Asian Cardiovasc Thorac Ann 2001;9:257-259
© 2001 Asia Publishing EXchange Pte Ltd
Coronary Artery Assessment by Epicardial Pulsed Doppler Ultrasound
Takeo Tedoriya, MD,
Henrik Siniawski, MD,
Luc Tambeur, MD,
Michael Huebler, MD,
Roland Hetzer, MD
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Department of Cardiothoracic and Vascular Surgery German Heart Institute Berlin Berlin, Germany
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For reprint information contact: Takeo Tedoriya, MD Tel: 81 86 235 7359 Fax: 81 86 235 7431 email: takeotedoriya{at}aol.comDepartment of Cardiovascular Surgery, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
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ABSTRACT
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An intraoperative method was developed for direct investigation of the coronary arteries using an epicardial high-frequency two-dimensional Doppler ultrasound transducer. This fingertip 7.5-MHz transducer was used in 30 patients undergoing coronary artery bypass surgery to measure blood flow in the coronary arteries and bypass grafts. In all the patients, clear images of the coronary arteries and the bypass grafts were obtained in the beating heart, and coronary blood flow could be measured to evaluate the degree of stenosis. There were no significant differences between the measurements obtained with the Doppler transducer and a transit-time ultrasonic flowmeter of blood flow in the left internal thoracic artery graft to the left anterior descending coronary artery, indicating that the Doppler method produces accurate and reproducible measurements. This method can provide useful intraoperative information about the coronary artery system in emergency operations such as acute aortic dissection.
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INTRODUCTION
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Real-time intraoperative observation of the coronary artery system can obviously be of great value for evaluating blood flow in the coronary arteries during a variety of cardiac operations, especially for monitoring flow patterns during coronary artery bypass grafting (CABG).1 Further-more, precise intraoperative assessment of the coronary artery system will be immensely valuable in emergency surgery, such as acute aortic dissection, where patients are operated on without prior knowledge of any coronary artery disease because of the urgency of their condition.2,3 The coronary system of the heart from elderly transplant donors could also be evaluated without using inter-ventional techniques such as coronary arteriography or depending on the uncertain assessment of operators based on direct palpation.4,5
Intraoperative investigation of the coronary artery system has been attempted by various methods.6–8 However, none have proven to be sufficiently useful for a general assessment of coronary artery circulation. We report a new approach to intraoperative analysis of the coronary arteries, including the possibility of investigating the condition of the coronary artery wall and intracoronary flow velocity, using an epicardial high-frequency twodimensional Doppler ultrasound transducer. To confirm the reliability of this transducer, we compared graft flow measured with this device against the values obtained with a transit-time ultrasonic flowmeter, which is known to be reliable. We also attempted to improve the quality of coronary artery imaging by the transducer.
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PATIENTS AND METHODS
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A fingertip 7.5-MHz Doppler transducer (Aloka, Tokyo, Japan) was used in 30 patients with normal left ventricular function who were undergoing elective CABG. There were 12 females and 18 males, aged 58 to 77 years (mean, 66.8 ± 5.9). Images were obtained with an ultrasound system (model SSD-2200; Aloka, Tokyo, Japan). After the revascularization procedure, cardiopulmonary bypass was discontinued in a stable hemodynamic condition. The coronary arteries and the bypass grafts were then investigated without decannulation and prior to adminis-tration of protamine sulfate (Kodama Ltd, Tokyo, Japan). The transducer was covered with a sterile plastic sleeve to prevent leakage of indirect current. To analyze the blood flow pattern in the coronary arteries, the transducer was positioned over the target coronary artery to obtain a two-dimensional color Doppler image of the artery (Figure 1
). Such images may reveal the condition of the coronary artery wall, such as the presence of calcification or atheromatous plaques. To measure flow velocity, the cursor of the image was positioned at the center of the image and pulsed Doppler measurements taken to produce the flow velocity curve (Figure 1). Blood flow was then calculated from the flow velocity and the area under the curve, which could be measured off the image.
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Figure 1. Pulsed Doppler measurements of blood flow in the left anterior descending coronary artery (A) before and (B) after grafting. Before grafting, the diastolic component was low. After grafting, blood flow increased, especially in the diastolic component.
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Measurements were made of 30 left internal thoracic arteries (LITAs), where the internal thoracic artery was anastomosed to the left anterior descending coronary artery (LAD), and 68 saphenous vein grafts (SVGs) in the 30 subjects. Of the SVGs, 28 were grafted to the right coronary artery system, 26 to the left circumflex artery, and 14 to the diagonal branches. There was no sequential bypass in this series. All flow measurements were completed without any hemodynamic problems, and there was no infection.
To evaluate the accuracy of the pulsed Doppler measurements, blood flow in the LITA was measured at the site of its distal anastomosis using this device as well as a transit-time flowmeter9 (Transonic System Inc., Ithaca, NY, USA) under the same hemodynamic conditions before closure of the chest, and the values were compared. Data are shown as the mean ± standard error of the mean and statistically analyzed by paired t test. Differences were considered statistically significant when p < 0.05.
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RESULTS
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Figure 1A
shows an image of the LAD before grafting and Figure 1B the LITA anastomosed to the LAD in the beating heart, with Doppler analysis of blood flow in the LAD. In all the patients, blood flow in the LITA and the SVG could be measured with the transducer. The left main trunk, the LAD, and the proximal portion of the right coronary artery could be visualized easily in the beating heart. It was difficult, however, to observe the lateral and posterior branches of the left coronary artery and the distal right coronary artery in the beating heart. Although it was possible to detect the lumen of individual coronary arteries, the degree of stenosis could not be rendered unequivocally. However, it could be evaluated from the Doppler flow pattern (Figure 1). When the flow of the diastolic component is lower than that of the systolic component, and/or the total graft flow is less than 20 mL•min-1, graft failure or problems of the anastomosis should be suspected.10 In this series, no grafts were revised based on findings from the transit-time flowmeter or the Doppler transducer.
The systolic flow in the LITA (n = 30) was 17 ± 6 and 15 ± 5 mL•min-1 measured with the Doppler and transit-time systems, respectively, while the diastolic flow was 42 ± 6 and 39 ± 7 mL•min-1, respectively. There were no significant differences between the values obtained by the 2 systems.
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DISCUSSION
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Knowledge of the blood flow pattern in the coronary artery system is valuable for evaluating the grade of coronary artery disease.10 The pattern reveals the full hemodynamic condition of the vessel, including the grade of stenosis, the run-off of the peripheral coronary bed and/or coronary artery resistance, and perhaps the regional wall dynamics of the myocardium. In this respect, precise evaluation of flow patterns is indispensable to the real-time intraoperative investigation of coronary artery circulation. The use of a thermal coronary imaging system has been reported for intraoperative assessment of the outcome of coronary revascularization,6 but the system could not accurately evaluate coronary circulation and, thus, existing hemodynamics. An ultrasound method that allows evaluation not only of the coronary arteries but also of cardiac function has a distinct advantage in this respect. The ultrasound transducer used in this study has selectable dominant ultrasound frequencies, thereby providing high-resolution and high-penetration images specific to the region of interest. It allows assessment of ventricular function at the same time, as with the intraoperative transesophageal approach.11 It can also process the color signals of 2 lines simultaneously, thereby providing a much higher frame rate. Unfortunately, it remains difficult to observe the full condition of the coronary arteries in the beating heart. Obviously, a higher-frequency ultra-sound method may eventually be developed to precisely depict the condition of the coronary system.7,8 However, at present, the quality of color Doppler imaging cannot be maintained beyond 10 MHz. Technical developments in this area most likely will lead to enhancement of the quality and usefulness of this method. Although this fingertip transducer was acceptable for studying the heart, it was originally designed for transvaginal observation of the uterus. Hence, it should be reshaped to facilitate its use in the pericardial cavity.
The results of this study indicate that this fingertip epicardial transducer enables intraoperative observation of flow patterns in a large portion of the coronary arteries and bypass grafts in the beating heart. Comparison of measurements obtained with the Doppler transducer and the transit-time flowmeter shows that flow analysis using the transducer is reliable and reproducible. The advantage of this device over other kinds of flowmeter, including the transit-time flowmeter, is its ability to evaluate not only bypass graft flow but also coronary artery flow itself, which will allow intraoperative assessment of the coronary artery system. Moreover, in the cardioplegic arrested heart, this method could permit rapid assessment of the condition of the coronary arteries in terms of calcified lesions or atheromatous plaques. Further techni-cal development should allow this method to detect intraoperatively coronary artery disease in patients undergoing emergency operations such as acute aortic dissection. Because of donor shortage, hearts from persons over 50 years old have recently been transplanted.5 Hearts of older donors should always be assessed for coronary artery involvement. The intraoperative epicardial approach permits the coronary system of donor hearts to be evaluated without using interventional procedures such as coronary arteriography or depending on the uncertain assessment of operators based on direct palpation. In view of this, further study of the relationship between coronary flow patterns obtained with pulsed Doppler ultrasound and the degree of stenosis of the coronary arteries should be conducted to determine if this system could detect the existence of coronary artery disease.
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Acknowledgments
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This study was supported by the Alexander von Humboldt Foundation, Bonn, Germany.
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TOP
ABSTRACT
INTRODUCTION
