| Abstract|| |
Improved cosmetic appearance, reduced pain and duration of post-operative stay have intensified the popularity of minimally invasive cardiac surgery (MICS); however, the increased risk of stroke remains a concern. In conventional cardiac surgery, surgeons can visualize and feel the cardiac structures directly, which is not possible with MICS. Transesophageal echocardiography (TEE) is essential during MICS in detecting problems that require immediate correction. Comprehensive evaluation of the cardiac structures and function helps in the confirmation of not only the definitive diagnosis, but also the success of surgical treatment. Venous and aortic cannulations are not under the direct vision of the surgeon and appropriate positioning of the cannulae is not possible during MICS without the aid of TEE. Intra-operative TEE helps in the navigation of the guide wire and correct placement of the cannulae and allows real-time assessment of valvular pathologies, ventricular filling, ventricular function, intracardiac air, weaning from cardiopulmonary bypass and adequacy of the surgical procedure. Early detection of perioperative complications by TEE potentially enhances the post-operative outcome of patients managed with MICS.
Keywords: Cardiopulmonary bypass; Minimally invasive cardiac surgery; Transesophageal echocardiography
|How to cite this article:|
Jha AK, Malik V, Hote M. Minimally invasive cardiac surgery and transesophageal echocardiography. Ann Card Anaesth 2014;17:125-32
|How to cite this URL:|
Jha AK, Malik V, Hote M. Minimally invasive cardiac surgery and transesophageal echocardiography. Ann Card Anaesth [serial online] 2014 [cited 2019 May 25];17:125-32. Available from: http://www.annals.in/text.asp?2014/17/2/125/129844
| Introduction|| |
There is growing enthusiasm among cardiovascular surgeons for minimally invasive cardiac surgery (MICS). Increasing trends of MICS have been prompted by increasing demand from patients, technological advancement and improvement in the technical expertise of the surgeons. Patients have now become more aware of anatomical, physiological and psychological consequences of the surgery. Minimal incision and minimal anatomic disruption of the body tissues give better cosmetic results and provide psychological comfort to the patients. Patients are always afraid of the consequences of surgery. MICS reduces the duration of convalescence and allows patients to resume activities earlier and thus may reduce the fear of surgery. Psychological comfort decreases stress level of patients and helps pre-operative preparation before surgery. However, the advantages and disadvantages of MICS should be explained to patients in detail pre-operatively. Inadequate surgical exposure, inadequate surgical correction and residual anatomic defects are inherent risks of MICS.  Increased cardiopulmonary bypass (CPB) and aortic cross clamp (ACC) times have their own negative consequences. Inadequate cardioplegia delivery and myocardial protection may negate the benefits associated with MICS. Modi et al., in a meta-analysis reviewed the effects of minimally invasive mitral valve surgery on morbidity and mortality compared with conventional mitral valve surgery and demonstrated equivalent perioperative mortality, reduced need for reoperation for bleeding and a trend toward shorter hospital stay. These benefits were evident despite longer CPB and ACC times in the MICS group.  However, Society of Thoracic Surgeons database observed a higher incidence of stroke in less invasive mitral valve surgery with an odds ratio of two when compared with traditional sternotomy.  This increased incidence of stroke was mainly due to inadequate deairing, fibrillating-heart techniques and prolonged CPB and ACC times.
MICS is applicable to the broadest range of cardiac lesions and performed through a smaller incision preferably <10 cm contrary to the traditional wide sternotomy. Therefore, venous and aortic cannulation and cardioplegia delivery through antegrade route may not be possible. However, whenever antegrade route is feasible, it is adopted. Coronary artery bypass grafting (CABG) may be performed as minimally invasive direct coronary artery bypass grafting through a left thoracotomy approach. CABG is also done with the help of endoscope or robot through multiple small incisions to insert specially designed surgical or robotic instruments. Mitral valve repair or replacement is achieved through port-access (5-7 cm right inframammary crease, 4 th or 5 th intercostal space), hemisternotomy or right parasternal incision for insertion of thoracoscopic instruments. Robotic mitral valve surgery requires multiple small incisions for robotic arms and camera. Atrial septal defect (ASD) is repaired with the help of a thoracoscope inserted through a 5-6 cm right inframammary incision or with the help of robotic arms. In aortic valve surgery, various approaches such as J sternotomy, right anterior thoracotomy or right parasternal incision is adopted according to the surgeon's preference.
| Patient Selection|| |
Patients with single cardiac lesion are suitable candidates for MICS. Single cardiac lesions include involvement of a single cardiac valve, coronary artery disease (CAD) with fewer coronary vessels involvement and a single site accessible atrial or ventricular septal defect. However, combined lesions such as involvement of more than one valve, ASD with mitral stenosis (MS; Lutembacher syndrome) or CAD with valvular lesions are not an absolute contraindication. Nevertheless, surgeons do not prefer MICS in such a scenario owing to prolonged CPB and ACC times, which may result in inadequate myocardial functional recovery and negative effects on other vital organs like brain and kidney. Severe pulmonary artery (PA) hypertension potentially worsens the prognosis and MICS is avoided if the cardiac lesions are associated with it.  Even a single cardiac lesion like sinus venosus ASD may not be operable through minimal access. Dense calcification of mitral annulus precludes minimal access mitral valve replacement. MICS is usually not performed in acute bacterial endocarditis or as an emergency surgery.
The pre-operative diagnostic evaluation aims to confirm the suitability of the patient for MICS and includes echocardiography, computed tomography angiography (CTA), cardiac magnetic resonance imaging and cardiac catheterization. If any one of the diagnostic modalities gives uncertain diagnosis, then other diagnostic modalities is sought to confirm the diagnosis.
Technical and procedure related issues
Visualization and dissection of underlying tissues become very difficult after previous cardiac or thoracic surgery, mastectomy and chest radiation. Complete assessment of peripheral venous and arterial system of the lower limb is mandatory if the history and clinical examination suggests thrombotic, embolic or atheromatous diseases. A thorough investigation should be done if there is an evidence of varicosity, intermittent claudication, rest pain and calf muscle pain. CTA of the descending aorta with distal runoff in addition to an intra-operative transesophageal echocardiography (TEE) assessment of the thoracic aorta is currently recommended in older patients or in those with risk factors such as peripheral vascular disease, cerebrovascular disease, atherosclerotic aorta, or dialysis dependence.  Aortic cannulation through peripheral approach may prove hazardous in these patients. Navigation of guide wire becomes difficult and may dislodge the thrombus or atheromatous plaque [Figure 1]. Guide wire may enter into the false passages. Presence of an additional left sided superior vena cava (SVC) virtually excludes MICS in a patient. Cardioplegia delivery becomes inadequate in the presence of aortic regurgitation (AR) and leads to left ventricular (LV) distension. Moderate to severe AR should be excluded, except in patient undergoing minimally invasive aortic valve replacement, where direct coronary ostial cardioplegia delivery is possible after the opening of ascending aorta. Endovascular balloon occlusion of aorta is difficult when its diameter exceeds 4.5 cm.
|Figure 1: 3-D echocardiography shows an atheromatous plaque in ascending aorta in deep transgastric view|
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Role of TEE
Intra-operative TEE influences cardiac surgical decisions in more than 9% of all patients undergoing cardiac surgery, with the greatest observed impact in patients undergoing combined (CABG) and valve procedures.  TEE provides an invaluable help in several steps of MICS. Incidence of cardiovascular complications is significantly reduced if TEE is used judiciously. A study by Aybek et al., has justified the use of intra-operative TEE in minimal invasive mitral valve surgery. 
Evaluation of the atria and interatrial septum
Integrity of inter atrial septum (IAS) needs extensive evaluation, if the target lesion is other than ASD. Sinus venosus ASD accounts for 4-11% of all ASD and partial anomalous pulmonary venous connection is present in about 90% of patients with sinus venosus ASD.  It is best visualized in ME bicaval view and the site of the ASD are located near the opening of the SVC. The sinus venosus ASD may be inaccessible through the minimally invasive route and the surgeons may not be able to close the defect properly with diversion of the anomalous pulmonary vein to the left atrium. Coronary sinus (CS) type ASD is frequently associated with left sided caval vein and the requirement of additional percutaneous central venous cannulation rules out the possibility of MICS. Isolated ostium secundum or primum type of ASD is operable through a minimal incision. Other intracardiac shunts such as ventricular septal defect and valvular abnormalities must be excluded prior to incision. The incidence of MS in patients with ASD is 4%; the incidence of ASD in patients with MS is 0.6-0.7%.  Rheumatic heart diseases usually involve multiple valves. So, if isolated mitral or aortic valve lesion has been identified for MICS, then a definite conclusion must be made about the normalcy of other valves. CABG is possible through a minimal incision provided fewer grafts are required and concomitant valvular abnormalities are excluded.
Assessment of ventricular function
Pre-operative evaluation of systolic and diastolic ventricular function is crucial for predicting the prognosis and inotropic requirements. LV systolic function is assessed and graded by fractional area changes, ejection fraction and regional wall motion abnormalities. Visual inspection of LV wall motion may be good enough in judging the myocardial contractility. Assessment and grading of diastolic dysfunction require application of pulsed wave Doppler (PWD) at the tip of mitral leaflets and at lateral and medial mitral annulus during tissue Doppler imaging. Calculation of E/A, E ' , E/E', duration of 'a' wave, duration of atrial reversal, ventricular propagation velocity, left atrial volume, deceleration time and isovolumetric relaxation time are vital for assessing the severity of diastolic dysfunction. Patients with severe ventricular systolic or diastolic dysfunction may not tolerate the prolonged CPB and ACC times. Abnormally prolonged bypass delays the functional recovery of the heart and may worsen the prognosis.
Assessment of pulmonary hypertension
Measurement of tricuspid and pulmonary regurgitation pressure gradient estimates PAP. If cardiac catheterization has not been done to assess pulmonary vascular resistance (PVR), then PVR should be calculated by measuring maximum tricuspid regurgitation velocity and the time velocity integral of the pulmonary blood flow across the pulmonary valve. The PVR is calculated by the following formula: PVR (Woods unit) = TRV/VTI (RVOT) × 10 + 1.6, where TRV: Tricuspid regurgitant velocity in m/s, VTI: Velocity time integral across the right ventricular outflow tract. PAP should also be estimated to assess the severity of pulmonary hypertension. PA systolic pressure = tricuspid regurgitation gradient + right atrial (RA) pressure and PA diastolic pressure = pulmonary regurgitation gradient + RA pressure.
Reestablishment of diagnosis and exclusion of other cardiac pathologies are vital before proceeding to MICS. The SVC should be evaluated for its patency for successful venous cannulation and ensuring continuous venous drainage. However, only the lower part of the SVC is visible on TEE in midesophageal (ME) bicaval or modified bicaval view. Continuous and an adequate venous inflow into the right atrium (RA) from SVC can be confirmed by applying color and PWD at RA-SVC junction. RA thrombi and myxomatous lesions should be excluded. RA can be visualized adequately in ME four chamber view, right ventricular inflow-outflow views and deep transgastric inflow-outflow view. Continuous and adequate venous drainage requires cannulation of both superior and inferior vena cava. The SVC is cannulated percutaneously through the right internal jugular approach. TEE helps in the navigation of guide wire and subsequent threading of venous cannula. Probe should be kept in ME position for acquiring bicaval or modified bicaval view during guide wire navigation [Figure 2] and [Figure 3].  Venous cannula should be kept at least 2 cm above the RA-SVC junction. This gives ample space for SVC snaring. If a single venous cannula is inserted for the complete venous drainage from IVC and SVC both, then an IVC cannula is placed through the femoral vein and advanced-up into the RA and into the lower part of the SVC [Figure 4] and [Figure 5]. Femoral vein is cannulated after preparation of the right groin either percutaneously or after surgical exposure of the femoral vein. Navigation of guide wire can be followed in the intrahepatic IVC and its presence is confirmed in the RA. Presence of a guide wire in the RA ensures successful femoral venous cannulation. If cannula placement is in question, agitated saline can be injected via the cannula to assess location of the cannula tip. However, ASD closure requires separate cannulation of the SVC and the IVC. The eustachian valve, an embryologic remnant of the right valve of the sinus venosus, located at the junction of the IVC and RA may obstruct the passage of IVC cannula into the RA and can block the venous drainage. The IAS must be evaluated for patent foramen ovale, which can be a source of an air lock in the venous line in an open chamber procedure. Venous cannula can be obstructed against or perforate the IAS. The IVC cannula can be visualized in the similar echocardiographic window used for SVC cannulation. Inadequate venous return from IVC cannula may be due to unintentional placement of cannula into the hepatic vein. Among hepatic veins, the IVC cannula frequently enters the right hepatic vein (RHV), which is large and joins the IVC at an obtuse angle [Figure 6]. TEE probe should be kept at the level of the aortic valve at 0°. Then the probe is advanced and turned to the patient's right (clockwise) to obtain a good image of the RA with the tricuspid valve and CS. The probe is further turned to the right and if required, advanced to identify the orifice of the IVC and to bring it in to the center of the imaging sector. The transducer plane is rotated to 40-60°, keeping the IVC in focus and the probe is subsequently advanced 2-3 cm along the IVC. RHV is identified by turning the probe to the right. The middle vein is found by rotating the transducer to 50-90° and turning the probe counter clockwise back toward the normal position from the RHV position. The left hepatic vein is identified by turning the probe further counter clockwise, with the transducer rotated to 80-130°. A short distance between the Eustachian valve and the RHV possibly predisposes to cannulation of the RHV. The incidence of venous cannulae placement in the RVH is around 10%.  We have not experienced malposition of IVC cannula until now in approximately 100 patients.
|Figure 2: Midesophageal bicaval view shows guide wire in the superior vena cava|
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|Figure 3: Midesophageal bicaval view shows guide wire in the right atrium during threading of venous cannula|
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|Figure 4: Midesophageal bicaval view shows venous cannula in the right atrium|
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|Figure 6: 2-D echocardiography shows right hepatic vein and inferior vena cava (see text for details)|
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Size and length of venous cannula is decided by the surgeons in consultation with the perfusionists and is usually based on age, weight and height of the patient. TEE can help in the estimation of diameter of the SVC and IVC and further facilitates in deciding the size. We usually select a venous cannula with an external diameter less than the internal diameter of venous lumen to avoid endothelial injury, venous tear and avulsion.
Successful cannulation of the femoral artery requires complete evaluation of the aorta and iliac artery. TEE has its own limitations; it can only assess the proximal ascending aorta, distal aortic arch and descending thoracic aorta. Aorta should be free from atheromatous plaque, debris, intimal tear and aortic dissection. Navigation of guide wire may dislodge the atheromatous plaque, debris and can lead to systemic embolization. Placement of endovascular clamp can be damaging and disastrous in the presence of calcification, atheromatous plaque and endoluminal debris in the ascending aorta. Absence of ascending aortic pathologies is confirmed by TEE in ME long-axis view, ME aortic valve long-axis view and deep transgastric long-axis view. Femoral artery is cannulated percutaneously or through direct exposure of the femoral artery. Navigation of guide wire is traced in descending thoracic aorta in short-axis and long-axis view. From the ME four-chamber view, the TEE probe is rotated approximately 90° to the patient's left side (toward the spine), the guide wire is located in the descending aorta and the aortic cannula is advanced into the femoral-iliac system [Figure 7]. Visibility of guidewire in ascending aorta is must for endovascular-balloon catheter insertion. Guidewire in ascending aorta can be seen during TEE in ME aortic valve long-axis view. Guidewire may enter the innominate artery or left common carotid artery with the theoretical possibility of spasm. A sudden and severe reduction in left radial invasive blood pressure is known during arterial catheter navigation, which immediately returns to normal after catheter removal. Hemodynamic parameters should be monitored carefully during catheter navigation and arterial cannula insertion. Intimal tear may produce immediate aortic dissection, while aortic tear produces torrential intraperitoneal or intrathoracic hemorrhage with very dismal prognosis. Outer diameter of arterial cannula should be less than the internal diameter of the femoral and iliac artery to avoid injury to intima, aortic dissection and aortic tear. In one of our patient, complete transection of the external iliac artery with torrential intraperitoneal hemorrhage occurred during the arterial decannulation following minimally invasive mitral valve replacement. The patient was immediately resuscitated by rapid volume infusion, concomitantly, laparotomy was performed, aorta was clamped which was followed by placement of an interposition prosthetic graft between the aorta and the femoral artery. Subsequently, the patient developed mild paraparesis.
|Figure 7: 2-D echocardiography shows guide wire in descending thoracic aorta|
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Clear communication among the members of the surgical team, anesthesiologists and perfusionists is paramount, especially during circumstances requiring cannula reposition such as venous injury, inadequate venous drainage, aortic tear, aortic dissection, unusually high arterial line pressure and high aortic-root pressure during cardioplegia delivery. The perfusionist should alert the team if difficulties of aortic-flow, venous-drain, or cardioplegia delivery are encountered. TEE helps in detection of wedging of the cannula, aortic or venous tear and dissection. The cannula position and endovascular balloon can migrate or dislodge with surgical manipulation. While on CPB, the cannula is difficult to visualize in an empty and flaccid heart. If the surgical technique permits, the perfusionist is instructed to fill the heart briefly. The filling of the heart facilitate TEE visualization of cannula, endovascular balloon and cardiac structures and manual adjustment of cannula as required.
Antegrade cardioplegia delivery
Our earlier practice was endovascular occlusion of ascending aorta just above the sinotubular junction with the help of a triple lumen balloon tipped catheter. This catheter is introduced over a guidewire through a side limb of the femoral arterial cannula or through the contralateral femoral artery in patients with small femoral artery and helps in the delivery of antegrade cardioplegia, venting of LV and aortic root pressure management. TEE helps in the measurement of aortic root diameter, correct placement of endovascular balloon and its proper inflation.  In our experience, balloon displacement occurred in numerous patients. We often check balloon displacement by simultaneous observation of the invasive arterial pressure tracings of both right and left radial artery. We have abandoned endovascular balloon occlusion and now we put direct antegrade long cardioplegia cannula for cardioplegia delivery and long vascular (Chitwood) clamp for ACC. Krapf et al., reported equal performances of endoaortic balloon occlusion and aortic transthoracic clamping in terms of feasibility and procedural success. 
Patency and diameter of CS is best visualized during TEE by starting from the high four-chamber view. The probe is then advanced until the CS is seen entering the RA adjacent to the tricuspid annulus. Rotation of the probe from 90° to 120° provides a second view of the CS entering the RA. Normal CS diameter is 7-15 mm and diameter >15 mm is suggestive of the presence of left SVC. However, a normal CS diameter does not exclude the possibility of left SVC. Abnormally dilated CS may also be an indicator of CS ostial narrowing or intracardiac shunts.  Presence of left superior caval vein (LSVC) is further confirmed by the presence of a venous loop adjacent to Coumadin ridge in ME four-chamber view or aortic valve short-axis view [Figure 8]. The presence of left SVC can also be confirmed by injecting agitated bubble contrast (normal saline mixed with patient's blood) into the patient's left-arm vein. Appearance of the contrast in the CS before appearing in the RA confirms the presence of left SVC; however, a negative study does not exclude LSVC.  A persistent LSVC is present in about 0.3% of the population at necropsy and in adults undergoing pacing. Nonetheless, it may occur in up to 9% of necropsies of children with congenital heart disease.  Uninterrupted retrograde cardioplegia delivery requires a patent and unobstructed CS and the absence of left SVC. Occasionally, right internal jugular and subclavian vein drain into the left SVC through right innominate vein.  In such cases, right SVC is usually small or it can be absent as in cases of persistent left SVC. Right SVC rarely drains into the left atrium and IVC rarely drains into the RA through CS.
|Figure 8: Midesophageal four chamber view shows left superior vena cava as a venous loop|
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Retrograde cardioplegia delivery
For retrograde cardioplegia, a 9 F triple-lumen catheter is placed in the CS through an 11 F internal jugular vein introducer. Three-lumens allow balloon inflation, retrograde cardioplegia delivery and measurement of CS pressure. Percutaneous cannulation of the CS for administration of retrograde cardioplegia during MICS can be accomplished safely and efficiently using TEE.  TEE helps in the navigation of the catheter from SVC to CS through the RA. Midesophageal bicaval view is useful for tracing the catheter from SVC to RA. The path of the catheter from SVC to CS orifices is facilitated by changing the imaging plane from 90° to 110° or more, which brings SVC and CS orifices in the same plane [Figure 9].  As the catheter is advanced, the path of the catheter tip is adjusted to bring it into alignment with the CS. The tip turns in response to application of torque. When the catheter tip is directed toward the IVC, clockwise torque should be applied at the point of entry and counterclockwise torque should be applied when the tip is directed toward tricuspid valve. TEE displays the movement of catheter tip in opposite direction to the applied torque in modified bicaval view while torque and catheter tip move in the same direction in four-chamber ME view. A prominent Eustachian valve may help in guiding the catheter tip toward the CS. Presence of abnormal thebesian valve may obstruct the passage of the CS catheter. Successful placement of catheter may be further confirmed by the examination of pressure trace. Once the catheter has been advanced into the CS orifice, it can be traced deeper within the CS lumen by bringing the probe little deeper than the classical ME four-chamber view with slight retroflexion. The mid to distal CS is visible in a two-chamber view. Progressively distal segments are displayed by turning the probe further left from a two-chamber view. Fluoroscopy is an ideal choice for tracing deeper into the CS. Live 3D echo-guided CS catheter insertion is feasible, safe and provide a "virtual surgeon's view" of the pertinent anatomy.  TEE guided cannulation of the CS prevents exposure of the patient and operating room personnel to unnecessary radiation from fluoroscopy and substantially decreases health care costs by reducing expenditures on accessory equipment and personnel. Endosinus balloon is inflated at 3-5 cm from the orifice with 1-2 ml of dilute contrast media. Measurement of CS diameter by the TEE is crucial to keep the balloon/vessel ratio below one to avoid CS injury.  Retrograde cardioplegia is delivered through the other lumen of the CS catheter. Catheter balloon is visible with TEE. Retrograde cardioplegia delivery is frequently visible with color flow Doppler at low aliasing velocities.
|Figure 9: Midesophageal modified bicaval view shows coronary sinus and superior vena cava in a single plane|
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Weaning from CPB and post CPB period
Due to limited exposure, removal of intracavitary air and visual assessment of cardiac function during MICS is not possible. TEE is especially helpful in weaning from CPB. Completeness of deairing is assessed just prior to and immediately following cardioplegia cannula removal and after separation from CPB. A quick and focused TEE evaluation is done to confirm the adequacy of surgical repair, absence of residual anatomic defects and absence of air bubble during brief weaning period from the CPB. Weaning is continued if satisfactory surgical correction is ensured. TEE further helps assessment of post-operative ventricular systolic and diastolic function, assessment of fluid requirement and inotropic adjustment.
| Conclusion|| |
The ever growing technical expertise coupled with patient's awareness has led to the tremendous growth of MICS. It is generally performed upon a simple, uncomplicated cardiac lesion. Therefore, the safe and complications-free conduct of MICS is a huge challenge, both for the anesthesiologist and the surgeon. Re-establishing the diagnosis is crucial before the surgical incision. Inadequate access to the surgical site necessitates retrograde placement of venous cannula, arterial cannula and cardioplegia delivery. Intraoperative TEE provides reliable, real time feedback thus facilitates and ensures safe and smooth conduct of the surgical procedure. An appropriate placement of these cannulae is extremely difficult without TEE. Misplaced cannula is always a danger, and hampers the smooth conduct of CPB and may threaten the patient's life. Continuous exchanges of information among caregivers are vital at every stage of surgery. TEE further ensures establishing the adequacy of surgical correction, complete de-airing and thus helps in successful weaning from CPB.
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Department of Cardiac Anaesthesia, All India Institute of Medical Sciences, Ansari Nagar, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]