Background Main pulmonary artery (MPA) dilation is reported to occur in association with pulmonary valve (PV) abnormalities and in genetic diseases of connective tissue.

Aim To determine whether MPA dilation occurs with bicuspid aortic valve (BAV) in the absence of PV abnormality.

Methods MPA and aortic dimensions were investigated in 194 subjects with BAV and 178 controls matched for age, sex and body surface area (BSA) using transthoracic two-dimensional echocardiography. Using control measurements, linear regression of each parameter versus age, gender, and BSA^2/3 provided expected values. For each subject with BAV, the percentage divergence from expected value ((observed − expected value)/expected value) for each dimension was analysed.

Results MPA and aortic measurements showed normal distribution in all subjects. PV annulus and MPA were larger in BAV; 17.7% positive divergence of MPA dimension from expected was found in diastole, and 16.7% in systole. Aortic dimensions at all levels measured were larger in BAV; divergence was greater distally than proximally (10% divergence at annulus, 31% at ascending aorta). In BAV, divergence of ascending aortic dimensions from expected values increased with age (r²=0.142, p=0.02), but MPA divergence from expected values did not increase with age (r²=0.001, p=0.296).

Conclusions MPA dilation occurs in association with BAV in the absence of PV abnormality, suggesting primary vessel wall pathology predisposing to arterial dilation. A systemic abnormality of connective tissue common to both arteries may be responsible, or the dilation may result from a common developmental exposure as both originate from the embryologic cono-truncus.