(Chest. 2002;121:951-956.)
© 2002
American College of Chest Physicians
Comparison of the Postoperative Blood Flow Waveforms of the Bypassing Grafts in Patients Following Minimally Invasive Direct Coronary Artery Bypass*
Tsung-Po Tsai, MD, PhD, FCCP;
Kwo-Cheng Ueng, MD;
Jung-Min Yu, MD;
Yu-Chuan Chang, MD and
Yi-Liang Wu, MD
*
From the Department of Cardiothoracic Surgery, Division of Cardiology, and Division of Neurology, Chung Shan Medical University Hospital, Taichung, Taiwan.
Correspondence to: Tsung-Po Tsai, MD, PhD, FCCP, No. 110, Sec l, Chien-Kuo N. Road, Taichung, Taiwan; e-mail: tsai{at}flower.csh.org.tw
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Abstract
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Purpose: To use Doppler ultrasound velocimetry to detect and compare the postoperative flow characteristics of the bypassing grafts in patients following minimally invasive direct coronary artery bypass surgery (MIDCAB).
Materials and methods: From January 1997 to June 1999, 34 patients underwent MIDCAB with the left internal thoracic artery (LITA) to the left anterior descending coronary artery (LAD) [n = 23], with the right gastroepiploic artery (RGEA) to the right posterior descending artery (RPD) [n = 3], or with the LITA with a saphenous vein graft extension to the LAD (n = 6), the diagonal coronary artery (n = 1), or the right acute coronary artery (n = 1). There were two patients with LITA to the LAD and RGEA to the RPD. Patients underwent MIDCAB due to coronary artery stenosis (100% occlusion, n = 10; 90 to 99% stenosis, n = 18; < 90% stenosis, n = 5) or unsuccessful percutaneous transcoronary angioplasty with dissection (n = 1). All patients underwent flow velocity measurement by Doppler ultrasound velocimetry in the immediate postoperative period, and at 6-month and 12-month intervals; graft flows were quantified based on Doppler velocimetric data.
Results: The results showed that in a patient with a totally occluded LAD or RPD, typical biphasic velocity waveforms were consistently observed. However, a delayed diastolic wave was noted in RGEA grafts. In patients with less-occluded stenotic lesions or with strong back flows, the flow velocity patterns showed biphasic waveforms but systolic reversal was observed in the area closest to the anastomotic site.
Conclusion: The presence of an LAD or RPD stenosis proximal to the anastomotic site significantly affects the LITA or RGEA graft flow volume. The biphasic flow pattern proves that an LITA or RGEA graft transports the blood primarily to coronary arteries during the diastolic phase.
Key Words: internal thoracic artery • minimally invasive direct coronary artery bypass • right gastroepiploic artery • saphenous vein graft
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Introduction
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The use of the internal thoracic artery (ITA) as a graft to the left anterior descending coronary artery (LAD) without cardiopulmonary bypass (CPB) was initiated by Kolesov.1
A series of articles2
3
4
have been published reporting coronary revascularization without CPB.
Even after the introduction of mechanical stabilizers, the ability to achieve a technically perfect anastomosis is less certain during beating-heart bypass surgery without CPB. Blood flow velocity and its dynamic patterns have relevance to coronary artery bypass conduit function and longevity.5
However, there are no data comparing phasic blood flow in the ITA and saphenous vein grafts (SVGs) in patients following minimally invasive direct coronary artery bypassing surgery (MIDCAB) at the late postoperative or follow-up periods. Previously, we use pulsed Doppler velocimetry to study the velocity profiles across the coronary artery bypass conduits in patients following MIDCAB.6
7
8
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Materials and Methods
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Patients
From January 1997 to June 1999, 34 consecutive patients (mean age, 65 years; range, 51 to 89 years; 4 women) with coronary atherosclerotic heart disease underwent MIDCAB. The indications for surgery were either LAD or right posterior descending artery (RPD) stenosis (total occlusion [n = 10], 90 to 99% stenosis [n = 18], and < 90% stenosis [n = 5]) or unsuccessful percutaneous transcoronary angioplasty with dissection (n = 1).
Surgery
Patients underwent routine MIDCAB as previously described.9
However, part of the fourth or fifth rib cartilage, as well as the tip of the xiphoid process, were removed by either disarticulation or Rongeur debridement in order to allow for better dissection of the left ITA (LITA)- or right gastroepiploic artery (RGEA)-pedicled grafts and for better location of the Doppler flow velocimeter. The bypass conduits included either LITA only (n = 23), RGEA only (n = 3), or LITA with an added SVG extension for either inadequate immediate blood flow volume (< 20 mL/min or mean graft flow < 5 mL/min) or for small diameter (< 1.2 mm) at the distal LITA (n = 10). All RGEA conduits were grafted into the RPD, and all LITA-only and eight composite (LITA plus SVG) conduits were grafted into the LAD. Two LITA-plus-SVG composite grafts were grafted to either the diagonal or the right acute coronary artery.
Doppler Ultrasound
A Doppler ultrasound 7.5/5.0-MHz pulsed velocimeter (Sonos 4500; Hewlett-Packard; Palo Alto, CA) was used for all patients in this study. All flow quantification of graft flow rates were calculated from the Doppler velocimetric data. All patients underwent flow velocity measurement at the time of surgery, at the immediate postoperative period, at 6 months and 12 months postoperatively, and at all subsequent visits. The follow-up period ranged from 6 to 37 months (mean, 18 months). Twenty-five patients (73.5%) underwent repeat cardiac catheterization during this period, and the ultrasound results were compared to the catheterization data.
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Results
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In the LITA-to-LAD patient group, the velocity profile across the LITA graft several centimeters proximal to the graft to the coronary anastomosis showed a biphasic velocity configuration characterized by a typical prevalent diastolic component. Transition of the typical coronary flow pattern with higher peak diastolic velocity seemed to occur in the middle or lower parts of the graft (Figs 1
2
3
). Total graft blood flow can be estimated from the mean velocity and the measured vessel diameter; resting flow ranged from 16 to 127 mL/min (mean, 39 mL/min).
In the RGEA-to-RPD patient group, delayed diastolic wave with a lower peak diastolic velocity configuration was noted (Fig 4 ). However, the resting blood flow volume was still adequate and acceptable (66, 70, and 90 mL/min in the three patients, respectively).
In the composite graft patient group (LITA plus SVG to LAD), the appearance of the waveform was similar to that seen in the LITA-to-LAD group, whether the Doppler velocity measurement was performed at the arterial or the SVG vein segment. This correlation remained consistent during postoperative follow-up, the longest of which was 37 months (Fig 5
, 6
).
Sometimes, systolic flow reversal might have been seen due to retrograde flow from the LAD or true flow diversion in systole to the chest wall. In patients with a less-occluded stenotic lesion or with strong back flow from the previous SVG, the flow velocity patterns showed biphasic waveforms, but systolic reversal was observed in the area closest to the graft to coronary anastomosis site (Fig 7
).
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Discussion
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Transthoracic echocardiography can provide information on blood velocity and anatomy and therefore has the potential to allow measurement of blood flow.10
Doppler velocimetric profiles of the bypassing grafts were obtained in all our study patients (100%). In all cases, a biphasic pattern of blood flow was recorded that corresponded to systole and diastole. We also found that a transition of the typical coronary flow pattern with higher peak diastolic velocity seemed to occur in the lower parts of the grafts (third or fourth intercostal spaces). And a more prevalent diastolic component was noted if velocimeter-measured site was closer to the graft to coronary anastomosis site. Crowley and Shapiro11
and de Bono et al10
acknowledged that 19% and 40%, respectively, in their series could not be viewed using ultrasound. They also noted the large potential for error in derived flow measurements in small-caliber vessels with Doppler ultrasound techniques. More satisfactory identification (98%) could be detected with duplex Doppler echocardiography from the supraclavicular fossa.12
Doppler velocimetric profiles of the bypassing grafts (LITA, RGEA, or composite grafts) were obtained in all of our MIDCAB patients (100%). During MIDCAB, we did not open the pericardial cavity completely; and, during ITA graft harvesting, we did not divide all branches and mobilize the vessel to the level of the subclavian artery beyond the first intercostal space. Therefore, we can avoid the natural tendency of the ITA graft falling away from the chest wall; therefore, we obtained a more satisfactory transcutaneous postoperative imaging by Doppler velocimetry. Invasive studies have shown that residual flow in the recipient artery may compete with flow in the patent LITA and reduce flow in the graft.13
Due to retrograde flow from the native LAD or from the previous stenotic SVG, systolic flow reversal was seen in three of our patients.
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Conclusion
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High-frequency transcutaneous ultrasound study with Doppler flow velocimetry (through the operation-created windows) allows identification of the LITA, RGEA, and composite grafts, as well as measurement of blood flow in patients following MIDCAB. The presence of an LAD or RPD stenosis proximal to the anastomotic site significantly affects the LITA or RGEA graft waveform and flow volume. Preliminary 3-year clinical experience demonstrates that the biphasic flow pattern detected in patients with MIDCAB proves that LITA or RGEA grafts transport the blood primarily to the coronary artery during the diastolic phase. While the change in characteristics of the waveform in the composite graft (LITA plus SVG), especially in the saphenous vein segment portion, is the same as the LITA graft at the beginning, only further clinical follow-up will define the final outcome. Use of this technique may allow noninvasive identification of the bypassing grafts and comparison of their postoperative blood flow waveforms in patients following MIDCAB. It may also detect the stenotic change of the bypassing graft in serial follow-up studies.
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Acknowledgements
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We thank Miss Shu-Yi Chou for data collection and article preparation.
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Footnotes
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Abbreviations: CPB = cardiopulmonary bypass; ITA = internal thoracic artery; LAD = left anterior descending coronary artery; LITA = left internal thoracic artery; MIDCAB = minimally invasive direct coronary artery bypass surgery; RGEA = right gastroepiploic artery; RPD = right posterior descending artery; SVG = saphenous vein graft
Received for publication February 13, 2001.
Accepted for publication October 25, 2001.
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References
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Abstract
Introduction
