Year : 2021  |  Volume : 14  |  Issue : 2  |  Page : 192--200

A systematic approach to epicardial echocardiography in pediatric cardiac surgery: An important but underutilized intraoperative tool


Neeraj Awasthy1, Sumir Girotra2, Nilanjan Dutta3, Sushil Azad2, Sitaraman Radhakrishnan2, Krishna Subramony Iyer2,  
1 Department of Pediatric Cardiology, Max Superspecialty Hospital, New Delhi, India
2 Department of Pediatric and Congenital Heart Sciences, Fortis Escorts Heart Institute, New Delhi, India
3 CTVS Surgeon, Narayana Superspeciality Hospital, Andul Road, Howrah, Kolkata, India

Correspondence Address:
Dr. Neeraj Awasthy
Department of Pediatric and Congenital Heart Disease, Max Hospital, Saket, New Delhi - 110 017
India

Abstract

Intraoperative echocardiography is an integral component of the peri-operative management of pediatric heart disease. It confirms the adequacy of surgery, identifies residual lesions, and can provide useful hemodynamic data. It, therefore, helps to decide on the need for revision of repair and guides the postoperative management strategy. Intraoperative echocardiography is done with the use of either an epicardial probe or a transesophageal probe. Epicardial echocardiography is a simple, useful modality and has the ability to perform imaging in cases where transesophageal echocardiography cannot be easily performed, for example, in low birth weight babies. We attempt to describe in detail the technique of epicardial echocardiography and the various views that we have found useful for a complete postsurgical evaluation. The limitations of the technique are also discussed in detail.



How to cite this article:
Awasthy N, Girotra S, Dutta N, Azad S, Radhakrishnan S, Iyer KS. A systematic approach to epicardial echocardiography in pediatric cardiac surgery: An important but underutilized intraoperative tool.Ann Pediatr Card 2021;14:192-200


How to cite this URL:
Awasthy N, Girotra S, Dutta N, Azad S, Radhakrishnan S, Iyer KS. A systematic approach to epicardial echocardiography in pediatric cardiac surgery: An important but underutilized intraoperative tool. Ann Pediatr Card [serial online] 2021 [cited 2021 Dec 2 ];14:192-200
Available from: https://www.annalspc.com/text.asp?2021/14/2/192/315287


Full Text



 Introduction



Intraoperative echocardiography is an important tool in the armamentarium of the surgeon. Echocardiographic assessment of the surgical repair on the surgical table at the end of surgery confirms not only the adequacy of repair but it also provides important information that helps titrate vasoactive and inotropic supports after cessation of cardiopulmonary bypass. More importantly, the timely detection of residual or previously undetected defects allows for remedial action at the same time, thereby eliminating a major cause of postoperative morbidity, mortality, and prolonged intensive care unit stay. Hospital resources are conserved and this is an important consideration in resource-limited environments.

Two diagnostic modalities are currently available for intraoperative echocardiography: transesophageal echocardiography (TEE) and epicardial echocardiography (EpiEcho). Although EpiEcho was the first modality to be used intraoperatively,[1],[2] it became unpopular with the advent of TEE.[3],[4] Most surgical teams worldwide now rely on intraoperative TEE. However, TEE necessitates the purchase of expensive TEE probes and the availability of a sonographer trained in the use of intraoperative TEE. Epicardial echocardiography on the other hand utilizes standard transthoracic probes and requires no additional skills other than knowledge of basic echocardiographic techniques.

This is of immense relevance to pediatric cardiac units in low- and middle-income countries which do a high volume of congenital heart repairs but are constantly struggling with financial and manpower constraints.[5]

EpiEcho has been the routine in our institution for the past 22 years and our experience extends to over 9000 EpiEcho examinations in this period of time.[6] EpiEcho is performed on all patients undergoing cardiac surgery through a mid-sternotomy incision. Evaluation of ventricular function forms an important component of every study.

Based on our experience, we feel that a systematically performed EpiEcho has many advantages over TEE and should be more widely utilized. We also describe a few additional views that we have found useful but are not hitherto described in the literature.[7],[8]

 Transesophageal Versus Epicardial Echocardiography



TEE has been energetically promoted as the procedure of choice for intraoperative echocardiography even in neonates – with the introduction of the miniaturized (albeit expensive) neonatal TEE probe. However, despite its overwhelming popularity and its published favorable influence on peri-operative clinical decision-making and eventual outcomes, TEE has limitations and a small but definite incidence of complications,[9],[10],[11] as enumerated below [Table 1]:{Table 1}

TEE imaging of some cardiac structures, e. g., the distal ascending aorta and aortic arch or right ventricular outflow tract (RVOT) and pulmonary artery (PA) bifurcation may be impaired by the interposition of the trachea and main bronchi and is therefore suboptimalThe TEE probe may occasionally be difficult or impossible to advance into the esophagus, and in patients with significant gastroesophageal pathology, the placement of a TEE probe may even be contraindicatedTEE may result in perioperative morbidity from oropharyngeal and gastroesophageal injury-causing dysphagia, gastrointestinal hemorrhage, or even rarely gastroesophageal ruptureThe TEE probe has to be inserted before administration of heparin to the patient and it continues to be in place for the entire length of the surgery. If an unplanned study is required in a heparinized patient then there is risk of bleeding•Then probe may suffer thermal damage during the rewarming phase of cardiopulmonary bypass. TEE probes are expensive, fragile, and require disinfection or sterilization before use. In a busy surgical unit, if multiple patients need to be evaluated, then multiple probes need to be available. Additional costs are also incurred in software upgrades and need for special storage facilities.

Epicardial echocardiography, on the other hand, was introduced as a diagnostic imaging modality to assist cardiac surgeons with intraoperative decision-making, more than a decade before the advent of TEE. A comprehensive epicardial echocardiographic examination can be performed efficiently and safely in almost any situation and in any size of patient.[12],[13] Some of the notable advantages of this technique are:

It is the only practical intraoperative imaging technique possible when a TEE probe cannot be inserted or when probe placement is contraindicatedEpiEcho provides more optimal image resolution when using higher frequency probesEpiEcho offers better windows for imaging anterior cardiac structures including the aorta, aortic valve (AV), pulmonary valve, and pulmonary arteries including the PA bifurcation and therefore is more useful in the evaluation of these structures[9]It requires no additional equipment other than what is available in a standard echocardiography unitThe surgeon can direct the views to interrogate the areas of the heart that he/she is most concerned about. The procedure can, therefore, be more goal directed. There is also less dependency on the availability of a trained echocardiographer[12]Concerns have been raised that the use of epicardial imaging predisposes to mediastinal infection due to potential cracks in the sterile sleeve cover. When a proper technique as described here is used, the risk of infection is low and possibly lesser than with a transesophageal probe that is placed in the GI tract, and reused repeatedly after disinfection, without being covered in a sterile sleeve. In resource-limited but busy units, sterility may be compromised when multiple TEE studies need to be performed with limited time for adequate disinfection between the cases.

EpiEcho also has some limitations. First, it can only be performed when the heart is exposed surgically. However, whenever the heart is exposed through sternotomy, epicardial imaging has a clear advantage. An argument often put forward against EpiEcho is that it requires interruption of the surgical procedure for imaging and so does not permit continuous echocardiographic monitoring.[9] However, in most instances, meaningful evaluation of the surgical repair is done only when cardiopulmonary bypass has been discontinued and stable hemodynamics have been achieved. The need for interruption of the surgical procedure, therefore, is not a tenable argument. Sometimes, the heart may be irritable and hemodynamic instability may preclude a detailed study. Patience and gentle handling of the probe often yields the desired result. With an enlarged heart, sometimes, true apical views may be difficult because of an inability access to the true apex of the heart.

The American Society of Echocardiography Council for Intraoperative Echocardiography has proposed a set of seven standardized and comprehensive views for epicardial examination.[11] We have used these routinely and in addition defined some more views which we feel provide for a more comprehensive study. The setup for epicardial imaging and the specific imaging views for evaluating specific areas of the heart and great vessels is described in the following narrative.

 Training Guidelines



There are no well-defined guidelines for training in EpiEcho in our country. ASE guidelines state that before a trainee should pursue independent interpretation and application of the information to peri-operative clinical decision-making, he or she should perform at least 25 epicardial examinations of which five are personally directed under the supervision of an advanced echocardiographer.[14]

 Epicardial Probe Preparation and Methodology



Epicardial echocardiography involves the placement of the transducer, encased in a sterile polyethylene sleeve, over the surface of the heart, for the acquisition of two-dimensional, color flow, and spectral Doppler images in multiple planes. The hardware includes:

An echocardiography machine with requisite transthoracic probes (5–12 MHz) [Figure 1]a. For neonates and infants, probes with the smallest footprint should be availableA sterile polyethylene sheath that is about 150 cm long and 8–10 cm wide and sealed at one end [Figure 1]bA sterile rubber band (which may be prepared on the table using the wrist portion of latex gloves) [Figure 2]aTwo artery forceps.{Figure 1}{Figure 2}

The setup involves the following steps:

The surgeon places an additional sterile drape over the anesthesia screen at the head and of the operation table as shown in [Figure 2]bThe surgeon clips the open end of the sterile sheath with an artery forceps and passes it to the echocardiographer at the head end of the table over the anesthesia screenThe echocardiographer fixes the edge of the sheath to the surgical drape on the other side of the screen with the second artery forceps so that the unsterile portion of the sheath does not slide back into the surgical field during manipulation [Figure 2]b•The transducer probe tip is coated with a blob of sterile acoustic jelly and is slid into the sterile sheath. The surgeon then grips the transducer with the sterile sheath and threads it down the remaining length of the sheath till an adequate length of the transducer is available for a comfortable study. The echo machine often has to be moved close to the head end of the table to achieve this. The sealed end of the sheath is then tightly folded over the tip of the transducer ensuring that there is no air bubble trapped and fixed in place with several loops of the rubber band. The study can now be performed by placing the probe on the epicardial surface of the heart. Sterile saline solution can be poured into the pericardial cavity to further enhance acoustic transmission from the probe to the epicardial surface.

The technique described above is designed to maintain sterility and also ensure that there is adequate jelly over the probe. The depth setting and the depth of transmit focus is then adjusted to visualize the near field. If a multifrequency probe is used, the frequency is increased to obtain the highest resolution image possible.

The surgeon obtains the images by appropriately manipulating the echocardiographic probe in the sterile arena and the image setting may be adjusted by the echocardiographer in the unsterile field. The images are seen and interpreted by them together. It is important to have a fluid interface between the probe and the heart. It is for this reason that the end of the probe is frequently wetted with squirts of saline to have optimum imaging.

Most of the views display the cardiac structures in the same orientation as the surgeon would view them intraoperatively and differ from the conventional views obtained in a standard transthoracic or transesophageal examination.

Imaging planes

For better understanding, we have listed the predominant structure that each specific view interrogates. Most of the evaluation is done with the probe placed at a single spot over the free wall of the right ventricle (RV). The long axis is marked in [Figure 3]. Rotation and tilting of the probe along the described axis enables imaging in the various views that are required for a complete evaluation. The only view requiring a change of probe position is the transaortic view where the probe is placed across the ascending aorta.{Figure 3}

Long-axis view

The echocardiographic probe is angled superiorly with marker pointing toward the patient's right shoulder to generate the epicardial long-axis view (LAX) view along the long axis of the heart [Figure 4]a. The echo probe is placed at the junction of the anterior and inferior surface of the heart. The probe is then gradually angled toward the patient's right shoulder. This view allows visualization of the inferolateral and anteroseptal walls of the left ventricle (LV) and the RV, left atrium (LA), left ventricular outflow tract (LVOT), AV, and mitral valve (MV) [Figure 4]b. Color Doppler interrogation of the AV and MV is possible in this view. With posterior and anterior tilt, different structures may be visualized as described below:{Figure 4}

Long axis: (without tilt) displays the interventricular septum, left ventricular outflow, AV, and the proximal part of the ascending aorta [Figure 4]bLong axis with leftward tilt [Figure 4]c displays the left ventricular inflow and pulmonary veinsLAX with rightward tilt [Figure 5]a allows for the evaluation of the right atrium and right ventricular inflow [Figure 5]b and [Figure 5]c. Spectral Doppler evaluation of the inflows may be done in this view. The rightward motion of the probe with marker oriented superiorly (12-o'clock) so that the transducer overlies the right atrium with marker oriented inferiorly shows a bicaval view of the systemic venous return and the atrial septum.{Figure 5}

Apical 4-chamber view

The apical 4-chamber view is obtained by sliding the probe toward the apex [leftward from the position in [Figure 4]a and orienting the probe rightward and posteriorly toward the inflows [Figure 6]a. The Doppler evaluation of both the valves may be done in this view. This view is important for both the inflows and interventricular septum evaluation [Figure 6]b. It is at times difficult to keep the probe stable at the apex. In such a scenario, the probe may be kept over the anterior surface of the RV (as close to the apex as possible) and oriented rightward and posteriorly. At times, the sternal retractor needs to be stretched to open up the sternum to expose the apex for this view. The heart may also be gently lifted up with a sponge in the pericardial cavity to improve access to the apex.{Figure 6}

The probe position directed further posteriorly may be useful not only to demonstrate TV inflow but also to investigate the coronary sinus [Figure 6]c.

Parasternal short-axis view (equivalent)

The RVOT view: This is obtained by sliding the transducer over the RVOT which is mostly on the anterior surface of the anterior ventricle and directing the transducer anteriorly with marker toward the left shoulder [Figure 7]a. Orienting a spectral Doppler beam parallel to blood flow permits the evaluation of RVOT. The RVOT, pulmonary valve, and proximal main PA can be visualized. Color flow Doppler can then be used to evaluate pulmonary regurgitation or stenosis [Figure 7]bShort-axis view (SAX) distal RVOT view: The transducer is directed toward the patient's left and slid superiorly. The transducer typically has to be rotated clockwise by approximately 30° from the LAX to develop this view [Figure 8]a. The marker faces the patient's left and the transducer beam is directed in the rightward direction. The right coronary cusp will be at the top of the monitor screen, the left coronary cusp will be on the right, and the noncoronary cusp will be on the left side of the screen adjacent to the interatrial septum [Figure 8]bShort axis with anterior tilt: Mild anterior tilt from this view identifies the RVOT including PA and proximal RVOT [Figure 9]a and [Figure 9]b. With color Doppler, this view may be used to demonstrate pulmonary stenosis or regurgitation. Doppler evaluation is used to quantitate the gradient across the RVOT [Figure 9]cShort axis with apical sweep: With the probe directed toward the patient's left (marker toward the left) and a sweep from the base to the apex, the whole of the interventricular septum can be scanned to look for muscular ventricular septal defects (VSDs) [Figure 10]a, [Figure 10]b, [Figure 10]c. Left ventricular function is well seen as well as areas of regional dysfunction. The MV and subvalvular apparatus can also be evaluated in the SAX [Figure 10]d.{Figure 7}{Figure 8}{Figure 9}{Figure 10}

Transaortic view

Transaortic views are obtained by keeping the transducer directly on the proximal ascending aorta.

Transaortic view (short axis): The transaortic SAX is obtained by positioning the transducer on the ascending with a marker toward the right [Figure 11]. The ultrasound beams transverse the base of the heart thus obtaining the images from the outflows.

With appropriate tilt of the probe, the PA bifurcation and proximal branch pulmonary arteries can be nicely visualized and also the SAX of the ascending aorta [Figure 12]. While the right PA is visualized coursing transversely beneath the aorta, the left PA is seen going away from the transducer probe. This view has a distinct advantage over TEE in imaging the PA bifurcation in situations where repair of the left PA has been performedTransaortic LAX: The transaortic LAX is obtained from the base of the heart (as described for SAX) with the transducer rotated by about 50°–90° from the SAX in an anticlockwise motion. The transducer is along the long axis of the heart [Figure 13]. The structure which is well identified in this view is the arch and the descending aorta [Figure 14] and [Figure 15]. When there is a right aortic arch, the marker of the probe is pointed in the direction of the right shoulder to get the same view{Figure 11}{Figure 12}{Figure 13}{Figure 14}{Figure 15}

To summarize the various views, suggested are listed below [Table 2]:{Table 2}

1. LAX

Long axis with leftward tilt shows LV, LVOT, and AVLAX with rightward (posterior) tilt

2. Four-chamber view

Four-chamber view with mitral and tricuspid valve inflowFour-chamber view with posterior tilt

3. Parasternal SAX (equivalent)

RVOT viewShort-axis distal RVOT viewShort axis with anterior tiltShort axis with apical sweep

4. Transaortic view:

Short axisLong axis.

Patch closure of ventricular septal defect

In doubly committed or perimembranous defects, a short-axis view with the transducer over the right ventricular free wall will demonstrate a residual defect and offer an opportunity for Doppler interrogation. The long axis may show the patch in other views. Short axis is important to demonstrate the left ventricular function [Table 3].{Table 3}

Intracardiac repair of tetralogy of Fallot

EpiEcho is preferable to TEE. The long axis and SAXs are used to interrogate the VSD patch and the RVOT view is used to assess the adequacy of the outflow resection. The transaortic view is used to display the branch pulmonary arteries [Table 3].

Total anomalous pulmonary venous return

EpiEcho is preferred over TEE because of the possibility of compression of pulmonary venous confluence posteriorly by the transesophageal probe.[4] The anastomosis and individual pulmonary veins can be viewed from short- and long-axis views. The transducer is placed over the right ventricular outflow or free wall and angled to image the anastomosis between the LA and the confluence in multiple planes.

Arterial switch operation for transposition of the great arteries

Visualizing the branch pulmonary arteries by TEE can be challenging due to their anterior position after the Le'compte maneuver. The area of interest is predominantly valvar and supravalvular, so epicardial echo is superior. With transducer placement directly over the right ventricular outflow and orientation of the index marker along the long axis of the outflow, the aortic and pulmonary valves as well as the neopulmonary and neoaortic anastomosis can be imaged. Apical view with cranial angulation will align the transducer with the outflows with the transducer over the PA bifurcation; the branch pulmonary arteries can also be imaged. Imaging of the coronary anastomoses and demonstration of flow in the coronary arteries is possible as well. Left ventricular function and regional wall motion abnormality may be seen in SAX. A few examples of residual defects picked up on epicardial echo are shown in Videos 1-5.

[MULTIMEDIA:1]

[MULTIMEDIA:2]

[MULTIMEDIA:3]

[MULTIMEDIA:4]

[MULTIMEDIA:5]

 Conclusion



Epicardial echocardiography is a resource-effective evaluation tool on the surgical table. Besides the evaluation of certain preprocedural surgical queries, its most important utility is the evaluation of a postoperative patient. The imaging views can be tailored to the respective lesion and its anticipated problems and residual lesions. The assessment of the residual lesion enables the surgeon to decide for a reoperative strategy and also to anticipate the possible problems in the immediate postoperative period. On the other hand, confirmation of an adequate repair allows the intensive care team to better plan the postoperative care.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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