Is greater than normal nocturnal heart rate in children with renal scars a predictor of reflux nephropathy?

BACKGROUND

The existence of renal scars constitutes the major etiologic factor for the development of hypertension during childhood. Elevated blood pressure in this setting can be considered a secondary form of hypertension. Certain forms of secondary hypertension have been associated with a lower than normal nocturnal fall in blood pressure. Resting heart rate per se has recently been reported to be an independent predictor of risk for cardiovascular mortality irrespective of age and the presence or lack of hypertension.

OBJECTIVE

To ascertain the responses of heart rate and blood pressure in normotensive children with renal scars without, however, proteinuria and renal failure.

METHODS

Ten children with renal scars documented by a 99Tc dimercaptosuccinic acid (DMSA) scan were subjected to ambulatory blood pressure monitoring. Ten age-matched and sex-matched healthy children served as the control group. Serum urea and creatinine levels, calculated rate of clearance of creatinine, microalbuminuria, plasma renin activity, and levels of aldosterone and catecholamines were determined for each subject.

RESULTS

Average daytime and night-time systolic and diastolic blood pressures for the two groups did not differ. Subjects in both groups demonstrated the physiologic decrease in blood pressure during sleep (normal 'dipper' response), which was of equal magnitude for these two groups. Mean daytime heart rates were 92+/- 13 beats/min in children with renal scars versus 80+/-11 beats/min in controls (NS). Mean and minimal heart rates during night-time in children with renal scars were found to be significantly greater [79+/-6 versus 65+/-5 beats/min (mean) and 61+/-10 versus 56+/-7 beats/min (minimal), P < 0.01]. Parameters of renal function, plasma renin activity, and levels of aldosterone and catecholamines were similar for these two groups.

CONCLUSION

Despite their having an equivalent physiologic dip in blood pressure during night-time, normotensive children with renal scars have a significantly greater nocturnal heart rate than do control subjects.