Midterm endothelial function and remodeling of radial artery grafts anastomosed to the aorta

Low-level-laser irradiation induces photorelaxation in coronary arteries and overcomes vasospasm of internal thoracic arteries

BACKGROUND AND OBJECTIVE

As low-level laser irradiation (LLLI) seems to induce vasodilation besides many other known biological effects, LLLI has been increasingly used in therapy of medical conditions with various irradiation parameters. The aim of this study was to investigate the effect of LLLI on photorelaxation of human coronary and internal thoracic arteries (ITA).

MATERIALS AND METHODS

Thirty vessel segments of ITA used for routine coronary artery bypass grafting as well as left anterior descending coronary arteries (LAD) of patients undergoing cardiac transplantation were cut into 4-mm rings stored in a modified Krebs-Henseleit solution and evaluated in a myograph. Both types of vessel segments were irradiated by a semiconductor non-thermal GaAs diode laser operating at a wavelength of 680 nm. After precontraction with thromboxane agonist U44619, respective relaxation responses were evaluated and compared to pharmacological dilatation induced by substance P.

RESULTS

Mean pharmacological vasodilation by substance P was 22.6 ± 3.3%, 12.8 ± 1.4%, and 20.4 ± 3.2% in macroscopic healthy LAD, LAD with atheromatous plaque, and ITA, respectively. Average photorelaxation induced by LLLI was 16.5 ± 2.0%, 1.9 ± 1.7%, and 6.8 ± 4.7%, accordingly. Vasodilatatory responses induced either by substance P or administration of LLLI were significantly decreased in LAD with atheromatous plaque (P < 0.0001). Vasospasms of ITA segments occurring during experiments could be abandoned when LLLI was administered.

CONCLUSION

Macroscopic healthy LAD exposed to LLLI revealed significant photorelaxation. With the administration of LLLI, 73% of the maximal obtainable effect by an endothelium-dependent vasodilator could be reached. Furthermore, LLLI has the potential to overcome vasospasms of ITA.

Early to midterm results with the radial artery in coronary artery bypass grafting following autotransplantation without pharmacological manipulation

BACKGROUND

In our unit when the radial artery is used as a conduit for myocardial revascularization routine, postoperative calcium-channel blockade is not practised. To preserve the radial artery, it is freed from the surrounding structures together with its venae commitantes and then left, in situ, in circulation, until needed for grafting. We evaluated the early to midterm patency of the radial artery using this strategy in our patients.

METHODS

We analysed prospectively collected data on 690 consecutive patients who had isolated primary coronary artery bypass grafting performed between June 1999 and February 2003 with at least one conduit being a radial artery.

RESULTS

Radial arteries were used for 851 of 2150 distal anastomoses (39.6%). Median follow-up was 399 days (range 20-1323) and was 99.9% complete. Early mortality was 2.0% (14). Late mortality was 3.0% (21), 12 late deaths were not cardiac related. Nine patients (1.4%) had angiography on clinical grounds a mean of 238 days (range 0-511) postoperatively. Six coronary artery territories were inadequately supplied by their radial artery grafts. Kaplan-Meier event-free survival was 94% and 90% at 1 and 3 years, respectively.

CONCLUSIONS

The results of coronary artery bypass grafting using the radial artery in our institution compare favourably with those of other contemporary workers. It is safe to leave the radial artery in situ in the circulation until it is required for grafting. The absence of postoperative pharmacological manipulation of the radial artery does not appear to affect early or midterm outcome.

Comparison of flow characteristics and vascular reactivity of radial artery and long saphenous vein grafts [NCT00139399]

Background

The morphological and functional differences between arteries and veins may have implications on coronary artery bypass graft (CABG) survival. Although subjective differences have been observed between radial artery (RA) and long saphenous venous (LSV) grafts, these have not been quantified. This study assessed and compared the flow characteristics and in-vivo graft flow responses of RA and LSV aorto-coronary grafts.

Methods

Angiograms from 52 males taken 3.7 ± 1.0 months after CABG surgery were analyzed using adjusted Thrombolysis in Myocardial Infarction (TIMI) frame count. Graft and target coronary artery dimensions were measured using quantitative coronary angiography. Estimated TIMI velocity (V_E) and volume flow (F_E) were then calculated. A further 7 patients underwent in-vivo graft flow responses assessments to adenosine, acetylcholine and isosorbide dinitrate (ISDN) using intravascular Doppler.

Results

The V_E for RA grafts was significantly greater than LSV grafts (P = 0.002), however there was no difference in volume F_E (P = 0.20). RA grafts showed positive endothelium-dependent and -independent vasodilatation, and LSV grafts showed no statistically significant response to adenosine and acetylcholine. There was no difference in flow velocity or volume responses. Seven RA grafts (11%) had compromised patency (4 (6%) ≥ 50% stenosis in the proximal/distal anastomoses, and 3 (5%) diffuse narrowing). Thirty-seven (95%) LSV grafts achieved perfect patency and 2 (5%) were occluded.

Conclusion

The flow characteristics and flow responses of the RA graft suggest that it is a more physiological conduit than the LSV graft. The clinical relevance of the balance between imperfect patency versus the more physiological vascular function in the RA graft may be revealed by the 5-year angiographic follow-up of this trial.

Analysis of Vasoreactivity of Isolated Human Radial Artery

Radial artery (RA) is increasingly used as graft for coronary artery bypass grafting due to its good long-term patency. However, the mechanism of peri- and post-operative spasm is still unclear. Because of that, the aim of our study is to analyze the contractility of RA and to determine whether the presence of functional endothelium alters its contractile properties. Contractions of isolated RA rings were provoked by exogenously applied vasoconstrictors or by electrical field stimulation (EFS, 20 Hz). The order of vasoconstrictors potency based on their EC50 values was as follows: angiotensin II > phenylephrine > 5-hydroxytriptamine. Presence of endothelium increased both EC50 and maximal contraction to phenylephrine and angiotensin II, but inhibited reactivity of RA to 5-hydroxytriptamine. Spontaneous rhythmic contractions (SRC, <4 mHz) and EFS-induced contractions of RA are endothelium-independent and weaker than contractions induced by exogenously applied vasoconstrictors. Our study concludes that RA shows marked sensitivity and reactivity to angiotensin II, phenylephrine, and 5-hydroxytriptamine. Further investigations are necessary to answer why angiotensin II and phenylepehrine induce stronger contractions in the presence of endothelium. In addition, SRC as well as contractions of neurogenic origin may take part in developing vascular spasm of RA.

Radial artery grafting

After its recent reintroduction in coronary surgery the radial artery is gaining wide acceptance as complementary arterial conduits for surgical myocardial revascularization. The main technical aspects of radial artery harvesting, the biological and vasoactive characteristics of radial artery grafts as well as the mid- to long-term angiographic results and the role of the antispatic therapy are reviewed.

Radial Artery Graft for Coronary Artery Bypass Surgery: Biological Characteristics and Clinical Outcome

The radial artery (RA) is gaining popularity as a bypass conduit for coronary artery bypass grafting, and its impact on clinical practice has been extensively explored. In the present article, we provide a review of postoperative hand circulation, vascular biological characteristics of the RA graft, the efficacy of vasodilator therapies, and mid-term clinical results of use of the RA graft. Fundamental studies revealed excellent vascular biological characteristics of the RA graft as a living arterial conduit, making it almost equivalent to the internal thoracic artery (ITA) graft. Clinical studies have yielded encouraging mid-term results. Most studies reported in favor of the RA graft over the saphenous vein graft with regard to patency rate, freedom from cardiac events, and survival. However, superiority of either the RA or right ITA graft has not been conclusively determined. The long-term results of RA grafts remain unknown, but at present, supplementary use of an RA graft with a left ITA graft appears feasible for CABG.

Implantation in coronary circulation induces morphofunctional transformation of radial grafts from muscular to elastomuscular

BACKGROUND

The purpose of this research was to investigate the in vivo morphofunctional changes induced in the radial artery (RA) by its use as coronary artery bypass conduit by comparing the morphological features and vasoreactivity of the native RA versus the coronary RA graft in the same patient.

METHODS AND RESULTS

Ten years after surgery, 10 patients were submitted to intravascular ultrasound examination of the RA graft of the controlateral (in situ) RA and of the internal thoracic artery (ITA) graft and to vasoactive challenges with acetylcholine and serotonin. Quantitative angiographic assessment showed that the mean diameter of the RA coronary grafts was significantly larger than that of the in situ RA and of the ITA (2.89+/-0.40 mm RA grafts, 2.14+/-0.52 mm in situ RA, 2.25+/-0.53 mm ITA grafts; P<0.001). The in situ RA demonstrated a typical muscular architecture, whereas RA coronary grafts showed a clear reduction of the thickness of the medial layer and had a less well-defined muscular component of the media with interposition of elastic tissue. Serotonin endovascular infusion elicited a strong spastic reaction in in situ RAs; the same challenge induced only moderate constriction in RA and ITA coronary grafts.

CONCLUSIONS

Implantation in the coronary circulation leads to major anatomic and vasoreactive modifications of the RAs that tend to lose the morphofunctional features of a muscular conduit and assume those of an elastomuscular artery, such as the ITA.

Chronic compensatory increase in ulnar flow and accelerated atherosclerosis after radial artery removal for coronary artery bypass

BACKGROUND

Only scant information is available on the chronic consequences of radial artery removal for coronary artery bypass surgery on forearm circulation.

METHODS

Twenty-five patients submitted to radial artery removal for coronary artery bypass were submitted to serial Doppler echocardiographic evaluation of the flow and morphology of the forearm arteries.

RESULTS

The peak systolic velocity of the ulnar artery of the operated side was significantly higher than that of the control site. The intimal-medial thickness of the ulnar artery was always significantly higher on the operated side, and this difference reached statistical significance at 10 years' follow-up. There was a significantly higher prevalence of atherosclerotic plaques in the ulnar artery of the operated versus control arm (7/25 vs 0/25, P = .03).

CONCLUSION

Radial artery removal for coronary artery bypass surgery leads to a chronic increase in ulnar flow accompanied by increased intimal-medial thickness and accelerated atherosclerotic disease. These findings might have potentially important implications for surgical indications and patient management.

Midterm Angiographic Patency and Vasoreactive Profile of Proximal Versus Distal Radial Artery Grafts

BACKGROUND

No data are available on the different angiographic results and the in vivo vasoreactivity of radial artery (RA) grafts obtained from different parts of the conduit, although it is known that the distal segment of the artery has a more pronounced muscular component. This study was conceived to evaluate the angiographic patency and tendency to spasm of proximal versus distal RA grafts.

METHODS

In 29 patients, at the time of surgical myocardial revascularization, the radial artery was divided into two separate conduits, so that these patients received a total of 58 radial grafts (29 from the proximal and 29 from the distal portion of the artery). All cases were submitted to midterm angiography and vasoactive challenges to verify angiographic patency and vasoreactive profile.

RESULTS

Radial artery patency rate was 28 of 29 for both groups. Nine cases of string sign were reported, all in the distal series (p = 0.001). The perfect patency rate of distal grafts was markedly lower than that of proximal grafts (19 of 29 versus 27 of 29; p = 0.02). Vasoactive challenges testified to a higher vasospastic attitude of distal grafts.

CONCLUSIONS

Radial artery grafts obtained from the distal portion of the artery have a higher vasospastic tendency, greater incidence of string sign, and lower midterm perfect patency rate than graft taken from the more proximal part of the artery. The proximal part of the RA should be preferred for use as a conduit for surgical myocardial revascularization.

Is postoperative calcium channel blocker therapy needed in patients with radial artery grafts?

BACKGROUND

Chronic calcium channel blocker therapy has traditionally been considered necessary in patients carrying a radial artery graft, even in the absence of objective data to support it. This report was conceived to evaluate the angiographic and clinical effects of calcium channel blocker therapy during the first postoperative year.

PATIENTS AND RESULTS

A total of 100 consecutive patients who received a radial artery graft at our institution were randomly assigned to receive (n = 53) or not receive (n = 47) calcium channel blocker therapy with oral diltiazem 120 mg/daily started in the early postoperative period. At 1-year follow-up, all patients were reassessed clinically and by Tl 201 myocardial scintigraphy, and 83 of them underwent control angiography. In 12 cases we also evaluated the response of the radial artery to the endovascular infusion of serotonin. No difference in terms of clinical outcome, scintigraphic results, and patency rate was found between patients who received or did not receive calcium channel blocker therapy. Endovascular serotonin infusion evoked an evident spastic reaction of radial artery grafts, not attenuated by calcium channel blocker therapy.

CONCLUSION

Calcium channel blocker therapy started immediately after surgery and continued for the first postoperative year does not affect radial artery graft patency and clinical and scintigraphic outcomes. On the basis of these data, the prophylactic use of calcium channel blocker therapy in patients with radial artery grafts seems unsubstantiated.

Atherosclerotic involvement of the radial artery in patients with coronary artery disease and its relation with midterm radial artery graft patency and endothelial function

BACKGROUND

The radial artery has recently been proposed as an alternative arterial conduit for surgical myocardial revascularization. This study was conceived to evaluate the degree of atherosclerotic involvement of the radial artery in patients with coronary artery disease and the eventual influence of a subtle degree of preoperative atherosclerosis on the midterm results of radial artery grafts.

METHODS AND RESULTS

The intima-media thickness of the radial artery, common carotid artery, and internal thoracic artery was evaluated in 42 coronary artery disease patients and in 26 control patients. All radial arteries were then used for myocardial revascularization; 30 patients submitted to control angiography after 5 years. The mean intima-media thickness was 0.92 +/- 0.22 mm for the common carotid artery, 0.54 +/- 0.16 mm for the internal thoracic artery, 0.55 +/- 0.11 mm for the radial artery in coronary artery disease patients versus 0.79 +/- 0.14 mm, 0.52 +/- 0.11 mm, and 0.56 +/- 0.09 mm, respectively, in control patients (P =.001 only for the common carotid artery). No correlation was found between the intima-media thickness of the carotid, internal thoracic, and radial artery. No correlation was found between the preoperative intima-media thickness of the radial artery and the midterm patency and endothelial-mediated vasodilating capacity of radial artery grafts.

CONCLUSION

In coronary artery disease patients, radial artery atherosclerotic involvement is more frequent than that of the gold standard internal thoracic artery but still by far less severe than that of the common carotid artery. The early atherosclerotic signs often observed in the radial artery do not seem to have the potential to influence radial artery graft patency and endothelial function.

Long-term results of the radial artery used for myocardial revascularization

BACKGROUND

No information is available on the long-term results of radial artery (RA) grafts used as coronary artery bypass conduits.

METHODS AND RESULTS

In this report, we describe the long-term (105+/-9 months) angiographic results of a series of 90 consecutive patients in whom the RA was used as a coronary artery bypass conduit directly anastomosed to the ascending aorta. The long-term patency and perfect patency rates of the RA were 91.6% and 88%, respectively, versus 97.5% and 96.3% for internal thoracic artery grafts. The severity of stenosis of the target vessel clearly influenced long-term RA patency, whereas location of the target vessel and long-term use of calcium channel blockers did not influence angiographic results. Preserved endothelial function and absence of flow-limiting, fibrous, intimal hyperplasia were also documented.

CONCLUSIONS

Ten years after surgery, RA grafts have excellent patency and perfect patency rates. Appropriate surgical technique and correct indication are the key factors for long-term RA patency.

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

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 (> or = 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.

Remodeling of arterial conduits in coronary grafting

In the initial decade of coronary surgery, serial angiography of internal thoracic artery grafts revealed increased caliber in some, decreased caliber in others, and "string sign" in a few, which was occasionally documented to be reversible. Although we speculated on possible causes of these changes, it was not until discovery of the endothelial role in modulating arterial diameter to maintain shear stress in a narrow range that we began to gain insight into the mechanisms responsible for remodeling of the arterial wall. This review provides a glimpse of the physiology and biology of arterial remodeling and summarizes observations on the various arterial conduits when subjected to flow alterations.

Radial artery for myocardial revascularization: long-term clinical and angiographic results

BACKGROUND

To evaluate the long-term clinical and angiographic results of the radial artery (RA) as a graft in coronary artery bypass surgery.

METHODS

One hundred sixty-four patients had a RA graft from July 1992 to July 1994. In 128 (group A) the RA was connected end to side (115) or end to end (13) to the left internal mammary artery. In 36 (group B) the proximal anastomosis was on the ascending aorta.

RESULTS

Early mortality was 1.8% (group A 1.6% and group B 2.8%). Eight-year survival was 83.2%+/-3.2% (group A 82.1%+/-3.8% and group B 86.7%+/-6.2%, p = not significant [NS]), and event free survival was 80.1%+/-3.5% (group A 79.9%+/-4.4% and group B 80.2%+/-7.3%, p = NS). Sixty-one patients (37.2%) had an early angiography within 90 days from the operation. Patency rate of RA distal anastomoses were 98.9% (88 of 89), 98.7% in group A (77 of 78), 100% in group B (11 of 11; p = NS). After a mean of 48+/-27 months (6 to 96), 72 patients (51.1% of the survivors) had a new angiography. Patency rate of RA distal anastomoses was 95.6% (87 of 91), 93.8% in group A (61 of 65) and 100% in group B (26 of 26; p = NS). All the intermediate RA-LIMA anastomoses were patent at the early and late control. Patency rate for RA and IMAs was similar both early (88 of 89 versus 82 of 82; p = NS) and after 48+/-27 months (87 of 91 versus 93 of 93; p = NS).

CONCLUSIONS

Long-term clinical results after RA grafting are satisfying. Angiographic patency rate, both early and after 48 months, is higher than 90% and is similar to that obtained with internal mammary arteries. The site of the proximal anastomosis does not influence early and late patency.