Atrial Septal Defect (ASD)
ASD is the second most common congenital heart defect, occurring in women two to three times as often as in men. ASDs include the following types: ostium secundum (70%), ostium primum (20%), sinus venosus (10%), and coronary sinus (rare).
Although not a “true” ASD, a patent foramen ovale (PFO) persists secondary to failure of fusion of the septum primum and secundum (Figure 18–5). The prevalence of probe patent PFO is as high as 26% in autopsy series. Clinical problems attributed to PFO include paradoxical embolism leading to cerebrovascular accidents, decompression illness in divers, and migraine headaches. In a meta-analysis, the presence of a PFO alone increased the risk of recurrent cerebrovascular events fivefold, with an even higher risk in the presence of an atrial septal aneurysm.7 Other identified risk factors are the size of the PFO, the number of microbubbles in the left atrium during the first seconds after release of a Valsalva maneuver, and the presence of a eustachian valve directed toward the PFO,8 hence the rationale of PFO closure to protect against recurrent strokes. Elective surgical closure of a PFO diagnosed as an incidental finding during routine intraoperative TEE is not currently thought to be of benefit unless the patient has experienced a prior stroke of uncertain etiology or as a result of known paradoxical embolism. Some surgeons choose to repair a PFO if the atrium is to be opened as part of the scheduled surgical procedure. However, it should be noted that, even when the PFO is surgically repaired, the risk of recurrent neurologic events is not completely eliminated. Catheter-based PFO closure can be performed as an outpatient procedure, is associated with minimal risk, and has superseded surgical closure.9
Color-flow Doppler imaging across a patent foramen ovale (PFO) showing left-to-right shunting. (LA, left atrium; RA, right atrium.)
Ostium secundum defects are located in the mid-portion of the interatrial septum in the region of the fossa ovalis and are associated with mitral valve prolapse and mitral regurgitation. Ostium primum defects are located at the inferior portion of the interatrial septum and are associated with a cleft mitral valve with variable degrees of mitral regurgitation. Sinus venosus defects may be of the superior or inferior vena caval type. Most defects in this category are located near the entrance of the superior vena cava and right pulmonary veins high in the atrial septum (superior vena caval type) and are associated with anomalous return of the right upper and lower pulmonary veins (Figure 18–6). The relatively uncommon defects in the inferior vena caval–atrial junction are characterized by a deficiency of the inferior limbic septum. Coronary sinus defects occur from a partial or complete absence of the roof of the coronary sinus, creating a left-to-right shunt from the left atrium to the coronary sinus and then into the right atrium. These lesions are associated with a persistent left superior vena cava. The fundamental physiology of all these lesions is a transatrial shunt, and the direction and magnitude of shunting is determined by the size of the defect and the relative compliance of the ventricles.
Schematic showing the anatomic locations of the three most common atrial septal defects. (ASD, atrial septal defect; IVC, inferior vena cava; SVC, superior vena cava; PA, pulmonary artery; AO, aorta; PV, pulmonary vein.)
TEE provides excellent interrogation of the interatrial septum, with a sensitivity exceeding that of transthoracic echocardiography for the detection of ASDs. Two-dimensional interrogation of the entire atrial septum should be performed in transverse and longitudinal planes to ensure that small defects at the margins of the septum are not missed. The dimension of and the relative size of the defect to the entire interatrial septum should be determined. The best views are midesophageal four chamber, two chamber, and bicaval.
Secundum defects are located in the midportion of the interatrial septum in the region of the fossa ovalis (Figure 18–7), and ostium primum defects are located at the inferior portion of the interatrial septum (Figure 18–8). The bicaval view is particularly useful in detecting inferior and superior sinus venosus ASDs (Figure 18–9). The least common type of atrial septal defect, the coronary sinus communication, is defined by an enlarged coronary sinus with a deficient roof (unroofed coronary sinus), and is found in association with a persistent left superior vena cava. In the transverse axis, this is seen as an echo-free space wedge between the left upper pulmonary vein and left atrial appendage, and in the longitudinal plane, it can be identified as it enters the coronary sinus.
An ostium secundum atrial septal defect located in the midportion of the interatrial septum in the region of the fossa ovale. Arrows point to the margins of the defect.
An ostium primum defect located at the inferior portion of the interatrial septum often is best seen on the midesophageal four-chamber view. (LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.)
A sinus venosus defect in the posterior portion of the interatrial septum near the entrance of the superior vena cava is often best visualized with the bicaval view. A central venous catheter is seen passing through the superior vena cava into the right atrium. Arrows point to the margins of the defect. (LA, left atrium; RA, right atrium; SVC, superior vena cava.)
Color-flow Doppler allows for evaluation of flow across the defect and the detection of mitral or tricuspid regurgitation. Saline contrast injection may be useful in confirming right-to-left shunting and aid in detection of small lesions, but it must be used cautiously in light of the potential for cerebral embolism. Spectral Doppler is used to assess the hemodynamic consequences of the lesion. Measurement of the tricuspid regurgitant jet velocity can estimate systolic pulmonary artery pressures and diagnose pulmonary hypertension. In the absence of significant valvular disease, the shunt magnitude can be determined by measuring the velocity-time integrals (VTIs) across the RV and LV outflow tracts. A ratio of pulmonary to systemic flow (Qp/Qs) of greater than 1.5 is considered significant. Further intraoperative evaluation includes detection of associated lesions, assessment of adequacy of surgical repair and postoperative atrioventricular valve competency, and evaluation of ventricular function.
Ventricular Septal Defect (VSD)
Even though VSDs are the most common congenital anomaly recognized at birth, they account for only 10% to 15% of defects observed in adults with CHD.10 VSDs can occur in isolation or as part of complex lesions, and are classified by location into four major groups: (1) supracristal (also known as subarterial, outlet, subpulmonic, doubly committed, and infundibular); (2) infracristal (perimembranous); (3) muscular; and (4) atrioventricular canal (inlet) types (Figure 18–10).
Schematic showing the anatomic locations of ventricular septal defects.
The perimembranous type (Figure 18–11) accounts for 70% of all VSDs and involves the membranous septum. The defect is adjacent to the aortic valve and the annulus of the tricuspid valve contributes to the rim of the defect. When the VSD is primarily adjacent to the tricuspid valve, it is called a perimembranous inlet defect but when the defect extends primarily toward the aortic valve, it is referred to as a perimembranous outlet defect. In an inlet defect, shunting of blood occurs from the LV outflow tract to the right ventricle just beneath the septal leaflet of the tricuspid valve. There may be an associated tricuspid valve aneurysm or redundant tricuspid septal leaflet tissue that may plug the defect. In 10% of cases, a perimembranous defect can undermine the right aortic cusp, causing herniation of the cusp and aortic insufficiency. Rarely, a perimembranous VSD may lead to the formation of a communication between the LV outflow tract and the right atrium known as Gerbode defect. Small membranous VSDs may close spontaneously during childhood by approximation of the tricuspid valve septal leaflet across the defect. This defect closure may be undetectable in adulthood, or a residual anatomic abnormality, a “ventricular septal aneurysm,” may be visualized at the closure site.
Small perimembranous outlet ventricular septal defect (arrow) with left-to-right shunting.
Muscular-type VSDs (20%) are located in the central (Figure 18–12) or apical trabecular portion of the septum. They are often quite large, isolated, or multiple, and can be associated with pulmonary vascular disease. In some cases, RV outflow tract hypertrophy occurs in association with the VSD and serves to limit the severity of pulmonary hypertension (known as Gasul phenomenon).
Large muscular-type ventricular septal defect (arrow), in this case occurring as a complication of myocardial infarction. (LV, left ventricle; RV, right ventricle.)
The crista supraventricularis can be considered synonymous with the infundibular septum—the muscle separating the outflow tracts of the left and the right ventricles. The supracristal defects (5%) are usually circular and are located within the infundibular portion of the right ventricular outflow tract. The superior edge of the VSD is the conjoined annulus of the aortic and pulmonary valves; both the outlet septum and septal component of subpulmonary infundibulum are absent. Thus, the superior rim may have a direct relationship with the right coronary cusp of the aortic valve such that the right aortic leaflet may prolapse into the VSD, resulting in functional restriction of the size of the VSD but worsening aortic regurgitation. Even in the presence of only mild aortic regurgitation and a small VSD, this defect should be surgically closed to prevent rapid progression of aortic valve regurgitation.11
The atrioventricular canal or inlet type defects (5%) are seen close to the atrioventricular valves in the posterior or inlet portion of the septum and usually are caused by a defect in the formation of the atrioventricular septum. As such, they can be a part of a complex defect (see below), and are associated with a cleft in the mitral or tricuspid valve, common atrioventricular valve, and fibrous aneurysms.
The physiologic consequences of these lesions are determined by the size of the defect and the relative vascular resistance in the pulmonary bed. Patients are also at a higher risk for infective endocarditis.
Two-dimensional echocardiographic assessment is focused on defining the anatomic abnormality, whereas color-flow Doppler enhances the sensitivity of detection of all forms of VSD and helps to determine the magnitude and direction of the shunt. The ventricular septum is best interrogated in the ME four-chamber view, ME long-axis (LAX) view, ME RV inflow-outflow view, and the transgastric short-axis (TG SAX) view.4 The ME RV inflow-outflow view is especially helpful in differentiating a perimembranous VSD from a supracristal VSD (Figure 18–13). Unlike the more common perimembranous type of VSD, a supracristal VSD does not lie near the tricuspid valve, and the tricuspid valve is not involved in partial closure of the defect. Color Doppler of a supracristal defect in this view shows left-to-right shunting with turbulent flow directed into the pulmonary outflow tract. It is important to remember that this defect may be missed in the ME four-chamber view. Distortion of the right aortic leaflet and aortic regurgitation may be the only clue to the presence of a significant supracristal defect.
Schematic of the right ventricular inflow-outflow view showing the locations of a perimembranous (left) and supracristal (right) ventricular septal defect. (LA, left atrium; PA, pulmonary artery; RA, right atrium; TV, tricuspid valve; AV, aortic valve; RV, right ventricle.)
“Ventricular septal aneurysms” are characterized on M-mode echocardiography by a pattern of multiple linear echoes moving into the right ventricle during systole. Two-dimensional imaging reveals a saccular protuberance with a rapid flicking motion extending into the right ventricle during systole and realigning with the ventricular septum during diastole.
For all types of VSDs, continuous-wave Doppler helps in measuring the peak jet velocity, and hence estimating RV systolic pressures and pulmonary artery systolic pressures. The pressure gradient between the right and left ventricle can be calculated by using the simplified Bernoulli equation as follows:
where PLV is the LV systolic pressure, which equals the aortic systolic blood pressure in the absence of LV outflow obstruction, and PRV is the RV systolic pressure, which equals the pulmonary artery systolic blood pressure in the absence of RV outflow obstruction.
The intracardiac shunt can be quantified by calculating the stroke volume across the pulmonic and aortic valves to develop the Qp/Qs ratio. The location for determining the stroke volume depends on the location of the shunt. Qp is typically measured at the level of the RV outflow tract, whereas Qs is measured at the level of the LV outflow tract. A Qp/Qs of 1.5 or greater is considered significant. The shunt volume (different from the shunt fraction) is the product of the cross-sectional area of the color-flow jet at the defect and the flow-velocity integral of the continuous-wave Doppler systolic flow signal.12
Postoperatively, residual shunting across the patch has to be excluded. A large dehiscence of the patch (>3 mm) is an indication for immediate surgical revision. The tricuspid valve also needs to be investigated carefully as surgical repair of a VSD through the right atrium may involve detachment of the septal tricuspid leaflet and reconstruction of the leaflet once the VSD is repair is completed. Also, both the right coronary cusp and the septal tricuspid leaflet can be tethered during repair of a perimembranous VSD.4
Atrioventricular Canal Defects
Also known as atrioventricular septal defects (AVSDs) or endocardial cushion defects, these lesions are produced by anomalies of the atrial and ventricular septa and the adjacent parts of the atrioventricular (AV) valve. Three types are described: (1) partial AVSDs, consisting of two separate atrioventricular valves, an ostium primum ASD, as well as a cleft mitral valve; (2) transitional AVSDs, made up of an ostium primum ASD, a small ventricular septal defect, and two distinct atrioventricular valves; and (3) complete AVSDs, the most common defect, made up of an ostium primum ASD, inlet-type VSD, and a common atrioventricular valve that bridges both the right and the left sides of the heart, creating superior (anterior) and inferior (posterior) bridging leaflets. The Rastelli classification describes three types of complete AV canal defects based on the morphology of the anterior (superior) bridging leaflet, its degree of bridging, and its chordal attachments (Table 18–2).13 These bridging leaflets may have chordal insertions into both ventricles. In such cases it must be surgically divided into left and right portions and resuspended from a central patch to create separate atrioventricular orifices.
Table 18–2. Rastelli Classification. |Favorite Table|Download (.pdf)
Table 18–2. Rastelli Classification.
Rastelli type A
Superior bridging leaflet is divided in two portions at the septum, one mitral portion and one tricuspid portion, both attached firmly to the left and right side of the inter-ventricular septum (IVS), respectively, with long chordae.
Rastelli type B
Superior bridging leaflet is divided but not attached to IVS. Mitral and tricuspid components are attached to anomalous papillary muscle arising in right ventricle.
Rastelli type C
Superior bridging leaflet is not divided and is not attached to the IVS (free-floating leaflet).
Down syndrome occurs in 35% of patients with atrioventricular septal defect. Other associated cardiac lesions include tetralogy of Fallot, double-outlet right ventricle (DORV), total anomalous pulmonary venous connection, and pulmonary atresia. Subaortic stenosis also may occur from a discrete fibromuscular narrowing or from abnormal chordal insertions traversing the outflow tract. Subaortic obstruction can also develop postoperatively as a consequence of the reduction of LV outflow tract size after repair of the mitral valve cleft. Based on the size of the ventricular septal communication and the competence of the atrioventricular valves, patients may become symptomatic early in life or remain relatively asymptomatic until young adulthood. Surgical repair consists of patch closure of ASDs and/or VSDs and repair of the atrioventricular valves.
TEE defines the precise anatomy and allows detection of intracardiac shunts, chordal attachments, subaortic stenosis, and the presence and severity of left and right atrioventricular valve regurgitation. Shunting may occur left to right across the atria, left to right across the ventricles, or left ventricle to right atrium. Atrioventricular canal defects are readily visualized in the ME views. A four-chamber view shows that both atrioventricular valves are inserted at the same level and defines the presence and size of ASDs and VSDs (Figure 18–14). Chordal and papillary muscle arrangements of both atrioventricular valves also should be defined. The mitral valve is well visualized in a basal transgastric view at 0° and 90° and with three-dimensional imaging for number of leaflets and presence of a cleft. Color Doppler is useful to determine the presence and severity of atrioventricular valve regurgitation and to determine the location and size of shunts. Careful inspection of the right ventricle for signs of volume overload, inspection of the LV outflow tract for signs of obstruction, and exclusion of associated cardiac lesions completes the examination. Postoperative assessment includes detection of residual shunting, evaluation of atrioventricular valve regurgitation, iatrogenic atrioventricular valve stenosis, and subaortic stenosis.
Complete atrioventricular canal defect with a primum atrial septal defect (small arrow), inlet-type ventricular septal defect (large arrow), and a common atrioventricular valve. (LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.)