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March 1999
Volume 63 |
Number 3
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| Cardiac Anesthesiology
Update: Transesophageal Echocardiography |
Scott T. Reeves, M.D.
Transesophageal echocardiography (TEE) technology has impacted
positively on the practice of cardiovascular anesthesiology. The
major areas of advancement in the subspeciality of cardiovascular
anesthesiology, including education and certification and advanced
intraoperative techniques, will be discussed.
Education and Certification
Educational efforts have advanced rapidly since the publication
by the American Society of Anesthesiologists (ASA) and the Society
of Cardiovascular Anesthesiologists (SCA) titled "Practice Guidelines
for Perioperative Transesophageal Echocardiography" was released.1
This publication standardized the indications and specific training
objectives needed for perioperative TEE. Shortly thereafter, the
SCA task force on certification for perioperative TEE published
a content outline of the necessary knowledge that would be included
in the first national certification exam in perioperative TEE
administered in April 1998 in Seattle.2
By having published guidelines and a content outline, TEE educational
efforts became more specific to perioperative transesophageal
echocardiography and therefore the needs of anesthesiologists.
Certification in perioperative transesophageal echocardiography
became possible in 1998 with the formation of the National Board
of Echocardiography. This board was established through the National
Board of Medical Examiners with direct input from the SCA and
the American Society of Echocardiography. The second examination
in perioperative TEE will be administered following the SCA annual
meeting in Chicago in April of 1999.
Advanced Intraoperative Techniques
Transesophageal echocardiography has greatly improved the ability
of cardiothoracic surgeons to perform more complicated minimally
invasive repairs, aortic or mitral valve repair/replacement and
to evaluate the adequacy of coronary artery bypass graft by having
immediate feedback following such repair.
Minimum Invasive Cardiac Surgery
Minimum invasive cardiac surgery has prospered due to the convenience
of cardiopulmonary bypass and hypothermic cardiac arrest without
requiring sternotomy. The ability of the cardiovascular anesthesiologist
to ensure proper cannula and catheter placement for this technique
is critical. In addition, with the Port-Access System (Heart Port
Incorporated, Red Wood City, California), the anesthesiologist
inserts a cardioplegia catheter into the coronary sinus from the
right internal jugular vein with TEE guidance.3The
ability to precondition the future ischemic segments prior to
prolonged coronary artery occlusion and the subsequent evaluation
of new regional wall motion abnormalities after prolonged occlusion
is critical to the success of minimum invasive procedures.
Stentless Aortic Valves
While the utility of TEE in the evaluation of mitral valve repair
and replacement is well-known, its utility in aortic valve replacement
is still subject to scrutiny. As stentless porcine aortic valves
such as the Toronto SPV (St. Jude Medical, St. Paul, Minnesota)
are used more frequently, the ability to measure the diameter
of the sinotubular junction and the aortic annulus is essential
in order to assist the surgeon in determining if a properly sized
stentless valve can be used at all. T. David et al. have demonstrated
that blood flow across the Toronto SPV bioprosthesis resembles
that of a normal aortic valve and is identical to that of an aortic
valve homograph.4 This valve offers
minimal resistance to flow and therefore allows for rapid regression
of left ventricular hypertrophy and restoration of normal left
ventricular function. The mean systolic gradient across the valve
actually decreases during the first year after implantation and
its effective orifice increases. It is felt that the reduction
in the gradient and increase in the effective valve orifice is
secondary to remodeling of the left ventricular outflow tract
and healing of the valve in the patient's aortic root.
The geometric arrangement of the Toronto SPV bioprosthesis is
such that the diameter of the valve at the level of the commissures
is similar to that of the annulus. For this reason, it is vital
to measure the diameters of the aortic annulus and the sinotubular
junction during diastole in order to select an appropriate size
valve. The valve size should be similar to the diameter of the
sinotubular junction rather than the aortic annulus. If the diameters
differ by more than two millimeters or approximately 10 percent,
it is necessary to reduce the diameter of the sinotubular junction
to that of the Toronto SPV bioprosthesis. It is therefore evident
that careful measurement by the anesthesiologist will facilitate
the surgeon's decision on whether to use a stentless valve as
well as the appropriate size valve to be used.
Contrast Echocardiography
The hand agitated saline solution technique of utilizing two
syringes joined by a three-way stopcock to generate a mixture
of air and saline is used for contrast injections. This technique
is beneficial for right-sided contrast studies such as the evaluation
of a patent foramen ovale. Agents specifically designed for echo
contrast have been developed such as the first generation sonicated
human albumin, Albunex, (Mallinckrodt, St. Louis, Missouri) with
a mean microbubble diameter of 4 µ. The air in first generation
agents is highly diffusible and rapidly escapes from the bubble
when mixed with blood resulting in a decrease in the back scattering
properties of these agents.5 Second
generation echo contrast agents such as Optison (Mallinckrodt,
St. Louis, Missouri) and Echogen (Sonus, Bothell, Washington)
have overcome this major limitation.
Contrast agents have greatly increased the ability to enhance
endocardial definition, wall motion and wall thickening, thus
improving the sensitivity and specificity of stress testing. Contrast
agents have also been used intraoperatively to evaluate regional
myocardial perfusion after CABG surgery as well as retrograde
cardioplegia delivery distribution.6,7
Finally, difficult to evaluate valvular lesions such as tricuspid
regurgitation, aortic stenosis, mitral regurgitation or pulmonary
venous flow can benefit from echo contrast, since the Doppler
envelope is more sharply defined (intensity of the Doppler signal)
without affecting the displayed velocity.
Conclusions
In the past several years, transesophageal echocardiography
technology has been effectively integrated into the practice of
cardiovascular anesthesiology. I encourage all members to become
familiar with this rapidly evolving modality.
References:
- American Society of Anesthesiologists.
Practice Guidelines for Perioperative Transesophageal Echocardiography.
Anesthesiology. 1996; 84:986-1006.
- Society of Cardiovascular Anesthesiologists
Task Force on Certification for Perioperative Transesophageal
Echocardiography. Content Outline.
- Clements F, Wright SJ, de Bruijn N. Coronary
sinus catheterization made easy for port-access minimally invasive
cardiac surgery. J Cardiothorac Vasc Anesth. 1998; 12:96-101.
- David TE, Puschmann R, Ivanov J, et al.
Aortic Valve Replacement with Stentless and Stented Porcine
Valves: A Case-match Study. J Thorac Cardiovasc Surg.
1998; 116:236-241.
- Cheng S, Dy TC, Feinstein SB. Contrast
echocardiography: Review and future directions. Am J Cardiol.
1998; 81(12A):41G-48G.
- Aronson S, Lee BK, Wiencek JG, Feinstein
SB, et al. Assessment of myocardial perfusion during CABG surgery
with two-dimensional transesophageal contrast echocardiography.
Anesthesiology. 1991; 75:433-440.
- Aronson S, Lee BK, Zaroff JG, et al. Myocardial distribution
of cardioplegic solution after retrograde delivery in patients
undergoing cardiac surgical procedures. J Thorac Cardiovasc
Surg. 1993; 105:214-221.
Scott T. Reeves, M.D., is Associate Professor,
Department of Anesthesia and Perioperative Medicine, Medical University
of South Carolina Children's Hospital, Charleston, South Carolina.
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