Ann Thorac Surg 1997;64:746-750
© 1997 The Society of Thoracic Surgeons
Original Article: Cardiovascular
Small Left Coronary Arteries After Arterial Switch Operation for Complete Transposition
Koichi Yatsunami, MD,
Makoto Nakazawa, MD,
Chisato Kondo, MD,
Hidetake Teshima, MD,
Kazuo Momma, MD,
Yoshinori Takanashi, MD,
Yasuharu Imai, MD
Departments of Pediatric Cardiology and Pediatric Cardiovascular Surgery, Heart Institute of Japan, Tokyo Women's Medical College, Tokyo, Japan
Accepted for publication March 26, 1997.
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Abstract
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Background. Myocardial perfusion is not completely normal and ventricular function is depressed in some patients after the arterial switch operation. The basic mechanism has not yet been defined totally.
Methods. The diameters of the right, left main trunk, anterior descending, and circumflex coronary arteries were measured by computer-assisted densitometry at 8 to 86 months (mean, 47.5 months) after the arterial switch operation in 86 patients.
Results. The Z scores, compared with control, were +2.0 ± 0.3, -1.8 ± 0.3, and -1.5 ± 0.3 for the right, left anterior descending, and circumflex coronary arteries, respectively. The Z score for the total cross-sectional area of the three vessels was -1.5 ± 0.3. These parameters did not correlate with left ventricular ejection fraction.
Conclusions. At the midterm follow-up after the arterial switch operation for complete transposition of the great arteries, the left coronary arteries are small. A careful follow-up study is mandatory to clarify the clinical significance of this finding.
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Introduction
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See also page 750.
The arterial switch operation has become the operation of choice for patients with complete transposition of the great arteries with an intact pulmonary valve, because the postoperative physiology and anatomy are theoretically normal [1, 2]. However, some studies have suggested that subtle cardiac dysfunction is seen in some patients after this operation [3, 4]. Radionuclide studies have shown that myocardial perfusion is not completely normal in some patients after the arterial switch operation [5–8]. Many of these studies, however, have not been able to correlate the area of the perfusion defect with a specific area of the coronary artery distribution, suggesting that the obstruction of the anastomosis was not its cause. Our preliminary study suggested that the size of the coronary arteries may be abnormal in patients who have undergone the arterial switch operation, but a definitive conclusion has not been drawn [9]. In the present study, therefore, we increased the number of patients and analyzed them (1) to clarify whether the coronary arteries are truly abnormal in size, (2) to look at the effect of differences in surgical strategy (ie, primary or two-stage operation), and (3) to show the effect of an association with a large ventricular septal defect on coronary artery dimensions in patients who have undergone the arterial switch operation.
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Patients and Methods
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The study included 86 patients who underwent cardiac catheterization, 8 to 86 months (mean ± standard deviation, 48 ± 20 months) after the arterial switch operation. During the study period, there was 1 patient who had complete obstruction at the origin of the left main trunk. This patient has been excluded from the present analysis. Postoperative cardiac catheterization was recommended for all study candidates before or at the time of their entry into primary school. We believe it is necessary to evaluate the cardiac condition in these patients at that time, because all schoolchildren have to participate regularly in strenuous sports, such as long distance running and diving, as a part of the physical education program in our country, which may cause cardiac events related to the coronary arteries. The subjects of the present study were those whose parents understood the value of the study and gave informed consent for their participation; thus, there should not be any bias in the patient selection.
The pattern of the coronary arteries was Shaher type 1 [10] in 68 patients, type 2 in 13 patients, and type 4 in 5 patients (Fig 1
). Sixty-two patients had an intact ventricular septum, 20 patients had a large ventricular septal defect, and 4 patients had a double-outlet right ventricle with a subpulmonary ventricular septal defect. Forty-five patients, including 29 neonates, underwent the primary (one-stage) arterial switch operation and 41 underwent a two-stage arterial switch operation (Fig 1).
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Fig 1. . Pattern of the coronary arteries according to the classification of Shaher and Puddu [10] is illustrated at the top, and the number of patients with each type are given at the bottom. The numbers in parentheses indicate those patients who underwent two-stage repair. (Ao = aorta; CX = circumflex coronary artery; DORV = double-outlet right ventricle; IVS = intact ventricular septum; LAD = left anterior descending coronary artery; PA = pulmonary artery; R = right coronary artery; VSD = ventricular septal defect.)
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Selective coronary artery angiography was performed in all the subjects. The posterior descending coronary artery was from the right coronary artery in all patients. The diameter of the coronary arteries was measured at a site approximately 1 cm proximal to the first branch in each of the right, anterior descending, and circumflex coronary arteries, and at the midportion of the left main trunk. Assuming that the cross-sectional area was completely circular, the maximum diameter on multiple projections was adopted for analysis. Each image of the coronary arteries with a part of the catheter was stored in a personal computer (Macintosh IIci) by using an image scanner, and a segment of a vessel of interest then was displayed on a screen. The diameter of a vessel was measured by a densitometer installed in a software NIH Image 1.51 (public domain, National Institutes of Health). From the density curve, the edge of a vessel was defined as the peak of the first derivative of the gray-scale density gradient [11], which was calculated with Acqknowledge III (BIOPAC Systems, Inc, Goleta, CA). The diameter of the catheter also was calculated by the same method, and was used as a calibration factor. We also calculated the total cross-sectional area of the right, left anterior descending, and circumflex arteries, because this parameter is well correlated with ventricular muscle mass [11, 12].
The data were compared with those obtained using the same method in children who had had Kawasaki disease and were followed up with serial echocardiography, and who did not show any evidence of coronary artery disease throughout their clinical course. Coronary artery involvement in Kawasaki disease ranges from only an increase in echo reflection of the vessel wall to large aneurysms leading to death. From our experience with the large number of patients in Japan, it is reasonable to assume that the vessels are normal, at least in size, in children who do not have abnormal findings, such as an increase in echo reflection or serial changes in the size of the vessels during the first few weeks to months of the acute phase of the illness. Thus, we adopted such children as controls in the present study. With parental consent, they underwent selective coronary angiography, which also confirmed that the coronary arteries were intact. Twenty children were selected from our files who were matched as closely as possible with the study patients in terms of age and body surface area. They ranged in age from 1 to 8 years and in body surface area from 0.42 to 0.93 m2 (mean, 0.67 ± 0.16 m2). The size of each coronary artery and the total cross-sectional area were plotted against the body surface area with a linear regression to serve as controls (Table 1). From ventriculograms, we calculated left ventricular volumes using the area-length method, and the left ventricular end-diastolic volume was expressed as the percentage of the normal value expected for the body surface area of the patients [13].
We obtained the Z-score of the diameter of each vessel and the total cross-sectional area in each patient, and compared mean values with controls. The values were expressed as mean ± standard deviation. The difference was analyzed by analysis of variance and by the Scheffé F test or the unpaired t test using a statistics software package, StatView II (Abacus Concepts, Berkeley, CA) for Macintosh. A p value of less than 0.05 was considered to be significant.
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Results
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The right coronary artery was larger in the patients than in the controls (Table 2; Fig 2). The left coronary arteries were smaller in the patients than in the controls (Table 1
; Figs 3–5), with the exception of the left main trunk in the group with an intact ventricular septum after two-stage repair, which was not different from the controls. The total cross-sectional area of the right, left anterior descending, and circumflex coronary arteries in the patients also was smaller than in the controls (Table 1; Fig 6). None of these values were affected by the type of transposition of the great arteries or were related to the performance of primary or staged repair.
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Fig 2. . Diameter of the right coronary artery in the study patients is compared with the normal range, which is the area between the two lines. The circles indicate patients with an intact ventricular septum (TGA/IVS) and the crosses indicate patients with a large ventricular septal defect (TGA/VSD) or a double-outlet right ventricle (DORV). The open circles show data for patients after primary repair and the closed circles show data for patients after two-stage repair. The right coronary artery was normal or larger than control in all but three patients, and it was not affected by association with a ventricular septal defect or by the surgical approach used.
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Fig 3. . Diameter of the left main trunk was normal or smaller than normal in all but 3 patients. The size of the left main trunk again was not influenced by association with a ventricular septal defect or by the surgical approach used. The symbols and lines are the same as in Figure 2.
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Fig 4. . Diameter of the left anterior descending artery was below the normal range in most patients, and it was not affected by association with a ventricular septal defect or by the surgical approach used. The symbols and lines are the same as in Figure 2.
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Fig 5. . Diameter of the circumflex artery was below the normal range in most patients. The symbols and lines are the same as in Figure 2.
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Fig 6. . Total cross-sectional area of the three vessels was normal or smaller than normal in all but 1 patient. The symbols and lines are the same as in Figure 2.
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Left ventricular end-diastolic volume ranged from 86% to 287% of normal, with a mean of 151% ± 41%, and the ejection fraction was 0.63 ± 0.08. Neither parameter was related to the sum of the diameters of the left anterior descending and circumflex arteries, or to the total cross-sectional area.
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Comment
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The present study has demonstrated that the left coronary arteries are smaller than normal and that the dominant, large right coronary artery does not compensate fully for this in most patients with complete transposition of the great arteries, even at midterm after the arterial switch operation. Oberhoffer and colleagues [14] measured the diameters of the proximal portion of the right and left coronary arteries in 20 autopsied cases with simple transposition and found that the diameters of both arteries were comparable to their normal data in all cases, including 4 patients who had undergone the arterial switch operation [14]. The diameter of the left main trunk was normal and only slightly smaller than normal in our patients, which is similar to their findings. An important new finding in the present study, however, was that the sizes of the left descending and circumflex coronary arteries were far below the normal range in most patients, despite the fact that the left ventricle was working normally against the systemic pressure for a long time. In contrast to our finding, the size of the right coronary artery did not differ from normal in the study by Oberhoffer and colleagues [14]. This difference probably is due to the fact that their normal range, taken from echocardiography, seems to be larger than that reported by Arjunan and associates [15], and by Ino [16], and it is larger than our control value. Another point that would be related to the difference is that they compared the postmortem data of patients with the echocardiographically obtained normal values.
It is well known that the diameters of the left coronary arteries are correlated with the left ventricular muscle mass in adult patients [11, 12]. Although we did not calculate the left ventricular muscle mass, it probably is parallel to the volume in the normally functioning state, and thus also would be normal or above normal in our patients. We expected, therefore, that the size of the coronary arteries would be normalized in these patients. As can be seen from the results, this was not the case. Even when the left coronary arteries were small, it was expected that this would be compensated for by enlargement of the dominant right coronary artery, but the total cross-sectional area of the three major vessels also was less than that of the controls. The lack of an increase in dimension, in spite of the normalization of left ventricular hemodynamics, could be due to obstruction of the translocated coronary arteries. Some clinical studies have implied that the coronary arteries grow after the arterial switch operation [17, 18], and an experimental study by Brutel de la Riviere and co-workers [19] showed that growth of the right coronary artery was not retarded by an aortocoronary anastomosis in pigs, whereas the body weight of the animals increased approximately sevenfold over a period of 10 to 14 months. We previously measured the diameters of coronary arteries before and a few years after the arterial switch operation, and showed that the growth of translocated coronary arteries was similar to that of normal controls [9]. Thus, it is very unlikely that the small left coronary arteries are the result of surgical intervention. It may be possible that the small size of the coronary vessels does not limit the coronary flow. The Poiseuille equation indicates that the fourth power of the radius of a vessel is one of the major factors in determining the flow through the vessel, and the right coronary artery could have been large enough to access a flow that met the demand of the heart in our patients. Therefore, it can be speculated that, in our patients, there was no shortage in the flow to meet the demand, and therefore growth of the vessels was not stimulated.
Recently, Weindling and associates [6] reported that myocardial perfusion scan abnormalities assessed by technetium-99m sestamibi were found in more than 90% of patients after the arterial switch operation, and that the perfusion defect was seen most frequently in the apicolateral free wall of the left ventricle. They also found that the abnormalities were unchanged by peak exercise following the Bruce protocol in most of the segments studied, and even were normalized by the exercise in 14% of the segments. Hayes and colleagues [7] showed that the frequency of perfusion defects was similar in patients after the arterial switch operation and after a simple open heart operation, and they concluded that the myocardial perfusion defect was related more to the open heart operation itself than to the coronary artery manipulation. These studies suggest that the cause of the abnormality may be related to microemboli to the coronary arteries. A classic study by Taber and co-workers [20] demonstrated that microemboli composed of platelet aggregates frequently were observed in the hypovascular area at the apical portion of the left ventricle in patients who died of low cardiac output syndrome after open heart operations. Thus, the small left coronary arteries seen in our patients could be susceptible to microembolization, leading to a myocardial perfusion defect.
Regardless of its pathogenesis, the outcome resulting from this finding should be observed carefully to determine whether the small coronary arteries may cause myocardial ischemia through the abnormal size of the vessels or possible microembolization, leading to cardiac dysfunction at later stages. Our data and those of many other studies have shown that left ventricular function is well preserved in patients after the arterial switch operation [1–3]. Vogel and associates [5] reported that a regional perfusion defect was evoked by isoproterenol in the left ventricle. Arensman and associates [4] reported that the shape of the left ventricle after the arterial switch operation tended to be more globular than normal, and they implied that its function was latently compromised. Although they did not find any apparent coronary artery problems, the subtle dysfunction could be related to a myocardial perfusion defect and to the abnormality in coronary artery size.
One of limitations of the present study was that we used patients who had had Kawasaki disease as controls, which may not be adequate because Kawasaki disease often is complicated by coronary dilatation [21, 22]. We are able to make a fairly accurate diagnosis of coronary artery involvement in this disease [23], and it has been and always is routine to examine the coronary artery regularly from the onset of the disease. Given this background, we selected our controls as described previously, and the values of our controls were completely comparable to the normal data of Arjunan and colleagues [15], and of Ino [16]. In addition, the data reported by Leung and co-workers [11] showed that the total cross-sectional area of normal coronary arteries was 32.88 ± 7.34 mm2 in patients whose age ranged from 15 to 34 years. This value was comparable with or even larger than that extrapolated from our regression equation (Table 1), indicating that our control data from patients with Kawasaki disease were not necessarily larger than normal.
In conclusion, at midterm follow-up after the arterial switch operation for complete transposition of the great arteries, the left coronary arteries were small and were not compensated for fully by the large right coronary arteries. A careful follow-up study is mandatory to clarify the clinical significance of this finding, especially in relation to left ventricular function.
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Acknowledgments
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We thank Ms Barbara Levine for English editing of the manuscript.
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Footnotes
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Address reprint requests to Dr Nakazawa, Department of Pediatric Cardiology, Heart Institute of Japan, Tokyo Women's Medical College, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162 Japan (e-mail: pnakazaw{at}nora.hij.twmc.ac.jp).
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Abstract
Introduction
