Ventricular pacing in children

Ventricular pacing was performed in forty-one children ranging from one day to twenty years of age (median age = 10). Weight of the recipient at implant ranged from 2 kg. to 86 kg. Indications included presyncope, syncope, dyspnea on exertion, congestive heart failure, postoperative infra-Hisian heart block, and inadequate cardiac rate during pharmacotherapy. Four patients died during follow-up, but no deaths were attributable to pacemaker management. In contrast, 66% of the patients required more than one pacemaker related-operative procedure, and 43% of leads implanted failed by 48 hours. Indications for permanent cardiac pacing in this population at this time are symptomatic congenital AV block, symptomatic sinus node disease, and AV block in the postoperative period. Technological developments which might reduce complications seen in this population and electrophysiologic techniques which may better define indications for pacing in children are also reviewed.

Repair of total anomalous pulmonary venous connection in patients younger than 6 months old. Late postoperative hemodynamic and electrophysiologic status

During a 31/2 year period, 11 consecutive infants with total anomalous pulmonary venous connection younger than 6 months of age underwent repair at our institution. Early mortality was 19% (one of 11) and long-term mortality 18% (two of 11), yielding an overall survival of 73%. One late death was due to bradyarrhythmia and the other was due to recurrent pulmonary venous obstruction. Postoperative catheterization in seven of eight survivors and in three additional patients disclosed normal or nearly normal pulmonary artery pressure and pulmonary arteriolar resistance. Left ventricular diastolic volume was normal before operation (n = 5) and on follow-up study (n = 9). Mild left ventricular outflow obstruction or coarctation or both developed during follow-up in two patients. Sinus node function was normal in all seven late survivors studied, and atrioventricular conduction was normal in three of four. This experience indicates that total anomalous pulmonary venous connection can be repaired early in infancy, with preservation of normal hemodynamics and electrophysiologic state.

Excitation of the double chamber right ventricle: electrophysiologic and anatomic correlation

To examine the excitation of the double chamber right ventricle and the possibility that it results from a displaced, hypertrophied moderator band, seven patients with double chamber right ventricle were studied. All seven had pre- and postoperative electrocardiograms. Intraoperative right ventricular epicardial maps were obtained in three; right ventricular endocardial activation maps performed at postoperative catheterization were obtained in four. In the three patients studied at operation the breakthrough point of right ventricular epicardial activation was demonstrated in a normal inferior location well below the obstructing muscle band. Two patients with right bundle branch block after operation and two others with only right ventricular conduction delay on postoperative electrocardiogram demonstrated high normal right ventricular time with prolongation of activation in the right ventricular outflow or inflow region, or both, suggesting only peripheral injury. These data suggest that activation of the double chamber right ventricle is similar to that of the normal heart. In addition, the observed normal activation sequence militates against the hypothesis that the moderator band is the obstructing bundle.

A possible variant of thyroxine-binding globulin in Australian Aborigines

We have recently described a major variation from the normal levels of serum thyroxine-binding globulin in many Australian Aborigines [1]. Subsequently we presented evidence that affected individuals were widely distributed throughout Australia, that "low values of thyroxine-binding globulin were not caused by environmental or health factors, but were inherited in an autosomal dominant fashion [2]. Refetoff [3] has shown that the cause of genetically determined low thyroxine-binding globulin levels in Caucasians is alteration in synthesis rate without any structural variation of the protein. Since however the "low" thyroxine-binding globulin of Aborigines is vastly more prevalent and genetically distinct from the X-linked type, we investigated the possibility that this may be a structural variant. Evidence suggestive of this includes results from heat inactivation, competitive binding of thyroxine to thyroxine-binding globulin to measure affinity, and use of a radioimmunoassay different from that used in the original work. The "Low thyroxine-binding globulin of Aborigines may be a protein with a structural variation at or near the binding site for thyroxine, resulting in low affinity for thyroxine and hence "low" results with assay methods which depend upon the thyroxine binding site. Since the Australoid peoples, to whom Australian Aborigines are racially related, are distributed widely throughout the southern hemisphere it is important to establish whether this variant is found outside Australia in order to avoid the likelihood of misdiagnosis of thyroid disease in such subjects.

Quantitative morphometric analysis of the pulmonary arteries in two patients with D-transposition of the great arteries and persistence of the fetal circulation

Quantitative morphometric studies were performed on the pulmonary arteries of two newborns who died at 1 and 3 days of age with both transposition of the great arteries and persistence of the fetal circulation. Similar studies were performed on two normal control subjects (age 2 and 6 days), one newborn infant (age 1 day) with secondary persistence of the fetal circulation, and one newborn infant (age 2 days) with isolated D-transposition of the great arteries, as compared to those without it. When wall thickness was related to external diameter of the vessel, the greatest difference in thickness was observed in the smallest vessels (less than 150 mu in diameter). Extension of smooth muscle peripherally and to the smallest vessels (less than 50 mu) was similarly most marked in those infants with persistence of the fetal circulation may coexist but at the same time be unrelated in a single patient. Furthermore when such coexistence is unrecognized, pharmacologic manipulation of the ductus arteriosus may be hazardous.

Clean Air and Noise Abatement Branch, Public Health Department, Western Australia

Whole blood lead levels, free erythrocyte protoporphyrin (FEP) concentrations, and hair lead levels were measured in 181 schoolchildren resident in and around the town of Northampton, Western Australia, where tailings from a lead mine have been used extensively for ground surfacing and other purposes. Mean blood lead levels were 0.68 mumol/L (14.0 micrograms/100 mL) in boys and 0.5 mumol/L (10.4 micrograms/100 mL) in girls, the highest being 2.27 mumol/L (47 micrograms/100 mL). Nine children (5%) had blood lead levels above 1.21 mumol/L (25 micrograms/100 mL) and four had levels above 1.21 mumol/L (25 micrograms/100 mL) and four had levels above 1.45 mumol/L (30 micrograms/100 mL). Four of these children had FEP levels above 2.0 mumol/L. There was a statistically significant difference between the mean blood lead levels of children resident in the town (man blood lead level, 0.63 mumol/L (13.1 micrograms/100 mL)) compared with those resident out of the town 0.55 mumol/L (11.3 micrograms/100 mL). The presence of lead tailings in the town may account for the small difference.

Ventricular tachycardia in children

Thirty-eight patients aged 1 to 20 years (mean 11.2) were evaluated because of recurrent ventricular tachycardia. The follow-up period ranged from 0.5 to 12 years (mean 6). The patients were separated into two groups according to the presence or absence of known structural heart disease. Seventeen of the 21 patients with known heart disease were symptomatic (cardiac arrest in 5, syncope in 5, dizziness in 7) compared with only 6 of the 17 patients without heart disease (syncope in 3 and dizziness in 3) (p less than 0.01). All symptomatic patients had ventricular tachycardia with rates of more than 150 beats/min, whereas all but one of the asymptomatic patients had rates of less than 150 beats/min (p less than 0.01). Graded treadmill exercise testing was performed in 21 of the 38 patients. Exercise increased the degree of ventricular arrhythmia in 8 of the 11 symptomatic patients but decreased or abolished the arrhythmia in 9 of the 10 asymptomatic patients (p less than 0.01). Antiarrhythmic therapy was used in 28 of the 38 patients. Effectiveness of therapy was assessed with both 24 hour Holter monitoring and graded treadmill exercise testing. Therapy effectively abolished ventricular tachycardia and greatly decreased the number of premature ventricular complexes in the symptomatic patients but was less effective in the asymptomatic patients. Thus, this study suggests that the presence of underlying heart disease, the rate of ventricular tachycardia and the results of graded treadmill exercise tests are important in predicting the prognosis of children with ventricular tachycardia.

Electrophysiologic delineation of the intraventricular His bundle in two patients with endocardial cushion type of ventricular septal defect

Two patients who had an endocardial cushion type of ventricular septal defect underwent electrophysiologic studies for detection of specialized conduction tissue during operative repair. In one patient, with an inferior leftward frontal plane QRS axis on the ECG, we recorded an intraventricular His bundle electrograms from both the anterosuperior and posteroinferior margins of the defect, suggesting dual atrioventricular conduction tracts (branching intraventricular His bundle). These anatomic and electrophysiologic findings may account for the more normally oriented QRS frontal plane axis on the surface ECG of both of these patients and support the hypothesis that the changes observed on the ECGs of patients with the various forms of endocardial cushion defect can be explained by alterations in the anatomic configuration of the specialized atrioventricular conduction tissue.

Distribution and inheritance of low serum thyroxine-binding globulin levels in Australian Aborigines: a new genetic variation

Evidence is presented that low serum thyroxine-binding globulin (TBG) levels in Aborigines are widely distributed throughout Australia, and that these are inherited rather than acquired. Levels of TBG in children, and lack of any correlation of low TBG levels with alcohol consumption or liver dysfunction, suggest that the low levels are not acquired in adult life. Genetic studies in eight families indicate (with one exception) an autosomal dominant pattern of inheritance with direct male-to-male transmission. These findings are in marked contrast to the much rarer X-linked pattern of inheritance of low TBG levels in Caucasians. This type of prevalent and inherited low level of TBG in serum appears so far to be unique to the Aboriginal race. The synthesis (or degradation) of TBG may be controlled by an autosomal gene in Aborigines.

Prevalent low serum thyroxine-binding globulin level in Western Australian aborigines: its effect on thyroid function tests

The first major variation from the normal human levels of thyroxine-binding globulin (TBG) in a racial group is reported in full-blood Aborigines of Western Australia. This finding has not only biochemical and anthropological interest, but also medical significance in that many common laboratory tests of thyroid function in this group are very liable to misinterpretation because of low TBG levels. In Aborigines in the Halls Creek area of Western Australia, 40% have TBG levels below the lower reference limit for Caucasians, and 18% have levels between half and one-third of the lower limit. Such subjects have low thyroxine levels by Caucasian standards, and frequently the results of triiodothyronine uptake (T3U) tests lend support to the false suggestion of hypothyroidism. Caucasian reference ranges are not valid in this large proportion of the Aboriginal population. It is not yet clear whether the low TBG levels are a normal feature in this racial population, or whether there is some other cause. The subjects of the study were not acutely ill and Aborigines with low TBG are well distributed throughout the State.

Intraoperative recording of specialized atrioventricular conduction tissue electrograms in 47 patients

Intraoperative mapping of the specialized atrioventricular conduction system was performed in 47 patients during cardiac surgery. Specialized conduction tissue electrograms were identified in 37, and atrioventricular conduction preserved in 92%. Specialized conduction tissue was identified in 27 patients with atrioventricular canal defect: complete heart block was avoided in 25. Conduction tissue was located in six of 12 patients with complex transpositions; atrioventricular conduction was preserved in all six. Other lesions in which the technique was useful were Ebstein's anomaly and single atrium. Limitations to the technique are 1) deep hypothermia and circulatory arrest; 2) interruption in atrioventricular conduction during mapping; 3) inadequate exposure and access to probable sites of conduction tissue; 4) variation of size and spatial relations of individual malformations; and 5) limited time for identification of unusually located conduction tissue. Indications for use of this technique include patients with both forms of atrioventricular canal, complex transpositions, atrioventricular discordance, single ventricle and single atrium.

Early and late results with the Mustard operation in infancy

Eighty-one patients, ranging in age from 36 hours to 24 months and in weight from 2.5 to 12 kg had a Mustard operation for D-transposition of the great arteries (D-TGA) (20 with complex D-TGA) using either deep hypothermic circulatory arrest (68 patients) or conventional cardiopulmonary bypass (13 patients). A Dacron patch was used for the intraatrial baffle and pericardium for augmentation of the pulmonary atrium. Ten patients died following operation. Thirty-two patients had cardiac catheterization 1 year after operation. Of 24 patients with D-TGA and intact ventricular septum, 23 had normal pulmonary artery pressures. In 20 patients left ventricular outflow tract gradients decreased from a mean of 32 mm Hg to a mean of 18 mm Hg after operation. Five patients who had D-TGA and ventricular septal defect and systemic pressures in the left ventricle before operation, had a notable decrease in left ventricular pressures after the procedure. Seven patients required reoperation for baffle obstruction. Mortality following Mustard repair was primarily related to the complexity of the lesion, maturity of the infant, and degree of pulmonary vascular changes. Caval obstruction was related to the configuration of the baffle used in the early part of this series.

His bundle electrogram after intracardiac repair of tetralogy of Fallot. Analysis of data in 59 patients

His bundle electrograms were recorded in 59 patients after intracardiac repair of tetralogy of Fallot and were correlated with the postoperative electrocardiogram. Except for five patients with first degree atrioventricular block postoperatively all patients in Group A (those with either a normal electrocardiogram or solitary right bundle branch block) had a normal A-H interval (77.7 +/- 21.6 msec) (mean +/- standard deviation); all had a normal H-V interval (39.5 +/- 7.2 msec). Patients in Group B (bifascicular block) tended to have a normal A-H interval (97.2 +/- 26.2 msec) with a prolonged H-V interval (48.8 +/- 10.7 msec). Patients in Group C (trifascicular block) had prolongation of both the A-H (160.0 +/- 32.4 msec) and the H-V interval (58.8 +/- 10.6 msec) by comparison with control values. Patients in Group D (transient complete heart block) had a normal A-H interval (79.5 +/- 28.2 msec) but a prolonged H-V interval (57.8 +/- 16.4 msec), similar to that in Group C. A good hemodynamic result was associated with a normal H-V interval; a prolonged interval accompanied a poor result.

An improved screening method for 3-methoxy-4-hydroxy mandelic acid excretion in urine

A screening method is described for urinary 3-methoxy-4-hydroxy mandelic acid using an initial ion exchange procedure, vanillin formation and extraction into toluene. The technique, is simple, rapid and specific, with a reference value up to 35 mumol (7.0 mg)/day established on 92 normal human subjects. Over 200 patients' urines were analysed by the method of which 18 gave values above the reference range. The majority of these increased excretions are attributed to the metabolic effects of drugs, one patient suffered from phaeochromocytoma and only 2 results remaining unexplained.