New Model Uses Ordinary Clinical Data to Estimate Ascending Aortic Diameter in Asymptomatic Individuals

Aneurysms of the ascending aorta are asymptomatic, usually discovered incidentally during thoracic imaging for other indications, but they are an important cause of sudden death.

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Massachusetts General Hospital researchers have developed and validated a clinical risk model, AORTA (aorta optimized regression for thoracic aneurysm), that uses readily available clinical data to estimate aortic diameter in ambulatory patients not suspected of having thoracic aortic disease. Patrick T. Ellinor, MD, PhD, acting chief of Cardiology and the co-director of the Corrigan Minehan Heart Center at Mass General, James P. Pirruccello, MD, a cardiologist at the Corrigan Minehan Heart Center, and colleagues describe the development and validation of the AORTA score in JAMA.

Training and Internal Validation

AORTA was developed by measuring ascending aortic diameters on magnetic resonance images from 30,018 participants in the UK Biobank. 52% were women, and the median age was 65.

The trained model retained all variables provided: age, sex, body mass index, heart rate, systolic and diastolic blood pressure, height, weight, the presence or absence of diabetes, hypertension, or hyperlipidemia, and several interaction terms between those variables.

The AORTA score's performance was internally validated by 6,681 other participants in the UK Biobank. The primary outcome, the correlation coefficient between AORTA and the actual measured aortic diameter, was 0.53 (95% CI, 0.52–0.55).

External Validation

AORTA was externally validated in the following ways:

• 1,367 participants in the Framingham Heart Study (FHS) Offspring cohort who had ascending aortic diameter measured for research purposes from noncontrast CT. The correlation coefficient was 0.56 (95% CI, 0.52-0.59)
• 50,768 primary care patients represented in the Mass General Brigham (MGB) Biobank who had ascending aortic diameter measured from transthoracic echocardiography for clinical indications. The correlation coefficient was 0.57 (95% CI, 0.56–0.58)

The score tended to underestimate the size of enlarged aortas in the external validation cohorts.

Clinically Relevant Threshold

The clinically relevant threshold for moderately enlarged aortic diameter was 4 cm. For detecting individuals with an ascending aortic diameter ≥4 cm, the AORTA score had an area under the receiver operator characteristic curve of:

• UK Biobank—0.77
• FHS cohort—0.81
• MGB Biobank—0.77

Stringent Threshold

Within the UK Biobank training set, the top 2.3% of the AORTA score corresponded to an estimated aortic diameter of 3.537 cm. Using a fixed-score threshold of 3.537 cm:

• UK Biobank—9.7 people would need imaging to confirm 1 individual with ascending aortic diameter ≥4 cm; the sensitivity at that threshold was 9%, but the specificity was 98%
• FHS cohort—1.8 people would need imaging; sensitivity, 11%; specificity, 99%
• MGB Biobank—4.6 people would need imaging; sensitivity, 18%; specificity, 96%

Future Directions

Ascending aortic diameter is highly heritable (40%–63%), so efforts to optimize the AORTA model could incorporate polygenic scores. To enable future research, including prospective trials, the researchers have made the source code and model weights freely available online along with the AORTA score calculator.

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