Beyond the Segmental Code: Anatomic Diversity and Surgical Pathways in Left Atrial Appendage Isomerism with the {A,L,I} Combination

Background/Objectives: Left atrial appendage isomerism (LAAI) is associated with substantial variation in venous connections and intracardiac anatomy. A subgroup of LAAI patients has L-loop ventricular topology together with a particular great artery relationship—a combination that corresponds historically to Van Praagh’s {A,L,I} segmental notation—but this subgroup has not been separately characterized. We aimed to describe the anatomical spectrum, rhythm and conduction abnormalities, biventricular repair eligibility, and surgical pathways in this subgroup. Methods: This single-center retrospective study included 15 patients with LAAI, L-loop ventricular topology, and a specific great artery relationship (aorta left-sided, pulmonary artery right-sided)—a combination corresponding historically to Van Praagh’s {A,L,I} notation—evaluated between January 2010 and December 2025. Diagnosis was confirmed independently by echocardiography and cardiac computed tomography in all patients. Anatomical suitability for biventricular repair was determined by multidisciplinary consensus. Results: Median age at presentation was 3.0 months, and median follow-up was 31.0 months. An interrupted inferior vena cava was present in all patients. The great artery relationship was aorta left-posterior/pulmonary artery right-anterior in 12 patients, aorta left-anterior/pulmonary artery right-posterior in 2, and side-by-side in 1. Ventriculoarterial connection was concordant in 8 patients, double-outlet right ventricle in 6, and double-outlet left ventricle in 1. A common atrioventricular valve was present in 7 patients. Right ventricular outflow tract obstruction was present in 7 patients. Arrhythmia was documented in 6 patients, and 2 required permanent pacemaker implantation. Ten patients (66.7%) were considered anatomically eligible for biventricular repair; repair had been completed in 4, 2 had received interim palliation, and 4 remained awaiting surgery. The remaining 4 patients followed a single-ventricle pathway. One death was confirmed, and 2 patients were lost to follow-up. Conclusions: Within LAAI, the coexistence of L-loop ventricular topology and a specific great artery relationship was associated with ventriculoarterial concordance in most patients, which may support biventricular repair. Anatomical eligibility for repair, however, did not always translate into completed repair. Larger, multicenter studies are needed to confirm these findings.