Morphologic Substrates for First-Branch Pulmonary Arterial Hypoplasia in Transposition of the Great Arteries

Abnormal Pulmonary Artery Bending Correlates With Increased Right Ventricular Afterload Following the Arterial Switch Operation

PURPOSE

In transposition of great arteries, increased right ventricular (RV) afterload is observed following arterial switch operation (ASO), which is not always related to pulmonary artery (PA) stenosis. We hypothesize that abnormal PA bending from the Lecompte maneuver may affect RV afterload in the absence of stenosis. Thus, we sought to identify novel measurements of three-dimensional cardiac magnetic resonance (CMR) images of the pulmonary arteries and compare with conventional measurements in their ability to predict RV afterload.

METHODS

Conventional measurements and novel measurements of the pulmonary arteries were performed using CMR data from 42 ASO patients and 13 age-matched controls. Novel measurements included bending angle, normalized radius of curvature (R_c), and normalized weighted radius of curvature (R_c-w). Right ventricular systolic pressures (as the surrogate for RV afterload) were measured by either recent echocardiogram or cardiac catheterization.

RESULTS

Conventional measurements of proximal PA size correlated with differential pulmonary blood flow (r = 0.49, P = .001), but not with RV peak systolic pressures (r = -0.26, P = .18). In ASO patients, R_c-w correlated with higher RV systolic pressures (r = -0.57, P = .002). Larger neoaortic areas and rightward bending angles correlated with smaller right pulmonary artery R_c (r = -0.48, P = .001; r = 0.41, P = .01, respectively). Finally, both pulmonary arteries had significantly smaller R_c compared to normal controls.

CONCLUSIONS

Pulmonary arteries exhibit abnormal bends following ASO that correlate with increased RV afterload, independent of PA stenosis. Future work should focus on clinical and hemodynamic contributions of these shape parameters.

The Concept of the Arch Window in the Spiral Switch of the Great Arteries

When the arterial switch operation includes the Lecompte maneuver, the arterial trunks are reconnected in parallel, rather than the spiral fashion observed in the normal heart. Thus, although the ventriculo-arterial connections are hemodynamically corrected, the anatomic arrangement cannot be considered normal. We hypothesized that, if feasible, it would be advantageous to restore a spiral configuration for the arterial trunks. In 58 patients, we reconstructed the arterial trunks such that, postoperatively, the pulmonary channel spirals round the aorta, passing to either the right or the left, and branches posteriorly. We compared the outcomes with those in 95 patients undergoing a standard non-spiraling operation over the same period. Average follow-up was 8.2 ± 4.5 years. The estimated 10-year survival was similar in the cohorts, at 94.7 % for those with spiraling trunks, as compared to 90.4 % for those with parallel outflow tracts. Reoperation-free survival at 10 years was not significantly different (87.6 vs. 90.5 %). Supravalvar pulmonary stenosis, aortic neo-coarctation, or left bronchial stenosis, however, was encountered in one-eighth of those undergoing a standard operation. None of these complications occurred in those patients who, postoperatively, had spiraling outflow tracts (P = 0.002). Reconstruction of spiraling trunks after the arterial switch has, thus far, avoided the complications of supravalvar pulmonary stenosis, neo-aortic kinking, or bronchial stenosis. The spiraling arrangement prevents compression of the pulmonary vessels and bronchial tree by the aorta, since it provides a wide window in the new aortic arch.

Comparison of bilateral pulmonary arterial level and diameter in transposition of the great arteries

In normal anatomy, the left pulmonary artery (LPA) is usually situated higher than the right pulmonary artery (RPA); however, transposition of the great arteries (TGA), the LPA is not always situated higher than the RPA. This study was performed to clarify the relative position of the RPA and the LPA in transposition of the great arteries (TGA) as well as the implications. We reviewed 101 angiograms of patients with TGA (age 4.1 ± 1.2 months). The width of the RPA, the LPA, and the pulmonary trunk (PT) were measured just before their first branch in the frontal view. They were classified into four groups according to the ratio between the RPA and the PT (RPA/PT). The initial courses of the LPA and the RPA were compared and defined according to their height in the frontal view, and the preferential flow (or not) to the RPA was recorded. The equation of hydrodynamics was applied to evaluate the bifurcation angle. Both PAs were the same size in all cases. Forty-eight patients (47.5 %) had a RPA/PT diameter ratio < 0.49. The LPA coursed higher than the RPA in the majority of cases (81 [80.2 %]); in a minority of cases the LPA and RPA were at the same level (6 [5.9 %]); and in some cases the RPA coursed higher than the LPA (14 [13.9 %]). Patients with a high degree of PA hypoplasia tended to have both PAs at the same level or a higher-positioned RPA. Autopsy (1 of 3 cases) showed a posterior ridge against the bronchus in the higher RPA. Hydrodynamic calculation showed that the greater the angle between the RPA/PT, the greater the preferential flow. Preferential flow to the RPA in TGA did not necessarily result in LPA hypoplasia before its first branch. Higher RPA position relative to the LPA was associated with greater flow in it against the posterior bronchus. This situation was more prevalent in patients with severe PA hypoplasia.

Restoration of Transposed Great Arteries to Nature

Surgical correction of transposition of the great arteries was proposed by many in the past half-century and was claimed as the anatomical correction, but the treatment of choice was ever changing. The current technique usually includes the Lecompte maneuver to bring the pulmonary bifurcation in front of the aorta. Although the ventricular–arterial connection is corrected, it is not “normal.” This review describes an innovative technique to reconstruct the great arteries in spiral fashion, which is the natural relationship of the aorta and pulmonary artery. The surgical principles of nature and even distribution using autologous tissues are emphasized. The structural and functional studies of the spiral great arteries in the last 2 decades are also presented.