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Eur J Cardiothorac Surg 2005;28:692-700
© 2005 Elsevier Science NL

Review

Does Doppler echography have a diagnostic role in patency assessment of internal thoracic artery grafts?{star}

Catherine M. Jones, Thanos Athanasiou * , Paris P. Tekkis, Vitali Malinovski, Sanjay Purkayastha, Ahmed Haq, John Kokotsakis, Ara Darzi

Academic Surgical Unit, Department of Cardiothoracic Surgery, Imperial College of Science Technology and Medicine, St Mary's Hospital, Praed Street, London W2 1NY, UK

Received 11 April 2005; received in revised form 3 July 2005; accepted 18 July 2005.

* Corresponding author. Address: Locum Consultant in Cardiothoracic Surgery, 70 St Olaf's Road, Fulham, London SW6 7DN, UK. Tel.: +44 207 886 1147; fax: +44 207 886 6777. (Email: tathan5253{at}aol.com).


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
The amount of literature published over the past decade comparing coronary angiography with transthoracic Doppler echocardiography assessment of internal thoracic artery graft patency after CABG is substantial. There has been no review of the available literature, and conflicting reports of diagnostic accuracy have prevented routine use of transthoracic Doppler in graft patency assessment. Thus, this article reviews the available literature on diagnostic accuracy of transthoracic Doppler echocardiography of coronary bypass grafts. Relevant studies were identified and meta-analysis of diagnostic accuracy was performed. Study quality was assessed. Quantitative data synthesis included calculation of sensitivity, specificity, summary receiver operating characteristic curve analysis, pooled analysis and meta-regression of accuracy against study quality, publication date, angina, probe frequency and diagnostic criteria. Twenty studies of 929 patients produced 26 results included for analysis. Grafts were not visualized in 93 (10%) patients. Pooled sensitivity (85%) and specificity (94%) and diagnostic odds ratio (100.7) were high. SROC analysis showed an area under the curve of 0.96. Heterogeneity of results was due to variations in diagnostic criteria and study size. Subgroup analysis showed best performance in patients with postoperative angina (p = 0.014). Study quality did not affect results. Diastolic fraction less than 0.5 (sensitivity 89%, specificity 94%) was shown to be the best criterion for prediction of stenosis. Performance was lower using peak diastolic to systolic velocity ratio less than 1 (sensitivity 85%, specificity 86%). Transthoracic Doppler echography is effective in first-line assessment of left internal thoracic artery graft patency. It shows high specificity, prevents invasive investigations and improves in patients with postoperative angina. TDE is best used in combination with other non-invasive tests due to its inability to visualize the graft. The potential for use in postoperative coronary bypass patients is high.

Abbreviations: CABG = coronary artery bypass grafting • TDE = transthoracic Doppler echocardiography • ECG = electrocardiogram • CA = coronary angiography • ITA = internal thoracic artery • LITA = left internal thoracic artery • LAD = left anterior descending artery • AUC = area under the curve (summary ROC analysis) • DOR = diagnostic odds ratio • CI = confidence interval

Key Words: Sensitivity and specificity • Coronary artery bypass • Doppler echocardiography • Internal thoracic artery


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
The left internal thoracic artery (LITA) is the conduit of choice to the left anterior descending (LAD) artery. It is associated with longer patency and survival than venous grafts [1]. However, graft failure and recurrence of angina may occur in both the immediate and late postoperative period.

Coronary angiogram (CA) is the conventional and current gold standard investigation for the detection of conduit stenosis. It is invasive, and has recognized risks including vascular trauma (1.2%), arrhythmia (1%), stroke (0.3%), myocardial infarction (0.2%), angina (0.2%) and rarely embolism causing renal failure, arterial dissection, and emergency angioplasty or surgery [2]. Following CABG, the risks from CA increase. These risks, as also cost considerations, prevent its routine use as a quality control tool in the postoperative setting.

Transthoracic Doppler echocardiography (TDE) of the LITA graft has been available for the past decade. It has potential use in all postoperative patients, and has few risks. However, despite numerous articles in the literature, its accuracy has not been assessed. This meta-analysis of the available literature aimed to compare TDE findings with CA findings with respect to ITA graft stenosis in patients after CABG.


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Results
 4. Discussion
 5. Conclusion
 References
 
2.1 Literature search
A literature search of Medline using Pubmed and Ovid as the search engines were used to identify studies reporting on TDE in assessment of graft patency, published between 1990 and January 1st 2005. The following keywords were used for the search: ‘transthoracic Doppler’, ‘internal mammary’ and ‘graft flow’ limited to ‘human subjects’. Articles were also identified using the function ‘related articles’ in PubMed. References of the articles identified were also searched. The Cochrane and Embase databases were also searched. No language restrictions were made.

2.2 Eligibility criteria and data extraction
All studies comparing postoperative ITA graft assessment on TDE with postoperative CA findings were considered. Studies where echocardiography was performed during surgery or angiography were excluded.

Data were extracted on author, date of publication, institution, study design, patient demographics, definition of stenosis, diagnostic criteria, probe frequency, and study endpoints. All data were extracted independently by two reviewers (CJ and TA), and discrepancy was resolved by consensus. Sensitivity and specificity were required for analysis and studies providing insufficient information for calculations were excluded. Assessment of the quality of the studies was undertaken using the guidelines published by the STARD initiative [3].

2.3 Verification bias
Verification bias occurs when the result of one test influences selection for the other test, and occurs only when subjects undergoing both tests are included for analysis [4]. The verification bias of each study was estimated and tabulated.

2.4 Endpoints and definitions
The primary endpoint was estimating TDE accuracy compared with CA in diagnosing LITA graft stenosis. As secondary endpoints, we considered accuracy of different criteria in diagnosing stenosis, and patient and study effects on accuracy. Significant stenosis was defined as at least 70–75%. Diagnostic variables include diastolic and systolic velocity time integral (VTI), diastolic peak velocity (DPV), systolic peak velocity (SPV), and the ratio of DPV to SPV. The diastolic fraction (DF) is the ratio of DVTI to (DVTI+SVTI).

2.5 Statistical analysis
True positive findings (TP) were defined as stenosis on both CA and TDE. True negative findings (TN) were non-stenotic graft on both CA and TDE. False positive findings (FP) were stenoses on TDE but not on CA. False negative findings (FN) were failures of TDE to detect stenosis found on CA. Pooled sensitivity and specificity, with 95% confidence intervals, were estimated. Random and fixed effects calculations were performed to calculate Q, a measure of heterogeneity across the studies.

SROC analysis quantified TDE performance using area under the curve (AUC), diagnostic odds ratio (DOR), and Q* values as summary estimates according to published guidelines for diagnostic meta-analysis [5]. SROC analysis was performed to assess interaction between sensitivity and specificity across results and give summary estimates of diagnostic accuracy based on data from multiple studies [5]. Subgroup analysis was performed for diagnostic criteria, minimally invasive surgical technique, postoperative angina symptoms, probe frequency, and late postoperative investigation. Analysis was also repeated for articles published in English language journals.

Meta-regression analysis was performed to assess the effect of study size, publication date, study quality, probe frequency, and diagnostic criteria on TDE accuracy. Meta-regression techniques identify statistically significant relationships between variables and allow multiple variables to be evaluated for independence of effect [6]. Study characteristics were examined to identify significant sources of heterogeneity in outcome results, when individual patient results were unavailable.

Analysis was conducted using SPSS Version 11.0 for Windows (SPSS Inc., Chicago, IL, USA) and Meta-Test Software Version 0.9 (developed by Joseph Lau). This study was undertaken in accordance with previously reported guidelines for meta-analyses evaluating diagnostic tests [7,8].


   3. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
4. Discussion
 5. Conclusion
 References
 
3.1 Eligible studies
Eight hundred and fifteen abstracts were identified using the above search keywords. Abstract examination and investigating the references identified 38 articles, which were retrieved in full. Eighteen papers were excluded in total for various reasons: repetition of data [9,10], insufficient data reporting [11–13], intraoperative TDE data [14–16], lack of patency assessment [17–22] and inclusion of patent grafts only [23–26]. The remaining 20 articles [27–46] were included for analysis after extraction of study characteristics (Table 1 ).


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  		Table 1. Characteristics of studies included in analysis
 
3.2 Quality assessment
Using the STARD initiative guidelines, a quality score for each of the 20 studies was constructed (Table 2 ). This score was divided into Title and Introduction, Methods, Results, Discussion and Total. These results were used in meta-regression of the accuracy to assess the effect of study quality.


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  		Table 2. Details of quality scoring
 
3.3 Verification bias
The majority of the studies recruited patients prospectively for both tests, with the CA indicated by recurrence of angina. Thus, in most of the studies, verification bias was small (Table 1). However, in some studies no information was given regarding recruitment process or criteria for undergoing CA and TDE [29,32,40–43,46].

3.4 Statistical analysis
Of the 20 studies included for analysis, six [30,34,38,40,41,43] estimated sensitivity and specificity for two different TDE criteria (Table 3 ). Initial analysis included duplicate results from these six studies. Overall pooled analysis showed sensitivity of 85% (95% CI 78–90) using both random and fixed effects models (Table 4 ). Random effects modeling (REM) showed superior specificity compared to the analysis using a fixed effect model (FEM). The difference in specificity results between fixed and random effects models suggests heterogeneity across the studies. High DOR, AUC, and Q* were obtained (Table 4).


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  		Table 3. Study data
 

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  		Table 4. Sensitivity analysis
 
One study [43] included 23 right internal thoracic artery (RITA) grafts. Analysis excluding this study showed sensitivity 88%, specificity 94% (random effects) and 87% (fixed effects). Q-value was 11.86, and DOR 157.9 (95% CI 78.4–318.1). AUC was 0.963. Taking the best result from each study, the analysis was repeated. Pooled sensitivity was 85%, specificity was 95% and AUC 0.95. The Q-value was 12.6.

The effect of study size on heterogeneity was analyzed. Studies including over 50 patients were examined (Table 4). Sensitivity was 78%, with specificity of 97%. Heterogeneity in this subgroup was 12.6.

Seven studies [30,32–34,38,39,41] took DF less than 0.5 to indicate a significant graft stenosis, and less than 0.66 in one study [45]. The sensitivity (89%) was higher than the overall analysis, with identical specificity (94%) (Table 4).

Using DPV/SPV ratio under 1 as diagnostic criteria [30,34,35,38,41,43] produced similar results to the overall analysis. Although performing inferiorly to DF, DPV/SPV proved a very good diagnostic indicator of graft stenosis. The remainder of the studies [27–29,31,36,37,40,42,44,46] used other criteria for diagnosing graft stenosis.

Fifteen articles [27–31,34–36,38–41,44–46] published in English produced 20 results (Table 4). Sensitivity, specificity, DOR, and AUC were higher than the overall data group.

Of 929 LITA grafts examined, 93 (10%) were not visualized by TDE. There were 18 confirmed occlusions (20%), 56 patent grafts (60%) and 19 without angiographic results in the literature (20%).

Meta-regression of study quality showed insignificant effect on diagnostic accuracy in unweighted (p = 0.98), inverse variance weighted (p = 0.74) and study size weighted (p = 0.50) analyses. Odds ratio was 1.00 (95% CI 0.90–1.12). Study size (coefficient = –0.011, p = 0.10), probe frequency (coefficient=1.104, p = 0.07), time of publication (coefficient = 0.003, p = 0.13), postoperative time to TDE (coefficient = 0.126, p = 0.57) and diagnostic criteria (coefficient = –0.07, p = 0.79) had insignificant effect on accuracy. Studies of patients with postoperative angina showed significantly higher accuracy (coefficient = 0.797, p = 0.014), maintained during co-analysis with study quality (coefficient = 0.873, p = 0.003).


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
5. Conclusion
 References
 
The LITA is the graft of choice to the LAD. Since its introduction in the 1960s, it has contributed to improved survival [47] and longer graft patency after CABG. Minimally invasive and robotically assisted techniques routinely use this graft. Routine postoperative CA is not performed due to risk. However, in patients with postoperative angina, hypoperfusion syndrome, undiagnosed subclavian stenosis and single robotically assisted grafts, graft patency assessment is indicated. (Fig. 1 ).


Figure 1
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  		Fig. 1. (a) SROC curve of overall dataset in diagnosis of LITA graft stenosis over 70%. (b) SROC of subgroup of studies of at least 50 patients. (c) SROC of subgroup of patients with postoperative angina. (d) SROC of subgroup of studies of quality over 16 (STARD guidelines).

 
TDE was first described by Gould [48] in 1972 as a non-invasive study of venous grafts. It was developed as an alternative to CA but was not widely used due to suboptimal sensitivity and specificity reports. Since then, understanding of graft flow has improved, with the realization that failure of graft visualization does not indicate graft failure unless patency had been previously established [30].

4.1 Physiological considerations
The ungrafted LITA has forward flow predominantly during systole. When grafted, proximal LITA flow becomes biphasic (systolic and diastolic) [49]. During systole, blood flows into the graft but cannot enter the myocardium due to high resistance. During diastole, the resistance drops and blood flows from the distal graft into the myocardium [27,49]. Flow and velocity should be greater in diastole than systole in a patent LITA graft [27] (Fig. 2 ). This differs from venous grafts, with predominantly diastolic flow throughout the entire graft [49].


Figure 2
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  		Fig. 2. Left. Normal, systolic dominant flow in the ungrafted LITA. Right. Biphasic, diastolic dominant flow in a grafted LITA.

 
Whilst the distal LITA adapts to coronary artery flow dynamics (predominantly diastolic flow), proximal LITA flow near the subclavian artery origin will retain predominantly systolic flow. This causes the DPV/SPV to physiologically increase from 0.6 proximally to 1.4 distally [49]. This is important when using TDE to diagnose stenosis, as DPV/SPV and DF will be reduced proximally even in patent grafts [28]. Whilst a parasternal approach lessens this risk, supraclavicular probe position increases TDE reproducibility by measuring flow proximal to remnant LITA branches [40] (Fig. 3 ), accounting for different surgical approaches to LITA branches. Additionally, poor LAD targets with competitive flow are associated with reduced diastolic graft velocity [28,30]. However, neither DPV/SPV nor DF is affected, making ratio variables preferable in diagnosis.


Figure 3
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  		Fig. 3. Typical view of the LITA origin using supraclavicular probe position. LIMA, left internal mammary (thoracic) artery; LSA, left subclavian artery; LVA, left vertebral artery; TCT, thyrocervical trunk.

 
Anastomosis assessment is difficult because blood flows to the anastomotic site from both the native LAD and LITA, causing competitive flow [31]. In CA studies, the contrast is injected under pressure, disrupting the baseline anastomotic dynamics [31]. TDE is performed without such injections and therefore elevated flow velocity represents true stenosis.

Moderate stenosis detection is difficult, as flow does not significantly differ between intermediately stenosed (50–75%) and patent grafts [30]. Vasodilator stress tests to assess flow reserve (ratio of peak hyperemic flow to rest flow) help identify intermediate stenosis, but carry risks of ischemia, arrhythmia, myocardial infarction, and dyspnea [29,30]. Flow reserve varies with target vessel quality and competitive LAD flow [28]. Additionally, vasodilator action on the myocardial microvasculature reduces the effects of LITA collateral branches on the Doppler pattern [40]. Reversible obstructions are difficult to assess without inotropic or exercise testing. The presence of a remnant LITA branch is difficult to assess, and the relative absence of distal graft flow may erroneously lead to assumption of graft failure [28]. Abnormal coronary microvasculature, myocardial viability and collateral flow also affect graft flow [50].

The angle between the pulsed Doppler and flow direction is difficult to estimate. Some studies [32,33] use angle correction, however, the signal with the highest audible frequency, velocity and most clearly defined spectral velocity envelope can be assumed to need minimal angle correction [30]. DPV/SPV and DF are unchanged by angle correction [28,30].

4.2 Diagnostic performance of TDE
When the LITA graft was visualized (90%), TDE performed well in diagnosing stenosis. DF less than 0.5 (or 0.66 in one case) [45] was the most accurate criterion, although DPV/SPV also performed well. SROC analysis showed AUC over 0.95 for each, indicating high accuracy.

Subgroup analysis of minimally invasive patients comprised four studies, showing excellent specificity (95%) but slightly reduced sensitivity (79%) compared to the overall dataset. Conclusions cannot be drawn from this small subgroup. Further research is required on patients with minimally invasive CABG.

The subgroup of 15 studies published in English produced better diagnostic results than the overall group. This may reflect differences in study design, or publication bias in English language journals. The data shows good diagnostic performance overall.

Meta-regression showed that only postoperative angina affected performance, improving it significantly even after factoring for study quality. The STARD guidelines [3] quality scores did not affect accuracy, validating inclusion of all studies into the analysis. Probe frequency did not affect accuracy, despite the potential for greater attenuation with higher frequencies [30]. The choice of diagnostic criteria did not significantly affect the results. This suggests that heterogeneity of results is due to patient, not study, characteristics. Differences in REM and FEM results despite isolating criteria and study size are due to inherent differences in patients, institutions and operators.

Grafts were not visualized in 10% of patients, with at least 60% of these patent on CA. Reasons for these failures are anatomical (LITA variations and patient habitus), operative (edema in the immediate postoperative period) and operator inexperience. The Doppler signals are low velocity, susceptible to heart pulsation and respiratory motion artifact, and can be hidden by the pleura and pericardium [40]. A patent graft may have little or no flow at rest [51] but contribute to myocardial supply during stress, causing difficulty in visualization.

4.3 Safety considerations
CA carries significant risks of complication. In stable postoperative patients, complications include arrhythmia (1.0%), major vascular trauma requiring surgery (0.6%), minor vascular trauma (0.6%), stroke (0.3%) myocardial infarction (0.2%), angina (0.2%) and rarely angioplasty or emergency CABG [2]. In unstable postoperative patients, complications include graft dissection (1.3%), myocardial infarction (1.3%), death (0.6%), arrhythmia (0.6%) and minor vascular trauma (0.6%), with angioplasty performed in 18% [2]. The overall complication rate in stable patients is 4.0%, and 4.8% in unstable patients. However, the incidence of major complications is higher in unstable (1.9%) than stable patients (0.9%). Patients with angina or hypoperfusion syndrome are therefore at high risk for major complications during CA.

TDE is non-invasive, inexpensive, fast and has low risk of complications. It can be performed both immediately and in the late postoperative period. Whilst it can be performed at the bedside or in the outpatient setting, it requires training in performing and interpreting results. Highly skilled operators are needed to prevent mistakes in diagnosis [40].

4.4 Alternative non-invasive investigations
Magnetic resonance angiography (MRA), CT angiography (CTA) and ventricular function echocardiography are other non-invasive investigations performed to assess graft patency. MRA has sensitivity of 96% and specificity of 67% in the diagnosis of LITA graft stenosis [52]. CTA has sensitivity and specificity of up to 90 and 75%, respectively [53], but lacks dynamic assessment. MRA shows sensitivity of 100% and specificity of 68% in the diagnosis of graft stenosis when compared to CTA [54]. This review shows TDE to have accuracy at least comparable to MRA and CTA. There have been no direct comparisons between TDE and MRA or CTA.

Each of these investigations is vulnerable to inter-reader variability and operator inexperience. Whilst TDE shows functional dynamic performance, it has suboptimal graft visualization. None of these investigations have excellent performance, and may be best used in combination.

4.5 Applications of TDE
Immediately postoperatively, hypoperfusion syndrome occurs in 1.4% of patients [55]. Hypoperfusion syndrome is the clinical manifestation of unexpected postoperative ischemia due to insufficient flow, refractory to inotropic support [55]. It results from mismatch in arterial supply and myocardial demand, due to insufficient graft length or size, flow [56], subclavian steal syndrome [57], acute dissection, intramural hematoma, vessel spasm and anastomotic stenosis. Investigation includes symptom assessment, ECG (for ST segment elevation), echocardiography and graft flow assessment. Deterioration is often sudden and rapid. CA cannot be performed at the bedside, or in patients on inotropes, making the decision to reoperate (and place additional grafts if necessary) based on the clinical judgment only. Low cardiac output needing inotropic support without ECG changes also prompts a decision about reoperation for suspicion of anastomotic failure. TDE is safe, reliable non-invasive and can be performed at the bedside to help make the decision about reoperation. TDE is particularly useful in this setting if the preoperative stenosis is marginal, as grafting is more likely to fail due to competitive flow from the native vessel [58].

Coronary-subclavian steal syndrome (CSSS) has been reported over the past decade [57,59,60]. In the presence of prevertebral subclavian stenosis, activity of the upper limb leads to reversed flow in the ITA graft. In one prospective study [57] of LITA to LAD grafts with 8-year follow-up, 31 of 207 (15%) showed clinical CSSS. Seventeen patients experienced angina after upper arm activity, indicating myocardial ischemia due to LITA flow reversal. CSSS is more common than previously thought, causes chronic angina and myocardial ischemia, and is a long-term complication of LITA to LAD. Investigation of CSSS is currently done via CA, although it has been reported [59] that color Doppler is effective in flow assessment of vertebral and subclavian arteries. TDE could be used to assess patients with angina after upper limb activity, avoiding routine CA. Regular assessment by TDE and color subclavian Doppler after LITA to LAD grafting would identify patients with undiagnosed CSSS.

Minimally invasive and robotic CABG patients routinely have LITA to LAD grafting. Symptomatic relief and survival depend on ongoing LITA graft patency. Similarly, patients with composite grafts off the LITA are at high risk of myocardial infarction and death if the LITA graft fails [61]. Postoperative CA is not routine due to its risks. TDE would be a safe and useful investigation in these patients, as grafting in this group leads to hypoperfusion (2.5%) [62], myocardial infarction and arrhythmia (24%) [63]. TDE would identify patients to benefit from angioplasty, reoperation or CA. A control check should be performed before discharge from follow-up. TDE is an appropriate first-line investigation with higher safety than CA.

Patients who present with late postoperative ischemic symptoms are candidates for further percutaneous or surgical intervention, pending graft assessment. They may have graft failure or new coronary stenosis. The benefits of TDE over CA in this subgroup are improved safety, speed, and capacity for investigation at the bedside or outpatient setting [40]. As outlined above, the risks of CA are highest in postoperatively patients with recurrent angina. Whilst TDE accuracy is imperfect, it has high specificity and is an appropriate test in combination with CTA or MRA to identify patients who require formal angiography.

Trans-esophageal echocardiography (TEE) in conjunction with TDE assesses graft patency, ventricular and valvular function and gives a more complete assessment of cardiac status. TDE could also be used in the outpatient setting to determine the appropriate timing of the next follow-up visit [40].

4.6 Limitations of this review
Only studies reporting sufficient data for sensitivity and specificity calculations were included. No attempts at author contact were made. The verification bias in some studies was high [28], or difficult to assess [29,32,40–43,46] contributing to reporting bias. Graft detection performance varied between studies, ranging from less than 50 up to 100%. Additionally, there is no information about hypertension, diabetes or hypercholesterolemia, all of which reduce myocardial coronary reserve and may mask graft patency [40].

This review only analyses diagnosis of graft stenosis over 70%. The choice of intercostal versus supraclavicular probe position varied between and within studies. Details of preoperative LAD stenosis were not universally reported, and the time between surgery and investigation varied within and between studies. Advances in Doppler technology such as high frequency, frame speed and separate frequencies for echocardiography and Doppler [35] may make future TDE more accurate still.

Some patients had minimally invasive CABG [27,28,32,39], whilst others had conventional sternotomy. Most studies evaluate graft flow, however, three analyze anastomotic patency [31,32,44]. There is insufficient literature to perform a separate review of diagnostic accuracy at the anastomosis.

This review does not address the predictive value of TDE findings on long-term survival. There is insufficient literature at present for such a review.


   5. Conclusion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
References
 
TDE is an accurate, safe first-line investigation of ITA graft patency following CABG. It is appropriate for patients with hypoperfusion syndrome, following minimally invasive or robotic CABG, composite grafts from the LITA and late recurrence of angina.

It has high sensitivity, specificity, DOR and AUC compared to CA. DF under 0.5 is the best indicator of graft stenosis, with DOR over 100, sensitivity of 89% and specificity of 94%.

TDE performs significantly better in patients with postoperative angina. There is no effect of surgical technique, time between surgery and TDE, probe frequency, study size or diagnostic criteria. Further research involving minimally invasive surgery is needed.

Despite graft non-detection in 10%, TDE is a useful investigation of graft patency post CABG, both in the immediate and late postoperative periods. Its accuracy is best in patients with postoperative angina, and when using DF under 0.5 as the diagnostic criteria for LITA graft stenosis. Its use in hypoperfusion syndrome, CSSS, postoperative angina investigation and robotically assisted CABG follow-up is recommended, in combination with other non-invasive investigations, to reduce exposure to the risks of CA.


   Footnotes
 
{star} No grants have been used in the research into this submission. Back


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 

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