Fig. 5.1
(a) Prenatal ultrasound performed in a fetus of 30 gestational weeks depicts a four-chamber view with a tripartite right ventricle. (b) Two weeks later in the 32 gestational week, the dysfunctional right ventricle was bipartite
Fig. 5.2
(a) Shows the right ventricular angiography in the lateral 90° plane; the ventricle is still bipartite (see Video 5.1), the pulmonary valve nearly completely closed. After crossing the valved membrane the right ventricular pressure decreased from supra- to sub-systemic pressure values by gradual balloon dilatation using a 5 mm (b), followed by a 7 × 20 mm balloon. The coronary support wire placed via the ductus in the descending aorta (DAO) was then used for duct stenting (c). Right ventricular pulmonary unit and the duct were delineated by angiography performed with hand-injected contrast medium (d). Based on the calculated length and width of the duct, a 4 × 20 mm Liberte premounted coronary stent was uneventfully implanted (e, f)
Fig. 5.3
Shown is a one-and-half (1.5) circulation with superior caval vein connection to the right pulmonary artery and antegrade flow through an obstructed right ventricular outflow tract, in which a melody-valve was implanted percutaneously. The passive laminar flow within the right lung was protected against the pulsatile flow of the right pulmonary circulation by a surgical pulmonary banding. PAP pulmonary artery pressure, PPVI percutaneous pulmonary valve implantation, RVP right ventricular pressure
We wish to summarize as follows:
The well-developed right ventricle has a triangular shape with tripartite morphology (inlet, trabecular, and outlet part). In addition to a genetic disposition, blood flow is a major determinant of RV growth. During fetal life and immediately postnatally the right ventricle can change from tri- to bi- and perhaps a unipartite morphology, and the latter may be associated with right ventricular dependent coronary blood flow disturbances, including coronary obstructions (Fig. 5.4, Video 5.3). In such circumstances the only therapeutic option is heart transplantation.
Fig. 5.4
Shown is a cartoon in which different morphologies of the right ventricle associated with pulmonary atresia (PAT) and intact ventricular septum are summarized. (a, b) Shows a tripartite right ventricle with an option of biventricular repair, (c) demonstrates a bipartite right ventricle with and (d) a unipartite ventricle, respectively. Reprinted with permission from Myung K. Park. In: Pediatric Cardiology for Practitioners. Mosby Elsevier; 5th edition 2008
However, the postnatally fully adapted and fully developed adult tripartite right ventricle has a three times greater compliance when compared to the left ventricle because of its three times thinner right ventricular wall diameter. The morphology of the RV is further characterized by a “moderator-band” (Latin “moderare” = contain) containing right ventricular dilatation, by the tricuspid valve, which has a papillary muscle fixed at the interventricular septum, and by a more apically positioned tricuspid valve annulus when compared to the mitral valve, which helps to identify the right from the left ventricle (Fig. 5.5). From a functional point of view, the right ventricle has, in comparison to the ellipsoid and coaxially contracting left ventricle, a time-delayed contraction pattern with movement from the inlet to outlet part; its coronary perfusion does not only occur during diastole, but preferentially during systole. The postnatal fully adapted RV is afterload sensitive and more preload dependent the younger the child. In general, the differences between the neonatal myocardium and the adult heart are summarized in Fig. 5.6.
Fig. 5.5
Depicted is a four-chamber view (MRI) in an adult patient with restrictive cardiomyopathy in whom a small atrial communication was performed by transcatheter technique to reduce left atrial pressure and the increased pulmonary artery pressure; the left atrium is still dominant, the PA-pressure decreased to normal values; In addition, the relationship of the mitral to tricuspid valve becomes demonstrable; the insertion of tricuspid valve at the ventricular septum is more apically positioned
Fig. 5.6
Characteristics of structure and function of the newborn heart. The newborn heart has the capability for hyperplasia and angiogenesis, and self-renewal
The principle of “form follows function” very much applies to the RV and its ability to adapt to different loading conditions. The volume loaded RV leads to ventricular dilatation, pressure loading of the RV to a myocardial hypertrophy, and the combination of obstruction and regurgitation to ventricular dilatation despite wall hypertrophy. Ischemia of the right ventricle leads to an acute right ventricular dilatation [8] and impairment of function. Figure 5.7 summarizes the major right ventricular stress factors: right ventricular ischemia, and right ventricular volume and pressure overload.
Fig. 5.7
Right ventricular (RV) failure might be caused by myocardial disease as ischemia, volume overload, high afterload, or all of these components together. CHD congenital heart disease, PH pulmonary hypertension, PR pulmonary valve regurgitation, TR tricuspid regurgitation
Congenital Heart Disease with a Volume Overloaded Right Ventricle
Three of the most common lesions associated with RV volume overload are: atrial septum defects, significant pulmonary and tricuspid valve regurgitation.
Atrial Septum Defect
Communications at the atrial level are described by their anatomical location. The ostium secundum defect, caused by an insufficiently developed septum primum, is with about 70 % the most prevalent ASD. An ASD-II exists as an isolated and also as an associated congenital defect. The ostium primum (ASD-I) defect is often associated with a cleft within the mitral valve. Sinus venosus defects are positioned at the connection of the superior or inferior caval vein respectively. A coronary sinus defect is rare [9]. In general, the pathophysiology of an ASD is described as follows: “a large (2 cm in adults) ASD results in hemodynamically significant left-to-right shunting, right ventricular volume overload and subsequently to right ventricular dilation [10].” Several questions remain unanswered in the context of an ASD associated with a shunt (Fig. 5.8a, b, Video 5.4): what causes left-to-right, right-to-left, or no shunting in a restrictive, nonrestrictive, or even missing interatrial septum (common atrium)? Considering normal anatomy, shunt-direction in an unrestricted atrial defect depends on the ratio of the right and left ventricular compliance; in a restrictive defect by the difference of the atrial pressures. Based on the above-mentioned normal right ventricular wall thickness the compliance of the right ventricle is three times that of the left, and therefore the Qp (pulmonary blood flow) to Qs (systemic blood flow) ratio is 3:1. Any higher Qp raises the question of an additional anatomical or functional cause, for example, an anomalous pulmonary venous connection or increased left ventricular end-diastolic pressure (LVEDP). An increased LVEDP combined with an unrestricted ASD might also be associated with severe pulmonary arterial hypertension (PAH) already during infancy. The mechanism remains currently unclear, but the assessment of PAH associated with an ASD has to include the measurement of the LVEDP and also a test occlusion of the ASD during LVEDP measurement, to find out whether the LVEDP increases during occlusion. Alternatively, incomplete closure by perforated patch or fenestrated occluder technique might be a sufficient therapeutic option; Fig. 5.8 the residual defect within the patch might be closed by a transcatheter device technique whenever the left ventricle is adapted to the acutely changed loading condition after ASD closure. Precapillary PH co-existing with ASD might be a hazard in children; in such cases, PAH might not be caused by the ASD, but based on currently unknown genetic disposition, in this case the ASD seemed to be associated.
Fig. 5.8
(a) Magnetic resonance imaging (MRI) four-chamber view of the heart of an 18-year-old young woman: right atrium and right ventricle are enormously dilated associated with a huge atrial septum defect (ASD) and “pseudo” small (34 mL/m2), but relatively unloaded left ventricle. (b) Intraoperative transesophageal echocardiogram shows the surgical patch by which the ASD was closed; in 3D-technique (top) the 3.7 mm perforated patch is nicely seen, which allows closure by a transcatheter device technique whenever the left ventricle is adapted to the acutely changed loading condition after ASD closure
An atrial right-to-left shunt, with well-tolerated cyanosis is observed in situations where the RV is poor developed or non-compliant, as it occurs in RV-hypoplasia, in patients with tricuspid and pulmonary valve atresia, stenosis, or severe insufficiency, as in the Ebstein anomaly.
An RV with normal anatomy tolerates volume overload due to an ASD well for many years. Symptoms caused by a significant atrial shunt are related to its pathophysiology, i.e., in young children a left-to-right shunt leads to active pulmonary hyperemia, which is responsible for pulmonary infections during infancy and early childhood and for the exercise intolerance of the adolescent. However, the exercise intolerance is in the beginning due to the limitation to increase the systemic blood flow—as during heavy exercise. The flow through the lungs is likely limited by a ratio of Qp/Qs ratio in a range of 3:1 at rest, and the regulating variable Qs of about 3.5 L/m2 × min. If there is no intrinsic LV diastolic dysfunction, acquired diastolic LV dysfunction occurs infrequently before the second decade of life. The same is true for the ASD associated with PAH. However, decades of volume overload can be detrimental and results in increased morbidity and mortality [11]. An interventional or surgical closure of an isolated ASD reverses the RV volume overload, best when performed during the first decade of life. ASD closure in an older patient can lead to an incomplete remodeling of an already structurally affected RV as well LV. Additionally, morbidity is further enhanced by atrial arrhythmias and left ventricular diastolic dysfunction [12–15]. Interventional ASD occlusion is the treatment of choice for most ASDs of the secundum type, while primum type and sinus venosus defects have to be closed surgically. A superior sinus venosus ASD is very frequently associated with a partial anomalous pulmonary venous return (PAPVR) of the right upper pulmonary vein, which aberrantly drains into the right atrium instead of the left atrium. PAPVR results in additional volume overload of the RV and should be corrected during the same operation if technically feasible.
Significant Pulmonary Valve Regurgitation
The absent pulmonary valve syndrome is a rare congenital variant of pulmonary valve regurgitation (Fig. 5.9). Already during fetal life the pulmonary vessel-bronchial unit might be affected by extreme pulmonary regurgitation; postnatally the pulmonary arterial branches are enormously dilated and may lead to airway obstructions, which might be life threatening despite immediate cardiovascular correction. However, acquired forms of pulmonary valve regurgitation are observed more frequently. The most frequent cause of significant pulmonary valve regurgitation is a repaired Tetralogy of Fallot (TOF), especially, when during corrective surgery a “transannular patch” has been used, which results in a loss of integrity of the pulmonary valve annulus and a certain degree of pulmonary valve sufficiency. Pulmonary regurgitation leads to RV dilation and can result in RV dysfunction [16]. There is a linear relationship between pulmonary regurgitation and RV size. Geometric remodeling after TOF repair can be associated with electrical remodeling characterized by a progressive right bundle brunch block and predisposition to atrial but in particular ventricular dysrhythmias [17]. The duration of the QRS complex correlates with RV volume load and serves as a primary predictor of life-threatening arrhythmias and sudden death. Adverse ventricular–ventricular interactions in patients with repaired TOF appear to be relevant but are still not well understood. There is a close relationship between RV and LV ejection fractions in patients with TOF [18, 19]. In addition, MRI studies show fibrosis of the LV myocardium in TOF patients [20], which illustrate that this disease, which was previously considered as an exclusive right ventricular disease, appears to be a biventricular disease. Timely pulmonary valve replacement can result in reverse remodeling of the RV dilation and may protect patients from adverse effects of pulmonary regurgitation. Especially, if serial imaging of the RV demonstrates progression of RV dilation, prompt referral for pulmonary valve replacement is usually recommended before RV dysfunction ensues. Serial follow-up measurements of RV volumes, ideally by MRI are recommended [21, 22]. Following pulmonary valve replacement, RV stress and volume overload usually decrease and RV function improves [23, 24].
Fig. 5.9
MRI in a patient with absent pulmonary valve syndrome. Characteristic is a pseudo-valve with extremely dilated central pulmonary arteries (+ dilated bronchial system) caused by systolic-diastolic shunt volume shift
Significant Tricuspid Regurgitation
Tricuspid valve dysplasia or Ebstein’s anomaly are malformations with a high incidence of tricuspid regurgitation. Ebstein’s anomaly is a complex heart malformation characterized by an apical displacement of the posterior and septal tricuspid leaflets (Video 5.5). As a consequence, the tricuspid valve shows significant regurgitation and the right heart chambers in particular the right atrium, can be significantly dilated. There are also forms of tricuspid valve dysplasia and Ebstein’s-like anomalies in patients with congenitally corrected transposition of the great arteries, where the tricuspid valve represents the systemic atrio-ventricular valve (see Chap. 8). Ebstein’s malformation is a rare defect, but from a pathophysiological point of view highly interesting. The malformation per se can present with a lifelong compensated hemodynamic situation but on the other end of the spectrum be associated with fetal hydrops and death before birth. As a rule of thumb, any congenital heart defect remains compensated as long as the tricuspid, mitral or common atrio-ventricular valve is not incompetent. A fetus with tricuspid dysplasia or Ebstein’s anomaly might develop heart failure because of ineffective forward flow across the pulmonary valve due to a combination of tricuspid regurgitation and functional- or morphological pulmonary atresia (PAT). The presence of pre- and persistent postnatal parallel circulations of the systemic and pulmonary vasculature is important for survival. However, if the fetal blood pressure rises after umbilical cut, the degree of tricuspid regurgitation increases, and the annulus of the tricuspid valve dilates. The pulmonary valve is held in a closed position by still high pulmonary vascular resistance and a pulmonary-aortic communication established by the ductus arteriosus; an open duct might be lifesaving, but the closed pulmonary valvular leaflets can develop to a morphological pulmonic stenosis or even atresia. The right atrium dilates in response to tricuspid regurgitation and becomes thin, and right-to-left shunting increases through the foramen ovale. Lymphatic flow is high due to the presence of high venous pressure, and the intravascular oncotic pressure (due to low fetal albumin) combine to produce a fetal hydrops. As a consequence of the described sequence of events, neonates who survive fetal heart failure, often present with profound cyanosis, and may require prostaglandins to maintain adequate flow of blood to the lungs during the early neonatal period when pulmonary resistance is high. In this situation, it is necessary to distinguish a functional from an anatomic PAT. Children with functional atresia can possibly be weaned off prostaglandins while maintaining adequate oxygen saturation as the pulmonary resistance falls. In neonates that cannot be weaned from prostaglandins, or in those with anatomic PAT, it is necessary to construct a systemic-to-pulmonary shunt to maintain adequate pulmonary blood flow by generating a surgical shunt or, as in our institution, by duct stenting [25, 26].
In addition to the described scenarios, severe tricuspid valve regurgitation is even rarely associated with a significant pulmonary valve regurgitation, which leads to pulmonary run off from the aorta through the duct, pulmonary artery, low pressure right ventricle and atrium; low cardiac output lastly leads to death, if the pulmonary valve is not immediately closed by surgical ligation or by transcatheter device placement.
Figure 5.10a, b shows chest film images from a newborn with Ebstein’s anomaly and respiratory failure. Right atrial plication in order to reduce the volume of the atrialized right ventricle might improve the lung volume.
Fig. 5.10
Shown is a chest X-ray (anterior-posterior view) of a newborn with Ebstein’s anomaly before and after right atrial reduction plasty with impressive improvement of the lung volume (Video by Dr. Grohmann, Department of Pediatric Cardiology, Freiburg)
In the older patients with Ebstein’s anomaly depending on the progressiveness of symptoms, a variety of surgical options exist to repair the malformed tricuspid valve depending on the progressiveness of symptoms. Most surgical strategies are based on techniques to mobilize the leading edge of the antero-superior leaflet, aiming to create a competent mono cusp valve with or without plication of the atrialized portion of the RV. Da Silva’s “Cone” operation is an additional surgical option, which generates impressive results [27]. Tricuspid valve replacement should only be the final option. Combining tricuspid repair with volume unloading Glenn shunt is an additional option, if the pulmonary vascular resistance allows cava superior right pulmonary artery connection (Fig. 5.11a–c).
Fig. 5.11
MRI pictures of an enormously dilated RV in Diastole and Systole as well as a bidirectional Glenn-anastomosis to unload the volume overloaded right ventricle due to a high degree of Ebstein tricuspid valve regurgitation
The question of early elective repair to preserve and possibly improve ventricular function, and reduce the risk of late arrhythmias in relatively asymptomatic children, continues to be debated [28, 29]. Ebstein’s anomaly carries one of the highest risks for arrhythmias because of associated pathological pathways such as WPW, which might contribute to the development of heart failure.
Other forms of tricuspid regurgitation are secondary, due to severe RV dilation causing tricuspid annular dilation, as it is seen in patients with RV dysplasia, in patients with RV dilation after a repair of TOF, or as a consequence of direct valvular trauma during reparative surgery [30].
Congenital Heart Disease Associated with a Pressure Overloaded Right Ventricle
Considering the anatomy, geometry, physiology, and normal right ventricular pressure-volume relations, the RV is several-fold more sensitive to changes in afterload compared to the left ventricle [31]. A small rise in afterload in an unprepared RV causes a rapid and linear decline in cardiac output. Such a scenario is often observed after heart transplantation in a recipient with pre-transplant increased pulmonary vascular resistance. Massive pulmonary thrombo- and air-embolism or any other acute obstructions of the pulmonary valve are situations in which the RV fails immediately. Its thin free wall is disposed to ventricular dilatation and acute impairment of the coronary artery perfusion (see also Chap. 9) the impact on the filling of the LV is often deleterious [32, 33].
Chronic pressure load is usually well tolerated by an adapted RV (see Chaps. 13 and 32), which may enable the right ventricle to generate systemic pressures (Chap. 8). Mild or moderate pressure load leads to a hypertrophic adaption of the RV myocardium, as well as an improvement of systolic RV function [34]. The well-adapted, hypertrophied RV can maintain its function for years. However, a normal sinus rhythm is needed and volume overload has to be avoided. The chronic pressure overloaded RV of patients with CHD is usually able to maintain its function well into the fourth or fifth decade of life. On the other hand, excessive RV pressure load triggers structural and functional maladaptation of the myocardium, which, if left untreated, ultimately results in RV dysfunction and failure. The transition from a compensated status to one of RV contractile dysfunction with decreased cardiac output, and elevated central venous pressures results from multifactorial, as yet poorly understood, causes. The type and degree of afterload, function of the tricuspid valve, responses of the LV and RV myocardium, and effects of associated abnormalities all modify the clinical course. Molecular mechanisms are being investigated; once identified to play an important role they will become therapeutic targets [35].
There are two major models exemplifying the chronic pressure overload of the RV in CHD:
RV outflow tract obstruction/pulmonary stenosis
Pulmonary valve stenosis represents the most frequent CHD, which generate a pressure (over-) loaded right ventricle. The pulmonary valve is mostly dome-shaped and in 10–20 % of patients dysplastic. However, obstruction may also occur at the sub- or supra-valvular level (Fig. 5.12). Dysplastic valve and pulmonary artery obstructions are frequently associated with Noonan, Williams-Beuren, and Alagille syndromes [36]. The severity of a pulmonary valve stenosis is defined by its pressure gradient across the subpulmonary outflow tract. However, the definition of a critical pulmonary valve stenosis is not determined by its gradient, but by its ability to permit a sufficient cardiac output at rest. A critical pulmonary valve stenosis or any other critical pulmonary obstruction is a life-threatening situation, which needs to be emergently treated. Pulmonary stenosis, when significant, results in compensatory RV hypertrophy, especially at the infundibular level [37]. When prominent, RVOT hypertrophy can lead to secondary dynamic sub-valvular stenosis. Pulmonary stenosis can also result in post-stenotic dilation of the pulmonary trunk, which is common in the dome form of pulmonary stenosis, which often extends to the proximal left pulmonary artery. This is thought to be the result of the high-velocity jet through the narrow valve orifice, which is anatomically aimed more toward the left pulmonary artery (natural continuation of the main pulmonary artery), and can produce unequal distribution of blood flow in favor of the left lung. However, intrinsic abnormalities of the pulmonary arterial wall also contribute to the pulmonary artery dilatation. Interestingly, post-stenotic dilatation of the pulmonary artery is rare in patients with dysplastic pulmonary valves. RV failure is rare and most patients with pulmonary stenosis remain asymptomatic for many years, even when the stenosis progresses from moderate to severe. Ever since percutaneous balloon valvuloplasty was introduced in 1982, it has become the treatment of choice for patients with valvular pulmonary stenosis. Balloon dilation is recommended for patients with a peak instantaneous Doppler pressure gradient >50 mmHg or a mean Doppler pressure gradient >35 mmHg [38]. Long-term outcome after balloon valvuloplasty is excellent, with a low rate of restenosis, whereas significant pulmonary regurgitation is rare [39]. Surgical treatment is warranted in patients with dysplastic valves in which balloon valvuloplasty is not successful or in patients with sub- as well as supra-valvular obstructions.
