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Ann Thorac Surg 2002;74:2097-2100
© 2002 The Society of Thoracic Surgeons

Original article: cardiovascular

Assessment of ascending aorta using epiaortic ultrasonography during off-pump coronary artery bypass grafting

Tomoki Shimokawa, MDa*, Naoki Minato, MDa, Noriko Yamada, MDa, Yuji Takeda, MDa, Yasushi Hisamatsu, MDa, Manabu Itoh, MDa

a Department of Thoracic and Cardiovascular Surgery, Fukuoka Tokushukai Hospital, Fukuoka, Japan

Accepted for publication July 23, 2002.

* Address reprint requests to Dr Shimokawa, Department of Thoracic and Cardiovascular Surgery, Fukuoka Tokushukai Hospital, 4-5 Sukukita, Kasuga City Fukuoka 816-0864, Japan.
e-mail: tshimokawa-circ{at}umin.ac.jp


   Abstract
Top
 Abstract
Introduction
 Material and methods
 Results
 Comment
 References
 
BACKGROUND: Use of an aortic partial clamp for proximal anastomosis during off-pump coronary artery bypass is known to increase the risk of fatal complications. The purpose of this study was to assess the management of the ascending aorta evaluated with epiaortic ultrasonography during off-pump coronary artery bypass.

METHODS: Intraoperative ultrasonography of the ascending aorta with a 10-MHz probe was performed consecutively in 155 patients undergoing off-pump coronary artery bypass between August 1999 and July 2001. The findings from ultrasonography, surgical modifications, and operative results were analyzed.

RESULTS: In 54 patients (34.8%), epiaortic ultrasonography showed atherosclerotic findings in the anterior side of the ascending aorta (group A). The remaining 101 patients had either normal findings or atherosclerotic findings in only the posterior side (group NA). A proximal anastomosis to the aorta was preoperatively planned in 117 patients (group A, 42; group NA, 75). In group A, a graft modification without clamping was implemented in 29 patients (24.8% of 117 patients), whereas the clamp site was modified to a different segment in 13 patients (11.1% of 117 patients). In all 75 patients in group NA, partial clamping was used in the standard fashion. There were no cerebral infarctions or operative deaths related to partial clamping. However, aortic dissection occurred in 1 patient in group NA.

CONCLUSIONS: In 35% of patients undergoing off-pump coronary artery bypass, epiaortic ultrasonography identified atherosclerotic findings in the anterior wall of the ascending aorta. This study suggests that revascularization without aortic manipulation during off-pump coronary artery bypass is indicated in as many as 25% of patients.


   Introduction
Top
 Abstract
 Introduction
Material and methods
 Results
 Comment
 References
 
Recently, off-pump coronary artery bypass (OPCAB) has been developed to reduce the morbidity associated with cardiopulmonary bypass and aortic manipulation. The incidence of stroke after OPCAB has been reported to range from 0% to 3.3% [1–3], and is lower than that of conventional coronary artery bypass grafting (CABG) [4]. Some investigators recommend performing total arterial bypass using the bilateral internal thoracic artery in all patients undergoing OPCAB to avoid ascending aortic manipulations [5, 6]. However, as the number of vessels and age of patients undergoing OPCAB has increased, the use of the saphenous vein graft and radial artery is indispensable for complete revascularization. Although the radial artery can be used as a composite or a free graft [7], we primarily elected to use it as free aortocoronary bypass graft, because the composite graft involves technical complexity and the risk of a low-flow state that is angiographically identified as string sign. If proximal anastomosis to the ascending aorta is performed, there are risky manipulations associated with aortic partial clamping. Therefore, the incidence of cerebrovascular accidents after partial clamping during OPCAB may be reduced by avoiding the procedure in patients with extensive aortic atheroma.

The purpose of this study was to identify the degree and location of atherosclerotic changes in the ascending aorta using epiaortic ultrasonography, and to assess a modification in the surgical technique of partial aortic clamping during OPCAB.


   Material and methods
Top
 Abstract
 Introduction
 Material and methods
Results
 Comment
 References
 
Study group
To identify atherosclerotic lesions in the ascending aorta we studied 155 consecutive patients undergoing OPCAB using epiaortic ultrasonography, between August 1999 and July 2001, at Fukuoka Tokushukai Hospital. All patients had given informed consent. The OPCAB was primary chosen in patients undergoing CABG without hemodynamic instability, and comprised 88.1% of patients undergoing CABG during the study period. The mean age of the patients was 67.1 years (range, 43 to 86 years), and 113 (72.9%) were men. There were 32 patients (20.7%) who underwent urgent operation for acute myocardial infarction or unstable angina. Table 1 summarizes the clinical characteristics of the study group. Preoperative cerebral vascular accident and peripheral vascular disease were comprehensively evaluated by symptomology and the findings of preoperative computed tomography, ultrasonography, and angiography. A postoperative cerebrovascular accident was diagnosed by a neurologist and confirmed by computed tomographic scan of the brain.


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  		Table 1. Patient Characteristics

 
On the basis of the results of ultrasonic imaging, the patients were divided into two groups: the anterior group (group A), having atherosclerotic findings in the anterior of the ascending aorta, and the nonanterior group (group NA), having either normal findings or atherosclerotic findings limited to the posterior wall of the ascending aorta.

Epiaortic ultrasonography study
Epiaortic ultrasonography was performed by the surgeon immediately after pericardotomy, using an Aloka SSD-2200 system (Aloka, Tokyo, Japan) with a 10-MHz probe and sonolucent water bag. A small volume of saline and water bag provided good visualization of the entire aspect of the aorta. The probe was placed directly on the ascending aorta, and was manipulated to obtain both transverse and longitudinal views along the entire ascending aorta, which was interrogated from the aortic annulus to the origin of the innominate artery. These images were intraoperatively displayed for assessment and recorded on videotape. For the purpose of analysis, the ascending aorta was divided into three equal segments: proximal, central, and distal. The diseased segment and severity of atherosclerotic finding are defined in Table 2.


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  		Table 2. Grading of Aortic Atherosclerotic Findings

 
Surgical technique
All patients underwent a median sternotomy for OPCAB. A mechanical stabilizer (Octopus-2 or Octopus-3 [Medtronic, Minneapolis, MN]) was used for visualization of the anastomosis based on the pressure fixation concept. The preoperative selection of the graft was determined mainly by the degree of stenosis and the perfusion area in the native artery, and by the age of the patient. The left internal thoracic artery was grafted to the left anterior descending artery in the majority of patients. The incidence of arterial grafting was 78.2%. If more than two proximal anastomoses were necessary, a composite graft or a sequential graft was indicated. In all patients, the systemic pressure was pharmacologically decreased at the times of application and removal of the partial clamp.

Statistics
Demographics of the patients and outcome variables were expressed either as a percentage of the total or as mean ± standard deviation. Univariate analysis between groups was performed using the Mann-Whitney test and {chi}2 analysis. Independent risk factors for group A that were found to be statistically significant in the univariate analysis were entered into a stepwise multiple logistic regression. A p value of less than 0.05 was considered to be statistically significant. SPSS software (Chicago, IL) was used for all analyses in this study.


   Results
Top
 Abstract
 Introduction
 Material and methods
 Results
Comment
 References
 
Assessment by epiaortic ultrasonography
Ultrasonographic evaluation disclosed atherosclerotic findings in the anterior side of the ascending aorta in 54 patients (34.8%) of group A, who were considered to be at increased risk of complications related to partial aortic clamping. In group A, 19 patients had localized disease and 35 patients had extensive disease. The remaining 101 patients of group NA had either normal findings (79 patients; 51.0%) or atherosclerotic findings limited to the posterior side (22 patients; 14.2%). The evaluations of the ascending aorta are shown in Table 3.


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  		Table 3. Results of Intraoperative Epiaortic Ultrasonography

 
The mean age of the patients in group A was significantly higher than that in group NA (70.2 ± 9.7 years versus 65.4 ± 11.9 years, p = 0.017), and male patients constituted a significantly greater proportion of group A than of group NA (83.3% versus 67.3%, p = 0.033). There were no significant differences in preoperative characteristics between the two groups, except for the history of cerebral vascular accident (52.9% versus 34.3%, p = 0.028) and peripheral vascular disease (25.5% versus 12.1%, p = 0.037). Multiple logistic regression analysis identified two variables as independent predictors for group A—age (p = 0.007) and male sex (p = 0.017)—as shown in Table 4.


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  		Table 4. Multivariate Analysis for Prediction of Group A

 
Surgical procedure and results
A proximal anastomosis to the ascending aorta was preoperatively planned in 117 patients. This included 42 group A patients, 13 of whom (11.1% of 117) required a different location of the partial clamp to the normal segment of the ascending aorta. In 10 of these 13 patients, in whom there was localized mild-to-moderate disease, the clamp site was easily modified to another normal segment. However, the other 3 patients had either localized severe disease or extensive disease, and the clamp site was carefully determined based on epiaortic ultrasonography. In the remaining 29 patients (24.8% of 117), graft modifications including composite graft and sequential graft were used for revascularization without partial aortic clamping. In group NA, all 75 patients (64.1% of 117) had a preoperatively planned proximal anastomosis to the ascending aorta in which partial clamping was used in the standard fashion. In total, the incidence of proximal anastomosis to aorta using partial clamping was 75.2% (88 of 117 patients).

There were two complications associated with either partial aortic clamping or cerebrovascular accidents. Iatrogenic acute aortic dissection occurred in 1 patient. Epiaortic ultrasonography showed normal findings in the ascending aorta (group NA). The patient was immediately treated by ascending aortic replacement under cardiopulmonary bypass with deep hypothermia. The other patient had cerebral infarction 4 days after operation. Because epiaortic ultrasonography showed localized severe disease in the anterior side of the ascending aorta (group A), we used a left internal thoracic artery–radial artery Y-composite graft without the partial clamp. Both patients were discharged well.

There were three operative deaths, two of which were emergency patients with acute myocardial infarction. The causes of death were pneumonia and low output syndrome.


   Comment
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
References
 
To prevent complications related to partial clamping, it is important to locate the atheroma and avoid it during manipulations. In this study, half of patients undergoing OPCAB had normal findings in the ascending aorta. However, in 34.8% of the patients, epiaortic ultrasonography showed atherosclerotic findings in the anterior side of the ascending aorta. These patients were considered to be at increased risk of complications related to partial clamping, and we attempted to perform surgical modifications including relocation of the partial clamp and graft modification without partial clamping. As a consequence of our strategy to use the partial clamp, which was that it should be applied only to the normal segment of the aorta, the incidence of use of the partial clamp was 75.2%, and there were no CVA complications or mortality associated with partial clamping.

Ascending aortic disease
Previous reports have shown that more conventional methods for detection of atheromatous disease, including preoperative radiographic studies and intraoperative inspection and palpation of the aorta, underestimate both the frequency and the extent of arteriosclerosis when compared with intraoperative epiaortic ultrasonography [8, 9]. Recent studies suggest that intraoperative epiaortic ultrasonography may have an advantage over multiplane transesophageal echocardiography for surgeons assessing target sites for surgical procedures involving the ascending aorta [10]. We believe that epiaortic ultrasonography is the most sensitive method to detect arteriosclerosis in the ascending aorta and find that it is easily performed, even in emergency cases.

The frequency of significantly atheromatous ascending aorta by epiaortic ultrasonography ranges from 21% to 62% [8–11], and is known to increase with age. Considering the risk of partial clamping during OPCAB, the presence of atheromatous disease in the anterior side of the ascending aorta is of much consequence. Marshall and colleagues [8] used epiaortic ultrasonography in 50 patients undergoing cardiac operation, and reported that 24 patients (48%) had atheromatous disease in the anterior half of the circumference of the ascending aorta. Other reports have also shown that the anterior half of the ascending aorta has much more disease than the posterior area both in the upper and lower halves [9, 11]. The incidence of atherosclerotic lesions in our study was similar to those in other reported series.

Partial aortic clamping
Wareing and colleagues [12] reported on the management of the ascending aorta based on findings of epiaortic ultrasonography during on-pump CABG. If a normal aorta or mild aortic disease (<=3 mm intimal thickening) is identified, they performed a standard operative procedure. Where moderate or severe aortic disease was identified, they recommend modifying the operative procedure to avoid manipulation, cannulation, or clamping of the diseased aortic segments. The risk of the complications related to partial clamping during OPCAB may be increased, compared with aortic cross-clamping during on-pump CABG because of the pulsatile pattern of the arterial pressure and its wide segment. Our guiding principle on partial clamping was (1) if there were normal findings in the anterior half of the ascending aorta, we performed a standard procedure; (2) if localized mild-to-moderate disease was identified, the clamp site was relocated more distally or more proximally so as to avoid the diseased segment; and (3) if severe or extensive disease was identified, a "no touch" revascularization using a composite graft was indicated. On the other hand, in this study the clamp was placed in 3 patients who had either localized severe or extensive disease, because the internal thoracic artery was of too poor a quality to use as a composite graft, and these patients had limited normal segment in the ascending aorta on ultrasonography. Ultimately, we based our decision on the individual factors in each patient, considering the graft quality and the results of epiaortic ultrasonography.

In our study, acute aortic dissection caused by clamping occurred in 1 group NA patient. Histologic examination showed mild arteriosclerosis in the ascending aorta. The clamp was performed at a blood pressure of 100 to 110 mm Hg. Then, in the next 68 patients, systemic pressure was pharmacologically maintained at 80 mm Hg during partial clamping, and no dissections were identified. Chavanon and colleagues [13] reported that the risk of aortic dissection may be increased with OPCAB. The incidence of aortic dissection is 0.97% in OPCAB and 0.04% in on-pump CABG. They recommend careful manipulation of the aorta with a single partial clamp and control of the arterial pressure to 100 mm Hg. Predisposing factors of this complication have been identified as: history of hypertension, arteriosclerosis of the aorta, thin dilated aortic wall, cystic medial necrosis, and inherited disorders of connective tissue [13–15]. Epiaortic ultrasonography evaluated the degree of thin, dilated wall as well as arteriosclerosis of the aorta. Aortic dilatation (>45 mm) was revealed in 4 patients in this study, one of whom had a thin aortic wall. Although there were no patients having thin aortic wall without aortic dilatation, additional study patients are needed to clarify the relevance of aortic diameter or aortic wall size as criteria for diagnosing thin aortic wall.

Study limitations
In this study, a major limitation was the method of postoperative neurologic evaluation. All patients underwent neurologic examination at the bedside, whereas brain imaging to detect more minor brain damage was performed only in selected patients. The other limitation was the possible bias introduced by preoperative planning for proximal anastomosis to the aorta. However, the proportion of group A within the entire patient population (54 of 155; 34.8%) was similar to that within patients in whom partial clamping had been planned (42 of 117; 35.9%). Therefore, we consider the bias in graft selection to be of marginal consequence.

In conclusion, epiaortic ultrasonography revealed atherosclerotic findings in the anterior side of the ascending aorta in 34.8% of patients undergoing OPCAB. In the context of surgical modifications, there were no cerebrovascular accidents related to partial clamping. This study suggests that in 25% of patients a "no touch" revascularization during OPCAB was indicated.


   References
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 References
 

  1. Weinschelbaum E.E., Machain A., Raffaelli H.A., et al. Off-pump coronary operation at the Favaloro Foundation. Results in 264 patients. Ann Thorac Surg 2000;70:1030-1033.[Abstract/Free Full Text]
  2. Hart J.C., Spooner T.H., Pym J., et al. A review of 1,582 consecutive Octopus off-pump coronary bypass patients. Ann Thorac Surg 2000;70:1017-1020.[Abstract/Free Full Text]
  3. Yokoyama T., Baumgartner F.J., Gheissari A., Capouya E.R., Panagiotides G.P., Declusin R.J. Off-pump versus on-pump coronary bypass in high-risk subgroups. Ann Thorac Surg 2000;70:1546-1550.[Abstract/Free Full Text]
  4. Trehan N., Mishra M., Sharma O.P., Mishra A., Kasliwal R.R. Further reduction in stroke after off-pump coronary artery bypass grafting: a 10-year experience. Ann Thorac Surg 2001;72:1026S-1032S.[Abstract/Free Full Text]
  5. Murkin JM. Neurological outcomes after OPCAB: how much better is it? The Heart Surgery Forum 2000;3:207–10
  6. Calafiore A.M., Mauro M.D., Contini M., et al. Myocardial revascularization with and without cardiopulmonary bypass in multivessel disease: impact of the strategy on early outcome. Ann Thorac Surg 2001;72:456-462.[Abstract/Free Full Text]
  7. Barner H.B. Arterial grafting: techniques and conduits. Ann Thorac Surg 1998;66:S2-5.[Abstract/Free Full Text]
  8. Marshall W.G., Jr, Barzilai B., Kouchoukos N.T., Saffitz J. Intraoperative ultrasonic imaging of the ascending aorta. Ann Thorac Surg 1989;48:339-344.[Abstract]
  9. Ohteki H., Itoh T., Natsuaki M., et al. Intraoperative ultrasonic imaging of the ascending aorta in ischemic heart disease. Ann Thorac Surg 1990;50:539-542.[Abstract]
  10. Wilson M.J., Boyd S.Y.N., Lisagor P.G., Rubal B.J., Cohen D.J. Ascending aortic atheroma assessed intraoperatively by epiaortic and transesophageal echocardiography. Ann Thorac Surg 2000;70:25-30.[Abstract/Free Full Text]
  11. Royse C., Royse A., Blake D., Grigg L. Assessment of thoracic aortic atheroma by echocardiography: a new classification and estimation of risk of dislodging atheroma during three surgical techniques. Ann Thorac Cardiovasc Surg 1998;4:72-77.[Medline]
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  13. Chavanon O., Carrier M., Cartier R., et al. Increased incidence of acute ascending aortic dissection with off-pump aortocoronary bypass surgery?. Ann Thorac Surg 2001;71:117-121.[Abstract/Free Full Text]
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This Article
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