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Aims Patients with tetralogy of Fallot (TOF) are often affected by right ventricular fibrosis, which has been associated with arrhythmias. This study aimed to assess fibrosis distribution in right ventricular outflow tract (RVOT) myocardium of TOF patients to evaluate the utility of single histology-section analyses, and to explore the possibility of fibrosis quantification in unlabelled tissue by second harmonic generation imaging (SHGI) as an alternative to conventional histology-based assays. Methods and results We quantified fibrosis in 11 TOF RVOT samples, using a tailor-made automated image analysis method on Picrosirius red-stained sections. In a subset of samples, histology- and SHGI-based fibrosis quantification approaches were compared. Fibrosis distribution was highly heterogeneous, with significant and comparable variability between and within samples. We found that, on average, 67.8 mm2 of 10 µm thick, histologically processed tissue per patient had to be analysed for accurate fibrosis quantification. SHGI provided data faster and on live tissue, additionally enabling quantification of collagen anisotropy. Conclusion Given the high intra-individual heterogeneity, fibrosis quantification should not be conducted on single sections of TOF RVOT myectomies. We provide an analysis algorithm for fibrosis quantification in histological images, which enables the required extended volume analyses in these patients.

BACKGROUNDAortic arch stenting is continuously emerging as a safe and effective option to alleviate aortic arch stenosis and arterial hypertension.CASE SUMMARYWe present a 15-year-old girl with aortic arch hypoplasia who had undergone implantation of an uncovered 22 mm Cheatham-Platinum stent due to severe (native) aortic arch stenosis. On follow-up seven months later, she presented a significant re-stenosis of the aortic arch. A second stent (LD Max 26 mm) was implanted and both stents were dilated up to 16 mm. After an initially unremarkable post-interventional course, the patient presented with hoarseness five days after the intervention. MRI and CT scans ruled out an intracranial pathology, as well as thoracic hematoma, arterial dissection, and aneurysm around the intervention site. Laryngoscopy confirmed left vocal fold paresis attributable to an injury to the left recurrent laryngeal nerve (LRLN) during aortic arch stenting, as the nerve loops around the aortic arch in close proximity to the area of the implanted stents. Following a non-invasive therapeutic approach entailing regular speech therapy, the patient recovered and demonstrated no residual clinical symptoms of LRLN palsy after six months.CONCLUSIONLeft recurrent laryngeal nerve palsy is a rare complication of aortic arch stenting not previously reported.