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To evaluate a possible neural or renal contribution to the hypertension that occurs in some patients following coarctation of aorta repair, 35 patients underwent graded bicycle exercise with serial measurements of plasma norepinephrine concentrations and plasma renin activity. Sixteen patients with coarctectomy who had systolic or diastolic hypertension at peak exercise were compared with 19 normotensive patients with coarctectomy. The average time interval between coarctation repair and study was significantly longer (p less than 0.05) in the hypertensive group than in the normotensive patients (12.8 +/- 4.8 versus 8.7 +/- 2.2 years). The heart rate response to exercise was similar for both patient groups. The systolic blood pressure in the hypertensive group was higher than in the normotensive group at rest in the supine and upright positions and at 5 minutes of recovery, in addition to peak exercise, and the diastolic blood pressure was increased at peak exercise. Plasma norepinephrine concentrations were significantly higher at peak exercise and during recovery in the hypertensive group than in the normotensive patients. Plasma renin activity was also significantly higher in the hypertensive group at peak exercise. These data suggest that patients with coarctectomy who have a hypertensive response to exercise have an augmented sympathetic nervous system output and increased plasma renin activity that may lead to peripheral vasoconstriction at peak exercise and that may contribute to the development of their hypertension.

A prospective comparison of physiologic response to single-rate ventricular and dual-chamber atrioventricular pacing was conducted in 14 pediatric patients (age 1 to 24 years, median 14) with symptomatic nonsurgical second- or third-degree atrioventricular block. All patients were studied acutely during cardiac catheterization before and after 1 hour of both pacing modes. Following pacemaker implant, eight patients were reevaluated after 1 month of each mode with symptom questionnaire, resting ECG, resting echocardiogram, and Doppler cardiac output measurement at rest and at peak treadmill exercise. Cardiac outputs (mean +/- standard error) increased acutely (n = 14) with both ventricular (32 +/- 12%) and dual-chamber (39 +/- 10%) pacing over intrinsic rhythm values (p less than 0.01 in both). During chronic pacing (n = 8), symptoms were reported only with the ventricular mode. Dual-chamber synchronous pacing was associated with improved mean resting shortening fraction and cardiac output, slower mean resting sinus rate (89 +/- 5 compared to 73 +/- 4 bpm (p less than 0.02), and a 23% increase in mean excerise cardiac output (4.2 +/- 0.4 compared to 3.4 +/- 0.3 L/min/m2) compared to single-rate ventricular pacing. Exercise-induced dysrhythmias occurred only with ventricular pacing. This study demonstrates that pediatric patients with nonsurgical atrioventricular block can compensate for loss of atrioventricular synchrony at rest but exhibit improved cardiac function with chronic dual-chamber atrioventricular compared to single-rate ventricular pacing.