We present the case of a 9-day-old, 3480-g infant with hypoplastic left heart syndrome (HLHS) undergoing Norwood-Sano surgical palliation. Attempts to contact the patient’s guardians were unsuccessful. Our IRB waived the need for consent for publication of this report. After uneventful induction of general anesthesia, a pediatric transesophageal echocardiography (TEE) probe was inserted (6.0–7.0 MHz, Vivid E9 ultrasound machine GE BT 11.1, GE Medical Systems, Waukesha, WI). Precardiopulmonary bypass (pre-CPB) imaging confirmed the diagnosis of HLHS (aortic atresia, severe mitral stenosis, hypoplastic left ventricle) and demonstrated a restrictive interatrial communication, competent tricuspid valve, and qualitatively normal right ventricular (RV) systolic function (Fig. 1; Supplemental Digital Content 1, Supplemental Video 1, http://links.lww.com/AA/B351). The main pulmonary artery (PA) was dilated with patent branches, and there was evidence of bidirectional shunting across the ductus arteriosus.
The infant underwent a Norwood-Sano operation consisting of aortic reconstruction, atrial septectomy, and placement of a Sano shunt (RV to PA 5-mm Gore-Tex® graft, W.L. Gore & Associates, Inc., Flagstaff, AZ). TEE was used for intraoperative monitoring, to document adequate cardiac deairing, and for assessment of the surgical intervention. Post-CPB TEE demonstrated unrestrictive (left to right) atrial shunting, no tricuspid regurgitation, and fair RV systolic function (Figs. 2 and 3; Supplemental Digital Content 1, Supplemental Video 2, http://links.lww.com/AA/B352). There was no evidence of flow acceleration across the neoaortic outflow or neoaortic valve regurgitation. Filling of the native aorta and coronary vessels was documented. Interrogation of the Sano shunt showed the expected systolic–diastolic (“to and fro”) flow pattern by color Doppler and mild flow acceleration by spectral Doppler, with a peak shunt velocity of 3 m/s.
After initial weaning from CPB, the infant became acutely hemodynamic unstable (hypotensive and bradycardic: 60/30 mm Hg/135 bpm relative to baseline values: 80/40 mm Hg/150 bpm), likely related to surgical manipulation. TEE demonstrated decreased RV contractility manifested by abnormal free-wall motion and a qualitative decreased color Doppler flow signal in the native aortic root. After adjusting the inotropic/vasoactive strategy and optimizing the hematocrit (increased from 35% to 45%), the hemodynamics improved in association with increased myocardial contractility and an enhanced color flow Doppler signal in the native aorta (Supplemental Digital Content 1, Supplemental Video 3, http://links.lww.com/AA/B353).
HLHS is characterized by failure of development of left-sided cardiac structures and accounts for 1.4% to 3.8% of congenital heart disease (Fig. 4). After a stepwise surgical strategy, the ultimate goal is that of passively directing the entire systemic venous return to the pulmonary bed while allowing the morphologic RV to function as the systemic pump. The initial step or stage I (Norwood) palliation consists of aortic reconstruction by creation of a neoaortic outflow using the native pulmonary valve as the systemic semilunar valve, incorporating the native aorta, and augmenting the aortic arch to provide unobstructed systemic output. The morphologic RV in this setting ejects not only to the systemic circulation across the reconstructed neoaortic outflow but also to the pulmonary bed via a systemic to PA connection (right innominate/subclavian artery to right PA) or directly via Sano shunt (RV to PA extracardiac connection).1–3 An adequately sized atrial communication ensures unobstructed degrees of pulmonary venous blood into the right atrium where it mixes with systemic venous blood.
The main goals of presurgical TEE in HLHS are to confirm the preoperative anatomy, assess the atrial communication/need for septectomy, evaluate tricuspid and pulmonary valve morphology and function, and examine RV systolic function. Postsurgical TEE includes the following evaluation by 2-dimensional, spectral and color Doppler (relevant views noted): neoaortic valve to exclude significant valve dysfunction (midesophageal [ME] RV inflow–outflow, transgastric [TG] RV inflow–outflow), atrial septum to ensure unrestricted blood flow (ME 4 chambers and bicaval), and RV function (ME 4 chambers; TG midpapillary short axis, RV basal, RV inflow). The assessment of RV systolic function in this population is mostly qualitative given the acuity of the operative setting and the fact that variables such as tricuspid annular plane systolic excursion and others have not been validated in this anatomic substrate.4 Aortic arch obstruction, usually a progressive pathology, can occur after the Norwood procedure (11%–37% incidence), accounting for significant morbidity and late postoperative deaths.5 Although the upper esophageal window allows for TEE assessment of the aorta and portions of the aortic arch, the limited evaluation allowed by these views is inadequate to definitively exclude residual aortic arch pathology. A relevant aspect of the post-CPB TEE examination, as highlighted in this report, is evaluation of the Sano shunt. This should be interrogated in multiple cross sections that provide for 2-dimensional assessment of the proximal RV anastomosis (ME RV inflow–outflow and TG RV basal) and distal PA connection (ME ascending aorta). It is emphasized that this examination is not limited to the standard American Society of Echocardiography/Society of Cardiovascular Anesthesiologists views but likely requires additional imaging planes. As part of a complete study, the RV-PA conduit should be interrogated by both spectral and color flow Doppler. Flow across the Sano is characterized by a “to and fro signal,” systolic flow toward the PA (highest velocity), and diastolic flow toward the RV. Free regurgitation across the shunt reflects the valveless nature of the conduit. Expected findings include flow acceleration across the conduit from the RV chamber at systemic pressures ejecting into a lower pressure pulmonary bed. Although the adequacy of pulmonary blood flow is primarily established clinically (i.e., arterial Po2 or arterial oxygen saturation), TEE interrogation serves to confirm shunt patency and exclude significant obstruction as would be suggested by aliased high-velocity Doppler flow exceeding 3.5 m/s.6
This case demonstrates the utility of TEE as an intraoperative monitor and during the post-CPB evaluation of a neonate undergoing stage 1 palliation for HLHS. Given the complexity of this malformation and the fragile circulation after surgical intervention, any residual problem such as a restrictive interatrial communication, more than mild neoaortic or tricuspid regurgitation, obstruction at the level of the aortic arch, compromised pulmonary blood flow from a RV to PA connection, or impaired ventricular function, is poorly tolerated. Early recognition of these issues facilitated by TEE may prompt early management, limit perioperative morbidity, and contribute to improved patient outcomes.
Clinician’s Key Teaching Points
By Nikolaos J. Skubas, MD, Kent H. Rehfeldt, MD, and Martin J. London, MD
- The left ventricle and aorta are not developed in hypoplastic left heart syndrome (HLHS). The single right ventricle (RV) accepts systemic and pulmonary venous blood (via an atrial septal defect) ejecting it into the pulmonary artery (PA), whereas systemic flow into the hypoplastic native aorta occurs via a patent ductus arteriosus. In palliative surgery (Norwood procedure), the native pulmonary valve and PA are used to construct a neoaorta with the RV functioning as the systemic ventricle. The interatrial communication is enlarged, and systemic venous blood mixes with pulmonary venous blood before being rerouted passively to the PA via a Blalock–Taussig shunt (right innominate or subclavian artery to the right PA) or by means of an artificial (Sano) shunt between the RV and a PA.
- The preoperative anatomy should be verified and the results of the corrective surgery evaluated with transesophageal echocardiography (TEE). The function of the RV and the venous communication to the PA should be the main focus of the postprocedure TEE examination. Assessment of the RV free-wall systolic function is qualitative, because quantitative methods, such as tricuspid annular plane systolic excursion, are not validated in this patient group. The proximal and distal Sano shunt should be evaluated with 2-dimensional and Doppler imaging. Residual aortic arch pathology is difficult to interrogate with TEE because of imaging limitations by the interposed trachea and left bronchus.
- In this case of a 9-day-old infant with HLHS, an atrial septectomy facilitated unobstructed pulmonary venous flow to the right atrium, and a Sano shunt was used to provide blood flow from the RV to the PA. The inflow to the shunt showed no evidence of flow acceleration based on the color and spectral Doppler evaluation. A higher, forward (systolic) velocity and a lower, retrograde (diastolic) velocity were recorded because the Sano shunt lacks the normal semilunar valve.
- In a HLHS case that is corrected with Sano shunt, both systemic and pulmonary flows are generated by a single (RV) ventricle. This should be interrogated first in the event of intraoperative hemodynamic instability. Verification with TEE of unrestricted blood mixing at the atrial level and unrestricted flow via the Sano shunt (verified by peak velocity <3.5 m/s) is expected in successful palliative procedures.
Name: Domingo A. Bianchi, MD.
Contribution: This author wrote the manuscript and processed the images and clips.
Attestation: Domingo A. Bianchi approved the final manuscript.
Name: Adrian Balbella.
Contribution: This author helped to obtain the images for the echo round.
Attestation: Adrian Balbella approved the final manuscript.
Name: Pablo Motta, MD.
Contribution: This author critically reviewed the manuscript and helped process the images.
Attestation: Pablo Motta approved the final manuscript.
This manuscript was handled by: Martin London, MD.
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