires an individualized approach to restore the sophisticated functions of the left ventricular outflow tract (LVOT) without injury to the surrounding vital structures. The procedure should be tailored to deal with all the varied components of the obstruction including fibrous trigones, accessory tissues, and papillary muscle fusion. Preoperative multimodality imaging and numerical modeling combined with intraoperative transesophageal echocardiography (TEE) are essential to define existing anomalies as well as assess the adequacy of the repair. The mitral valve can be conserved in virtually all patients. The operation can be conducted with very low mortality and morbidity with predictable good outcomes both in the short and long term. Nevertheless, surgical relief of LVOTO is still grossly underused.

Wave Intensity Analysis Can Identify Eccentric Cardiac Hypertrophy in Hypertensive Patients With Varied Left Ventricular Configurations

OBJECTIVES

The primary aim of this study was to determine whether wave intensity can discriminate cases of eccentric hypertrophy in patients with essential hypertension who have varied left ventricular configurations.

METHODS

A total of 155 hypertensive patients with different ventricular configurations (27 normal configuration, 42 concentric remodeling, 62 concentric hypertrophy, and 24 eccentric hypertrophy) were recruited. We performed a noninvasive wave intensity analysis of the common carotid artery and conventional echocardiography. Blood pressure and flow velocity were measured in the right carotid artery of all patients.

RESULTS

The left ventricular ejection fraction (LVEF) in the eccentric hypertrophy group was significantly lower than the values in the other groups (P < .05). The R-W1 interval/W1-W2 interval ratio (where W1 indicates the first positive peak and W2 the second positive peak) in the eccentric hypertrophy group was much higher than the values in the other groups (P < .05). However, there were no significant differences in W1, W2, and negative area among these groups. Pearson correlation analysis showed that R-W1/W1-W2, R-W1, and W1-W2were correlated with the LVEF, whereas there was no correlation between W1, W2, negative area, and the reflection coefficient with the LVEF.

CONCLUSIONS

We propose that by using the R-W1/W1-W2 ratio, wave intensity analysis can identify hypertensive patients with eccentric hypertrophy without the need for echocardiography.

Pattern and degree of left ventricular remodeling following a tailored surgical approach for hypertrophic obstructive cardiomyopathy

Background The role of a tailored surgical approach for hypertrophic cardiomyopathy (HCM) on regional ventricular remodelling remains unknown. The aims of this study were to evaluate the pattern, extent and functional impact of regional ventricular remodelling after a tailored surgical approach. Methods From 2005 to 2008, 44 patients with obstructive HCM underwent tailored surgical intervention. Of those, 14 were ineligible for cardiac magnetic resonance (CMR) studies. From the remainder, 14 unselected patients (42±12 years) underwent pre- and post-operative CMR studies at a median 12 months post-operatively (range 4–37 months). Regional changes in left ventricular (LV) thickness as well as global LV function following surgery were assessed using CMR Tools (London, UK). Results Pre-operative mean echocardiographic septal thickness was 21±4 mm and mean LV outflow gradient was 69±32 mmHg. Following surgery, there was a significant degree of regional regression of LV thickness in all segments of the LV, ranging from 16% in the antero-lateral midventricular segment to 41% in the anterior basal segment. Wall thickening was significantly increased in basal segments but showed no significant change in the midventricular or apical segments. Globally, mean indexed LV mass decreased significantly after surgery (120±29g/m2 versus 154±36g/m2; p<0.001). There was a trend for increased indexed LV end-diastolic volume (70±13 mL versus 65±11 mL; p=0.16) with a normalization of LV ejection fraction (68±7% versus 75±9%; p<0.01). Conclusion Following a tailored surgical relief of outflow obstruction for HCM, there is a marked regional reverse LV remodelling. These changes could have a significant impact on overall ventricular dynamics and function.

Effects of myocardial fibrosis assessed by MRI on dynamic left ventricular outflow tract obstruction in patients with hypertrophic cardiomyopathy: a retrospective database analysis

BACKGROUND

While implications of myocardial fibrosis on left ventricular (LV) function at rest have been studied in hypertrophic cardiomyopathy (HCM), the pathophysiological consequences on dynamic LV outflow tract (LVOT) gradient have so far not been investigated in detail.

OBJECTIVE

To evaluate the influence of myocardial fibrosis, detected by MRI as late-gadolinium enhancement (LGE), on LVOT gradient in HCM.

DESIGN

Retrospective database analysis.

SETTING

A single Italian cardiomyopathies referral centre.

PATIENTS

Seventy-six HCM patients with normal ejection fraction at rest.

INTERVENTIONS

Patients underwent cardiac MR and performed bicycle exercise echocardiogram within a month.

RESULTS

LGE was present in 54 patients (71%), ranging from 0.2% to 32.4% of LV mass. There was a weak correlation between the amount of fibrosis and LVOT gradient variation during exercise in the overall population (r=-0.243, p=0.034) and a stronger correlation in patients with obstructive HCM at rest (r=-0.524, p=0.021). Patients with an LVOT gradient increase ≥50 mm Hg during exercise had a significantly lesser extent of fibrosis than those with an increase <50 mm Hg (0.7% (IQR 0-2.4) vs 3.2% (IQR 0.2-7.4), p=0.006). The extent of fibrosis was significantly lower among the highest quartiles of LVOT gradient increase (p=0.009).

CONCLUSIONS

In patients with HCM and normal ejection fraction at rest, myocardial fibrosis was associated with a lower increase in LVOT gradient during exercise, probably due to a lesser degree of myocardial contractility recruitment. This negative association was more evident in patients with an obstructive form at rest.