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Eur J Cardiothorac Surg 2001;20:755-759
© 2001 Elsevier Science NL

Morphological differences of the internal thoracic artery in patients with and without coronary artery disease – evaluation by duplex-scanning

R. Marxa, T.W. Jaxb, G. Plehnb, C.M. Schannwellb, M. Horlitza, R.M. Kleina, H. Lappa, H. Gülkera

a Heart Center Wuppertal, Department of Cardiology, University of Witten-Herdecke, Wuppertal, Germany
b Department of Cardiology, Pneumology and Angiology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany

Received 25 January 2001; received in revised form 11 July 2001; accepted 12 July 2001.

Corresponding author. Tel.: +49-202 896-0; fax: +49-2104 809513
e-mail: marxr{at}uni-duesseldorf.de


   Abstract
Top
 Abstract
1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
 References
 
Objective: The internal thoracic artery is an established arterial graft for myocardial revascularisation, especially of the left anterior descending artery because of a higher patency rate compared to venous grafts. It has never been investigated, whether there are morphological differences in this vessel between patients with or without coronary artery disease or if they are comparable to morphological changes in the common carotid artery. Methods: We investigated the internal thoracic artery and the common carotid artery of 24 patients (12 with coronary artery disease, 12 without coronary artery disease) with an ultrasonic system on both sides. The intima-media thickness and the diameter of both vessels were estimated. Results: The intima-media-thickness of the internal thoracic artery was comparable in all patients, independent of the presence of a coronary artery disease (0.51±0.11 mm with coronary artery disease, 0.50±0.17 mm without coronary artery disease, P>0.05). Compared with this the intima-media-thickness of the common carotid artery was thicker in patients with coronary artery disease (0.84±0.13 mm with coronary artery disease, 0.73±0.07 mm without coronary artery disease, P<=0.014). There was no correlation between the thickness of the internal thoracic artery and the common carotid artery (r=0.018, P>0.05). Conclusions: It could be demonstrated for the first with non-invasive ultrasound, that the intima-media-complex of the internal thoracic artery is protected of the influence of arteriosclerosis. There are no morphological differences like the intima-media-thickness of the common carotid artery. The proven protective mechanism underlines the widespread use of the internal thoracic artery as a coronary artery bypass graft.

Key Words: Internal thoracic artery • Ultrasonic scanning • Intima-media-thickness • Coronary artery disease


   1. Introduction
Top
 Abstract
 1. Introduction
2. Patients and methods
 3. Results
 4. Discussion
 References
 
The internal thoracic artery has proved as the bypass graft of choice especially in revascularization of the left anterior descending artery of left coronary artery. In comparison to a sole installation of venous bypasses respectable improved survival rates and significantly longer frankness rates were shown [1]. Essentially, the minor incidence of an atherosclerosis together with a noticeable delayed development of critical stenoses within the vessel are responsible for it [2,3,4].

No information is found in literature concerning morphological findings of this vessel. which were set up by means of non-invasive ultrasound examinations. Determination of the intima-media-thickness, particularly of the common carotid artery, serves as detection of former morphological alterations of the arterial wall. It plays an important role in epidemiological studies and it is a marker for the further progression of arteriosclerosis. This procedure shows a high correspondence to histological determinations [5].

According to different investigators the increase of thickness of the intima media complex is said to be the earliest morphological alteration in pathogenesis of an arteriosclerosis [6]. In this examination the thickness of the intima media of the internal thoracic artery is determined and compared with the thickness of the intima media of the common carotid artery in patients with and without coronary heart disease for the first time. With this the extent of effect of the atherosclerosis development onto different vessels is to be determined and possible differentiations are to be shown.


   2. Patients and methods
Top
 Abstract
 1. Introduction
 2. Patients and methods
3. Results
 4. Discussion
 References
 
The group of patients consists of 24 male patients. Twelve of them are patients with angiographic documented coronary artery disease and 12 control patients according to their age after exclusion from a coronary macroangiopathy or a significant organic heart defect. Inclusion criteria of the consecutive examined patients were a stable clinical symptomatic and a comparable body mass index besides a sufficient possibility for ultrasound investigation. Excluding criteria were a compromising attendant disease as for example infections, tumor or an immunological disease. Additional excluding criteria were carotid pathology like stroke or TIA. The measurements were carried out 2 days after cardiac catheter examination, declaration of consent for the participation in the examination was obtained verbally after giving the appropriate explanation.

Ultrasound examinations were carried out by means of a Toshiba–Sonolayer device SSA 140 A (Toshiba, Tokyo. Japan) and a linear probe of 7.5 megahertz focussing in the superficial area. Measurements at each examination time were documented on video tape for subsequent evaluation.

2.1. Study-protocol
At first diameter of the common carotid artery was determined on both sides at three measuring points, which had been defined before (10 mm, 15 mm and 20 mm proximal to bifurcation). At these points as well thickness of the intima-media was quantified on both sides. The measuring were carried out on that side, which was distant to the ultrasound probe according to the ‘leading-edge‘-method [7]. Here, the distance between the first echogenic border line (transition vascular lumen – intimal region) and the second echogenic border line (medial adventitial region) is determined. Regions of the vessel with visible plaques or stenoses were not included.

The internal thoracic artery [8] was looked for in the 3rd intercostal region. On both sides the diameter of the vessel and the intima media thickness was determined at three defined points (proximal, distal and as well in the middle of the intercostal space).

2.2. Statistical analysis
Description of the measured parameters occurred as mean values ± standard deviation. Double-sided significance values with a value of P<0.05 were evaluated as being significant. Chi square test and Mann–Whitney U-test were used for comparison analysis. Comparisons within a group were examined by means of the Wilcoxon test. For the determination of correlations Pearson's correlation coefficient (r) was determined.

A linear regression analysis was carried out among the intima media thickness and the independent influencing factors (amount of risk factors, age, fibrinogen level, systolic blood pressure, diastolic blood pressure, height, weight, body mass index, total cholesterol level, low-density lipoprotein cholesterol level, high-density lipoprotein cholesterol level, triglyceride level and blood glucose value). Evaluation occurred by means of the statistics program SPSS 8.0 (SPSS for Windows release 8.0, statistical software, Chicago: SPSS, 1998).


   3. Results
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
4. Discussion
 References
 
3.1. Patients characteristics
The basic patients‘ characteristic features were comparable in both groups with and without coronary artery disease (Table 1). Patients with coronary artery disease differed from the control group solely in more frequent taking nitrates and lipid lowering therapy.


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  		Table 1. Characteristics of patients

 
3.2. Morphological criteria
Diameter of the common carotid artery was shown not significantly lower at 7.1±0.6 mm on average in patients without coronary artery disease than in patients with coronary artery disease (7.4±1.1 mm). The intima-media-thickness, which was determined by means of ultrasound, was larger in patients with coronary artery disease than in patients without coronary artery disease. Concerning the median diameter and the median intima-media-thickness the internal thoracic artery was shown comparable in the groups of patients (Fig. 1 , Table 2) and as well concerning the relation of intima-media-thickness to the vascular diameter no difference war found between both groups of patients.



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  		Fig. 1. Intima-media-complex of the internal thoracic artery in B-mode.

 

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  		Table 2. Morphological characteristics

 
There was no correlation between intima-media-thickness of the common carotid artery and the internal thoracic artery, correlation coefficient amounted r=0.018 (P<0.05) for both groups of patients. Independent of an existing coronary artery disease the linear regression analysis for the intima-media-thickness of the internal thoracic artery amounted (r=0.523, P<0.05) for blood glucose value on empty stomach and a correlation for body mass index (r=0.411, P<0.05).

In patients with coronary artery disease a correlation to the high density lipoprotein cholesterol value (r=0.579, P<0.05) is found for the intima-media-thickness of the common carotid artery. No dependence is found for intima-media-thickness for the remaining examined parameters classified to the presence of coronary artery disease or exclusion of coronary artery disease.


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
References
 
Concerning the measured values for the intima-media-thickness of the common carotid artery a significant difference was found in patients with and without coronary artery disease. The connection of the larger intima-media-thickness in patients with coronary artery disease was also shown in other major observation series [9]. The enlarged intima-media-thickness of the common carotid artery is interpreted as an index of a generalized arteriosclerosis.

The values for the intima media thickness, which we had determined, are found comparably to the described results of intima-media-thickness [10,11] in literature and the diameter for the common carotid artery [5,7,11]. A dependence of intima-media-thickness of the common carotid artery to high-density lipoprotein cholesterol concentration was found in patients with coronary artery disease. No interrelation was found in the correlation of the remaining factors. Former studies demonstrated a positive correlation between the intima-media-thickness of the common carotid artery to age, to systolic blood pressure and to serum cholesterol [12].

Compared with this the internal thoracic artery does not show any significant difference of intima-media-thickness in patients with and without coronary artery disease. This may point to a protection mechanism. Therefore hypothesis can be corroborated and even is verifiable that this vessel is not as much affected by a generalized atherosclerotic development as it is the case in other vascular regions, e.g. in the common carotid artery, in patients with coronary artery disease. Thickening of the intima-media complex and increasing of the intima-media-thickness demonstrate a sensitive sign for a beginning atherosclerosis [7,9], as we know. The ITA is not immune to intimal thickening and it occurs much later than coronary artery stenoses. Even in patients with severe coronary artery disease the degree of atherosclerosis in the ITA is not of functional relevance [13]. Several histological studies have reported [2,14,15] the low incidence of atherosclerosis. They assume an important role in a predominantly elastic type of ITA wall. Whereas most studies identify an elastic histological structure of the ITA, Barner [16] found muscular and hybrid patterns. Van Son [17] observed a considerable interindividual variability of histological type from the origin at the subclavian artery to the transition of the superior epigastric artery with regard to the extent of a preliminary elastic media in the ITA.

The existing sonographic examinations of the own group [8,18], which had served for determination of the diameter, showed similar measured values as well as it was the case in other working groups [19,20]. Comparable sonographic studies for the determination of the intima-media-thickness do not exist, here has to be fallen back on histological examinations for the classification of our measured values. Comparable data is found, but clinical studies do not differentiate between the prevalence of coronary artery disease or a missing coronary artery disease.

Thus, Ferro [21] describes a median intima-media-thickness postmortem of 0.23 mm with an existing vascular diameter of 1.26 mm and an amounting relation of intima media thickness/vascular diameter of comparably 0.18. The lower absolute values in this case are due to shrinkages caused by fixation. Other authors [3] describe similar values for the intima-media-thickness with 0.35 mm in fixed condition. In vitro examinations of the internal thoracic artery after pressure fixation (until 200 mmHg) found out similar values for the thickness of the vascular wall [22] by means of ultrasound.

In comparison of the intima-media-thickness of the common carotid artery and the internal thoracic artery no correlations are found. This corresponds to the results of other clinical studies which have not found any conformity of the intima-media-thickness values of the common carotid artery and the femoral artery [23]. It is speculated that different, still unknown factors participate in the development of an arteriosclerosis of the femoral artery and the common carotid artery [23]. A similar mechanism could exist as well in this case in the development of an atherosclerosis of the internal thoracic artery in comparison to the common carotid artery.

Although this study is limited concerning extension a very important aspect of ultrasound examinations in arteriosclerosis is demonstrated: in the morphological examination of the internal thoracic artery no thickening of the intima-media complex is found in patients with coronary artery disease in comparison to patients without evidence of coronary artery disease. This is in contrast to the findings at the common carotid artery. On morphological level there is a lacking involvement of the internal thoracic artery in the generalized atherosclerotic process. This protection from arteriosclerotic development supports in this way the frequent use of the vessel in coronary surgery and obtains an increasing importance. How far functional differences in vascular regulation of the internal thoracic artery do are existing in patients with and without coronary artery disease remains to be clarified in further examinations.


   References
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
 References
 

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