Patency of no-touch saphenous vein grafts incoronary artery bypass grafting. An angiographicfollow up

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Örebro University Medical School

Bachelor thesis, 15 credits January 2020

Patency of no-touch saphenous vein grafts in

coronary artery bypass grafting. An angiographic

follow up.

Version 2

Author: Rebecka Sölvenäs Supervisor: Ninos Samano, MD, PhD Department of Cardiothoracic and Vascular Surgery,

University Health Care Research Center Örebro University Hospital, Örebro, Sweden

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Abstract

Objective

The objective was to investigate whether vein grafts harvested with the no-touch technique have a better patency than conventional grafts in coronary artery bypass surgery.

Methods

The study population consist of 103 patients operated at Örebro University Hospital between 2005 and 2017 and came back for a clinically induced coronary angiography. The study population was divided into two groups according to the harvesting technique of the vein, conventional or no-touch. The patency and survival were compared between the two groups.

Results

The conventional group came back for angiography after a mean time of 1.7 years, compared to 3.6 years for the no-touch group. Patency was 50% in the conventional group and 63% in the no-touch group. Survival was 50% and 71.6% respectively, 12 years postoperative.

Conclusions

No-touch grafts provide a better patency and a higher rate of survival than conventional grafts.

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Acronyms

BITA bilateral internal thoracic arteries BMI body mass index

C conventional

CABG coronary artery bypass grafting ECC extracorporeal circulation LITA left internal thoracic artery

NT no-touch

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Introduction

Ischemic heart disease

Ischemic heart disease, defined as angina pectoris and myocardial infarction, is the most common cause of death in the world [1]. Between the years 2000 and 2016 even an increase in incidence is seen. Ischemic heart disease is caused by a build-up of atherosclerotic plaque, that reduce the blood flow in the coronary arteries causing ischemia. The disease could express itself through stable coronary obstructive lesions or as a combination of fixed lesions, vasospasm, platelet aggregation, thrombosis and the rupture of the plaques [2]. Symptoms and signs of ischemic heart disease depends on the type of disease. The severity can vary from silent ischemia to dramatic chest pain with sudden death [3]. An acute coronary event usually causes chest pain, cold sweats, shortness of breath and nausea, but the symptoms may also be more diffuse.

Coronary artery bypass grafting

One of the best ways to treat advanced ischemic heart disease is by coronary artery bypass grafting (CABG) [4] [5]. In CABG, the blocked vessel is bypassed with a graft, an artery or a vein. One graft can be connected to several native coronary arteries, called sequential grafting. The goal is to achieve full revascularization of the myocardium. The gold standard is to use the left internal thoracic artery (LITA) to the left anterior descending artery [6], because of its good long-term patency. In most cases more than one graft is needed. Arterial grafts have been preferred because of their long-term patency, compared to the great saphenous vein [7]. But there are limitations associated with arterial grafts. Firstly, it is always a risk of ischemia after removal of arterial grafts from its original anatomic site. Secondly, spasm of arterial grafts is a critical clinical problem [8]. Thirdly, when using bilateral internal thoracic arteries (BITA) there is an increased risk for mediastinitis, especially in diabetic and obese women [9]. Currently the most common graft used is the saphenous vein (SV) [6] and the long-term patency of this graft is therefore crucial.

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Vein graft failure

The life expectancy of the saphenous vein limit the benefits of CABG surgery [6] [10]. Vein graft failure is associated with recurrent angina and is one of the primary reasons for reoperation in CABG patients [11]. About 15-30% of SV grafts occlude in the first year, and after ten years the graft occlusion rates are >50% [12]. In order to keep the graft patent, the important pathologic processes that causes graft failure must be delayed or prevented.

Pathogenesis of vein graft disease

There are three different processes responsible for vein graft failure; thrombosis, intimal hyperplasia and accelerated atherosclerosis [6]. Thrombosis is held responsible for most of the acute (less than a month) graft failures but can partly be prevented by the administration of perioperative antiplatelet therapy. Atherosclerosis causes most of the failures in the later postoperative period. The risk for atherosclerosis can, as in native coronaries, be reduced by intensive blood lipid lowering. Intimal hyperplasia is the most common cause of vein graft failure in the subacute period (one to twelve months). The pathology behind the intimal hyperplasia is thought to have at least two reasons. The first is the adaption of the vein to the higher pressure that is present in the arterial circulation. The second is the damage to the tunica intima, which is injured by the manual distention with saline, technique used in conventional harvesting. The injury causes loss of inhibition to hyperplasia that the intima normally provides. Hyperplasia of the intima causes the lumen to narrow and the risk for vein graft failure and ischemia increases. Evidence shows that surgical injury during preparation leads to neointimal thickening, and also vascular smooth muscle proliferation [11].

Surgical techniques

There are two different techniques for harvesting the great saphenous vein, the conventional (C) technique and the no-touch (NT) technique, see figure 1. When using the C technique the vein grafts are stripped of the adventitia layer at the time of harvesting [6]. This causes the vessel to go into spasm, requiring manual distension with normal saline. Distention of the graft causes trauma and is an important cause of vein graft failure [6].

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With the NT technique, the saphenous vein graft is harvested complete with its surrounding tissue, avoiding grafts spasm and the need for manual distension. The NT technique of harvesting the SV was developed as an attempt to improve the patency of the SV graft [12] [13], with the hypothesis that the preserved perivascular tissue would prevent spasm of the vein.

Preparation of the graft is important because injury during surgery leads to both biochemical and functional changes in the graft [11]. The NT harvesting approach prevents endothelial damage to the saphenous vein, which will minimise the risk of intimal hyperplasia and graft failure [6].

C NT NT

FIGURE 1. Saphenous veins harvested with conventional (C) and no-touch (NT) technique [13]. The NT

vein is harvested complete with its perivascular tissue whereas the surrounding fat is removed in the C vein. The picture at the right shows the cushion of perivascular adipose tissue (PVAT) and a patent lumen.

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The no-touch technique

The SV is mapped preoperatively to locate the vein, reduce the injuries on soft tissue and predetermine the best segment of the vein [13]. To expose the SV an incision is made through the skin and the edges of the skin are lifted. The diathermy knife is used to mark the pedicle approximately 0,5 cm from the vein. Then both scissors and a diathermy knife are used to remove the saphenous vein from the its bed.

Angiography and patency

The patency of the grafts is usually evaluated by coronary angiography. Vein grafts tend to be fully patent, occluded or stenosed [15]. It is established that the higher the flow, the higher the patency, regardless of the technique used [16]. Poor vein quality affects patency irrespective of choice of technique.

Former studies show that harvesting the saphenous vein with its surrounding tissue provides high patency in both short- and long-term perspectives [16] [17] [18] . According to a randomised-controlled-trial from 2006, the patency rates of saphenous veins are comparable to those of the left internal thoracic artery [19], with 90 percent patency after 8,5 years. In a long-term-study from 2015 the patency was significantly higher in the NT SV compared to C veins, 16 years after the CABG [20].

Aim

The objective of this study was to investigate if grafts harvested with the NT technique have a better patency than those harvested with the C technique. Several studies show that the no-touch technique provides better patency, but further investigation is warranted.

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Material and methods

Study design

The study is a retrospective analysis of data aquired from Swedish quality registers CARATH and SWEDEHEART. Additional data was extracted from patient charts.

Study population

The study population consists of all patients who underwent a CABG surgery in Örebro between 2005 and 2017 and came back for a clinically induced angiography. Patients with a least one SV graft and angiographic results were included. The SV grafts were harvested by either the C or NT techniques, and compared according to patency of the grafts. Over the last 10 to 15 years, patients at USÖ are routinely operated by the NT technique, and the conventional technique is used only under certain circumstances. These include poor perivascular tissue, superficial SV or the surgeon’s choice of C technique. The study population was chosen because of the reliable and easily accessible data from the registers.

CABG patients operated at USÖ 2005-2017

No veingraft

(excluded) vein graft≥ one

No results in SWEDEHEART

(excluded) Angiographic vein graft results in SWEDEHEART

Operated with

NT technique Operated with C technique

FIGURE 2: Flow chart of the study population. Patients who went through a CABG surgery between

2005-2017, got at least one vein graft and came back for a coronary angiography were included. Depending on the technique used to harvest the saphenous vein, the population was divided into two different groups.

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Data and statistics

A database was established in agreement with the law of GDPR and local routines. The baseline and perioperative data were taken from the local quality register CARATH, and the angiographic results from the national Swedish registry SWEDEHEART. Missing or unclear data was double-checked against the patient charts. The categorical data was compared with chi-square-test and the continuous data was compared with t-test or Mann-Whitney U test. The results were judged as significant when p ≤ .05. All the data was processed in excel and SPSS version 22 (SPSS Inc., Chicago, IL. US).

Angiography and patency

The angiographic follow up occurred with a mean time of 3.2 years after surgery. The outcome could be one of three states; patent, occluded or stenosed. When a graft was not opacified fully by contrast media it was judged as occluded. A graft stenosis was judged as significant when the narrowing of the lumen diameter was over 50% relative to the adjacent part of the vessel. The images were reviewed by interventional cardiologists.

Ethics

The study did not require any patient intervention. All data was taken from registries and patient journals after approval from the director of department of Cardiothoracic and Vascular Surgery, Örebro University Hospital, Örebro, Sweden. The study was a quality assurance and did not require any approval from the Ethics Review Board. The collected data was encoded and only identifiable together with a study number.

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Results

Baseline characteristics

The mean age was significantly higher in the C group compared to the NT group, 68 ± 10 vs 64 ± 9. The proportion of women was also higher in the C group, 27.3% compared to 19.8. Mean body mass index (BMI) was 29 and 28 in the C and NT group respectively. Overweight is defined as BMI > 25, which means that the patients in both groups, on average, are overweight. The majority of patients in both groups had hypertension and hyperlipidaemia. The prevalence of smoking and chronic obstructive pulmonary disease (COPD) were almost the same in the two groups. The prevalence of diabetes, mainly diet treated, was higher in the C group. Left ventricular function, the prevalence of angina and NYHA classification show that the severity of cardiovascular disease was on the same level in the two groups. According to EuroSCORE the mean operation risk was low in both groups, low risk defined as EuroSCORE 2-3 [21], but with a range of 0-12 and 0-15 in the C vs NT groups respectively. In total, 36-37% had suffered a myocardial infarction, with no difference between the groups. However, the C group had a higher rate of use of anticoagulation, 59.1% compared to 42% in the NT group. See table 1.

To summarize, the two groups were of different sizes, but had similar data regarding risk factors and most medical treatment. The only statistically significant difference between the groups was in age.

Perioperative characteristics

The operation time, ECC time, respiration time and cross clamp time were shorter in the C group. More patients were operated off pump in the NT group compared to the C group. Two patients in each group were operated in an acute situation, defined as within 24 hours after arrival to hospital. The average length of stay at the hospital was eight days for the C group and nine days for the NT group. New onset of atrial fibrillations or flutter was more common in the C group. Five patients (6.2%) in the NT group went through a reoperation due to bleeding or tamponade, while no reoperation occurred in the C group. See table 2.

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Total

NT

C

p-value

No. of patients 103 81 22

Mean age, yrs ± SD 65 ± 10 64 ± 9 68 ± 10 .037259

Male, n/total N 81/103 (76%) 65/81 (80.2%) 16/22 (72.7%) .445368

BMI1_{, mean}_±_SD_{28 ± 4} _{28 ± 4} _{29 ± 5} .44758

Smoking

Never smoked Former smoker (> 1 month) Smoker Unknown 42 (40.8%) 44 (42.7%) 14 (13.6%) 3 (2.9%) 33 (40.7%) 34 (42%) 11 (13.6%) 3 (3.7%) 9 (40.9%) 10 (45.5%) 3 (13.6 %) 0 .987964 Hypertension Yes No Unknown 66 (64.1%) 36 (35.1%) 1 (1%) 51 (63%) 29 (35.8%) 1 (1.2%) 15 (68.2%) 7 (31.8%) 0 .70007 Hyperlipidaemia Yes No Unknown 80 (77.7%) 12 (11.7%) 11 (18.7%) 63 (77.8%) 9 (11.1%) 9 (11.1%) 17 (77.3%) 3 (13.6%) 2 (9.1%) .769 Diabetes Insulin treated Diet treated Tablet + insulin Tablet treated No diabetes 33 (32%) 9 (8.7%) 3 (2.9%) 5 (5.9%) 16 (15.5%) 70 (68%) 24 (29.6%) 7 (8.6%) 1 (1.2%) 4 (4.9%) 12 (14.8%) 57 (70.4%) 9 (40.9%) 2 (9.1%) 2 (9.1%) 1 (4.5%) 4 (18.2%) 13 (59.1% .389232 COPD2 Yes No Unknown 4 (3.9%) 97 (94.2%) 2 (1.9%) 3 (3.7%) 77 (95.1%) 1 (1.2%) 1 (4.5%) 20 (90.9%) 1 (4.5%) .83241 Angina Unstable Stable Progress in 2 months No 45 (43.7%) 37 (35.9%) 14 (13.9%) 7 (6.8%) 34 (42%) 30 (37%) 11 (13.6%) 6 (7.4%) 11 (50%) 7 (31.8) 3 (13.6%) 1 (4.5%) .897636 Myocardial infarction 39/103 (36.9%) 30/81 (37%) 8/22 (36.4%) .92878

Reduced left ventricular

function 22 (21.4%) 15 (21%) 5 (22.7%) .586295 NYHA3 I II III IV Unknown 3 (2.9%) 25 (24.3%) 58 (56.3%) 13 (12.6) 4 (3.9%) 2 (2.5%) 23 (28.4%) 43 (53.1%) 10 (12.3%) 3 (3.7%) 1 (4.5%) 2 (9.1%) 15 (68.2%) 3 (13.6%) 1 (4.5%) .301531

EuroSCORE4_{, mean, range} 4, 0-15 3, 0-15 4, 0-12 .12852

Higgins score5_{, mean, range} _{2, 0-12} _{2, 0-12} _{3, 0-10} _.16452 Anticoagulation Yes No Unknown 47 (45.6%) 55 (53.4%) 1 (1%) 34 (42%) 46 (56.8%) 1 (1.2%) 13 (59.1%) 9 (40.9%) 0 .166788

TABLE 1. Baseline characteristics. Data for the total, no-touch (NT) and conventional (C) group.

1 _{Body mass index,}2 _{Chronic obstructive pulmonary disease,}3 _{New York Heart Association,}4

Euro-pean System for Cardiac Operative Risk Evaluation, 5 _{Stratification of morbidity and mortality outcome by}

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In total 142 vein grafts were used to the 103 patients. In the C group, 34 of the grafts were used, which means 1.5 per patient in mean. In the NT group 108 grafts were used, in mean 1.3 per patient. The total number of grafts used, arterial grafts included, were 231. In mean it was 2.4 per patient in the C group and 2.2 grafts per patient in the NT group. See table 2 and 3.

Patency and survival

Of the 142 vein grafts 59.9% were open at angiography with a mean time of 3.2 years after surgery. In the C group 50% were open, compared to 63% in the NT group. The C grafts were occluded in 38.3% of cases and stenosed in 11.8%. In contrast, 22.2% and 14.8% of the grafts in the NT group were occluded and stenosed, respectively. See figure 3.

Total

NT

C

p-value

Procedure time, mean ± SD (min) 218 ± 83 226 ± 88 188 ± 54 .026707

ECC1_{time, mean}_±_{SD (min)*} _{91 ± 39} _{94 ± 38} _{80 ± 41} .064231

Cross clamp2_{time, mean}_±_SD (min)**

57 ± 30 60 ± 29 48 ± 30 .060494

Respirator time, mean, range (min) 473, 115-2910 405, 115-2910 360, 137-945 .23885

Surgery off pump 10 (9.7%) 9 (11.1%) 1 (4.5%) .6851

Urgent3_operation 4 (3.9%) 2 (2.5%) 2 (9.1%) .1991

Mean hospital stay, days ± SD 9 ± 7 9 ± 7 8 ± 3

New onset AF4_/AFL5 35 (31.8%) 26 (32.1%) 9 (40,9%) .439105

Reoperation (bleeding/tamponade) Yes No Unknown 5 (4.9%) 97 (94.2%) 1 (1%) 5 (6.2%) 76 (93.8%) 0 0 21 (95.5%) 1 (4.5%) Grafts LIMA SV (NT) SV (C) A.radialis 231 86 108 34 3 179 68 108 0 3 52 18 0 34 0

Number of anastomosis, mean ± SD 3 ± 1 3 ± 1 3 ± 1

TABLE 2: Perioperative characteristics. Data for the total, no-touch (NT) and conventional (C) group.

1 _{Extracorporeal circulation,}2 _{Crossclamp of the aorta,}3 _{defined as within 24 hours,}4 _{atrial fibrillations,} 5 _{atrial flutter}

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The C group came back for coronary angiography after a mean time of 1.7 years, compared to the NT group that came back after a mean time of 3.6 years. Data of survival was collected 2019-12-05 and the survival was higher in the NT group. The mean time between surgery and collection of data was 11.8 and 12 years in the C and NT groups respectively. The number of deceased was nominally higher in the C group but did not reach a level of significans. This means, close to 12 years after surgery, 50% was alive in the C group and 71,6% in the NT group.

TABLE 3. Patency and survival. Data for the total, no-touch (NT) and conventional (C) group.

FIGURE 3: Patency for the total, no-touch (NT) and conventional (C) group. Patent = fully opacified with

contrast media, occluded = not opacified fully by contrast media, stenosed = narrowing of the lumen diameter was over 50% relative to the adjacent part of the vessel.

Patency total

Patent Occluded Stenosed

Patency NT

Patency C

Total

NT

C

p-value

Number of SV grafts 142 108 34

Time (yrs) between surgery and angiography, mean, range

3.2, 0.1-9.3 3.6, 0.1-9.3 1.7, 0.1-5.7 .00014

Deceased until 2019-12-05 34/103 (33%) 23/81 (28.4%) 11/22 (50%) .056004

Mean time between surgery and 2019-12-05 days ± SD 11.9 ± 2.1 11.8 ± 2.4 12 ± 1.7 .213725 Angiography result Patent graft Occluded graft Stenosed graft 85 (59.9%) 37 (26.1%) 20 (14.1%) 68 (63%) 24 (22.2%) 16 (14.8%) 17 (50%) 13 (38.2%) 4 (11.8) .178931

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Discussion

The main message of this study is that harvesting the SV with the NT technique provides a better patency than with the C technique. The mean time before the patients came back for a coronary angiography was more than twice as high in the NT group, compared to the The survival was also nominally better in the NT group 12 years postoperatively.

A higher rate of patency for the NT grafts compared to the C grafts, 63% vs 50%, despite the longer follow up time in the NT group speaks its clear language. However, more factors than choice of technique affect the patency. Younger age and a lower ejection fraction are patient variables associated with reduced graft patency [22]. The NT group was in mean 4 years younger than the C group, despite this a higher patency rate was achieved. Left ventricular function, on the other hand, did not differ between groups. More factors, that we do not have any data about in this study, are coronary and conduit diameter, and what coronary artery that was grafted. Lowest patency in the right coronary artery and highest in the left descending artery territory. Also, the learning curve could affect the patency, since recent operations show better patency. Furthermore, there is no data on the vein quality and harvesting site (thigh or calf) of the grafts.

An additional observation is that more vein grafts were used per patient in the C group. The average number of vein grafts used were 1.5 per patient in the C group, compared to 1.3 per patient in the NT group. The total number of grafts used per patient, arterial grafts included, were 2.4 and 2.2 respectively. This means, if arterial grafts are included, more grafts were actually used in the NT group. However, the differences are small and probably inconsiderable.

Concerning the data of survival, only the time between the date of surgery and the date of data collection is known. To summarize, 67% of the patients were alive in a mean time of 12 years postoperatively. The real date or cause of death is not known. It would have been of interest to collect that data and see whether the cause of death was related to

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cardiovascular disease or not. It would also be intriguing to investigate if it was the patients with occluded or stenosed grafts that died within this 12-year period.

Most of the patients went through several coronary angiographies during the years 2005-2017. In this study, the first angiography was always used, therefore the time between surgery and angiography was quite short, in mean 3.2 years. It would have been of interest to investigate the later results as well, and also follow the patency over time.

A longer mean operation time was also observed in the NT group. A possible explanation could be that seven patients in the NT group went through a heart valve surgery during the same procedure, compared to only two patients in the C group.

The patients included in the study were patients who went through a CABG surgery between the years 2005-2017, and who came back for a coronary angiography. This means that the patients included had symptoms and a reason to go through an angiography, which is an invasive examination. Patients who were symptom-free and did not require any medical treatment were not included in the study. That means that the patency rates appear lower than it would be if all operated patients went through a follow-up. Furthermore, patients who had symptoms but did not apply for health care were not included. Lastly, patients who died without going through an angiography, were not available for this study. Since these patients were not included, the patency rates in this study could possibly differ from reality.

Another limitation is the difference in number of patients between the two groups. Of the 103 patients included, only 22 were operated with the C technique and the remaining patients were operated with the NT technique. The explanation to this unequal distribution is that the NT technique has been used as the standard method for the last 10-15 years in Örebro, due to considerable evidence supporting a better patency with the NT technique [14] [23]. The C technique is therefore used only under certain circumstances. The small number of patients in the C group also complicates the analysis of the results.

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A strength of this study is the specific and detailed data collected from local and national registries CARATH and SWEDEHEART. Those quality registries are considered to be both reliable and accurate. Missing and unclear data was always checked against patient charts.

Conclusion

In conclusion, this study shows that using NT grafts for CABG provides both a higher patency and a higher rate of survival than C grafts. The study is small and includes only 33 C grafts, and therefore the differences were not statistically significant. The study does however support former studies on the same subject.

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Patency of no-touch saphenous vein grafts incoronary artery bypass grafting. An angiographicfollow up