David S. Buckles

Actuarial Survival of Transvenous Pacing Leads in a Pediatric Population

This study was undertaken to examine the actuarial survival of endocardial pacing leads in a pediatric population. We prospectively followed 148 children and young adults age 4 months to 38 years. Of these, 58 had normal cardiac anatomy and 90 had surgically corrected congenitai heart disease. A total of 213 leads were inserted in these patients. Actuarial analysis showed that at 5 years 76.0% of the pacemaker leads were still in use. The reasons for abandonment included death (10), exit block (8), lead fracture (8), adapter malfunction (7), and other including infection, lead migration, and pacemaker malfunction (12). Excluding deaths, an actuarial survival curve was constructed. Stepwise discriminant analysis and independent measures of association showed a significant difference in lead abandonment when the leads placed in the atrium were compared to those placed in the ventricle (30 vs 5: P < 0.0005). Lead insulating material, cardiac anatomy, and/or indication for pacemaker placement had no statistically significant impoct on lead survival.

Atrial antitachycardia pacing in children and young adults

Atrial antitachycardia pacing was tested in 23 children and young adults. The majority of these patients had had operative repair of congenital cardiac defects and had both bradycardia and tachycardia. Pacemakers were usually implanted by the transvenous technique using bipolar leads. In each patient it was possible to find a tachycardia termination algorithm that successfully converted the tachycardia. In some patients very complex algorithms were necessary. In each patient it was also possible to find an algorithm that successfully differentiated the abnormal tachycardia from sinus tachycardia. Twelve patients required no antiarrhythmic drugs after pacemaker implantation, while 10 patients required one drug and one patient required two drugs. Eight of 23 patients had symptomatic tachycardias that required reprogramming the pacemaker to a different tachycardia termination sequence. Seven patients required reoperations, five for adapter problems and two for infection or erosion. Cardiac function improved in 15 of the 23 patients. Antitachycardia pacing is a viable option for management of tachycardias in children and young adults.

Computer‐Enhanced Mapping of Activation Sequences in the Surgical Treatment of Supraventricular Arrhythmias

Surgical treatment of accessory pathways and ectopic foci requires accurate information on the physical locations of the arrhythmogenic substrates. AJthough electrophysiology studies during cardiac catheterization frequently provide accurate and reliable data, the physical locations of the sites to be ablated must be verified in situ by electrical activity mapping. We have developed a microcomputer‐based system that facilitates creation of electrical activity maps, supplanting the manual method formerly used. Signals produced by mapping and reference electrodes, as well as cardiac diagrams with grid coordinates and times, are presented on a monitor in formats that are easily interpreted by the surgeon and cardiologist. The system is rapid, accurate, and reliable, and has reduced the time required to localize conduction abnormalities from 30 to 45 minutes for the manual method, down to an average of 12 minutes per case. The system is simple to operate, requiring only minimal training. All of the components of the system are commercially available; no specialized hardware is required.

Frequency of atrioventricular valve dysfunction after radiofrequency catheter ablation via the atrial approach in children

Abstract Unlike the retrograde approach, the atrial approach has not been associated with significant postprocedure valvular dysfunction. Given equal efficacy of both methods, this study might indicate that the atrial approach would be preferable.

Real-time, automated, interactive cardiac electrophysiology testing

We describe a new automated interactive system that performs all of the functions required for complete evaluation of the intracardiac conduction system, for inducing, terminating and analyzing tnchydys‐rhythmias, and for locating and characterizing accessory atrioventricuJar (AV) connections and ectopic foci. In the first year of operation, the system was used to conduct 220 electrophysiology studies. These ranged from simple postoperative evaluation of the conduction system to complete tachycardia studies during pharmacological manipulation of the patient. Patient age at time of catheterization ranged from 6 days to 70 years, with median age of 8 years and 7 months. Advantages accruing from automated electrophysiology testing with this system included great precision and accuracy of timing measurements, flexibility in designing and implementing pacing protocols, and rapid management of induced or spontaneous dysrhythmias. Significant savings of time and labor were achieved by computer generation of reports and graphs as opposed to manual data extraction and plotting. The single most significant advantage is the ability of the system to provide information on a real‐time basis, permitting the electrophysiol‐ogist to analyze, modify, extend or curtail the procedure.

Subcutaneous lidocaine affects inducibility in programmed electrophysiology testing in children: a follow-up study.

Invasive cardiac electrophysiology testing during cardiac catheterization requires local anesthesia at the point of entry for the catheters. Frequently, lidocaine is employed for this purpose. A prospective study completed in 1990 indicated that subcutaneous administration of lidocaine adversely influenced the inducibility of arrhythmias in pediatric patients. Upon completion of that study, lidocaine concentration was reduced from 1% to 0.5%, and extra caution was taken to avoid deep penetration during administration. A follow-up, prospective study was performed to evaluate inducibility under these changed conditions. Because the depressant effect of lidocaine on inducibility was age- and weight-related, the second study group was required to have statistically indistinguishable age and weight distributions from the first group to eliminate these variables as factors in inducibility. A total of 177 subjects were collected in the second group before a periodic random computer match with the first group produced 99 individuals with the required age and weight distributions. Analysis of the electrophysiology tests in the second study revealed that: (1) incidence of inducibility was higher in the second group (58 of 99 versus 43 of 99, p < 0.05); (2) average lidocaine dose per kilogram was lower (1.8 mg/kg versus 3.28 mg/kg, p < 0.0001); (3) average lidocaine serum concentration was also lower (0.58 micrograms/ml versus 1.47 micrograms/ml, p < 0.0003); (4) in contrast to the first study, neither lidocaine dose nor serum concentration had any effect on inducibility. We conclude that the new procedures for lidocaine administration effectively removed lidocaine as a factor in inducibility.

Subcutaneous Lidocaine Affects Inducibility in Programmed Electrophysiologic Testing of Children

Subcutaneous Lidocaine Affects Inducibility. A prospective study of 99 patients undergoing invasive electrophysiologic testing was conducted to determine whether the administration of lidocaine for local anesthesia influenced the inducibility of arrhythmias. Of the 99 patients, 42 had inducible arrhythmias. Multiple stepwise discriminant analysis indicated that the most important factor influencing inducibility was lidocaine dosage per weight, with a calculated cutoff of 3.2 mg/kg. There were 26/54 (48%) of patients who had no inducible arrhythmias below the cutoff, compared with 31/45 (69%) above the cutoff (P < 0.04). Of the 21 patients who had dose/kg > 3.2 mg/kg and serum concentration above 1.4 μg/mL (therapeutic range 1‐5 μg/mL) 1 hour after administration, 18 had no inducible arrhythmias (86%). Younger, smaller patients were more affected (P < 0.0001). It is recommended that dose/kg and serum concentrations be recorded during electrophysiologic testing. If the dose/kg is > 3.2 mg/kg or the serum concentration is > 1.4 μg/mL, failure to induce may be suspect.

Assessment of the maximum frequency components and digital sampling of cardiac Purkinje fiber action potentials

An investigation was made into a reasonable continuous sampling frequency for cardiac Purkinje fiber action potentials. Under the assumption that digital sampling will effectively capture frequency components up to half the sampling rate, action potential records made at 25 kHz were low-pass filtered at various cutoff frequencies. The filtered and unfiltered records were compared by calculating Vmax to determine the effects of progressive loss of high frequency components. It was determined that sampling at 13 kHz is adequate for action potentials with upstroke velocities up to 500 V/sec, and that estimation of Vmax in excess of 800 V/sec is possible.

The acute effects of flecainide in the swine heart failing from incessant supraventricular tachycardia

The acute hemodynamic and electrophysiologic effects of flecainide in tachycardia-induced ventricular dysfunction were investigated using an animal model. Seven swine were initially (CON) evaluated by echocardiography and then by right heart catheterization and provocative electrical ventricular stimulation both before and after treatment with intravenous flecainide. Rapid atrial pacing at 210 to 240 beats/min (SVT) was then employed for 2 to 4 weeks until echocardiographic evidence of left ventricular dysfunction developed. Immediately upon termination of pacing, the above studies were repeated both before and after treatment with flecainide. Significant (p less than 0.0001) pacing-related hemodynamic effects on the cardiac output (CON:3.0 L/min versus SVT:1.6 L/min), right ventricular ejection fraction (CON:55% versus SVT:17%), and pulmonary wedge pressure (CON:8 mm Hg versus SVT:22 mm Hg) were observed. Pacing-related electrophysiologic effects included increases in the PR interval (CON:94 msec versus SVT:119 msec, p less than 0.001) and QTc interval (CON:418 msec versus SVT:450 msec, p = 0.016). With serum flecainide concentrations in the human therapeutic range, no significant effect on hemodynamic or electrophysiologic parameters in either the normal or failing heart were detected. Nonsustained ventricular tachycardia induced prior to pacing in one animal and after pacing in another animal was seen before but not following use of flecainide. No acute proarrhythmic effects were observed. In summary, intravenous flecainide had no significant acute adverse hemodynamic, electrophysiologic, or proarrhythmic effects in an animal model of tachycardia-induced ventricular dysfunction.

Inducible ventricular tachyarrhythmia in children with Wolff-Parkinson-White syndrome

Adult patients with the Wolff-Parkinson-White syndrome (WPW) appear to have a substrate for ventricular arrhythmia inducibility, which is higher than that of the general population.1,2 Because it is unclear whether a similar susceptibility exists in the pediatric patient with WPW. a retrospective study was performed to examine the incidence of and factors associated with ventricular arrhythmia inducibility in children.