Aims
To observe, describe, and evaluate management and timing of intervention for patients with untreated thoracic aortic aneurysms.

Methods and results
Prospective study of UK National Health Service (NHS) patients aged ≥18 years, with new/existing arch or descending thoracic aortic aneurysms of ≥4 cm diameter, followed up until death, intervention, withdrawal, or July 2019. Outcomes were aneurysm growth, survival, quality of life (using the EQ-5D-5L utility index), and hospital admissions. Between 2014 and 2018, 886 patients were recruited from 30 NHS vascular/cardiothoracic units. Maximum aneurysm diameter was in the descending aorta in 725 (82%) patients, growing at 0.2 cm (0.17–0.24) per year. Aneurysms of ≥4 cm in the arch increased by 0.07 cm (0.02–0.12) per year. Baseline diameter was related to age and comorbidities, and no clinical correlates of growth were found. During follow-up, 129 patients died, 64 from aneurysm-related events. Adjusting for age, sex, and New York Heart Association dyspnoea index, risk of death increased with aneurysm size at baseline [hazard ratio (HR): 1.88 (95% confidence interval: 1.64–2.16) per cm, P < 0.001] and with growth [HR: 2.02 (1.70–2.41) per cm, P < 0.001]. Hospital admissions increased with aneurysm size [relative risk: 1.21 (1.05–1.38) per cm, P = 0.008]. Quality of life decreased annually for each 10-year increase in age [–0.013 (–0.019 to –0.007), P < 0.001] and for current smoking [–0.043 (–0.064 to –0.023), P = 0.004]. Aneurysm size was not associated with change in quality of life.

Conclusion
International guidelines should consider increasing monitoring intervals to 12 months for small aneurysms and increasing intervention thresholds. Individualized decisions about surveillance/intervention should consider age, sex, size, growth, patient characteristics, and surgical risk.