Bubble contrast echocardiography in detecting pulmonary arteriovenous shunting in children with univentricular heart after cavopulmonary anastomosis

Quantitative plasma proteomic analysis in children after superior cavopulmonary anastomosis with pulmonary arteriovenous malformations

Approximately 1000 children are born every year in the United States with one effective cardiac pumping chamber, or single ventricle heart disease. One of the early causes of mortality in this population is pulmonary arteriovenous malformations (PAVMs), which allow blood to bypass gas exchange in the lungs. PAVMs most frequently occur in children after superior cavopulmonary anastomosis (SCPA), a procedure that redirects venous blood from the upper body to the lungs. Because plasma proteins are in part responsible for directing angiogenesis, we hypothesized that differential protein concentrations would be observed in superior caval blood among children after SCPA according to PAVM status. We performed quantitative plasma proteomics from 11 children with PAVMs and in seven children without PAVMs; an additional 11 children with Fontan circulation were included as a reference. Among children with SCPA, there were no significant differences in the plasma proteomes for those with and without PAVMs. When comparing children with Fontan circulation to those with SCPA and PAVMs, 18 proteins exhibited differential expression (10 downregulated and eight upregulated) in superior caval plasma. These results suggest that factors other than, or in addition to, plasma proteins may be responsible for single ventricle patients' susceptibility to PAVMs after SCPA. IMPACT: What is the key message of your article? We did not identify significant differences in plasma proteins when comparing those children with and without pulmonary arteriovenous malformations (PAVMs) after superior cavopulmonary anastomosis (SCPA). What does it add to the existing literature? The etiology of PAVMs in this population is likely due to factors other than, or in addition to, differences in plasma proteins. What is the impact? Further studies are needed to identify causes of PAVMs among children after SCPA.

Glenn circulation causes early and progressive shunting in a surgical model of pulmonary arteriovenous malformations

Pulmonary arteriovenous malformations (PAVMs) universally develop in patients with single ventricle congenital heart disease. Single ventricle PAVMs have been recognized for over 50 years but remain poorly understood. To improve our understanding, we developed a surgical rat model of Glenn circulation and characterized PAVM physiology over multiple time points. We performed a left thoracotomy and end-to-end anastomosis of the left superior vena cava to the left pulmonary artery (unilateral Glenn), or sham surgical control. To assess PAVM physiology, we quantified intrapulmonary shunting using two independent methods (bubble echocardiography and fluorescent microsphere injection). Additionally, we performed arterial blood gas measurements to assess oxygenation and plethysmography to assess ventilation. We identified pathologic intrapulmonary shunting by bubble echocardiography as early as 2 weeks post-Glenn, and shunting continued at 2- and 6-months post-Glenn. Shunting also progressed over time, demonstrated by increased shunting of 10 μm microspheres at 6 months. Shunting was accompanied by mildly decreased oxygenation but no differences in ventilation. Our surgical animal model of unilateral Glenn circulation recreates the clinical condition of single ventricle PAVMs with early and progressive intrapulmonary shunting. This model is poised to characterize single ventricle PAVM pathophysiology and lead to mechanistic and therapeutic discovery.

Angiographic tool to detect pulmonary arteriovenous malformations in single ventricle physiology

OBJECTIVE

Individuals with single ventricle physiology who are palliated with superior cavopulmonary anastomosis (Glenn surgery) may develop pulmonary arteriovenous malformations. The traditional tools for pulmonary arteriovenous malformation diagnosis are often of limited diagnostic utility in this patient population. We sought to measure the pulmonary capillary transit time to determine its value as a tool to identify pulmonary arteriovenous malformations in patients with single ventricle physiology.

METHODS

We defined the angiographic pulmonary capillary transit time as the number of cardiac cycles required for transit of contrast from the distal pulmonary arteries to the pulmonary veins. Patients were retrospectively recruited from a single quaternary North American paediatric centre, and angiographic and clinical data were reviewed. Pulmonary capillary transit time was calculated in 20 control patients and compared to 20 single ventricle patients at the pre-Glenn, Glenn, and Fontan surgical stages (which were compared with a linear-mixed model). Correlation (Pearson) between pulmonary capillary transit time and haemodynamic and injection parameters was assessed using angiograms from 84 Glenn patients. Five independent observers calculated pulmonary capillary transit time to measure reproducibility (intraclass correlation coefficient).

RESULTS

Mean pulmonary capillary transit time was 3.3 cardiac cycles in the control population, and 3.5, 2.4, and 3.5 in the pre-Glenn, Glenn, and Fontan stages, respectively. Pulmonary capillary transit time in the Glenn population did not correlate with injection conditions. Intraclass correlation coefficient was 0.87.

CONCLUSIONS

Pulmonary angiography can be used to calculate the pulmonary capillary transit time, which is reproducible between observers. Pulmonary capillary transit time accelerates in the Glenn stage, correlating with absence of direct hepatopulmonary venous flow.

Glenn circulation causes early and progressive shunting in a surgical model of pulmonary arteriovenous malformations

Background

Pulmonary arteriovenous malformations (PAVMs) universally develop in patients with single ventricle congenital heart disease (CHD). Single ventricle PAVMs have been recognized for over 50 years, yet they are poorly understood, and we lack any medical therapies. To improve our understanding of single ventricle PAVM initiation and progression, we developed a surgical rat model of Glenn circulation and characterized PAVM physiology over multiple time points.

Methods

Using adult rats, we performed a left thoracotomy and end-to-end anastomosis of the left superior vena cava to the left pulmonary artery (unilateral Glenn), or sham surgical control. To assess for PAVM physiology in the left lung, we quantified intrapulmonary shunting using two independent methods (bubble echocardiography and fluorescent microsphere injection) at 2 weeks, 2 months, and 6 months. Additionally, we performed arterial blood gas measurements to assess oxygenation and plethysmography to assess ventilation.

Results

We identified pathologic intrapulmonary shunting by bubble echocardiography as early as 2 weeks post-Glenn surgery, and shunting continued chronically at 2- and 6-months post-Glenn. Shunting also progressed over time, demonstrated by increased shunting of 10µm microspheres at 6 months. Shunting was accompanied by mildly decreased arterial oxygenation, but there were no differences in ventilation as quantified by plethysmography.

Conclusions

Our surgical animal model of unilateral Glenn circulation re-creates the clinical condition of single ventricle PAVMs with early and progressive intrapulmonary shunting. This model is poised to characterize single ventricle PAVM pathophysiology and lead to mechanistic and therapeutic discovery.

Graphic Abstract

Objective Quantification of Bilateral Bubble Contrast Echocardiography Correlates with Systemic Oxygenation in Patients with Single Ventricle Circulation

Bubble contrast echocardiography is commonly used to diagnose pulmonary arteriovenous malformations (PAVMs) in single ventricle congenital heart disease (CHD), yet previous studies inconsistently report a correlation between bubble echoes and oxygenation. In this study, we sought to re-evaluate the correlation between bubble echoes and oxygenation by assessing total bilateral shunting and unilateral shunting. We conducted a single-center, retrospective study of patients with single ventricle CHD and previous Glenn palliation who underwent a cardiac catheterization and bubble echocardiogram during the same procedure from 2011 to 2020. Spearman's rank correlation was performed to examine the relationship between total bilateral shunting and measures of systemic oxygenation, as well as unilateral shunting and ipsilateral pulmonary vein oxygenation. For all patients (n = 72), total bilateral shunting moderately correlated with peripheral oxygen saturation (SpO2) (rs = -0.44, p < 0.0001). For patients with Glenn/Kawashima circulation (n = 49), total bilateral shunting was moderately correlated (SpO2: rs = -0.38, p < 0.01). In contrast, unilateral shunting did not correlate with ipsilateral pulmonary vein oxygenation for any vein measured (p = 0.16-p > 0.99). In conclusion, the total burden of bilateral bubble shunting correlated with systemic oxygenation and may better reflect the total PAVM burden from all lung segments. Unilateral correlation may be adversely influenced by non-standardized approaches to pulmonary vein sampling.

Angiographic Tool to Detect Pulmonary Arteriovenous Malformations in Single Ventricle Physiology

Background

Individuals with single ventricle physiology who are palliated with superior cavopulmonary anastomosis (Glenn surgery) may develop pulmonary arteriovenous malformations (PAVMs). The traditional tools for PAVM diagnosis are often of limited diagnostic utility in this patient population. We sought to measure the pulmonary capillary transit time (PCTT) to determine its value as a tool to identify PAVMs in patients with single ventricle physiology.

Methods

We defined the angiographic PCTT as the number of cardiac cycles required for transit of contrast from the distal pulmonary arteries to the pulmonary veins. Patients were retrospectively recruited from a single quaternary North American pediatric center, and angiographic and clinical data was reviewed. PCTT was calculated in 20 control patients and compared to 20 single ventricle patients at the pre-Glenn, Glenn, and Fontan surgical stages (which were compared with a linear-mixed model). Correlation (Pearson) between PCTT and hemodynamic and injection parameters was assessed using 84 Glenn angiograms. Five independent observers calculated PCTT to measure reproducibility (intra-class correlation coefficient).

Results

Mean PCTT was 3.3 cardiac cycles in the control population, and 3.5, 2.4, and 3.5 in the pre-Glenn, Glenn, and Fontan stages, respectively. PCTT in the Glenn population did not correlate with injection conditions. Intraclass correlation coefficient was 0.87.

Conclusions

Pulmonary angiography can be used to calculate the pulmonary capillary transit time, which is reproducible between observers. PCTT accelerates in the Glenn stage, correlating with absence of direct hepatopulmonary venous flow.

Pulmonary Complications in Patients With Fontan Circulation: JACC Review Topic of the Week

The Fontan operation has resulted in significant improvement in survival of patients with single ventricle physiology. As a result, there is a growing population of individuals with Fontan physiology reaching adolescence and adulthood. Despite the improved survival, there are long-term morbidities associated with the Fontan operation. Pulmonary complications are common and may contribute to both circulatory and pulmonary insufficiency, leading ultimately to Fontan failure. These complications include restrictive lung disease, sleep abnormalities, plastic bronchitis, and cyanosis. Cyanosis post-Fontan procedure can be attributed to multiple causes including systemic to pulmonary venous collateral channels and pulmonary arteriovenous malformations. This review presents the unique cardiopulmonary interactions in the Fontan circulation. Understanding the cardiopulmonary interactions along with improved recognition and treatment of pulmonary abnormalities may improve the long-term outcomes in this growing patient population. Interventions focused on improving pulmonary function including inspiratory muscle training and endurance training have shown a promising effect post-Fontan procedure.

Pulmonary Vascular Sequelae of Palliated Single Ventricle Circulation: Arteriovenous Malformations and Aortopulmonary Collaterals

Children and adults with single ventricle congenital heart disease (CHD) develop many sequelae during staged surgical palliation. Universal pulmonary vascular sequelae in this patient population include two inter-related but distinct complications: pulmonary arteriovenous malformations (PAVMs) and aortopulmonary collaterals (APCs). This review highlights what is known and unknown about these vascular sequelae focusing on diagnostic testing, pathophysiology, and areas in need of further research.

A Comparative Study of Invasive Modalities for Evaluation of Pulmonary Arteriovenous Fistula after Bidirectional Glenn Shunt

Development of pulmonary AV fistula (PAVF) after bidirectional glenn shunt (BDG) results in significant cyanosis, impaired exercise performance, and increased morbidity and mortality. We attempted to detect and quantify PAVF in post-BDG patients by saline contrast transesophageal echocardiography (TEE) and compare with pulmonary angiography and pulmonary vein oximetry. This was a prospective study done between 2017 and 2018. Twenty-five children who underwent BDG and planned for cardiac catheterization prior to Fontan completion were included in the study. All patients underwent pulmonary angiography, oximetry, and saline contrast TEE at the time of cardiac catheterization. Twenty-two patients had undergone unilateral BDG surgery and three were palliated by bilateral BDG. The mean oxygen saturation was 80 ± 5.2%. Thirteen patients (52%) had preserved antegrade pulmonary blood flow. Eighteen patients (72%) had PAVF by angiography and oximetry, while 19 (76%) had PAVF identified by contrast echocardiography. There was moderate correlation between the degree of pulmonary venous desaturation and grading of PAVF by contrast echocardiography. PAVF was predominantly located in the lower zones of the lungs. Higher grades of PAVF were not seen in patients with preserved antegrade flow after BDG. Angiographically detected PAVF showed a steady increase with increasing delay to cardiac catheterization from BDG. Significant reduction in systemic saturation was limited to advanced grades of PAVF in patients after BDG. Saline contrast TEE, pulmonary venous oximetry, and pulmonary angiography equally identified PAVF in patients after BDG. Prognostic utility of the same needs to be assessed by long-term follow-up of these subjects.

Agitated saline contrast to delineate central venous catheter position in neonates

OBJECTIVE

Central venous catheter (CVC) insertion is required for the management of sick neonates. Ultrasonography/targeted neonatal echocardiography (TNE) with/without normal saline (NS) flush is used to identify CVC position. The present study compared the visibility and safety of agitated saline (AS) with normal saline (NS) flush.

STUDY DESIGN

This prospective interventional study included 110 CVC insertions, both umbilical venous catheterization (UVC) and peripherally inserted central catheterization (PICC). Catheter position was monitored by real-time TNE.

RESULTS

Overall visibility of catheter tip (combined UVC and PICC) was significantly better in AS (n = 55) compared with NS group (n = 55) [48/55 (87.2%) vs. 28/55 (50.9%); p < 0.0001]. Time to detect catheter tip by AS push was significantly less than that of NS push. There was no difference in the amount of saline flush required with either method. No major adverse effect was observed.

CONCLUSIONS

AS push can be used as a safe method to delineate CVC position in neonates.

Pulmonary arteriovenous malformations in children after the Kawashima procedure: Risk factors and midterm outcome

BACKGROUND

Pulmonary arteriovenous malformations (PAVMs) are the major cause of progressive cyanosis in patients palliated with bidirectional cavopulmonary connection (BCPC). The aim of our study is to analyze the occurrence of PAVMs in patients after Kawashima procedure, to study the effect of total cavopulmonary connection (TCPC) on PAVMs, to evaluate the effect of axillary arteriovenous fistula (AAVF) creation on PAVMs, and to study the risk factors for PAVMs.

METHODS

In this retrospective cohort study, all patients with left isomerism and azygous continuation of an interrupted inferior vena cava who underwent Kawashima procedure from July 2001 to December 2017 were included.

RESULTS

Twenty.six patients after Kawashima procedure were included in our study. PAVMs were diagnosed in 12 patients (46%). Five of these 12 patients underwent TCPC with complete resolution of hypoxemia. Three patients underwent AAVF creation, 2 had complete resolution, while 1 had partial resolution of hypoxemia. Fourteen patients (54%) did not develop PAVMs. Nakata index below 267 mm2/m2and McGoon ratio below 1.9 predicted the development of PAVMs with high sensitivity and specificity.

CONCLUSIONS

PAVMs represent a serious complication in patients who undergo Kawashima procedure. Small size of pulmonary arteries is an important risk factor for the development of PAVMs. Resolution of hypoxemia after TCPC completion supports the hepatic factor hypothesis. Early TCPC completion in these patients may help to avoid the development of PAVMs by restoring the hepatic factor. Resolution of hypoxemia after AAVF creation may support the lack of pulsatile flow hypothesis.

Asking Bubbles for Direction: Assessment of a Classic Glenn Shunt Using Agitated Saline Contrast Echocardiography

•

Glenn shunt is a common palliative surgery for congenital heart disease.

•

PAVMs are a frequent complication.

•

A saline contrast study can show bubbles first appearing in the left atrium.

•

Treatment options include coil embolization and surgery.

Aortopulmonary Collaterals in Single Ventricle Physiology: Variation in Understanding Occlusion Practice Among Interventional Cardiologists

Although aortopulmonary collaterals (APCs) frequently develop in patients with single ventricle palliation, there is a lack of understanding of pathophysiology, natural history, and outcomes with no universal guidelines for management and interventional practice. We conducted a study to assess the views held by interventional congenital cardiologists regarding the hemodynamic impact of APCs in patients with single ventricle palliation, and their embolization practice. An electronic survey using the Pediatric Interventional Cardiology Symposium (PICS) mailing list was conducted between February and March 2019 with one reminder sent 2 weeks after initial invitation for participation. Of the 142 interventional cardiologist respondents, 95 (66.9%) reside in North America and 47 (33.1%) worldwide. We elected to exclude the data from interventionalists outside North America in this analysis as it was not representative of worldwide practice. Hypoxemia was considered to be the most common trigger for development of APCs by 56 (58.9%) respondents. After completion of total cavopulmonary connection, 30 (31.6%) respondents reported the APC burden stays the same while 31 (32.6%) feel it decreases. In evaluating the burden of APC flow, only 4 (4.2%) reported measuring oxygen saturation at different pulmonary artery segments, 21 (22.1%) perform segmental aortic angiograms, and 18 (19%) perform selective bilateral subclavian artery angiograms. A majority of respondents, 71 (74.7%), occlude the feeder vessel at different locations, while 10 (10.5%) occlude only the origin of the vessel. Our study demonstrates significant variation in the understanding of the cause and prognosis of APCs in patients with single ventricle palliation. Furthermore, there is variation in the approach for diagnosis and management among interventional cardiologists. Further studies are required to improve understanding of APCs and develop universal management guidelines.

Long-term Outcomes of Extracardiac Total Cavopulmonary Connection for Apicocaval Juxtaposition

BACKGROUND

The long-term outcomes of a total cavopulmonary connection (TCPC) with an extracardiac conduit (ECC) for patients with apicocaval juxtaposition (ACJ) remain unclear.

METHODS

A total of 38 patients with ACJ who underwent TCPC with ECC between 1998 and 2014 were enrolled in this study. For 19 patients with a superior vena cava - inferior vena cava contralateral position, a long-curved route rounding the opposite side of the apex was selected (CC group). For 11 patients with a superior vena cava-inferior vena cava ipsilateral position, a long-curved route was principally selected (IC group); however, a short, straight route was selected for 8 patients because there was sufficient space behind the ventricular apex (IS group).

RESULTS

Follow-up was completed in all patients, with a mean follow-up duration of 13.2 ± 4.9 years. The angles of the caudal conduit anastomosis site measured from the frontal view of cineangiography had significantly straightened in the CC group from 1 year to 15 years (P < .05) and in the IC group from 1 year to 10 years (P < .05). There were 2 late mortalities and 6 reoperations during follow-up. Overall survival and freedom from reoperation rates at 15 years were 95% and 82%, respectively. There were no conduit-related or route-related complications such as death, reoperations, pulmonary venous obstructions, conduit obstructions, or pulmonary arteriovenous malformations in any of the groups.

CONCLUSIONS

Even though chronologic geometric changes of curved ECCs were observed, TCPC with ECC for patients with ACJ can be safely applied without conduit- or route-related complications in long-term follow-up.

Efficacy of bubble contrast echocardiography in detecting pulmonary arteriovenous fistulas in children with univentricular heart after total cavopulmonary connection

BACKGROUND

Development of pulmonary arteriovenous fistulas in patients with cavopulmonary anastomosis may result in a significant morbidity. Although the use of bubble contrast echocardiography with selective injection into both the branch pulmonary arteries in identifying pulmonary arteriovenous fistulas has been increasing, the actual efficacy of this diagnostic modality has not been properly evaluated. Thus, this study aimed to assess the efficacy of bubble contrast echocardiography in detecting pulmonary arteriovenous fistulas in children with total cavopulmonary connection.

METHODS

A total of 140 patients were included. All patients underwent cardiac catheterisation. Bubble contrast echocardiographic studies were performed by injecting agitated saline solution into the branch pulmonary arteries. Transthoracic echocardiograms that use an apical view were conducted to assess the appearance of bubble contrast in the systemic ventricles. Then, the contrast echocardiogram results and other cardiac parameters were compared.

RESULTS

No correlation was found between contrast echocardiogram grade and other cardiac parameters, such as pulmonary capillary wedge saturation and pulmonary artery resistance. Moreover, only 13 patients had negative results on both the right and left contrast echocardiograms, and 127 of the 140 patients had positive results on contrast echocardiograms even though they had normal pulmonary capillary wedge saturation. Results showed that bubble contrast echocardiography was a highly sensitive method and was likely to obtain false-positive results.

CONCLUSIONS

Bubble contrast echocardiography might be highly false positive in detecting pulmonary arteriovenous fistulas in patients with cavopulmonary anastomosis. We have to consider how we make use of this method. Further standardisation of techniques is required.

Saline Contrast Transesophageal Echocardiography in Fontan Patients: Assessment of the Presence, Type, and Size of Right to Left Shunts

Right to left (R-L) shunts resulting in cyanosis or systemic embolization occur after the Fontan procedure. The primary modality of diagnosing these is angiography. Successful delineation of these shunts in Fontan patients using selective saline contrast transesophageal echocardiography (SCTEE) may allow for reduced radiation and contrast exposure. We hypothesized that SCTEE could accurately determine the presence, type, and semiquantitative shunt size of R-L shunts in Fontan patients. SCTEE was performed in Fontan patients undergoing angiography for clinical indications. Injections were performed in six sites: mid-Fontan, right and left pulmonary arteries, superior and inferior vena cavae, and innominate vein. R-L shunt size was subjectively graded as 0 = absent, 1 = small, and 2 = medium or large based on echo contrast density in the left atrium. SCTEE was compared to angiography. 33 patients with Fontan were studied with median age 15 years, median weight 50.1 kg, and median O₂ saturation of 90% in the R-L shunt group and 95% in the no R-L shunt group. R-L shunt types included intracardiac shunts (ICS), veno-venous collaterals (VVCs), arteriovenous malformations (AVMs), and their combinations. SCTEE versus angiography results were the same for the presence, type, and size of R-L shunts in 79% (26/33). SCTEE identified shunts in 88% (29/33). Angiography identified shunts in 85% (28/33). Neither method missed any medium or large R-L shunts. SCTEE and angiography had similar accuracy. SCTEE accurately detected the presence, type, and size of R-L shunts in most Fontan patients in this study. This can be used to guide targeted angiography, reducing radiation exposure and contrast load.

Enhanced needle visibility by microbubbles generated with negative pressure using an in-plane technique

BACKGROUND AND OBJECTIVES

Our previous work found that needle visibility could be improved by introducing microbubbles into needles. The primary aim of this study was to test the hypothesis that the negative pressure method is superior to two other methods for enhancing needle visibility by introducing microbubbles into needles. The secondary aim was to evaluate the impacts of three factors on the visibility of microbubble-filled needles.

METHODS

In the first phase, three methods, including the negative pressure method, the mixing method and commercialized microbubbles, were applied to generate microbubbles inside needles for comparison of visibility in a porcine meat model. In the second phase, three factors were tested with a 2×5×5 factorial design to explore their influence on the visibility of microbubble-filled needles. The three factors included types of needles, insertion angles and types of contents inside needles. Needles filled with saline without microbubbles were used as the control in both phases. Insertion videos were recorded, and ultrasound images of needles were captured for the objective visibility analysis.

RESULTS

Needle visibility was highest in the negative pressure method group (p<0.001). Needle visibility was mainly determined by insertion angles (p<0.001). Microbubble-filled needles were more visible than control needles at 40°, 50° and 60° (p<0.001, p<0.001 and p<0.001, respectively).

CONCLUSIONS

Needle visibility can be significantly improved by microbubbles generated with the negative pressure method when insertion angles are 40°, 50° and 60° in porcine meat.

Physiological Fontan Procedure

Objective: The conventional Fontan circulation deviates the superior vena cava (SVC = 1/3 of the systemic venous return) toward the right lung (3/5 of total lung volume) and the inferior vena cava (IVC = 2/3 of the systemic venous return) toward the left lung (2/5 of total lung volume). A "physiological" Fontan deviating the SVC toward the left lung and the IVC toward the right lung was compared with the conventional setting by computational fluid dynamics, studying whether this setting achieves a more favorable hemodynamics than the conventional Fontan circulation. Materials and Methods: An in-silico 3D parametric model of the Fontan procedure was developed using idealized vascular geometries with invariant sizes of SVC, IVC, right pulmonary artery (RPA), and left pulmonary artery (LPA), steady inflow velocities at IVC and SVC, and constant equal outflow pressures at RPA and LPA. These parameters were set to perform finite-volume incompressible steady flow simulations, assuming a single-phase, Newtonian, isothermal, laminar blood flow. Numerically converged finite-volume mass and momentum flow balances determined the inlet pressures and the outflow rates. Numerical closed-path integration of energy fluxes across domain boundaries determined the flow energy loss rate through the Fontan circulation. The comparison evaluated: (1) mean IVC pressure; (2) energy loss rate; (3) kinetic energy maximum value throughout the domain volume. Results: The comparison of the physiological vs. conventional Fontan provided these results: (1) mean IVC pressure 13.9 vs. 14.1 mmHg (= 0.2 mmHg reduction); (2) energy loss rate 5.55 vs. 6.61 mW (= 16% reduction); (3) maximum kinetic energy 283 vs. 396 J/m3 (= 29% reduction). Conclusions: A more physiological flow distribution is accompanied by a reduction of mean IVC pressure and by substantial reductions of energy loss rate and of peak kinetic energy. The potential clinical impact of these hemodynamic changes in reducing the incidence and severity of the adverse long-term effects of the Fontan circulation, in particular liver failure and protein-losing enteropathy, still remains to be assessed and will be the subject of future work.

Echocardiography and Focused Cardiac Ultrasound

OBJECTIVES

The following review will describe the use of focused cardiac ultrasound performed by noncardiologists and its role as an acute hemodynamic monitoring tool in pediatric cardiac critical care.

DATA SOURCE

MEDLINE and PubMed.

CONCLUSION

The use of focused cardiac ultrasound has grown tremendously over recent years, and is increasingly being performed and interpreted by intensivists, anesthesiologists, and emergency medicine physicians. These imaging techniques are useful in establishing etiologies of cardiac dysfunction and should compliment the physical examination and standard hemodynamic monitoring.

Intrapulmonary arteriovenous malformation causing recurrent strokes

This case reveals a left pulmonary arteriovenous malformation (PAVM) as a cause of recurrent cerebral and cerebellar emboli. Extensive workup excluded other etiologies of emboli formation, and the patient was transferred to a tertiary care center for percutaneous embolotherapy. In the absence of a clear etiology, PAVM should be considered as a potential cause of recurrent cerebral emboli, especially in the absence of carotid disease, intracardiac thrombus, atrial septal defect, and patent foramen ovale. Diagnostic work-up for the PAVM can be cost effective and expedited by utilization of agitated saline contrast echocardiography, as noted in our case.

Clinical implications of pulmonary shunting on saline contrast echocardiography

Pulmonary right-to-left shunting can be encountered using transthoracic contrast echocardiography (TTCE) with agitated saline. Diseases associated with pulmonary shunting on saline TTCE include hereditary hemorrhagic telangiectasia (HHT), hepatopulmonary syndrome, and some congenital heart defects after partial or complete cavopulmonary anastomosis. Furthermore, small pulmonary shunts on saline TTCE are also documented in a proportion of healthy individuals. Pulmonary shunting carries the risk for severe neurologic complications due to paradoxical embolization. In HHT, additional chest computed tomography is recommended in case of any pulmonary shunt detected on saline TTCE, to evaluate the feasibility for transcatheter embolotherapy of pulmonary arteriovenous malformations. Furthermore, antibiotic prophylaxis is advised in case of any pulmonary shunt on saline TTCE to prevent brain abscesses after procedures with risk for bacteremia. The present review provides an overview of important aspects of pulmonary shunting and its detection using saline TTCE. Furthermore, advances in understanding the clinical implications of different pulmonary shunt grades on saline TTCE are described. It appears that small pulmonary shunts on saline TTCE (grade 1) lack any clinical implication, as these shunts cannot be used as a diagnostic criterion for HHT, are not associated with an increased risk for neurologic complications, and represent pulmonary arteriovenous malformations too small for subsequent endovascular treatment. This implies that additional chest computed tomography could be safely withheld in all persons with only small pulmonary shunts on saline TTCE and sets the stage for further discussion about the need for antibiotic prophylaxis in these subjects. Besides further optimization of the current screening algorithm for the detection of pulmonary arteriovenous malformations in HHT, these observations can be of additional clinical importance in other diseases associated with pulmonary shunting and in those healthy individuals with documented small pulmonary shunts on saline TTCE.

Pulmonary arteriovenous malformations after the superior cavopulmonary shunt: mechanisms and clinical implications

Children with functional single ventricle heart disease are commonly palliated down a staged clinical pathway toward a Fontan completion procedure (total cavopulmonary connection). The Fontan physiology is fraught with long-term complications associated with lower body systemic venous hypertension, eventually resulting in significant morbidity and mortality. The bidirectional Glenn shunt or superior cavopulmonary connection (SCPC) is commonly the transitional stage in single ventricle surgical management and provides excellent palliation. Some studies have demonstrated lower morbidity and mortality with the SCPC when compared with the Fontan. Unfortunately the durability of the SCPC is significantly limited by the development of pulmonary arteriovenous malformations (PAVMs) which have been commonly attributed to the absence of hepatic venous blood flow and the lack of pulsatile flow to the affected lungs. Abnormal angiogenesis has been suggested as a final common pathway to PAVM development. Understanding these fundamental mechanisms through the investigation of angiogenic pathways associated with the pathogenesis of PAVMs would help to develop medical therapies that could prevent or reverse this complication following SCPC. Such therapies could improve the longevity of the SCPC, potentially eliminate or significantly postpone the Fontan completion with its associated complications, and improve long-term survival in children with single ventricle disease.

Pulmonary Artery-Pulmonary Vein Fistula: Contrast Echocardiography using Agitated Saline for Indirect Evaluation of Adequacy of Surgical Repair

Direct right pulmonary artery-left atrial communications are rare causes of congenital cyanotic heart disease. Bypassing of the pulmonary circulation and the filtering function of the lung predisposes these patients to high risk of stroke or cerebral embolism. Contrast echocardiography using transesophageal echocardiography helps in detection and/or confirmation of diagnosis of these extracardiac shunts as two-dimensional echocardiography of the heart is essentially normal in such patients. Additionally, it can help in the assessment of adequacy of surgical repair in the postoperative period.

How to cite this article

Narula J, Choudhury M, Chowdhary UK, Kiran U. Pulmonary Artery-Pulmonary Vein Fistula: Contrast Echocardiography using Agitated Saline for Indirect Evaluation of Adequacy of Surgical Repair. J Perioper Echocardiogr 2014;2(2):61-64.

Normal and abnormal pulmonary arteriovenous shunting: occurrence and mechanisms

Severe cyanosis due to pulmonary arteriovenous fistulas occurs often after a bidirectional superior cavopulmonary anastomosis (Glenn operation) and also in some congenital anomalies in which hepatic venous blood bypasses the lungs in the first passage. Relocation of hepatic flow into the lungs usually causes these fistulas to disappear. Similar pulmonary arteriovenous fistulas are observed in hereditary haemorrhagic telangiectasia, and in liver disease (hepatopulmonary syndrome). There is no convincing identification yet of a responsible hepatic factor that produces these lesions. Candidates for such a factor are reviewed, and the possibility of angiotensin or bradykinin contributing to the fistulas is discussed.

Pulmonary artery endothelial cell phenotypic alterations in a large animal model of pulmonary arteriovenous malformations after the Glenn shunt

BACKGROUND

Longevity of the superior cavopulmonary connection (SCPC) is limited by the development of pulmonary arteriovenous malformations (PAVM). The goal of this study was to determine whether phenotypic changes in pulmonary artery endothelial cells (PAEC) that favor angiogenesis occur with PAVM formation.

METHODS

A superior vena cava to right pulmonary artery connection was constructed in 5 pigs. Pulmonary arteries were harvested at 6 to 8 weeks after surgery to establish cultures of PAEC and smooth muscle cells, to determine cell proliferation, gene expression, and tubule formation. Abundance of proteins related to angiogenesis was measured in lung tissue.

RESULTS

Contrast echocardiography revealed right-to-left shunting, consistent with PAVM formation. While the proliferation of smooth muscle cells from the right pulmonary artery (shunted side) and left pulmonary artery (nonshunted side) were similar, right PAEC proliferation was significantly higher. Expression profiles of genes encoding cellular signaling proteins were higher in PAECs from the right pulmonary artery versus left pulmonary artery. Protein abundance of angiopoietin-1, and Tie-2 (angiopoietin receptor) were increased in the right lung (both p < 0.05). Tubule formation was increased in endothelial cells from the right pulmonary artery compared with the left pulmonary artery (404 ± 16 versus 199 ± 71 tubules/mm(2), respectively; p < 0.05).

CONCLUSIONS

These findings demonstrate that PAVMs developed in a clinically relevant animal model of SCPC concomitantly with differential changes in PAEC proliferative ability and phenotype. Moreover, there was a significant increase in the angiopoietin/Tie-2 complex in the right lung, which may provide novel therapeutic targets to attenuate PAVM formation after a SCPC.

Management of the postoperative pediatric cardiac surgical patient

OBJECTIVE

To review the salient aspects and latest advances in the management of the postoperative pediatric cardiac patient.

DATA SOURCE

A Medline-based literature source.

CONCLUSION

The practice of pediatric cardiac intensive care has evolved considerably over the last several years. These efforts are the result of a collaborative effort from all subspecialties involved in the care of pediatric patients with congenital heart disease. Discoveries and innovations that are representative of this effort include the extension of cerebral oximetry from the operating room into the critical care setting; mechanical circulatory devices designed for pediatric patients; and surgery in very low birth weight neonates. Advances such as these impact postoperative management and make the field of pediatric cardiac intensive care an exciting, demanding, and evolving discipline, necessitating the ongoing commitment of various disciplines to pursue a greater understanding of disease processes and how to best go about treating them.

Regression of pulmonary arteriovenous malformations after transcatheter reconnection of the pulmonary arteries in patients with unidirectional Fontan

OBJECTIVE

Pulmonary arteriovenous malformations (PAVM) develop in patients with a lung deprived of hepatic blood flow. Unidirectional Fontan patients have superior vena cava (SVC) blood directed to the left or right pulmonary artery (PA), and inferior vena cava (IVC) and hepatic blood baffled to the contra-lateral PA. Cyanosis often develops due to PAVM in the lung deprived of hepatic blood. We report experiences with transcatheter PA reconnection in patients with unidirectional Fontan and PAVM.

DESIGN

Patients with unidirectional Fontan, cyanosis, and PAVM underwent transcatheter PA reconnection. Following simultaneous injection of contrast into PAs, a transseptal needle was used to puncture from one PA to the other. A balloon-mounted, uncovered stent was positioned bridging the pulmonary arteries. The procedure provided a nonrestrictive, permanent communication between the PAs. Results were retrospectively reviewed. Catheterization data and oxygen saturations before and after procedure were analyzed.

RESULTS

Six patients with a median age of 14 years (range 13-35 years) were identified. All patients had functional single ventricle with unidirectional Fontan and PAVM in the lung supplied solely by SVC flow. The reconnection procedure was performed successfully without complications in all cases. The median follow-up time for all 6 patients was 12.8 months (range 5.8-19.3 months). Median oxygen saturation was 0.86 (range 0.81-0.92) prior to the procedure, and 0.95 (range 0.92-0.98) on follow-up, with a median increase of 9% (range 8-11%).

CONCLUSION

Patients with unidirectional Fontan and PAVM demonstrate increased oxygen saturations following reconnection of PAs, suggesting regression of PAVM. This procedure can be performed safely using uncovered stents, and it is effective in improving systemic oxygen saturations.

The adult with a Fontan operation

Since 1971, the Fontan operation has been performed for the repair of single-ventricle physiology. This ingenious operation commits a single ventricle to the systemic circulation and takes advantage of cardiovascular and respiratory physiology to propel deoxygenated blood to the lungs, thus minimizing right-to-left shunting and cyanosis. Initially performed as a right atrial to pulmonary artery anastomosis, the Fontan operation has gone through evolutionary steps that have resulted in progressive improvements in mortality, morbidity, and outcomes. Inclusion of the right atrium in the slow-flowing Fontan circuit results in progressive dilation and incessant arrhythmias. This spurred forth efforts to create modifications that partially or completely exclude the atrium from the Fontan circuit. The transcatheter completion of the Fontan operation has been performed in a small number of patients and we expect minimally invasive, transcatheter, and hybrid interventions to play an important role in the future management of these patients.

Incorporation of the hepatic veins into the cavopulmonary circulation in patients with heterotaxy and pulmonary arteriovenous malformations after a Kawashima procedure

BACKGROUND

In patients with polysplenia syndrome and azygous continuation of an interrupted inferior vena cava (IVC), pulmonary arteriovenous malformations (PAVMs) are relatively common after bidirectional cavopulmonary anastomosis (BCPA, Kawashima procedure). Resolution of PAVMs after hepatic vein (HV) inclusion into the cavopulmonary circulation has been reported, but there has been no systematic investigation of the effects of this therapy in a population of more than 3 patients.

METHODS

We studied 16 patients with heterotaxy, univentricular congenital heart disease, and azygous continuation of the IVC who underwent incorporation of the HV into the cavopulmonary circuit for treatment of significant PAVMs after a Kawashima procedure.

RESULTS

The median preoperative systemic arterial oxygen saturation (SsaO2) was 76% (65%-85%), compared with 89% (85% to 92%) early after BCPA. Among 15 early survivors, the median early postoperative SsaO2 was 76% (56%-85%). In 11 of the 15 survivors, SsaO2 rose to 90% or greater within a year and remained at 93% or greater at follow-up of 2.8 to 10 years. Four patients had persistent hypoxemia and residual PAVMs at follow-up catheterization 1.5 to 8 years postoperatively; these patients had the most severe hypoxemia prior to HV inclusion, and in 2 the residual PAVMs were unilateral, with HV flow streaming to the contralateral lung, in which PAVMs had resolved.

CONCLUSIONS

Hypoxemia resolved after cavopulmonary incorporation of the HV in the majority of our patients with PAVMs after the Kawashima operation, presumably due to a combination of PAVM resolution and elimination of hepatic venoatrial right-to-left shunting. These findings support the theory that development of PAVMs is facilitated by exclusion of HV effluent from the pulmonary circulation.

Redirection of the hepatic venous flow for the treatment of pulmonary arteriovenous malformations after Fontan operation

A 45-month-old boy who had complex cardiac anomalies with interrupted inferior vena cava and polysplenia underwent extracardiac Fontan operation. He redeveloped deep cyanosis postoperatively. Cardiac catheterization showed a preferential flow of the hepatic venous blood to the right lung and arteriovenous malformations (PAVMs) in the left lung. He underwent revision of the conduit to attain balanced hepatic venous drainage with subsequent regression of the PAVMs and disappearance of cyanosis. Our experience shows that deficiency of hepatic venous flow played a crucial role in the development of PAVMs and that redistribution of the flow retained potential to ameliorate the pathological condition.

Effects of postural change on oxygen saturation and respiration in patients after the Fontan operation: platypnea and orthodeoxia

The aim of this study was to assess whether platypnea and orthodeoxia occur in Fontan patients. We divided 14 Fontan patients into 2 groups: 8 patients who had pulmonary arteriovenous fistulas and/or intra-atrial shunts (group A) and 6 patients who had neither pulmonary arteriovenous fistulas nor intra-atrial shunts (group B). They were compared with 9 controls (group C). Arterial oxygen saturation, minute ventilation per body weight and ventilatory equivalent for carbon dioxide were measured in the supine and then sitting positions. In group A, 1 patient had platypnea and 3 patients had orthodeoxia (changes in the saturation from the supine position to the sitting position were -4% to -7%) accompanied with slight hyperpnea, and all 4 patients had both pulmonary arteriovenous fistulas and intra-atrial shunts. Contrary, patients in group B had neither platypnea nor orthodeoxia. The saturation was significantly lower and the minute ventilation was significantly higher in the sitting position than in the supine position in group A (p < 0.05). The other groups showed no significant difference in the saturation or the minute ventilation between the 2 positions. All groups showed the ventilatory equivalent was significantly higher in the sitting position than in the supine position (p < 0.05 to 0.01). We demonstrated platypnea and orthodeoxia in Fontan patients with pulmonary arteriovenous fistulas and intra-atrial shunts. We believe platypnea and orthodeoxia should be regard as a complication in Fontan patients with pulmonary arteriovenous fistulas and/or intra-atrial shunts.

Maintenance of pulmonary vasculature tone by blood derived from the inferior vena cava in a rabbit model of cavopulmonary shunt

INTRODUCTION

After cavopulmonary shunt in which the superior vena cava is anastomosed to the right pulmonary artery, the right lung is in a unique condition without flow pulsatility and hepatic venous effluent. In a previous study, we reported that hypoxic pulmonary vasoconstriction disappeared in the pulmonary circulation after cavopulmonary shunt. In this study, however, to investigate the influence of pulsatility and hepatic venous effluent on hypoxic pulmonary vasoconstriction in the pulmonary circulation, we developed an alternative cavopulmonary shunt rabbit model that included hepatic venous effluent in the pulmonary circulation and reduced the pulsatility of the pulmonary arterial blood flow. We then observed the physiologic characteristics of the peripheral pulmonary artery after cavopulmonary shunt, specifically the disappearance of hypoxic pulmonary vasoconstriction.

METHODS

Sixteen Japanese white rabbits (12-16 weeks old) were used in this study. With general anesthesia, a cavopulmonary shunt was established by anastomosing the right superior vena cava to the right pulmonary artery in an end-to-side fashion. Of the 16 rabbits for the study, the proximal right pulmonary artery was completely ligated in 5 (atresia group) and partially ligated in 6 (stenosis group). Sham operation was performed in the remaining 5 rabbits. Two weeks later, we analyzed the response of the pulmonary artery (which was divided into three categories: segmental, lobular, and acinar level artery) to hypoxia (8% oxygen inhalation) with a specially designed video radiographic system. Morphometric analysis of the resistance pulmonary artery was done in each group after angiography.

RESULTS

Mean pressure and pulse pressure in the right pulmonary artery were not significantly different between the atresia and stenosis groups. The mean pulmonary artery pressures in the atresia and stenosis groups were 8 and 11 mm Hg, respectively. However, the pulse pressure was less than 2 mm Hg in both groups. The baseline internal diameter of the resistance pulmonary artery of the atresia group was significantly different from those of the stenosis and sham groups. In the atresia group, the resistance pulmonary arteries did not respond to hypoxia. In contrast, significant constriction (as assessed by percentage change of internal diameter of the resistance pulmonary arteries in the acinar and lobular level arteries) was observed in the pulmonary arteries of the sham and stenosis groups (atresia vs stenosis vs sham 0.4% vs - 19.0% vs - 18.8%, P = .01). In our morphometric study, we observed vasodilation of the resistance pulmonary artery with a thinner medial layer in the atresia group, consistent with the result of microangiography.

CONCLUSION

We developed a cavopulmonary shunt rabbit model in which the inferior vena caval blood was derived from the right ventricle. Hypoxic pulmonary vasoconstriction was maintained in the model with the blood flow from the right ventricle. When the blood flow was not maintained, however, hypoxic pulmonary vasoconstriction disappeared. This phenomenon strongly suggests that a substance in hepatic venous effluent partially regulates the physiological pulmonary vascular function in the rabbit lung.

Pulmonary arteriovenous shunting in the normal fetal lung

OBJECTIVES

We hypothesized that pulmonary arteriovenous shunting (PAVS) is normally present in fetal lungs and that cavopulmonary anastomosis-induced PAVS may represent a return to an earlier morphologic stage of development.

BACKGROUND

The surgical superior cavopulmonary anastomosis is performed as part of the staged Fontan pathway to treat univentricular forms of congenital heart disease; PAVS is a known sequela after superior cavopulmonary anastomosis and may have important clinical consequences. Although the etiology and true morphology of the structures responsible for PAVS are unknown, a leading theory is that PAVS is caused by absence of normal hepatic venous drainage to the pulmonary circulation.

METHODS

To determine whether normal fetal lungs demonstrate PAVS, we performed contrast echocardiograms on 13 fetal lambs, 8 neonatal lambs, 4 juvenile lambs, and 4 adult sheep using a blended mixture of saline and blood injected directly into the proximal pulmonary artery.

RESULTS

Pulmonary arteriovenous shunting was detected by direct epicardial echocardiography in all fetal lambs (n = 13) and neonatal animals studied at one and three days of life (n = 4) and in two of four animals studied at six to nine days of life. Pulmonary arteriovenous shunting was not present in animals studied at four weeks of life (n = 2) and in adult sheep (n = 5).

CONCLUSIONS

These studies demonstrate that PAVS is normally present in late gestation fetal and early neonatal lambs but then disappears during the later neonatal period. Furthermore, these findings suggest that PAVS associated with cavopulmonary anastomosis or other processes affecting the developing pulmonary circulation may represent a return to an earlier morphologic stage of development.

The biological "scrabble" of pulmonary arteriovenous malformations: considerations in the setting of cavopulmonary surgery

Pulmonary arteriovenous fistulas are vascular malformations, which, by virtue of producing abnormal vascular connections proximal to the units of gas exchange, result in intrapulmonary right-to-left shunting. These malformations or fistulas reflect at least in part disordered angiogenesis, and less commonly recruitment and dilation of pre-existing vascular channels. Pulmonary arteriovenous fistulas occur in a number of diverse clinical settings. Such fistulas are a well-established feature of the Weber-Osler-Rendu complex, or hereditary haemorrhagic telangiectasia, an autosomal dominant vascular dysplasia characterized by mucocutaneous telangiectasis, epistaxis, gastrointestinal haemorrhage, and arteriovenous malformations in the lung, brain, liver and elsewhere. They are also seen in the patient with acute or chronic liver disease, disease that is usually but not invariably severe, or those with non-cirrhotic portal hypertension. They may occur as congenital malformations, single or diffuse, large or small in isolation, and when large or extensive enough may result in hypoxaemia, clinical cyanosis, and heart failure. Cerebral vascular accidents are also a well-known complication of this disorder. An extensive literature has accumulated with regard to the pulmonary arteriovenous fistulas seen in the setting of the Weber-Osler-Rendu complex, and there is considerable information on the genetics, basic biology, clinical findings, complications and therapeutic interventions of these malformations in the setting of this syndrome. These issues, however, are not the primary considerations of this review, although some aspects of this fascinating disorder will be discussed later. Rather the focus will be on pulmonary arteriovenous malformations that develop in the setting of cavopulmonary surgery, and their relationship to the pulmonary arteriovenous fistulas occurring in the hepatopulmonary syndrome. The complex tapestry of these overlapping and intersecting clinical observations will be unfolded in the light of their chronology.

Pulmonary expression of the hepatocyte growth factor receptor c-Met shifts from medial to intimal layer after cavopulmonary anastomosis

OBJECTIVE

Pulmonary arteriovenous malformations occur in up to 60% of patients after cavopulmonary anastomosis. We compared the effects of cavopulmonary anastomosis and pulmonary artery banding on lung gene expression in an ovine model to study the abnormal pulmonary vascular remodeling after the exclusion of inferior vena caval blood independent of reduced pulmonary blood flow. We previously demonstrated by contrast echocardiography that pulmonary arteriovenous malformations develop by 8 weeks after cavopulmonary anastomosis but not after pulmonary artery banding. Hepatocyte growth factor, a pleiotropic factor with morphogenic, mitogenic, and angiogenic activities, signals via its specific receptor c-Met to induce the antiapoptotic factor Bcl-2. In this study, we examined pulmonary artery expression of these factors and their potential role in pulmonary artery remodeling after cavopulmonary anastomosis and pulmonary artery banding.

METHODS

Eighteen lambs aged 35 to 45 days were placed into 3 groups: cavopulmonary anastomosis, pulmonary artery banding, and control (n = 6/group). In the cavopulmonary anastomosis group, the superior vena cava was anastomosed to the right pulmonary artery in an end-to-end fashion. In the pulmonary artery banding group, the left pulmonary artery was banded to reduce blood flow to 20% of control. The control group had a simple right pulmonary artery clamp for 30 minutes. Lung was harvested for Western blot, reverse transcriptase-polymerase chain reaction, and immunostaining at 2 weeks (n = 3/group) and 5 weeks (n = 3/group) after surgery.

RESULTS

The expression of c-Met mRNA after cavopulmonary anastomosis was increased by twofold compared with the control or pulmonary artery banding group. The total lung expression of c-Met by Western blot was also up regulated at 2 weeks (P <.05). However, total lung expression of hepatocyte growth factor and Bcl-2 by Western and reverse transcriptase-polymerase chain reaction was not different from the control and pulmonary artery banding groups at both 2 and 5 weeks after surgery. Immunohistochemical analysis revealed that c-Met expression was localized to the intimal layer of the pulmonary artery in the cavopulmonary anastomosis, while its expression in the control and pulmonary artery banding lungs was localized to the medial layer. Localization of Bcl-2 on the intimal layer in lambs with cavopulmonary anastomosis followed the same pattern as c-Met.

CONCLUSIONS

After cavopulmonary anastomosis, pulmonary artery expression of the hepatocyte growth factor receptor c-Met and one of its downstream effectors, Bcl-2, had increased in the intimal layer and decreased in the medial layer. Because the hepatocyte growth factor signaling promotes increased endothelial cell survival, it may have a role in pulmonary artery remodeling following cavopulmonary anastomosis. In addition, the change of c-Met expression in the medial layer after cavopulmonary anastomosis suggests a possible mechanism for the smooth muscle cell alteration related to abnormal angiogenesis.

Hypoxic pulmonary vasoconstriction disappears in a rabbit model of cavopulmonary shunt

BACKGROUND

Cavopulmonary shunt is widely known as an interim staging procedure in patients with single-ventricle physiology. However, the physiologic characteristics of the pulmonary arterial system after cavopulmonary shunt are not clearly understood. In this article, we developed a rabbit cavopulmonary shunt model and studied the morphologic changes and physiologic characteristics (namely, hypoxic pulmonary vasoconstriction) of pulmonary arteries after cavopulmonary shunt.

METHODS

Male Japanese white rabbits aged 12 to 16 weeks were used for the study. In 5 rabbits, the superior vena cava was anastomosed to the right pulmonary artery in an end-to-side fashion, followed by a proximal side ligation of the right pulmonary artery (cavopulmonary shunt group). In 4 rabbits, the superior vena cava and the right pulmonary artery were dissected and clamped for 10 minutes without making a cavopulmonary shunt (sham group). Two weeks after the operation, we then measured the internal diameter of the acinar (internal diameter, 164 +/- 7 microm), the lobular (305 +/- 13 microm), and the segmental (669 +/- 16 microm) pulmonary arteries in both controlled and hypoxic conditions by using a specially designed x-ray television system. Also, morphometric measurements were made in the pulmonary arteries around the terminal bronchioles.

RESULTS

Two weeks after the operation, the arterial oxygen tension under room air conditions was significantly lower in the cavopulmonary shunt group than in the sham group (68.2 +/- 2.2 mm Hg vs 91.1 +/- 1.9 mm Hg; P =.01). The baseline internal diameters in the acinar and the lobular (resistance), but not the segmental (conduit), pulmonary arteries on the anastomosed side of the cavopulmonary shunt group were significantly larger than those of pulmonary arteries on the nonanastomosed side of the cavopulmonary shunt group and the sham group. Moreover, the pulmonary arteries on the anastomosed side of the cavopulmonary shunt group did not respond to hypoxia, whereas those on the nonanastomosed side of the cavopulmonary shunt and sham groups did have local internal diameter reductions in the acinar and lobular arteries (-1.1% +/- 1.0% in the anastomosed side vs -17.7% +/- 3.5% in the nonanastomosed side vs -20.9% +/- 6.1% in the sham group; P =.03). In the morphometric studies, the internal diameter of the pulmonary artery accompanying the terminal bronchiole in the anastomosed side of the cavopulmonary shunt group was significantly larger, and the ratio of medial thickness relative to the outer diameter was smaller compared with ratios in the nonanastomosed side of the cavopulmonary shunt group and the sham group.

CONCLUSIONS

We developed a rabbit cavopulmonary shunt model. In the anastomosed side of the cavopulmonary shunt group, the peripheral pulmonary arteries, which contributed greatly in regulating the pulmonary vascular resistance, had a local reduction in the basal vascular tone and no hypoxic vasoconstriction 2 weeks after the operation.

The role of oxidative stress in the development of pulmonary arteriovenous malformations after cavopulmonary anastomosis

BACKGROUND

Cavopulmonary anastomosis is used for palliation of cyanotic heart disease. Clinically significant pulmonary arteriovenous malformations occur in up to 25% of patients after surgical intervention. Cavopulmonary anastomosis creates several modifications to pulmonary physiology that may contribute to the development of pulmonary arteriovenous malformations, including reduced pulmonary blood flow and the exclusion of inferior vena caval effluent.

OBJECTIVE

By comparing the expression of angiogenic and stress-related proteins after cavopulmonary anastomosis and pulmonary artery banding, we sought to determine which genes were upregulated independent of reduced pulmonary blood flow.

METHODS

Lambs aged 35 to 45 days were placed into 1 of 3 groups: cavopulmonary anastomosis (n = 6), pulmonary artery banding (n = 6), and sham control (n = 6) animals. In our model pulmonary arteriovenous malformations are detectable by means of bubble-contrast echocardiography 8 weeks after cavopulmonary anastomosis. Lung tissue was harvested for Western blotting at 2 and 5 weeks after surgery.

RESULTS

Cavopulmonary anastomosis and pulmonary artery banding both increased angiogenic gene expression, but only cavopulmonary anastomosis induced the expression of endothelial stress-related genes. Vascular endothelial growth factor was upregulated 2.5-fold after both cavopulmonary anastomosis (P =.002) and pulmonary artery banding (P =.007). Only cavopulmonary anastomosis upregulated 2 stress-related genes, HO1 and GLUT1, 2.7-fold (P =.002) and 3.8-fold (P =.03), respectively. Hypoxia-inducible factor was upregulated 4-fold (P =.003) after cavopulmonary anastomosis. Pulmonary artery banding failed to induce the increased expression of any of these proteins.

CONCLUSIONS

Reduced pulmonary blood flow induces a pulmonary angiogenic response but not an endothelial stress response. These results suggest that oxidative stress is more relevant to the formation of pulmonary arteriovenous malformations than angiogenic signaling alone because pulmonary artery banding does not result in pulmonary arteriovenous malformations. Oxidative stress of the pulmonary endothelium resulting from cavopulmonary anastomosis may predispose the affected vasculature to arteriovenous shunting.

Cavopulmonary anastomosis induces pulmonary expression of the angiotensin II receptor family

BACKGROUND

Cavopulmonary anastomosis is used for palliation of cyanotic cardiac lesions. Postoperative development of pulmonary arteriovenous malformations can be significant in 10% to 25% of patients. To study the basis for formation of arteriovenous malformations, we developed an ovine model that reliably induces their development 8 weeks after cavopulmonary anastomosis. Previously, we found that cavopulmonary anastomosis inhibits the expression of pulmonary angiotensin-converting enzyme and suppresses angiotensin II production.

OBJECTIVE

This study examines the role of the angiotensin II receptors, type 1 and type 2, in this setting of pulmonary vascular remodeling.

METHODS

Lambs, aged 40 to 50 days, underwent cavopulmonary anastomosis. In age-matched control animals, a sham operation was performed. Messenger RNA and protein expression in lung specimens was measured at successive time points after cavopulmonary anastomosis or sham operations (n = 3 at each time point).

RESULTS

Angiotensin type 1 mRNA was maximally upregulated 2-fold at 5 weeks after cavopulmonary anastomosis (P =.006). Expression of angiotensin type 1 protein was increased at least 2-fold at 2, 5, and 15 weeks after cavopulmonary anastomosis (P =.005). Cavopulmonary anastomosis also increased angiotensin type 2 mRNA and protein expression at least 2-fold at 2 and 5 weeks (P =.02) after surgical intervention. At 15 weeks, expression of angiotensin type 2 mRNA and protein was unchanged from that seen in control animals. Immunolocalization in pulmonary tissue sections 2 weeks after cavopulmonary anastomosis revealed markedly enhanced staining of angiotensin II receptor type 1 in vascular smooth muscle and angiotensin II receptor type 2 in the endothelium of pulmonary arteries.

CONCLUSIONS

Rapid elevation in the expression of the type 1 and 2 angiotensin II receptors in the affected pulmonary vasculature after cavopulmonary anastomosis suggests their involvement in the pathologic vascular remodeling that occurs after cavopulmonary anastomosis.

Comparison of contrast echocardiography versus cardiac catheterization for detection of pulmonary arteriovenous malformations

Because clinical diagnosis of pulmonary arteriovenous malformations (AVMs) is difficult and cardiac catheterization invasive, contrast echo has been used to aid in the diagnosis. Correlation between contrast echo and catheterization data in these patients remains poorly defined. We examined the ability to detect pulmonary AVMs by contrast echocardiography, pulmonary angiography, and pulmonary vein saturations in patients who have undergone cavopulmonary (Glenn) shunts. Pulmonary vein saturations were obtained from catheterization reports. Blinded observers reviewed angiographic and contrast echo data retrospectively in 27 patients who had undergone a Glenn shunt and in 19 controls with biventricular hearts. Contrast echo was positive in 68 of 99 lungs (69%). Angiography showed AVMs in 65 of 98 lungs (66%). Pulmonary vein desaturation was found in 13 of 45 lungs sampled (29%). Only 10 of 38 lungs with positive contrast echo had pulmonary vein desaturation, but only 1 patient had pulmonary vein desaturation without positive contrast echo. The degree of desaturation did not correlate with severity of contrast echo return; 6 of 11 patients with 3+ contrast echo studies had normal pulmonary vein saturations. In a control group of patients with biventricular hearts, only 1 of 19 (5.3%) contrast echos was weakly positive. Contrast echo correlates poorly with angiography and pulmonary vein saturation for evaluation of AVMs. Contrast echo is extremely sensitive and often positive despite normal pulmonary vein saturation. Assessment of pulmonary vein desaturation in 100% oxygen may improve its sensitivity and correlation with contrast echo. Additional studies are needed to follow patients with mildly positive contrast echo studies to enable determination of their clinical relevance.

Complications associated with heterotaxy syndrome in Fontan patients

Enormous progress has been made in the last decade toward decreasing the risk of the Fontan operation and optimizing early and intermediate outcomes. Heterotaxy syndrome patients, with their extensive constellation of anatomic abnormalities, constitute a challenging group to manage surgically. Palliative procedures early in life are directed at creation of a satisfactory balance between pulmonary and systemic blood flow and at the same time assurance of unobstructed pulmonary venous return. For heterotaxy patients who survive beyond the newborn period, and are considered to have nonseptatable hearts, early reduction of the volume load of the functional single ventricle is extremely important. Early conversion from parallel pulmonary and systemic circulations to a superior cavopulmonary anastomosis (bidirectional Glenn or hemi-Fontan) is the preferred strategy. Traditionally, those patients with heterotaxy who survive initial surgical management have been considered a very high-risk population with respect to an eventual Fontan procedure. In heterotaxy patients it is particularly important to understand the unique and variable anatomy of the sinus node and conduction system, the potential for occult pulmonary venous obstruction, the tendency for development of atrioventricular valve regurgitation in volume loaded ventricles, and the potential for recurrent or persistent cyanosis because of intrahepatic shunting or pulmonary arteriovenous malformations.