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Ann Thorac Surg 2001;72:2008-2011
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Adequacy of flow capacity of bilateral internal thoracic artery T graft

^a Department of Surgery II, Division of Cardiovascular Surgery, Nippon Medical School, Tokyo, Japan
^b Department of Internal Medicine I, Nippon Medical School, Tokyo, Japan

Accepted for publication July 31, 2001.

* Address reprint requests to Dr Ochi, 1-1-5 Sendagi Bunkyo-ku Tokyo, 113-8603, Japan
e-mail: ochi/surg2{at}nms.ac.jp

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. With the T graft configuration, multiple arterial revascularization can be accomplished using bilateral internal thoracic arteries. However, concern remains about the flow capacity of the main stem of the left internal thoracic artery (LITA).

Methods. Forty patients who underwent multiple revascularization of the entire territory of the left coronary system with a T graft were investigated. Six months after the operation, they were examined angiographically. During the same period, dobutamine stress echocardiography was performed to evaluate the adequacy of the myocardial blood supply from the T graft. The T graft revascularized two branches in 5 patients, three branches in 23, four branches in 11, and five branches in 1 of the left coronary system. Other conduits were used if revascularization was required for the right coronary system.

Results. Complete revascularization was achieved in the left coronary territory in all patients. The LITA main stem showed a wide lumen in all patients. Luminal narrowing was present in the distal segment of the LITA in 3 patients. The right internal thoracic artery (RITA) was patent in all patients, whereas luminal narrowing was observed in the distal segment of the RITA in 5 patients. No patient exhibited ischemic wall motion abnormality in the anteroseptal, lateral, or posterolateral region of the left ventricle where the T graft revascularized. Eight patients showed ischemic response in the inferoposterior region, that is, the territory of the right coronary artery.

Conclusions. The LITA main stem, forming a T-graft configuration with the free RITA, has an adequate flow reserve to supply at least the entire left coronary arterial system with sufficient blood. Therefore, multiple coronary revascularization using the T-graft technique is feasible.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
To obtain multiple coronary revascularization using only the internal thoracic arteries (ITA), a composite graft in which a free right ITA (RITA) is attached to the side wall of a left ITA (LITA) has been applied [1–7]. More recently the radial artery (RA), since its revival in clinical use, has also been used to form a composite graft with the LITA [8, 9].

In this type of composite graft, the blood flow to the myocardium perfused by the grafted coronary arteries depends on the blood supply from the LITA. Studies on the clinical and angiographic midterm and long-term results of the T graft configuration have been reported [2, 4–6]. However, a concern still exists whether the flow of the LITA can provide adequate blood to the grafted coronary arteries.

To investigate the flow capacity of the LITA, we conducted a postoperative echocardiographic and angiographic study in patients who underwent coronary artery bypass grafting (CABG) with a T graft using bilateral ITAs (BITA) to revascularize the entire left coronary system.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
From August 1997 to December 2000, of 420 patients with isolated CABG at our institute, 125 patients underwent CABG using bilateral ITAs (BITA) as composite T grafts to revascularize the entire left coronary system, that is, the left anterior descending artery (LAD) to the circumflex artery (Cx) territory.

No exclusion criteria were instituted for performing the T graft procedure except for patients in cardiogenic shock. The free blood flow rate of the LITA was not specified for the use of the T graft procedure unless flow disturbance of any kind was noticed intraoperatively. When required, the right coronary artery was grafted using the RA, the right gastroepiploic artery (GEA), or the saphenous vein (SVG).

To confirm the postoperative status of the T graft as well as that of the coronary artery, an angiographic examination was conducted 6 months after the operation. Informed consent to undergo this procedure was obtained preoperatively from 40 patients, including 28 men and 12 women, with ages ranging from 46 to 76 years (mean 64.8 years). Six patients had double-vessel disease, 34 had triple-vessel disease, and 12 patients had a lesion of the left main trunk. Twenty-three patients were diabetic, but none of them was insulin dependent. All the patients were free of symptoms of angina.

During the same period, when the angiographic examination was performed, the patients were offered the option of dobutamine stress echocardiography (DSE) to document the adequacy of the myocardial blood flow. Informed consent for the DSE was obtained in all patients who underwent angiography.

In this group of patients, the total number of grafted vessels was two to six (mean 3.9) in each patient. The T graft revascularized two branches in 5 patients, three branches in 23, four branches in 11, and five branches in 1 patient in the left coronary territory. The LITA was anastomosed to the LAD in all patients. Sequential anastomoses were constructed in 16 LITAs and 26 RITAs. To revascularize the right coronary territory, the SVG was used in 12 patients, the GEA in 16, and the RA in 5 (Table 1).

The angiographic status of the lumen of each segment of the T graft was evaluated as follows: normal, mild-to-moderate luminal narrowing, severe (string-like) luminal narrowing, and occlusion.

Protocol for dobutamine stress echocardiography
All patients were permitted to continue all of their medication except for ß-blockers, which were withdrawn 48 hours before the DSE study. Transthoracic echocardiography at rest was performed with the patient in the left decubitus position using a SONOS 2500 with a 2.5-MHz transducer (Hewlett-Packard, Andover, MA). Echocardiographic standard views (parasternal long axis, parasternal short axis at two levels, apical four-chamber, apical two-chamber, and apical long axis) were obtained [10]. The left ventricle was divided into 16 segments according to the recommendation of the American Society of Echocardiography [11]. Segmental wall motion was scored as follows: 1 = normal, 2 = mildly hypokinetic, 3 = severely hypokinetic, 4 = akinetic, and 5 = dyskinetic.

After the base line echocardiographic examination, dobutamine was infused intravenously at a dose of 5 µg · kg^-1 · min^-1, with 0.5 mg of atropine if necessary, and increased by 5 to 10 µg · kg^-1 · min^-1 every 3 minutes up to 40 µg · kg^-1 · min^-1. All echocardiographic images of the baseline and the DSE study were digitally obtained on-line and edited in quad screen cineloop format with simultaneous display of the rest, low dose, peak dose, and recovery stages on optical disks. The images were analyzed qualitatively using the quad screen cineloop format.

The presence of an ischemic response to the DSE was diagnosed when one of the following involving two or more wall segments was identified: development of asynergy in the patients without a wall motion abnormality at rest; or worsening of the wall motion abnormality in the patients with a wall motion abnormality at rest (ie, deterioration from hypokinesis to akinesis or dyskinesis).

The interpretation of wall motion analysis in the DSE was performed by two experienced echocardiographers who were blind to the clinical data. The interobserver and intraobserver variability of the results of analysis was 90% and 96%, respectively.

Surgical technique of T grafting
The ITA was harvested skeletonized or semiskeletonized to obtain its maximal length. Cautery was always used. The side branches were clipped and divided with scissors. When the artery was semiskeletonized, the accompanying veins were removed after harvesting. The RITA was cut at the bifurcation distally. After confirming the free blood flow, the proximal end of the RITA was cut to form a free graft.

All patients were operated on a cardiopulmonary bypass. After the heart was arrested, the right coronary artery was grafted first with grafts other than the ITA, that is, SVG, RA, or GEA. Anastomoses between the free RITA and the coronary arteries were constructed, followed by an anastomosis between the LITA and the LAD. When indicated, a side-to-side anastomosis between the LITA and the diagonal branch was constructed before the LITA to LAD anastomosis.

All the distal side-to-side anastomoses between the ITA and the coronary artery were constructed in a parallel fashion. A diamond anastomosis, in which the ITA is attached to the coronary artery perpendicularly, was not used to avoid stenotic deformity (Seagull deformity) of the ITA graft at the anastomosis. After all the distal anastomoses were completed, an arteriotomy as large as the diameter of the RITA was made on the pleural side of the LITA and the proximal end of the RITA was anastomosed with an 8-0 monofilament continuous suture during the aortic cross-clamp period. The total number of stitches required for each anastomosis did not exceed 12. The anastomosis was constructed so that the RITA was attached to the LITA perpendicularly (T shape) in most instances. Before tying a suture, the bull-dog clamp was removed from the LITA allowing blood to spring out of the arteriotomy. The suture was tightened only enough to stop the bleeding. This maneuver efficiently prevented anastomotic stenosis. The mediastinal fat pad was dissected off the pleura and the pericardium was incised longitudinally just above the left atrial appendage to allow the LITA to take the shortest course to the heart.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Angiography
All the vessels with a significant perfusion area were revascularized successfully. The LITA main stem showed a wide lumen in all patients when compared with the lumen of a 5F angiographic catheter of 1.7 mm diameter. The distal segment of the LITA and the attached RITA was also patent in all patients (Fig 1). Stenosis of a moderate degree (less than 75%) at the T anastomosis was present in 1 patient.

View larger version (122K): [in this window] [in a new window]   Fig 1. Triple grafting of the T graft. Note that the main stem of the left internal thoracic artery is widely open. Distal segment of the left internal thoracic artery was anastomosed sequentially to the diagonal branch and the left anterior descending artery. The right internal thoracic artery was anastomosed to the obtuse marginal branch of the circumflex artery. The distal branch of the circumflex artery was visualized through the right internal thoracic artery.

Sixteen GEA grafts were patent, whereas luminal narrowing of the GEA due to flow competition between the coronary artery was observed in 2 patients. The radial artery was widely patent in 5 patients. Four of the 14 anastomoses of the venous grafts were occluded, all of which were grafted to the distal branch of the RCA.

Dobutamine stress echocardiography
In the DSE study, none of the patients exhibited ischemic wall motion abnormality in the anteroseptal, lateral, and posterolateral regions of the left ventricle. These regions represent the territory of the left coronary system. Eight patients, however, showed ischemic response in the inferoposterior region that represents the right coronary territory. None of these patients complained of anginal symptoms or showed S-T segment change in electrocardiograms. Judging from the angiographic findings, the ischemic response in the DSE was attributed to vein graft occlusion in 4 patients, inadequate flow of the patent GEA in 2, and to the presence of ungrafted residual coronary lesion in 2.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
To expand utilization of the ITA in coronary artery operations, composite graft techniques have been developed and practiced [1–9]. In this type of graft configuration, the main concern is whether flow reserve of the LITA main stem can perfuse not only the LAD region but also the Cx and the RCA. To date, however, there are few reports on whether the LITA can generate an adequate blood flow to the grafted coronary arteries [12, 13].

A flow dynamic study in the LITA main stem using a Doppler flow guidewire [12] has shown that the flow reserve of the proximal LITA of the T graft increased significantly 6 months postoperatively. In that study, the flow reserve of the LITA was found to be adequate for multiple coronary anastomoses irrespective of the choice of the second arterial graft, that is, either the RITA or the RA. Another study on intraoperative Doppler flow measurement has shown that there is considerable flow reserve in the LITA as an inflow source for the composite conduit [13].

In the present study, the angiographic results were satisfactory and equal to or even better than those in other studies [4, 5, 12]. The LITA main stem showed a wide lumen in all patients. Although segmental narrowing of the ITA was observed in some patients, the distal LITA and the RITA were patent in all patients. Furthermore, in the DSE, which is a sensitive diagnostic means for detecting regional myocardial hypoperfusion, none of the patients exhibited an ischemic wall motion abnormality in the region revascularized by the T graft. These results confirmed that, even under conditions of a stress, the flow capacity of the LITA main stem is adequate as an inflow source of the T graft to generate a myocardial blood supply to the entire territory of the left coronary system.

ITAs are sensitive to competitive flow when the T configuration technique is used [5]. Segmental luminal narrowing of the ITA was observed in 5 patients and eight ITAs. However, all of these segments were just proximal to the terminal end-to-side anastomosis to a coronary artery of less than 75% stenosis. Luminal narrowing seemed to have resulted from flow competition between the native coronary artery.

Although the luminal narrowing was present in the ITA segment, no ischemic wall motion abnormality was identified in the ITA-grafted region in DSE. These findings strongly suggest that the myocardial blood supply may be maintained with a balance between the blood flow of the native coronary artery and that of the T graft, reflecting physiologic adaptation of the ITA in response to the flow demand of the coronary bed [14]. As the native coronary flow decreases, the ITA may be able to regain its function as a graft to the coronary artery [15, 16]. Therefore, the development of luminal narrowing of the ITA cannot be considered as graft failure [5].

The GEA tends to be involved in flow competition with the coronary artery more frequently than the ITA [17, 18]. In our recent study on the flow capacity of the GEA evaluated by DSE, an ischemic wall motion abnormality in the GEA-grafted region was identified by DSE even in patients whose GEA seemed to be functioning well on the angiogram [19]. We have found that the flow capacity of the GEA was limited and correlated mainly with the caliber of the artery. In this regard, the flow reserve of the ITA is different from and may be much greater than that of the GEA.

In conclusion, from the results of the current study, the LITA main stem, by forming a T graft configuration with the free RITA, has an adequate flow reserve to supply the entire left coronary artery with sufficient blood. Multiple coronary revascularization using the T graft technique can therefore be rationalized.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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