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Ann Thorac Surg 2002;74:119-121
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Severity of coronary artery stenosis at preoperative angiography and midterm mammary graft status

^a Department of Cardiac Surgery, Catholic University, Rome, Italy
^b Department of Cardiology, Catholic University, Rome, Italy

Accepted for publication March 18, 2002.

* Address reprint requests to Dr Gaudino, Divisione di Cardiochirurgia, Policlinico Universitario A. Gemelli, Largo A. Gemelli 8, 00168 Rome, Italy
e-mail: mgaudino{at}tiscalinet.it

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. The purpose of this study was to evaluate the correlation between the midterm angiographic results of mammary artery grafts and the preoperative stenosis of the target vessel.

Methods. We analyzed preoperative and postoperative angiograms of 93 patients who underwent postoperative midterm (3 years) angiograms of an internal mammary artery (IMA) to left anterior descending artery graft for clinical or study purposes. Patients were divided into three groups on the basis of the percentage of the coronary artery stenosis at preoperative angiography: <70%, 70% to 90%, and >90% stenosis.

Results. Preoperative characteristics were similar in the three groups. The overall incidence of IMA occlusion was 19% in the entire population, without significant differences between groups (19% versus 29% versus 14%). The mean mammary artery diameter significantly increased in direct proportion to the severity of the coronary stenosis (2.0 ± 0.2 mm in the <70% versus 2.5 ± 0.3 mm in the 70% to 90% and 2.7 ± 0.4 mm in the >90% series; p < 0.05).

Conclusions. Chronic native competitive flow does not significantly affect midterm graft status but does influence mammary graft diameter.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
The effect of chronic coronary competitive flow on the midterm and long-term angiographic results of mammary artery grafts is still controversial and the use of the mammary artery to revascularize a target vessel with moderate stenosis is not unanimously accepted [1–10]. This study was intended to correlate the midterm angiographic results of mammary grafts with the preoperative stenosis of the target coronary vessel and to evaluate the effect of the native stenosis on midterm mammary artery diameter.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Patient population
As internal mammary artery (IMA) occlusion is a rare occurrence and to minimize the possibility of a type II statistical error we decided to enroll in this investigation a population of patients at high risk of IMA malfunction. For this purpose we screened all cases who have undergone midterm (3 years) control angiography of a IMA to left anterior descending (LAD) graft at our institution during a 5-year period (January 1996 to January 2001). As control angiography is a rare event in asymptomatic patients this method allowed the selection of a patient population at high risk of IMA malfunction.

To minimize potential bias we used the following enrollment criteria: (1) performance of preoperative and postoperative angiography and operative procedure at our institution, use of a single, pedicled IMA graft, and compliance with our standard antiplatelet regimen (ASA 100 mg per day); (2) absence of multiple LAD lesions; and (3) absence of changes 10% of the LAD stenosis between preoperative and postoperative angiograms (to avoid bias related to the dynamic evolution of the plaque).

With these criteria we enrolled 93 of 209 screened cases. Seventy-six of these 93 patients (81.7%) underwent postoperative angiography for clinical or instrumental evidence of recurrent ischemia and 17 because they were involved in different study protocols. The mean interval between surgery and postoperative angiography was 53 ± 13 months.

Quantitative angiographic measurement
Following a methodology already described by our group [11, 12] multiple angiographic views were analyzed for both the LAD and the IMA; TIMI flow grade was visually estimated separately by two different observers. Digital angiograms were analyzed using computerized quantitative angiography (Medis, Neuen, The Netherlands) to measure the LAD stenosis. The IMA graft status was then assessed and the IMA diameter measured 5 to 10 mm proximally to the anastomosis.

Statistical analysis
Patients were grouped on the basis of the percentage of the LAD stenosis at preoperative angiography: <70% stenosis, 70% to 90% stenosis, and >90% stenosis. Incidence of graft failure was considered a dichotomic variable, as were demographic and clinical characteristics. Continuous data are expressed as median and interquartile range. Categoric variables were compared by the ² test or Fisher’s exact test for observations fewer than 5. Relative risk (RR) with 95% of confidence interval (CI) was calculated. In order to evaluate the possibility of a type II statistical error, power analysis for an value of 0.05 was performed both for the entire population and for the three subgroups. Analysis for the total population revealed a p value of 0.273 whereas subgroup analysis revealed p = 0.22 for the <70% versus 70% to 90% groups, p < 0.01 for the <70% versus >90% series, and p = 0.48 for the 70% to 90% versus >90% subgroups.

The statistical analysis was performed using the Statistical Package for Social Sciences software (SPSS-10.0 for Windows, SPSS, Chicago, IL). All p values <0.05 were considered significant.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
The main preoperative clinical and angiographic characteristics of the three groups of patients are summarized in Table 1. Major demographic and clinical characteristics were similar in the three groups; however, there was a significantly higher rate of female patients in the >90% group and of smokers in the 70% to 90% series.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
The effect of chronic native competitive flow (CNCF) on an IMA graft is still controversial. In fact, although several authors have reported that using the IMA to revascularize coronary vessels with less than severe stenosis results in graft malfunction and even occlusion [1–3] there is consistent experimental and clinical evidence that the IMA is able to adapt to a situation of CNCF by reducing its caliber and flow and to regain full patency if the coronary stenosis progresses [5–10].

Nasu and associates [1] studying 20 cases with IMA-LAD graft by means of intravascular Doppler velocimetry found that CNCF significantly affected mammary flow and diameter and that a lower degree of LAD stenosis could result in an IMA string sign [1]. Shimizu and coauthors [2] using the same methodology in a group of 50 coronary artery bypass graft (CABG) patients confirmed the negative effect of CNCF on mammary flow. Experimental data seem to support the observations performed in humans. Pagni and associates [3, 4] in a canine model repeatedly described how mammary flow is dependent on CNCF and that the IMA is more vulnerable than a vein graft to the detrimental effects of competitive flow.

In contrast to these findings the possibility that an angiographically occluded IMA graft anastomosed to a moderately stenotic coronary artery can reopen after progression of the native stenosis has been described by several authors [5–7]. Kawasuji and colleagues [8] in a large angiographic study showed how CNCF does not predispose to IMA string or occlusion and suggested routine mammary artery use even to revascularize a moderately stenotic coronary artery. Moreover additional experimental data from the Pagni and Spence group minimized the effect of competitive flow on IMA graft patency (at least in the short term) [9] and more than one author (including our group) reported cases of a perfectly patent IMA graft anastomosed to a nonobstructed coronary artery [10, 13].

Owing to the well-recognized benefits of IMA use during surgical myocardial revascularization these controversies assume an obvious importance and have major implications for both the early and midterm prognosis. In our study the status of the IMA-LAD graft at midterm angiography was correlated to the LAD stenosis at the time of surgery in a cohort of 93 CABG patients. Although the severity of the coronary lesion influenced mammary luminal diameter and patients with more severe coronary lesions had significantly larger grafts, no correlation between IMA status and coronary stenosis could be established. This observation seems to demonstrate how the mammary graft adapts to CNCF by reducing its diameter and flow but remains fully patent even in competitive flow situations.

A major limit of our study is the possibility of a type II statistical error. As IMA occlusion is a rare occurrence (despite the fact that we enrolled a population at high risk of graft failure) only 18 of our cases were found to have a nonfunctioning mammary graft at midterm angiography, obviously limiting the statistical power of the study. Conversely, the present investigation has two main points in support of its reliability: the large number of patients restudied by angiography (actually one of the largest for studies of this type) and the rigorous enrollment criteria used to avoid bias and to "isolate" the effect of CNCF.

In conclusion we have found that CNCF does not affect IMA graft status at midterm angiography. Although the possibility of a type II statistical error can not be definitely ruled out, this finding is concordant with the described adaptive properties of the "live" mammary conduit [14] and suggests that mammary artery grafts can be adopted even to revascularize vessels with moderately severe stenosis.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

1. Nasu M., Akasaka T., Okazaki T., et al. Postoperative flow characteristic of left internal thoracic artery grafts. Ann Thorac Surg 1995;59:154-162.[Abstract/Free Full Text]
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3. Pagni S., Storey J., Ballen J., et al. Factors affecting internal mammary artery graft survival: how is competitive flow from a patent native coronary vessel a risk factor?. J Surg Res 1997;71:172-178.[Medline]
4. Pagni S., Storey J., Ballen J., et al. ITA versus SVG: a comparison of instantaneous pressure and flow dyn competitive flow. Eur J Cardiothorac Surg 1997;11:1086-1092.[Abstract]
5. Feld H., Navarro V., Kleeman H., Shani J. Early postoperative occlusion of a left internal mammary artery bypass graft with subsequent restoration of patency. Catheter Cardiovasc Diag 1992;27:280-283.
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11. Possati G., Gaudino M., Alessandrini F., et al. Mid term clinical and angiographic results of radial artery grafts used for myocardial revascularization. J Thorac Cardiovasc Surg 1998;116:1015-1021.[Abstract/Free Full Text]
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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Mario Gaudino Francesco Alessandrini Piergiorgio Bruno Gianfederico Possati Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gaudino, M. Articles by Possati, G. Search for Related Content PubMed PubMed Citation Articles by Gaudino, M. Articles by Possati, G. Related Collections Coronary disease