HYPERTROPHIC CARDIOMYOPATHY. LITERATURE REvIEW

Hypertrophic cardiomyopathy is a common hereditary heart disease with a heterogeneous clinical picture and a natural history. Recent advances in diagnosis and treatment methods have played an important role in reducing the incidence of adverse clinical events; however, the complete elimination of sudden cardiac death is still an unattainable achievement. Despite the heterogeneous clinical profile and complex pathophysiology, effective treatment strategies are available, including implantable defibrillators to prevent sudden death, medical and surgical myectomy (or, alternatively, alcohol ablation of the septum) to alleviate outflow obstruction and symptoms of heart failure, as well as pharmacological strategies (and possibly radiofrequency ablation) to control atrial fibrillation and prevent embolic stroke. Now, after more than 50 years, hypertrophic cardiomyopathy has been transformed from a rare and largely untreatable disorder to a common genetic disease with management strategies that permit realistic aspirations for restored quality of life and advanced longevity. This article discusses some aspects of this condition: epidemiology, clinic, diagnosis and surgery technique. Objective. Evaluate the effectiveness of surgical treatment of patients with hypertrophic cardiomyopathy. Material and methods. This literature review was carried out in accordance with the PRISM statement. The databases searched in this review included Pubmed, Web of Science, Scopus, and Cochrane for systematic reviews. Conclusion. The diagnosis of HCMP is based mainly on echocardiographic variables including the dynamic parameters of LV, LVOT the distribution of increased muscle thickness, the mechanism and severity of MR as well as the degree of diastolic dysfunction.


Relevance
Hypertrophic cardiomyopathy is a common hereditary cardiovascular disease occurring in one out of 500 people in the whole population [1][2][3]. It is caused by more than 1400 mutations in 11 or more genes [4][5][6][7][8] encoding cardiac sarcomere proteins. Although hypertrophic cardiomyopathy is the most common cause of sudden death in young people (including trained athletes) [9,10] and can lead to functional disability as a result of heart failure and stroke, most affected people probably remain undiagnosed, and many do not have a significant reduction in life expectancy or significant symptoms. The diagnosis is most often made by echocardiographic assessment of left ventricular hypertrophy, gradients of the left ventricular outlet tract, systolic and diastolic function, as well as mitral valve anatomy and function. Magnetic resonance imaging of the heart also plays a diagnostic role, determining the degree and localization of left ventricular hypertrophy, and anatomical abnormalities of the mitral valve and papillary muscles.

Pathophysiology in HCMP
HCMP is defined as an abnormal thickening of the LV without expansion of the chamber, which is usually asymmetric, develops in the absence of an identifiable cause (for example, aortic valve stenosis, hypertension) and is associated with a violation of myocardial fibers [11,12]. The main structural anomalies underlying HCMP are [1] disorder of myocardial cells when the cells are in an unorganized state, in contrast to the normal parallel arrangement of myocytes; [2] dysfunction of the coronary microcirculatory bed due to an increase in the wall/lumen ratio; and [3]remodeling changes [13,14]. In intramiocardial arterioles <80 microns, studies have shown a 2-fold increase in the wall-to-lumen ratio, predisposing patients with silent myocardial ischemia, ongoing myocardial damage and fibrosis. Moreover, these changes are not limited to the areas of LVH and myocardial remodeling, which occur as a compensatory mechanism and may include changes in myocytes, fibroblasts and interstitials. These changes develop over many years before symptoms appear. Disorganized pattern of myocytes, increased wall/lumen ratio of coronary arteries and remodeling changes in patients with HCMP lead to impaired coronary reserve, diastolic dysfunction, supraventricular and ventricular rhythm disturbances, and sudden death. LV remodeling may include fibrosis, diffuse, asymmetric, focal or concentric hypertrophy, as well as a decrease in the size of the cavity [15,16]. Obstruction of the excretory tract of the left ventricle occurs with HCMP, and it was initially thought that basal septum hypertrophy invading the LVOT caused the obstruction. However, later studies have shown that during ventricular systole, the flow against the incorrectly positioned mitral valve apparatus (MV) leads to the appearance of resistance forces on part of the valves, which are then pushed into LVOT [17][18][19][20][21] anomalias of the MK apparatus may include displacement of papillary muscles in front, hypertrophied papillary muscles in contact with the septum, elongated mitral flaps or abnormal insertion of the papillary muscle into the anterior mitral flap [18,21,22].
The enlargement of the left ventricle may be accelerated or aggravated by a decrease in the final diastolic volume or systemic arterial resistance or an increase in contractility or heart rate [23].
Modern classification of diseases: Idiopathic hypertrophic subaortic stenosis. Asymmetric hypertrophy of the septum without changes from the aortic and mitral valves, without obstruction of the LV exit tract.
Apical HCMP with restriction of the hypertrophy zone to the apical region. Symmetrical HCMP with concentric LV myocardial hypertrophy. The last 3 forms are rare and are not accompanied by the development of obstruction of the LV outflow tract.
Classification of the new York Heart Association's HCMP: • I degree -pressure gradient not higher than 25 mm Hg.
• II degree -pressure gradient from 25 to 36 mm Hg.
• III degree -pressure gradient from 36 to 44 mm Hg.
Classification by degree of hypertrophy: * moderate -the thickness of hypertrophy is 15-20 mm; * average -hypertrophy thickness of 21-25 mm; * pronounced -the thickness of hypertrophy is more than 25 mm. Surgical technique: In this article we will carefully focus on the technique: transaortic myoectomy. An attempt at a basal septum myectomy using transaortic access was originally described by Morrow in 1961 [25-31], but it was first performed in 1958 and subsequently described by Kleland in 1963 [32][33][34][35][36][37]. The initial report described a limited myectomy without a specific anatomical resection. The technique of formal basal myectomy was later published in 1975. Initially, this method involved excision of a rectangular segment of the septum myocardium under the flap of the right coronary aortic valve which extended apically to the Table 1.  Table 2. Echocardiographic focus in hypertrophic cardiomyopathy point of contact of the septum of the anterior flap of the mitral valve. This point is usually delimited by a fibrous scar which develops a second time due to the constant contact of the valve leaf with the septum myocardium during systole. The total myocardial sample excised during Morrow's myectomy is approximately 3-4 cm long, 1 cm wide and 1.5 cm deep [27]. More recently the standard transaortic procedure has turned into an extended septal myectomy. This procedure creates a longer myocardial excision and opens the LVOT more apically than the Morrow procedure. Following the initiation of artificial circulation (CPB), the exposure of the left ventricle is achieved by an oblique aortotomy performed through the midpoint of the non-coronary sinus of the aorta and ending about 1 cm above the aortic ring. Polypropylene seams remain or not. The Ross retractor keeps the aorta open, and the suction tip for cardiotomy is used to retract and protect the anterior flap of the mitral valve. Depending on the surgeon's preferences, scalpel No. 10 or 11 is used to cut the septum, starting directly under the nadir of the right aortic valve leaf and directed to the left. to the anterior flap of the mitral valve, removing the basal part of the hypertrophied septum. The incision in this area is carefully marked, because a tissue rupture further to the right of the midpoint of the right valve leaf will increase the risk of damage to the membranous septum and disruption of the conductive tissue, thereby significantly increasing the likelihood of complete heart block. Then, starting again from the area of the initial incision, the area of the cut-out septum is lengthened to the apex of the heart, making sure that the excision is performed outside the endocardial fibrous scar and in the apical trabeculations. The completed myectomy extends from the subaortic level, about 5 mm below the aortic ring, to the level of the middle ventricle, opposite the base of the anterior papillary muscle of the mitral valve, with a total length of about 7 cm.  Conclusion. The diagnosis of HCMP is based mainly on echocardiographic variables including the dynamic parameters of LV, LVOT the distribution of increased muscle thickness, the mechanism and severity of MR as well as the degree of diastolic dysfunction. Current indications for surgical intervention include patients with symptoms that are immune to drug therapy who can tolerate the risk of surgical intervention and patients with pronounced outflow gradients, even if they are asymptomatic.

Electro-and Echocardiographic examinations at HCMP
Despite the ambiguity the mechanism underlying the improvement of symptoms, LV condition and long-term survival after myectomy is at least partially due to LV regression. It is extremely important for cardiac surgeons to understand the mechanisms of this disease in order to best manage these patients in perioperative conditions. It is very important to diagnose these HCMP patients in time, provide the necessary therapy and hospitalization for surgical treatment.