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J Thorac Cardiovasc Surg 2003;126:634-637
© 2003 The American Association for Thoracic Surgery
Editorial |
a the University of Cincinnati, Department of Surgery, Cincinnati, Ohio, USA
b University of Leipzig, Clinic for Heart Surgery, Leipzig, Germany
Received for publication December 20, 2002; accepted for publication March 4, 2003. * Address for reprints: Randall K. Wolf, MD, University of Cincinnati, Director, Institute for Surgical Innovation, 231 Albert B. Sabin Way, M.L. 0558, Cincinnati, OH 45267 USA
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We make the path by walking...
It is no exaggeration to predict that the acceptance of alternate coronary artery bypass grafting (CABG) techniques, such as off-pump coronary artery bypass, minimally invasive direct coronary artery bypass (MIDCABG), and endoscopic CABG, will ultimately depend on graft patency in comparison with open, standard, on-pump techniques. Graft patency will also be the final determinant of success for evolving anastomotic devices in CABG. Results of early, but not intraoperative, angiography after conventional CABG reveal that 45% to 100% of the patients in the study (operated) had follow-up angiography but document a patency rate for left internal thoracic artery (LITA) to left anterior descending artery (LAD) grafts of 94% to 98%.1 It is known that LITA graft patency changes little after the initial period. This suggests that long-term arterial graft patency is excellent and that the majority of arterial graft failures occur early and are most likely caused by technical problems. It follows that graft patency could be improved if technical problems are identified early. Logically, the arterial conduit and anastomosis should be assessed immediately. This is best accomplished in the operating suite at a time when problems can be readily addressed by the surgical team. There are several technologies, some accepted and some evolving, that can be used in intraoperative coronary graft assessment. These are summarized in Table 1. 2
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Despite encouraging technologic advances in noninvasive scanning and in physiologic measures of blood flow in the coronary tree, coronary angiography has remained the gold standard for both the cardiologist and the surgeon both preoperatively and postoperatively. Intraoperative coronary angiography can be performed with a fixed unit installed in the operating suite or with portable units. The disadvantage of portable units is a possible lack of definition in the study. All coronary angiography techniques share the disadvantages of the presence of ionizing radiation, time required, high expense, and use of an invasive technique. Even intraoperative angiography, the gold standard, suffers some predictive value. Documented intraoperative angiographic anastomotic abnormalities, such as hematomas and stenoses, have been observed to resolve in follow-up angiographic assessment without intervention.1 Intraoperative angiography might become more common if we move toward more same-day hybrid procedures. However, this shift, if it occurs, will take some time because hybrid procedures, especially same-day procedures, are uncommon, and combined operating-catheterization suites are generally not available.
Thermal imaging
Thermal imaging or thermal coronary angiography (TCA) is a unique technology in which small differences in surface temperature can be detected and analyzed to create a visual image of a coronary conduit and coronary arteries.3,4 This results in a thermal angiogram. Falk and colleagues4 demonstrated in a large series (370 patients) that TCA technology detected intraoperative graft dysfunction in 1% of venous grafts and 5.3% of ITA grafts. The authors reported that most occlusions of the ITA (16/19) were due to technical problems at the distal anastomosis. Proximal ITA occlusion was found in 3 patients. Unfortunately, TCA requires a relatively expensive thermal camera, and anastomotic sites are not routinely clearly seen. Falk and colleagues no longer use this imaging modality routinely.
Intraoperative assessment by means of ultrasonography
The following ultrasound technologies have been used in CABG assessment in the operating room: handheld epicardial Doppler ultrasonography, transit-time (TT) Doppler ultrasonography, and high-frequency epicardial echocardiography. The simple handheld Doppler devices have been superseded by more sophisticated devices.
Ultrasonic TT measurements are the topic of an article in this issue of the Journal.5 The technique is noninvasive, simple, quick, safe, and relatively low cost. According to Transonic Systems, Inc (Ithaca, NY), manufacturer of one of the TT probes, Transonic has flowmeters in approximately 31% of cardiac centers in the United States (356 flowmeters in 1144 cardiac centers; personal communication, Matt Woolson, 2003). This suggests that there is significant interest on the part of cardiac surgeons concerning intraoperative graft assessment. We do not have data on the extent of routine use of these purchased TT flowmeters, and it is clear that not all centers have the technology to use them routinely in cardiac cases.
The potential shortcoming of TT measurement in CABG graft assessment lies in the fact that the TT depends on physiologic data, including blood pressure, peripheral bed resistance, and competitive flow. The current literature suggests that more sophisticated analyses (not just a mean or peak flow measurement) of the flow pattern in TT are crucial in predicting short-term graft patency. D'Ancona and associates6 revised 34 (3.2%) of 1145 off-pump CABGs in 33 patients. All grafts revised had low flow rates. Three of the low-flow-rate grafts had normal pulsatility indexes. In all the revised grafts with low flow rates and high pulsatility indexes, there was improvement after revision. In the 3 grafts with low flow rates and normal pulsatility indexes, no technical problems were identified, and values remained unchanged after revision. This and another report7 conclude that all grafts that demonstrate both low flow values and a high pulsatility index should be revised. Unfortunately, in the current report in this issue of the Journal,5 pulsatility index was not reported. For TT Doppler ultrasonography to be of significant clinical value, the pulsatility index must be assessed. In addition, when using TT, observing the diastolic waveform can be helpful, particularly in LITA-LAD grafts. In properly functioning grafts a significant diastolic curve is easily detected visually. Lack of a significant diastolic curve suggests poor LITA-LAD flow and, in the presence of a high pulsatility index and low mean flow, predicts a poorly functioning graft.
High-frequency epicardial echocardiography
Previous reports in the 1980s8 demonstrated that epicardial high-frequency ultrasonic probes could provide information about target sites in the coronary tree. As has been previously noted,2 these probes were quite large and bulky. Recent technological advances in transducer designs have resulted in a clinically available 10-MHz ultrasonographic minitransducer that can be applied epicardially during off-pump bypass surgery (OPCAB). Eikelaar and coworkers9 recently reported that with the minitransducer, in 11 of 13 OPCAB cases, the anastomotic orifice could be adequately visualized. Color Doppler images could be displayed (see Figure 29).
The authors postulate "that this minitransducer will become a valuable tool to detect technical errors before chest closure." We predict that the 10-MHz high-frequency color Doppler minitransducers applied epicardially will provide adequate graft assessment and, in the case of new transesophageal echocardiography (TEE), wall-motion abnormalities after graft placement will serve to rule out dissection of the ITA or significant anastomotic problems. This type of algorithm might become routine because many heart centers already routinely use TEE in all cardiac cases. The addition of epicardial assessment would require only the purchase of the probe that would connect to the TEE machine in the operating suite.
There are other experimental and clinical intraoperative methods of assessing acute graft flow in CABG surgery, but with the exception of TEE, most technologies are either not ready for prime time or have not been thoroughly studied in large series. In a discussion of an article on the assessment of the quality of the distal anastomosis,10 Frank Selke stated that he found TEE to be very valuable intraoperatively in concert with other methods to assess graft flow. Significant new wall-motion abnormalities on TEE suggest possible acute graft problems.
Wolfe10 stated "that the diversity and limitations of the techniques for assessment of the adequacy of the distal anastomoses, coupled with the scarcity of proper studies that correlate these techniques to long term graft patency and other outcomes, account for the lack of consensus among cardiac surgeons in regard to the utility of assessing the adequacy of the distal anastomosis in their current clinical practice."
We should measure flow in the newly constructed CABG to rule out a correctable intraoperative problem, especially checking the ITA graft to the anterior circulation because this graft, when patent, predicts a survival advantage. As we enter a new era of biosurgery, as evidenced by the testing of medications such as an E2F decoy that might improve long-term saphenous graft patency, it is important to exclude early technical failures that could adversely affect a drug trial, such as E2F, but have nothing to do with the efficacy of the drug.
The current study by Schmitz and associates in this issue of the Journal5 is important because it allows us to continue a critical evaluation of intraoperative graft assessment technologies as newer CABG techniques and devices evolve. Correlation of the accuracy of noninvasive techniques to assess graft flow with the gold standard of intraoperative angiography has not been documented in large series, and no control postoperative angiography was performed in the present study on this issue.
We as cardiac surgeons will continue to "make the path by walking" to improve the technical results of CABG in on- pump, off-pump, and endoscopic procedures. As mentioned earlier, we predict this is now possible with a combination of high-frequency, epicardial, ultrasonic minitransducer, color flow imaging, and TEE. A proved noninvasive technique would serve us well as we continuously change the operative approaches and will speed the evaluation and possible adoption of newer anastomotic devices or antihyperplasia drugs as they are introduced into clinical CABG procedures. If nothing else, minimally invasive CABG techniques have focused our attention on documenting graft patency and will continue to foster industry support for emerging technology in this field. By improved identification and correction of technical problems in the operating suite, overall graft patency will improve, resulting in a better operation not only for the surgeon but also for the patient.
References
This article has been cited by other articles:
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  C. Detter, S. Wipper, D. Russ, A. Iffland, L. Burdorf, E. Thein, K. Wegscheider, H. Reichenspurner, and B. Reichart Fluorescent Cardiac Imaging: A Novel Intraoperative Method for Quantitative Assessment of Myocardial Perfusion During Graded Coronary Artery Stenosis Circulation, August 28, 2007; 116(9): 1007 - 1014. [Abstract] [Full Text] [PDF]
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 W. Hassanein, A. Albert, I. Florath, Y. Y. Hegazy, U. Rosendahl, S. Bauer, and J. Ennker Concomitant aortic valve replacement and coronary bypass: the effect of valve type on the blood flow in bypass grafts Eur. J. Cardiothorac. Surg., March 1, 2007; 31(3): 391 - 396. [Abstract] [Full Text] [PDF]
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 H. Stein, J. M. Smith, J. R. Robinson, and M. R. Katz Target vessel detection and coronary anastomosis assessment by intraoperative 12-MHz ultrasound. Ann. Thorac. Surg., September 1, 2006; 82(3): 1078 - 1084. [Abstract] [Full Text] [PDF]
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 J. Garbade, C. Ullmann, M. Hollenstein, M. J. Barten, S. Jacobs, S. Dhein, T. Walther, J. F. Gummert, V. Falk, and F.-W. Mohr Modeling of temperature mapping for quantitative dynamic infrared coronary angiography for intraoperative graft patency control J. Thorac. Cardiovasc. Surg., June 1, 2006; 131(6): 1344 - 1351. [Abstract] [Full Text] [PDF]
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R. P.J. Budde, R. Meijer, T. C. Dessing, C. Borst, and P. F. Grundeman Detection of construction errors in ex vivo coronary artery anastomoses by 13-MHz epicardial ultrasonography J. Thorac. Cardiovasc. Surg., May 1, 2005; 129(5): 1078 - 1083. [Abstract] [Full Text] [PDF]
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 R. P.J. Budde, T. C. Dessing, R. Meijer, P. F.A. Bakker, C. Borst, and P. F. Grundeman Robot-assisted 13 MHz epicardial ultrasound for endoscopic quality assessment of coronary anastomoses Interactive CardioVascular and Thoracic Surgery, December 1, 2004; 3(4): 616 - 620. [Abstract] [Full Text] [PDF]
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