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This investigation sought to study single dose pharmacokinetics of amiodarone in a chronic animal model. We developed a new chronic animal model that allows serial direct access to the heart of the immature piglet via an implanted acrylic thoracic window. Following instrumentation and 72-hour recovery, amiodarone (5 mg/kg) was administered as a single intravenous bolus in immature piglets. Timed paired serum samples and myocardial biopsies for amiodarone level were obtained prior to, and up to 72 hours following, amiodarone administration. Peak concentrations of amiodarone in both serum (3.60 +/- 1.02 micrograms/ml) and tissue (84.2 +/- 6.50 ng/mg) occurred within 5 minutes of drug administration. As reported by others, this study demonstrated that the volume of distribution (VD) of amiodarone was large (33.31 +/- 35.21 L/kg), and the clearance (Cl) was low (13.6 +/- 4.4 ml/min/kg). Marked prolongation of both the serum t1/2 (29.98 +/- 29.26 hours) and the myocardial t1/2 (29.20 +/- 29.49 hours) were noted as well. The early, rapid myocardial peak of amiodarone in the immature myocardium corresponds with recent clinical observations of onset of antiarrhythmic efficacy 5 to 10 minutes following intravenous amiodarone administration in young children.

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Between January 1990 and October 1992, we implanted 16 steroid-eluting ventricular epicardial pacing leads (Medtronic 10295A and 10295B/4965) in 12 patients. There were 8 males and 4 females ranging in age from 3 months to 49 years (mean 8.7 +/- 13.2, median 6.0 years). Structural cardiac disease was present in 11 of 12 patients. Follow-up ranged from 3-73 months postimplant (mean 35.7 +/- 22.3, median 28.5 months). Lead fracture (10295A) occurred in 1 of 12 patients. Of the remaining 11 patients, 8 of 11 have very low long-term pacing thresholds. Unexpectedly, 3 patients demonstrated precipitous threshold increases from 3 months to 3.5 years postimplant. Although no deaths resulted in these exit block patients, 1 of 3 exit block patients developed marked worsening of congestive heart failure. We reviewed and analyzed the data obtained at 4 weeks postimplant for all of the 10295A and 4965 patients in the entire Medtronic clinical study database. Using the criterion of a 4 week postimplant pacing threshold > or = 0.12 ms (5 V), we found that the long-term risk of eventual exit block was 27.3% for the 10295A lead (P = 0.005) and 7.5% for the 10295B/4965 lead (P = 0.03). We, therefore, recommend that in patients implanted with the 4965 steroid-eluting epicardial lead, ventricular pacing thresholds > or = 0.12 ms (5 V) measured at 4 weeks postimplant should prompt frequent threshold testing to detect late and potentially sudden ventricular pacing threshold increases.

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Ventricular arrhythmias in patients after total surgical repair of tetralogy of Fallot have been associated with late sudden death. In this large multicenter retrospective study of 359 patients with postoperative tetralogy of Fallot, spontaneous ventricular premature complexes (VPCs) on 24-hour ambulatory electrocardiographic monitoring and laboratory-induced ventricular tachycardia (VT) by electrophysiologic stimulation were analyzed. The mean age at surgical repair was 5 years and the mean follow-up duration after repair was 7 years. Spontaneous VPCs on ambulatory monitoring were found in 48% and induced VT on electrophysiologic stimulation was found in 17% of patients. Both spontaneous VPCs and induced VT were significantly related to delayed age at repair, longer follow-up interval, symptoms of syncope or presyncope and right ventricular systolic hypertension (greater than 60 mm Hg) (p less than 0.05), but not to right ventricular diastolic pressure greater than 8 mm Hg. The VPCs on ambulatory monitoring were more complex with increasing age at repair and follow-up duration. Induction of VT on electrophysiologic stimulation correlated with spontaneous VPCs including VT on 24-hour ambulatory electrocardiographic monitoring. The electrophysiologic stimulation protocol varied and the induction of VT increased with a more aggressive stimulation protocol. While induced sustained monomorphic VT was related to all forms of spontaneous VPCs, induced nonsustained polymorphic VT was related to more complex forms of VPCs on ambulatory monitoring. VT was not induced in asymptomatic patients who had normal 24-hour ambulatory electrocardiographic monitoring and normal right ventricular systolic pressure. (ABSTRACT TRUNCATED AT 250 WORDS)

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Since 1983 we have performed electrophysiologic studies in 6 patients who had previously undergone repair of an ostium primum atrioventricular septal defect. Information obtained during electrophysiologic studies was crucial in guiding appropriate pacemaker therapy in these patients. As judged from the resting electrocardiogram, sinus or junctional bradycardia was present in 3/6, atrial flutter / fibrillation in 2/6, and paced rhythm in 2 patients who had had ventricular pacemakers implanted for complete atrioventricular block. During maximal exercise testing 4 patients had reduced heart rates; 2 had sudden drops in heart rate at 1 min postexercise; 1 patient had exercise induced ventricular bigeminy; and 1 patient with atrial flutter and 2: 1-4: 1 block at rest developed 1: 1 conduction during Stage II with an effective ventricular rate of 220/min. During electrophysiologic studies, the maximum corrected sinus node recovery time was abnormal in five of the six, ranging from 410 to 5630 msec. There was no spontaneous atrial rhythm in the other patient. Complete atrioventricular block was present in 2 patients while the atrioventricular Wenckebach phenomenon occurred abnormally at atrial pacing cycle lengths greater than 450 msec in 2 others. Supraventricular tachycardia or atrial flutter/fibrillation, was either spontaneous or induced in 2/6 patients, while ventricular tachycardia was induced in 1/3 patients who underwent programmed ventricular stimulation. Electrophysiologic studies were important in unmasking severe sinus node disease in 3 patients and atrioventricular node disease in 2. We therefore recommend that electrophysiologic studies be strongly considered as part of the evaluation of conduction abnormalities following repair of ostium primum atrioventricular septal defect.

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Between July, 1963, and July, 1983, a total of 69 patients (35 boys and 34 girls) underwent ostium primum defect repair. There were four perioperative deaths and four patients were subsequently lost to follow-up, leaving 61 children followed for 6 months to 20 years (mean 5 years). Results of surgery were assessed by cardiac catheterization in 17 of 61 patients, while the remaining patients were evaluated noninvasively. Postoperative mitral insufficiency was found to be absent in 19 patients, mild to trivial in 35, moderate in four, and severe in two. Four patients were found to have large residual atrial septal defects. Significant late postoperative arrhythmias were found in 14 of 61 patients. The types of arrhythmias included isolated complete atrioventricular block in 5 of 14, complete atrioventricular block with sinus node dysfunction in 2 of 14, and isolated sinus node dysfunction in 7 of 14. Pacemakers have been implanted in 8 of 14 of these patients. Based on this 20-year review of a large number of children: (1) ostium primum defect repair is associated with a low mortality rate, (2) residual mitral insufficiency although common is usually mild to trivial and nonprogressive, and (3) significant arrhythmias are a frequent complication and often require pacemaker implantation.

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A new type of vascular ring formed by a hemitruncal pulmonary artery is described. Early reimplantation of the hemitruncal pulmonary artery resulted in resolution of the respiratory distress, protection of the pulmonary arterial bed from obstructive vascular disease, and preparation of the pulmonary artery for future surgical correction.

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We evaluated six children for syncope of unknown etiology between March, 1983, and March, 1984. All had undergone previous neurologic evaluation which was normal. Cardiac examination, chest roentgenograms, and two-dimensional echocardiograms were also normal in all of the patients. Abnormal noninvasive findings in five patients included Mobitz type II atrioventricular (AV) block (one patient), sinus bradycardia (three patients), and supraventricular tachycardia (one patient). Four patients had one or more abnormal findings at invasive electrophysiologic study including evidence of sinus node dysfunction (three patients), AV node dysfunction (three patients), and distal His-Purkinje system disease (two patients). All children had a normal right heart hemodynamic catheterization. We conclude that arrhythmias are an important cause of syncope in some children with an otherwise normal heart when neurologic causes have been excluded.

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The present study uses a technique that enables the collection of multiple freeze-biopsy samples from the myocardium of the conscious pig (i.e., through a thoracic window). This technique enables sequential analysis of the metabolic state of the myocardium during different behavioral conditions. The results demonstrate that with daily adaptations to an unfamiliar environment (i.e., stress reduction), the phosphorylase activation ratio (phosphorylase a/total phosphorylase) in the quiescent pig declines steadily from approximately 80% to 30% (r = -0.91, P less than 0.01). This decline occurs with both the mean resting heart rate and left ventricular blood pressure remaining constant. The decline is seen within individual subjects during the whole adaptation sequence as well as between subjects whose samples were taken either early or late in the adaptation series. The dissociation of hemodynamic functional and metabolic activation in the unadapted, psychologically stressed pig may be associated with the occurrence of increased vulnerability of the ischemic heart to ventricular fibrillation, a phenomenon previously observed under the same behavioral conditions.

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Sick sinus syndrome (SSS) occurs infrequently in children who have not undergone cardiac surgery. The symptoms, electrocardiograms, and electrophysiologic data in 11 patients aged 2 to 17 years who had nonsurgical SSS were reviewed. Syncope occurred in 5 patients and sinus bradycardia in 9. Sinus nodal recovery times were prolonged in 6 patients. The atrial effective refractory period was prolonged in 2 patients and the atrioventricular nodal functional or the effective refractory period, or both, was prolonged in 5 patients. Because patients with nonsurgical SSS may have abnormalities not only of the sinus node but also of the atrium and the atrioventricular node, it is recommended that patients with symptomatic SSS be evaluated by electrophysiologic study. The proper choice of antiarrhythmic drug therapy or permanent pacing procedure depends on a complete analysis of the cardiac conduction system.

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Controversy exists as to which of several ECG criteria are necessary for the diagnosis of left atrial (LA) rhythm. We performed invasive electrophysiologic study in five patients (6 to 15 years-of-age) who had symptomatic supraventricular tachycardia (SVT) that could not be controlled by aggressive pharmacologic treatment. All patients were found to have automatic atrial tachycardia with the earliest site of activation during SVT in the LA. The ECG of each patient demonstrated negative P waves in lead I. The frontal plane P wave axis ranged between +90 to +270 degrees in each of our patients. Spontaneous "dome-and-dart" P waves occurred in lead V1 in two of our patients. We conclude that the necessary criterion for the diagnosis of LA rhythm should be negative P waves in lead I. The finding of "dome-and-dart" P waves in V1 is an additional useful and definitive criterion but is not present in each case.

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Ravelo recently reported the results of surgical repair of coarctation of the aorta in eight patients with Turner's syndrome. Three of these patients had serious hemorrhagic complications. At Texas Children's Hospital, we have operated on four patients with Turner's syndrome and coarctation of the aorta without complications. Of the 12 patients in both series, nine patients had uncomplicated courses when they had Dacron aortoplasty (4/12) or end-to-end anastomosis (5/12). The three other patients with end-to-end anastomoses had significant perioperative hemorrhage. Whereas Ravelo reported serious complications in 38% (3/8), the combined series suggest that only about 25% (3/12) of patients with Turner's syndrome undergoing repair of coarctation of the aorta may experience significant perioperative hemorrhage. We conclude, as did Ravelo, that attention to technical details should keep surgical morbidity in these patients to a minimum.

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