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NewsletterPRO: Transesophageal Echocardiography Should Be Routinely Used In All Patients Undergoing Cardiac Surgery Mark A. Chaney, MD
An enormous amount of clinical information is obtained from transesophageal echocardiography (TEE) that cannot be obtained via any other diagnostic instrument. This information is useful for the perioperative management of patients undergoing cardiac surgery, and potentially improves outcome. Perhaps the most important routine clinical information obtained from TEE involves assessment of myocardial function (systolic and diastolic), myocardial ischemia, and volume status. Global systolic function can be assessed via fractional area change, ejection fraction, stroke volume, and cardiac output, all of which are easily obtained with TEE. Furthermore, intracardiac pressures (intraatrial, intraventricular, pulmonary artery) can be quantified by TEE via simple calculations involving the modified Bernoulli equation. Regional systolic function is assessed in a wide variety of TEE views and the information obtained may help guide intraoperative decisions regarding myocardial viability, potential for improvement with revascularization (thus guiding revascularization), and quality of revascularization. Diastolic function is readily assessed via pulsed-wave Doppler interrogation of mitral valve flow from the left atrium into the left ventricle and characterized into three broad categories (abnormal relaxation, restrictive physiology, pseudonormalization) that represent specific clinical entities (volume changes, myocardial ischemia, decreased left ventricular compliance, etc.). TEE is very sensitive for detecting myocardial ischemia. Systolic function alterations associated with myocardial ischemia include wall motion abnormalities (decreased wall thickening, hypokinesia) and diastolic function alterations include abnormal relaxation filling profile. TEE, by direct visualization of the atrial and ventricular chambers, yields the best information obtainable regarding volume status (central venous pressure and pulmonary artery occlusive pressure are much less sensitive and specific). Thus, TEE assessment of myocardial function, myocardial ischemia, and volume status provides invaluable information in patients undergoing cardiac surgery that enhances perioperative management by allowing appropriate hemodynamic intervention. Information obtained from TEE has proven to be more useful in managing patients undergoing cardiac surgery than information obtained from the pulmonary artery catheter (1,2). Changes in both ventricular compliance and loading conditions occur continuously during cardiac surgery, altering the relationship between ventricular pressure and volume, making the pulmonary artery catheter unreliable, especially in the presence of left ventricular dysfunction and extremes of preload (hypovolemia or hypervolemia) (1). In one study, TEE was the single most important source of information in 17% of interventions involving fluid administration (more important than the pulmonary artery catheter) and was also useful in guiding anti-ischemic and vasoactive medications (2). In another study, TEE initiated at least one major hemodynamic intervention in 50% of patients undergoing cardiac surgery (3). The importance of TEE during valve repair / replacement cannot be overstated (4). In contrast to valve replacement, valve repair is associated with improved perioperative morbidity and mortality and improved long-term survival. Thus, valve repair is always preferable (when possible) and TEE is vital in assessing feasibility of repair. Various studies have revealed that new information is obtained via TEE in approximately 10-20% of patients undergoing valvular surgery, information that alters the planned surgery (repair vs replacement) in approximately 10% of patients. TEE is also vital in assessing adequacy of valve repair / replacement and evaluation following cardiopulmonary bypass may prompt immediate reintervention in approximately 2-10% of patients, problems that if left uncorrected, would certainly increase postoperative morbidity and mortality. Neurologic complications continue to be a significant cause of morbidity and mortality following cardiac surgery. Aortic atherosclerosis is perhaps the most important risk factor for perioperative stroke and investigators have demonstrated a direct relationship between extensive atheromatous disease of the ascending aorta and stroke. TEE readily detects lesions in the ascending aorta that can be further evaluated with epiaortic scanning (5). Information gained may alter surgical technique (decreased aortic manipulation, altered cannulation site, avoidance of cardiopulmonary bypass, aortic atherectomy, etc.) in hopes of decreasing risk of perioperative stroke. Accumulating evidence indicates that TEE improves clinical outcome in a wide variety of scenarios, including persistent, severe hemodynamic disturbances of unknown etiology, valve repair, congenital heart surgery, repair of hypertrophic obstructive cardiomyopathy, endocarditis, and suspected aortic aneurysm / dissection (6). Other potentially beneficial applications include evaluation of pericardial effusion, intracardiac air / emboli, intracardiac foreign bodies / catheters, and cardiac tumors (6). In summary, TEE provides an enormous amount of accurate, real-time, structural and physiologic information in patients undergoing cardiac surgery that is not obtainable by conventional intraoperative monitors. Information obtained from TEE may directly alter surgical management and anesthetic management in 30% and 50% of patients, respectively (3), and therefore may beneficially affect morbidity and mortality. With the recent emergence of minimally invasive (7) and "off-pump" (8) cardiac surgery, TEE has proven to be even more invaluable. Thus, TEE should be routinely used in all patients undergoing cardiac surgery. REFERENCES
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