Rhythmicity in 24 hour blood pressure measurements after pediatric kidney transplantation and its relation to cardiovascular end organ damage

Objective: Cardiovascular risk factors, especially arterial hypertension, are very common after kidney transplantation (KTx) during childhood. Ambulatory blood pressure monitoring (ABPM) is the gold standard of hypertension diagnostics. The present study analyzes circadian and ultradian rhythms in ABPM and their association with left ventricular mass and aortic pulse wave velocity as markers of cardiovascular end organ damage. Design and method: From a prospective international multicenter observational study ABPMs of 151 children and adolescents after KTx could be analyzed. They were compared to a healthy cohort of 299 schoolchildren matched for gender and body length. Partial Fourier analysis was used to examine oscillatory fluctuations at 24, 12, 8 and 6 hours (h) period lengths in order to detect rhythms in both mean arterial pressure (MAP) and heart rate (HR). These rhythms could be further characterized in their amplitude as well as their acrophase which is the time interval until maximum amplitude after midnight. Results: In patients after KTx, a 12h rhythm in the MAP (figure panel A) and an 8h rhythm in HR were significantly more frequent than in healthy children. No difference in rhythm frequency was found for the other period lengths. Amplitudes in MAP were significantly smaller after KTx (24h, 8h, 6h) and MAP acrophases were significantly longer (24h, 12h, 8h) than in the control group (figure panel B and C). Significantly smaller amplitudes and longer acrophases were observed in the KTx cohort for HR as well. Data assessing cardiovascular end organ damage was available for children after KTx: We observed a positive correlation of 24h MAP amplitude with arterial pulse wave velocity (r=0.19; p=0.036) and a comparable trend with 8h MAP amplitude (r=0.31; p=0.053). Left ventricular mass did not correlate with any of the rhythm parameters after KTx. Conclusions: Our analysis demonstrates altered circadian and ultradian cardiovascular rhythmicity after KTx. Compared to healthy children, the described rhythms are flattened and delayed. Interestingly, there was a correlation of MAP amplitudes with vascular stiffness that warrants further investigation. Hence, we are going to analyze follow-up ABPM measurements in the described cohort after KTx.