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Newer concepts for imaging anomalous aortic origin of the coronary arteries in adults

Paolo Angelini, MD, Scott D. Flamm, MD

Introduction

In the clinical literature, discussion of coronary artery anomalies (CAAs) has traditionally been based on a fragmented knowledge of pathologic anatomy. A common belief, long held by both specialists and generalists, is that CAAs are a class of anatomic variants that can cause sudden death, typically in young athletes [[1-3]]. Over the last few years, however, important new insights into CAAs have been changing and refining this characterization [[4-6]]. Researchers have come to realize that coronary anomalies include many different entities with highly variable clinical implications [[5][6]]. Most CAAs are simply benign anatomic variations. Others, such as anomalous origin of the left coronary artery (LCA) from the pulmonary artery, or ALCAPA, entail a severe prognosis from birth onward. Still other CAAs can cause chest pain, dyspnea, palpitations/arrhythmias, and/or syncope in adults. Only a few anomalies are potentially lethal in adults, especially athletes and soldiers. These insights have largely been supported by newer imaging modalities that facilitate detection of CAAs and quantification of their severity in individual cases. Such quantification has become mandatory, particularly since the advent of stent-angioplasty as an interventional therapeutic option [[7][8]].

Having extensively reviewed the subject of CAAs elsewhere [[9]], we will refer readers to that review for a general discussion. The present article will focus on the latest CAA imaging modalities, as applied to the study of a specific subgroup of CAAs that involve an increased risk of clinical manifestations: ACAOS, or Anomalous origin of a Coronary Artery from the Opposite Sinus of Valsalva with an intramural course (inside the aortic wall). In particular, we will describe the mechanisms of stenosis in ACAOS and their spectrum of functional/clinical consequences. Because these consequences have not been documented in cases of anomalous origin without an intramural course, we believe that CAAs with a prepulmonic, intraseptal, or retrocardiac course [[5][10]] should generally be excluded from the ACAOS category, as defined here. The retroaortic course is most frequently (but not always) extramural and clinically benign. Figure 1 shows the courses that an ectopically arising coronary artery can take to reach its normal area of distribution. Familiarity with these courses (see all the figures for examples) will not only enhance diagnostic accuracy but also help to guide prognostic subclassification.

Figure 1.
Conceptual diagram showing most of the possible paths (1 through 5) by which the RCA, LAD, and circumflex artery (Cx) can potentially connect with the opposite coronary sinuses. Paths: 1, retrocardiac; 2, retroaortic; 3, preaortic, or between the aorta and pulmonary artery; 4, intraseptal (supracristal), which passes underneath the pulmonary valve on its way to the upper ventricular septum (intramyocardial course); 5, prepulmonary (precardiac). The aortic and pulmonary sinuses are labeled according to their position in space. AL, antero-left; AR, antero-right; P, posterior; M, mitral valve; T, tricuspid valve. (Modified from Angelini et al. Normal and anomalous coronary arteries in humans. In: Angelini P, editor. Coronary Anomalies: A Comprehensive Approach, 1999, Vol. 52 (5), © Lippincott Williams & Wilkins. reprinted with permission).

We will subdivide the discussion of imaging modalities into those designed for screening (to detect the presence of ACAOS) and those most appropriate for evaluating lesion severity (to identify specific interventional indications). We will refer to ACAOS of the right and the left coronary arteries as right and left ACAOS, respectively.

Imaging modalities for screening

For initial screening purposes, preferred imaging modalities should (1) be noninvasive; (2) be applicable to a wide population, at a reasonable cost, with a minimal level of side effects such as those that could be involved in the use of ionizing radiation; and (3) have reliable diagnostic accuracy. Traditional techniques that have been used to identify CAAs include echocardiography and selective coronary angiography (SCA). Newer imaging modalities that are increasingly being used for screening purposes include coronary magnetic resonance angiography (CMRA) and multidetector computed tomography (MDCT).

Echocardiography

Echocardiography is not commonly used to examine the coronary arteries, but it is an attractive screening option in view of its relative simplicity, noninvasiveness, and lack of ionizing radiation [[11]]. In pediatric patients-particularly newborns with congestive heart failure and/or shock-echocardiography, supplemented with Doppler interrogation, is routinely performed because it is highly accurate in diagnosing some CAAs such as ALCAPA and large coronary fistulas. In this age range, ALCAPA is the most relevant diagnostic challenge, because it necessitates emergency surgical intervention at a specialized center.

As a child grows, identifying the coronary ostial location and proximal coronary course becomes the most compelling diagnostic challenge, particularly to rule out ACAOS. Unfortunately, however, as age and body mass increase, echocardiography becomes progressively less accurate for coronary artery imaging [[11-15]]. In a recent continuous series of echocardiograms from a pediatric service, Davis et al. [[13]] found that the total incidence of CAAs was only 0.1%, which is much lower than that typically observed in a continuous series of coronary angiograms. Our group has reported an angiographic incidence of 1.1% for ACAOS alone and 5.4% for all forms of CAAs [[5]]. In neither Davis's study nor ours was the pretest probability of ACAOS or other CAAs quantified. Also, in Davis's echocardiographic study, follow-up evaluation revealed that one patient, in whom echocardiography was done for a history of syncope yielded a negative result, later underwent sudden cardiac death. Left ACAOS was found at autopsy, adding to the concerns about the reliability of this testing modality [[13]]. Also, the 1:1 ratio of right to left ACAOS found in the Davis study [[13]] and the similar 4:6 ratio found by Frommelt et al. [[14]] are inconsistent with the 4:1 ratio usually seen in necropsy or angiographic series [[5]], suggesting the possibility of both a pretest bias and methodologic limitations in identifying the smaller right coronary artery (RCA). Transesophageal echocardiography can frequently identify some forms of CAAs but is a poor screening test because of its expense, invasiveness, patient discomfort, and incomplete imaging quality (because of limitations in imaging windows and spatial reconstruction of the coronary anatomy).

Dedicated studies using color Doppler mapping can often identify the intramural course of the ectopic vessel inside the wall of the aorta (versus simply a course running between the aorta and pulmonary artery), even though these techniques cannot clarify the severity of luminal narrowing at this level [[14]]. Prospective, nonselective studies of competitive athletes yield quite a low incidence of positive findings [[15]].

The discriminating power of echocardiography is intrinsically limited (both temporally and geometrically), and few opportunities are available for aligning the echocardiographic imaging planes with the coronary anatomy, which presents curves and phasic movements. Therefore, this technology is less than ideal for firmly diagnosing most types of CAAs in adults. Echocardiographic detection of one coronary ostium at each of the two anterior sinuses of Valsalva generally suggests ACAOS or ALCAPA but, by itself, is inconclusive in ruling out these CAAs. For example, in the presence of right ACAOS, a normally originating prominent conal branch could be misinterpreted as a normally originating RCA. Some operators have recently reported a new capacity to evaluate anterior coronary vessels for severity of obstruction by means of contrast-enhanced, color-guided, pulsed-wave Doppler-flow interrogation during transthoracic echocardiography [[16][17]]; this development may be of interest with respect to future applications in ACAOS.

Selective Coronary Angiography

For detecting CAAs, generalized imaging of large, low-risk populations with traditional SCA would seem excessive in terms of cost and acceptability. In fact, millions of patients undergo SCA each year, typically for coronary artery disease, and this population has also been a source of important observations about CAAs [[5]]. Experience with SCA in evaluating CAAs can be summarized as follows:

  1. When performed by an angiographer specifically trained in CAAs, SCA consistently enables correct identification of all forms of CAAs, but it can only vaguely suggest the severity of proximal stenosis in ACAOS. Specific experience and modified techniques are required to selectively catheterize the ectopic ostia.
  2. In ACAOS, consistent, correct angiographic identification of the different possible courses followed by the ectopic vessel is achievable, but it requires specific training. In fact, it is more difficult with SCA than with CMRA or MDCT, as discussed below. With SCA, confusion frequently arises in differentiating the between the aorta and the pulmonary artery course from the intraseptal one, as extensively discussed previously [[5]]. Figures 2 and 3 give helpful diagnostic hints for facilitating this process.
  3. SCA is essential both to exclude atherosclerotic obstructive disease [[18]] and to clarify the extent of the vulnerable territory of the anomalous vessel (dominant versus nondominant RCA, single coronary, etc.), which is likely a fundamental risk factor for clinical consequences of ACAOS; the larger the dependent territory, the more important the expected clinical consequences for a given type of ACAOS.
  4. Though inconclusive in most cases of ACAOS, SCA can sometimes provide evidence of proximal ectopic-vessel stenosis but only in an angiographic projection orthogonal to the plane of compression: for example, in cases of right ACAOS, the right anterior oblique, cranio-caudal projection (Fig. 4).

Figure 2.
(A, B) Selective coronary angiographic images of anomalous origin of the left coronary artery (LCA) from the right sinus of Valsalva with an intramural course (preaortic, path no. 3), in the left anterior oblique (A) and right anterior cranial oblique (B) projections. The ectopic coronary artery crosses to the left at the level of the sinotubular junction. This segment tilts upward, is devoid of side branches (namely septals), and wraps around the anterior aortic wall. This course differs anatomically, physiologically, and prognostically from the intraseptal course shown in Figure 3 and Figure 7 (coronary magnetic resonance angiogram of an intraseptal course) for comparison. Arrows A and B indicate the sites of the cross-sectional IVUS images shown in Fig. 13A and B, respectively. Ao, aorta; RCA, right coronary artery.

Figure 3.
(A, B) Selective coronary angiographic images of the left coronary artery (LCA) originating from the right sinus of Valsalva with an intraseptal course (path no. 4). The LCA courses inferiorly and anteriorly, providing one or more early septal branches (SEP). This course is not usually associated with negative prognostic implications (see text) and is not included in the ACAOS group.

Figure 4.
(A, B) Selective coronary angiographic frames in the left anterior (A) and right anterior oblique (B) projections in a case of anomalous origin of the right coronary artery from the left sinus, with an intramural course (path no. 2). Whereas view A does not reveal proximal obstruction, view B clearly shows significant proximal obstruction, which intravascular ultrasonography (Fig. 15B and C) shows as being due to hypoplasia and lateral compression.

Coronary Magnetic Resonance Angiography

Coronary magnetic resonance angiography (CMRA) is a noninvasive technique that necessitates neither ionizing radiation nor a potentially nephrotoxic contrast agent [[19]]. As a tomographic imaging technique, CMRA allows three-dimensional (3D) reconstruction and omnidirectional visualization of a CAAs origin and course, thereby circumventing some problems of SCA (Figs. 5 and 6).

Figure 5.
(A) Coronary magnetic resonance angiographic images, using the Soap-Bubble reconstruction software tool, showing a common or juxtaposed origin of the left and right coronary arteries from the right sinus of Valsalva with a retroaortic course of the left main coronary artery (path no. 2). The right coronary artery has a normal course (single arrow). The left main coronary artery (single arrowhead) has a benign course, running posterior to the aortic root, then dividing normally into the left anterior descending (double arrows) and left circumflex (double arrowheads) coronary arteries. This view approximates a shallow left anterior oblique projection rotated 45° clockwise. Ao, aorta; LA, left atrium; PA, pulmonary artery; RA, right atrium.

Figure 6.
Soap-Bubble reconstruction of a coronary magnetic resonance angiographic image (approximating a shallow left anterior oblique projection) revealing a common origin of both the left and right coronary arteries from the right sinus of Valsalva. The right coronary artery (RCA) has a normal course (arrow) and is visible to the crux; the left main coronary artery (arrowheads) has a benign course running anterior to the right ventricular outflow tract (RVOT, path no. 5), then dividing normally into the left anterior descending artery (not included in this image) and the left circumflex artery. Ao, aorta.

The enhanced ability to visualize 3D datasets is emphasized in Figs. 5-8, in which 3D CMRA datasets were reconstructed with the Soap-Bubble custom software tool [[20]]. Unlike most standard display techniques, the Soap-Bubble tool does not present the coronary arterial tree as a single specific, defined imaging plane but, instead, effectively wraps the imaged portions of the coronary arteries around a sphere, then flattens the sphere into a 2D image similar to a world map. The relationships of adjacent structures (vascular and nonvascular) are preserved, though the relationships between remote structures may be distorted.

Currently, six published CAA series are available for comparing imaging modalities [[19][21-25]]. Five of these series included patients without a coexistent congenital heart defect [[19][21][23-25]], and one series involved adults with congenital heart disease [[22]]. In all six studies, CMRA appeared as accurate as SCA in defining the origin and proximal course of the coronary arteries, with the additional advantage of enhancing visualization of the topographic environment (Table I). In particular, CMRA facilitates the differential diagnosis of between the aorta and pulmonary artery and intraseptal courses in ACAOS, an important distinction in view of the contrasting prognostic implications (Figs. 7 and 8).

Figure 7.
Coronary magnetic resonance angiographic image with Soap-Bubble reconstruction (approximating a shallow left anterior oblique projection rotated 45° clockwise). The left main coronary artery (black arrowhead) originates from the right sinus of Valsalva and courses within the upper ventricular septal myocardium, between the aortic root and the right ventricular outflow tract (RVOT, path no. 4). Note that the epicardial fat is suppressed (it turns black) as a result of a fat-suppression pulse used in the imaging sequence; the myocardium is gray. Both the left anterior descending (black arrow) and the left circumflex artery (double white arrowheads) also have intramyocardial courses for their proximal portions. The right coronary artery (white arrow) has a normal course within the right atrioventricular groove. Ao, aorta; LA, left atrium, RA, right atrium.

Figure 8.
Anomalous left coronary artery originating from the opposite sinus, with an interarterial course (path no. 3), as seen by Soap-Bubble reconstruction of a coronary magnetic resonance angiographic image. This view approximates a shallow left anterior oblique projection rotated 45° clockwise. The right coronary artery (black arrow) arises from the left sinus of Valsalva and courses between the aortic root and the pulmonary artery (PA). Ao, aorta; DAo, descending aorta; LA, left atrium.

 

Table I. Comparison of Imaging Techniques

Technique TTE SCA CMRA MDCT IVUS
Spatial resolution (mm) 0.8 × 1.5(4-MHz transducer) 0.3 0.6 × 0.6 × 1.5(3.0 T); 0.7 × 0.7 × 1.5 (1.5 T) 0.4-0.5 (isotropic) 0.15 × 0.25(30-MH z transducer)
Temporal resolution 30 ms 7-20 ms 60-80 ms 85-240 ms Variable
Dynamic imaging? Yes Yes No Yes (limited resolution) Yes
Visualizes surrounding structures? Yes No Yes Yes Yes (limited range)
Characterizes tissue? Yes (limited) No Yes Yes (limited) Yes (limited)
CMRA, coronary magnetic resonance angiography; IVUS, intravascular ultrasonography; MDCT, multidetector computed tomography; SCA, selective coronary angiography; TTE, transthoracic echocardiograpy.

The spatial resolution of CMRA is satisfactory in defining the coronary course associated with ACAOS but remains limited in precisely defining the detailed anatomy of the critically important proximal ectopic vessel (Fig. 1 and Table I); in particular, the intramural course and degree of compression inside the aortic wall can only be guessed at.

With 3.0-T MRI scanners, an in-plane spatial resolution of 0.6 mm can be obtained; with 1.5-T scanners (which are more common in clinical practice), the best in-plane spatial resolution is typically 0.7 mm [[26][27]]. Nonetheless, because of its 3D visualization abilities, CMRA can clarify the acuity of the proximal coronary artery origin (tangential takeoff), its location at the level of the sinotubular junction or above it, and the sinus of origin (Fig. 8). By itself, tangential origin of a coronary artery does not necessarily have a stenotic effect. Still, it is usually associated with an intramural course, which is clearly correlated with stenosis (see the IVUS section).

Computed Tomographic Angiography of the Coronary Arteries and MDCT

Computed tomographic angiography of the coronary arteries has been available since the advent of electron-beam computed tomographic imaging (EBT). For studying CAAs, however, computed tomographic angiography has seen a dramatic rise in interest since the introduction of MDCT scanners with four detector rows in 1998. The earliest reports on CAAs were based on experience with electron-beam computed tomographic scanning, which correlated closely with SCA [[28-30]]. Current MDCT scanners with 16, 32, and 64 detectors can define coronary artery atherosclerotic disease in selected patient populations nearly as well as SCA can [[31][32]].

Initial reports concerning the use of MDCT for identifying and characterizing anomalies of coronary origin and course are as encouraging as CMRA reports and similarly highlight the benefits of 3D image acquisition and visualization. In reviewing coronary artery data obtained with MDCT, Shi et al. [[33]] and Sato et al. [[34]] found a total CAA incidence of 6.6% (16/242) and 0.43% (5/1,153), respectively, which likely reflected an unquantified differential selection bias, since MDCT is becoming a preferred test for patients with suspected or known CAAs, including ACAOS.

Multiple MDCT studies of CAAs have been performed, including correlations with SCA [[33][35-38]]. Whereas some investigators have noted a close agreement between MDCT and SCA in defining the origin and course of CAAs [[36][38]], other researchers have noted limitations in SCA interpretations relative to MDCT findings [[33][35][37]]. In two studies, nearly half of the SCA interpretations were inconclusive regarding the precise course of the proximal anomalous vessels, but MDCT identified it unambiguously [[33][37]]. In a study by Datta and coworkers [[35]], 17 of the 18 patients with ACAOS who underwent MDCT did so because of equivocal findings on SCA. In all 18 cases, MDCT unequivocally defined the origin and course of the CAAs. Clearly, because of its 3D capabilities, MDCT facilitates accurate description of ACAOS anatomy and is advantageous even in the hands of operators not specifically trained in diagnosing CAAs (Figs. 9 and 10). Nevertheless, MDCT involves a substantial radiation burden and the use of a potentially nephrotoxic contrast agent. The radiation burden necessitates special consideration of the risk/benefit ratio, particularly in younger patients, for whom screening programs are most likely to be considered (Fig. 9).

Figure 9.
Sixteen-slice multidetector computed tomography (MDCT) demonstration of the intramural (aortic) origin of a right coronary artery (RCA) originating superior to the left sinus of Valsalva (right ACAOS, path no. 3). In the lower image (a multiplanar reconstruction through the proximal tubular portion of the ascending aorta and the proximal RCA), note the acute angulation of the RCAs origin (black arrow) from the tubular portion of the ascending aorta (Ao). The three images in the upper row are cross-sections of the RCA that correspond to the lettered locations in the lower image. Each is approximately in a right lateral view. At point A, the RCA has a normal, round appearance (extramural); at point B, the vessel becomes oval in shape (intramural segment); at point C, the RCA becomes markedly eccentric and flattened as it nears its slit-like ostium. This example is the first published evidence of the potential of MDCT to describe the narrowing of the proximal ectopic segment, similar to the findings at intravascular ultrasound (IVUS) imaging. Because the aortic wall is poorly seen, MDCT images remain somewhat inferior to those of IVUS. Ao, aorta; PA, pulmonary artery.

Figure 10.
Three-dimensional volume-rendered reconstruction of a multidetector computed tomography (MDCT) image in a left anterior projection with steep cranial angulation. This reconstruction illustrates the same case of anomalous origin of the right coronary artery from the left sinus as shown in Figure 9 (preaortic path, no. 3). The right ventricular outflow tract has been removed to better illustrate the findings. The left coronary artery (arrowhead) arises from a site located just above the left sinus of Valsalva, and the right coronary artery (arrow) arises next to the left ostium. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Another important limitation of MDCT is that, compared with IVUS, it has a lower spatial resolution (Table I) and, therefore, cannot as accurately detail the anatomy of the intramural proximal ectopic artery in ACAOS (Fig. 9). In MDCT acquisitions, the spatial resolution partly depends on the field of view acquired. In theory, the finest in-plane spatial resolution achievable approaches 0.4 mm; in practice, however, coronary artery motion produces both spatial and temporal blurring, resulting in an effective spatial resolution closer to 0.5 mm. The other limitation is in the skill of those who interpret noninvasive examinations. In most of the previously noted MDCT studies, CAAs with an interarterial course were considered malignant even if, on review, some were clearly shown to have an intraseptal course - an important difference with respect to clinical implications.

Imaging techniques for evaluating lesion severity: Intravascular ultrasonography

Determining the severity and prognostic importance is particularly relevant in ACAOS, as its spectrum of repercussions ranges from clinical silence through mild sequelae to sudden cardiac death. Presently, to early IVUS investigators, the fundamental pathophysiologic mechanism of ACAOS seems to relate not so much to the presence of the ectopic origin itself as to the specific anatomy of the ectopic proximal trunk as it courses toward the proper side of the heart. Intravascular ultrasonography achieves high anatomic precision: at 30 MHz, its wavelength is 50 m, which yields a practical axial resolution of about 150 m (0.15 mm) [[39]]. In patients with ACAOS, systematic IVUS studies, carried out mainly by our group, have suggested that neither an ectopic origin by itself, an acute take-off from the aortic wall, a course between the aorta and pulmonary artery, an associated ostial ridge, nor a slit-like ostium necessarily causes stenosis at rest or during exercise [[7][8][40]], even though, in the literature, all of these mechanisms have previously been claimed to be culprits on the basis of anatomo-pathologic observations [[4-7][10][41][42]]. Superimposed spasm, atherosclerotic intimal plaque development, and clotting have also been theorized to explain why persons with CAAs may suddenly, de novo, manifest the deleterious effects of ACAOS [[18][43][44]], but these theories have not been substantiated.

A few anatomic, surgical, and echocardiographic descriptions of ACAOS [[14][18][41][42]] have mentioned the presence of an intramural course of the proximal ectopic artery (right or left coronary stem) inside the wall of the aortic root, as shown in Figs. 11 and 12 [[45]]. Not until the recent introduction of systematic IVUS in clinical cases of ACAOS [[7]], however, was the constant presence of such an intramural course identified and related to a clear, though tentative, theory about the mechanism of stenosis, clinical manifestations, and prognosis [[6-8]]. These IVUS investigations begun at our institution in 2000, after our institutional review board approved a protocol that allowed the use of stent-angioplasty in selected cases [[40]].

Figure 11.
Gross anatomic specimen from a 17-year-old basketball player who died suddenly during a competitive game. The probe is passed from left (intraaortic) to right, at the intramural segment of a right coronary artery (RCA) that originates anomalously from the left sinus, with a preaortic path, no. 3). The intramural segment was 8-mm long. Note the location of the pulmonary artery (PA). The distal, extramural RCA has been severed to show the probe's exit from the aortic wall. Ao, aorta. (Photo courtesy of Dwayne A. Wolf, PhD, Office of the Medical Examiner of Harris County, Texas). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 12.
Histologic cross-section of the aortic root, from the same necropsy as in Figure 11, clarifying the intramural course of the right coronary artery (RCA) at its proximal segment. The intramural RCA is laterally compressed and irregular (noncircular) in shape, as its media is the aortic media, within which it travels. The pulmonary artery (PA) seems to be remote from the RCA and to behave as an innocent bystander, despite the fact that this condition is traditionally labeled between the aorta and pulmonary artery, implying a risk of coronary compression between the great vessels. IVS, intraventricular septum. (Photo courtesy of Dwayne A. Wolf, PhD, Office of the Medical Examiner of Harris County, Texas) [[45]]. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

In fact, IVUS affords precise sequential cross- sectional imaging of the coronary lumen and coronary wall thickness with a discriminating power, based on superior spatial resolution, well above that of transthoracic or transesophageal echocardiography, SCA, CMRA, or MDCT, which typically do not clearly recognize stenosis at the ectopic vessel. Though less than definitive in some respects, current experience in cases of ACAOS with a proximal course between the aorta and pulmonary artery (also called preaortic or interarterial) suggests the following consistent findings [[7][8][40]]:

  1. An intramural course (Figs. 13 and 14B) is constantly present for a segment ranging from 5 to 25 mm in length (and possibly even longer if the anomalous ostium is located high above the sinotubular junction, as it sometimes is, particularly in transposition of the great vessels [[46]]). This course, along with the related acute takeoff, implies a slit-like ostium (which, by itself, does not cause a fixed stenotic effect). Interestingly, the slit-like ostial morphology does not change with simulated exercise during IVUS examination, as it does in the saline- atropine-dobutamine test, described below.
  2. The specific features and degree of stenosis in ACAOS depend on additional consistent peculiarities that vary in individual cases, namely:
    1. Hypoplasia of the intramural segment (Figs. 13 and 15), which becomes apparent when the proximal-stem cross-section is compared with one of the more distal, extramural segments. The hypoplasia index, which we recently introduced [[7][8]], denotes the ratio between the intramural minimal circumference and the distal reference circumference. The hypoplasia indices for our left ACAOS series [[8]] ranged from 0.3 to 0.7.
    2. The lumen of the intramural segment is also laterally compressed, yielding an ovoid cross-section (Figs. 13-15), which may be quantified by the asymmetry index, or ratio between the shortest and longest diameters [[47]]. This ratio features systo-diastolic phasic variations, whereby the shortest diameter apparently decreases in systole and early diastole.[Note *]The saline-atropine-dobutamine test was introduced in our laboratory to study possible factors affecting the modulation of stenosis in ACAOS, especially regarding reasons for sudden death during or after exercise, which is the ultimate manifestation of ACAOS. It is likely that in severe left ACAOS, for example, the anomalous artery could become critically obstructed during exercise, lowering the cardiac output and establishing a negative feedback mechanism. So far, no definite conclusion has been reached about discriminating criteria, mainly because of the electrocardiographic signal issues mentioned earlier. The saline-atropine-dobutamine test entails dobutamine infusions at progressively higher dosages (10, 20, or 40 mcg/kg/min), rapid intravenous infusion of saline solution (500 cc over 15 min), and additional atropine (0.5 mg intravenously) if the heart rate is <140 beats/min at the end of dobutamine infusion [[7][40]].
    3. The severity of area obstruction at rest-as measured by IVUS imaging of the cross-sectional area of the intramural, intussuscepted segment compared with a distal reference segment-varies between 30 and 70%. Diameter narrowing, as commonly used in SCA, is not a precise method for measuring eccentric stenosis.

Figure 13.
Intravascular ultrasound images (obtained with an Atlantis® [SR Pro Coronary Imaging Catheter]; Boston Scientific, Natick, MA) of the case of anomalous origin of a left coronary artery from the left sinus illustrated angiographically in Figure 2 (In that figure, arrows A and B correspond to views 13A and 13B, respectively). The intramural proximal left coronary artery (LCA) is severely stenotic (A) with respect to the extramural distal LCA (B). On IVUS, the area stenosis was 62% at baseline, the asymmetry index was 0.5, and the hypoplasia index was 0.4. Note that this mechanical-rotation IVUS system consistently features nonuniform rotational distortion (NURD) in arteries that have an acutely angled take-off from the aorta (as seen in B). Ao, aorta; RCA, right coronary artery.

Figure 14.
A rare case of anomalous origin of the left coronary artery (LCA) from the noncoronary sinus of Valsalva with a retroaortic course (path no. 2). (A) Selective coronary angiogram. (B) Coronary magnetic resonance angiogram. This view approximates a shallow left anterior oblique projection rotated 45° clockwise). L, left sinus of Valsalva; LA, left atrium; NC, noncoronary sinus of Valsalva; R, right sinus of Valsalva; RA, right atrium; RVOT, right ventricular outflow tract. (C,D) Intravascular ultrasound images. The proximal LCA is intramural, stenotic, and laterally compressed, even though it is not preaortic but retroaortic (path no. 2). Area of stenosis = 60%; asymmetry index = 0.6; and hypoplasia index = 0.38. *Calcific plaque.

Figure 15.
Selective coronary angiographic (A) and intravascular ultrasound (B-D) images obtained with the Volcano technique (Volcano Corporation, Rancho Cordova, Calif.) in a case of anomalous origin of the right coronary artery from the left sinus (intramural path, no. 3). The left anterior oblique angiographic projection (A) reveals an ectopic right coronary artery (RCA) taking off next to the left coronary artery (LCA) at the left sinus of Valsalva. In this projection, the RCA appears angiographically to have an enlarged proximal diameter. Ao, aorta. (B) IVUS reveals that the proximal RCA is actually severely hypoplastic, compressed, and stenotic with respect to the more distal extramural RCA (C). Area stenosis = 66%; asymmetry index = 0.48; hypoplasia index = 0.30. Ao, aorta. Note that this solid-state IVUS technology avoids the rotational artifacts observed while using a mechanical rotating transducer, as shown in Fig. 13. Arrows A and B indicate the sites of the cross-sectional IVUS images shown in Fig. 15B and C, respectively. Ao, aorta; RCA, right coronary artery.

Figure 16.
Intravascular ultrasound image of anomalous origin of the right coronary artery from the left sinus (with path no. 3), in which the probe seems to cause mild distorsion of the eccentric side of the intramural segment (arrow). Ao, aorta. Asymmetry index = 0.18.

A pressure wire (RADI Medical Systems, Uppsala, Sweden) also can be used to evaluate patients with ACAOS. Though limited to only three cases, our experience with this method has been disappointing because even patients with severe symptoms and 60% area narrowing did not have a significant stenotic effect when assessed by the pressure-wire protocol. In contrast, a recent report by Lim et al. [[48]], of a single case of right ACAOS, suggested possibly promising findings (including a significant pressure decrease after adenosine administration).

Presently, no definitive guidelines are available for the optimal workup and treatment of ACAOS. However, our group at the Texas Heart Institute has established a Coronary Artery Anomalies Center (http://texasheart.org/education/resources/caac.cfm), which is collecting a large database of diagnostic and clinical information intended eventually to suggest therapeutic indications [[49]] and to document the results of alternative treatment modalities.

Conclusion

Imaging of CAAs has reached an advanced stage of sophistication and precision, allowing greatly improved evaluation of these unusual and somewhat mysterious abnormalities. We believe that enhanced techniques, mainly using IVUS and MDCT, will eventually clarify CAAs and allow definite clinical guidelines to be established for effectively managing these disorders.

Acknowledgements

The authors thank Steffen Huber, MD, for helping to reconstruct the CMRA Soap-Bubble images and Virginia Fairchild for expert editorial assistance.

Endnotes

These measurements are still being assessed quantitatively in our laboratory because of persistent technical limitations related to the electrocardiographic signal in the IVUS images: the electrocardiogram is absent in the Atlantis software package (Boston Scientific, Natick, MA) and is present only in the Volcano package (Volcano Corporation, Rancho Cordova, CA). Unfortunately, the latter package has some temporal resolution limitations that cause it to provide only four to six images for the systolic interval. Additionally, we must acknowledge the possibility of a small artifact, particularly in severe cases of ACAOS: the presence of an IVUS probe inside the ectopic, tangentially oriented vessel may reduce the precision of measurements by inducing temporary stenting and/or spasm (Fig. 16). The possibility of such spasm (or guiding catheter-related obstruction) is confirmed by the fact that, during IVUS testing, 3 of our 31 patients developed ST-T ischemic changes and angina unresponsive to intracoronary nitroglycerin and were relieved only by stent deployment or catheter removal. Because some of our ACAOS patients presented with resting chest pain and transient electrocardiographic changes (as in Prinzmetal's angina), we began to systematically test for a spastic potential by infusing intracoronary ergonovine or acetylcholine [[7][40]]. Such testing was eventually abandoned, however, because of its consistently negative or inconclusive results and its technical complexity [[7]].

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Autor: Paolo Angelini, MD, Scott D. Flamm, MD

Fuente: Catheterization and Cardiovascular Interventions

Ultima actualizacion: 3 DE DICIEMBRE DE 2007

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