DOI:10.2214/AJR.05.0242
AJR 2007; 188:W17-W20
© American Roentgen Ray Society
Myocardial Bridging of the Left Anterior Descending Coronary Artery and Anomalous Origin of Circumflex Coronary Artery: Preoperative Assessment with MDCT
Pietro Spagnolo1,
Sandro Sironi2,3,4,
Toufik Khouri5,
Giacomo Garlaschi1 and
Ferruccio Fazio2,3,6
1 Department of Radiology, University of Genova, Genova, Italy.
2 University Milano-Bicocca School of Medicine, Milan, Italy.
3 IBFM-CNR, Institute for Molecular Bioimaging and Physiology, Milan,
Italy.
4 Department of Diagnostic Radiology, H. S. Gerardo, Monza, Milan, Italy.
5 Department of Radiology, Policlinico di Monza, Monza, Milan, Italy.
6 Division of Nuclear Medicine, Scientific Institute H. S. Raffaele, Milan,
Italy.
Received February 12, 2005;
accepted after revision June 7, 2005.
Address correspondence to S. Sironi, University of Milano-Bicocca,
Department of Diagnostic Radiology, H. S. Gerardo, Monza, Milan, Italy
(sandrosironi{at}libero.it).
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Keywords: coronary arteries • CT coronary arteriography • cardiovascular disease • MDCT
Introduction
Myocardial bridging is anatomically defined as the muscle overlying the
intramural segment of a major epicardial coronary artery—mainly the
midportion of the left anterior descending (LAD) coronary artery. This
congenital variation has been associated with myocardial ischemia, conduction
disturbances, myocardial infarction, and sudden death
[1]. The pathophysiology of
myocardial bridges is characterized by external phasic systolic vessel
compression with a persistent mid to late diastolic diameter reduction
[2]. Percutaneous transluminal
coronary angioplasty with stent placement, traditional coronary artery bypass
grafting, and longitudinal myotomy of the overlying myocardial tissue band
have all been used to treat symptomatic patients refractory to medical
management [1].
We report the case of a patient with symptomatic myocardial bridging of the
LAD coronary artery evaluated using MDCT for preoperative assessment.
Case Report
A 38-year-old man presented for evaluation of retrosternal chest pain. He
had a history of smoking as a risk factor for coronary artery disease.
Physical examination findings were unremarkable, and ECG showed sinus rhythm.
The results of blood tests, including a complete blood count, electrolytes,
liver enzymes, and a lipid profile, were in the normal ranges. Exercise
tolerance testing using bicycle ergometry showed significant ST segment
depression in the anterior leads. Cardiac catheterization revealed a
hypoplastic right coronary artery and myocardial bridging of the mid LAD
coronary artery but was unable to show the circumflex artery (Figs.
1A and
1B). The coronary segments
visualized were free from atherosclerotic lesions.
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Fig. 1A —38-year-old man with history of smoking who presented for
evaluation of chest pain. Exercise tolerance testing using bicycle ergometry
showed significant ST segment depression in anterior leads. Cardiac
catheterization revealed hypoplastic right coronary artery and myocardial
bridging of mid left anterior descending (LAD) coronary artery but was unable
to show circumflex artery. Coronary angiograms of mid LAD coronary artery in
diastole (A) and systole (B) show systolic constriction
(arrows), which is consistent with myocardial bridging.
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Fig. 1B —38-year-old man with history of smoking who presented for
evaluation of chest pain. Exercise tolerance testing using bicycle ergometry
showed significant ST segment depression in anterior leads. Cardiac
catheterization revealed hypoplastic right coronary artery and myocardial
bridging of mid left anterior descending (LAD) coronary artery but was unable
to show circumflex artery. Coronary angiograms of mid LAD coronary artery in
diastole (A) and systole (B) show systolic constriction
(arrows), which is consistent with myocardial bridging.
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The patient underwent contrast-enhanced MDCT of the coronary arteries. A
16-MDCT scanner was used (LightSpeed 16, GE Healthcare). Angiographic CT was
performed after IV administration of 120 mL of nonionic contrast material
(iohexol [Omnipaque 350, Amersham Health]) at a flow rate of 4.5 mL/s followed
by a 40-mL saline bolus chaser administered at the same flow rate as the
contrast material with the use of a double-head injector. The patient's heart
rate was 70 beats per minute (bpm), and additional ß-receptor blocking
medication (100 mg of metoprolol) was administered 60 minutes before the
examination.
Scanning was performed in 19 seconds, during which the patient's heart rate
ranged from 59 to 62 bpm. The main scanning parameters were as follows:
detector number, 16; 120 kVp; 370 mAs; scanning time delay, 20 seconds;
effective slice width, 0.625; and effective dose, 5.8 mSv. Retrospective
ECG-gated reconstructions were obtained from 40% to 80% at every 10% of the
R-R interval; the best data sets were acquired at 70% of the cardiac
cycle.
Postprocessing was performed on a workstation (Advantage 4.2, GE
Healthcare) using multiplanar reformation, maximum intensity projection, and
direct volume rendering. Contrast-enhanced MDCT examination revealed the
circumflex artery arising from a separate orifice of the right sinus of
Valsalva, which had a benign retroaortic course
(Fig. 1C). Contrast-enhanced
MDCT showed lack of atherosclerotic lesions in all of the coronary segments
documented and confirmed myocardial bridging of the mid LAD coronary artery as
the only cause of angina.
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Fig. 1C —38-year-old man with history of smoking who presented for
evaluation of chest pain. Exercise tolerance testing using bicycle ergometry
showed significant ST segment depression in anterior leads. Cardiac
catheterization revealed hypoplastic right coronary artery and myocardial
bridging of mid left anterior descending (LAD) coronary artery but was unable
to show circumflex artery. Volume-rendering image shows anomalous origin of
circumflex artery (arrow) arising from right sinus of Valsalva.
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Medical therapy based on ß-blockers and a calcium channel antagonist
was initiated and administered for 5 weeks, but no significant improvement in
the patient's clinical symptoms was achieved; therefore, the patient was
scheduled for surgery.
MDCT examination allowed a more accurate preoperative evaluation of this
patient than the angiographic study did. The myocardial bridge of the LAD
coronary artery measured 35 mm in length and had a maximum width of
approximately 3 mm (Figs. 1D
and 1E). MDCT examination also
showed that less than 3 mm of endocardial wall separated the tunneled segment
from the right ventricular cavity (Fig.
1F). All these morphologic data were important in choosing the
approach: a longitudinal myotomy approach via median sternotomy. In fact,
because of the close pathway to the right ventricular chamber, surgical vessel
dissection was performed with an oblique orientation from the left side of the
interventricular groove toward the right side, thus avoiding possible injury
to the ventricular wall.
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Fig. 1D —38-year-old man with history of smoking who presented for
evaluation of chest pain. Exercise tolerance testing using bicycle ergometry
showed significant ST segment depression in anterior leads. Cardiac
catheterization revealed hypoplastic right coronary artery and myocardial
bridging of mid left anterior descending (LAD) coronary artery but was unable
to show circumflex artery. Coronary angiogram shows tunneled segment of mid
LAD coronary artery (arrows).
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Fig. 1E —38-year-old man with history of smoking who presented for
evaluation of chest pain. Exercise tolerance testing using bicycle ergometry
showed significant ST segment depression in anterior leads. Cardiac
catheterization revealed hypoplastic right coronary artery and myocardial
bridging of mid left anterior descending (LAD) coronary artery but was unable
to show circumflex artery. Multiplanar reformation (MPR) image corresponding
to D clearly displays same segment of mid LAD coronary artery (thin
arrows) surrounded by myocardium (thick arrow).
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Fig. 1F —38-year-old man with history of smoking who presented for
evaluation of chest pain. Exercise tolerance testing using bicycle ergometry
showed significant ST segment depression in anterior leads. Cardiac
catheterization revealed hypoplastic right coronary artery and myocardial
bridging of mid left anterior descending (LAD) coronary artery but was unable
to show circumflex artery. MPR image shows myocardial bridging in mid LAD
coronary artery and its morphologic features: thickness, length, and depth of
tunneled artery and distance from endocardial surface of ventricular wall.
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The patient was discharged 4 days later after an uneventful postoperative
course. Six weeks after surgery, the bicycle ergometry stress test results
were normal. The patient has remained asymptomatic for 7 months.
Discussion
A myocardial bridge is the most common congenital coronary anomaly, with an
incidence of between 1.5% and 16% as assessed on coronary angiography and up
to 80% as assessed at necroscopy. Although in most patients it has been
considered a harmless vessel malformation, clinically relevant complications
may occur such as anginal symptoms, conduction disturbances, myocardial
infarction, and sudden death
[1]. Coronary hemodynamics in
cases of myocardial bridging are characterized by phasic systolic vessel
compression with a localized peak pressure, persistent diastolic diameter
reduction, increased blood flow velocities, retrograde flow, and a reduced
flow reserve [2].
In cases of myocardial bridging refractory to medical therapy, surgical
myotomy is associated with reversal of local myocardial ischemia and
resolution of the clinical symptoms
[3]. Although cleavage of the
bridging muscle bundles eliminates the underlying cause of the myocardial
bridge, this treatment strategy carries considerable risk because of the
unpredictable intramural course of the coronary artery. In addition,
myocardial myotomy may require deep incision of the ventricular wall,
potentially leading to subsequent ventricular wall injury and aneurysm
formation [4,
5].
Myocardial bridging has been investigated recently by Amoroso et al.
[6] using a 4-MDCT scanner.
Those researchers evaluated two patients with asymptomatic myocardial bridging
and compared images of the mid LAD coronary artery in the systolic and
diastolic phases to determine the phasic lumen narrowing. However, in that
work, no information was given in either case regarding the length and depth
of the tunneled segment and its anatomic relationship with the ventricle
chambers. By contrast, we evaluated a symptomatic patient in whom the presence
of atherosclerosis lesions in all coronary segments could be ruled out because
of the higher spatial and temporal resolution of the 16-MDCT scanner that we
used, thus allowing the diagnosis of myocardial bridging to be established as
the cause of the clinical symptoms reported.
We also obtained precise measurements of the length and depth of the
tunneled segment, information that can be correlated to the severity of the
clinical symptoms [7]. More
important, the knowledge of such measurements allowed the surgical risk
related to the unpredictable intramural pathway of the coronary segment to be
avoided. Supraarterial myotomy was performed with a longitudinal and oblique
orientation from the free wall of the left ventricle toward the left side of
the interventricular groove without mobilization of the intramural segment to
abolish the phasic external vessel compression and reduce the risk of right
ventricle wall injury.
Coronary angiography is the imaging technique currently considered the
reference standard for diagnosing myocardial bridging and for quantifying the
degree of systolic narrowing. However, the present case suggests that MDCT may
be a complementary study that allows a better evaluation of the morphologic
features (e.g., length and depth) of myocardial bridging, which may also
influence the choice of treatment techniques.
References
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- Zwaan C de, Wellens HJJ. Left ventricular aneurysm after cleavage
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- Amoroso G, Battolla L, Gemignani C, et al. Myocardial bridging on
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- Ferreira AG Jr, Trotter SE, Konig B Jr, et al. Myocardial bridges:
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Introduction
Case Report
