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Ann Thorac Surg 2005;80:1375-1380
© 2005 The Society of Thoracic Surgeons

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Original article: Cardiovascular

The Arterial Sling Operation: One-Year Follow-Up

^a Department of Thoracic Surgery, Heart Centre, Rigshospitalet, Copenhagen, Denmark
^b Department of Cardiology, Heart Centre, Rigshospitalet, Copenhagen, Denmark

Accepted for publication March 4, 2005.

^_* Address reprint requests to Dr Parvaiz, Department of Thoracic Surgery, Heart Center, Rigshospitalet, Blegdamsvej 9, Copenhagen, Denmark (Email: imran{at}dadlnet.dk).

	Abstract

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BACKGROUND: Coronary artery bypass graft surgery with total arterial revascularization, particularly the use of bilateral in situ internal thoracic arteries, is considered an improved treatment of patients with ischemic heart disease. The sling operation connects the internal thoracic arteries with the radial artery, creating an arterial arcade with double inlet of blood to the peripheral vascular bed. In this paper we present 1-year follow up of angiographic and clinical results of the arterial sling operation.

METHODS: The arterial sling operation was performed in 28 patients in the period from October 2000 to September 2001, and all patients were offered an angiographical and clinical examination 1 year postoperatively. All angiograms were systematically reviewed by an interventional cardiologist and a cardiac surgeon.

RESULTS: Twenty-three patients participated in the 1-year angiographic follow up. Of these 3 patients had a fully open arterial sling, 15 patients had stenosis or occlusion of one segment, and 5 patients had occlusion or stenosis of 2 segments of the radial artery. Eight of the total 93 peripheral anastomoses were occluded. The 1-year graft patency rate was 91.4%.

CONCLUSIONS: The arterial sling operation is safe and the one year patency rate is high. Although one or two segments of the arterial sling may degenerate due to competitive blood flow, this does not affect blood flow in the vascular bed in patients without disease progression. However, arterial revascularization should be performed in a way to minimize competitive flow.

	Introduction

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An improved long-term patency rate for the left internal thoracic artery (LITA) compared with the saphenous vein (SV) has been demonstrated for grafting of the left anterior descending artery (LAD) during coronary artery bypass grafting (CABG) surgery [1, 2], an improvement that has resulted in a better patient survival with fewer cardiac events [2, 3].

Because of the low long-term patency rate for the SV there has been a search for better alternative conduits [4]. The fibrointimal hyperplasia and atherosclerosis of the SV leading to stenosis and subsequent occlusion of the vessel have directed the interest of the surgeons towards bilateral internal thoracic artery (ITA) grafts and other arteries for full arterial revascularization. The most common conduit in addition to the LITA, are the right internal thoracic artery (RITA) and the radial artery (RA) [4]. The RITA is recommended to be used as an in situ graft [5], which on the other hand gives limitations due to its length. An in situ RITA graft can rarely reach the posterior descending or postero-lateral branch of the right coronary artery. However, an RA graft anastomosed either to the aorta or to the LITA as a T or Y graft has the length to reach all branches of the coronary vessels [4]. By using the T- or Y-graft technique side clamping of the aorta can be omitted. However, this graft technique makes the poststenotic myocardial blood flow totally dependent on a well functioning LITA.

The sling operation gives an opportunity to avoid some of the problems involved with the abovementioned techniques. The connection of the two internal thoracic arteries with the RA creates an arterial arcade instead of an end artery, which subsequently offers a double inlet of blood flow to the myocardium. The early results and perioperative flow measurements of this technique have been described previously [6]. In this report we present 1 year follow up data in patients who have undergone the arterial sling operation.

	Patients and Methods

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Patients
The arterial sling operation was performed in 28 selected patients, 6 women and 22 men, in the period from October 2000 to September 2001 at the University Hospital of Copenhagen. All patients had three-vessel disease. The age of the patients ranged from 29 to 82 years (mean 59 years), 6 patients had type 2 diabetes, 2 had a body mass index above 30, and 1 had claudication of the lower limbs. Twenty-three of the patients had a coronary angiography performed prior to discharge.

All patients were also offered a control angiography 1 year postoperatively, and 23 patients (82%) accepted the offer. Four patients declined to have an additional angiography performed and 1 patient died of lung cancer 8 months after the CABG operation. The coronary angiography was performed 7 to 20 months (mean 12 months) after the operation.

Coronary angiography was performed using the femoral approach with selective cannulation of both the native coronary artery and the ITA ostias. Whenever possible, simultaneous contrast injections in the ITAs were performed. Nitroglycerine was injected before contrast in the native vessels and a calcium-antagonist was injected before contrast in the ITAs.

An interventional cardiologist and a cardiac surgeon systematically studied all angiograms obtained before, immediately after CABG and at 1-year follow up.

All patients were interviewed at the time of angiography, with recording of angina threshold and medication.

Patients who where not interested in having the follow-up angiography performed, were contacted by telephone and interviewed about angina and medication.

Surgical Technique
The principle of the sling operation is a complete arterial coronary revascularisation using both ITAs and the RA. These arteries are harvested and both ITAs are used as in situ grafts [6, 7]. The RA is first anastomosed end-to-end to RITA, and then side-to-side with the stenotic/occluded branches of the right and circumflex arteries. LITA is anastomosed end-to-side with LAD and if convenient also to a diagonal branch. Finally the radial artery is anastomosed end-to-side to the LITA (Fig 1, group A). This technique creates a double inlet of blood to the revascularised areas, and results in an increased blood flow capacity to the diseased areas of the myocardium [6].

View larger version (24K): [in this window] [in a new window]   Fig 1. Schematic drawing of the arterial sling operation and the findings at the 1-year follow up. (LAD = left anterior descending artery; LITA = left internal thoracic artery; PDA = posterior descending artery; PLA = posterior lateral artery; RA = radial artery; RITA = right internal thoracic artery.)

Exclusion criteria were an abnormal Allen's test and a difference in blood pressure in the 2 brachial arteries (measured sphygmomanometrically) greater than 10 mm Hg to avoid any steal phenomenon through a sling graft in patients with a subclavian artery stenosis.

All patients consented to undergo the arterial sling graft operation after detailed information.

	Results

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The coronary angiography prior to discharge of the 23 patients showed that all the anastomoses and sling grafts were fully open in all cases [6].

One patient died of lung cancer 8 months after the bypass operation. One patient had only the 1-year follow-up coronary angiography performed; 1 patient had only the postoperative angiography performed, whereas 3 patients were examined neither postoperatively nor after 1 year. Thus, 23 patients (85 %), 4 women and 19 men with the age range of 29 to 82 years old (mean 59 years old) accepted to have a repeat coronary angiography performed 1 year after the CABG. Angiographic changes in segments of the arterial sling graft were classified as either degeneration or occlusion, corresponding to a lumen reduction in comparison with the reference segment of either 50% to 99% or 100%, respectively. Patients were subsequently divided into four groups according to this classification (Fig 1): (group A) patients with no changes in any graft segment (n = 3) (Fig 2); (group B) patients with degeneration of one graft segment (n = 7) (Fig 3); (group C) patients with occlusion of a graft segment (n = 8); and (group D) patients with degeneration and occlusion of 2 segments of the arterial sling graft (n = 5).

View larger version (111K): [in this window] [in a new window]   Fig 2. A capture from a 1-year follow-up angiogram of a 54-year-old male in December 2001. The contrast was injected in LITA and RITA simultaneously. The capture demonstrates a fully open sling with fully open and well functioning distal anastomoses. (LAD = left anterior descending artery; LITA = left internal thoracic artery; M1 = first marginal branch; PDA = posterior descending artery; PLA = posterior lateral artery; RA = radial artery; RITA = right internal thoracic artery.)

View larger version (133K): [in this window] [in a new window]   Fig 3. A capture from a 1-year follow-up angiogram of a 55-year-old male in June 2001. The contrast was injected in LITA and RITA simultaneously and demonstrates occlusion of the segment between PDA and the marginal branch. A capture from the same patient of the postoperative angiography that showed a fully open sling has been published before [25]. (LAD = left anterior descending artery; LITA = left internal thoracic artery; PDA = posterior descending artery; RA = radial artery; RITA = right internal thoracic artery.)

The total number of distal anastomoses in the 27 patients was 110 (3.9 per patient). In the reangiography group the total number of grafts was 93 (an average of 3.7 per patient). Eight of the distal anastomoses were occluded. The overall 1 year distal anastomoses patency was 91.4%. The degree of stenosis in the bypassed native vessels is shown in Table 1.

One year after the operation 25 patients out of 27 (93%) did not have any angina and were not physically constrained in any part of their lives. Two patients had angina Canadian Cardiovascular Society (CCS) class 1 and 2, respectively. The first patient has diffuse peripheral disease of his native coronary arteries and an occlusion of the RA graft segment between the posterior descending artery and the first marginal branch. All his distal anastomoses were open after 1 year, but severe progression of the coronary atheromatosis in the native vessels was observed and treated with percutaneous coronary intervention. The second patient was the one with two occluded distal anastomoses. We found it hard to explain the patient's symptoms, because angiographically there were no significant stenoses of the native vessels 1 year after CABG. Therefore, apparently regression of the atheromatosis had occurred.

All patients received amlodipin 10 mg postoperatively for a minimum of 3 months. At the 1-year follow up 26 patients were taking aspirin and one patient was taking clopidogrel, 26 patients had a cholesterol-lowering drug and 14 patients were treated with amlodipin. Three patients were treated with isosorbiddinitrate at the time of the follow-up angiography. One patient stopped using this medication at the time of the follow-up angiography.

	Comment

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The low long-term patency rate of SV grafts has contributed to the search for alternative conduits for the CABG operation [1, 4]. Because of the good patency rate of the LITA, several different arteries have been evaluated as supplementary conduits: the RITA, RA, ulnar, inferior epigastric, and right gastroepiploic arteries. The most commonly used second conduits of these are RITA and RA [4]. There has been encouraging reports on the patency rate for RITA grafts of 98%, 95% and 65% at 5, 10 and 15 years, respectively [8], and accordingly a better clinical outcome [9, 10]. Lytle et al. have conducted retrospective studies of the use of a single internal thoracic artery versus bilateral internal thoracic arteries and concluded that elective patients receiving 2 internal thoracic arteries grafts had a reduced risk of death, re-operation and angioplasty [11] and a better survival after 20 years [12]. Moreover, it appears that in situ RITA grafts have a better patency than free RITA grafts [5]. Even though others have found similar patency rates and clinical outcomes, there is a need for randomized trials to document the proposed additional benefits of bilateral internal thoracic artery grafting [9, 10, 13].

After reintroduction of the RA as an arterial conduit in the 1990s its use has increased considerably. The early reported RA graft patency was 99%, 92%, and 83% immediately postoperatively, and after 1 and 5 years, respectively [14]. Recently published studies have shown similar results of the patency rates concluding that the RA conduit is as good as any other graft [8, 15, 16], while others have surprisingly shown a lower patency rate of the RA graft compared to the SV graft in patients presenting with myocardial ischemia after CABG [17]. On the other hand, studies of the clinical out come of patients receiving an RA have shown promising results with improvement of both morbidity and mortality [18, 19].

Factors affecting the RA graft patency include target vessel location and the severity of the stenosis in the bypassed native vessel [20]. One report indicates that an anastomosis to a non-LAD vessel increases the risk of RA graft failure [20], although others have not been able to verify this [8, 21]. The flow in the native coronary arteries seems to affect the RA graft patency in a similar manner. When the stenosis in the target coronary artery is only moderate (and subsequently has a greater competitive flow to the graft flow), the RA graft failure increases considerably [8, 20, 21]. Even the patency rates of internal thoracic arteries appear to depend on the target vessel size and quality, whereas their dependency on the degree of the target vessel stenosis is a matter of dispute [5, 22].

In our material all patients who had a coronary angiography performed prior to discharge, had an open arterial sling graft [6]. Angiography 1 year postoperatively showed a patency of 91% of the distal anastomoses in 23 patients, which we regard as acceptable.

A low degree of stenosis of the native target vessels was highly associated with occlusion of the distal anastomoses. In all cases of double inlet graft occlusion the stenoses of the native target vessels were only moderate (Table 1), whereas at least one inlet to native vessels with high-grade stenoses (>70%) were open after 1 year.

There was no relationship between perioperative measured flow and occlusion of any segments of the sling graft. This study shows that the 1 year patency rate for the sling operation is comparable with the patency rates of the established complete arterial revascularisation techniques.

Apart from 1 patient with progressive peripheral coronary disease and 1 patient with unexplainable angina, none of our patients had any cardiac symptoms or felt constrained in their daily activities.

Blood supply via an artery arcade is known from many parts of the body (eg, the central nervous system, the gastric, the great bowel and the extremities) and gives the organ a larger blood flow reserve capacity. We raised the questions whether this also applies when the arcade is artificially constructed and whether clinical benefit of such an operation ensues. The results of the present study are promising in these regards, but to answer these questions a randomized comparison with conventional CABG techniques is needed.

In those patients with a well functioning arterial sling, some areas of the myocardium were potentially receiving blood flow from three sources: from LITA, RITA, and from the native (albeit stenotic) vessel. One can only guess about the nature of the triple flow's maintenance, but it is certainly tantamount to a high blood flow reserve to the myocardium. Occlusion of the RITA and RA in the present study occurred in cases where there was no need for the graft, due to low degree stenosis of the native vessel. Occlusion of a segment of the arterial sling does not necessarily affect the distal anastomoses. It appears that the occlusion occurs as a "natural" consequence of competitive flow. This explains why these patients are free from angina and major cardiac events despite occlusion of a graft segment.

Another interesting observation of this study was that the anastomosis between RITA and RA could hardly be identified angiographically. Thus, apart from 3 cases all anastomoses between the RITA and RA were patent and the internal diameter of the RITA and RA nearly identical.

After the initial 28 patients the results of the present study has decided the fate of the sling operation. Although the sling operation is safe and the patency rate and the level of freedom from angina is acceptable it seems logic to perform arterial revascularization minimizing competitive flow.

We have therefore taken the consequences of the present results and perform full arterial revascularization in a different manner. The full arterial revascularization is performed by using the RA as an extension on the RITA in order to reach the right coronary branches and the marginals. LITA is used for grafting LAD and occasionally a diagonal. We omit the end-to-side anastomosis between the RA and LITA. Thereby we maintain the following benefits: the blood supply is provided by two ITAs, which remain in situ; all vessels can be reached; and there is no need for side clamping of the aorta. Optimal arterial graft flow to the jeopardized myocardium is obtained and competitive flow is only dependent of native vessel disease.

The experience with extension of RITA with the RA is still scarce [23, 24]. Future research will show whether this extension is as effective as the presently used full arterial revascularization techniques.

	Southern Thoracic Surgical Association: Fifty-Second Annual Meeting

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The Fifty-Second Annual Meeting of the Southern Thoracic Surgical Association (STSA) will be held November 10–12, 2005, in Orlando, Florida.

The Postgraduate Course will be held the morning of Thursday, November 10, 2005, and will provide in-depth coverage of cardiothoracic surgical topics selected primarily as a means to enhance and broaden the knowledge of practicing thoracic and cardiac surgeons.

Please visit the STSA (http://www.stsa.org) or CTSNet (http://www.ctsnet.org) websites for detailed information on submitting abstracts.

 

	References

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