Published online before print January 25, 2008, 10.1148/radiol.2463062071
(Radiology 2008;246:754-762.)
© RSNA, 2008
Myocardial Bridging: Depiction Rate and Morphology at CT Coronary Angiography—Comparison with Conventional Coronary Angiography1
Sebastian Leschka, MD,
Pascal Koepfli, MD,
Lars Husmann, MD,
André Plass, MD,
Robert Vachenauer, MD,
Oliver Gaemperli, MD,
Tiziano Schepis, MD,
Michele Genoni, MD,
Borut Marincek, MD,
Franz R. Eberli, MD,
Philipp A. Kaufmann, MD, and
Hatem Alkadhi, MD
1 From the Institute of Diagnostic Radiology (S.L., L.H., B.M., H.A.), Clinic for Cardiovascular Surgery (A.P., R.V., M.G.), and Cardiovascular Center (P.K., O.G., T.S., F.R.E., P.A.K.), University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland; and Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland (P.A.K.). Received December 6, 2006; revision requested February 14, 2007; revision received April 27; accepted May 29; final version accepted August 1. Supported by the National Center of Competence in Research, Computer Aided and Image Guided Medical Interventions of the Swiss National Science Foundation.
Address correspondence to H.A. (e-mail: hatem.alkadhi{at}usz.ch).
 |
ABSTRACT
|
|---|
Purpose: To prospectively assess the depiction rate and morphologic features of myocardial bridging (MB) of coronary arteries with 64-section computed tomographic (CT) coronary angiography in comparison to conventional coronary angiography.
Materials and Methods: Patients were simultaneously enrolled in a prospective study comparing CT and conventional coronary angiography, for which ethics committee approval and informed consent were obtained. One hundred patients (38 women, 62 men; mean age, 63.8 years ± 11.6 [standard deviation]) underwent 64-section CT and conventional coronary angiography. Fifty additional patients (19 women, 31 men; mean age, 59.2 years ± 13.2) who underwent CT only were also included. CT images were analyzed for the direct signs length, depth, and degree of systolic compression, while conventional angiograms were analyzed for the indirect signs step down–step up phenomenon, milking effect, and systolic compression of the tunneled segment. Statistical analysis was performed with Pearson correlation analysis, the Wilcoxon two-sample test, and Fisher exact tests.
Results: MB was detected with CT in 26 (26%) of 100 patients and with conventional angiography in 12 patients (12%). Mean tunneled segment length and depth at CT (n = 150) were 24.3 mm ± 10.0 and 2.6 mm ± 0.8, respectively. Systolic compression in the 12 patients was 31.3% ± 11.0 at CT and 28.2% ± 10.5 at conventional angiography (r = 0.72, P < .001). With CT, a significant correlation was not found between systolic compression and length (r = 0.16, P = .25, n = 150) but was found with depth (r = 0.65, P < .01, n = 150) of the tunneled segment. In 14 patients in whom MB was found at CT but not at conventional angiography, length, depth, and systolic compression were significantly lower than in patients in whom both modalities depicted the anomaly (P < .001, P < .01, and P < .001, respectively).
Conclusion: The depiction rate of MB is greater with 64-section CT coronary angiography than with conventional coronary angiography. The degree of systolic compression of MB significantly correlates with tunneled segment depth but not length.
Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/2463062071/DC1
© RSNA, 2008
|
INTRODUCTION
|
|---|
Myocardial bridging (MB) is a congenital anomaly in which a usually epicardial portion of a major coronary artery courses through the myocardium (1). The myocardial tissue covering the artery is termed a myocardial bridge, and the artery itself is called a tunneled segment. Although MB is generally thought to be a normal variant, multiple instances of myocardial ischemia, tachycardia-induced ischemia, conduction disturbances, myocardial infarction, and sudden death have been reported in association with MB that suggest the clinical importance of the anomaly (2–7). The diagnosis of MB usually is made with conventional coronary angiography (1). Conventional coronary angiography indirectly indicates the anomaly by demonstrating systolic compression of the tunneled segment and a localized change in direction of the vessel course toward the ventricle (8).
Reports of autopsy studies have indicated the prevalence of MB to range from 15% to 85% (1,9), while the depiction rate with conventional coronary angiography is only 0.5%–4.5% (5,10). This difference has been suggested to be caused by superficial MB not constricting the tunneled segment during systole to an extent that allows the indirect identification of MB with conventional coronary angiography (7).
Regarding MB, only a few reports (11–13) have described the feasibility of computed tomography (CT) in visualizing MB of coronary artery segments, and, to our knowledge, no study to date has analyzed the depiction rate and morphologic characteristics of MB with CT in a large patient population. Thus, the purpose of our study was to prospectively assess the depiction rate and morphologic features of MB of the coronary arteries at 64-section CT compared with those at conventional coronary angiography.
|
MATERIALS AND METHODS
|
|---|
Study Groups
Between October 2004 and July 2005, we consecutively enrolled 115 patients in this study. These patients were simultaneously enrolled in a prospective study comparing CT coronary angiography and conventional coronary angiography, for which approval of the ethics committee of the University of Zurich and written informed consent had been obtained. All participants were informed about our study aims and about the risks of contrast medium administration and the possible risks of radiation exposure. All conventional coronary angiography procedures were clinically indicated. Patients were excluded because of previous allergic reactions to iodinated contrast media (n = 5), nephropathy (creatinine level, >120 µmol/L; n = 7), and nonsinus rhythm (n = 3). Thus, a total of 100 patients (38 women, 62 men; mean age, 63.8 years ± 11.6 [standard deviation]; range, 31–84 years) were included in the part of the study comparing CT and conventional coronary angiography.
The patients underwent CT coronary angiography and conventional coronary angiography within a time interval of 8.5 days ± 13.5 (range, 1–68 days). CT was performed in 99 (99%) of 100 patients before conventional coronary angiography. One 31-year-old patient underwent both CT and conventional coronary angiography because he was suspected of having a coronary anomaly at initial conventional angiography and was therefore referred for CT. Patients had experienced stable angina pectoris (n = 83), atypical chest pain in combination with high risk for coronary artery disease (n = 9), or recurrent symptoms after previous balloon angioplasty with (n = 3) or without (n = 5) stent placement. Sixty-five patients (65%) were receiving unchanged β-receptor blocking treatment as part of their baseline medications during both CT and conventional coronary angiography.
Within the same time interval (between October 2004 and July 2005), an additional 110 patients (41 women, 69 men; mean age, 57.7 years ± 15.1; range, 27–85 years) were examined with CT coronary angiography but not with conventional coronary angiography. CT was clinically indicated in all 110 patients. To increase the statistical power, we included the first 50 consecutive patients (19 women, 31 men; mean age, 59.2 years ± 13.2; range, 27–85 years) from among those who underwent 64-section CT coronary angiography within the same time interval in the part of our study analyzing morphologic characteristics of MB as determined with CT. Conventional coronary angiography was not performed in these 50 patients because invasive work-up was not clinically indicated. The patients had experienced atypical chest pain in combination with high risk for coronary artery disease (n = 40) or recurrent symptoms after previous balloon angioplasty with (n = 4) or without (n = 6) stent placement. Thirty-four (68%) of these 50 patients were receiving β-receptor blocking treatment as part of their baseline medications. Thus, morphologic features of MB at CT were investigated in a total of 150 patients (57 women, 93 men; mean age, 60.2 years ± 13.7; range, 27–85 years).
CT Protocol
CT coronary angiography was performed with a 64-section CT system (Somatom Sensation 64; Siemens Medical Solutions, Forchheim, Germany). After a scout scan, 80 mL of iodixanol (Visipaque 320 [320 milligrams of iodine per milliliter]; GE Healthcare, Buckinghamshire, England) followed by 30 mL of saline solution were continuously injected at a flow rate of 5 mL/sec and was controlled with a bolus-tracking technique. Scanning started automatically with a delay of 5 seconds after a predefined threshold of 140 HU was reached in the ascending aorta. Scanning was performed from the tracheal bifurcation to the diaphragm by using the following parameters: physical detector collimation, 32 x 0.6 mm; resulting section collimation, 64 x 0.6 mm by means of a z-flying focal spot (14); gantry rotation time, 330 msec; pitch, 0.2; tube potential, 120 kV; and tube current–time product, 650 mAs (effective). The reconstructed field of view was individually adjusted to encompass the heart (mean field of view, 148 mm ± 22; range, 121–178 mm; image matrix, 512 x 512 pixels). Electrocardiographic dose modulation was not implemented in this study, to enable sufficient image quality. Synchronized to the electrocardiographic data, 10 CT data sets with a section thickness of 1.0 mm (increment, 0.8 mm) and a medium soft-tissue convolution kernel (B30f) were retrospectively reconstructed from 10% to 100% of the cardiac cycle in 10% steps of the R-R interval. The "adaptive cardio volume" approach was used for image reconstruction (15). Electrocardiographic pulsing for radiation dose reduction was not applied so that we could obtain sufficient image quality for coronary arteries in systole (16–20).
CT Image Analysis
Reconstructed images were anonymized and evaluated at an external workstation (Leonardo; Siemens Medical Solutions) for all 15 coronary artery segments defined according to the guidelines of the American Heart Association (21). Coronary artery segments with a luminal diameter of less than 1.5 mm at their origin were excluded from analysis.
CT data were analyzed in consensus by two readers (S.L., with 5 years of experience in cardiovascular radiology, and H.A., with 8 years of experience) who were both blinded to the clinical history and to the results of conventional coronary angiography. First, the reconstruction interval with the smallest degree of motion artifacts was identified for each patient. In that reconstruction interval, the image quality of each coronary artery segment was classified by both observers as being diagnostic (no or moderate artifacts, acceptable for evaluation) or not evaluable (severe artifacts impairing evaluation). Then, the end-systolic and end-diastolic phases were defined as the last reconstruction interval with an opened and closed aortic valve, respectively, to obtain the appropriate reconstruction time points within the cardiac cycle for measurements of systolic compression.
Multiplanar and curved planar reformations were used for depiction of MB in at least two planes—one parallel and one perpendicular to the course of the vessel. MB was defined as when part of a coronary artery was completely surrounded by myocardium. The location of the tunneled segment was noted, and the length and depth of the segment were measured on ribbon planar reformations by using dedicated vessel analysis software (Card IQ, Advantage Workstation 4.0; GE Medical Systems, Milwaukee, Wis). The mean vessel diameter of the tunneled segment at maximum depth was measured on magnified views in two planes—one parallel and one perpendicular to the course of the vessel—by using electronic calipers. Vessel diameter measurements were performed in both the end-systolic and end-diastolic phase. The degree of systolic compression was given as a percentage and was calculated from the mean of these four measurements in end systole and four measurements in end diastole (Fig 1a). Depth, length, and systolic compression were measured in consensus by the readers twice, and the average of the two measurements was used for further analysis.
View larger version (138K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1a: MB in distal left anterior descending (LAD) artery in 46-year-old woman that was identified with 64-section CT and conventional coronary angiography. (a) Ribbon planar reformations of CT data in end diastole (upper image; 100% of R-R interval) and end systole (lower image; 30% of R-R interval) illustrate systolic compression of tunneled segment. 1–6, Perpendicular views of coronary artery proximal (1 and 4), within (2 and 5, arrow), and distal (3 and 6) to tunneled segment depict systolic compression. Comparison of luminal vessel diameter between end diastole and end systole revealed luminal diameter narrowing of 38% at CT. Tunneled segment length was 33 mm; depth was 2.8 mm. (b) Corresponding conventional coronary angiogram in right anterior oblique view in end diastole (upper image) and end systole (lower image) demonstrates the step down–step up phenomenon without milking effect (arrow). Systolic compression, as calculated at conventional angiography, was 33%.
|
|
View larger version (98K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1b: MB in distal left anterior descending (LAD) artery in 46-year-old woman that was identified with 64-section CT and conventional coronary angiography. (a) Ribbon planar reformations of CT data in end diastole (upper image; 100% of R-R interval) and end systole (lower image; 30% of R-R interval) illustrate systolic compression of tunneled segment. 1–6, Perpendicular views of coronary artery proximal (1 and 4), within (2 and 5, arrow), and distal (3 and 6) to tunneled segment depict systolic compression. Comparison of luminal vessel diameter between end diastole and end systole revealed luminal diameter narrowing of 38% at CT. Tunneled segment length was 33 mm; depth was 2.8 mm. (b) Corresponding conventional coronary angiogram in right anterior oblique view in end diastole (upper image) and end systole (lower image) demonstrates the step down–step up phenomenon without milking effect (arrow). Systolic compression, as calculated at conventional angiography, was 33%.
|
|
Conventional Coronary Angiography
Conventional coronary angiography was performed by one cardiologist (F.R.E., with 13 years of experience in performing conventional coronary angiography) according to standard techniques, and multiple views were stored on a compact disc. Briefly, conventional coronary angiography was performed with a transradial or transfemoral approach, and at least two different projections for each coronary artery were obtained after intracoronary application of iodinated contrast material. The angiograms were evaluated in consensus by two cardiologists (P.K. and F.R.E., with 4 and 13 years of experience in interventional cardiology, respectively) who were both blinded to the clinical history and the results of CT coronary angiography. Analysis of conventional coronary angiographic data was performed in two steps: First, all angiograms were reviewed by both readers, and each vessel segment was visually analyzed for the presence of MB on the basis of the following indirect signs: systolic diameter narrowing; milking effect, defined as diameter narrowing limited to a restricted vessel segment with extraction of contrast agent not explainable by normal coronary artery flow; and/or the step down–step up phenomenon, defined as a localized change in direction of the vessel course toward the ventricle (1,8). Second, if MB was considered to be present, the grade of systolic diameter narrowing was determined—similarly to how the CT measurements were determined—by comparing the luminal diameter within the bridged segments in end systole and end diastole with automated quantitative coronary angiography software (Fig 1b). The coronary artery tree was subdivided according to the same guidelines (21) as for CT analysis.
Statistical Analysis
In the descriptive statistical analysis, quantitative variables were expressed as means ± standard deviations, and categoric variables were expressed as frequencies or percentages. The Wilcoxon two-sample test was used to compare quantitative parameters (eg, age, body mass index, and mean heart rate) between patients with and those without MB. The Fisher exact test was used to evaluate categoric data (eg, sex, β-blocking medication). Pearson correlation analysis was used to analyze the relation between length, depth, and degree of systolic compression of the tunneled segment as assessed with CT. For the purpose of this comparison, we included the additional 50 patients who underwent CT (described above) in our study to increase the statistical power of the analysis. Pearson correlation analysis was also performed to compare the degree of systolic compression assessed with conventional coronary angiography with that assessed with CT. All instances of MB were treated as independent rather than clustered observations, because none of the patients had more than one lesion.
The Wilcoxon two-sample test was used to compare length, depth, and systolic compression of the tunneled segment (as measured with CT) between patients with MB identified with conventional coronary angiography and patients in whom MB remained unidentified at conventional coronary angiography. P < .05 was considered to indicate a statistically significant difference. All statistical analyses were performed by using a commercially available software package (SPSS, version 12.0; SPSS, Chicago, Ill).
|
RESULTS
|
|---|
With CT, a total of 2177 segments were evaluated in 150 patients (34 segments were missing because of anatomic variations, and 39 segments had a diameter < 1.5 mm at their origin). CT image quality was rated as being diagnostic in 2130 (97.8%) and not evaluative in 47 (2.2%) of all 2177 segments when the reconstruction interval was used as described above.
The end of systole took place at variable time intervals from 20%–50% of the R-R interval, depending on the heart rate during scanning (mean percentage of the R-R interval, 32.5% ± 9.1). The end of diastole was found to occur between 90% and 10% of the R-R interval (mean, 97.1% ± 8.6).
Depiction Rate of MB with CT and Conventional Coronary Angiography
In the 100 patients who underwent both conventional coronary angiography and CT, MB was detected with conventional coronary angiography in 12 (12%) patients and with CT in 26 (26%) patients. Conventional coronary angiography failed to identify MB in 14 (54%) of the 26 patients with MB detected with CT. CT enabled direct identification of MB by visualization of the intramyocardial course of the coronary segments in all 26 patients. Indirect identification of MB with conventional coronary angiography in the 12 patients was based on the step down–step up phenomenon (n = 4), the milking effect (n = 6), and systolic compression (n = 12). MB was suspected at conventional coronary angiography in the middle part of the LAD artery in one patient (on the basis of a supposed step down–step up phenomenon and a calculated systolic compression of 11%), while CT demonstrated an entirely epicardial course of the artery.
Morphologic Characteristics of MB at CT
Among the 150 patients who underwent 64-section CT, MB was detected in 43 (28.7%) (Table E1, http://radiology.rsnajnls.org/cgi/content/full/2463062071/DC1). Including the additional 50 patients who underwent CT only, 43 instead of only 26 patients with MB were available for determining the relationship between the different morphologic features of MB at CT. In these 43 patients, the tunneled segments were located in the middle part of the LAD artery (n = 22), the distal part of the LAD artery (n = 20), and the proximal part of the right coronary artery (n = 1) (Figs 2, 3). Single-site involvement was found in all patients.
View larger version (93K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2a: MB of distal LAD artery in 47-year-old man that was identified with both 64-section CT and conventional coronary angiography. (a) Conventional angiogram (right anterior oblique projection in diastole) demonstrates normal distal LAD artery (ar-row). (b) Conventional angiogram (right anterior oblique projection in systole) shows considerable luminal diameter narrowing (arrow) that was calculated to be 52%. (c) Curved planar CT reconstruction in end diastole (10% of R-R interval) along center line of LAD artery directly depicts intramyocardial course of the vessel segment. 1–3, Perpendicular cuts proximal (1), within (2), and distal (3) to the tunneled segment show covering of the tunneled segment with myocardium (arrow).
|
|
View larger version (96K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2b: MB of distal LAD artery in 47-year-old man that was identified with both 64-section CT and conventional coronary angiography. (a) Conventional angiogram (right anterior oblique projection in diastole) demonstrates normal distal LAD artery (ar-row). (b) Conventional angiogram (right anterior oblique projection in systole) shows considerable luminal diameter narrowing (arrow) that was calculated to be 52%. (c) Curved planar CT reconstruction in end diastole (10% of R-R interval) along center line of LAD artery directly depicts intramyocardial course of the vessel segment. 1–3, Perpendicular cuts proximal (1), within (2), and distal (3) to the tunneled segment show covering of the tunneled segment with myocardium (arrow).
|
|
View larger version (145K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2c: MB of distal LAD artery in 47-year-old man that was identified with both 64-section CT and conventional coronary angiography. (a) Conventional angiogram (right anterior oblique projection in diastole) demonstrates normal distal LAD artery (ar-row). (b) Conventional angiogram (right anterior oblique projection in systole) shows considerable luminal diameter narrowing (arrow) that was calculated to be 52%. (c) Curved planar CT reconstruction in end diastole (10% of R-R interval) along center line of LAD artery directly depicts intramyocardial course of the vessel segment. 1–3, Perpendicular cuts proximal (1), within (2), and distal (3) to the tunneled segment show covering of the tunneled segment with myocardium (arrow).
|
|
View larger version (148K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a: MB of proximal right coronary artery (RCA) in 51-year-old man that was identified with 64-section CT coronary angiography. (a) Curved planar CT reconstruction in end diastole (100% of R-R interval) shows origin of LAD artery, left circumflex (CX) artery, and right coronary artery. The proximal segment of the right coronary artery courses through the right ventricular myocardium (dotted circle). In systole, the compression of the tunneled segment was calculated to be 6%. (b) Volume-rendered CT image in end diastole (100% of R-R interval) in right anterior oblique view depicts tunneled proximal right coronary artery segment (dotted circle in magnified view). (c) Conventional coronary angiogram of right coronary artery (arrow) during systole shows no compression and no milking effect in the segment; thus, the diagnosis of MB was not made with conventional angiography.
|
|
View larger version (134K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b: MB of proximal right coronary artery (RCA) in 51-year-old man that was identified with 64-section CT coronary angiography. (a) Curved planar CT reconstruction in end diastole (100% of R-R interval) shows origin of LAD artery, left circumflex (CX) artery, and right coronary artery. The proximal segment of the right coronary artery courses through the right ventricular myocardium (dotted circle). In systole, the compression of the tunneled segment was calculated to be 6%. (b) Volume-rendered CT image in end diastole (100% of R-R interval) in right anterior oblique view depicts tunneled proximal right coronary artery segment (dotted circle in magnified view). (c) Conventional coronary angiogram of right coronary artery (arrow) during systole shows no compression and no milking effect in the segment; thus, the diagnosis of MB was not made with conventional angiography.
|
|
View larger version (94K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3c: MB of proximal right coronary artery (RCA) in 51-year-old man that was identified with 64-section CT coronary angiography. (a) Curved planar CT reconstruction in end diastole (100% of R-R interval) shows origin of LAD artery, left circumflex (CX) artery, and right coronary artery. The proximal segment of the right coronary artery courses through the right ventricular myocardium (dotted circle). In systole, the compression of the tunneled segment was calculated to be 6%. (b) Volume-rendered CT image in end diastole (100% of R-R interval) in right anterior oblique view depicts tunneled proximal right coronary artery segment (dotted circle in magnified view). (c) Conventional coronary angiogram of right coronary artery (arrow) during systole shows no compression and no milking effect in the segment; thus, the diagnosis of MB was not made with conventional angiography.
|
|
In these 150 patients, the mean length of the tunneled segment as assessed with CT was 24.3 mm ± 10.0 (range, 8–50 mm) (first measurement: 24.5 mm ± 10.2 [range, 8–47 mm]; second measurement: 24.2 mm ± 10.1 [range, 8–53 mm]), and the mean depth was 2.6 mm ± 0.8 (range, 1.4–4.8 mm) (first measurement: 2.6 mm ± 0.8 [range, 1.5–5.3 mm]; second measurement: 2.6 mm ± 0.8 [range, 1.1–4.6 mm]). The mean systolic compression of the tunneled segment as assessed with CT was 15.6% ± 13.6 (range, 0%–45%).
No significant correlation was found between the percentage of systolic compression and the length of the tunneled segment as assessed with CT (r = 0.16, P = .25) (Fig 4a). In contrast, a significant correlation was found between the percentage of systolic compression and the depth of the tunneled segment (r = 0.65, P < .01) (Fig 4b). Regarding demographic data and distribution of MB in patients with stable angina pectoris and atypical chest pain and patients with recurrent symptoms after previous balloon angioplasty (Table), no statistically significant difference was present for age (P = .86), body mass index (P = .34), mean heart rate (P = .69), sex (P = .82), and β-receptor blocker treatment (P = .54) between patients with and patients without MB.
View larger version (13K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4a: (a) Linear regression plot of percentage of systolic compression as measured with 64-section CT coronary angiography in all 43 patients with MB versus tunneled segment length. Dashed lines represent 95% confidence limits. Linear correlation indicates no significant relation between percentage of systolic compression and tunneled segment length (Pearson correlation, r = 0.16; P = .25). n.s. = Not significant. (b) Linear regression plot of percentage systolic compression measured with CT in all 43 patients with MB versus tunneled segment depth. Dashed lines represent 95% confidence limits. Linear correlation indicates significant relation between the percentage of systolic compression and tunneled segment depth (Pearson correlation, r = 0.65; P < .01).
|
|
View larger version (14K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4b: (a) Linear regression plot of percentage of systolic compression as measured with 64-section CT coronary angiography in all 43 patients with MB versus tunneled segment length. Dashed lines represent 95% confidence limits. Linear correlation indicates no significant relation between percentage of systolic compression and tunneled segment length (Pearson correlation, r = 0.16; P = .25). n.s. = Not significant. (b) Linear regression plot of percentage systolic compression measured with CT in all 43 patients with MB versus tunneled segment depth. Dashed lines represent 95% confidence limits. Linear correlation indicates significant relation between the percentage of systolic compression and tunneled segment depth (Pearson correlation, r = 0.65; P < .01).
|
|
View this table:
[in this window]
[in a new window]
|
Demographic and Clinical Data and Depiction Rate of MB in Patient Subgroups at 64-Section CT Coronary Angiography
|
|
Comparison of Morphology of MB between CT and Conventional Coronary Angiography
Among the 43 patients with MB identified at CT, 26 had conventional coronary angiographic data available (Table E1, http://radiology.rsnajnls.org/cgi/content/full/2463062071/DC1). The length (mean, 28.3 mm ± 11.1; range, 12–50 mm) of the tunneled segments identified with conventional coronary angiography was significantly higher than the length (mean, 20.9 mm ± 8.4; range, 8–34 mm) of the tunneled segments missed at conventional coronary angiography (P < .001). Similarly, the depth (mean, 2.9 mm ± 0.5; range, 2.0–4.1 mm) of the tunneled segments identified with conventional coronary angiography was significantly greater than the depth (mean, 2.6 mm ± 0.9; range, 1.4–4.2 mm) of the tunneled segments that were missed at conventional coronary angiography (P < .01).
The percentage of systolic compression as assessed with CT (mean, 31.3% ± 11.0; range, 9%–45%) significantly correlated with measurements obtained at conventional coronary angiography (mean, 28.2% ± 10.5; range, 10%–52%) (n = 12, r = 0.72, P < .001) (Fig 5).
View larger version (15K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5: Linear regression plot shows percentage of systolic compression in the 12 patients in whom MB was identified with both 64-section CT and conventional coronary angiography (CCA). Linear correlation between the percentage of systolic compression calculated with conventional coronary angiography and that calculated with CT indicates similar measurements between modalities (Pearson correlation, r = 0.72; P < .001).
|
|
The percentage of systolic compression as assessed with CT and conventional coronary angiography (n = 12; mean, 31.3% ± 11.0; range, 9%–45%) was significantly higher than the percentage of systolic compression at CT in the patients in whom conventional coronary angiography failed to demonstrate MB (n = 14; mean, 9.9% ± 6.7; range, 0%–23%; P < .001). In two (14%) of these 14 patients with no MB at conventional coronary angiography, no systolic compression could be found with CT.
|
DISCUSSION
|
|---|
We found a higher depiction rate of MB with direct visualization at CT than with indirect visualization with conventional coronary angiography. Sixty-four–section CT enabled us to determine morphologic characteristics such as length and depth of the tunneled segments and allowed quantification of the degree of systolic compression with results comparable to those at conventional coronary angiography. The depth but not the length of the tunneled segment significantly correlated with the percentage of systolic compression, a finding that—to the best of our knowledge—has not been reported before.
The large discrepancy between the prevalence of MB in autopsy studies of 15%–85% (1,9) and the depiction rate of MB in conventional coronary angiography studies of 0.5%–4.5% (5,10) indicates the absence of an accurate reference imaging modality. On one hand, autopsy studies (1) may have overestimated the true prevalence of MB by including only selected patients (9). On the other hand, conventional coronary angiography is likely to underestimate the prevalence of MB by delivering a visualization that is limited to the vessel lumen and thus necessitating that investigators rely on indirect signs (12). Even though demonstration of systolic compression and the milking effect is considered diagnostic (8), the signs are rather insensitive in shallow variants of MB that demonstrate only minimal or no systolic compression (7,22). Similarly, the step down–step up phenomenon may be absent in superficial variants of MB.
In an autopsy study, Ferreira and colleagues (7) distinguished two types of MB: superficial bridges crossing the artery perpendicularly or at an acute angle toward the apex and deep bridges characterized by muscle bundles arising from the right ventricular apical trabeculae that cross the affected artery transversely, obliquely, or helically before terminating in the interventricular septum. Ferreira et al (7) hypothesized that systolic compression would be minimal or absent in the first type and markedly present in the latter type, where the bridging myocardium would twist and constrict the tunneled segment (22).
The higher depiction rate of MB with conventional coronary angiography in our study (12%) compared with depiction rates reported in the conventional coronary angiography literature (0.5%–4.5%) (5,10) may reflect increased recognition resulting from review of the angiograms with the specific purpose of detecting the anomaly. The depiction rate of MB at CT in our study was 28.7%, which is in line with the average of autopsy study data, which reveals a prevalence of MB of one-third in adults (1). Compared with conventional coronary angiography, CT enables direct visualization of coronary arteries, including surrounding tissue, and thus allows the depiction of tunneled segments even when there is only minimal or no systolic compression and no change in vessel course. The difference in the depiction rate of MB between conventional coronary angiography and CT was significantly related to length, depth, and degree of systolic compression. Although we had no autopsy proof in our patients to indicate the correctness of the CT findings, more than half of the tunneled segments were missed with conventional coronary angiography, suggesting that recognition of MB by visual estimation at conventional angiography is limited to segments with systolic compression of more than 20%.
MB is generally considered a benign condition, with a reported 5-year survival rate of more than 97% (23). However, MB has infrequently been associated with unstable angina, myocardial infarction, conduction disturbances, and sudden cardiac death (2–6). In addition, the segment immediately proximal to MB frequently shows a disproportionate degree of atherosclerotic plaque formation that has been explained by low wall shear stress proximal to the MB promoting atherosclerotic plaque formation, whereas the high wall shear stress within the tunneled segment is thought to be protective (1,24). Therefore, even MB without systolic compression may represent a vulnerable site of the coronary artery tree, and early identification with CT coronary angiography could become important. Association between ischemic symptoms and the length of the tunneled segment or the degree of systolic compression has been inconsistently reported (1,7). Some reports described an increased likelihood of ischemia (25) and risk for sudden death in deep tunneled segments (7). As demonstrated in our study, the percentage of systolic compression significantly correlated with the depth of MB, while the length of the tunneled segment showed no relationship with the degree of systolic compression.
Our study had limitations. First, conventional coronary angiographic data were not available in all 150 patients examined with CT. Therefore, we have no proof that the cohort of the additional 50 patients who underwent CT only would behave in the same way as the main cohort of 100 patients who underwent CT and conventional coronary angiography. As a matter of fact, the inclusion criteria and indications for conventional coronary angiography were different for the 100 patients who underwent both conventional coronary angiography and CT and the 50 patients who underwent CT only. In addition, length and depth measurements could only be obtained with CT. We could not include a reference standard for these measurements. Second, the presence or absence of MB at conventional coronary angiography was visually estimated. This might be inferior to a quantitative analysis with conventional coronary angiography in all patients and segments and could explain some of the discrepancy in depiction rate between the methods. On the other hand, visual appreciation of conventional coronary angiography data with regard to the presence of MB represents the common method of conventional coronary angiography interpretation in daily clinical practice.
Third, image quality impairment in systole may have rendered vessel diameter measurements with CT inaccurate. Nevertheless, measurements of systolic compression with CT significantly correlated with values obtained at quantitative coronary angiography. Fourth, we did not use electrocardiographic pulsing in our patients. This algorithm has been shown to be effective in reducing the radiation dose at CT coronary angiography from approximately 14.8 to 9.4 mSv (26). Because our patients were primarily enrolled in a study investigating the ability of 64-section CT in the detection of coronary stenosis, electrocardiographic pulsing was waived to allow us to be able to reconstruct images in systole for the diagnostic accuracy study and to analyze the degree of systolic compression of coronary segments in the present study.
Fifth, our measurements of systolic compression with CT may be inaccurate because of motion artifacts and limitations in spatial resolution. Therefore, our measurements should be considered as an approximation of the real systolic compression of the tunneled segments. To reduce inaccuracies, we performed all measurements in two perpendicular planes twice and calculated the average. Because of this, values obtained at CT correlated well with the results of conventional coronary angiography, which may indicate that CT measurements are at least partially reliable. Finally, our study did not investigate the relationship between MB and clinical symptoms; this limits the clinical relevance of the results.
In conclusion, 64-section CT coronary angiography enables the depiction of MB through direct visualization of the tunneled coronary segment and surrounding myocardium with a higher rate than that at conventional coronary angiography. Depth but not length of the tunneled segment correlated with the degree of systolic compression of MB segments.
|
ADVANCES IN KNOWLEDGE
|
|---|
- The depiction rate of myocardial bridging (MB) with 64-section CT (26 [26%] of 100) is greater than that with conventional coronary angiography (12 [12%] of 100).
- The degree of systolic compression significantly correlates with depth (P < .01) but not length (P = .25) of the tunneled coronary segment.
|
IMPLICATION FOR PATIENT CARE
|
|---|
- Sixty-four–section CT coronary angiography allows the noninvasive identification and morphologic evaluation of MB with a higher depiction rate than that at conventional coronary angiography.
|
FOOTNOTES
|
|---|
Abbreviations: LAD = left anterior descending • MB = myocardial bridging
Author contributions: Guarantors of integrity of entire study, S.L., P.K., F.R.E., H.A.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, S.L., L.H., A.P., R.V., T.S., F.R.E., P.A.K., H.A.; clinical studies, all authors; statistical analysis, S.L., O.G., H.A.; and manuscript editing, all authors.
Authors stated no financial relationship to disclose.
|
References
|
|---|
- Mohlenkamp S, Hort W, Ge J, Erbel R. Update on myocardial bridging. Circulation 2002;106:2616–2622. [Free Full Text]
- Kracoff OH, Ovsyshcher I, Gueron M. Malignant course of a benign anomaly: myocardial bridging. Chest 1987;92:1113–1115. [CrossRef][Medline]
- Bestetti RB, Finzi LA, Amaral FT, Secches AL, Oliveira JS. Myocardial bridging of coronary arteries associated with an impending acute myocardial infarction. Clin Cardiol 1987;10:129–131. [Medline]
- Bestetti RB, Oliveira JS. Myocardial bridging of a coronary artery: a not-so-benign anomaly. Chest 1989;95:706–707. [Medline]
- Noble J, Bourassa MG, Petitclerc R, Dyrda I. Myocardial bridging and milking effect of the left anterior descending coronary artery: normal variant or obstruction? Am J Cardiol 1976;37:993–999. [CrossRef][Medline]
- Tauth J, Sullebarger T. Myocardial infarction associated with myocardial bridging: case history and review of the literature. Cathet Cardiovasc Diagn 1997;40:364–367. [CrossRef][Medline]
- Ferreira AG Jr, Trotter SE, Konig B Jr, Decourt LV, Fox K, Olsen EG. Myocardial bridges: morphological and functional aspects. Br Heart J 1991;66:364–367. [Abstract/Free Full Text]
- Irvin RG. The angiographic prevalence of myocardial bridging in man. Chest 1982;81:198–202. [CrossRef][Medline]
- Polacek P, Kralove H. Relation of myocardial bridges and loops on the coronary arteries to coronary occlusions. Am Heart J 1961;61:44–52. [CrossRef][Medline]
- Rossi L, Dander B, Nidasio GP, et al. Myocardial bridges and ischemic heart disease. Eur Heart J 1980;1:239–245. [Abstract/Free Full Text]
- Kulkarni M, Sodani A, Rosita, Puranik C, Sullere S, Saha B. Right myocardial bridge on CT coronary angiography. J Assoc Physicians India 2004;52:661–662. [Medline]
- Goitein O, Lacomis JM. Myocardial bridging: noninvasive diagnosis with multidetector CT. J Comput Assist Tomogr 2005;29:238–240. [CrossRef][Medline]
- Amoroso G, Battolla L, Gemignani C, et al. Myocardial bridging on left anterior descending coronary artery evaluated by multidetector computed tomography. Int J Cardiol 2004;95:335–337. [CrossRef][Medline]
- Flohr T, Stierstorfer K, Raupach R, Ulzheimer S, Bruder H. Performance evaluation of a 64-slice CT system with z-flying focal spot. Rofo 2004;176:1803–1810. [Medline]
- Flohr T, Ohnesorge B. Heart rate adaptive optimization of spatial and temporal resolution for electrocardiogram-gated multislice spiral CT of the heart. J Comput Assist Tomogr 2001;25:907–923. [CrossRef][Medline]
- Ehara M, Surmely JF, Kawai M, et al. Diagnostic accuracy of 64-slice computed tomography for detecting angiographically significant coronary artery stenosis in an unselected consecutive patient population: comparison with conventional invasive angiography. Circ J 2006;70:564–571. [CrossRef][Medline]
- Leschka S, Alkadhi H, Plass A, et al. Accuracy of MSCT coronary angiography with 64-slice technology: first experience. Eur Heart J 2005;26:1482–1487. [Abstract/Free Full Text]
- Mollet NR, Cademartiri F, van Mieghem CA, et al. High-resolution spiral computed tomography coronary angiography in patients referred for diagnostic conventional coronary angiography. Circulation 2005;112:2318–2323. [Abstract/Free Full Text]
- Pugliese F, Mollet NR, Runza G, et al. Diagnostic accuracy of non-invasive 64-slice CT coronary angiography in patients with stable angina pectoris. Eur Radiol 2006;16:575–582. [CrossRef][Medline]
- Raff GL, Gallagher MJ, O'Neill WW, Goldstein JA. Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography. J Am Coll Cardiol 2005;46:552–557. [Abstract/Free Full Text]
- Austen WG, Edwards JE, Frye RL, et al. A reporting system on patients evaluated for coronary artery disease: report of the Ad Hoc Committee for Grading of Coronary Artery Disease, Council on Cardiovascular Surgery, American Heart Association. Circulation 1975;51:5–40. [Medline]
- Alegria JR, Herrmann J, Holmes DR Jr, Lerman A, Rihal CS. Myocardial bridging. Eur Heart J 2005;26:1159–1168. [Abstract/Free Full Text]
- Kramer JR, Kitazume H, Proudfit WL, Sones FM Jr. Clinical significance of isolated coronary bridges: benign and frequent condition involving the left anterior descending artery. Am Heart J 1982;103:283–288. [CrossRef][Medline]
- Malek AM, Alper SL, Izumo S. Hemodynamic shear stress and its role in atherosclerosis. JAMA 1999;282:2035–2042. [Abstract/Free Full Text]
- Morales AR, Romanelli R, Tate LG, Boucek RJ, de Marchena E. Intramural left anterior descending coronary artery: significance of the depth of the muscular tunnel. Hum Pathol 1993;24:693–701. [CrossRef][Medline]
- Hausleiter J, Meyer T, Hadamitzky M, et al. Radiation dose estimates from cardiac multislice computed tomography in daily practice: impact of different scanning protocols on effective dose estimates. Circulation 2006;113:1305–1310. [Abstract/Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
P. J. Kim, G. Hur, S. Y. Kim, J. Namgung, S. W. Hong, Y. H. Kim, and W. R. Lee
Frequency of Myocardial Bridges and Dynamic Compression of Epicardial Coronary Arteries: A Comparison Between Computed Tomography and Invasive Coronary Angiography
Circulation,
March 17, 2009;
119(10):
1408 - 1416.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. Sundaram, S. Patel, N. Bogot, and E. A. Kazerooni
Anatomy and Terminology for the Interpretation and Reporting of Cardiac MDCT: Part 1, Structured Report, Coronary Calcium Screening, and Coronary Artery Anatomy
Am. J. Roentgenol.,
March 1, 2009;
192(3):
574 - 583.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
