Single ventricle or total ventricle or univentricular heart is a relatively rare congenital malformation. Its incidence is about 1:6500 in live infants and accounts for about 1.5% of congenital heart disease in which the ventricle receives blood from both the tricuspid and mitral valves or from the common atrioventricular valve.
I. Clinical pathology
Embryologically, the formation of a single ventricle is due to the failure of the atrioventricular canal to align properly with the developing ventricle, thereby aligning both atrioventricular valves to one ventricle. The common complication of subpulmonary valve obstruction may be due to deviation of the funicular septum.
The single ventricle itself can be subdivided into many subtypes.
VanPraagh et al. classified it into four types based on the morphology of the main body of the ventricle.
Type A, morphologically left ventricle with a primitive outflow tract portion that includes the funicular portion of the right ventricle.
Type B, morphologically right ventricle without a left ventricular sinus portion (the remnant of the left ventricle may appear as a nonfunctional fissure or pocket)
type C, ventricle comprising the main part of both the left and right ventricles without the septum or with only its vestiges
Type D, in which the ventricle does not have features of either the right or left ventricle (absence of the right ventricle and left ventricular sinus portion).
Each of these four types can be further classified as type I (normal), II (right collaterals), or III (left collaterals) depending on their connection to the great arteries and the spatial arrangement of the great arteries. According to VanPraagh, type A accounted for 78%, type B for 5%, type C for 7%, and type D for 10%; while the number of cases of transposition of the great vessels was similar for right or left collaterals, 42% and 43% respectively, and 15% of the cases had normal arrangement of the great arteries.
Anderson divided the single ventricle into three types.
1, left ventricular type: the left ventricular form is dominant, with only a small remnant of the right ventricle.
2, right ventricular type: the right ventricular form is dominant, and the left ventricle is only a remnant chamber, which is rarely seen clinically.
3, intermediate type: left and right ventricular morphology coexist and ventricular septum is absent.
II. Clinical physiology
The pathophysiology of the single ventricle depends on the presence or absence of pulmonary stenosis, subaortic stenosis, atrioventricular valve closure insufficiency, and their degree, as well as the functional status of the ventricle. Those with significant pulmonary stenosis present with cyanosis and erythrocytosis with time extension. In cases without pulmonary stenosis, there is increased blood flow in the pulmonary circulation, with signs and symptoms of pulmonary congestion and congestive heart failure, and later increased pulmonary vascular resistance and pulmonary hypertension. Ventricular hypoperfusion and atrioventricular valve insufficiency can be due to chronic ventricular volume overload or pre-existing abnormalities of the atrioventricular valve. As atrioventricular valve insufficiency worsens and cardiac function deteriorates, the manifestations of congestive heart failure progressively worsen. Subaortic stenosis often accompanies pulmonary stenosis, or is particularly common in patients who have undergone pulmonary annuloplasty for high pulmonary blood content, probably due to excessive ventricular wall hypertrophy, and the risk of death is particularly high in such cases when corrective surgery is performed. The incidence of spontaneous or surgical conduction block is particularly high in type A-III univentricular ventricles because of the abnormal location of the AV node and the common conduction bundle. McGoon et al. reported that the incidence of preoperative AV block was 17%, while it was compounded by 30% after ventricular separation.
Clinical presentation
Most patients with single ventricle have obvious manifestations of congenital heart disease early in life, such as cyanosis, tachycardia or slow weight gain, which are noticed in the newborn or early infancy. In patients with more pulmonary blood, early detection is often absent. Without treatment, the natural life expectancy of patients with univentricular heart disease is short. According to Toronto Children’s Hospital, 117 of 182 cases (64%) died, 50% within the first month of life and 74% within the first 6 months. 83 patients who were not treated surgically and most of whom had passed through infancy were analyzed by Moodie et al. The presence or absence of pulmonary valve stenosis does not affect the length of life. The main causes of death are congestive heart failure and arrhythmias, or sudden death of unknown origin.
Physical examination
Cyanosis and pestle-like fingers (toes) can be seen in those with reduced pulmonary blood flow. In chronic congestive heart failure, poor growth and wasting can be seen in cases of increased pulmonary blood flow. In congestive heart failure or right atrioventricular valve stenosis without atrial septal defect, the jugular vein is full or angry. If the right atrioventricular valve closure insufficiency is severe, the jugular vein and liver will have systolic pulsations.
Visual examination and palpation show diffuse heart beats, and because many patients have a relatively anterior aorta, closure of the aortic valve can be perceived at the left sternal border during palpation.
On auscultation, the first heart sound may be augmented and the second heart sound may be strong and homogeneous. In most patients, a loud systolic murmur may be heard, either from pulmonary stenosis or subaortic stenosis. In patients with increased pulmonary blood flow, a diastolic murmur can be heard in the apical region from relative stenosis of the left atrioventricular valve.
V. Auxiliary examinations
1.Electrocardiographic examination: It varies depending on the subtype of single ventricle, but most patients have ventricular hypertrophy.
2. Chest X-ray: most patients have enlarged heart shadow, and the increase or decrease of pulmonary blood depends on the presence or absence of pulmonary valve stenosis. Left atrial enlargement is seen in patients with increased pulmonary blood or atrioventricular valve closure insufficiency. Other aspects vary depending on the pathological anatomy of each subtype.
3. Cardiac catheterization and cardiovascular imaging: Between the advent of two-dimensional echocardiography and color Doppler diagnostic techniques, cardiac catheterization and cardiovascular imaging are relied upon to confirm the diagnosis of single ventricle and its type and combined malformations.
The goals and objectives of the examination should include.
(1) The type of single ventricle.
(2) The presence and location of the exit chambers.
(3) The spatial location of the pulmonary artery of the aorta and atrial-ventricular interrelationships.
(4) the presence or absence of pulmonary or aortic flow obstruction and its location
(5) the number, location, and functional status of atrioventricular valves and their deviation and ride
(6) Pulmonary artery pressure and resistance.
(7) Ventricular function (body fraction and end-diastolic pressure).
(8) Pulmonary artery thickness, distribution, or distortion due to prior circumferential fasciculation
(9) Concomitant malformations.
Although the venous blood of the body and pulmonary circulation is mixed in a single ventricle, the oxygen saturation of the pulmonary artery and the aorta cannot be considered identical because of the different blood flow in the cardiac chambers, so the oxygen saturation and pressure of the two arteries must be measured separately to accurately calculate the resistance of the pulmonary and body circulations.
4.Echocardiography
Two-dimensional echocardiography has largely replaced invasive cardiac catheterization for many aspects of observation and analysis in patients with a single ventricle. For example, the basic anatomy of the heart, the relationship of the great arteries, the accompanying cardiac malformation, pulmonary valve stenosis or not, and the situation of the ventricular outlet can be observed and understood by two-dimensional echocardiography. Newer Doppler techniques also allow quantitative determination of the extent of pulmonary stenosis, ventricular outlet obstruction, and atrioventricular valve insufficiency. Echocardiographic techniques are significantly better than cardiovascular imaging for understanding the morphology, deviation and span of the atrioventricular valve.
5.M-mode echocardiography
Two-dimensional echocardiography has largely replaced invasive cardiac catheterization for the observation and analysis of many aspects of single ventricle patients. For example, the basic anatomy of the heart, the relationship of the great arteries, the accompanying cardiac malformations, the stenosis of the pulmonary valve and the exit part of the ventricle can be observed and understood by two-dimensional echocardiography. Newer Doppler techniques also allow quantitative determination of the extent of pulmonary stenosis, ventricular outlet obstruction, and atrioventricular valve insufficiency.
Two-dimensional echocardiography is the primary method for diagnosing single ventricle, and usually clearly demonstrates the major combined anomalies, such as absence of septal echoes in the heart chambers, two or single atrioventricular valves, atrioventricular valve apparatus malformations, abnormal arrangement of the great arteries, connection between the great arteries and the ventricles, and other combined anomalies.
In order to identify the aorta and main pulmonary artery, attention should be paid to the aortic arch and the left and right pulmonary arteries.
6.Doppler echocardiography
It can show the direction of blood flow in the cardiovascular cavity. Usually, blood flow from both sides of the atria converges into the main ventricular cavity, and there is no septal echo in the ventricular cavity, and the blood flow in the ventricular cavity is mixed.
In cases of pulmonary stenosis, blood flow enters the pulmonary valve orifice in a colorful mosaic, and the convergence of the inlet effect marks the level of the stenosis. Continuous Doppler can detect the velocity of high-speed blood flow in the pulmonary artery and calculate the pressure difference. In cases of combined atrioventricular regurgitation, blue multicolored mosaic of regurgitant blood flow is detected on the atrial side.
VI. Treatment
According to the specific pathologic anatomy and pathophysiology of each subtype of single ventricle, the following procedures are selected.
1.Palliative surgery
To improve the symptoms by increasing (body-pulmonary artery bypass) or decreasing (pulmonary artery circumferential bypass) pulmonary blood flow. However, palliative surgery also has its disadvantages, such as the distortion of the pulmonary artery after body-pulmonary artery bypass, which makes it difficult to correct later; too much increase in pulmonary blood flow may contribute to heart failure by increasing the ventricular volume load; superior vena cava-pulmonary artery anastomosis (Glenn procedure) does not increase the ventricular volume load, but sometimes ipsilateral pulmonary artery fistula occurs in the late stage; the distal displacement of the pulmonary artery bundle may cause distortion of the pulmonary artery, etc. Moodie et al. analyzed the effect of palliative surgery for single ventricle and found that 30% of type A and 75% of type C single ventricles died within 10 years of diagnosis, regardless of whether the surgery was performed to increase or decrease pulmonary blood flow, so palliative surgery is both useful and inadequate or unsatisfactory.
2. Ventricular exclusion surgery (Fontan surgery)
The ventricular exclusion procedure (Fontan procedure) is performed to allow the pulmonary circulation to enter the pulmonary artery directly from the atrium (suture closure of the atrioventricular valve orifice and the root of the pulmonary artery on that side), leaving a single ventricle for the exclusive use of the body circulation. 128 patients with a single ventricle had undergone the Fontan procedure at the Mayo Clinic up to 1983, with a mortality rate of 25% (32 cases), which was reduced to 14% (7 cases) in the last 50 cases. The risk of Fontan surgery is particularly high in patients with stenosis of the blood flow pathway between the ventricle and the aorta.
3.Ventricular separation surgery
A large piece of artificial fabric is used to separate the ventricular cavity into two, each receiving blood from one side of the atrioventricular valve and supplying the pulmonary artery and aorta respectively. The operation is complex and difficult, but the early and late mortality rates are still unsatisfactory despite continuous improvement of the operation technique. 45 cases were reported by Feldt at Mayo Clinical Hospital, with early and late mortality rates of 47% (21 cases) and 18% (8 cases), respectively. 12 of the 16 surviving cases were in good condition and 4 cases had poor outcomes. 11 cases were left anterior subaortic outflow tract chambers, without preoperative The survival rate was 82% in 11 cases with left anterior subaortic outflow tract chambers, no preoperative congestive heart failure, no prior palliative surgery, and no preoperative cyanosis.
VII. Complications
Single ventricle combined with other congenital cardiac anomalies, most commonly pulmonary stenosis and atrial septal defect, seen in 51% and 27% of patients, respectively; also combined with coronary anomalies; abnormal and variable conduction system position, with an abnormal anterior atrioventricular node in patients with an exiting ventricle and those with inconsistent atrioventricular and ventricular-artery interrelationships (left collaterals), and an abnormal posterior atrioventricular node in patients without an exiting ventricle. In patients without an exiting ventricle, the position of the AV node is elusive and can be posterior, lateral, or anterior; when the exiting ventricle is left-anterior, the common conduction bundle encircles the anterior aspect of the inferior outflow tract of the pulmonary valve, close to the pulmonary valve attachment; if the exiting ventricle is right-anterior and anterior, the conduction bundle is located inferior-posterior to the pulmonary valve annulus; in the absence of an exiting ventricle, the conduction bundle is located posterior to the ventricular body.