Background
Multiple barriers to transthoracic echocardiography are present in critically ill infants immediately after surgery. Transesophageal echocardiography (TEE) is sometimes needed to obtain specific important information that transthoracic echocardiography fails to demonstrate. Formerly, the investigators used the AcuNav intracardiac echocardiographic (ICE) intravascular ultrasound transducer (8 Fr, 2.5 mm, 64-element crystal array, multifrequency [5.5–10 MHz], single longitudinal plane, linear phased array [Siemens Medical Solutions USA, Inc., Mountain View, CA]). Recently, the investigators have also used the microTEE transducer (8-mm transducer tip, 5.2-mm shaft, multifrequency [3–8 MHz], multiplane phased array, 32-element probe [Philips Medical Systems, Andover, MA]). Both transducers have two-dimensional, M-mode, color Doppler, and pulsed-wave and continuous-wave Doppler capabilities. The aim of this study was to compare the efficacy, safety, ease of insertion, capabilities, utilization, and cost of the AcuNav ICE transducer versus those of the microTEE transducer.
Methods
A retrospective review of all 50 postoperative critically ill infants who underwent TEE using the AcuNav and microTEE in the past 5 years was conducted. TEE was performed as ordered by the attending physician to answer a specific question not answered by transthoracic echocardiography.
Results
In all cases, the clinical information sought was obtained. The AcuNav ICE transducer was safe, easy to insert through the transnasal route, and did not require paralysis; however, it had a limited number of echocardiographic views and had greater sterilization cost. The microTEE transducer had greater echocardiographic capabilities and lower sterilization cost; however, it was slightly more difficult to insert, had a few manageable complications, and required more sedation and paralysis.
Conclusions
TEE in this setting has increased because of demonstrated efficacy and safety. Both the AcuNav ICE and microTEE transducers are useful and effective in this critical clinical scenario.
The utility, limitations, and complications of standard equipment and protocols for transesophageal echocardiography (TEE) in patients with congenital heart disease have been well established. However, there remains a subset of the small and most critically ill infants in whom TEE is performed with either an intracardiac transducer or a miniaturized transesophageal transducer. There are multiple barriers to obtaining complete transthoracic echocardiograms in these critically ill infants in the acute postoperative period. These include inadequate echocardiographic windows due to surgical dressings, chest tubes, partially open chest, intravascular catheters, and extracorporeal membrane oxygenation (ECMO) cannulas. TEE is sometimes needed to obtain specific important clinical information that transthoracic echocardiography (TTE) fails to demonstrate. Formerly, the only option available in this setting was the AcuNav intracardiac echocardiographic (ICE) transducer (Siemens Medical Solutions USA, Inc., Mountain View, CA), which was found to be relatively safe and effective because of its availability, small size, and ease of use. Recently, reports regarding the use of the microTEE miniaturized multiplane transesophageal echocardiographic probe (Philips Medical Systems, Andover, MA) in children have been published.
We herein present our experience with TEE using both the AcuNav ICE transducer and the microTEE transducer in this challenging patient population and clinical setting. In addition, we review previous published reports on the use of these transducers in small children.
The aim of this study was to determine the effectiveness to answer the designated clinical question, ease of insertion, echocardiographic modality capabilities, complications, changes in utilization, and relative cost in those undergoing TEE using the AcuNav ICE transducer versus the microTEE transducer.
Methods
We conducted a retrospective review of all perioperative echocardiograms and medical records from all critically ill infants who underwent TEE in the immediate postoperative setting within the past 5 years. All patients aged < 6 months who were in the immediate postoperative period and underwent TEE were included.
The AcuNav ICE intravascular ultrasound transducer is an 8-Fr, 2.5-mm, 64-element crystal array, multifrequency (5.5–10 MHz), single–longitudinal plane, linear phased-array probe with two-dimensional, color, and continuous-wave and pulsed-wave Doppler imaging modalities. It was connected to an Acuson Sequoia C256 echocardiographic system (Siemens Medical Solutions USA, Inc.). It has controls for anterior-posterior flexion and for right-left flexion. It lacks a temperature monitor. The transducer was manufactured for intravascular use, but it has also been used for TEE in infants and small animals. We must emphasize that the AcuNav ICE transducer is being used “off label” for TEE.
The microTEE transducer measures 8 mm wide at the transducer tip and has a 5.2-mm-diameter endoscope shaft. It is a multifrequency (3–8 MHz) multiplane phased-array 32-element probe with two-dimensional, M-mode, color Doppler, and pulsed-wave and continuous-wave Doppler capabilities. It was connected to an iE33 echocardiographic system (Philips Medical Systems). It has anterior-posterior flexion and transducer array 180° rotation controls. The use of this transducer in small infants has been reported. See Figure 1 , which demonstrates the relative sizes of the two transducers compared with a standard pediatric multiplane transesophageal echocardiographic transducer.
TEE was performed for clinical purposes as ordered by the attending intensivist or cardiac surgeon to answer a specific clinical question not clearly answered by TTE. All transesophageal echocardiographic examinations were specifically directed at answering important specific clinical questions and were performed by or under the direct supervision of one of the senior echocardiographers (D.A.R., V.W.C.). Because of the lack of a temperature monitor on the AcuNav ICE transducer, the study was limited to 15 min. The infant’s overall clinical status, level of sedation, hemodynamics, and ventilator parameters were monitored by a pediatric cardiac intensivist during the study. Transesophageal echocardiographic results were reviewed in detail, and comparisons were made between information obtained on TEE and the previous transthoracic echocardiographic examination. A positive yield was defined as specific clinically significant information obtained on TEE that could not be viewed clearly during TTE.
Additional information, including the ease of insertion, echocardiographic modality capabilities, complications, change in use, and relative cost in the group undergoing TEE using the AcuNav ICE transducer versus the microTEE transducer were compared.
This study complied with all institutional guidelines for patient confidentiality and safety, including institutional review board approval. Informed consent was obtained for all transesophageal echocardiographic studies.
Results
Patient Features
Fifty infants in the immediate postoperative period were studied. Twenty-five infants (weight range, 2.0–5.1 kg; median, 3.0 kg) underwent 27 studies with the AcuNav ICE transducer. Representative AcuNav ICE echocardiograms are presented in Figures 2 and 3 . Twenty-five infants (weight range, 1.8–5.4 kg; median, 2.9 kg) underwent 26 studies with the microTEE transducer. Representative micro TEE echocardiograms are presented in Figures 4-6 . All patients were critically ill postoperative infants located in the pediatric cardiac surgical intensive care unit. Patient demographics, diagnoses, and characteristics were similar in the two groups and are summarized in Table 1 . All patients underwent TTE within the 12 hours preceding TEE.
| Variable | AcuNav | microTEE |
|---|---|---|
| Number of patients | 25 | 25 |
| Number of studies | 27 | 26 |
| Age (days) | 1–36 (18) | 1–63 (12) |
| Body weight (kg) | 2.0–5.1 (3.0) | 1.8–5.4 (2.9) |
| Increased ventilator and oxygen | 0 | 3 |
| Hemodynamic changes | 0 | 0 |
| Major complications | 0 | 0 |
| Transnasal route | 20 | 0 |
| Difficult insertion | 0 | 3 |
| Sedation (fentanyl/midazolam) | 25 | 25 |
| Paralysis (vecuronium) | 11 | 23 |
| ECMO | 16 | 7 |
| Heparinized | 16 | 9 |
| Open sternum | 14 | 12 |
| Capabilities | Single plane | Multiplane |
| Efficacy | 27/27 | 26/26 |
| Studies per year | 7 | 22 |
| Additional sterilization cost per case | $400 | $0 |
Diagnoses were similar in the two groups, including a total of 20 with hypoplastic left heart, eight with double-outlet right ventricles, seven with heterotaxy syndrome, six with total anomalous pulmonary veins, and two with neonatal Ebstein’s anomaly. There was one of each of the following diagnoses: D-transposition, tricuspid atresia, pulmonary atresia with intact ventricular septum, Shone complex, truncus arteriosus, interrupted aortic arch complex, and ectopia cordis.
The most common surgical procedures performed before TEE were the Norwood-Sano procedure and the hypoplastic left heart stage 1 palliation hybrid procedure. Twenty-three infants were receiving ECMO, and 26 patients had open sternotomies with Gore-Tex (W.L. Gore & Associates, Newark, DE) patch skin closure. All patients were on ventilators and receiving at least two inotropic agents at the time of TEE. Sedation was achieved with fentanyl and midazolam boluses or continuous infusions.
Indications for TEE after failed TTE were to analyze aortopulmonary shunt patency; pulmonary vein obstruction; atrial septal defect patency, flow direction, and gradient; distal conduit patency; mechanism and severity of valve regurgitation; presence of thrombus or vegetation; presence, size, Doppler blood flow pattern, and pressure gradient of residual ventricular septal defect; residual valve obstruction; ventricular systolic function; and pulmonary hypertension.
Efficacy
The efficacy of both probes to obtain specific clinically important echocardiographic information that was not seen on TTE was comparable ( Table 1 ). In all cases, the specific clinical information sought was obtained.
Safety
No major complications were encountered in either group. No apparent minor complications were encountered in the AcuNav ICE transducer group. In three of the microTEE patients, inspired oxygen and increased peak inspiratory ventilator pressure were required to maintain stable respiratory status. No transesophageal echocardiographic examination was interrupted or stopped because of unmanageable clinical instability. No other complications occurred in the microTEE group in this series.
Ease of Insertion
All AcuNav ICE probes were inserted via the transnasal route. There was no difficulty inserting the AcuNav ICE transducer transnasally in any case. In three of the 22 microTEE patients, a laryngoscope was used to insert the probe after the usual maneuvers failed. In one of these infants, who was cannulated for ECMO in the neck vessels, a fiber optic endoscope was used to insert the microTEE transducer after the usual maneuvers failed. Insertion failure in these cases was due to interference from the endotracheal tube. The three infants with difficult microTEE insertion had body weights of 2.2, 3.2, and 3.6 kg.
Capabilities
The AcuNav ICE transducer’s capabilities include 2-dimensional, M-mode, and pulsed-wave, continuous color, and tissue Doppler modes. It was limited by the transducer array being fixed in only the longitudinal orientation. An additional limitation was that deep transgastric views, which are analogous to transthoracic subcostal views, were typically difficult or not possible to obtain. Given these limitations, it was not possible to obtain a complete segmental transesophageal echocardiographic examination with the AcuNav ICE transducer, whereas the microTEE transducer does provide the capabilities for a complete examination. Despite these limitations, the AcuNav ICE transducer was used effectively in each instance to obtain the specifically sought, albeit limited, echocardiographic information that was not seen on TTE.
The microTEE transducer included all modalities present on the AcuNav ICE transducer plus full multiplanar capabilities for rotating the transducer array from 0° to 180°. In addition, we were able to obtain deep transgastric views without difficulty in all cases. After using it in several cases, we noted deterioration in two-dimensional image quality with the microTEE transducer due to air leaking into the transducer array cover. This was caused by a manufacturing problem that has been repaired and has not recurred. When functioning properly, there was no apparent subjective two-dimensional, pulsed-wave Doppler, or color Doppler flow mapping image quality difference between the two imaging systems.
Changes in Utilization
At the beginning of this series, only the AcuNav ICE transducer was commercially available. Therefore, subjects enrolled early by default underwent TEE using this transducer. Starting in 2009, utilization of the microTEE transducer inevitably increased by the mere facts that it became available and it has multiplanar imaging capabilities. However, it did not eliminate the use of the AcuNav ICE transducer. In cases in which ECMO cannulas were present in the neck and the patient was fully heparinized, or when tenuous hemodynamic or respiratory status was present, the intensivist and surgeons occasionally requested that the AcuNav ICE transducer be used, because of its ease of insertion via the transnasal route and lesser requirement for sedation and paralysis.
Cost Comparison
An additional cost of $400 for shipping and sterilization of the AcuNav ICE transducer was incurred for each case, because the transducer requires gas sterilization by a company that specializes in sterilizing reusable multipolar electrophysiologic catheters. The microTEE transducer was cleaned using the usual recommended methods for transesophageal echocardiographic probe cleaning.
Results
Patient Features
Fifty infants in the immediate postoperative period were studied. Twenty-five infants (weight range, 2.0–5.1 kg; median, 3.0 kg) underwent 27 studies with the AcuNav ICE transducer. Representative AcuNav ICE echocardiograms are presented in Figures 2 and 3 . Twenty-five infants (weight range, 1.8–5.4 kg; median, 2.9 kg) underwent 26 studies with the microTEE transducer. Representative micro TEE echocardiograms are presented in Figures 4-6 . All patients were critically ill postoperative infants located in the pediatric cardiac surgical intensive care unit. Patient demographics, diagnoses, and characteristics were similar in the two groups and are summarized in Table 1 . All patients underwent TTE within the 12 hours preceding TEE.
