Ann Thorac Surg 2004;78:477-480
© 2004 The Society of Thoracic Surgeons
Original article: cardiovascular
Midterm results of coronary artery bypass graft surgery with internal thoracic artery under low free-flow conditions
Mitsumasa Hata, MDa*,
Motomi Shiono, MDa,
Tatsuya Inoue, MDa,
Akira Sezai, MDa,
Nanao Negishi, MDa,
Yukiyasu Sezai, MDa
a The Second Department of Surgery, Nihon University School of Medicine, Tokyo, Japan
Accepted for publication February 18, 2004.
* Address reprint requests to Dr Hata, The Second Department of Surgery, Nihon University School of Medicine, 30-1 Ooyaguchi Kamimachi Itabashi-ku, Tokyo 173-8610, Japan
e-mail: mihata{at}med.nihon-u.ac.jp
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Abstract
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BACKGROUND: We use the left internal thoracic artery (LITA) even when flow is very low. In this study, we investigated midterm outcome of coronary artery bypass graft surgery with low free-flow LITA.
METHODS: One hundred patients undergoing coronary artery bypass graft surgery using LITA with a free flow of less than 20 mL/min were reviewed. The mean follow-up duration was 47.4 months, ranging from 1 to 65 months. Graft angiography was performed postoperatively. The diameter of the LITA was assessed angiographically. Cumulative graft patency, cardiac-related event-free rate, and actuarial survival rate were calculated by the Kaplan-Meier method.
RESULTS: An early postoperative Doppler study showed that the diastolic-to-systolic ratio in the LITA was 1.76 ± 0.33. A 1-month postoperative angiography revealed LITA string sign in 2 patients. One had a percutaneous coronary intervention, whereas string sign was not detected in the second patient, and LITA patency showed a marked improvement in 1-year postoperative angiogram. One month postoperatively the LITA diameter was 1.6 ± 0.4 mm, and significantly enlarged in the second angiogram (1.9 ± 0.4 mm, p = 0.0003). There was a significant correlation between the diameter of the LITA and the left anterior descending coronary artery (r = 0.889, p = 0.0001). The cumulative graft patency rate at 1 and 4 years was 99.0% and 94.3%, respectively. The cardiac-related event-free rate at 1 and 5 years was 97.0% and 93.3%, respectively. The actuarial survival rate at 5 years was 97.1%.
CONCLUSIONS: Even with a very low LITA free flow, graft function improves with LITA growth, if there was no mechanical damage that impedes recovery.
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Introduction
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The use of the left internal thoracic artery (LITA) graft to revascularize the left anterior descending coronary artery (LAD) has significantly improved the long-term results of coronary artery bypass grafting (CABG) [1]. However, it is commonly believed that the LITA should not be used when free flow is too low. Several investigators recommend some intraluminal maneuvers to increase free flow, such as papaverine injection, metallic cannula insertion, and balloon dilation [2, 3]. However, the LITA intima may deteriorate as the result of such procedures [4, 5]. Even when the LITA flow is very low, we recommend anastomosis without any further intraluminal maneuvers [6]. The LITA is a so-called living conduit because the diameter can increase in the late postoperative period [7]. In the present study, we investigated the medium-term outcome of CABG using the LITA under low free-flow conditions.
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Patients and methods
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Between January 1998 and December 2001, CABG was performed on 371 patients at our institution, except for off-pump CABG. In all patients, the LITA was anastomosed to the LAD. We reviewed 100 patients, consisting of 78 men and 22 women with an average age of 63.7 ± 11.8 years, with a LITA free flow of less than 20 mL/min. The LITA was dissected with a pedicle using electrocauterization and titanium hemoclips. After complete mobilization, the LITA was cut at the proximal end of its bifurcation. We confirmed pulsatile blood flow from the cut end of the LITA. The distal cut end was then closed by a hemoclip. The mobilized LITA was then covered with 0.2% papaverine-soaked gauze for 15 minutes. If no blood flow appeared or only a few blood drops appeared from the LITA cut end, we would give up on using the LITA. Papaverine administration, metallic cannula insertion, or balloon dilation were not used. Before the cardiopulmonary bypass was initiated, the chest retractor was released as much as possible, and the free flow was then measured by allowing the cut end of the LITA to bleed into a graduated cylinder for 15 seconds. If pulsatile blood flow was detected, even when LITA flow was less than 20 mL/min, we anastomosed the LITA to the LAD without any further maneuvers. A CABG was performed at the midportion of the LAD with an 8-0 polypropylene nonabsorbable suture. Saphenous vein grafts were used for all diseased vessels except for the LAD. On the first postoperative day, LITA function was assessed near the anastomosis using apical transthoracic Doppler echocardiography, as we have previously reported [8]. Ninety-nine patients had a graft angiography and a second Doppler echocardiography 1 month after the operation. The mean follow-up time was 47.4 months, ranging from 1 to 65 months. A second graft angiography was performed in 62 patients (62%) 12 to 48 months (mean, 28.6 months) after the operation. The diameter of the LITA just proximal to the anastomosis was assessed by an angiography comparing the first and second angiographic diameter. The results are expressed as the mean ± standard deviation. Statistically significant differences were determined from paired Student's t test. Correlation between the diameter of the LITA and the LAD was determined from a Bartlett's test and Fisher's r to z test. Coefficients (r) of more than 0.7 were interpreted as indicative of a significant correlation. A p value of less than 0.05 was considered statistically significant. Cumulative LITA graft patency, cardiac-related event-free rate, such as recurrent angina or heart failure, and actuarial survival curves were analyzed by the Kaplan-Meier method.
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Results
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There was no patient in whom we were unable to use the LITA. The average number of grafts was 2.7 ± 1.9. The average LITA free flow rate was 12.4 ± 5.9 mL/min, ranging from 4 to 20 mL/min. The average systolic blood pressure, heart rate, and central venous pressure during evaluation of free flow were 102.2 ± 14.3 mm Hg, 78.2 ± 17.7 beats/min, and 2.1 ± 1.6 mm Hg, respectively. All patients were easily weaned from cardiopulmonary bypass. None of the patients had low-output syndrome or perioperative myocardial infarction. Maximum postoperative creatine kinase-MB levels were 35.9 ± 29.7 IU/L. The early postoperative Doppler studies showed that the diastolic-to-systolic ratio of the LITA was 1.76 ± 0.33. One month after the operation, the diastolic-to-systolic ratio increased significantly to 1.87 ± 0.35 (p = 0.025), and a postoperative angiography revealed LITA string sign in 2 patients. One had a percutaneous coronary intervention for recurrent angina, and was the only patient complicated by postoperative myocardial ischemia and angina during the study period, whereas in the other patient, the string sign was not detected and LITA patency had markedly improved in the angiogram 1 year after the operation. In 1 patient a late occlusion of the LITA was detected in the 15-month postoperative angiogram. One month after the operation, the LITA diameter was 1.6 ± 0.4 mm, and was significantly enlarged in the second angiogram (1.9 ± 0.4 mm; p = 0.0003; Fig 1). There was a significant correlation between the diameters of the LITA and the LAD 1 month after the operation (r = 0.773), which remained strong after 1 year (r = 0.889; p = 0.0001; Fig 2). Operative death occurred in 1 patient as a result of a stroke. One patient died of renal cancer 4 years after the operation. The cumulative graft patency rate at 1 and 4 years was 99.0% and 94.3%, respectively (Fig 3). The cardiac-related event-free rate at 1 and 5 years was 97.0% and 93.3%, respectively (Fig 4). The actuarial survival rate at 5 years was 97.1%.
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Fig 1. Left internal thoracic artery graft angiogram 1 month after the operation (left) and a second postoperative angiogram (right). Left internal thoracic artery diameter (arrow) was significantly enlarged in the second angiogram.
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Fig 2. Correlation between the diameter of the left internal thoracic artery (LITA) and the left anterior descending coronary artery (LAD). One-month postoperative study (left; n = 99; y = 0.114 + 0.877x: r = 0.773; R2 = 0.598). Correlation from second angiogram (right; n = 62; y = 0.279 + 0.811x: r = 0.887; R2 = 0.790). There was a strong correlation between the diameter of the left internal thoracic artery and the left anterior descending coronary artery (r = 0.889; p = 0.0001).
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Fig 3. Cumulative graft patency curve. The cumulative graft patency rate at 1 and 4 years was 99.0% and 94.3%, respectively.
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Fig 4. Cardiac-related event free curve. The cardiac-related event-free rate at 1 and 5 years was 97.0% and 93.3%, respectively.
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Comment
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The main causes of LITA low free flow is considered to be temporary spasm or mechanical damage inflicted by surgical maneuvers. He and colleagues [9] reported that variations in reactivity are shown along the full length of the human LITA and that the distal portion of the LITA is most sensitive. Therefore, the portion of the LITA in which we assessed free flow may be more readily affected by vasospasm. Even with a low free flow owing to spasm, if pulsatile blood flow is maintained from the cut end we are certain that there would be no mechanical damage of the intima. Pulsatile blood flow is evidence of blood transmission through the LITA. Tector [10] also emphasized the importance of measuring blood flow and testing for a pulse in the spatulated distal end of the LITA before initiating cardiopulmonary bypass. Even though mobilized LITA free flow was very low, there were no cases of hemodynamic instability in the present study. On the first day after the operation, the Doppler velocity waveform of the LITA near the anastomosis showed that the diastolic-to-systolic ratio was greater than 1.0. This means that the transient spasm in the LITA had disappeared and that the graft was working well in the early postoperative phase.
Arterial conduits may develop spasm during harvesting. This condition varies in its severity and is not always effectively treated with topical papaverine. However, we believe that LITA flow may increase in proportion to myocardial blood demand if there is no mechanical damage during mobilization. Therefore, we did not use intraluminal maneuvers, such as retrograde papaverine injection, metallic cannula insertion, or balloon dilation for low free-flow LITA, which might cause endothelial damage and compromise long-term patency [4, 5, 11]. In the present study, none of the patients had low-output syndrome or perioperative myocardial infarction, and the early postoperative blood flow velocity waveform was excellent despite low free flow during the procedure. Thus, it is likely that the transient spasms of the LITA have already subsided in the acute postoperative phase. One month after the operation, the Doppler study showed that the LITA diastolic-to-systolic ratio was significantly higher than on the first postoperative day. Furthermore, the second angiogram revealed that LITA diameter was significantly enlarged. Akasaka and colleagues [7] reported that LITA flow capacity increased in the late postoperative period because of increases in the LITA diameter. In the present study, we detected enlargement of the LITA diameter and a significant correlation between the diameters of the LITA and the LAD. Furthermore, this correlation was stronger in the later phase. These results suggest that the diameter of the LITA and flow increased in proportion to the myocardial blood demand.
Excellent long-term graft quality and flow dynamics can be maintained in the LITA [12]. Even though LITA free flow is very low during surgery, this continued long-term? In the present study, a string sign of the LITA was detected in 2 patients. One required a percutaneous coronary intervention to the LAD; however, in the second patient, the string sign disappeared and LITA graft patency completely recovered by the time of the second angiogram. In the latter patient, native LAD disease increased from 50% before the operation to 99% at the time of the second angiogram. Dincer and Barnar [13] reported a rare case of a once-occluded LITA recanalized in the late period. They showed that the LITA, once occluded because of competition for blood flow with the native LAD, was recanalized in the late postoperative period and associated with the progression of native LAD stenosis. We have also reported a unique case in which the LITA string sign improved in the late postoperative period [14]. The LITA string sign may improve in the late period if no damage has occurred during surgery. The LITA has a potent endogenous nitrate system that helps prevent vasospasm, thrombus formation, and graft occlusion, so long as the endothelium is preserved during surgical preparation [15]. Thus, even with a low free flow during surgery, the LITA will continue to work for the long term. In the present study, LITA graft occlusion was detected in 2 patients. Myocardial ischemia as a result of LITA occlusion was a complication in only 1 patient. The cumulative graft patency rate of low free-flow LITA was 94.3% at 4 years. The cardiac-related event-free rate at 1 and 5 years was 97.0% and 93.3%, respectively. The actuarial survival rate at 5 years was 97.1%. We think these results are quite acceptable. Therefore, even though the LITA free flow is very low, it should still be used for grafting to the LAD, and no intraluminal maneuvers are required.
Even with a very low free flow, graft function improves with growth of the LITA, and performs well for the long term, in the absence of mechanical damage that would impede recovery.
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References
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Abstract
Introduction
