Intraoperative coronary graft assessment

Flow-Based Coronary Artery Bypass Graft Patency Metrics: Uncertainty Quantification Simulations to Guide Development

PURPOSE

Over time, transit time flow measurement (TTFM) has proven itself as a simple and effective tool for intra-operative evaluation of coronary artery bypass grafts (CABGs). However, metrics used to screen for possible technical error show considerable spread, preventing the definition of sharp cut-off values to distinguish between patent, questionable, and failed grafts. The simulation study presented in this paper aims to quantify this uncertainty for commonly used patency metrics, and to identify the most important physiological parameters influencing it.

METHODS

Uncertainty quantification was performed on a realistic multiscale numerical model of the coronary circulation, guided by Morris screening sensitivity analysis of a simpler, lumped-parameter model. Simulation results were qualitatively verified against results of a recent clinical study.

RESULTS

Correspondence with clinical study data is reasonable, especially considering that the model was not fitted in any way. Stenosis severity was confirmed to be an influential parameter. However, also cardiac period and graft diameter were observed to be important, particularly for mean flow rate and pulsatility index.

CONCLUSION

Metrics quantifying the flow waveform's diastolic dominance show the highest sensitivity to graft stenosis, and seem to be least affected by autoregulation. Among these, the novel diastolic resistance index shows the strongest sensitivity to stenosis severity.

SIGNIFICANCE

The approach used in this study is expected to benefit the development of improved patency metrics, by allowing medical engineers to include sensitivity and uncertainty in assessing, in-silico, the potential of novel metrics, thus enabling them to provide better guidance in the design of clinical studies.

A laboratory feasibility study using a computer algorithm for anastomosis segmentation of epicardial ultrasonography images from distal coronary artery bypass anastomoses

BACKGROUND

The outcome of coronary artery bypass grafting (CABG) depends on several factors, including the quality of the distal anastomoses to the coronary arteries. Early graft failure may be caused by, e.g., technical suture failures, and such failures may be detected using intraoperative quality assessment. High-intensity epicardial ultrasonography (ECUS) allows anatomical visualization of the anastomoses during surgery, but currently, the images must be assessed manually. Here, we aim to describe an automatic quality assessment of distal coronary anastomoses using in-house software for vessel area and diameter extraction.

METHODS

A postoperative, laboratory, investigational feasibility study comparing computer readings of longitudinal and transverse ultrasonographic images of distal coronary artery anastomoses with manual readings was performed, including ECUS images from 30 patients undergoing elective, isolated on-pump CABG. Vessel and anastomosis segmentation performance metrics from images obtained intraoperatively were compared to assess agreement between the manual and automatic segmentation methods. Scatter plots, the Dice coefficient and correlation analyses were used as measures of similarity between the two readings. p < 0.05 was considered significant.

RESULTS

The number of dimensions of anastomotic vessel structures that are relevant for stenosis quantification and the Dice coefficient were 0.888 between the automatic and manual segmentations. The correlation coefficient between the manual and automatic stenotic rates was 0.674.

CONCLUSIONS

An anastomosis segmentation software for automatic and objective extraction of the anatomical dimensions of relevant distal coronary anastomotic structures from ECUS images obtained during CABG was developed. The framework allows for quantifying stenotic in the anastomotic structures and has the potential to assist surgeons during quality assessment of coronary anastomoses when the described segmentation of vessels and anastomoses is available for real-time epicardial ultrasonography use during surgery.

TRIAL REGISTRATION

The study was registered on September 29, 2016, before enrolment of the first participant (ClinicalTrials.gov ID: NCT02919124).

Intraoperative coronary angiography and fractional flow reserve measurement with dobutamine infusion in supra-arterial myotomy for a myocardial bridge: a case report

Background

A myocardial bridge (MB) is a congenital coronary anomaly, wherein the epicardial coronary artery tunnels through the myocardial band. Treatment is indicated when clinical symptoms occur, and β-blockers are the first choice of treatment. Symptomatic patients refractory to medical therapy are considered for other options, including stent placement, coronary artery bypass grafting, or surgical supra-arterial myotomy. Supra-arterial myotomy is effective; however, the symptoms might persist if myocardial resection is inadequately performed.

Case summary

We encountered a patient experiencing exertional chest pain. Coronary angiography revealed a MB at the mid-left anterior descending artery with systolic compression. The patient's fractional flow reserves (FFRs) were 0.93 at rest and 0.72 with intravenous administration of 50 µg/kg/min dobutamine. The symptoms were refractory to drugs, and supra-arterial myotomy was performed with intraoperative coronary artery angiography, which revealed the milking effect of the residual myocardium; therefore, additional myocardial resection was performed. Postoperative coronary artery angiography showed no systolic compression, and the postoperative FFRs were 0.88 at rest and 0.92 with intravenous administration of dobutamine 50 µg/kg/min.

Discussion

Although surgical supra-arterial myotomy is safe and effective, inadequate myocardial resection might cause symptom recurrence. Intraoperative coronary artery angiography during the surgery can indicate whether additional resection is required. Objective assessment of ischaemia might be useful in cases with a MB, which can cause asymptomatic myocardial ischaemia and sudden cardiac death. FFRs before surgery can help in evaluating the need for surgery and for confirming the therapeutic effect and subsequent treatment.

[Method of optimal hydraulic dilatation of venous conduits for coronary artery bypass grafting]

Hydraulic dilatation is used in everyday cardiac surgical practice for assessment of leak-proofness and prevention of spasm of autovenous shunts. The classical technique envisages manual high-pressure solution injection, which exerts a negative effect on venous conduits and is one of the causes of incompetence of shunts in the postoperative period. Limiting pressure during hydraulic dilatation is necessary to minimize morphological changes and preserve functional viability of venous conduits. The purpose of the present study was to develop and assess efficacy of a standardized methodology of controlled hydraulic dilatation of venous conduits. We worked out an original technique of controlled hydraulic dilatation of venous conduits under perfusion pressure of artificial circulation. This was followed by assessing morphological changes and functional viability of venous segments after controlled hydraulic dilatation as compared with veins after conventional uncontrolled hydraulic dilatation and the control intact veins. Uncontrolled hydraulic dilatation was accompanied by endothelial damage (p<0.05), multiple conduit wall tears (p<0.05) according to the findings of light microscopy, leading to a significant decrease in the functional vitality of the venous conduit (a decreased reaction to hyperpotassium solution, phenylephrine, acetylcholine and sodium nitroprusside (p<0.05) according to the findings of biophysical examination. Our original technique of controlled hydraulic dilatation of venous conduits under perfusion pressure of artificial circulation made it possible not only to evaluate leak-proofness of the vessel but also to achieve comparable to the control segments parameters of structural integrity of the venous wall and functional viability of the conduit. Thus, using the developed method of controlled hydraulic dilatation makes it possible to minimize morphofunctional alterations in venous conduits, influencing the function of autovenous shunts.

A novel fluorescent cardiac imaging system for preclinical intraoperative angiography

BACKGROUND

Intraoperative coronary angiography can tremendously reduce early coronary bypass graft failures. Fluorescent cardiac imaging provides an advanced method for intraoperative observation and real-time quantitation of blood flow with high resolution.

METHODS

We devised a system comprised of an LED light source, special filters, lenses and a detector for preclinical coronary artery angiography. The optical setup was implemented by using two achromatic doublet lenses, two positive meniscus lenses, a band-pass filter, a pinhole and a CCD sensor. The setup was optimized by Zemax software. Optical design was further challenged to obtain more parallel light beams, less diffusion and higher resolutions to levels as small as arterioles. Ex vivo rat hearts were prepared and coronary arteries were retrogradely perfused by indocyanine green (ICG). Video angiography was employed to assess blood flow and plot time-dependent fluorescence intensity curve (TIC). Quantitation of blood flow was performed by calculating either the gradient of TIC or area under curve. The correlation between blood flow and each calculated parameters was assessed and used to evaluate the quality of flow.

RESULTS

High-resolution images of flow in coronary arteries were obtained as precise as 62 µm vessel diameter, by our custom-made ICG angiography system. The gradient of TIC was 3.4-6.3 s^-1, while the area under curve indicated 712-1282 s values which ultimately gained correlation coefficients of 0.9938 and 0.9951 with relative blood flow, respectively.

CONCLUSION

The present ICG angiography system may facilitate evaluation of blood flow in animal studies of myocardial infarction and coronary artery grafts intraoperatively.

A new way to use transit-time flow measurement for coronary artery bypass grafting

OBJECTIVES

Transit-time flow measurement is a recognized method for graft evaluation in coronary surgery. However, single flow measurement has been associated with a low specificity for detecting graft dysfunction. The goal of this study was to assess the value of transit-time flow measurement for assessing in situ internal mammary artery grafts during non-existent native coronary circulation and the relevance of collateral blood flow in target vessels.

METHODS

Between 2014 and 2018, a total of 134 patients undergoing on-pump coronary artery bypass grafting were evaluated using transit-time flow measurement. We analysed 111 single left internal mammary artery and 57 single right internal mammary artery bypasses. Correlations between coronary relevant parameters were calculated using Spearman's ρ coefficient. Risk factors for decreased flow with an arrested heart (FAH) <30 ml/min and an increased pulsatility index (PI) >3.0 as well as flow reduction >30% were calculated.

RESULTS

FAH correlated with the diameter of the target vessel (Spearman's ρ = 0.32; P < 0.001), the amount of blood distribution (Spearman's ρ = 0.34; P < 0.001), the PI (Spearman's ρ = 0.19; P = 0.019) and the degree of stenosis (Spearman's ρ = -0.17; P = 0.042). The percentage of flow change was found to correlate with the PI (Spearman's ρ = -0.47; P < 0.0001), the degree of stenosis (Spearman's ρ = 0.42; P < 0.001), the diameter of the target vessel (Spearman's ρ = -0.22; P = 0.008) and the area of blood distribution (Spearman's ρ = -0.19; P = 0.018). A small blood distribution area was the only risk factor for decreased FAH [odds ratio (OR) 8.43, confidence interval (CI) 95% (3.04-23.41); P < 0.001]. Binary logistic regression identified PI [OR 2.05, CI 95% (1.36-3.10); P = 0.001], FAH [OR 0.98, CI 95% (0.97-0.99); P = 0.005] and degree of stenosis [OR 0.95, CI 95% (0.92-0.99); P = 0.011] as risk factors for decreased flow after cardiopulmonary bypass (<30 ml/min). An increased PI (>3) was mainly influenced by percentage of flow change [OR 0.99, CI 95% (0.98-1.00); P = 0.031].

CONCLUSIONS

FAH and percentage of flow change are related to the dimensions of the target vessel and the degree of stenosis. The addition of flow measurements with the heart arrested provides additional information about the bypass graft, the quality of the anastomosis and the physiology of the coronary circulation.

Improving coronary artery bypass grafting: a systematic review and meta-analysis on the impact of adopting transit-time flow measurement

Despite there being numerous studies of intraoperative graft flow assessment by transit-time flow measurement (TTFM) on outcomes after coronary artery bypass grafting (CABG), the adoption of contemporary TTFM is low. Therefore, on 31 January 2018, a systematic literature search was performed to identify articles that reported (i) the amount of grafts classified as abnormal or which were revised or (ii) an association between TTFM and outcomes during follow-up. Random-effects models were used to create pooled estimates with 95% confidence intervals (CI) of (i) the rate of graft revision per patient, (ii) the rate of graft revision per graft and (iii) the rate of graft revision among grafts deemed abnormal based on TTFM parameters. The search yielded 242 articles, and 66 original articles were included in the systematic review. Of those articles, 35 studies reported on abnormal grafts or graft revisions (8943 patients, 15 673 grafts) and were included in the meta-analysis. In 4.3% of patients (95% CI 3.3–5.7%, I² = 73.9) a revision was required and 2.0% of grafts (95% CI 1.5–2.5%; I²=66.0) were revised. The pooled rate of graft revisions among abnormal grafts was 25.1% (95% CI 15.5–37.9%; I²=80.2). Studies reported sensitivity ranging from 0.250 to 0.457 and the specificity from 0.939 to 0.984. Reported negative predictive values ranged from 0.719 to 0.980 and reported positive predictive values ranged from 0.100 to 0.840. This systematic review and meta-analysis showed that TTFM could improve CABG procedures. However, due to heterogeneous data, drawing uniform conclusions appeared challenging. Future studies should focus on determining the optimal use of TTFM and assessing its diagnostic accuracy.

Patient and haemodynamic factors affecting intraoperative graft flow during coronary artery bypass grafting: an observational pilot study

Transit-time flow measurement (TTFM) is frequently used to evaluate intraoperative quality control during coronary artery bypass grafting (CABG) and has the ability to assess graft failure intraoperatively. However, perioperative factors affecting TTFM during CABG remain poorly understood. Patients who underwent CABG at a single institution between July 2016 and May 2018 were prospectively evaluated. TTFM and blood viscosity were measured haemodynamically, while mean flow (mL/min), pulsatility index, and diastolic filling were recorded. Arterial blood gas was analysed immediately after left internal mammary artery to left descending artery anastomosis and before sternal closure. Factors associated with TTFM were assessed using multiple linear regression analysis. We evaluated 57 of the 62 patients who underwent CABG during the study period, including 49 who underwent off-pump and 8 who underwent on-pump surgeries. Blood viscosity was not significantly associated with TTFM (p > 0.05). However, TTFM was significantly associated with body mass index, systolic blood pressure, and cardiac index (p < 0.05 each). In conclusion, maintaining the SBP in the perioperative period and maintaining the CI with inotropic support or fluid resuscitation can be important in improving blood flow of graft vessels after surgery.

Peroperative epicardial ultrasonography of distal coronary artery bypass graft anastomoses using a stabilizing device. A feasibility study

Background

Widespread use of intraoperative epicardial ultrasonography (ECUS) for quality assessment of coronary artery bypass graft anastomoses during coronary artery bypass grafting (CABG) has not occurred - presumably due to technological and practical challenges including the need to maintain stable and optimal acoustic contact between the ultrasound probe and the target without the risk of distorting the anastomosis. We investigated the feasibility of using a stabilizing device during ultrasound imaging of distal coronary bypass graft anastomoses in patients undergoing on-pump CABG. Imaging was performed in both the longitudinal and transverse planes.

Methods

Single-centre, observational prospective feasibility study among 51 patients undergoing elective, isolated on-pump CABG. Ultrasonography of peripheral coronary bypass anastomoses was performed using a stabilizing device upon which the ultrasound transducer was connected. Transit-time flow measurement (TTFM) was also performed. Descriptive statistical tests were used.

Results

Longitudinal and transverse images from the heel, middle and toe were obtained from 134 of 155 coronary anastomoses (86.5%). After the learning curve (15 patients), all six projections were obtained from 100 of 108 anastomoses scanned (93%). Failure to obtain images were typical due to a sequential curved graft with anastomoses that could not be contained in the straight cavity of the stabilizing device, echo artefacts from a Titanium clip located in the roof of the anastomoses, and challenges in interpreting the images during the learning curve. No complications were associated with the ECUS procedure. The combined ECUS and TTFM resulted in immediate revision of five peripheral anastomoses.

Conclusions

Peroperative use of a stabilizing device during ultrasonography of coronary artery bypass anastomoses in on-pump surgery facilitates imaging and provides surgeons with non-deformed longitudinal and transverse images of all parts of the anastomoses in all coronary territories. Peroperative ECUS in addition to flow measurements has the potential to increase the likelihood of detecting technical errors in constructed anastomoses.

Trial registration

The study was registered on September 29, 2016, ClinicalTrials.gov ID: NCT02919124.

Qualitative angiographic and quantitative myocardial perfusion assessment using fluorescent cardiac imaging during graded coronary artery bypass stenosis

Intraoperative graft assessment in coronary artery bypass (CAB) grafting is important to avoid early graft failure. This study aimed to evaluate the accuracy of fluorescent cardiac imaging (FCI) for intraoperative qualitative angiographic and quantitative myocardial perfusion assessment during graded CAB stenosis compared to coronary angiography (CA). After CAB grafting to the left anterior descending coronary artery, graded distal bypass stenoses were created in ten pigs by 25, 50, 75, and 100% flow reduction assessed by transit-time flow measurement (TTFM). Visual angiographic assessment was performed by FCI and CA during baseline and graded bypass stenoses. Altered myocardial perfusion was assessed by quantitative intraoperative fluorescence intensity (QIFI) derived from FCI and correlated to TTFM. Patent bypass grafts and graft occlusion were visualized successfully by FCI and CA, while discrimination between various graded bypass stenosis was possible in 73.3%. The degree of CAB stenosis was overestimated in 16.7% and underestimated in 10.0% by FCI compared to CA. Graded CAB stenosis reduced regional myocardial perfusion quantified by decreased QIFI value (p < 0.001). Mean QIFI value was 76.8 (95% CI 67.2-86.3) during baseline, 55.6 (95% CI 45.3-65.9) during 25% flow-reduction, 30.6 (95% CI 22.3-39.0) during 50% flow-reduction, 20.3 (95% CI 15.4-25.3) during 75% flow-reduction, and 0 during CAB occlusion (p < 0.001) with a significant correlation to TTFM (r = 0.955; p < 0.0001). Solely visual assessment of CAB quality using FCI is limited as compared to CA. Additional QIFI assessment identified graded CAB stenosis and occlusion with a significant correlation to TTFM.

An Improved Algorithm for Coronary Bypass Anastomosis Segmentation in Epicardial Ultrasound Sequences

Epicardial ultrasound (EUS) can be used for intra-operative quality assessment of coronary artery bypass anastomoses. To quantify the anastomotic quality from EUS images, the area of anastomotic structures has to be extracted from EUS sequences. Currently, this is done manually as no objective methods are available. We used an automatic anastomosis segmentation algorithm to extract the area of anastomotic structures from in vivo EUS sequences obtained from 16 porcine anastomoses. The algorithm consists of four major components: vessel detection, vessel segmentation, segmentation quality control and inter-frame contour alignment. The segmentation accuracy was assessed using m-fold cross-validation based on 830 manual segmentations of the anastomotic structures. A Dice coefficient of 0.879 (±0.073) and an absolute area difference of 16.95% (±17.94) were obtained. The proposed segmentation algorithm has potential to automatically extract the area of anastomotic structures.

Techniques and standards in intraoperative graft verification by transit time flow measurement after coronary artery bypass graft surgery: a critical review

Transit time flow measurement (TTFM) is a quality control tool for intraoperative graft evaluation in coronary artery bypass graft (CABG) surgery. A critical review of the literature available using TTFM in CABG surgery is the focus of this article. The main objectives will be to detail precise parameters for flow evaluation, to show limitations of TTFM and to prove its predictive impact on postoperative graft failure rate. Publications listed in the PubMed database were reviewed, searching for intraoperative graft verification in coronary surgery by TTFM, with postoperative imaging follow-up (FU) modality and with a special focus on publications released after European guidelines from 2010. Nine included publications revealed an overall graft failure rate of ∼12%. Mean graft flow had a positive predictive value in the largest study, and cut-offs, of at least 20 ml/min for internal mammary artery (IMA) grafts, therein partially confirming guidelines, and 30-40 ml/min for saphenous venous grafts (SVGs) were proposed. An explicit correlation between graft flow, patency rate and severity of coronary stenosis, by indicating the fractional flow reserve, was found for IMA grafts. Increased pulsatility index and increased systolic reverse flow probably predict worse outcome and may help identifying competitive flow. Diastolic filling, rarely indicated, could not be confirmed as the predictive marker. No significant correlation of TTFM and graft failure rate for radial and other arterial grafts could be found, partially due to the small number of these types of grafts analysed. Larger target vessels and lower postoperative CK-MB levels may predict better graft patency rates. Low sensitivity for TTFM to reliably detect graft failure is certainly a major issue, as found in randomized analyses. However, methodical limitations and varying threshold values for TTFM render a general consensus difficult. Influence of quantity (vessel territory distribution) and quality (myocardial scar) of the graft perfusion area, on TTFM and FU outcome, was not included by anyone and should be part of future research. TTFM is probably not the tool of choice to detect progressive late graft failure of SVG. Peroperative TTFM values should be correlated with one type of conduit, differentiating between early and late graft failure (by applying a uniform, appropriated definition), to precise and confirm threshold values.

Intraoperative graft assessment during coronary artery bypass surgery

Coronary artery bypass grafting (CABG) is an established revascularization method for treating multivessel coronary artery disease. The goal of CABG is to achieve complete revascularization with a durable, patent graft without reintervention. However, early graft failure, including that associated with technical errors, has been reported. This makes intraoperative verification of graft patency one of the most important ways in which surgeons can reduce the rate of early graft failure. Conventional angiography is considered the gold standard for graft assessment. However, because it is invasive and inconvenient, several alternatives to intraoperative graft assessment have become available that help reduce early graft failure by allowing revision of the anastomosis intraoperatively. The aim of this article is to review the advantages and disadvantages of several intraoperative graft assessment methods for CABG.

Angiography for Management of Perioperative Myocardial Ischemia: Does it Have Any Role?

Objective

Perioperative myocardial ischemia (PMI) is a relatively rare but potentially fatal complication after coronary artery bypass grafting and is due to graft-related problems in a significant proportion of cases. The usual indicators of MI in the postoperative setting are unreliable and therefore have uncertain diagnostic value. Angiography, the criterion standard for preoperative angina, remains underused for evaluation of PMI. The aim of this study was to evaluate the role of angiography in the management of PMI.

Methods

Between January 2011 and September 2012, a total of 2312 isolated primary consecutive coronary artery bypass graft surgeries were performed, of which 2057 (89%) were carried out on the beating heart. Twenty-six (1.12%) of these patients needed perioperative angiography. The patients needing angiography were selected on the basis of a number of clinical, biochemical, and other diagnostic parameters

Results

Twenty-six patients with PMI required angiography, of which 18 (69 %) were found to have graft-related issues. The mean (SD) time between operation and angiography was 24.58 (6.71) hours. Of the 18 patients, 17 (94.44%) required surgical intervention and 1 patient was treated with angioplasty. There were 2 deaths (11.1%) in the group undergoing intervention. Angiographic findings included occluded vein graft (n = 7), narrowing of the left internal mammary artery (n = 3), and kinking or stretching of grafts (n = 8).

Conclusions

Angiography is useful in diagnosing graft-related problems in the perioperative period. In presence of signs of graft compromise, we suggest that having a low threshold for angiographic graft evaluation may be beneficial in a carefully selected subset of patients after coronary artery bypass.

Coronary artery bypass grafting: Part 2--optimizing outcomes and future prospects

Since first introduced in the mid-1960s, coronary artery bypass grafting (CABG) has become the standard of care for patients with coronary artery disease. Surprisingly, the fundamental surgical technique itself did not change much over time. Nevertheless, outcomes after CABG have dramatically improved over the first 50 years. Randomized trials comparing percutaneous coronary intervention (PCI) to CABG have shown converging outcomes for select patient populations, providing more evidence for wider use of PCI. It is increasingly important to focus on the optimization of the short- and long-term outcomes of CABG and to reduce the level of invasiveness of this procedure. This review provides an overview on how new techniques and widespread consideration of evolving strategies have the potential to optimize outcomes after CABG. Such developments include off-pump CABG, clampless/anaortic CABG, minimally invasive CABG with or without extending to hybrid procedures, arterial revascularization, endoscopic vein harvesting, intraprocedural epiaortic scanning, graft flow assessment, and improved secondary prevention measures. In addition, this review represents a framework for future studies by summarizing the areas that need more rigorous clinical (randomized) evaluation.

The Accuracy of Transit Time Flow Measurement in Predicting Graft Patency after Coronary Artery Bypass Grafting

Objective

Transit time flow measurement (TTFM) is a method used to assess intraoperative blood flow after vascular anastomoses. Angiography represents the criterion standard for the assessment of graft patency after coronary artery bypass grafting (CABG). The purpose of this study was to compare flow measurements from TTFM to diagnostic angiography.

Methods

From October 9, 2009, to April 30, 2012, a total of 259 patients underwent robotic-assisted CABG procedures at a single institution. Of these, 160 patients had both TTFM and either intraoperative or postoperative angiography of the left internal mammary artery to the left anterior descending coronary artery graft. Transit time flow measurements were obtained after completion of the anastomosis and after administration of protamine before chest closure. Transit time flow measurement assessment included pulsatility index, diastolic fraction, and flow (milliliters per minute). Angiograms were graded according to the Fitzgibbon criteria. The patients were grouped according to angiographic findings, with perfect grafts defined as FitzGibbon A and problematic grafts defined as either Fitzgibbon B or O.

Results

Overall, there were 152 (95%) of 160 angiographically perfect grafts (FitzGibbon A). Of the eight problematic grafts, five were occluded (Fitzgibbon O) and three had significant flow-limiting lesions (FitzGibbon B). Two patients had intraoperative graft revision after completion angiography, one had redo CABG during the same hospitalization, and five were treated with percutaneous coronary intervention. A significant difference was seen in mean ± SD flow (34.3 ± 16.8 mL/min vs 23.9 ± 12.5 mL/min, P = 0.033) between patent and nonpatent grafts but not in pulsatility index (1.98 ± 0.76 vs 1.65 ± 0.48, P = 0.16) or diastolic fraction (73.5% ± 8.45% vs 70.9% ± 6.15%, P = 0.13).

Conclusions

Although TTFM can be a useful tool for graft assessment after CABG, false negatives can occur. Angiography remains the criterion standard to assess graft patency and quality of the anastomosis after CABG.

Real-time intraoperative visualization of myocardial circulation using augmented reality temperature display

For direct visualization of myocardial ischemia during cardiac surgery, we tested the feasibility of presenting infrared (IR) tissue temperature maps in situ during surgery. A new augmented reality (AR) system, consisting of an IR camera and an integrated projector having identical optical axes, was used, with a high resolution IR camera as control. The hearts of five pigs were exposed and an elastic band placed around the middle of the left anterior descending coronary artery to induce ischemia. A proximally placed ultrasound Doppler probe confirmed reduction of flow. Two periods of complete ischemia and reperfusion were studied in each heart. There was a significant decrease in IR-measured temperature distal to the occlusion, with subsequent return to baseline temperatures after reperfusion (baseline 36.9 ± 0.60 (mean ± SD) versus ischemia 34.1 ± 1.66 versus reperfusion 37.4 ± 0.48; p < 0.001), with no differences occurring in the non-occluded area. The AR presentation was clear and dynamic without delay, visualizing the temperature changes produced by manipulation of the coronary blood flow, and showed concentrically arranged penumbra zones during ischemia. Surface myocardial temperature changes could be assessed quantitatively and visualized in situ during ischemia and subsequent reperfusion. This method shows potential as a rapid and simple way of following myocardial perfusion during cardiac surgery. The dynamics in the penumbra zone could potentially be used for visualizing the effect of therapy on intraoperative ischemia during cardiac surgery.

Semi-automatic vessel tracking and segmentation using epicardial ultrasound in bypass surgery

The purpose of intraoperative quality assessment of coronary artery bypass graft surgery is to confirm graft patency and disclose technical errors to reduce cardiac mortality, morbidity and improve clinical outcome for the patient. Epicardial ultrasound has been suggested as an alternative approach for quality assessment of anastomoses. To make a quantitative assessment of the anastomotic quality using ultrasound images, the vessel border has to be delineated to estimate the area of the vessel lumen. A tracking and segmentation algorithm was developed consisting of an active contour modeling approach and quality control of the segmentations. Evaluation of the tracking algorithm showed 91.96% of the segmentations were segmented correct with a mean error in height and width at 5.65% and 11.50% respectively.

Accurate preoperative echocardiography has more impact on prediction of long-term mortality than intra-operatively measured flow in coronary bypass grafts

OBJECTIVE

Our study aimed to analyze the predictive value of intra-operative bypass graft flow measurements for long-term mortality.

METHODS

A total of 1593 consecutive coronary artery bypass graft (CABG) patients routinely underwent intra-operative bypass graft flow measurements with the transit-time flow meter (TTFM: Cardiomed(®)). The results of the flow measurements and the demographics were analyzed retrospectively.

RESULTS

The mean follow-up was 3.8 years (0.5-8.8 years) with no losses to follow-up. Overall mortality was 10.1%. The preoperative left ventricular ejection fraction (LVEF) (echocardiograph) was the highest independent predictor of long-term survival (hazard ratio 0.97, p = 0.004) in all groups. The univariate analysis for the CABG I group showed that besides LVEF, female gender (hazard ratio 3.6, p = 0.02) was also significant. For the CABG II group, additive EuroSCORE (European System for Cardiac Operative Risk) (ES) (hazard ratio 1.4, p = 0.0001) and age (hazard ratio 1.1, p = 0.001) were significant. In the CABG III group, ES (hazard ratio 1.2, p < 0.0001), age (hazard ratio 1.04, p = 0.001), IMA (hazard ratio 0.5, p < 0.0001) and concomitant aortic valve replacement (AVR) (hazard ratio 2.1, p = 0.03) were significant, in addition to the LVEF.

CONCLUSION

With quality-controlled surgeons checked by intra-operative TTFM, accurate quantification of preoperative LVEF significantly predicts long-term outcome. Effective bypass graft flows failed to predict outcome in CABG patients, regardless of the degree of coronary artery disease (CAD) and concomitant AVR.