## 4 Discussion  
The PATHFINDER-CHD Registry was established in response to a notable gap in the scientific and clinical discourse: while obesity is firmly established as a major cardiovascular risk factor in general cardiology, its relevance in the context of adult congenital heart disease has only recently garnered scientific attention. A targeted literature review confirms that this topic has been more intensively addressed within the last decade, with overall limited published evidence to date [16]. Reported prevalence rates for obesity in the ACHD populations vary substantially, ranging from 7% to 26%, while rates of overweight status lie between 22% and 53% depending on study design, patient cohort, and geographic region [7; 16; 17]. There are no data on obesity in ACHD with different stages of HF. In contrast to this emerging epidemiological data, current ACHD guidelines still reflect a surprising lack of engagement with the issue. Neither the 2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease [2] nor the 2020 ESC Guidelines [3] include specific recommendations on the assessment, monitoring, or management of obesity in ACHD patients. At best, obesity is mentioned in passing, without substantive discussion of its implications for pathophysiology, prognosis, or therapy. This neglect is particularly striking when compared to general HF guidelines, where obesity is consistently recognized as a key modifiable risk factor that influences disease onset, progression, and treatment outcomes [18; 19]. In contrast, ACHD care has largely overlooked this issue, likely due to the outdated perception that congenital heart defects are primarily pediatric conditions and that adult survivors form a small, exceptional group. Yet this perspective no longer holds: more than 350,000 ACHD patients live in Germany, and an estimated 50 million worldwide [5], with most surviving into adulthood and accumulating additional comorbidities over time. Studies from Europe and North America consistently show that ACHD--especially those with simple or moderately complex defects--face a comparable or even elevated burden of obesity and associated cardiometabolic risk factors, including hypertension, dyslipidemia, and diabetes mellitus [20; 21; 22]. Yet, lifestyle counselling and structured weight management are rarely incorporated into their routine follow-up. In a large multicenter study from the German National Register for Congenital Heart Defects, over 50% of ACHD were classified as overweight or obese, while targeted preventive measures were inconsistently applied [23]. The findings from the PATHFINDER-CHD Registry corroborate these observations in a systematically documented, real-world cohort. Nearly half of the included ACHD with HF were overweight or obese (46.1%), with overweight alone affecting one-third of the cohort. This prevalence is consistent with prior international reports [17; 24] and highlights the need for structured obesity screening and intervention as part of ACHD care. Importantly, in PATHFINDER-CHD, BMI was significantly associated with cardiovascular and metabolic comorbidities such as arterial hypertension, obstructive sleep apnea,