Residual abnormalities in aortic geometry may increase the risk of hypertension late after aortic coarctation repair. However, the role of residual abnormalities in regional aortic stiffness and resultant impedance mismatching (IM) has received less attention, despite IM being a key determinant of ventricular afterload. We hypothesized that both aortic geometry and IM between the ascending and proximal descending aorta are correlated with brachial (bSBP) and central (cSBP) systolic blood pressure.Design and method:
Phase contrast (PC) MRI was obtained in the proximal ascending aorta (AAp), transverse arch (TA), descending aorta distal to the coarctation site (DAc) and descending aorta at the diaphragm (DAd). Pulse wave velocities (PWV) in aortic segments were calculated as path length (from a TrueFISP angiogram) / transit time (from PC flow upstroke delay). Impedance mismatching was quantified as a reflection coefficient from vessel areas and PWV. cSBP was estimated by segmenting the AAp cross-sectional area waveform from PC magnitude images and calibrating to brachial mean and diastolic pressures. Aortic geometry was characterised as the aortic height-to-width ratio (H/W).Results:
Mean ± SD age at operation and MRI was 3.3 ± 4.3 and 29 ± 7 years. Repair type was subclavian flap (N = 13), end-to-end anastomosis (N = 5) or patch (N = 1). cSBP was lower than bSBP (104 ± 12 vs 122 ± 13 mmHg, p < 0.001). H/W was positively correlated with bSBP (R2 = 0.23, p < 0.04) and cSBP (R2 = 0.27, p < 0.02). PWV in the AAp-TA, AAp-DAc, TA-DAc and DAc-DAd segments were 5.0 ± 3.0, 5.9 ± 1.5, 8.0 ± 5.5 and 5.5 ± 3.2 m/s respectively. There were no relationships between bSBP or cSBP and AA-DAc PWV or DAc-DAd PWV. However, TA-DA PWV was positively related to bSBP (R2 = 0.28, p < 0.02) and more strongly to cSBP (R2 = 0.37, p < 0.007). This, and a counterintuitive negative linear relationship between AAp-TA PWV and cSBP (R2 = 0.24, p = 0.03; trend with bSBP, R2 = 0.19, p = 0.06), imply that IM may be a key determinant of systolic blood pressure. Indeed, IM between the AA-TA and TA-DAc segments (0.44 ± 0.35, range –0.31 to 0.8) showed a positive linear relationship with bSBP (R2 = 0.3, p = 0.017) and cSBP (R2 = 0.3, p = 0.014).Conclusions:
Aortic arch shape (H/W) and IM between the ascending aorta and proximal descending aorta may contribute to hypertension after coarctation repair.