Graft revision after transit time flow measurement in off-pump coronary artery bypass grafting

A randomized comparison of intraoperative indocyanine green angiography and transit-time flow measurement to detect technical errors in coronary bypass grafts

BACKGROUND

Early coronary bypass graft failures may be preventable if identified intraoperatively. The purpose of this investigation was to compare the diagnostic accuracy of two intraoperative graft assessment techniques, transit-time ultrasound flow measurement and indocyanine green fluorescent-dye graft angiography.

METHODS

Patents undergoing isolated coronary artery bypass grafting with no contraindications for postoperative angiography were enrolled in the study. Patients were randomly assigned to be evaluated with either indocyanine green angiography (Novadaq Spy angiography system; Novadaq Technologies Inc, Concord, Ontario, Canada) and then transit-time ultrasonic flow measurement (Medtronic Medi-Stim Butterfly Flowmeter TTF measurement system; Medtronic Inc, Minneapolis, Minn) or transit-time flow then indocyanine green angiography. Patients underwent x-ray angiography on postoperative day 4. The primary end point of the trial was to determine the sensitivity and specificity of the two techniques versus reference standard x-ray angiography to detect graft occlusion or greater than 50% stenosis in the graft or perianastomotic area.

RESULTS

Between February 2004 and March 2005, 106 patients were enrolled and x-ray angiography was performed in 46 patients. In total, 139 grafts were reviewed with all three techniques and 12 grafts (8.2%) were demonstrated to have greater than 50% stenosis or occlusion by the reference standard. The sensitivity and specificity of indocyanine green angiography to detect greater than 50% stenosis or occlusion was 83.3% and 100%, respectively. The sensitivity and specificity of transit-time ultrasonic flow measurement to detect greater than 50% stenosis or occlusion was 25% and 98.4%, respectively. The P value for the overall comparison of sensitivity and specificity between indocyanine green angiography and transit-time flow ultrasonography was .011. The difference between sensitivity for indocyanine green angiography and transit-time flow measurement was 58% with a 95% confidence interval of 30% to 86%, P = .023.

CONCLUSION

Indocyanine green angiography provides better diagnostic accuracy for detecting clinically significant graft errors than does transit-time ultrasound flow measurement.

Dual-Beam Ultrasound versus Transit-Time Flow Meter for Intraoperative Graft Flow Measurement during Coronary Artery Bypass Grafting

Objective

Assessment of graft flow during coronary artery bypass grafting (CABG) is increasingly practiced as a quality measure, particularly in patients undergoing minimally invasive or “off-pump” revascularization. Transit-time flow meters such as Transonic system (TS) are currently the most frequently used technology. The QuantixOR flow probe (QOR) is a novel technology comprised of dual-beam ultrasound transducer and a digital pulse-wave Doppler, allowing immediate, quantitative blood flow measurements. Excellent correlation between QOR and TS was observed in phantom and animal models. This study evaluated the QOR in patients undergoing CABG.

Methods

Graft flow was measured in 75 patients undergoing CABG (203 grafts). Intraobserver (n = 169) and interobserver (n = 33) variability was assessed and the QOR was compared with the TS (n = 155).

Results

An average of 2 probe sizes per case and “skeletonization” of a short segment of the vessel were required to measure flow in arterial conduits using TS. In contrast, measurements of flow with the QOR were achieved using a single probe without special vessel preparation for all types of conduits. Average intraobserver and interobserver variability using the QOR were 5 ± 41% and 4 ± 40%, respectively. Correlation was observed between 2 sets of measurements by the same observer (R2 = 0.746, P < 0.0001) and between 2 different observers (R2 = 0.667, P < 0.0001). Correlation was also observed between the QOR and TS (R2 = 0.542, P < 0.0001) with a variance of 12 ± 21%.

Conclusions

The QOR technology provides a reliable quantitative graft flow assessment that is simpler to obtain compared with TS. Correlation between the QOR and TS is excellent.

Pre-Clinical Validation of a New Intra-Operative "Dual Beam Doppler" Blood Flowmeter in an Artificial Circuit

BACKGROUND

Intra-operative flow measurement during coronary or peripheral bypass operations is helpful for ruling out technical failures and for prediction of complication and patency rates. Preclinical validation of the flowmeters is required in order to rely on the intra-operatively measured results. The aim of this study is to evaluate a new "dual beam Doppler" blood flowmeter before clinical application and to compare it with the established "transit time flow measure-ment" technique in an artificial circuit.

METHODS

Measurements were performed in an experimental flow model using pig blood and pig arteries. Three different flowmeters were used: Quantix OR (dual beam doppler flowmeter), CardioMed (transit time flowmeter), and Transonic (transit time flowmeter). Three validation tests were performed to assess correlation, precision, and repeatability of devices. (1) Correlation and agreement analysis was performed with various flow amounts (10-350 mL/min) (n = 160). (2) Device reproducibility and measurement stability were tested with a constant flow (flow amount = 300 mL/min) (n = 30). (3) A user accuracy test (intra- and inter-observer variability) was performed by 5 different observers with a constant flow (flow amount = 205 mL/min) (n = 75). Time collected true flow was used as a reference method in all steps and all tests were performed in a blind manner. Results are shown as mean values +/- standard deviations. Pear-son's correlation and Bland-Altman plot analyses were used to compare measurements.

RESULTS

The mean flow was 167 +/- 98 mL/min for true flow and 162 +/- 94 mL/min, 165 +/- 94 mL/min, and 166 +/- 100 mL/min for Quantix OR, CardioMed, and Transonic, respectively. Correlation coefficients between Quantix OR, Medi-Stim, Transonic, and time collected true flow were over 0.98 (P = .01). Most of the measured results ( > 90%) were between +/- 1.96 SD agreement limits in Bland and Altman plot analysis. All devices showed good results in the reproducibility test. During the user accuracy test, larger variance changes were observed between intra- and inter-observer results with the dual beam Doppler flowmeter compared to the 2 used transit time flowmeters when used for single sided vessel access without stabilization device (available from the manufacturer).

CONCLUSION

All 3 tested flowmeters showed an excellent correlation to the true flow in an artificial circuit and the accuracy of the tested devices was within agreement limits. Reproducibility of all devices was good and linear. The new dual beam Doppler flow measurement technique compares favorably to the classic transit time method. Clinical use may depend on operator, location, and condition, thus more studies may be required to ensure uniform results using the currently available blood flow measurement devices.

Quality of Anastomosis in Conventional On-Pump Coronary Artery Bypass Graft Surgery: Influence of the Interrupted Technique Using U-Clips and Correlation with Intraoperative Graft Flow Patterns

BACKGROUND

The interrupted suture technique in creating graft-coronary artery anastomoses in coronary artery bypass graft (CABG) surgery is hypothesized to be superior to the standard continuous technique. However, because of the increased time and knot tying involved with the interrupted technique, the continuous suture became standard. In 2000, the U-clip (a self-closing metal clip) was introduced to help in creating an interrupted anastomosis, although data regarding its clinical use are still somewhat limited. Intraop-erative transit-time flow measurement (TTFM) of blood flow through an anastomosis is frequently used to assess quality of anastomosis creation; mean flow and pulsatile index (PI) are analyzed. PI should typically be between 1 and 5; higher values are associated with errors of anastomosis creation. The current study analyzes the difference in TTFM between U-clips and standard suture in CABG surgery.

METHODS

The study population consists of 30 prospectively enrolled patients undergoing first-time on-pump conventional CABG surgery at St. Anthony Medical Center who were randomized to have their anastomosis created with either U-clips or suture. TTFM were recorded for left internal mammary artery to left anterior descending artery (LIMA-LAD) anastomoses.

RESULTS

Of the 30 subjects enrolled (10 women), 12 operations were done with U-clips and 18 with suture. Body mass index (BMI) in the 2 groups was similar. In terms of mean flow, there was no difference between the 2 groups (29.8 +/- 18.4 mL/min for U-clips versus 26.6 +/- 11.0 mL/min for suture, P = .57). In terms of PI, again no difference was found (3.1 +/- 1.3 for U-clips versus 2.5 +/- 0.8 for suture, P = .12).

CONCLUSIONS

The findings of this study suggest that U-clips are comparable to the standard suture for LIMA-LAD anastomoses in conventional on-pump CABG surgery in terms of intraoperative assessment of graft flow.

Endothelial injury and acquired aspirin resistance as promoters of regional thrombin formation and early vein graft failure after coronary artery bypass grafting

OBJECTIVE

The predominant mechanism of early graft failure after coronary artery bypass grafting remains in doubt. Aspirin administered in the initial hours after coronary artery bypass grafting improves graft patency, implicating prostanoid synthesis in the pathogenesis. We hypothesized that synergy between endothelial disruption in the venous conduit and aspirin resistance would cause vein graft failure.

METHODS

Aspirin resistance, defined by diagnostic findings on at least two of three separate assays, was serially assessed in 225 patients undergoing off-pump coronary artery bypass grafting. Endothelial cell integrity was determined in surplus segments obtained from 408 vein grafts. The deposition of intraluminal thrombin within the vein was determined by comparing serum F1.2 levels between the coronary sinus and the aorta after grafting. Intraoperative blood flow in the grafts was measured with transit-time technology, and patency was assessed with electrocardiographically gated multichannel computed tomographic coronary angiography on day 5. Aspirin was the sole antithrombotic agent used during the study.

RESULTS

Thrombosed grafts (16/408) showed more endothelial cell loss at the time of grafting than did those grafts that remained patent (10.8% +/- 21.5% vs 51.4% +/- 39.1% integrity, P < .01). Aspirin resistance occurred in 67 patients (30%). Graft thrombosis was associated with aspirin resistance (P < .04) and reduced endothelial integrity (P < .01). These factors coexisted in 14 of 16 grafts that failed and were associated with elevated coronary sinus F1.2 levels.

CONCLUSION

Aspirin resistance and relatively compromised venous endothelial cell integrity together marked patients whose vein grafts failed within days after off-pump coronary artery bypass grafting. These observations form a basis for identifying patients at risk and developing approaches to prevent vein injury or to selectively intervene in high-risk circumstances.

Transit-time flow measurement is essential in coronary artery bypass grafting

BACKGROUND

Patent bypass grafts are fundamental to successful coronary artery bypass grafting. Intraoperative flow measurement through newly constructed grafts is a test of patency. We studied the use of transit-time flow measurement to determine its ability to detect technical errors in grafts, to measure the mean flow norms for Asian patients, and to compare arterial and vein grafts.

METHODS

From January 1, 2001, to June 30, 2002, 116 patients underwent isolated primary coronary artery bypass grafting. Sixty-seven patients underwent conventional coronary artery bypass grafting and 49 patients underwent off-pump coronary artery bypass grafting. There were 125 arterial and 197 vein grafts. Transit-time flow measurement was carried out on all completed grafts. Graft patency was assessed using flow curves, mean flow, and pulsatility index. Average of mean flows was calculated to determine mean flow norms. Arterial and vein grafts were compared by statistical analysis between the variables mean flow and pulsatility index.

RESULTS

In 6 patients with seven grafts, intraoperative graft assessment detected technical errors, which were corrected. Average mean flow was 37.4 +/- 23.5 mL/min for left anterior descending coronary artery-to-left internal mammary artery grafts, and values ranging from 21.2 to 36.0 mL/min for the rest. There were no statistically significant differences in mean flow or pulsatility index between arterial and vein grafts.

CONCLUSIONS

Transit-time flow measurement enables technical problems to be diagnosed accurately, allowing prompt revision of grafts. It should be mandatory in coronary artery bypass grafting to improve surgical outcomes.

Perioperative Patency of Coronary Artery Bypass Grafting is Not Influenced by Off-Pump Technique

BACKGROUND

Some concerns have been raised about technical accuracy and quality of distal anastomoses in off-pump myocardial revascularization (OPCAB), which could affect graft patency.

METHODS

Transit-time flowmetric results and clinical, enzymatic, and echocardiographic findings from 201 consecutive isolated on-pump coronary artery bypass graft cases (cardiopulmonary bypass coronary artery bypass grafting; group A) were compared with 96 consecutive OPCAB (group B) cases performed at our institution between January 2003 and December 2004. Maximum, mean, minimum flow, and pulsatility index were compared, stratifying the two groups according to graft type and coronaries revascularized. Graft flow reserve was evaluated in patients undergoing preoperative intraaortic balloon pump during baseline conditions and at a 1 to 1 ratio of intraaortic balloon pump augmentation.

RESULTS

No differences were recorded between the two groups in hospital mortality, perioperative myocardial infarction, postoperative enzymatic leakage, echocardiographic recovery, or hospital stay (p = not significant). Off-pump coronary artery bypass and cardiopulmonary bypass coronary artery bypass grafting demonstrated similar intraoperative maximum (75.8 +/- 10.4 mL/min vs 82.3 +/- 15.8; p = 0.190), mean (50.1 +/- 13.3 vs 46.3 +/- 7.7; p = 0.420), minimum flow (12.7 +/- 5.3 vs 11.9 +/- 5.4; p = 0.811), and pulsatility index (2.9 +/- 0.2 vs 2.6 +/- 0.8; p = 0.360). After stratifying the population according to graft type, no differences were detected between the two groups in transit-time flowmetric results of left internal mammary artery, radial artery, and single and sequential saphenous vein grafts. A one to one ratio of intraaortic balloon pump augmentation did not result in any difference in graft flow reserve when left internal mammary artery (p = 0.699), radial artery (p = 0.066), and saphenous vein graft anastomoses (p = 0.772) were considered.

CONCLUSIONS

Off-pump coronary artery bypass grafting and cardiopulmonary bypass coronary artery bypass grafting demonstrated similar clinical, biochemical, and transit-time flowmetric results, as well as comparable graft flow reserve. These data exclude a lower anastomotic quality in off-pump coronary artery bypass grafting.

Intraoperative Transit Time Flow Measurement: Off-Pump Versus On-Pump Coronary Artery Bypass

BACKGROUND

Off-pump coronary artery bypass grafting (OPCAB) has attracted increasing attention. Performing the anastomosis off-pump is technically more demanding. The objective of the study is to assess the quality of anastomosis in OPCAB in comparison with conventional on-pump coronary artery bypass grafting using the transit time flow measurement.

METHODS

Four hundred forty-five patients operated on using OPCAB technique were included in the study. For each patient in this group a similar patient from the on-pump coronary artery bypass grafting population was selected according to the number of grafts, bypass material, and target coronary arteries. The mean flow and the pulsatile index were measured in every bypass graft in both groups.

RESULTS

The average pulsatile index in OPCAB was 2.09 +/- 1.03 (mean flow, 39 +/- 22.63 mL/min), whereas with on-pump coronary artery bypass grafting it was 1.9 +/- 0.98 (mean flow, 44.19 +/- 23.58 mL/min); p = 0.005. Subgroup analysis showed significantly lower mean flows and higher pulsatile index with OPCAB in grafts to the obtuse marginal, diagonal, and right coronary artery, but not to the left anterior descending territory.

CONCLUSIONS

The quality of the anastomosis performed using the OPCAB technique might be jeopardized by less accessibility as in the case of lateral and posterior wall coronary arteries. Techniques to optimize the accessibility of the coronary artery like combining sling support with cup stabilizers, together with systematic training, should be strongly considered in OPCAB. Whenever there is good accessibility of the coronary artery as in the case of the left anterior descending, the anastomosis performed under OPCAB has a quality as good as that performed using the conventional technique.

Prediction of Graft Flow Impairment by Intraoperative Transit Time Flow Measurement in Off-Pump Coronary Artery Bypass Using Arterial Grafts

BACKGROUND

We assessed the validity of intraoperative transit time flow measurement (TTFM) in predicting graft flow abnormalities.

METHODS

Intraoperative graft flow measurement using TTFM and early postoperative coronary angiography was performed in 58 patients who underwent total arterial off-pump coronary artery bypass. Five variables (flow pattern, mean flow, pulsatility index, insufficiency ratio, and fast Fourier transformation ratio) were measured and compared between 103 normal and 14 abnormal (occluded or competitive) grafts.

RESULTS

The grafts anastomosed to the right coronary territories showed significantly less diastolic dominant pattern, lower mean flow and fast Fourier transformation ratio, and higher pulsatility index than grafts to the left coronary artery territories (p < 0.05). None of the abnormal grafts showed a diastolic dominant flow pattern. The abnormal grafts demonstrated significantly lower mean flow and fast Fourier transformation ratio and higher pulsatility index and insufficiency ratio than normal grafts (p < 0.05). When our criteria for detection of abnormal graft flow, [(1) systolic dominant or balanced pattern of the flow curve in the left coronary territories, systolic dominant pattern of the flow curve in the right coronary territories; (2) mean flow < 15 mL/min; (3) pulsatility index > 3 in the left coronary territories and > 5 in the right coronary territories; and (4) insufficiency ratio > 2%] were applied, the sensitivity and specificity of TTFM to detect the graft flow abnormality were 96.2% and 76.9%, respectively.

CONCLUSIONS

Our data suggest that TTFM is a reliable intraoperative tool to predict graft flow impairment.

A comparison of transit-time flowmetry and intraoperative fluorescence imaging for assessing coronary artery bypass graft patency

BACKGROUND

Intraoperative graft patency assessment during coronary artery bypass grafting enables detection and immediate correction of graft failure. Currently transit-time flowmetry is used to assess graft patency on the basis of mean graft flow and derived values, such as the pulsatility index. Intraoperative fluorescence imaging, based on the fluorescence of indocyanine green dye, provides direct visual images to confirm graft patency.

METHODS

We performed a prospective observational study to assess intraoperative graft patency in patients undergoing coronary artery bypass grafting, by using an intraoperative fluorescence imaging system (SPY) and transit-time flowmetry (BF 2004). Poor flow with the intraoperative fluorescence imaging system was defined if there was an absence of fluorescence or if it did not appear within 15 seconds in the graft. A persistent mean graft flow value less than 5 mL/min and a pulsatility index greater than 5 with transit-time flowmetry were considered unacceptable and prompted graft revision.

RESULTS

We assessed the intraoperative patency of 266 grafts in 100 coronary artery bypass grafting patients. Intraoperative fluorescence imaging and transit-time flowmetry confirmed adequate flow in 241 (91%) grafts in 75 patients (75%). Transient poor flow was detected with both intraoperative fluorescence imaging and transit-time flowmetry in 7 (2.6%) grafts in 7 (7%) patients. This subsequently proved to be adequate on repeat testing and hence did not necessitate graft revision. Both intraoperative fluorescence imaging and transit-time flowmetry confirmed persistent poor flow in 8 (3%) grafts in 8 (8%) patients that necessitated graft revision. However, in a further 10 (3.8%) grafts in 10 (10%) patients, transit-time flowmetry indicated persistently poor flows on the basis of mean graft flow and pulsatility index values, whereas the intraoperative fluorescence imaging system demonstrated satisfactory flow. These grafts were not revised.

CONCLUSIONS

In most patients, both intraoperative fluorescence imaging and transit-time flowmetry are useful to confirm intraoperative graft patency. However, in a small proportion of patients (10%), graft patency assessment with transit-time flowmetry alone might prompt unnecessary graft revision.

Detection of construction errors in ex vivo coronary artery anastomoses by 13-MHz epicardial ultrasonography

OBJECTIVE

Intraoperative detection of suboptimal coronary anastomoses allows revision before chest closure. We evaluated an epicardial 13-MHz ultrasound minitransducer as a means to detect three different coronary anastomosis construction errors.

METHODS

In total, 120 internal thoracic artery-to-coronary artery anastomoses were constructed correctly (n = 60) or incorrectly (n = 60) with one technical error: suture crossover, purse-string or deep toe stitch (n = 20 each). Anastomoses were performed on ex vivo pressure-perfused porcine (96 anastomoses) and human hearts (24 anastomoses). Two blinded observers scanned and scored the anastomoses with epicardial ultrasonography. In 24 human and 24 porcine anastomoses, angiograms were made of 24 correct and 24 incorrect anastomoses and scored by two other blinded observers. Angioscopy and cast injection served as a reference.

RESULTS

Overall, 119 of 120 anastomoses were accurately scored as correct or incorrect within a median of 67 seconds (8-381 seconds) by both observers (sensitivity 0.98, specificity 1.00, kappa 1.00 (1.00, 1.00, and 1.00 in angiography subset, respectively). One deep toe stitch that induced outflow corner stenosis was spotted by both observers but regarded as insignificant and thus inaccurately scored as correct. In 5 anastomoses, unintended irregularities were detected. By angiography, anastomoses were accurately scored with a sensitivity of 0.75 and a specificity of 0.81 ( P < .001 vs ultrasonography) and kappa of 0.54. Angioscopy and cast confirmed ultrasonographic findings and did not reveal irregularities other than detected by ultrasonography.

CONCLUSION

Ex vivo epicardial 13-MHz ultrasonography allowed rapid and accurate evaluation of coronary anastomoses and detected technical construction errors with higher sensitivity and specificity than angiography.

Do Coronary Bypass Graft Flows Differ Between On-Pump and Off-Pump Operations?

BACKGROUND

The aim of this study is to compare hemodynamic factors in coronary bypass grafts on-pump and off-pump.

METHODS

Two propensity score-matched groups of 89 patients each including 408 dual beam Doppler flow measurements were compared. The study included only patent and single terminolateral bypass grafts.

RESULTS

Flow was 64.9 +/- 37.3 mL/min in the on-pump group versus 58.6 +/- 35.0 mL/min in the off-pump group (p = 0.063); velocity was 23.8 +/- 10.5 versus 20.5 +/- 10.4 cm/s (p = 0.004); resistance measured as mm Hg/(mL/min(-1)) was 1.50 +/- 1.09 versus 1.76 +/- 1.14 (p = 0.020); pulsatility index was 1.98 +/- 1.52 versus 2.44 +/- 1.62 (p = 0.004). The hematocrit was 23.5 +/- 3.8% in the on-pump and 32.9 +/- 4.1% in the off-pump groups (p < 0 0.001). Multivariate analysis showed that hematocrit was the most significant factor influencing flow (p < 0.001) and velocity (p < 0.001), along with resistance (p = 0.004) and pulsatility index (p < 0.001). In a subset of 50 hemodynamic measurements made on left internal thoracic arteries implanted onto left anterior descending arteries and matched for hematocrit, there were no differences between on-pump and off-pump groups regarding flow, velocity, resistance, or pulsatility index.

CONCLUSIONS

Off-pump compared with on-pump bypass surgery is associated with lower velocity and higher resistance in the grafts, mainly caused by changes in hematocrit and viscosity related to hemodilution.

Endoscopic lesser saphenous vein harvesting for coronary artery bypass grafting: first reported case

Endoscopic vessel harvesting has become a widely used modality for harvesting venous and arterial conduits for coronary artery bypass grafting. Specifically, it has been used to harvest the greater saphenous vein, internal thoracic artery, and the radial artery. A case of endoscopic lesser saphenous vein harvesting for coronary artery bypass grafting is reported.

Flow in Coronary Bypass Conduits On-Pump and Off-Pump

BACKGROUND

The purpose of the study was to measure the blood flow in coronary artery bypass grafting conduits on-pump and off-pump and to estimate the total conduit flow.

METHODS

In a 3.5-year period, 120 patients having coronary artery bypass grafting on-pump and 97 patients having coronary artery bypass grafting off-pump with the left internal mammary artery anastomosed to the left anterior descending artery and saphenous vein grafts to the remaining diseased coronary arteries were included in the study. Flow in the bypass conduits was measured with the transit-time method.

RESULTS

In men the left internal mammary artery flow (mean +/- standard error of the mean) was 33.7 +/- 2.0 mL/min on-pump and 34.4 +/- 2.9 off-pump (p > 0.05). In women the left internal mammary artery flow was 29.4 +/- 3.0 mL/min on-pump and 22.8 +/- 1.9 mL/min off-pump (p > 0.05). In men the vein graft flow per anastomosis was 30.4 +/- 1.3 mL/min on-pump and 37.8 +/- 5.4 mL/min off-pump (p > 0.05). In women the vein graft flow per anastomosis was 28.0 +/- 2.9 mL/min on-pump and 23.2 +/- 2.9 mL/min off-pump (p > 0.05). Consistently in women, the mean conduit flows were numerically lower than in men. In patients undergoing coronary artery bypass grafting on-pump the total conduit flows (left internal mammary artery plus vein grafts) were 131.4 +/- 2.5 mL/min in men and 108.4 +/- 3.2 mL/min in women.

CONCLUSIONS

There were no major differences in conduit flow on-pump versus off-pump. Conventional coronary artery bypass grafting on-pump may restore up to approximately half of the normal resting coronary artery blood flow (250 mL/min).

Digital tools to facilitate intraoperative coronary artery bypass graft patency assessment

Intraoperative graft failure is an important cause of cardiac mortality and morbidity. Hence, verification of graft patency should be one of the most important aspects of coronary artery bypass grafting. Although several techniques have been advocated to assess intraoperative graft patency, there is no unanimously accepted method. Intraoperative fluorescence imaging is a novel technique based on the fluorescence of indocyanine green dye, which provides real-time visual images of graft flow in the operating room. Transit-time flowmetry is based on the ultrasound principle and provides mean graft flow and derived values such as pulsatility index. This article describes the usefulness and limitations of various techniques in general and summarizes the current knowledge with the use of these two techniques in the setting of intraoperative coronary artery bypass graft patency assessment.

Does off-pump total arterial grafting increase the incidence of intraoperative graft failure?

BACKGROUND

Early graft failure is a common cause of cardiac mortality and morbidity after coronary artery bypass grafting, but there is little information on its natural incidence. Furthermore, there is particular concern about graft patency in off-pump coronary artery bypass grafting and total arterial grafting.

METHODS

We performed a prospective observational study to assess intraoperative graft patency in patients undergoing off-pump and on-pump coronary artery bypass grafting, who also underwent total arterial grafting. We used an intraoperative imaging system, SPY (Novadaq Technologies Inc), based on the fluorescent properties of indocyanine green dye.

RESULTS

We assessed the intraoperative graft patency of 533 conduits in 200 patients. The mean number of grafts was 2.7 per patient. Of these patients, 155 (78%) had off-pump coronary artery bypass grafting, and 45 (22%) had on-pump coronary artery bypass grafting. Overall, 161 (80%) had total arterial grafting, with composite arterial grafting performed in 120 (60%) patients. Fluorescence, confirming graft patency, was observed in all but 8 (1.5%) conduits in 8 (4%) patients, necessitating graft revision. Six (3.9%) and 2 (4.4%) of these patients, respectively, had off-pump coronary artery bypass grafting and on-pump coronary artery bypass grafting.

CONCLUSION

Intraoperative fluorescence imaging demonstrated a low (1.5%) but well-defined incidence of intraoperative graft failure, which affects around 4% of patients. This emphasizes the need for routine assessment of graft patency. Intraoperative fluorescence imaging permits detection and revision of failed grafts in the operating room. We found no difference in the incidence of failed grafts when comparing on-pump and off-pump total arterial grafting.

CARDIOMED CORONARY FLOW METER FOR PREVENTION OF EARLY OCCLUSION IN AORTOCORONARY BYPASS GRAFTING

INTRODUCTION

The number of patients undergoing technically demanding off-pump myocardial revascularization is increasing, these days. Some researchers question the quality of the aortocoronary bypasses done on the beating heart and consequently their good patency.

MATERIAL AND METHODS

50 consecutive patients underwent off pump coronary surgery using sequential bypass technique, at our department. The quality of constructed grafts was evaluated using the CardioMed Trace System (CM4008, Medi-Stim As, Oslo, Norway) (TTFM).

RESULTS

All sequential bypasses showed good per-operative quality with a mean fl ow of 69.4 ml/min.

CONCLUSION

TTFM seems to be an effective tool for the per-operative aortocoronary bypass patency verification and should help to prevent early graft occlusion.

ABBREVIATIONS

TTFM transit time flow meter.

Transit time flow measurement in on-pump and off-pump coronary artery surgery

OBJECTIVE

Transit time flow measurement is frequently used during coronary artery bypass with and without cardiopulmonary bypass to detect graft dysfunction resulting from technical errors.

METHODS

Intraoperative transit time flow measurement measurements of 896 patients requiring surgery for double- or triple-vessel disease were reviewed retrospectively. Six-hundred and ninety-five patients were operated on-pump (Group A: coronary artery bypass with cardiopulmonary bypass), and 201 patients off-pump (Group B: coronary artery bypass without cardiopulmonary bypass). Transit time flow measurement measurements were analyzed for mean flow (mL/min). In total, measurements of 2247 grafts were analyzed.

RESULTS

Transit time flow measurement flows were lower in coronary artery bypass without cardiopulmonary bypass patients (left internal thoracic artery to left anterior descending artery: Group A, 37 [31, 40] mL/min vs Group B, 24 [20, 26] mL/min; saphenous vein graft to left anterior descending artery: Group A, 46.5 [40, 56] mL/min vs Group B, 21 [14, 57] mL/min. Troponin I release was reduced in the coronary artery bypass without cardiopulmonary bypass patients, with median values of 7.8 [7.0, 8.3] microg/L in Group A and 1.2 [0.9, 2.3] microg/L in Group B.

CONCLUSION

Evaluation of transit time flow measurement is valuable in determining coronary graft patency after coronary artery bypass with cardiopulmonary bypass and coronary artery bypass without cardiopulmonary bypass. Decreased troponin I release suggests a myocardial benefit of coronary artery bypass without cardiopulmonary bypass compared to coronary artery bypass with cardiopulmonary bypass, although the intraoperative transit time flow measurement flow measurements are markedly lower.

Anesthesia for off-pump coronary artery bypass grafting

Off-pump coronary artery bypass presents special challenges for the anesthesiologist and surgeon, who must work closely together to provide optimal care. Displacement and immobilization of the heart for exposure of the coronary arteries, as well as occlusion of these vessels, can result in periods of significant hemodynamic instability. Appropriate preparation, guided therapy, and technical maneuvers can lessen such adverse hemodynamic impact. It is important for anesthesiologists to be aware of the special problems associated with this surgery, as well as the different therapies and maneuvers that can be useful in providing the best possible care. As surgeons develop greater expertise and better devices for the management of these patients, the number of coronary revascularizations without CPB is likely to increase.

Intraoperative color Doppler ultrasound assessment of LIMA-to-LAD anastomoses in off-pump coronary artery bypass grafting

BACKGROUND

Although techniques for off-pump coronary artery bypass grafting (CABG) are continually being refined, angiographic follow-up studies have indicated a higher rate of anastomoses-related stenoses than expected after traditional on-pump CABG. This study was performed to evaluate the use of intraoperative epicardial color Doppler ultrasound to quality-assess left internal mammary artery (LIMA) to left anterior descending coronary artery (LAD) anastomoses performed on the beating heart.

METHODS

Twenty-four LIMA-to-LAD anastomoses were evaluated with real-time epicardial ultrasound imaging using an ultrasound transducer positioned between the paddles of the stabilizer during off-pump procedures. The length of the anastomosis (D(A)), diameters of LIMA (D(M)), LAD at the toe of the anastomosis (D1), and 5 mm distally to the anastomosis (D2) were measured, and the ratios between these variables were calculated. The flow velocity through the anastomoses was visualized by color Doppler coding, and flow was assessed with transit-time flowmetry.

RESULTS

The epicardial color Doppler ultrasound allowed accurate assessment of the anastomoses. Twenty-three (96%) of the primary anastomoses were confirmed as patent. Mean ratios of D1/D2, D(A)/D2, and D(M)/D2 were 0.89 +/- 0.13, 3.01 +/- 1.04 and 1.32 +/- 0.32, respectively. One anastomosis had a stenosis more than 50% detected by color Doppler ultrasound. After surgical revision, transit-time flow increased from 22 to 40 ml/min.

CONCLUSIONS

Intraoperative color Doppler ultrasound allowed adequate imaging for quality assessment of LIMA-to-LAD anastomoses performed on the beating heart. One anastomosis was revised due to a technical error detected by epicardial color Doppler imaging. Epicardial ultrasound scanning is a valuable tool for intraoperative assessment of LIMA-to-LAD anastomoses during off-pump coronary surgery.

The coronary artery bypass conduit: II. Assessment of the quality of the distal anastomosis

The outcome of coronary artery bypass grafting procedures is highly dependent on the technical adequacy of the distal anastomosis. Various methodologies, including flow measurement and imaging techniques, have been used by the cardiothoracic surgeon to assess the adequacy of the distal anastomosis. The limitations of these techniques outweigh their advantages and limit their widespread clinical applicability. Recent improvements in the technique for online measurement of regional myocardial pH provide a promising new metabolic approach to assessing the adequacy of the distal anastomosis in cardiac surgery.

Comparison of milrinone versus nitroglycerin, alone and in combination, on grafted internal mammary artery flow after cardiopulmonary bypass: effects of alpha-adrenergic stimulation

OBJECTIVES

To compare changes in blood flow in a grafted internal mammary artery (IMA) after cardiopulmonary bypass (CPB) in response to the administration of milrinone or nitroglycerin and to establish the effects of alpha-adrenergic stimulation.

DESIGN

Randomized study.

SETTING

A university medical center hospital and a Veterans Affairs Medical Center hospital.

PARTICIPANTS

Thirty consenting adults scheduled for elective coronary artery bypass graft surgery.

INTERVENTIONS

Patients were randomized to receive a 2 microg/kg/min infusion of nitroglycerin (n = 10), a loading dose of 50 microg/kg of milrinone (n = 10), or both drugs combined (n = 10) shortly after CPB. Intravenous phenylephrine was administered to increase mean arterial pressure by 20%. IMA flow was measured with a calibrated laser Doppler flow probe. Hemodynamic and flow measurements were obtained before and after every intervention.

MEASUREMENTS AND MAIN RESULTS

Nitroglycerin and milrinone increased mean IMA flow, but the increase was greater with milrinone. Both drugs combined were superior to nitroglycerin alone but not to milrinone. The addition of phenylephrine to nitroglycerin increased IMA flow in 6 of 10 patients. IMA flow decreased in 4 of 10 patients, however. Phenylephrine significantly increased IMA blood flow in patients receiving milrinone or in those given both drugs combined.

CONCLUSION

After CPB, milrinone and nitroglycerin vasodilate the IMA; however, the combination of both drugs was not superior to milrinone alone. When using alpha-adrenergic stimulation, milrinone proved superior to nitroglycerin in preserving IMA flow.

Intraoperative assessment of coronary artery bypass graft: transit-time flowmetry versus angiography

BACKGROUND

Transit-time flowmetry has been used to assess graft status intraoperatively. This study examines the validity of this method by comparing its results with the findings of simultaneously performed graft angiography.

METHODS

The left internal thoracic artery (LITA) anastomosed to the left anterior descending artery (LAD) was assessed intraoperatively with both transit-time flowmetry and graft angiography in 30 patients. The patients were stratified into two groups based on intraoperative angiographic findings. In 18 patients (group A), the LITA and the LAD were well filled with contrast medium and the anastomosis was widely patent. In the other 12 patients (group B), spastic LITA or LAD was observed. Postoperative angiography was also performed before discharge from the hospital.

RESULTS

The mean graft flow was 44.0 +/- 25.4 mL/min in group A and 23.4 +/- 10.0 mL/min in group B (p = 0.0129). Diastolic-dominant flow pattern was observed in both groups, and the ratio of peak diastolic flow to peak systolic flow and the percent diastolic time-flow integral were not statistically different between the groups. The pulsatility index was almost the same between the two groups and was acceptable in both. Postoperative angiography revealed that all grafts were patent without spasm or anastomotic stenosis.

CONCLUSIONS

LITA graft status is satisfactory when high graft flow with diastolic dominance is obtained. When there is vasospasm but no anastomotic problems, decreased graft flow with an acceptable pulsatility index and diastolic augmentation is observed.

Myocardial revascularization of the beating heart in high-risk patients

OBJECTIVE

Myocardial revascularization without cardiopulmonary bypass (CPB) has been proposed as an alternative technique in patients at high risk for conventional coronary artery bypass grafting (CABG). The purpose of this article is to evaluate the potential benefit of such an approach.

METHODS

We retrospectively evaluated the perioperative results of off-pump CABG (OPCAB) performed from January 1995 to December 1999. Patients were divided into three groups on the basis of their preoperative risk factors: age greater than 80 years, reoperative CABG, and left ventricular ejection fraction percentage (LVEF%) less than 40%. The three subgroups were compared with patients operated on-CPB (ONCAB) during the same period of time. A total of 172 octogenarians had ONCAB versus 97 OPCAB, 307 reoperations were ONCAB versus 274 OPCAB, and 514 patients with LVEF% less than 40% were operated ONCAB versus 220 OPCAB.

RESULTS

Preoperative comorbidities were homogeneously distributed in the OPCAB and ONCAB groups. More extensive coronary artery disease was found in the ONCAB groups. A trend for a lower number of perioperative complications was reported in the OPCAB groups. Freedom from overall complications was significantly higher (p < 0.005) in the OPCAB group. Actual mortality rates in the OPCAB and ONCAB groups were comparable (p = NS).

CONCLUSIONS

CABG can be performed safely without CPB in patients with a high preoperative risk profile. Freedom from perioperative complications is markedly higher when the OPCAB approach is utilized.

Hemodynamic effects of elevation and stabilization of the heart during off-pump coronary surgery

BACKGROUND

Coronary artery bypass grafting (CABG) surgery is now being performed without the use of cardiopulmonary bypass (CPB). To achieve complete myocardial revascularization off-CPB, a technique has been developed to expose target coronary arteries while hemodynamics are maintained.

METHODS

Complete myocardial revascularization was performed in 18 consecutive patients. Exposure of target coronary arteries was achieved by a "single-suture" technique, placed in the oblique sinus of the pericardium. Traction on the suture elevates and rotates the heart, thereby exposing all target coronary arteries. Cardiac index (CI) and intracardiac pressures were measured with a Swan-Ganz catheter during the different phases of the operation.

RESULTS

All patients were successfully operated on without CPB. There were no postoperative complications or deaths. There were no major hemodynamic changes during the different stages of the operation; in other words, CI was unchanged during elevation of the heart and snaring of the main coronary branches. Pulmonary artery wedge pressure (PAWP) increased markedly during occlusion and stabilization of the circumflex coronary artery (p < 0.05). A marked increase in CI and cardiac output (CO) from baseline values was also recorded before chest closure (p < 0.05).

CONCLUSION

Complete myocardial revascularization can be achieved safely without CPB. The single-suture technique allows for exposure of all target coronary arteries without hemodynamic compromise.

Preoperative angiography and intraoperative transit time flow measurement to detect coronary graft patency in reoperations: an integrated approach--a case report

Coronary angiography is the gold standard for preoperative diagnosis of coronary artery disease. In reoperative coronary artery surgery the physiologic significance of suspect lesions by angiography can be confirmed by direct intraoperative measurement of blood flow in the old grafts; such interpretation can prevent unnecessary graft revisions.

Role of coronary graft flow measurement during reoperations for early graft failure after off-pump coronary revascularization

Doppler-based techniques of coronary graft flow measurement are frequently used, especially during coronary artery bypass grafting (CABG) without cardiopulmonary bypass (CPB), to exclude graft dysfunction resulting from technical errors. Nevertheless, early graft failure in the immediate postoperative period continues to affect a small percentage of patients who may require emergent reoperation as a result of severe hemodynamic deterioration. In this setting, in which coronary angiography is infrequently an option, expeditious intraoperative assessment of previously constructed coronary grafts may be performed by using the Doppler-based technique Transit Time Flow Measurement (TTFM). As a result, the hemodynamic values obtained during reoperations may guide the operative strategy. In this study we report on eight patients who underwent "off-pump" CABG and necessitated early reintervention as a result of presumed graft dysfunction. In these patients, graft dysfunction was confirmed or excluded by using intraoperatively the TTFM technique, comparing newly obtained flow hemodynamic variables with those recorded as a baseline during primary operations.