The assessment of kidney hemodynamics by kidney Doppler in adolescents after correction of coarctation of the aorta

The aim of our study was to compare kidney Doppler signals in adolescents with coarctation of aorta after surgical repair or after balloon dilatation to healthy controls and additionally to find out whether kidney Doppler signals might differ in patients with re-coarctation.

A total of 20 adolescents were included in our prospective study, 15 after coarctation repair, (4 of them with re-coarctation) and 5 controls. The age, body mass index (BMI), serum creatinine, average daily systolic (SBP) and diastolic blood pressure (DBP) obtained by ABPM  (ambulatory blood pressure measurement) were analyzed. Scans of kidneys were performed using ultrasound machine Esaote MyLabX8, convex probe having frequency range from 2 to 5 MHz. Right and left kidney were examined in each patient and control subject. Kidney length and Doppler study were performed with patient in supine position. Blood flow velocities were measured in segmental arteries of the upper, medial and lower part of both kidneys and average resistant index (RI) and acceleration index (AI) were calculated. The stenosis of renal arteries was excluded in all subjects, peak systolic velocities were less than 120 cm/s. 

All together 40 kidneys were analyzed in 20 patients, who were classified to group 0 (5 controls/10 kidneys), group 1 (11 patients after coarctation repair without re-coarctation/22 kidneys) and group 2 (4 patients with re-coarctation/8 kidneys). 

The groups 0 and 1 did not differ in BMI (24,5 ± 3,1 vs. 23,3 ± 6,0 kg/m2), creatinine (64,8 ± 13,8 vs. 61,3 ± 8,0 µmol/L), SBP (127 ± 4,7 vs. 129 ± 8,0 mmHg) and kidney length (108,2 ± 7,0 vs. 104,9 ± 8,5 mm). There was statistically significant difference in age (16,6 ± 2,6 vs. 15,2 ± 2 years; p=0,039) and DBP (72,8 ± 5,8 vs. 65,8 ± 6,9 mmHg; p=0,04). 

The groups 1 and 2 did not differ in age (15,2 ± 2,0 vs. 14,0 ± 0,73 years), creatinine (61,3 ± 8,0 vs. 65,5 ± 10,4 µmol/L), SBP (129 ± 9,4 vs. 129,3 ± 4,3 mmHg), DBP (65,8 ± 6,9 vs. 61,5 ± 6,7) and kidney length (104,9 ± 8,5 vs. 106,2 ± 6,6 mm). There was statistically significant difference in BMI (23,3 ± 6,2 vs. 18,18 ± 2,0 kg/m2; p=0,03). 

Calculated RI of kidneys was significantly lower in group 1 comparing to group 0 (0,62 ± 0,03 vs. 0,57 ± 0,04; p<0,001) and even lower in group 2 comparing to group 1 (0,53 ± 0,04 vs. 0,57 ± 0,04; p=0,033). Blood pressure and age were not associated with RI, which was significantly lower in children after coarctation repair or in re-coarctation (p<0,001).

There was no significant difference in calculated AI of kidneys between 0 and 1 (6,67 ± 3,17 vs. 4,79 ± 3,18 m/s2), and 1 and 2 (4,79 ± 3,18 vs. 6,03 ± 2,47 m/s2) groups. 

According to our study, adolescents after aortic coarctation repair (without renal artery stenosis) have significantly lower resistance index compared to controls. RI was the lowest in patients with re-coarctation, that may be helpful during follow-up of these patients.