The abnormal aorta: a statistical definition and strategy for monitoring change.

Abstract

This study defines a protocol for monitoring the growth of small abdominal aortic aneurysms based on age-related abnormality thresholds, observed aortic growth patterns and the limits of precision of the measurement technique. 13000 men aged 60 - 75 years were invited to their GP's surgery for measurement of the maximum diameter of the infrarenal aorta. Seventy-six percent responded and measurement was possible in 97.1% of the respondents. The AP diameter of the aorta was measured according to a strict protocol, with a portable ultrasound scanner. Cases were recruited from the conurbation of Birmingham and Solihull, U.K. CHIEF OUTCOME MEASURE: A statistical description of the differences in distributions of aortic diameters of four age groups of males. The aorta expands in diameter during the seventh and eighth decade for up to 25% of all those screened. The order of magnitude of this change is similar to that previously attributed to the growth of small aneurysms. Age-related thresholds for abnormality should range from 24 mm for a 60 year old to 37 mm for a 75 year old. Using data on the expected maximum rate of change of the dilated aorta and statistically derived thresholds from this analysis a monitoring strategy is suggested for those with an abnormal aorta.