Role of ambulatory blood pressure monitoring after pediatric renal transplantation

Abstract

Background: Office blood pressure (BP) readings, i.e., BP obtained in a clinical setting, are the basis of the present knowledge concerning the risks associated with hypertension. However, adult studies indicate that ambulatory BP measurements obtained over a 24-h period (ABPM) provides a much better representation of the patient s BP pattern than office readings, and that ABPM is a much better predictor of adverse outcome than office BP. Therefore, there has been a lot of focus on ABPM as a clinical tool to improve the estimate of true BP in hypertensive children. Since hypertension is a common post renal-transplant complication we carried out a series of studies in an attempt to determine the actual role of ABPM in our pediatric renal transplant recipients.

Methods: In all, 96 recipients from Argentina (72% male) were included in papers I and III and 136 recipients from Sweden (55% male) were included in papers II, IV, and V. Office BP was measured either by mercury manometer (paper I and III) or by an automated device (paper II). ABPM was applied in papers II, III, IV, and V.

Results: In paper I we observed that 76% of our study population was on antihypertensive treatment at recipients last follow-up. We noted that a rather low number of recipients (prevalence 19%) were diagnosed as having non-controlled hypertension, i.e., office BP within the hypertensive range while on antihypertensive treatment. A limitation in the data interpretation is that BP was in fact not evaluated by means of ABPM and therefore we may have derived a misleading conclusion. In paper III, and in line with this hypothesis, we found that almost one-third of the treated hypertensive recipients, in whom BP appeared to be controlled according to office BP, had in fact non-controlled hypertension by ABPM criteria. We also observed that the two methods of BP measurement did not agree closely. In a previous study (paper II), we demonstrated that long-term reproducibility of ABPM is superior to that for office BP. In paper IV we aimed to analyze the impact of BP on arterial wall structure, which is regarded as a potential surrogate marker of hypertensive vascular damage, as evaluated by repeated vascular ultrasound examinations. Baseline carotid artery intima-media thickness (cIMT) was found to be significantly higher in renal transplants compared with healthy controls. After a 4-year follow-up, and regardless of recipients ambulatory BP status, follow-up cIMT was not significantly different compared with baseline cIMT. In paper V we analyzed the role of repeated ABPM following transplantation as a reference method to better characterize recipients BP pattern. At the recipients last follow-up visit we observed that more than three quarters of our treated hypertensive recipients displayed controlled BP. This figure was significantly higher compared to our historical control group, in whom ABPM was applied for the first time during antihypertensive treatment after transplantation while therapeutic decisions were driven by office BP measurements (difference between proportions 48.6% (80.6% - 32%); 95% CI for difference, 36% to 60%, P = 0.001).

Conclusions: In a population at high risk for hypertension we observed that the reproducibility of ABPM was superior to that for office BP measurements and that the two methods of BP measurement do not closely agree. We infer, therefore, that office BP and ABPM should not be used interchangeably. In our study population, cIMT was not found to be a reliable surrogate marker of hypertensive organ damage. Finally, we demonstrated that the routine use of repeated ABPM following transplantation has significantly improved our method of identification and management of hypertensive renal transplant recipients.