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< Vol. 37 Issue 5 | May 2014 | pp. 349 - 426

Intra-operative graft blood flow measurements for composite and sequential coronary artery bypass grafting

Abstract

Objectives

Intraoperative assessment of coronary artery bypass grafts (CABG) anastomotic quality can be performed using transit-time flowmetry (TTF). The aim of this study was to compare on- versus off-pump coronary graft TTF and early postoperative outcomes.

 Materials and methods

Between January 2009 and January 2010, 521 distal graft flows were assessed using TTF measurements in 253 consecutive patients undergoing primary isolated CABG surgery. Data were analyzed using multilevel models accounting for clustering among surgeons and grafts performed in the same patient.

 Results

Mean age was 66 ± 10 years and 22% were female (n = 55) with 34% diabetics (n = 86) and 40% preoperative myocardial infarction (MI) (n = 101). The surgeries were performed off-pump in 67% (n = 170) with sequential vein grafts in 57% (n = 144) of patients. Off-pump patients had higher pre-operative left ventricular ejection fractions (LVEF), fewer urgent surgeries, fewer distal anastomoses, and fewer sequential vein grafts (all p<0.001). Intra-operative coronary graft TTF measurements were lower in sequential vein grafts performed off-pump versus on-pump. More patients in the on-pump group needed milrinone or dobutamine 24-48 h postoperatively (p = 0.005). Independent predictors of lower TTF included female gender and off-pump surgery, whereas predictors of better TTF were preoperative MI, larger coronary diameter at the site of the distal anastomosis, and sequential vein grafting.

 Conclusions

Lower intra-operative TTF measurements were found in sequential vein grafts in off-pump CABG. However, off-pump patients experienced similar short-term outcomes compared to on-pump patients.

Int J Artif Organs 2014; 37(5): 382 - 391

Article Type: ORIGINAL RESEARCH ARTICLE

DOI:10.5301/ijao.5000327

Authors

Jessica Forcillo, Nicolas Noiseux, Marc-Jacques Dubois, Samer Mansour, Ignacio Prieto, Fadi Basile, Louis-Mathieu Stevens

Article History

  • • Accepted on 23/03/2014
  • • Available online on 08/05/2014
  • • Published in print on 15/06/2014

Disclosures

Financial Support: None.
Conflict of Interest: None.

This article is available as full text PDF.

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INTRODUCTION

Over the last two decades, there has been increased interest in seeking a less invasive alternative to standard “on-pump” coronary artery bypass grafting (CABG) surgery in order to avoid cardiopulmonary bypass. On-pump CABG is associated with a systemic inflammation response by the release of various cytokines and multiple organ dysfunction after CABG (1). The technique of performing CABG without cardiopulmonary bypass (off-pump) using heart stabilizers has been used more extensively in high-risk and older patients who could not tolerate on-pump CABG (2). Numerous studies have reported the safety and efficacy of off-pump CABG surgery (3-4-5). Despite tremendous enthusiasm from surgeons, patients, industry, and the media, skepticism exists about the impact of off-pump CABG on the completeness and quality of revascularization and clinical outcomes. This attitude is limiting the adoption of off-pump CABG worldwide. Off-pump CABG surgery may be associated with a higher incidence of incomplete revascularization, recurrent angina, and graft occlusion, suggesting poorer graft quality and anastomotic accuracy in some series (6). Whether this is related to the technical expertise of the surgeon for off-pump CABG surgery in these trials is a matter of debate (3-4-5).

The transit time flowmetry (TTF) method is a non-invasive Doppler-based technology generating real-time graft flow waveforms measurements (7). TTF measurements are fast, easy, and reproducible. The results are also predictive of graft occlusion at short-term angiographic follow-up, and are less affected by artefacts than are other graft assessment techniques (8, 9). However, the TTF method is not perfect as it is possible to have a patent anastomosis with a low graft TTF or, conversely, a partially compromised anastomosis with a high graft TTF. Moreover, graft TTF may not change significantly until graft stenosis is greater than 75% (10). Therefore, absolute TTF values must be interpreted in conjunction with the pulsatile index (PI) and the diastolization of the flow curve (DF) as well as patient characteristics (graft characteristics, coronary diffuse disease, impaired vascular bed, and competitive flow) (11). The aim of this study was to assess risk factors associated with lower TTF measurements and to compare on-pump versus off-pump graft TTF and early outcomes.

MATERIALS AND METHODS

From January 2009 to January 2010, 521 distal graft flows were assessed using TTF measurements (MediStim ASA, Horten, Norway) in 253 consecutive patients undergoing primary isolated CABG without intra-aortic balloon pump, for a total of 860 distal coronary anastomoses. Diastolic filling percentage (DF), pulsatility index (PI), and graft flow were taken from the TTF registered data. DF is the percentage of diastolic filling of the coronaries during diastole. PI represents the total vascular resistance of the vessel. According to the manufacturer’s documentation, a PI≥5 suggests a possibly compromised anastomosis or poor outflow bed (12, 13). Mean arterial pressure (MAP) during each TTF measurement was recorded at the time of the TTF measurements and retrieved from the perfusionist’s database. Patient characteristics, operative procedure, and postoperative outcomes were retrieved from a prospectively collected institutional clinical database. This study was approved by the ethical committee of the hospital.

Surgical technique

All patients underwent CABG via a median sternotomy. The left internal mammary artery (LIMA) was harvested, pedicled, sectioned at the distal portion after systemic heparinization, injected with a solution of verapamil (5 mg in 30 mL of 0.9% sodium chloride), clipped at the distal end, and left in a gauze soaked in verapamil. Saphenous vein grafts (SVG) were usually harvested in a partially open fashion at the level of the thigh using skip skin incisions. The COR-VASC system from CORONEO (Montreal, Canada) was used for all procedures. LIMA graft was used for the left anterior descending coronary in all patients except when the LIMA graft was unusable or the patient presented no suitable grafting site in the anterolateral territory. When the patient presented more than one grafting site on the anterolateral territory (LAD, diagonal branch, ramus intermedius), we used a composite LIMA-venous bridge graft to distribute LIMA outflow. This composite graft is constructed using a short saphenous vein bridge interposed between the LAD and one (or more) other anterolateral targets with the LIMA grafted on the hood of the venous bridge just above the LAD anastomosis. This technique preserves an almost-direct LIMA-to-LAD connection while providing additional LIMA blood flow to other anterolateral grafting sites. Single or sequential aorto-coronary SVGs were used for the other territories.

In the on-pump CABG patients, 300 IU of heparin per kilogram were administered and the cardiopulmonary bypass was started after reaching an activated clotting time (ACT) of at least 480 s. Mild hypothermia at 34°C was induced and cold blood cardioplegia was administered via a needle vent in the ascending aorta. The distal SVG anastomoses were done first followed by the arterial anastomoses on the anterolateral territory. In off-pump CABG patients, 150 IU of heparin per kilogram were administered and target ACT was greater than 300 s. The coronary vessels were isolated and stabilized using the CORONEO compression-type retractor and coronary flow obstructed using soft vessel loops. Coronary shunts were rarely used; if the coronary vessels were too diseased to safely use the soft vessel loops, the surgery was performed on-pump. Techniques for anastomosis were the same as mentioned previously except that LIMA or the composite LIMA-venous bridge graft anastomoses were performed first. The ratio of off-pump to on-pump surgery was not different among the four surgeons involved in this study.

Transit-time flow measurements

Before making any TTF measurement, adequate systemic blood pressure was maintained and recorded, traction on the pericardium was released, and the heart was allowed to return to its anatomic position. Mean graft TTF was documented before reversing heparin with protamine. For single and sequential saphenous vein grafts, TTF measurements were taken in the proximal portion of the saphenous vein graft near the ascending aorta. For the LIMA, skeletonization of a small portion of the LIMA was performed whenever needed in order to have better access for the flowmeter probe. Ultrasound gel was applied to the flowmeter probe lumen before positioning it on the graft such that at least 75% of the flowmeter probe lumen was occupied. In the on-pump group, coronary graft TTF measurements were taken after reperfusion and weaning from cardiopulmonary bypass. In the off-pump group, TTF measurements were obtained 1) immediately after distal anastomosis for in situ LIMA grafts, and 2) after the completion of the distal and proximal anastomosis for SVGs and free arterial grafts. For grafts with more than one distal anastomose (sequential grafts), one overall graft flow was recorded. The coronary arteries were grouped by “coronary territories,” including the anterior territory (left anterior descending and diagonal branches), lateral territory (ramus intermedius, obtuse marginal and all posterolateral branches whether or not they were issued from the left circumflex or right coronary artery), and inferior territory (right coronary and posterior descending coronary whether or not the posterior descending branch was issued from the left circumflex or right coronary artery).

TTF measurements for composite grafts were generally available only for the LIMA, which provide an overall assessment of the blood flow to the LAD and other anterolateral coronary branches supplied by the LIMA and saphenous vein bridge. In some patients, we measured the TTF measurements 1) for the LIMA with the saphenous vein bridge temporally occluded and 2) for the saphenous vein bridge. The decrease observed in LIMA blood flow with the saphenous vein bridge temporally occluded was usually equivalent to the blood flow measured for the saphenous vein bridge.

Statistical analysis

Data are expressed as mean ± standard deviation or median and range for continuous variables, and as frequencies (percentages) for categorical variables. Statistical analyses were done using the Fisher’s Exact Test for categorical data. The t-test or Wilcoxon test was used for continuous data, as appropriate, and the Spearman correlation for scatter-plot analyses. Since the distribution of coronary graft TTF measurements was right-skewed and the linearity assumption of the regression model not met, logarithmic transformation of TTF measurements was used for multivariate models. Log-TTF were then analyzed at the level of the graft using multilevel, random-effect models accounting for clustering among surgeons and grafts performed in the same patient (the MIXED procedure in SAS release 9.2; SAS Institute, Cary, NC, USA). For sequential grafts, we considered the average coronary diameter at the site of the distal anastomoses for all grafting sites included in the sequential graft. Random effect models were used to account for the correlation between repeated cardiac enzyme measurements in the same patient at baseline and at 6 h, 24 h, and 48 h postoperatively.

RESULTS

Patients characteristics

Mean age was 66 ± 10 years and 22% of patients were female (n = 55). Patients received on average 3.4 ± 1.1 distal anastomoses with complete revascularization in 98% of patients (n = 246). Off-pump CABG was used in 67% of patients (n = 170). There was no difference between patients undergoing CABG on-pump or off-pump with respect to age, gender and major comorbidities (Tab. I). However, off-pump CABG patients had more prior PCI, higher left ventricular ejection fraction (LVEF), and less urgent surgery.

PATIENT CHARACTERISTICS FOR THE ON-PUMP VERSUS THE OFF-PUMP CORONARY ARTERY BYPASS GRAFTING GROUPS

On-pump (n = 82) Off-pump (n = 170) P
Age, y 67 ± 10 65 ± 9 0.104
Sex (% female) 20 (24%) 35 (21%) 0.517
Diabetes 32 (39%) 54 (32%) 0.260
Hypertension 61 (74%) 131 (77%) 0.639
Dyslipidemia 60 (73%) 142 (84%) 0.064
Chronic renal failure 5 (6%) 15 (9%) 0.620
Peripheral vascular disease 8 (10%) 13 (8%) 0.629
Left ventricular ejection fraction, % 48% ± 16% 55% ± 11% <.001
Prior percutaneous coronary intervention 5 (6%) 26 (15%) 0.041
Emergent status 9 (11%) 1 (1%) <.001
Recent myocardial infarction (<2 weeks) 40 (49%) 61 (36%) 0.056
Left main stenosis 34 (41%) 65 (38%) 0.680
Number of diseased coronaries (excluding left main) 0.014
 • None 0 (0%) 6 (4%)
 • One 6 (7%) 33 (19%)
 • Two 27 (33%) 51 (30%)
 • Three 49 (60%) 80 (47%)

Operative data

LIMA was used in 96% (n = 242) with composite LIMA-venous bridge grafts in 53% (n = 133) and sequential vein grafts in 57% (n = 144) of patients. Operative time was lower in the off-pump group, but fewer distal anastomoses and sequential vein grafts were performed (Tab. II).

OPERATIVE DATA FOR THE ON-PUMP VERSUS THE OFF-PUMP CORONARY ARTERY BYPASS GRAFTING GROUPS

On-pump (n = 82) Off-pump (n = 170) P
aOne measurement per distal graft.
Number of CABG 3.9 ± 1.0 3.2 ± 1.1 <.001
Left internal mammary artery use 76 (93%) 166 (98%) 0.083
Sequential vein grafts 61 (74%) 83 (49%) <.001
Complete revascularization 79 (96%) 167 (98%) 0.394
Operative time, min 186 ± 47 148 ± 44 <.001
Transit-Time Flow (TTF) dataa:
 • Diastolic filling, % 63 ± 10 66 ± 13 0.020
 • Pulsatility index 2.2 [1.5-3.0] 2.4 [1.8-3.3] 0.063
 • Pulsatility index >5 20/165 (12%) 32/309 (10%) 0.542
 • Graft flow, mL/min 53 [38-85] 42 [28-64] <.001
 • Mean arterial pressure 72 ± 9 77 ± 12 <.001

Higher diastolic filing percentages and lower pulsatility indexes were associated with better coronary graft TTF measurements (Fig. 1). Mean arterial pressure and left ventricular ejection fraction were not associated with a change in coronary graft TTF measurements in the range of blood pressures recorded (Fig. 2). On average, DF, PI, and MAP were higher and TTF measurements were lower in the off-pump compared to the on-pump group (Tab. II). However, when coronary graft TTF measurements were assessed by graft type, off-pump TTF were lower only for sequential vein grafts to one or two coronary territories (Tab. III). Off-pump was identified as an independent risk factor of lower TTF measurements along with female gender, whereas factors associated with better TTF measurements were preoperative myocardial infarction, larger coronary diameter, and sequential vein grafts (Tab. IV). Off-pump was not identified as a predictor of higher PI or lower DF.

TRANSIT-TIME FLOW (TTF) MEASUREMENTS INCLUDING PULSATILITY INDEX (PI) AND DIASTOLIC FILING PERCENTAGE (DF) BY TYPE OF GRAFT FOR THE ON-PUMP VERSUS THE OFF-PUMP CORONARY ARTERY BYPASS GRAFTING GROUPSa

Type of graft On pump Off pump
TTF N TTF N P
aData are presented as median and interquartile range. One measurement per distal graft. See text for the definition of the lateral and inferior territories.
Single internal mammary artery graft Flow, ml/min 45 [33-67] (33) 36 [26-52] (77) 0.071
PI 2.2 [1.5-3.0] 2.3 [1.8-2.8] 0.570
DF, % 67 [62-70] 71 [63-77] 0.042
Composite internal mammary artery and venous bridge graft Flow, ml/min 48 [41-74] (43) 46 [34-72] (90) 0.296
PI 1.9 [1.5-2.6] 2.5 [2.0-3.5] 0.003
DF, % 65 [59-72] 72 [61-79] 0.007
Single aorto-coronary graft to the lateral territory Flow, ml/min 34 [24-70] (19) 35 [22-51] (58) 0.531
PI 2.3 [1.7-3.9] 2.5 [1.8-3.5] 0.961
DF, % 65 [59-67] 62 [55-71] 0.867
Single aorto-coronary graft to the inferior territory Flow, ml/min 43 [35-73] (20) 43 [28-53] (35) 0.323
PI 2.1 [1.4-3.2] 1.6 [1.3-2.2] 0.052
DF, % 64 [57-69] 67 [60-69] 0.445
Sequential aorto-coronary grafts to one territory (lateral or inferior) Flow, ml/min 59 [43-95] (18) 33 [22-49] (21) 0.011
PI 2.3 [1.6-4.3] 2.2 [1.6-4.9] 0.880
DF, % 65 [58-68] 47 [33-69] 0.201
Sequential aorto-coronary grafts to both the lateral and inferior territories Flow, ml/min 75 [50-102] (47) 42 [29-65] (64) <.001
PI 2.2 [1.6-3.0] 2.6 [2.0-4.2] 0.067
DF, % 65 [58-68] 63 [52-69] 0.302

MULTIVARIATE RANDOM EFFECT MODEL OF PREDICTORS FOR CORONARY GRAFT TTF MEASUREMENT

Coeff.a ± 95% CI P
aA logarithmic transformation of TTF measurement was performed to address the linearity assumption of the model. Coefficients (coeff.) are provided here to assist the comparison of the relative strengths of the binary and categorical predictors on the logarithmic scale. See text for the definition of the lateral and inferior territories.
Improved coronary graft TTF measurement
 • Recent myocardial infarction (<2 weeks) 0.17 ± 0.06 0.003
 • Coronary diameter (mm) 0.30 ± 0.06 <.001
 • Type of graft <.001
  - Single internal mammary artery graft 0.09 ± 0.06 0.117
  - Composite internal mammary artery and venous bridge graft 0.32 ± 0.05 <.001
  - Single aorto-coronary graft to the lateral territory (reference group) 0 -
  - Single aorto-coronary graft to the inferior territory 0.02 ± 0.07 0.780
  - Sequential aorto-coronary grafts to one territory (lateral or inferior) 0.15 ± 0.08 0.064
  - Sequential aorto-coronary grafts to both the lateral and inferior territories 0.42 ± 0.06 <.001
Decreased coronary graft TTF measurement
 • Female gender -0.23 ± 0.07 0.001
 • Off pump CABG -0.26 ± 0.06 <.001

Coronary graft transit-time flow (TTF) by (A) diastolic filling percentage (DF) and (B) pulsatility index (PI). TTF and PI are represented on a logarithmic axis.

Coronary graft transit-time flow (TTF) by (A) mean arterial pressure (MAP) (mmHg) and (B) by left ventricular ejection fraction (LVEF). On-pump and off-pump graft flow results are represented with black squares and X, respectively (overall correlation presented; no differences between on-pump and off-pump correlations). TTF is represented on a logarithmic axis.

Postoperative outcome

More patients in the on-pump group presented a low output syndrome and required milrinone or dobutamine postoperatively (Tab. V). CKMB and CKMB ratio were higher in the first 6 h in the on-pump group compared to the off-pump group, but this difference became non-significant after that point time (Fig. 3). Thirty-day mortality and myocardial infarction between groups were infrequent with no difference between off-pump and on-pump groups (Tab. V). Lower TTF measurements were associated with an increased incidence of low output syndrome (p = 0.049). The event rate for other early outcomes was too low to assess their association with lower TTF measurements.

POSTOPERATIVE OUTCOMES

On pump (n = 82) Off pump (n = 170) P
30 day mortality 1 (1.2%) 2 (1.2%) >.999
Low output syndrome 9 (11%) 7 (4%) 0.052
Myocardial infarction 2 (2.4%) 4 (2.4%) >.999
Levophed 24-48 h postoperatively 15 (18%) 16 (9%) 0.064
Milrinone or dobutamine 24-48 h postoperatively 12 (15%) 7 (4%) 0.005
Maximum perioperative troponin 0.33 [0.18-1.04] 0.13 [0.05-0.35] <.001
Maximum postoperative CK MB, IU/L 30 [22-42] 22 [17-32] 0.002
Maximum postoperative CK MB/CK ratio 0.11 [0.07-0.17] 0.07 [0.05-0.12] 0.002

Maximum postoperative (A) CKMB, in UI/L, and (B) CKMB/CK ratio for on-pump vs. off-pump groups at different points in time (p<0.001). CKMB: creatine kinase isotype MB; CK: creatine kinase. Statistical tests assess whether there is an overall difference between groups, between time points and whether there is a difference in the profile of these laboratory value through time between groups (group * time interaction).

DISCUSSION

In our study, off-pump coronary surgery was associated with lower intra-operative coronary graft TTF measurements, especially for sequential vein grafts to one or two coronary territories (lateral or inferior territories). On average, coronary graft TTF measurements in off-pump patients showed no gradual increase from single venous graft to sequential vein graft for one territory to sequential vein graft for two territories. Conversely, coronary graft TTF measurements in on-pump patients presented an almost dose-response increase from single vein graft to sequential vein graft for one territory to sequential grafts for two territories.

Sequential grafting leads to a greater outflow bed and lower overall vascular resistances compared to non-sequential grafts (14). Increased graft flow rate has been associated with decreased SVG intimal proliferation (15). Some series have reported better TTF measurements (16, 17) or patency (15, 18) results with sequential grafting strategy compared to single graft while others have not (19-21). A meta-analysis of 12 studies comparing the patency of sequential and individual vein grafts concluded that the mid- and long-term patency of sequential vein grafts were superior to single vein grafts (14). Authors did not report the proportion of on-pump versus off-pump surgery, but none of these studies directly compared coronary graft TTF or patency in sequential grafts performed on-pump versus off-pump.

In this paper, our interest was to assess the impact of off-pump coronary artery bypass grafting and sequential grafting on transit-time flow measurements. One of the original aspects of our practice is the grafting strategy using a composite-sequential venous graft to distribute LIMA inflow to the LAD, but also to the other branches of the anterolateral territory, thereby promoting a higher flow through the LIMA pedicle with an almost direct LIMA-LAD connection. Preliminary data using this technique has been very favorable both in term of clinical outcomes and graft patency results (13). A randomized clinical trial (the AMI-PONT trial; ClinicalTrials.gov: NCT01585285) is underway to assess whether a CABG strategy including a LSVB to distribute the LIMA outflow provides non-inferior patency rates compared to conventional CABG surgery with separated LIMA graft to LAD and aorto-coronary SVG to other anterolateral targets. Several graft morphology parameters and more extensive transit-time flow measurements are also recorder per protocol. The trial protocol has been published (22).

The vein graft is usually larger than the LIMA graft. In the composite graft design, the vein graft serves to distribute LIMA blood flow to a larger cardiac territory. The LIMA graft is anastomosed on the hood of the vein graft anastomosis on the LAD with an almost direct LIMA to LAD connection. In this retrospective study, the impact of the composite graft design on coronary graft TTF measurement is difficult to elucidate since we generally assessed TTF measurement for the LIMA graft only and not the saphenous vein bridge. We can only speculate that the LIMA TTF measurement may be increased in a composite graft design compared to a direct LIMA-to-LAD anastomosis. The ongoing AMI-PONT trial will provide further insights on the impact of a composite graft design on TTF measurements (22).

The main disadvantage of sequential grafting is that a larger mass of myocardium may be compromised with a proximal graft lesion and latero-lateral anastomoses may be technically challenging (19-20-21). In our study, the relatively lower coronary graft TTF measurements for sequential grafts in the off-pump group compared with the on-pump group may be associated with anastomotic compromises. However, 1) it may be difficult to interpret the anastomotic quality as a single function of the TTF measurements; 2) it is possible to have a low coronary graft TTF measurement with a patent anastomosis; and 3) if an anastomotic error is present, it is unclear whether the problem is situated at the level of the latero-lateral or termino-lateral anastomoses. Moreover, several studies showed that TTF values do not always correlate with clinical outcome or long-term patency (23, 24). Despite lower TTF measurements for sequential grafts in the off-pump group, we found lower CK-MB release in this group and the two groups did not differ in their short-term complications rate, including low output syndrome, myocardial infarction, and 30-day mortality. While using TTF, the clinician has to consider all parameters (TTF measurements, PI, DF) as a whole in the interpretation of the result in order to decide to reintervene or not on the anastomosis. An abnormal PI, defined as a PI>5 in any one graft measured intra-operatively, is independently associated with adverse in-hospital outcome (11), including mortality (12). In our study, 89% of grafts had a PI lower than 5 and this was no different for on- or off-pump CABG patients.

It is likely that other mechanisms may explain the differences in coronary graft TTF measurements between on-pump and off-pump CABG patients. Coronary artery vasodilation in the on-pump group can be explained by: A) anaerobiosis and acidosis with progressive duration of ischemia in the arrested heart; B) release of inflammatory mediators; and C) ischemia-reperfusion phenomenon after release of the aortic crossclamp (1, 25). Conversely, in the off-pump group: A) local coronary occlusions of short duration probably are unable to trigger a “vasodilation effect”; B) vasopressors used to stabilize hemodynamics during off-pump surgery can constrict the coronary vascular bed; and 3) coronary snaring has been associated with microthrombosis, atherosclerotic plaque rupture, focal endothelial denudation, distal embolization, and injury to target vessel branches (26). Intracoronary shunting may protect against back wall suturing, another cause of early graft failure, however it is also associated with more technically demanding anastomoses and intimal injury (17).

In addition to off-pump surgery, female gender was identified as a predictor of lower coronary graft TTF measurements. Female gender may be related to smaller coronary diameter and greater overall vascular bed resistance. Correspondingly, another study reported lower coronary graft TTF measurements in women, but no significant difference in coronary graft TTF measurements between on-pump and off-pump CABG groups. Other predictors of higher TTF measurements included pre-operative MI, coronary diameter, and sequential vein grafts. Patients with recent MI may present with more critical coronary stenoses or acute occlusion where there is no or only partial competitive flow. Coronaries with larger diameter have less resistance to blood flow and possibly a greater capillary bed.

LIMITATIONS

This study has limitations due to its retrospective design. Only one overall graft TTF measurement per sequential graft was available for our analyses. For better accuracy of graft patency, grafts flow could be reassessed at the end of protamine and after normalization of corporal temperature. The percentage of revised coronary grafts due to low TTF was not recorded, but recent experience in our group indicate that 3.6% of patients (23/640) had coronary graft repeated due to unsatisfactory TTF. The rate of short-term adverse postoperative events was low in this cohort of CABG patients, which limits the assessment of the impact of a low coronary graft TTF measurement on postoperative outcomes. Postoperative coronary angiography or transthoracic echocardiogram was performed on a limited subset of patients and was driven by clinical indication; therefore no correlation between graft patency, wall motion score, and coronary graft TTF measurements can be derived.

Lower intra-operative coronary graft TTF measurements were found in sequential vein grafts performed off-pump compared to sequential vein grafts in the on pump-group. Coronary graft TTF measurements for other grafts were no different for the on-pump and off-pump groups, and were no different for all grafted territories, including accessible grafting sites on the anterior wall as well as technically challenging grafting sites such as circumflex obtuse marginals and posterolaterals. Clinical short-term outcomes were not affected by lower coronary graft TTF measurements. We believe that TTF systems should be routinely used as a validity tool after the completion of bypass grafts. Future studies should evaluate whether differences in graft TTF measurements for sequential grafts in on-pump versus off-pump groups influence long-term graft patency or late outcome.

ACKNOWLEDGEMENTS

We would like to thank all surgeons from the CHUM (University of Montreal Hospital Center) for their surgical contributions.

Disclosures

Financial Support: None.
Conflict of Interest: None.
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Authors

  • Forcillo, Jessica [PubMed] [Google Scholar] 1, * Corresponding Author ([email protected])
  • Noiseux, Nicolas [PubMed] [Google Scholar] 1
  • Dubois, Marc-Jacques [PubMed] [Google Scholar] 2
  • Mansour, Samer [PubMed] [Google Scholar] 1
  • Prieto, Ignacio [PubMed] [Google Scholar] 1
  • Basile, Fadi [PubMed] [Google Scholar] 1
  • Stevens, Louis-Mathieu [PubMed] [Google Scholar] 1

Affiliations

  • Division of Cardiac Surgery and Cardiology, University of Montreal Hospital Center (CHUM), CHUM Research Center (CRCHUM), Montreal, Quebec - Canada
  • Department of Critical Care, University of Montreal Hospital Center (CHUM), CHUM Research Center (CRCHUM), Montreal, Quebec - Canada

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