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Transthoracic echocardiography for imaging of the different coronary artery segments: a feasibility study
© Vegsundvåg et al; licensee BioMed Central Ltd. 2009
Received: 26 August 2009
Accepted: 22 December 2009
Published: 22 December 2009
Transthoracic echocardiography (TTE) may be used for direct inspection of various parts of the main coronary arteries for detection of coronary stenoses and occlusions. We aimed to assess the feasibility of TTE to visualise the complete segments of the left main (LM), left descending (LAD), circumflex (Cx) and right (RCA) coronary arteries.
One hundred and eleven patients scheduled for diagnostic coronary angiography because of chest pain or acute coronary syndrome had a TTE study to map the passage of the main coronary arteries. LAD, Cx and RCA were each divided into proximal, middle and distal segments. If any part of the individual segment of a coronary artery with antegrade blood flow was not visualised, the segment was labeled as not satisfactorily seen.
Complete imaging of the LM was achieved in 98% of the patients. With antegrade directed coronary artery flow, the proximal, middle and distal segments of LAD were completely seen in 96%, 95% and 91% of patients, respectively. Adding the completely seen segments with antegrade coronary flow and segments with retrograde coronary flow, the proximal, middle and distal segments of LAD were adequately visualised in 96%, 96% and 93% of patients, respectively. With antegrade directed coronary artery flow, the proximal, middle and distal segments of Cx were completely seen in 88%, 61% and 3% and in RCA in 40%, 28% and 54% of patients. Retrograde coronary artery flow was correctly identified as verified by coronary angiography in seven coronary segments, mainly in the posterior descending artery (labeled as the distal segment of RCA) and distal LAD.
TTE is a feasible method for complete demonstration of coronary flow in the LM, the proximal Cx and the different segments of LAD, but less suitable for the RCA and mid and distal segments of the Cx. (ClinicalTrials.gov number NTC00281346.)
Non-invasive imaging of coronary arteries by transthoracic echocardiography (TTE) is an emerging diagnostic tool for studying flow in the left main (LM), the left descending artery (LAD), the circumflex (Cx) and the right coronary arteries (RCA) [1, 2]. Direct visualisation of segments of the coronary arteries may help in diagnosing significant coronary artery stenoses [2–4]. With this technique, a coronary stenosis typically exhibits local flow acceleration and turbulence expressed as colour aliasing by colour flow Doppler and accelerated flow velocities across the stenosis [2–5]. Total occlusion of a coronary artery may be detected by retrograde flow in the same artery [6–9]. However, demonstration of stenosis or retrograde flow in the main coronary arteries by TTE is dependent on optimal visualisation of the different segments of each main coronary artery. The aim of this study was to assess the feasibility of TTE to visualise the complete segments of the LM, LAD, Cx and RCA in a larger set of patients.
Patients were consecutively included in the study if they fulfilled the following criteria: (i) already scheduled for diagnostic coronary angiography because of chest pain (typical or atypical angina pectoris), or coronary angiography was planned because of acute coronary syndrome; (ii) patient age above 18 years; (iii) met no exclusion criteria. The exclusion criteria were: (i) previous coronary artery bypass surgery; (ii) presumed insufficient acoustic windows because of severe emphysema or gross overweight; (iii) significant valvular disease; (iv) atrial fibrillation; (v) administrative reasons (logistics).
The study protocol was approved by the Regional Committee for Medical and Health Research Ethics and the Norwegian Data Inspectorate. All participants gave written, informed consent. ClinicalTrials.gov number NTC00281346.
Baseline characteristics of the study cohort (n = 111)
No of subjects (%) mean ± SD
62,9 ± 9,6
Heart rate (strokes/minute)
63 ± 7,4
26 ± 3,6
Total cholesterol (mmol/L)
4,9 ± 1,1
Blood pressure (mm Hg)
141 ± 20
82 ± 12
Hypertension (>140/90 mm Hg)
Organic nitrate, daily maintenance
Patients were examined with an Acuson Sequoia c 512 (Siemens Medical Solutions Inc, USA) ultrasound system connected to standard 4V1C and 7V3C transthoracic transducers. The anatomical course of the coronary arteries was examined by use of colour Doppler mapping with data postprocessing mix function, which makes the colours transparent. The velocity scale of colour Doppler was set to 0,24 m/s, but was actively changed to provide optimal images. Contrast agent was not used.
As outlined above, the LM had one segment and the other main coronary arteries (LAD, Cx and RCA) had each a proximal, middle and distal segment. For each segment three different possibilities were defined: (i) the segment was completely visualised; (ii) the segment was not satisfactorily visualised if any part of the individual segment was not seen or the segment was not visualised at all; (iii) the segment was defined with retrograde flow.
Coronary angiography was performed using standard techniques. All angiograms were classified according to left or right dominance. Collateral flow to occluded arteries was graded according to the Rentrop classification (grade 0, no visible filling of any collateral channel, grade 1, filling of side branches of the occluded artery, grade 2, partial filling of the epicardial vessel and grade 3, complete collateral filling of the epicardial vessel) .
Continuous variables are presented as mean and standard deviation (SD), or median (5-95 percentiles) if the variables were skewed. Categorical variables are presented as fractions/percent. Univariate regression analyses were used to explore relationships between success rate and demographic and clinical variables. Variables in univariate testing with p < 1.10 were entered in multivariate forward analyses. The success rates among different patient sub-populations were compared using the unconditional z-pooled test for binomial proportions, with confidence interval method with coefficient 0.9999. P < 0.05 was considered statistically significant. All analyses were done with SPSS for windows (SPSS Inc, Chicago, IL, v 15,0).
Visualisation of different coronary artery segments
Left main coronary artery
Findings of visualisation of individual coronary artery segments
Antegrade flow or retrograde flow
Left anterior descending artery
Visualisation of several coronary artery segments combined
No of subjects (%)
LM + pLAD + mLAD + dLAD
LM + pLAD
LM + pLAD + mLAD
pCx + mCx + dCx
pCx + mCX
pRCA + mRCA + PDA
pRCA + PDA
LM + all segments of LAD/CX/RCA
LM + pLAD + mLAD + pCx + mCx + pRCA + mRCA
LM + pLAD + pCx + pRCA
LM + pLAD + pCx
Circumflex coronary artery
With antegrade directed coronary artery flow, the proximal, middle and distal segments of Cx were completely seen in 88%, 61% and 3% of the patients, respectively (Table 2). No patient was found to have retrograde flow. Both pCx and mCx could be visualised in 61% of patients, while all three segments of Cx could be seen in 3% of patients (Table 3). Visualisation of the complete Cx or the proximal and mid segments was negatively related to patient age (p = 0,03) in univariate regression analyses. Visualisation of the complete Cx was negatively related to age (p = 0,01) and heart rate (p = 0,03) in multivariate analyses.
Right coronary artery
Adding the patients with completely seen segments with antegrade coronary flow and patients with segmental retrograde coronary flow, the pRCA, mRCA and PDA were adequately visualised in 40%, 29% and 59%, respectively (Table 2). With antegrade directed coronary artery flow, the proximal and middle segments of the RCA and PDA were entirely seen in 40%, 28% and 54%, respectively (Table 2). Retrograde coronary artery flow was seen in one mRCA and five PDAs (Table 2). Coronary angiography showed corresponding findings apart from two PDAs which had antegrade flow on angiography. In the cases where retrograde Doppler flow in PDA was confirmed angiographically collateral circulation in PDA was Rentrop class ≥ 2. Both the pRCA and PDA were visualised in 27% of patients, while the total RCA/PDA was adequately imaged in 15% of patients (Table 3). Visualisation of the complete RCA/PDA was negatively related to patient BMI in regression analyses (p = 0.01).
Visualisation of proximal versus distal coronary segments
Visualisation of all segments of the coronary arteries was achieved in only one patient (1%) (Table 3). There were significant differences in the visualisation of proximal versus distal segments between the different coronary arteries. In contrast with Cx and RCA, the rate of visualisation of distal and proximal segments of LAD was equal (Table 2). In Cx the distal segment was visualised in only a minority of patients. In RCA it was the middle segment which was most difficult to visualise (Table 2). The LM and proximal segments of LAD, Cx and RCA were visualised in 35% of patients. Excluding RCA, LM and proximal segments of LAD and Cx were adequately seen in 85% of patients (Table 3).
Right versus left coronary dominance
Coronary angiograms were available for 108 patients, and 8 patients were found to have dominant Cx, supplying the PDA from the distal continuation of the Cx. The remaining patients had the RCA as the dominant artery, supplying the PDA. Among the eight patients with left coronary dominance, the pCx, mCx and dCx were completely visualised in seven, six and one patients, respectively. Among the same patients, the pRCA, mRCA and PDA were completely visualised in zero, one and two patients, respectively. The statistical analyses showed a trend towards lower feasibility of adequate visualisation of pRCA and mRCA and a trend towards higher feasibility of visualisation of pCx and mCx when the Cx was the dominant coronary artery.
Visualisation of different coronary artery segments according to clinical presentation
Statistical analyses showed no significant differences in the degree of adequate visualisation of the various main coronary segments when comparing patients with or without acute coronary syndrome, or comparing patients with or without known coronary disease.
In this study of consecutively included patients with suspected or definite coronary artery disease the feasibility of transthoracic echocardiography for visualisation of different segments of the main coronary arteries was examined. The purpose of the study was to elucidate the feasibility of viewing the complete coronary artery segments with antegrade flow or findings of retrograde coronary artery flow. The main finding was that the left main, the LAD segments and the proximal Cx segment could be completely imaged in the great majority of patients while the mid and distal Cx segments and the RCA were less well imaged.
Use of TTE for direct inspection of various parts of the main coronary arteries has been the subject of several studies, both for detection of coronary stenoses and occlusions [2, 3, 3–9, 11–15]. Coronary occlusions may be detected by retrograde flow in the coronary artery [6–9]. Coronary stenoses can be identified by local flow acceleration and turbulence expressed as colour aliasing by colour flow Doppler and accelerated flow velocities across the stenosis, with further quantification of the individual stenosis by comparing flow velocities at the site of aliasing with nearest upstream non-accelerated prestenotic flow velocities [2–5, 11, 12]. A stenotic to prestenotic flow velocity ratio (SPVR) exceeding 2 has been proposed as a cut-off value for significant stenosis [2, 3]. Accelerated coronary artery flow velocities typically give a stronger colour Doppler signal than normal laminar coronary flow, and these turbulent flow signals may be detected without visualisation of adjacent up- or downstream coronary portions . However, entire imaging of the individual coronary segment should ease the demonstration of possible stenoses with further Doppler measurements of flow velocities. So far, the largest study identifying stenoses by searching the various main coronary artery segments for flow turbulence and a stenotic SPVR included 84 patients, without performing detailed analyses on the visibility of the different coronary artery segments by TTE . In contrast with previous studies, our study tried to elucidate the feasibility of complete visualisation of the various main coronary artery segments, in a larger set of patients with various degrees of atherosclerotic coronary disease.
Findings of retrograde flow in the main coronary arteries by TTE have high accuracy in documenting LAD occlusions [6–8] and RCA/PDA occlusions [7, 9]. Retrograde coronary artery flow was rarely found in our patient cohort; in only nine main coronary artery segments, mainly in the PDA and dLAD (Table 2). Our findings of retrograde flow by TTE corresponded well with findings by coronary angiography, with matching findings in seven of nine patients. In the two patients falsely found with retrograde flow in the PDA by TTE, we suspect that the distal part of PDA was confused with the recurrent branch of the dLAD running around the apex of the heart.
Although large portions of any coronary artery segment with antegrade flow often could be satisfactorily seen in our study, the whole segment (with antegrade flow) had to be imaged to be labeled completely visualised, as outlined above. Complete visualisation of the various main coronary artery segments was dependent on both the artery and segment investigated (Table 2). Our study demonstrates that TTE is a feasible method for complete visualisation of different coronary artery segments with antegrade flow, especially the LM, the proximal segments of LAD and Cx, and the middle and distal segments of LAD. The distal Cx and the RCA segments were not adequately visualised. This may be due to several factors including individual variations in coronary anatomy for the Cx and the RCA. Even with use of invasive coronary angiography the distal segments of Cx may be difficult to define in some patients. The small study group with left coronary dominance showed a trend towards more complete visualisation of the proximal and mid segments of Cx and of less adequate visualisation of pRCA and mRCA. Patients' BMI was a significant predictor of success rate in our study. Our results are indicative of what can be expected with this technique in the hands of experienced echocardiographers and currently available equipment. Further developments of echocardiographic technology may both increase the feasibility of visualisation of coronary arteries by TTE and diminish echocardiographic limitations caused by overweight.
Earlier studies using coronary colour flow Doppler TTE are not directly comparable to our study, since those studies primarily focused on searching for coronary artery stenoses and occlusions [2–4, 6–9, 11–14], without fully describing the degree of completeness of imaging of the coronary artery segment investigated. Several of these studies only concentrated on the LM and proximal and mid segments of LAD [6, 8, 11–14]. Studies focusing on coronary stenoses by use of coronary flow turbulence and stenotic SPVR have reported high accuracy for detecting stenotic lesions in the LM and LAD, but lower precision for detection of stenoses in the Cx and RCA/RDP [2–4, 12]. Incomplete imaging of the individual coronary segments could explain failure of identification of stenotic coronary flow turbulence.
Limitations of the study
There are several limitations to our study. Use of intravenous ultrasound contrast agent might have improved the results. Because of limited clinical experience in patients with acute coronary syndrome, we chose not to use ultrasound contrast when planning the study. We can not exclude the possibility of overstating the completeness of imaging of the individual coronary artery segments. However, when changing the echocardiographic view we always tried to find overlapping end-portions of the coronary artery compared with the foregoing views, and alternative views were used to fill in any missing portions of the individual coronary artery segment. Moreover, we can not exclude that nearby parallel coursing coronary artery branches occasionally may have been mistaken as the main coronary segment of the dLAD or PDA. In addition, retrograde flow of the distal part of PDA may have been confused with the recurrent branch of the dLAD, which runs around the apex of the heart. Finally, we can not exclude selection bias in our results, since our study cohort only included patients planned for coronary angiography and excluded patients with previous coronary artery bypass surgery, presumed insufficient acoustic windows, significant valvular disease or atrial fibrillation.
Complete visualisation of the various main coronary artery segments is dependent on both the artery and segment investigated. TTE is a feasible method for complete demonstration of antegrade coronary flow in the LM, the proximal Cx and the different segments of LAD, but less suitable for RCA and mid and distal segments of Cx. Complete visualisation of individual coronary segments might ease the demonstration of coronary stenoses by TTE. Detection of segmental retrograde coronary flow by TTE corresponds well with coronary angiography.
The study was funded by grants from Sunnmore Health Trust Research Fund and Helse Midt-Norge Regional Health Trust Research Fund.
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