**2. Anatomy and physiology of mitral valve**

**1. Introduction**

40 Structural Insufficiency Anomalies in Cardiac Valves

Atrial myxomas are primary cardiac tumors which are more than usually found accidentally on routine clinical investigations toward other medical ailments commonly growing on the interatrial septum with the fossa ovalis been the most common site. However, it might also arise from the posterior, anterior and left atrial appendage. Cardiac myxomas are generally a rear occurrence with benign left atrial myxomas (LAM) being the most predominant type after pathological examinations. They are however two known basic types of cardiac myxoma; firm smooth and gelatinous irregular fond-like surface type with LAM mainly exhibiting symptoms of left-sided heart failure such as dyspnea when lying flat or on either the left or right side, arrhythmias, pulmonary edema, and even paroxysmal nocturnal dyspnea as a result of obstruction of the mitral valve orifice. Other associating symptoms such as malaise, Reynaud phenomenon, clubbing localized swelling, weight loss without trying and joint pain present themselves as the myxoma increases in size. LAM could also be sessile or pedunculated with pedunculated myxomas being the more frequent of the two. LAM is a multifactorial entity as at its diagnosis could spell the presence of diverse underlying cardiac alignments apart from the classic Goodwin's triad while been silent and/or masked as some could be asymptomatic or vague presenting with just fever and fatigue. Apart from the required prompt clinical investigative and the timely surgical interventions long-term morbidity and the permanent damage done by the constant pendulum-like movement to the mitral valve and its associated apparatus only but leads to possible irreversible progressive permanent cardiac damage and eventually sudden death. The resultant life-threatening complications encountered with LAM such as stroke, acute heart failure, arrhythmias and sudden death produces a thromboembolic- ischemic effect, valvular obstructions and other constitutional symptoms due to the silent masking nature of all LAM with vague symptoms which eventually lead to evident mitral valve insufficiencies [1]. Normal heart valve ensures a one-way blood flow all through the entire cardiac cycle with little interference and without any form of regurgitation. The semilunar valve [i.e., the aortic valve and the pulmonary valve] prevents backflow of blood into the ventricles during the diastolic phase, and the atrioventricular valves [mitral valve and tricuspid valve] prohibit reverse flow from the ventricle to the atrium during systole. The ability for the mitral valve to allow unrestricted forward flow largely depends on the structure, pliability, integrity, and mobility of the entire mitral valve apparatus. The longtime continuous left atrial pendulumlike movement made by the LAM leads to disturbances in the function of the mitral valve which affects the entire cardiac function due to the failure of the valve to shut properly allowing blood leak into the left atrium [regurgitation]. Significant changes done to the structure of the mitral valve such as annular dilatation results to an increase in mechanical stress over the entire valve structure sufficient enough to eventually produce Mitral valve regurgitation coupled with poor leaflet appositions or leaflet tears caused by the size of the myxoma as it constantly rebounds against the leaflets protruding into the left ventricle during systole as far as rupturing the tendinaes and over extending both the papillary muscle base initiating a vicious circle leading to mitral regurgitation. The resultant thromboembolic-ischemic effect of the papillary muscle caused by the multi-level blockage of the coronary artery plays a major role to the degree of mitral regurgitation seen [mild, moderate and sever] as the posterior aspect of the muscle receives blood supply from branches of the posterior descending artery,

The mitral valve is a complex anatomical structure made of an annulus, two leaflets, chordae tendineae, and the anterior and posterior papillary muscle. A synchronized movement of all the mitral valve apparatus is essential for the valve to function normally and their structural architecture enables them to cause a very low level of mechanical stress during the ventricular systole. Mitral valve insufficiencies occur due to structural defects or change affecting the normal architecture of the mitral valve apparatus as an effective function of the mitral valve solely depends on an efficient interaction of the whole mitral valve components including the left ventricle itself. The annulus is generally saddled in shape taking a kidney-like shape in systole and a round shape at diastole. However, it is anatomically divided into two distinct parts; an anterior and posterior portion with the former considered to be non-distensible found between two fibrous bodies while the latter accounts for about 2/3 of the mitral valve orifice and is considered to be easily prone to distention and dilatation with LAM and other diseases affecting the mitral valve and the left heart [4, 5] (**Figure 1**). The two leaflets are also described as anterior and posterior with the anterior leaflet being wider with a shorter base while the posterior leaflet is narrower but with a much broader attachment. Three distinctive scallops can be related to the posterior leaflet which is clinically distinctive and vital for proper mitral valve function in addition to the lateral and medial small commissural scallops namely; medial, middle and a lateral scallop with the middle scallop being the largest among the three (**Figure 2**) [6–8]. The rough zone of each leaflet comes in contact with that of its other counterpart as the total surface area of the leaflets is twice the total surface area of the mitral orifice itself giving a border surface area for leaflet coaptation during systole which in turn decreases the mechanical stress during a single cardiac circle. A decrease in mechanical stress is achieved with a synchronous contractive action produced by the papillary muscles during left ventricular systole which further leads to an adequate tethering of the mitral valve thereby ensuring that the rough zones of both leaflets are in a properly oriented vertical direction [9–11]. Any destructive or nondestructive change to the normal structure and architecture of the mitral valve apparatus caused by the resultant long-standing pendulum-like effect of the LAM such as annular dilatation [anterior and posterior], leaflet prolapse and/or retraction

[anterior and posterior], chordae tendineae rupture or elongation and left ventricular abnormalities produced during the course of forward and backwards movement into the left ventricle and back to the left atrium during systole and diastole results in mitral valve regurgitation

Mitral Valve Insufficiency, a Constituent of Left Atrial Myxoma: Pathobiology, Physiopathology…

http://dx.doi.org/10.5772/intechopen.76510

43

**Figure 2.** Carpentier classification of a well-structured mitral valve leaflet. A: anterior; P: posterior.

Myxomas are the most prevalent primary cardiac tumors, with 80–85% found in the left atrium and an annual incidence of 0.5 per million commonly arising from the interatrial septum at the fossa ovalis to be precise but can, however, be found in any chamber of the heart and structures with timely surgical resection playing a vital role in its treatment and recovery. The "tumor plop" sound heard during auscultation is a pathognomonic sign as a result of the penetrating myxoma in and out of the left ventricle. Symptoms caused by LAM are intermittent due to the occasional prolapse of the tumor through the atrioventricular valve and is also highly dependent on body position [1]. Cardiac myxomas usually occur between the third and sixth decades of an adult life taking a preference for the female sex with varying growth rate ranging from an absolute nonexistent growth to several millimeters per month. Familial inheritance, multicentricity, metastasis and inadequate excision increases the chance of cardiac myxomas recurrences, increased morbidity and mortality rates leading to poor prognosis and further possibly irreversible cardiac conditions either by medicamentous therapy alone and/or in combination with other various surgical therapies. Planned scheduled follow-up is of great importance in ruling out the possibility of a tumor reoccurrence even after proper surgical therapy employed. Cardiac computed tomography, magnetic resonance imaging, Doppler assessment and a combination of both outpatient transthoracic echocardiography with intra and postoperative Transesophageal echocardiography are essential for identifying and grading the regurgitation which is essential for an adequate left atrial myxoma therapy as they help in making precise judgment and assessment of anatomical valvular structures, which are destroyed by the tumor and are easily missed as most regurgitation are masked by the sole presence of LAM, different loading conditions, body structure and position [1, 12–24].

[1, 4, 7, 11] .

**3. Left atrial myxoma**

**Figure 1.** Schematic of the mitral annulus (black lines) (A): Time frames during the cardiac cycle and the volume change (gray lines) between both time frames (B): End systole and diastole (shaded gray). Saddle horn, the annular region closest to the aortic annulus.

Mitral Valve Insufficiency, a Constituent of Left Atrial Myxoma: Pathobiology, Physiopathology… http://dx.doi.org/10.5772/intechopen.76510 43

**Figure 2.** Carpentier classification of a well-structured mitral valve leaflet. A: anterior; P: posterior.

[anterior and posterior], chordae tendineae rupture or elongation and left ventricular abnormalities produced during the course of forward and backwards movement into the left ventricle and back to the left atrium during systole and diastole results in mitral valve regurgitation [1, 4, 7, 11] .

#### **3. Left atrial myxoma**

diseases affecting the mitral valve and the left heart [4, 5] (**Figure 1**). The two leaflets are also described as anterior and posterior with the anterior leaflet being wider with a shorter base while the posterior leaflet is narrower but with a much broader attachment. Three distinctive scallops can be related to the posterior leaflet which is clinically distinctive and vital for proper mitral valve function in addition to the lateral and medial small commissural scallops namely; medial, middle and a lateral scallop with the middle scallop being the largest among the three (**Figure 2**) [6–8]. The rough zone of each leaflet comes in contact with that of its other counterpart as the total surface area of the leaflets is twice the total surface area of the mitral orifice itself giving a border surface area for leaflet coaptation during systole which in turn decreases the mechanical stress during a single cardiac circle. A decrease in mechanical stress is achieved with a synchronous contractive action produced by the papillary muscles during left ventricular systole which further leads to an adequate tethering of the mitral valve thereby ensuring that the rough zones of both leaflets are in a properly oriented vertical direction [9–11]. Any destructive or nondestructive change to the normal structure and architecture of the mitral valve apparatus caused by the resultant long-standing pendulum-like effect of the LAM such as annular dilatation [anterior and posterior], leaflet prolapse and/or retraction

42 Structural Insufficiency Anomalies in Cardiac Valves

**Figure 1.** Schematic of the mitral annulus (black lines) (A): Time frames during the cardiac cycle and the volume change (gray lines) between both time frames (B): End systole and diastole (shaded gray). Saddle horn, the annular region

closest to the aortic annulus.

Myxomas are the most prevalent primary cardiac tumors, with 80–85% found in the left atrium and an annual incidence of 0.5 per million commonly arising from the interatrial septum at the fossa ovalis to be precise but can, however, be found in any chamber of the heart and structures with timely surgical resection playing a vital role in its treatment and recovery. The "tumor plop" sound heard during auscultation is a pathognomonic sign as a result of the penetrating myxoma in and out of the left ventricle. Symptoms caused by LAM are intermittent due to the occasional prolapse of the tumor through the atrioventricular valve and is also highly dependent on body position [1]. Cardiac myxomas usually occur between the third and sixth decades of an adult life taking a preference for the female sex with varying growth rate ranging from an absolute nonexistent growth to several millimeters per month. Familial inheritance, multicentricity, metastasis and inadequate excision increases the chance of cardiac myxomas recurrences, increased morbidity and mortality rates leading to poor prognosis and further possibly irreversible cardiac conditions either by medicamentous therapy alone and/or in combination with other various surgical therapies. Planned scheduled follow-up is of great importance in ruling out the possibility of a tumor reoccurrence even after proper surgical therapy employed. Cardiac computed tomography, magnetic resonance imaging, Doppler assessment and a combination of both outpatient transthoracic echocardiography with intra and postoperative Transesophageal echocardiography are essential for identifying and grading the regurgitation which is essential for an adequate left atrial myxoma therapy as they help in making precise judgment and assessment of anatomical valvular structures, which are destroyed by the tumor and are easily missed as most regurgitation are masked by the sole presence of LAM, different loading conditions, body structure and position [1, 12–24].
