Responses of non-obese white children to treadmill exercise.

OBJECTIVE: To determine the response to maximal treadmill exercise with the Bruce protocol in a cohort of healthy non-obese American children and adolescents. STUDY DESIGN: A retrospective review of treadmill exercise studies on 347 white American children (188 boys, 159 girls) aged 5 to 18 years was performed with metabolic criteria to verify maximal exercise effort. Data on exercise endurance time, heart rate, blood pressure, and metabolic variables were assessed and compared between age groups and sexes by unpaired t testing and analysis of variance. RESULTS: Exercise endurance time was lower in all age groups when compared with earlier published data. Girls had a lower endurance time than boys at all ages. There was no significant difference in maximum heart rate with respect to age or sex. The maximum systolic blood pressure and diastolic blood pressure increased with increasing age in both boys and girls. Boys had significantly higher maximum systolic blood pressure and diastolic blood pressure after 13 years of age. The maximum absolute oxygen consumption and indexed oxygen consumption showed similar trends for both sexes. CONCLUSION: Lower exercise endurance times are seen despite physiologic evidence of maximal effort, raising the possibility that cardiovascular conditioning is reduced in contemporary American children.

Procainamide for rate control of postsurgical junctional tachycardia.

This study was conducted to determine the efficacy of procainamide therapy for rapid rate control of postoperative junctional tachycardia (JT). Postoperative JT is one of the most difficult forms of tachycardia to manage. Reported success with a variety of treatments of JT in infants and children has been inconsistent and limited. Rate control using procainamide was achieved in 17 children having rapid JT (heart rate >200 beats/min) between 1986 and 1997. In the first 5 patients (protocol A), following a loading dose of 3 mg/kg over 20 minutes, a continuous procainamide infusion was initiated at a rate of 20 microg/kg/min. The infusion dose was increased in 10 microg/kg steps every 30 minutes to 40-120 microg/kg/min until the heart rate decreased below the target rate of 180 beats/min. In the other 12 patients (protocol B), after a higher loading dose of 10 mg/kg the infusion rate was increased every 10-15 minutes until the heart rate decreased below the target rate of 180 beats/min. Procainamide decreased JT rates in all patients but the response was significantly faster in protocol B. In the patients treated with protocol A, pretreatment JT rates ranged from 203 to 240 (213+/-17) beats/min and decreased to 195+/-10 beats/min at 2 hours (p = ns), 186+/-8.8 at 4 hours (p<0.02), and 179+/-8 at 6 hour postinitiation of PA. In protocol B, pretreatment JT rates ranged from 201 to 240 (218+/-17) beats/min and decreased to 183+/-20 beats/min at 2 hours (p<0.001) and 171+/-12 at 4 hours after starting the procainamide therapy. The mean duration to decrease JT rates below the target rate of 180 beats/min was 3.2+/-1.1 hours in protocol B compared to 6.4+/-3.8 hours in protocol A (p<0.02). Eight of 12 patients in protocol B achieved rate control below the target rate of 180 beats/min within 4 hours despite remaining on significant inotropic support. The procainamide infusion rates to maintain heart rates below 180 beats/min were 40-120 (68.4+/-22.1) microg/kg/min. No proarrhythmia, bradycardia, or significant hypotension was observed. In this series procainamide provided safe, effective, and rapid rate control of JT occurring in the immediate postoperative period.

Exaggerated blood pressure response to exercise in children with increased low-density lipoprotein cholesterol.

Arterial vascular responses are characteristically altered with hypercholesterolemia: conduit vessels manifest increased stiffness, and conduit and resistance vessels demonstrate impaired endothelium-dependent dilation and augmented vasoconstriction to neurohumoral stimulation. These changes should be reflected in an exaggerated blood pressure increase in response to exercise. To evaluate this hypothesis, we compared the blood pressure response to treadmill exercise in children with hypercholesterolemia and children with normal lipid levels. In a preliminary retrospective study, 15 hypercholesterolemic boys 10 to 18 years old underwent treadmill exercise testing, and their blood pressure results were compared with those of 32 normolipidemic children in the same age group who had undergone treadmill exercise electively in the same time period. In the second phase, 10 hypercholesterolemic boys and 10 normolipidemic age-matched boys were evaluated prospectively according to the same protocol. Treadmill exercise involved a modified Bruce protocol with heart rate and blood pressure measured before exercise, immediately after exercise, and throughout recovery. Office blood pressures were normal in all children, with no significant difference between groups. With treadmill exercise, all subjects achieved >95% of predicted maximum heart rate and endurance times, maximum oxygen consumption, and maximum respiratory ratio did not differ between groups. Results of the retrospective and prospective groups were similar and were therefore combined. Children with increased low-density lipoprotein (LDL) cholesterol had significantly higher systolic and diastolic blood pressures immediately before treadmill exercise (systolic 120 +/- 13 mm Hg vs 113 +/- 13 mm Hg, p < 0.03; diastolic 68 +/- 8 mm Hg vs 63 +/- 9 mm Hg, p < 0.01). After exercise, blood pressures were again significantly higher in the subjects with high LDL cholesterol (systolic 182 +/- 20 mm Hg vs 160 +/- 23 mm Hg, p < 0.0003; diastolic 77 +/- 12 mm Hg vs 72 +/- 9 mm Hg, p < 0.03). At the end of recovery, systolic blood pressures remained significantly higher in subjects with high LDL cholesterol (120 +/- 9 mm Hg vs 112 +/- 12 mm Hg, p < 0.005). In this study, children with severely increased LDL cholesterol had an exaggerated blood pressure response to exercise when compared with normolipidemic control subjects. The study findings suggest that control of arterial vascular tone may already be altered in children with hypercholesterolemia.

Postoperative assessment of a modified surgical approach to repair of tetralogy of Fallot. Long-term follow-up.

BACKGROUND: After repair of tetralogy of Fallot, right ventricular (RV) dilation has been associated with increased risk of ventricular arrhythmias and sudden death. To address this, a modified repair was developed. METHODS AND RESULTS: We followed two postoperative groups: group 1 (n = 20) received repair of tetralogy of Fallot with the modified technique with transatrial ventricular septal defect closure, a short infundibular incision with avoidance of muscle resection, and patch expansion of the RV outflow tract; group 2 (n = 22) received repair of tetralogy of Fallot by the traditional technique with ventricular septal defect closure through a ventriculotomy with resection of obstructing muscle. Six patients were excluded from further follow-up: two patients, one in each group, who required RV-pulmonary artery conduit placement at original repair; one patient in group 1 who developed double-chamber RV; and three patients, two in group 1 and one in group 2, who were lost to our follow-up < 5 years postoperatively. We compared postoperative findings > 10 years after repair. Despite similar residual RV outflow tract stenosis and obligatory pulmonary insufficiency by examination and Doppler echocardiography, RV size was smaller in the modified group, as reflected by RV/left ventricle on M-mode echocardiography (0.66 +/- 0.22 versus 0.81 +/- 0.17, P = .02), cardiothoracic ratio (0.53 +/- 0.04 versus 0.58 +/- 0.06, P = .03), and QRS duration (126 +/- 19 versus 143 +/- 23, P = .03). RV systolic function was more impaired in group 2, as reflected by decreased systolic tricuspid annulus excursion on two-dimensional echocardiography. Exercise endurance time was significantly higher in group 1 patients. Lown grade 4 ventricular ectopy on ambulatory ECG was present in three patients in group 2 and none in group 1. CONCLUSIONS: The modified technique results in significantly less RV dilation and better preservation of RV function at late follow-up.

Loss of sinus rhythm after total cavopulmonary connection.

BACKGROUND: Total cavopulmonary connection (TCPC) to repair functional single ventricle involves the sinus node area, in contrast to the Fontan procedure. We compared ECG findings after TCPC and Fontan to evaluate the impact of the cavopulmonary connection on sinus rhythm postoperatively. METHODS AND RESULTS: The Fontan group consisted of 17 patients repaired at 7.8 +/- 3.1 years of age (mean +/- SD): 11 for tricuspid or pulmonary atresia (TA/PA) and 6 for single ventricle. The TCPC group consisted of 19 patients repaired at 5.1 +/- 3.2 years of age (mean +/- SD) (P < .001): 9 for TA/PA, 4 for single ventricle, and 6 for hypoplastic left heart syndrome. Mean follow-up after Fontan was 7.7 +/- 2.7 years versus 2.8 +/- 1.6 years for TCPC (P < .001). Preoperative ECGs on all TCPC patients showed sinus rhythm (SR), whereas 16 of 17 Fontan patients had SR and one had nonsinus atrial rhythm (NSAR) since birth. On the first postdischarge ECG, 12 of 19 TCPC patients (63%) were in SR, 4 were in junctional rhythm (JR), and 3 were in NSAR. In comparison, 15 of 17 Fontan patients (88%) were in SR with 1 of 17 in NSAR and 1 in supraventricular tachycardia (P < .05 with chi 2 test). By 2 years postoperatively, only 6 of 15 TCPC patients available for follow-up (40%) were in SR, with 7 of 15 in JR and 2 of 15 in NSAR. By contrast, 13 of 17 Fontan patients (76%) remained in SR, with 1 in NSAR and 3 in JR (P < .05 with chi 2 test). TCPC patients with loss of SR did not differ from other patients in the group in age at repair, preoperative diagnosis, or surgeon performing the procedure. CONCLUSIONS: This significant incidence of loss of SR temporally related to surgery suggests that operative compromise of the sinus node area is common with TCPC.

Modified technique for balloon valvuloplasty of critical pulmonary stenosis in the newborn.

OBJECTIVES: We report our experience in eight consecutive neonates who underwent attempted balloon dilation as an initial therapy for critical valvular pulmonary stenosis, and we review in detail technical modifications that improved the success rate. BACKGROUND: Balloon dilation of the pulmonary valve has become the treatment of choice for valvular pulmonary stenosis in children and adults. There are few reports of its effectiveness in critical pulmonary stenosis in the newborn. In this setting, application of the technique of balloon dilation has been limited by the ability to advance the necessary guide wires and catheters across the stenotic, often near-atretic, pulmonary valve. METHODS: The pulmonary valve was crossed in all patients. When this could not be accomplished with an end-hole catheter, a soft guide wire was advanced directly across the pulmonary valve through the end-hole catheter positioned in the right ventricular outflow tract below the valve. Initial predilation was achieved in all patients by using a coronary dilation catheter in an effort to facilitate introduction of the definitive balloon dilation catheter. Definitive dilation with a balloon diameter of > or = 110% of the diameter of the pulmonary valve annulus was possible in six patients. RESULTS: Right ventricular pressure declined from a mean value of 108 +/- 32 mm Hg to a mean value of 49 +/- 11 mm Hg after balloon dilation, with no change in heart rate or aortic pressure in these six patients after definitive balloon dilation. CONCLUSIONS: The results of this small series suggest that critical valvular pulmonary stenosis in the newborn can be successfully treated by transluminal balloon valvuloplasty.

When is echocardiography unreliable in patients undergoing catheterization for pediatric cardiovascular disease?

Technologic advances in echocardiography (e.g., better spatial resolution, Doppler, and color flow mapping) have improved our ability to demonstrate anatomy and physiology in previously problematic conditions, precluding catheterization and angiography in some instances. However, diagnostic catheterization remains necessary in other instances. The aims of this study were to determine whether echocardiography alone was sufficient to delineate the anatomic and flow abnormalities in patients subsequently selected to undergo catheterization and, if not, under what circumstances was echocardiography unable to establish the definitive diagnosis. Echocardiograms of 252 infants and children who underwent catheterization during a 14-month interval were analyzed retrospectively to determine whether the echographic assessment was nondiscrepant (group 1) or discrepant (group 2) with the catheterization assessment. Any deviation in the complete accurate assessment constituted a discrepancy; identification of more than one discrepancy in a single patient was possible. Independent variables included patient's age, weight, operative status, use of color flow mapping, echocardiograph operator, and interval between echocardiogram and catheterization. To determine whether the discrepancies were clinically significant, data from patients in group 2 were reviewed independently by three cardiologists to determine whether patient management would have changed given the added data provided by catheterization. Echocardiographic evaluations were discrepant in 155 instances. In 54 of 155 instances (35%), discrepancies were judged to be clinically significant (group 3). Twenty-three of 54 cases (43%) involved extracardiac lesions (i.e., aortic arch, pulmonary arterial, bronchial collateral, and pulmonary venous anomalies), 20 of 54 (37%) involved pressure gradients, 7 of 54 (13%) involved intracardiac lesions, and 4 of 54 (7%) involved coronary arterial lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in electromechanical properties of canine ventricular muscle: effect of ouabain.

In this report, alterations between the electrical and mechanical responses of isolated neonatal and adult canine ventricular muscle preparations before and after ouabain exposure are described. No significant differences were observed between the two age groups in the concentration-dependent effects of ouabain on increasing contractile force or decreasing maximum diastolic transmembrane potential. The action potential plateau duration was decreased by high concentrations of ouabain (0.3-1 microM) in both neonatal and adult ventricular muscle. In addition, more adult preparations developed delayed afterdepolarizations associated with aftercontractions after exposure to ouabain than did neonatal preparations. These results suggest that the higher glycoside tolerance in neonatal dogs as compared with adults may be due in part to differences in the mechanisms responsible for development of abnormal ventricular automaticity. The results may also indicate that immature animals do not require higher glycoside levels to produce augmentation of cardiac contractility.

Age-related digoxin effects in an intact canine model.

The inotropic and electrophysiologic effects of digoxin were studied in anesthetized neonatal and adult dogs to test the hypothesis that digoxin had comparable effects in these groups. Recordings of the ECG and central arterial pressure were made starting at 5.75 hours after an intravenous injection of 50 micrograms/kg of the drug. Parameters measured were heart rate (HR); PR interval; mean, systolic, and diastolic blood pressure; preejection period (PEP); and ejection time (ET). Two indices of systolic function were calculated, the systolic time interval (STI = PEP/ET) and total electromechanical systole (TMS = PEP + ET), which was indexed for HR. There was no significant difference from control animals in either the adult or neonatal groups in the PR interval or blood pressure. In the neonatal dogs, HR and STI were also not significantly different from control. However, in the neonatal dogs, there was a significant decrease in the indexed TMS, 288 +/- 7 vs 270 +/- 11 msec (p less than 0.01). In the adult animals, HR decreased from 116 +/- 35 to 66 +/- 25 bpm (p less than 0.01), STI decreased from 0.559 +/- 0.059 to 0.447 +/- 0.069 (p less than 0.01), and indexed TMS decreased from 333 +/- 10 to 291 +/- 13 msec (p less than 0.001). Two-way analysis of variance demonstrated that digoxin differed significantly in its effects on HR (p = 0.005), STI (p = 0.018), and TMS indexed for HR (p = 0.003) in neonatal compared to adult dogs. Pharmacokinetic studies showed a rapid distribution phase and equilibrium conditions at the time of physiologic measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow-independent improvement by diltiazem of ischemia-induced conduction delay in porcine hearts.

The calcium channel blocking agent, diltiazem, improves ischemia-induced conduction delays in the canine heart. It is not known, however, if the improvement of myocardial blood flow caused by diltiazem participates in this response. Accordingly, ischemia-induced conduction delay was measured during brief coronary artery occlusion before and after administration of diltiazem in nine anesthetized pigs with fixed heart rate. Acute coronary occlusion prolonged subendocardial (mean +/- standard error of the mean, 39.9 +/- 3.9 ms) and subepicardial (41.6 +/- 4.1 ms) conduction times (time to peak of the bipolar electrogram in each region) by 51 +/- 4 and 58 +/- 5%, respectively. Regional myocardial blood flow at the ischemic electrode sites was 0.006 +/- 0.002 ml/min per g and was unaffected by diltiazem. Intravenous diltiazem pretreatment (0.01, 0.1, 0.3 and 1.0 mg/kg) 5 minutes before coronary occlusion significantly reduced the ischemia-induced conduction delay in both subendocardial and subepicardial regions during coronary occlusion. The pigs in which ventricular fibrillation occurred within 10 minutes showed a significantly longer conduction delay than that observed in pigs in which ventricular fibrillation occurred later (greater than 10 minutes). Thus, the data suggest that the reduction of ischemia-induced conduction delay produced by diltiazem is independent of blood flow changes and, therefore, that diltiazem may have a beneficial antiarrhythmic action.

Age-related changes in electrophysiological properties of canine Purkinje fibers: effect of ouabain.

Transmembrane potentials were recorded in Purkinje fibers obtained from dogs aged 1 day, 1 week, 2 weeks, 4 weeks and more than 1 year. After the initial impalements there was a time-dependent increase in diastolic potential. This hyperpolarization was more pronounced in the younger Purkinje fibers. Maximum diastolic potentials from 1-day-old puppies (-78.0 +/- 1.2 mV), after 10 min of continuous impalement, were significantly less negative than those for adults (-84.2 +/- 1.9 mV). Fibers from neonates exposed to ouabain do not depolarize as much as fibers from adults.

Primary benign intramural ventricular tumors in children: pre- and postoperative electrocardiographic, echocardiographic, and angiocardiographic evaluation.

The clinical, ECG, echocardiographic, and angiographic data, as well as the operative findings and postoperative courses of three children with intramural ventricular tumors are presented. In all three children, the specific diagnosis of intramural tumor was unsuspected. The ECGs showed a superior axis in all patients. M-mode echocardiography missed the mass in one patient and was nonspecific in the other two; however, two-dimensional echo (2DE) was able to accurately delineate the tumors preoperatively in all three. Angiographic findings were nonspecific, only demonstrating the presence of space-occupying lesions. All three patients underwent surgery and the tumors were removed successfully. This investigation emphasizes the clinical picture that led to the diagnostic evaluations, and demonstrates the usefulness of 2DE in accurately diagnosing the intramural ventricular tumors. In addition, the sequential ECGs and 2DEs after removal of the tumors are delineated as well as showing the resolution of the tumor craters by 2DE examinations.

Chaotic atrial tachycardia in childhood.

Ten cases of chaotic atrial tachycardia (CAT) in childhood are reported. Patients' ages ranged from 1 day to 18 years (average, 3.5 years) at the time of diagnosis. The patients were divided into groups according to the following criteria: (1) no cardiac disease (n = 5), (2) congenital heart disease (n = 4), and (3) acquired heart disease (n = 1). Nine of the children were treated with digoxin; however, it appears there was no beneficial effect. In fact, the single death in our study group may have been attributable to digitalis intoxication. No children have had recurrence of the arrhythmia after discontinuation of the drug. The duration of the tachyarrhythmia was extremely variable; however, CAT was well tolerated and was self-limiting in our patients.

Ventricular tachycardia in infancy: evidence for a reentrant mechanism.

Ventricular tachycardia is unusual in infancy. Three infants are described in whom this arrhythmia was documented by electrophysiologic studies. The ability to start and terminate this rhythm by critically timed premature ventricular stimulation suggests a reentrant mechanism. All three patients have remained free of arrhythmias on oral propranolol therapy.