Image-based display of activation patterns derived from scattered electrodes.

Presentation of electrophysiologic data, such as activation patterns, can take many forms, the most common of which are hand- or machine-drawn isochronal maps. We present an image-based method which provides accurate matching between electrophysiologic data and the anatomic sites from which the data were derived. This method is linear, simple, and straightforward to implement, and presents results in a format which is easy to understand and interpret.

Computational methods for wide-field reconstruction of transoesophageal echocardiographic images.

Transoesophageal echocardiography imaging is limited by the proximity of the transducer to many cardiovascular structures. The location of the transducer causes these structures to appear near the apex of the backscatter image, and since the angle of the scan cannot exceed 90 degrees, much of the image information appears in a constricted area. We describe a computer-based, wide-field reconstruction technique which pieces together the picture fields from adjacent sector scans to form composite images. This description includes information regarding lessons learned, as well as technical details of the algorithms, in sufficient depth to permit reproduction of the system by interested parties. Significant aspects of wide-field image reconstruction, including computational complexity, image-pair alignment processes, requirements of alignment resolution, and image acquisition techniques, are addressed in depth. We believe that wide-field presentation of echocardiographic backscatter data enhances the utility of the transoesophageal approach, particularly when dealing with posteriorly located cardiovascular lesions.

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 congenital 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 impact on lead survival.

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.

Preoperative prediction of postoperative pulmonary arteriolar resistance after surgical repair of complete atrioventricular canal defect.

The natural history of patients with complete atrioventricular canal defect is one of unrelenting development of pulmonary vascular obstructive disease. Corrective surgery, which can be performed with low mortality during infancy, reduces the time that the pulmonary vascular bed is exposed to excessively high pressure and blood flow. In some patients, however, advanced vascular disease may already be established at operation. Surgical intervention in these patients may not prevent the progression of obliterative pulmonary vascular disease and may in time even result in right ventricular failure, since after the corrective operation there is no ventricular septal defect to shunt away the right ventricular pressure overload. This article outlines a numeric method for predicting pulmonary vascular resistance after surgical correction; the method is based on age and hemodynamic data available from preoperative cardiac catheterization. Retrospective analysis of preoperative and postoperative data from 20 patients produced a regression equation in which a linear combination of inverse pulmonary/systemic blood flow ratio and age at operation predicted pulmonary vascular resistance after operation, with a multiple correlation coefficient of 0.85. This newly discovered relationship may provide valuable insight into the probable outcome of surgical intervention in cases in which pulmonary vascular obstructive disease is suspected as significant.

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.

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.

Cellular electrophysiology of neonatal and adult rabbit atrioventricular node.

Adult and neonatal rabbit atrioventricular node (AVN) preparations were studied using transmembrane and surface electrogram recordings. Action potentials were categorized into four types, atrionodal (AN), nodal (N), "high" nodo-His (NH) (HNH), and "low" NH (LNH), according to their action potential characteristics and their location within the A-H interval. The electrophysiological parameters of the lower three regions were identical between the two age groups. Action potentials from the neonatal AN region were lower in amplitude and maximum diastolic potential than they were in the adult. The N cell action potential parameters did not differ between the two age groups, however, there did appear to be qualitative differences. AVN conduction times (A-H intervals) were the same in both age groups, as were the antegrade and retrograde refractory periods, and the Wenckebach intervals. Pacemaker activity was significantly greater in the neonates than in the adults and, in 11 of 13 neonatal preparations, originated in the AN region or higher. In 13 of 14 adult preparations, pacemaker activity resided within the AVN.

The longitudinal time course of QTc in early infancy. Preliminary results of a prospective sudden infant death syndrome surveillance program.

Eleven hundred one healthy neonates in Charleston County, SC, were enrolled in a prospective, serial measurement sudden infant death syndrome/QT surveillance program. Automated computer-enhanced ECGs were recorded at 1 day of age in the hospital nursery and again at 1 week and 1, 2, and 3 months in the participant's home. At 1 year, the families were contacted by phone or mail and questioned as to the health of the child. Validation studies demonstrated the computer-enhanced ECGs to be 96% accurate, whereas traditional ECG recording and measurement was 94% accurate. No systematic differences in the QTc according to race and sex were observed. There were parallel longitudinal time courses for each race and sex group with a significant (P less than .001) shortening of the QTc at 1 week. There was no evidence of tracking of the QTc during the first 3 months of life. In conclusion, (1) automated, enhanced ECG QTc intervals are superior to traditional electrocardiography while retaining the advantages of automation; (2) there is a significant shortening of the QTc during the first month of life; and (3) a home follow-up sudden infant death syndrome surveillance program is feasible and produces accurate, reliable information.

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. Although 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.

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 tachydysrhythmias, and for locating and characterizing accessory atrioventricular (AV) connections and ectopic foci. In the first year of operation, the system was used to conduct 210 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 electrophysiologist to analyze, modify, extend or curtail the procedure.

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.