Asian Cardiovasc Thorac Ann 1998;6:300-305
© 1998 Asia Publishing EXchange Pte Ltd
Establishment and First Audit of a New Perioperative Echocardiography Service
Michael John Morris, MBBS, FANZCA,
Peter Lindsay Klineberg, FANZCA,
Richard Chard, FRACS,
Veronica Hanrahan, DMU,
Ken Harrison, FANZCA,
George Larcos, FRACP,
Yugan Mudaliar, FRACP,
William Meldrum Hanna, FRACS,
Hugh Paterson, FRACS,
David Shaw, FANZCA
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Department of Anaesthesia Department of Cardiac Surgery Department of Intensive Care Department of Nuclear Medicine and Ultrasound Westmead Hospital Westmead, Australia
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For reprint information contact: Michael John Morris, MBBS, FANZCA Department of Anaesthesia Westmead Hospital Cnr Hawkesbury & Darcy Roads Westmead NSW 2145, Australia Tel:61 2 9477 1930 Fax:61 2 9477 6598 Email:mmorris{at}ibm.net
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ABSTRACT
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Intraoperative echocardiography has become an integral service for cardiothoracic surgery. Establishing a service requires new ultrasound technologies and a dedicated team prepared to be trained in this new discipline. The establishment of a new perioperative service at Westmead Hospital, Australia is outlined. Early experience, current practice, teaching and research programs are presented and the first audit is reported.
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INTRODUCTION
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The introduction of echocardiography into the perioperative setting can be traced back to the report by Frazin and colleagues1 in 1976. The initial equipment was bulky and limited to M-mode so there was little interest until the 1980s. As the capabilities increased with two-dimensional images that were much easier to interpret and spectral Doppler that detected and examined blood flow, the interest in echocardiography increased. The latest development is the reduction in size of the transducer. The large transducers wrapped in sterile sleeves and used by the surgeon directly on the heart surface have been replaced by smaller transducers introduced into the esophagus and operated without interference in the surgical field. In the 1990s, these transducers are able to provide the full range of ultrasound capabilities in a transesophageal probe that can image in an indefinite series of planes.2,3
As the technology has improved so has the use of these machines.4 Initially, echocardiography was used in a monitoring mode for myocardial ischemia and the detection of venous air embolism.5,6 Now, echocardiography is used additionally as a powerful diagnostic tool. The advantages of this technology are that it is minimally invasive and outside the surgical field, it gives real-time imaging, it is transportable and can be brought to the patient. It involves no radiation and it has no toxic effects.
In 1996, a task force on perioperative transesophageal echocardiography comprising representatives of the Society of Cardiovascular Anesthesiologists, the American Society of Echocardiography and the American College of Cardiology published the practice guidelines for perioperative transesophageal echocardiography.7 These indications included cardiac valvular surgery, congenital heart surgery, endocarditis, pericardial procedures, hypertrophic obstructive cardiomyopathy, thoracic aortic surgery, myocardial ischemia, cardiac aneurysms, cardiac tumors, foreign bodies, air and solid emboli, intracardiac thrombectomy, anastomotic sites during heart and lung transplantation, cardiac assist devices, hemodynamic disturbances, and direct assessment of the aorta for suitable cannulation sites.8–17 This paper discusses the establishment of a perioperative echocardiography service emphasizing the coordination of a group of departments. In addition, we report the results of an audit of the first 12 months of its operation.
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WESTMEAD HOSPITAL EXPERIENCE
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Westmead Hospital is an 800-bed university hospital established in 1978. The operating suite has 18 operating theaters. There are 4 cardiac surgeons who perform approximately 700 cardiac operations each year. The department of anesthesia has a comprehensive involvement in the cardiothoracic surgical unit and the cardiac postoperative intensive care unit, cardiopulmonary perfusion service, and now the perioperative echocardiography service.
The department of nuclear medicine and ultrasound is responsible for all ultrasound imaging within the hospital. Under this arrangement, 4 consultant physicians specialize in nuclear medicine and ultrasound. All other physicians involved with ultrasound services such as obstetricians, cardiologists, and anesthetists access this department for both equipment and more importantly, expertise from these physicians. For echocardiography, a full range of transthoracic and transesophageal studies are performed in the department on a referral basis. The department trains candidates for the Diploma of Diagnostic Ultrasound examination as established by the Australian Society for Ultrasound in Medicine. In addition, the department trains the cardiology registrars in conjunction with the staff cardiologists in accordance with the program established by the cardiac society. By all measures, the department of ultrasound and nuclear medicine coordinates the best aspects of interdepartmental cooperation and sharing of equipment. It also has an active training program with regular examinations for the Australian Society for Ultrasound in Medicine and strong research interests with extensive successful projects. Quality assurance programs, administration, reporting, and archiving of all studies are centralized in this department, drawing together a number of specialist physicians with diverse interests but a common use of ultrasonography.
Early Experience
From early 1992, intraoperative echocardiography was performed by ultrasound physicians who brought one of their machines into the operating suite on an ad hoc basis, mainly for assessment of cardiac valve repair. In 1993, a consultant anesthetist trained in echocardiography at Duke University, North Carolina, joined the staff at Westmead for 12 months. He commenced training anesthetists in echocardiography in association with the cardiologists and physicians in the ultrasound department. By 1995, 2 anesthetists had undergone formal training over a 12-month period and had completed over 250 cases in transthoracic and transesophageal echocardiography. Following this training, they established the perioperative echocardiography service using machines from the ultrasound department. In 1996, funding was granted through the hospital's charitable trust and a Hewlett Packard Sonos 2500 (Hewlett Packard, Inc., Andover, MA, USA) ultrasound machine was commissioned for the operating theaters.
Equipment
The Hewlett Packard Sonos 2500 machine was installed with anesthesiology software specific for perioperative echocardiography, namely the automated border detection system. This can differentiate between the ventricular wall and the ventricular cavity (Figure 1
). Using this system, the movement of the left ventricle can be followed continuously throughout contraction and relaxation. It can measure end-diastolic area and end-systolic area and thus calculate the area change, termed the fractional area change, which is proportional to the ejection fraction. The area of the ventricle is tracked and plotted on a graph. The peak filling rate, time to peak filling rate, and peak emptying rate are calculated to estimate systolic and diastolic function of the ventricle. This information on ventricular function and performance allows objective calculation of ventricular performance throughout surgery and at specific critical times such as separation from cardiopulmonary bypass or commencement of therapy.
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Figure 1. The automated border detection system: the top right of the picture shows a cross-sectional view of the left ventricle and the bottom section of the picture displays the graph and calculations.
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The automated border detection system can also be used to measure movement of the ventricular wall. This system, called Color Kinesis (Hewlett-Packard, Inc., Andover, MA, USA), analyzes regional wall motion and determines how and when each wall segment moved with respect to the other segments (Figure 2). With this system, it is possible to measure wall motion and score it as normal, hypokinesis, akinesis, or dyskinesis. The 3 transducers for this ultrasound machine are a multiplane multi-hertz transesophageal probe for all intraoperative work, a short-focus surface transducer that can be used for epiaortic and epicardial imaging, and a standard transthoracic surface probe. Recording is made on both VHS tape and optical disc, with a color printer available for the patient records.
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Figure 2. The Color Kinesis System: the picture shows a cross-section of the left ventricle with movement from end-diastole to end-systole colored. The area of minimal movement is indicated with an arrow.
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Imaging Techniques
There are currently 3 consultant anesthetists trained in echocardiography who provide the perioperative echocardiography service. For each patient studied, an initial examination is performed after induction of general anesthesia but prior to commencing cardiopulmonary bypass. A complete examination of the heart and great vessels is carried out in every case. The standard views include a transgastric 5-chamber view where aortic transvalvular gradient and cardiac output are measured. Transgastric short-axis and long-axis views of the left ventricle are used for estimation of ischemia and function and include use of the automated border detection system as described above.
Lower esophageal 4-chamber views are employed to examine the heart and by using the multiplane facility of the transesophageal transducer each chamber and valve can be carefully studied. Finally, examination of the aorta for atheroma in all segments by transesophageal or epiaortic scanning is performed. Relevant findings are discussed with the surgeon and final surgical decisions are made at this time. After corrective surgery and initial separation from cardiopulmonary bypass, the second study is performed and implications are relayed again to the surgical team.
A permanent record of patient details including date of study, indication, findings, operator, and tape-counter readings are made and important findings are archived on both VHS tape and disc for future reference. A detailed report of the study is then dictated in the ultrasound department office with copies for the patient's notes, the attending surgeon, and other attending physicians. All reports remain coordinated within the ultrasound department and are available on the radiology information system ensuring that all relevant outpatient, inpatient and perioperative studies are held in one source.
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PRIMARY AUDIT
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Table 1 summarizes the experience during the first 12 months. Transesophageal echocardiography can accurately detect dissection of the wall of the thoracic aorta as well as examining the aortic valve to establish if the dissection has spread to this valve rendering it regurgitant. Following aortic reconstruction, the function of the aortic valve can be established as well as documentation of entry and exit sites of dissection and confirmation of decompression of the false lumen.
Mitral valve surgery is the most prominent indication for intraoperative echocardiography. Often, mitral regurgitation is due to ischemia causing papillary muscle dysfunction and echocardiography can avoid unnecessary intervention. Where the mitral valve is infected, extension into surrounding areas can be outlined. Intraoperative echocardiography has proved highly successful for immediate assessment of mitral valve repairs. Of the 25 cases included in this audit, 6 demonstrated the initial repair to be unsatisfactory. Following further surgical intervention, these were successfully corrected. One case of outlet obstruction involved systolic anterior motion of the mitral valve associated with annuloplasty ring insertion.
Coronary artery bypass graft patients are the largest group in this audit. Areas of ischemia, seen as wall motion abnormalities were documented and quantified using the Color Kinesis system. Echocardiography was particularly useful during separation from cardiopulmonary bypass by helping to differentiate the causes and manage low cardiac output states with further fluid challenge or increasing doses of inotropic drugs. In one case of routine coronary artery grafting, a mass on the left coronary cusp of the aortic valve was discovered (Figure 3). The aorta was therefore opened to confirm a 5 x 5 mm mass that was resected and shown to be a rare papillary fibroelastoma. Intraoperative echocardiography detected the tumor and assessed aortic valve competence after resection.
Aortic valve surgery including repair and replacement procedures were studied in 28 cases. Three cases of paravalvular leakage were located and corrected. Echocardiography was indicated at the time of separation from cardiopulmonary bypass to assess hemodynamic function. As part of an international study on a new Medtronic bioprosthetic aortic valve (Freedom; Medtronic Inc., Minneapolis, MN, USA), 16 patients were studied during this audit. The study set specific measurements by echocardiography including calculation of the valve area using planimetry (Figure 4), calculation of transvalvular pressure gradients across the implanted valve (Figure 5), and evidence of leakage of the newly implanted valves. In one case, the implanted valve was close to the left coronary ostia and after separation from cardiopulmonary bypass, there was poor ventricular function. Echocardiography confirmed flow in the left coronary vessels using color Doppler (Figure 6) and so excluded the implanted valve as the cause of this temporary malfunction.
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Figure 6. Transverse view of the implanted Medtronic valve and color Doppler confirming flow along the left main coronary artery.
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Adult congenital heart procedures accounted for 14 cases during this 12-month period and included Epstein's anomaly, tricuspid valve repair, tetralogy of Fallot, and mitral valve cleft. Echocardiography was particularly helpful in delineating the right ventricular outflow tract, pulmonary valve, interventricular septum, and conduit function. One patient thought to have an atrial septal defect had in fact anomalous pulmonary venous drainage.
Hypertrophic obstructive cardiomyopathy was studied in 3 patients who underwent resection of hypertrophied muscle septum. One was investigated by angiography and diagnosed as having severe aortic stenosis with a transvalvular gradient of 90 mm Hg. This patient was scheduled for aortic valve replacement but intraoperative studies showed subaortic stenosis and a normal aortic valve (Figure 7). A septal resection was then carried out and the outflow tract was studied after separation from cardiopulmonary bypass. Residual systolic anterior motion of the mitral valve accompanied by moderate mitral regurgitation and continuing high pressure gradients in the outflow tract confirmed the need for further septal resection. After the second procedure, correct outflow tract dynamics were confirmed. The other 14 cases included emboli during total hip replacement, trauma, abdominal aortic aneurysm surgery, pericardial window, the Ross procedure, pulmonary valve replacement, and unexplained collapse during surgery.
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Figure 7. Hypertrophic obstructive cardiomyopathy showing systolic anterior motion of the mitral valve and critical narrowing of the left ventricular outflow tract.
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Teaching Program
Teaching is an integral part of the perioperative echocardiography service at Westmead Hospital. It forms the main arm of our quality management program by constantly requiring all practitioners to review their work and knowledge. The teaching program is divided into an internal and external program. The internal program is directed at all members of our anesthetic department who may learn basic echocardiography to whatever level they require. For the past 3 years, we have had a training position in perioperative echocardiography for a clinical fellow with attachment to the ultrasound department to learn both transesophageal and transthoracic echocardiography and also with attachment to the perioperative echocardiography service where 3 consultant anesthetists act as supervisors. The appointment fulfills the training requirements set by the cardiac society and the Australian Society for Ultrasound in Medicine. The external program is directed at other members of the hospital staff including intensivists and anesthetists working in other hospitals within Australia. A working party within the Special Interest Group for Cardiovascular Anesthetists has been formed, which has been looking at credentialing practitioners. Frequent workshops and presentations allow this service to draw in other interested anesthetists. Membership of overseas groups such as the Society of Cardiovascular Anesthesiologists and the European Society of Cardiovascular Anesthesiologists build links to ensure the practice at Westmead hospital is at a high level.
Research Program
Perioperative echocardiography is still in an early stage of development in Australia and provides a great opportunity for research into its applications. Research programs at Westmead hospital are encouraged and centered around the clinical fellowship and consultant programs. These programs also form part of the quality management process and strengthen the link between the ultrasound department and the cardiologists. The major project during this audit was the Medtronic bioprosthetic aortic valve study. The Westmead group was one of 24 around the world investigating its clinical applications. The valve incorporates a stentless design with no supporting ring when inserted into the aorta. The valve has the advantages of not requiring anticoagulation postoperatively and flow characteristics that are particularly impressive, offering high cardiac output for even small-sized valves. However, the sizing and orientation of this valve are critical. The Westmead study was able to improve the assessment of these valves intraoperatively using transesophageal echocardiography.18,19
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FUTURE DIRECTIONS
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Perioperative echocardiography has an exciting future as it changes our practice of cardiac anesthesia and surgery. Current applications and indications are well-established and have become the standard of care with the publication of the practice guidelines.7 The future will be shaped by changes in technology and application. New technology including better imaging modes, smaller transducers, and the advent of three-dimensional images will increase our knowledge and promise further changes in the practice of cardiac anesthesia and surgery. New procedures such as minimally invasive cardiac surgery require intraoperative echocardiography. Perfusion systems must be correctly placed and information relating to cannulation of the coronary sinus, intraluminal balloons, hemodynamics, and ventricular function rely on accurate echocardiography.
This article describes the establishment of a perioperative echocardiography service that requires a large number of ingredients to be successful. It is not enough to have good machines. A perioperative echocardiography service needs good relationships between each member of the team. Specialists in ultrasound, cardiac surgeons, cardiologists, intensivists, and anesthetists are drawn together and rely on each other to teach, learn, investigate, and provide reliable information that will benefit the patient.
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ABSTRACT
INTRODUCTION
