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L. Leonardo Rodriguez, MD
Stress Echo Laboratory, Cleveland Clinic
Cleveland, Ohio, USA
The use of echocardiography in the operating room is now well established. Intraoperative echo is used for diagnosis, to guide the surgical procedure, to assess immediate results, to detect complications and to monitor left ventricular function. As new surgical procedures appear they often require the assistance of intraoperative echo for immediate assessments of the results.
Intraoperative echo is particularly useful in valvular disease but is also routinely used during aortic surgery, hypertrophic cardiomyopathy, off-pump bypass, Maze procedure, congenital heart disease, etc. Intraoperative echo gives an excellent opportunity for the interaction between the cardiologist and the surgeon that translate in better patient care.
This technique has matured over the years and is currently used in most of the cardiovascular surgery programs.
There are 2 basic modalities of intraoperative echo: epicardial echo and transesophageal echo. Transesophageal echo is the most commonly used technique because cardiologist and anesthesiologist are more familiar with this technique and also because don't interfere with the operative field and offer excellent visualization of posterior structures.
Epicardial echo is used more often in the evaluation of atherosclerosis of the ascending aorta or in cases where it is not possible to introduce the TEE probe (i.e.; esophageal pathology). It requires placing a high frequency probe in the surface of the heart therefore interfering with the surgical field and also increasing the potential for contamination.
Several aspects must be kept in mind that may interfere with the application of this technique. The lighting conditions of the room are often unfavorable for the display of the images on screen often requiring compensatory increase in gains. Also the use of diathermy can interfere with the Doppler recordings. It is of critical importance to understand that the hemodynamic conditions in the OR are very different with preload and afterload affected by anesthesia and volume status. This may affect the degree of regurgitant lesion and often in necessary to increase the blood pressure with the use of vasopressors.
Possible the most important aspect in the use of intraoperative echo is the interaction between the cardiologist and the surgeon. The surgeon expects instant feedback of the echo findings but he/she must recognize that in many instances it is necessary to use multiple views for optimal assessment of the lesions. Trust between the cardiologist and the surgeon needs to be built with exchange of the echocardiographic information and correlation with the surgical findings.
The major indications for intraoperative echo include:
* Valve surgery: repair, reconstruction, prosthetic function,
necessity for operation
* Aortic surgery: dissection, aneurysm
* Revascularization-LV function, adequacy of revascularization, need for MV surgery, VSD
* Congenital heart disease
* General: assess cannulation site, aortic atherosclerosis, difficulty coming off pump
VALVULAR HEART DISEASE
The assessment of valvular heart disease constitutes the classical indication of the use of intraoperative echo. This allows exquisite definition of the anatomy of the mitral and aortic valves, presence and severity of stenosis or regurgitation, mechanism of the regurgitant lesions and associated abnormalities.
Mitral valve repair
In patients undergoing mitral valve surgery is important to determine the mechanism and severity of the regurgitation, left ventricular function and other associated lesions.
Carpentier has classified the mechanism of mitral regurgitation in 3 groups:
Normal leaflet motion: dilated cardiomyopathies, perforated leaflet.
Excessive leaflet motion: mitral valve prolapse and flail.
Restrictive leaflet motion: rheumatic heart disease, ischemic heart disease.
The most common cause of severe mitral regurgitation in the US is mitral valve prolapse. Intraoperative echo gives us information the anatomy of the valve whether the anterior or posterior leaflet is affected and which of the scallops is involved. The 60-70 degree view and the transgrastric short axis view are the most important in determining the scallop involved. Using color flow mapping we can determine the severity of the regurgitation and the origin and direction of the regurgitant jet. The direction of the jet helps to identify the leaflet involved. Anterior jet usually represents posterior leaflet pathology and vice versa. In some cases the anatomy appears to involve one leaflet but the jet is directed opposite to what one expects, i.e.; posterior mitral flail with posteriorly directed jet. In those cases one should strongly suspect commissural involvement.
Quantification of the severity of mitral regurgitation requires information on pulmonary vein flow, visualization of the proximal convergence region, CW Doppler of the MR and, when possible, visualization of the vena contracta.
After the repair is performed IOE is essential to evaluate the presence of residual mitral regurgitation, the presence of systolic anterior motion of the mitral valve and left ventricular function.
AORTIC VALVE SURGERY
Intraoperative echocardiography widely used in patients with aortic insufficiency. As in the case of mitral regurgitation, IOE give us vital information about the anatomy ( ) and mechanism and severity of the aortic regurgitation.
Mechanism of aortic insufficiency
*Leaflet restriction: rheumatic, calcific
*Leaflet prolapse: bicuspid aortic valve ( )
*Leaflet perforation: SBE ( )
Aortic Root Abnormalities
* Annular dilatation: Annulo-aortic ectasia ( ), AAA
* Aortic dissection
In evaluating aortic regurgitant lesions we must assess the anatomy in the short axis, measure the aortic annulus, sinus of Valsalva, sinotubular junction and ascending aorta diameters. Color flow evaluation of the severity and direction of the regurgitant jet (long axis, 120-140 degree view).
Evaluation of the Aorta
IOE is routinely used in patients with aortic dissection. This technique allows us definition of the extent of the dissection, presence of intimal tear, intramural hematoma and in many cases involvement of the coronaries or arch vessels. In cases of resuspension of the leaflets IOE is critical to assess the presence of residual aortic regurgitation and the need for further repair or replacement.
In addition, the IOE offers information about presence of atherosclerotic changes in the ascending and descending aorta. The presence of significant atherosclerosis in the ascending aorta may modify the cannulation access to try to avoid embolic complications.
Surgical myectomy is a proven effective therapy for patients with obstructive hypertrophic cardiomyopathy. In good hands this procedure has low mortality and excellent short and long term results. IOE can define the location of the maximal septal thickness, the point of mitral-septal contact and the distance from this point to the aortic valve. LVOT ( ) gradients can also be obtained intraoperatively. In some cases epicardial echo provides better alignment with the LVOT flow and therefore more accurate gradients at rest and during isoproterenol infusion. This is seen in with transducer placed between the aorta and the superior vena cava. After myectomy the gradients are then obtained under similar conditions. A successful myectomy is considered when there is no mitral-septal contact, the provoked gradients are <50 mmHg and there is no significant mitral regurgitation. About 18% of the patients will need a second pump run for a more extensive myectomy. It is also important to carefully look for ventricular septal defects that are a known complication in cases of a too generous myectomy.
Transesophageal echo is routinely used in the evaluation of patients with suspected bacterial endocarditis. It provides high quality images of vegetations, abscesses and valvular perforations and fistulas ( ). Periaortic abscesses are difficult to see with transthoracic echo but are easily visualized during IOE ( ). This technique help to evaluate the extension of the infection to surrounding structures which is of critical importance to allow complete extirpation of the infection.
New technological advances will allow the routine use of three dimensional echo in the operating room. Real time 3D will have the advantage of better anatomical display particularly in cases of congenital heart disease or complex bacterial endocarditis with abscesses and fistulas. Better definition of the location and extent of LVOT obstruction in cases of HOCM may help the surgeon during myectomy. Finally, the use of second harmonics and contrast echo will allow us to perform myocardial perfusion studies in the OR to evaluate the results of revascularization of vessels with poor targets or questionable viability. Advances in digital echocardiography are already making possible to have available prior studies of the patient in the OR for immediate comparison.
1. Griffin BP, Stewart WJ. Echocardiography in patient selection, operative planning and intraoperative evaluation of mitral valve repair. In Otto CM, ed The Practice of Clinical Echocardiography. Philadelphia: WB Saunders, 1997
2. Carpentier A, Chauvaud S, Fabiani JN eto al , Reconstructive surgery of mitral valve incompetence: Ten-year appraisal. J. Thoracic Cardiovasc Surg 1980;79:338-348
3. Herman D. Movsowitz, Robert A. Levine, Alan D. Hilgenberg, Eric M. Isselbacher. Transesophageal echocardiographic description of the mechanisms of aortic regurgitation in acute type A aortic dissection: implications for aortic valve repair. JACC. 36:884-90, 2000
4. Stewart WJ, Thomas JD, Klein AL et al. Ten year trends in utilization of 6340 intraoperative echos. Circulation 1995;92:1-514 (abs)
5. Klein A, Stewart WJ, Cosgrove DM, Salcedo EE. Intraoperative epicardial echocardiography: Technique and imaging planes. Echocardiography 1990;7:241-251
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