Atrial Septal Defect (ASD) is a common clinical left-to-right shunt preconditioning disease, which is a hole remaining in the left and right atria when they are separated during embryonic life. It accounts for 5%-10% of the total precardiac disease, with a male to female sex ratio of 1:2.
I. Pathological anatomy
According to embryogenesis, atrial septal defect can be divided into four types as follows.
(A) Primary foramen ovale defect: also known as I foramen ovale septal defect, accounting for about 15%, the defect is located at the intersection of endocardial cushion and atrial septum. The defect is located at the junction of the endocardial cushion and the atrial septum. It is often combined with anterior mitral valve cleft or tricuspid valve septal cleft, which is called partial endocardial cushion defect.
(B) Secondary foramen ovale defect: the most common, accounting for about 75%. The defect is located in the central fossa of the atrial septum, which is also called the central type.
(c) Venous sinus type atrial defect: about 5%, divided into superior and inferior ventricular type.
Superior vena cava sinus type atrial defect: accounting for 4%, the defect is located at the entrance of superior vena cava, and the right superior pulmonary vein often drains ectopically into the right atrium through this defect.
Inferior vena cava atrial defect: less than 1%. The defect is located at the entrance of the inferior vena cava and is often combined with ectopic drainage of the right inferior pulmonary vein into the right atrium. This condition is commonly seen in Scimitar syndrome.
(d) Coronary sinus type atrial defect: about 2%, the defect is located at the superior end of the coronary sinus and the left atrium, causing the left atrial blood to flow into the right atrium through the gap in the coronary sinus. This type of defect is also known as coronary sinus defect and unroofed coronary sinus. It may be present alone, but is often combined with other malformations. There are two clinical types: complete coronary sinus septal defect, also known as unroofed coronary sinus, often combined with residual left superior vena cava, left or right atrioventricular valve stenosis or atresia, complete atrioventricular septal defect, anosplenic syndrome, and polysplenic syndrome. Partial coronary sinus septal defect, which can be single or multiple.
II. Hemodynamics and clinical manifestations
After birth, the left atrial pressure is higher than the right atrium, and if there is atrial defect, left-to-right shunt occurs. The shunt flow is related to the size of the defect, the pressure difference between the two atria and the compliance of the ventricles. In the early postnatal period, the wall thickness of the left and right ventricles are similar, and the compliance is also similar, so the shunt flow is not much. As the pulmonary vascular resistance and right ventricular pressure decrease with age, the right ventricular wall is thinner than the left ventricular wall, and the filling resistance of the right ventricle is lower than that of the left ventricle, so the fractional flow increases. Due to the increase in right heart blood flow, the diastolic load increases, so the right atrium and right ventricle are enlarged. The increased blood volume and pressure in the pulmonary circulation may lead to thickening of the myocardium and intima of the small pulmonary arteries and narrowing of the lumen in late stages, resulting in Eisenmenger syndrome in adulthood.
In most children, there are no obvious signs in infancy and early childhood, but after 2 to 3 years of age, the heart enlarges, the anterior chest bulges, and there is a sense of lifting impulse in the precordial region on palpation, and there is usually no tremor, but a few large defective fractional flow can appear tremor. Due to the enlargement of the right ventricle, a large amount of blood flow through the normal pulmonary valve (forming a relative stenosis) can be heard as a grade 2 to 3 jet systolic murmur at the left second intercostal space near the sternum. When the blood flow in the pulmonary circulation exceeds that of the body circulation by a factor of 1 or more, a short and low-frequency mid-diastolic murmur of relative stenosis of the tricuspid valve can be heard at the left lower 4th to 5th intercostal space of the sternum, which is louder during inspiration and diminishes during expiration. The 1st heart sound is hyperactive, and the 2nd heart sound of the pulmonary artery is enhanced. Due to increased right ventricular volume and prolonged jet flow time during systole, the pulmonary valve closes more behind the aortic valve, resulting in a wide and respiratory-independent fixed splitting of the 2nd heart sound.
III. Echocardiographic diagnosis
(A) Two-dimensional echocardiography
1. Direct signs
In the apical four-chamber view, because the echogenic beam is almost parallel to the atrial septum, it is easy to produce echogenic loss, and the echogenic interruption seen in this view is not a reliable indicator for the diagnosis of atrial defect. The subxiphoid two-chamber view and the four-chamber view are the best views, because the sound beam is almost perpendicular to the atrial septum, and the combination of color Doppler imaging showing the shunt flow through the atrial septum can make a clear diagnosis. A four-chamber view of the parasternal sternum and a short-axis view of the aorta showing the flow through the septum can help to diagnose atrial defects. The free end of the atrial defect has a bulbous thickening, shaped like a match head, which is also called the “T” sign.
In the superior atrial defect, the echogenic interruption of the septum is seen in the subxiphoid view over the superior vena cava, often with ectopic drainage of the right superior pulmonary vein. The inferior atrial defect can be seen at the entrance of the inferior vena cava and is often associated with ectopic drainage of the right inferior pulmonary vein. When the above views are not clear, a longitudinal view of the right sternal margin can be used for diagnosis. This view is not limited by the patient’s age or weight, especially in heavier adolescents or adults. During the examination, the patient is placed in a right-lying position, and the probe is pointed between 12 and 1 o’clock with slight adjustment up and down, which can clearly show the superior vena cava and part of the atrial septum, and is an excellent view for the diagnosis of superior cavernous atrial defect.
Coronary sinus septal defect: The subxiphoid double atrium shows the superior and inferior vena cava, the atrial septum, the right and left atria, and then gradually sweeps toward the apex of the heart to reveal a round coronary sinus defect. After displaying the apical four-chamber view and the subxiphoid four-chamber view, the probe is tilted back to reveal the coronary sinus septal defect. The long-axis view of the parasternal sternum can be observed in the enlarged coronary sinus. Sweeping the probe to the right and down can show the long axis of the coronary sinus and determine whether there is a coronary sinus septal defect.
2. Indirect signs
Increased right ventricular volume load, manifested by large right atrium and right ventricle, and widened pulmonary artery. The septal motion is flat or isotropic with the posterior wall of the left ventricle.
(B) Color and spectral Doppler flow imaging
Usually the left atrial pressure is higher than the right atrium, which can show the red septal blood flow from the left atrium into the right atrium, so that the type and size of the defect can be determined. Note that the degree of shunt does not depend entirely on the size of the defect but, importantly, on the compliance of the right ventricle. If the right atrial pressure is higher than the left atrial pressure, a bidirectional shunt or a right-to-left shunt may be seen, manifesting as a lan-colored septal flow.
During pulsed Doppler ultrasonography, the sampling volume is placed on the right atrial side of the shunt, and care is taken to make the flow direction as small as possible in relation to the angle of the ultrasound beam. Generally, one to three positive waves in diastole and one negative wave in early systole can be obtained, and the maximum flow velocity is generally below 1.3 m/s. The maximum flow velocity is generally below 1.3m/s. The shunt flow can be estimated based on the shunt spectrum and the size of the defect.
Due to the presence of a left-to-right shunt, the flow velocity at the tricuspid and pulmonary valve orifices is accelerated. However, the flow velocity at the pulmonary valve orifice generally does not exceed 2.5 m/s, otherwise, attention should be paid to the combined pulmonary valve stenosis.
IV. Diagnosis of coronary sinus septal defect
(A) Two-dimensional echocardiography
1. In the subxiphoid short-axis view, the probe is first directed to the right side, showing the superior vena cava and inferior vena cava, the atrial septum, the left and right atria, and then gradually sweeping toward the apex of the heart, a round coronary sinus defect can be seen.
The coronary sinus defect can be observed in apical four-chamber view, subxiphoid four-chamber view and parasternal long-axis view.
3. If the coronary sinus is enlarged, the coronary sinus located behind the interatrial septum and its septum separated from the left atrium, if accompanied by the residual left superior vena cava, is located behind it when the probe is slightly deflected toward the apex.
(ii) Color Doppler echocardiography
Depending on the pressure in the left and right atria, the left atrial pressure is generally higher than the right atrial pressure, producing a left-to-right shunt, i.e., left atrial blood flows into the right atrium through the defect in the coronary sinus septum. The right ventricular volume load is increased and manifests as a large right atrial right ventricle.
Note: In the case of an unroofed coronary sinus combined with left superior ventricular remnant, the diagnosis is easily missed because it does not show the left superior vena cava reflux well. A definitive diagnosis is required by cardiac catheterization.
Section 2: Ventricular septal defect
Ventricular Septal Defect (VSD) is the most common congenital heart disease in pediatric patients due to incomplete development of the ventricular septum during embryonic development. Ventricular septal defect alone accounts for about 25%-50% of all congenital heart diseases, and is often a component of complex malformations.
I. Pathological anatomy
(a) According to the anatomical parts of the ventricular septal defect, it can be divided into 4 types and 10 kinds.
1. Perimembranous type: the most common, accounting for about 75% of all ventricular septal defects. The periphery of the defect is all membranous, or the upper edge is fibrous and the lower edge is muscular. Because of the small size of the membranous part of the septum, purely membranous defects are rare. When the defect is large, it often extends to other parts, so it is often called perimembranous ventricular defect. (1) Perimembranous inflow tract ventricular defect: the defect extends into the inflow tract, and the edge of the defect may have tricuspid valve tissue attachment or pseudoventricular septal tumor formation. (2) Perimembranous outflow tract ventricular defect: the ventricular defect extends into the outflow tract. (3) Perimembranous trabecular ventricular defect: the ventricular defect extends into the trabecular part of the muscle. (4) perimembranous fusion ventricular defect: the defect involves 2 or 3 parts of the myocardial septum; in this case, if the defect is located below the aortic noncoronary valve, the aortic valve is often prolapsed and embedded in the ventricular defect, resulting in aortic valve closure insufficiency and valve regurgitation.
2. Muscle: about 10% to 20%. The edges of the defect are muscle tissue, and there is muscle tissue separating the tricuspid valve from the aortic valve and the tricuspid valve from the mitral valve. According to the site can be divided into: (1) muscle inflow tract ventricular defect. (2) Myocardial outflow tract ventricular defect, also known as subpulmonary artery ventricular defect. (3) Myocardial trabecular defects. The ventricular defect can be located in any part of the myocardial septum, with the apical part being the most common, followed by the central and marginal parts.
(3) Double subarterial type: the edges of the ventricular defect are the fibrous rings of the aortic and pulmonary valves, mostly accompanied by pulmonary hypertension.
4. malalignment defect: named by the misalignment of the ventricular outflow tract and the great arteries, i.e., the two are not aligned in a straight line, commonly seen in malformations such as tetralogy of Fallot, right ventricular double outlet, pulmonary atresia, and permanent arterial trunk.
(B) Classification according to the size of ventricular septal defect
Small ventricular septal defect The defect is less than 25% of the aortic valve annulus.
2. Medium-sized ventricular septal defect The defect is 25% to 50% of the aortic valve annulus.
3. Large ventricular septal defect, the defect is more than 50% of the aortic annulus.
II. Hemodynamics and clinical manifestations
The embryonic small pulmonary artery has a thick muscle layer and small lumen, so the resistance is high. After the fetus is born and begins to breathe, the thickness of the small pulmonary artery muscle layer decreases, and the pressure of the pulmonary artery is about 1/2 of that of the body circulation in the first 3 days after birth, and approaches that of the adult in 3-6 weeks. Ventricular septal defects are rarely symptomatic in the neonatal period when a large left-to-right shunt occurs. Full-term infants with large spatial septal defects tend to develop symptoms of cardiac insufficiency at 2 to 6 months of age. In preterm infants, large left-to-right shunts and heart failure occur earlier because of the thinner walls of the small pulmonary arteries, which help reduce vascular resistance more rapidly.
Left-to-right shunt flow is related to the size of the defect, pulmonary vascular resistance, and the pressure step difference between the two ventricles. A left-to-right shunt must result in increased pulmonary blood flow, increased left ventricular volume load, and reduced left ventricular output. In small defects, the left-to-right shunt is low, the left and right ventricles have only a slight increase in volume and normal pressure, and the size of the heart and blood vessels can be normal. In medium-sized defects, the pulmonary blood flow can exceed the body circulation by one to two times, and the pulmonary artery and pulmonary small vessel blood flow increases, and the blood flow back to the left atrium and left ventricle also increases, thus increasing the workload of left ventricular ejection and diastolic load, resulting in left atrial and left ventricular hypertrophy. As the disease progresses, not only the left atrium, left ventricle and pulmonary artery expand, but also the small pulmonary artery spasmodically contracts to produce dynamic high pressure due to the continuous increase of pulmonary circulation, and the ventricle eventually expands and hypertrophies due to the increase of beat volume and resistance. The wall of the small pulmonary artery becomes hyperplastic and the lumen becomes smaller, or even completely obstructed, resulting in organic pulmonary hypertension, a decrease in left-to-right shunt, and a bidirectional shunt, leading to a right-to-left shunt, which is known as Eisenmenger’s syndrome. In a small number of cases, the small pulmonary arteries maintain a thickening of the muscular layer after birth. Therefore, pulmonary hypertension is present in infancy.
In small defects, a loud and rough grade 4 full systolic murmur with limited tremor and no diastolic murmur is heard only at the third to fourth rib at the left sternal border, and the heart borders are mostly normal. When the defect is very small or about to close, the murmur may be a short high-pitched whistling sound. In addition to the rough systolic murmur described above, a low-pitched rumble-like diastolic murmur with relative mitral stenosis can be heard in the apical region, and the second heart sound in the pulmonary valve region is hyperactive. In large defects, there may be an augmentation deformity in the anterior chest, and there may be a distinct heart beat in the apical region or subxiphoid process. A rough fourth-grade all-systolic murmur with systolic tremor may be heard between the 4th and 5th ribs at the left sternal border. A short diastolic murmur can still be heard in the apical region, and a systolic murmur due to dilatation of the common pulmonary artery trunk caused by high pulmonary artery flow can also be heard in the pulmonary valve region, with a hyperactive second heart sound in the pulmonary valve region. In large defects with pulmonary vascular obstructive lesions, the murmur is instead lighter, shorter or even absent; tremor may also be less pronounced, and the second pulmonary artery sound is a single metallic sound.
Ultrasound diagnosis
The purpose of echocardiographic evaluation of ventricular septal defect: (1) the presence of ventricular defect; (2) the location, number and size of ventricular defect; (3) the relationship between ventricular defect and atrioventricular valve and semilunar valve; (4) the combination of pulmonary hypertension; (5) the detection of combined malformations; (6) the measurement of the internal diameter of the heart chambers and the assessment of ventricular function.
(A) Detection of ventricular defects
Membranous defects are most common and can be seen in subxiphoid four-chamber views, apical and parasternal four-chamber views, five-chamber views, and parasternal short-axis views of the aorta. Direct connection of the tricuspid valve to the aortic valve and the tricuspid valve to the mitral leaflet and as part of the edge of the defect is the diagnostic criterion for perimembranous ventricular septal defects. When the perimembranous ventricular defect involves the inflow tract portion of the muscular septum posteriorly, it can be seen in four-chamber views; when the defect is larger and extends farther posteriorly it resembles an atrioventricular access type ventricular defect with the tricuspid and mitral valves attached at the same level. If the perimembranous ventricular septal defect extends forward to the supraventricular crest, i.e., a perimembranous outflow tract defect, the defect is visible in the subaortic in a long-axis view of the parasternal left ventricle. The normal inferior border of the membranous septum is the trabecular myocardial septum, the boundaries of which are difficult to determine in ultrasound views; it is generally accepted that if the septal end of the inferior border of the defect is wide, blunt, or if the defect extends more than half of the aortic internal diameter apically, the defect involves the trabecular myocardial septum. When the defect involves two to three parts of the myocardial septum, it is called perimembranous fusion type ventricular defect. The perimembranous ventricular defect has the highest rate of natural closure, and approximately 70% to 80% can be closed within 2 years of age. The principle of closure is that the defect hole is closed by the proliferation of fibrous tissue around the defect hole, adhesion and attachment to the tricuspid septum and tendon or myocardial hypertrophy of the ventricular septum. If the tissue at the defect site is thin, it may protrude locally to the right to form a pseudoventricular septal tumor due to high left ventricular pressure.
The myocardial inflow tract ventricular defect can be seen in a four-chamber view, with muscle tissue separating the edges of the defect from the atrioventricular valve fibrous annulus. Ventricular defects in the myocardial trabeculae are visible in apical four-chamber views and need to be biased near the apex.
Both the myocardial outflow tract and the double subarterial ventricular defect are funnel septal defects, also known as supraventricular crest type ventricular defects, with a higher incidence in Asia, accounting for approximately 20% of ventricular defects. They are seen in the subxiphoid aortic long-axis, ventricular short-axis, subxiphoid five-chamber view, apical five-chamber, and aortic short-axis, with the subxiphoid right ventricular outflow tract being more accurate and specific in the long-axis view. The myocardial outflow tract defect, also known as subpulmonary septal defect, has muscular tissue separating the upper edge of the defect from the pulmonary valve annulus; because the funnel septal defect deprives the aortic valve of support, coupled with the aspiration effect of the Venturi effect, it often results in aortic coronary valvelessness or right coronary valve prolapse, embedded in the ventricular defect, partially or completely blocking the ventricular defect, resulting in reduced shunting and reduced disease; however, with age, aortic valve However, with age, aortic valve deformation increases, resulting in aortic valve closure insufficiency can aggravate the condition, and should be operated as early as possible. The edges of the double subarterial ventricular defect are the fibrous rings of the pulmonary valve and aortic valve, which are often combined with pulmonary hypertension at an early stage and should be operated as early as possible.
The apical ventricular defect is mostly spongy, and because the septum does not close tightly, it causes multiple shunts at the ventricular level, forming multiple VSDs, also known as “swiss cheese”. It should be carefully scanned in the long-axis and four-chamber views of the apical left ventricle, subxiphoid and parasternal short-axis views of the left ventricle.
Poorly aligned ventricular septal defect: A long-axis view of the left ventricle may show the aorta riding over the septum. It is commonly seen in anomalies such as tetralogy of Fallot, right ventricular double outlet, pulmonary artery atresia, and permanent arterial trunk.
When small perimembranous or myocardial ventricular defects are difficult to identify with 2D ultrasound, they can be clarified with color flow imaging. In this case, color flow imaging may show a colorful mosaic of blood flow through the defect and may simply show a red left-to-right shunt or bidirectional shunt if pulmonary hypertension is present. Spectral Doppler ultrasound can be used to measure the shunt velocity of the ventricular defect and thus assess the degree of pulmonary hypertension.
(B) Relationship between ventricular defect and atrioventricular valve and semilunar valve
Mitral valve: observation of mitral blood flow, presence of supravalvular annulus, and presence of mitral stenosis or regurgitation.
Tricuspid valve: perimembranous ventricular defect is located below the tricuspid septal valve, which often adheres to it to form a pseudo-ventricular septoma, which is one of the principles of ventricular defect closure. However, careful observation should be made for tricuspid valve riding and regurgitation.
Aortic valve: perimembranous outflow tract ventricular defect is often combined with prolapse of the aortic uncrowned valve or right coronary valve embedded in the ventricular defect; subpulmonary ventricular defect is often combined with prolapse of the right coronary valve embedded in the ventricular defect; the closure of the aortic valve and regurgitation should be carefully evaluated at this time. Due to the impact of the ventricular shunt, a fibrous ridge may appear under the aortic valve, causing obstruction of the left ventricular outflow tract. The subaortic fibrous crest can be demonstrated in apical five-chamber views and parasternal long-axis views. If the left ventricular outflow tract pressure difference is greater than 15 mmHg, surgical intervention should be performed.
Pulmonary valve: In pulmonary hypertension, the pulmonary artery is widened and the valve is convex toward the right ventricular surface, which should show the closure of the pulmonary valve and assess the presence of regurgitation.
(C) Detection of pulmonary hypertension
In pulmonary hypertension, the right ventricular afterload increases, and gradually the right ventricle may appear enlarged; due to the elevated right ventricular pressure, the septum projects toward the left ventricular surface, suggesting that the right ventricular pressure/left ventricular pressure is greater than 0.5.
If tricuspid regurgitation is present, a simplified Bernoulli equation (ΔP=4V2,V is the maximum regurgitant velocity) can be applied to obtain the trans-tricuspid pressure difference. If there is no right ventricular outflow tract obstruction, then: pulmonary artery systolic pressure (PASP) = right ventricular systolic pressure (RVSP) = right atrial pressure (RAP) + tricuspid transvalvular pressure difference (ΔP). The right atrial pressure is usually 5 mmHg; if the tricuspid valve regurgitates significantly and the inferior vena cava is dilated, 10 mmHg is used; in severe pulmonary hypertension and right heart failure, 15 mmHg is used. trans-pulmonary valve pressure difference can be calculated according to pulmonary regurgitation: pulmonary artery diastolic pressure (PADP) = pulmonary artery transvalvular pressure difference (ΔP) + right ventricular early diastolic pressure (RVDP). If right ventricular early diastolic pressure is zero in the absence of right heart failure, then: PADP = pulmonary artery transvalvular pressure difference (ΔP) and mean pulmonary artery pressure (PAMP) = PADP + 1/3 (PASP-PADP).
The pressure difference between the left and right ventricles can be calculated from the shunt of the ventricular septal defect, at this point: RVSP=LVSP-ΔP. If there is no left or right ventricular outflow tract obstruction, then: PASP=RVSP BASP=LVSP PASP=BASP- 4VMAX2. where VMAX is the maximum shunt velocity of the ventricular defect and should be carefully measured in multiple views. The perimembranous ventricular septal defect can be measured in parasternal and subxiphoid long-axis views, and the myocardial ventricular septal defect can be measured in parasternal and subxiphoid short-axis views.
(iv) Detection of combined deformities
In the diagnosis of ventricular septal defect, attention should also be paid to: whether there are abnormal muscle bundles in the right ventricular outflow tract, resulting in obstruction of the right ventricular outflow tract; whether there are right ventricular double chambers.
Left ventricular outflow tract: In perimembranous fusion type ventricular defect, due to the influence of blood flow impact, the subaortic fibrous crest is often formed, resulting in left ventricular outflow tract obstruction.
(V) Assessment of cardiac function
Because of the presence of a large left-to-right shunt and left ventricular volume overload, large left atria, enlarged left ventricles, and even double ventricles may be found. Application of M-mode echocardiography in the short-axis view of the left ventricle next to the sternum can measure the size of the left ventricle and calculate the ejection fraction to assess the left cardiac function.
Section 3: Arterial ductus arteriosus
The ductus arteriosus is a normal channel between the pulmonary artery and the aorta in the fetal circulation and closes automatically early after birth. If the closure mechanism is impaired, the ductus arteriosus remains open, resulting in patent ductus arteriosus (PDA), which accounts for approximately 5% to 10% of all precardiac disease. The disease is most common in premature infants and those living on highlands, with about 50% of the former combined with patent ductus arteriosus, and 30 times more common in those living above 4500 meters above sea level. The male to female sex ratio is 1:3.
I. Anatomical arteriovenous ductus arteriosus staging
(A) According to the anatomical pattern
1. Tube type: The aortic end of the arterial duct and the pulmonary artery end are roughly equal in thickness, which is clinically common and accounts for about 80%.
2. Funnel type: The diameter of the aortic end of the catheter is larger than the diameter of the pulmonary artery end in a funnel shape.
3. Window type: The catheter is short, the lumen is thick, the wall is thin, and the aorta communicates with the pulmonary artery in a window-like manner.
4. Mute type: The middle of the catheter is thin and the two ends are thick in a mute shape.
5. Aneurysmal type: The catheter is thin at both ends, with aneurysmal expansion in the middle and a thin and brittle wall.
(B) According to the connection pattern
(1) Obtuse angle type: The arterial catheter enters the descending aorta posteriorly along the long axis of the common trunk of the pulmonary artery, and the angle with the distal descending aorta is obtuse. 2. Acute angle type: The arterial catheter enters the descending aorta from the pulmonary artery upward, and the angle with the distal descending aorta is acute.
II. Hemodynamics and clinical manifestations
Due to the opening of the arterial catheter so that there is a pathway between the main and pulmonary arteries, in general, the pressure of the body circulation is higher than the pressure of the pulmonary circulation. Therefore, some of the oxygen-saturated blood in the body circulation is shunted from the aorta to the pulmonary artery through the arterial catheter in both systole and diastole. The size of the shunt depends on three factors: the pressure step difference between the aorta and the pulmonary artery; the diameter and length of the arterial catheter; and the resistance difference between the body and pulmonary circulations. The thicker the catheter, the greater the pressure difference and the greater the shunt flow. Due to the aortic shunt, the pulmonary circulation volume increases, resulting in pulmonary artery dilation and pressure increase, which returns to the left atrium causing enlargement of the left atrium and left ventricular hypertrophy or even failure. The volume of blood in the body circulation decreases due to shunting to the pulmonary circulation, and the diastolic pressure of the peripheral arteries decreases due to the presence of shunting in diastole, and there is a widening of pulse pressure.
In typical cases, the precordial region is elevated, the apical beats are diffusely intense, and systolic tremor can be palpated at the left second intercostal space near the sternum, and in a few cases diastolic tremor can also be palpated. A coarse, continuous, machine-like murmur can be heard in this area. The murmur is predominantly systolic and gradually increases to the loudest second tone, and then decreases without interruption to the diastolic phase. The murmur is conducted to the precordial region, the neck and the left shoulder.
Sometimes the murmur can also be heard lateral to the midclavicular line in the left 2nd intercostal space. The second pulmonary artery sound is markedly hyperactive and may be masked by the murmur. A low-frequency mid-diastolic murmur with relative mitral stenosis can be heard apically when the pulmonary circulation is more than double the volume of the body circulation. Most children have a widened pulse pressure (often >5.3 kPa) and peripheral vascular signs, such as femoral artery gunshot sounds, capillary pulsations, and hydropulse pulses are helpful in the diagnosis.
Echocardiographic diagnosis
(a) The purpose of echocardiography diagnosis
To determine the location, size and shape of the arterial duct. 2. To clarify the direction and phase of the arterial duct. 3. To clarify whether pulmonary hypertension is combined. 4. To detect combined malformations.
(B) Two-dimensional echocardiography
Long-axis view of the right ventricular outflow tract at the left edge of the sternum: it corresponds to the sagittal view of the second intercostal space at the left edge of the sternum. After showing the common pulmonary artery trunk and the left and right pulmonary arteries, point the marker to 2 to 3 points and you can see the common pulmonary artery trunk extending to the left pulmonary artery and the descending aorta in longitudinal alignment. The length, internal diameter and shape of the duct can be observed in this view.
High parasternal short-axis view: After showing the common pulmonary artery trunk and the right and left pulmonary arteries at the second intercostal space on the left edge of the sternum, the probe is rotated against the clock, and if there is a tube connecting the pulmonary artery to the descending aorta, it is an arterial catheter. At this point, three openings of the right and left pulmonary arteries and the ductus arteriosus are visible.
Long-axis view of the aortic arch in the superior sternal fossa: after showing the long-axis view of the aortic arch, the probe is rotated counterclockwise and slightly to the left (or clockwise in the case of the right aortic arch) until the ascending aorta disappears and the descending aortic arch and the left pulmonary artery are seen. If there is a conduit connecting the pulmonary artery to the descending aorta, it is an arterial conduit.
Since the course of the ductus arteriosus varies from person to person, it should be carefully examined in combination with the three views to improve the accuracy of the diagnosis.
Indirect signs of an unclosed arterial duct: enlarged left atrium and left ventricle.
(iii) Color and spectral Doppler ultrasonography
When the arterial duct is small (less than 1 mm), it is often difficult to display by two-dimensional ultrasound. Color flow imaging can show the shunt beam, which is mainly red in color, rushing through the arterial duct to the pulmonary valve orifice, which can help in the diagnosis. The width and color of the shunt beam depends on the size of the arterial duct and the pressure difference between the two ends of the arterial duct. The thicker the arterial duct, the wider the shunt bundle; when the pulmonary artery pressure is normal, the shunt is faster and bright red or orange-red; as the pulmonary artery pressure increases, the left-to-right shunt gradually decreases, and only the diastolic shunt may be seen as orange-red. When secondary to Eisenmenger’s syndrome, a bidirectional shunt (i.e., a light pink diastolic shunt entering the main pulmonary artery via the arterial duct, and a light blue systolic shunt entering the descending aorta from the pulmonary artery via the arterial duct) or even a right-to-left shunt may be seen. Color Doppler ultrasound can significantly reduce and eliminate false positives and false negatives caused by arterial ducts that are not detected by general two-dimensional echocardiography, or by omissions in the examination and by loss of echoes between the descending aorta and the main pulmonary artery, and improve the accuracy of diagnosis.
The sampling volume is placed at the opening of the pulmonary artery end of the arterial catheter, and the systolic and diastolic shunt velocity V of the arterial catheter can be measured by applying pulsed Doppler ultrasound and continuous wave Doppler ultrasound techniques. Applying the simplified Bernoulli equation (ΔP=4V2), the pressure step difference between the main and pulmonary arteries at the two ends of the catheter can be calculated: pulmonary artery systolic pressure = brachial artery systolic pressure – 4 (systolic shunt velocity)2, and Pulmonary artery diastolic pressure = brachial artery diastolic pressure – 4 (diastolic shunt velocity)2.
Descending aortic diastolic overflow: In the long-axis view of the infrapopliteal abdominal aorta, negative systolic flow in the abdominal aorta can be detected, while a slow, low-velocity flow spectrum is often seen in diastole, i.e., diastolic overflow. It is commonly seen in malformations such as ductus arteriosus, aortic regurgitation, main pulmonary window, and coronary arteriovenous fistula.
(iv) Detection of combined malformations
The presence or absence of combined subaortic fibrous crest and aortic constriction should be noted in large arteriovenous ductus arteriosus.
The development and morphology of the arterial duct are related to the early onset and severity of right ventricular outflow tract obstruction during fetal life. In patients with pulmonary atresia, the right ventricle to pulmonary artery obstruction exists during fetal life, and the patient is supplied with blood from the aorta to the pulmonary artery via the arterial duct, so the arterial duct is sharply angled, also known as vertical PDA; tricuspid valve and right ventricular dysplasia, severe tetralogy of Fallot, etc. can also be combined with vertical PDA. vertical PDA can be shown in the upper sternal fossa view.
Section 4: Atrioventricular septal defect
Atrioventricular Septal Defect (AVSD), also known as endocardial cushion defect and atrioventricular channel defect, is a deformity of the upper and lower atrioventricular septum and left and right atrioventricular valves caused by endocardial cushion tissue hypoplasia.
I. Pathological anatomy
1. Partial atrioventricular septal defect
In primary foramen ovale septal defect combined with anterior mitral valve cleft and/or tricuspid septal cleft, the mitral annulus and tricuspid annulus are attached to the septal ridge and are at the same level. In this case, the septum is intact and there is no shunt at the ventricular level.
2. Complete atrioventricular septal defect
Complete atrioventricular septal defect has the following three characteristics: primary foramen ovale, common atrioventricular valve, and inflow tract ventricular septal defect. The common atrioventricular valve generally consists of two anterior valves on the left and right, two lateral valves on the left and right, and a posterior valve. The posterior valve leaflet has a more constant morphology and a larger body, and typically the middle part of the valve crosses the septum and is the posterior common valve or posterior bridge valve. Septal defects in the middle of the heart are generally larger and include atrial septal defects and ventricular septal defects. 1966 Rastelli classified complete atrial septal defects into three subtypes, A, B, and C, based on whether the anterior coaptation valve is attached to the right ventricular papillary muscle or the ventricular septum.
Type A: the tendon of the anterior coaptation valve is attached to the septal ridge, and the leaflet movement is somewhat restricted, mostly in Down’s syndrome (Down’s syndrome).
Type B: The tendons of the anterior common valve are attached to the papillary muscle on the right ventricular surface of the septum.
Type C: The common atrioventricular valve is completely free, the anterior coaptation is not separated, and the tendons are not attached to the septal ridge but to the free wall of the right ventricle.
Most complete atrioventricular septal defects have the right and left atrioventricular valve annulus in line with the left and right ventricles and symmetrical to the left and right, called balanced type. If the tricuspid or mitral annulus is riding on the ventricular septum, causing one ventricle to be underdeveloped, it is called unbalanced type.
3. Transitional atrial septal defect
It is characterized by a primary foramen ovale septal defect; mitral and/or tricuspid fissures; separation of the anterior commissure leaflets, direct attachment of the tendons to the septal ridge, tight tendons, blood shunts between the tendons, or a small septal defect.
II. Hemodynamics and clinical manifestations
There are four anatomical abnormalities that cause hemodynamic changes in AV septal defects: 1. shunt through atrial defect. 2. shunt through ventricular defect. 3. mitral cleft with regurgitation. 4. tricuspid cleft with regurgitation. The physiological changes of partial atrial septal defect are the same as those of atrial septal defect, which manifest as increased volume load of the right ventricle, increased pulmonary blood, and enlarged right atrium and right ventricle. In combination with atrioventricular valve dehiscence, left atrial and left ventricular enlargement may occur due to valve regurgitation. In complete atrioventricular septal defect, due to the coexistence of four malformations, the intracardiac shunt can be multidirectional, i.e., left atrium to right atrium, left ventricle to right ventricle, left ventricle to left atrium, right ventricle to right atrium, and left ventricle to right atrium. Bidirectional shunts occur when the defect is large or is associated with increased resistance to pulmonary circulation and pulmonary hypertension.
Infants and children with a history of recurrent respiratory infections present earlier with congestive heart failure, growth retardation, marked shortness of breath after exercise, and may even develop mild cyanosis.
The precordial drive is elevated and the apical pulses are diffuse. Systolic tremor may be palpable at the apex of the heart or at the left sternal border. Complete endocardial cushion defect: the apical first heart sound is diminished, and the second heart sound of the pulmonary valve is fixedly split and hyperactive. A full systolic regurgitant murmur due to mitral valve dehiscence is heard in the apical region and travels forward to the sternum or even the right chest. The systolic murmur of the ventricular defect can be heard at the left edge of the sternum. A systolic murmur of tricuspid regurgitation can also be heard at the subxiphoid and left sternal margins. When the pulmonary artery pressure increases, the murmur of ventricular defect is diminished and the murmur of tricuspid regurgitation is increased. Partial endocardial cushion defect: The auscultation of simple primary foramen ovale septal defect is similar to the murmur of secondary foramen ovale defect, and the corresponding systolic murmur can be heard in the presence of mitral or tricuspid cleft defect.
Echocardiographic diagnosis
(a) The purpose of echocardiographic diagnosis
To determine the extent of atrioventricular traffic. 2. To determine the anatomy of the atrioventricular valve and the location of its tendon cords. 3. To evaluate the degree of atrioventricular regurgitation. 4. To exclude ventricular inflow and outflow tract stenosis and the degree of atrioventricular valve span. 5. To exclude other combined malformations.
(B) Ultrasonographic views
1. Four-chamber subxiphoid and four-chamber apical views: to evaluate the extent of atrial septal defect, symmetrical relationship between atrioventricular valve and ventricle and its tendon attachment site, the direction and degree of intracardiac shunt and regurgitation. The presence of atrial shunt only is a partial atrial septal defect, which can be combined with atrioventricular valve dehiscence. The presence of atrial and ventricular shunts and a common atrioventricular valve is considered a complete atrial septal defect. If the anterior bridging valve is attached to the septal ridge by the tendon cord, it is called a complete AV septal defect type A; if the anterior bridging valve is attached to the right ventricular surface of the septum or to the free wall of the right ventricle, it is type B; if the anterior bridging valve is suspended above the septal ridge, it is type C. If there is a shunt at the atrial level and a rougher tubercle-like structure at the ventricular level with less shunt, then it is a transitional atrial septal defect.
2. Subxiphoid and parasternal left ventricular short-axis views: From the subxiphoid four-chamber view, the probe can be rotated 30° to 45° clockwise to show the common valve pattern. The parasternal left ventricular short-axis view can show the location and number of papillary muscles.
3. Apical four-chamber and five-chamber views and parasternal left ventricular long-axis views: show primary foramen ovale septal defect and inflow ventricular septal defect, with the left ventricular inflow tract distance (atrioventricular valve annulus to ventricular apex) shorter than the outflow tract (ventricular apex to aortic annulus). The presence of left ventricular outflow tract obstruction should be determined by the anterior displacement of the aortic origin instead of being embedded between the two atrioventricular valves and the prolongation of the left ventricular outflow tract in a gooseneck shape.
4. Apical four-chamber views and parasternal short-axis views of the left ventricle can show large right atrium, large right ventricle, or large double ventricle due to volume overload, and further assess the function of the left and right ventricles.
Color Doppler ultrasound can show shunts at the atrial level, ventricular level, and ventricular to atrial regurgitation. In the absence of pulmonary hypertension left-to-right shunts at the atrial and ventricular levels are common, and conversely, right-to-left or bidirectional shunts can occur. Spectral Doppler ultrasound can measure the shunt velocity of the ventricular defect and the regurgitation velocity of the valve to assess whether pulmonary hypertension is combined and the degree of hypertension.
Section V. Pulmonary Stenosis
Pulmonary stenosis (PS) is a common congenital heart disease. Simple pulmonary stenosis accounts for about 10% of congenital heart disease and about 20% of congenital heart disease combined with pulmonary stenosis.
I. Pathologic anatomy
The normal pulmonary valve leaflets are three semilunar valves, with the leaflet junction completely separated and the annulus connected to the right ventricular funnel muscle. Pulmonary stenosis is divided into two types depending on the location of the lesion.
(i) Typical pulmonary stenosis
The junction of the three pulmonary valve leaflets fuses with each other, limiting the opening of the valve and narrowing the valve orifice; the junction of only two leaflets fuses as pulmonary valve bivalvular malformation; and the leaflet without junction leaves only a small hole in the center as monovalvular malformation. The pulmonary trunk is dilated after stenosis, sometimes extending to the left pulmonary artery, but the degree of dilatation is not exactly proportional to the severity of stenosis.
(B) Dysplastic pulmonary valve stenosis
The pulmonary valve leaflets are irregular and significantly thickened or nodular, with no adhesions between the leaflets, inflexible leaflet opening and closing, poorly developed annulus, and a non-dilated or poorly developed pulmonary trunk. There is often a family history of this disease, and most cases of Noonan syndrome are combined with this lesion.
Secondary changes in pulmonary stenosis are right ventricular centripetal hypertrophy and, in severe stenosis, small ventricular chambers and ischemic changes in the subendocardial myocardium. There is secondary enlargement of the right atrium, thickening of the atrial wall, and opening of the foramen ovale, or with an atrial septal defect.
II. Hemodynamics and clinical manifestations