bluuebunny/crossref_metadata_2025 huggingface dataset:
Transepicardial Defibrillation Dose Response: Current Versus Energy
Authors: WESLEY ROBERT C. , FARKHANI FARZAD , PORZIO DAVID , KOURI JASON , RESH WILLIAM , ZIMMERMAN DONALD
Published: July 2006

In pentobarbital‐anesthetized dogs, we compared the relative efficacy of current versus energy in applying the dose response method in transcardiac defibrillation. Damped sinusoidal shocks via epicardial patches were administered by a custom defibrillator permitting precise current delivery. Following the establishment of an initial estimated defibrillation threshold for energy and current, the dose response method was performed with regard to either energy defibrillation threshold (group E, n = 8) or current defibrillation threshold (group C, n = 8). Two sequential sets (I, II) of shocks (21 shocks each) were delivered in random order at each of seven doses: 0.55, 0.70, 0.85, 1.00, 1.15, 1.30, and 1.45 × defibrillation threshold. Data were subjected to nonlinear logistic regression analysis. There were no significant differences between sets I and II in either groups E or C for resistance or for raw and normalized values associated with 50% and 80% success expressed as energy, current, or voltage. Correlation coefficients (r) associated with nonlinear logistic regression analysis were significantly different for normalized current and energy for group E (0.70 ± 11 and 0.71 ± 12) compared to group C (0.86 ± 0.60 and 0.88 ± O.0.6). The difference. however, could be explained by a significantly narrower range of normalized current values tested in group E (0.79 to 1.31) versus group C (0.54 to 1.46). Thus, when resistance does not change, transcardiac current offers limited advantage over energy when applying a dose response method. The efficacy of nonlinear logistic regression analysis depends upon an adequate dose range.
Real‐Time Arrhythmia Identification from Automated Analysis of Intraatrial and Intraventricular Electrograms
Authors: CHIANG CHIH‐MING J. , JENKINS JANICE M. , DICARLO LORENZO A. , LIN DONGPINC , LI PAI‐CHI
Published: July 2006

Implantable cardioverter defibrillators have dramatically improved survival rates for patients at risk of sudden cardiac death, but the occurrence of inappropriate shocks remains an unresolved problem. Various means for better tachycardia detection, chiefly morphological analysis, have been proposed to address this problem. A new computerized scheme entitled Two‐Channel Rate‐Morphology (2CRM) was introduced. It is a real‐time arrhythmia detection algorithm that combines timing and morphology information from intraatrial and intraventricular electrograms for arrhythmia diagnosis. The program 2CRM applies an initial cycle‐by‐cycle coding scheme followed by contextual diagnosis of underlying rhythm. The program was tested on 36 distinct passages of two‐channel intracardiac signals from 30 patients. The distribution of the arrhythmias are as follows: 4 atrial fibrillation, 6 atrial flutter, 6 supraventricular tachycardia, 10 ventricular tachycardia, and 10 ventricular flutter‐fibrillation. Of the analyzed 3,417 individual cardiac cycles 3,135 (91.7%) were correctly identified. Contextual diagnosis reversed 123 single‐cycle errors to obtain a performance of 3,258 correct out of 3,417 (95.3%). Utilizing an uninterrupted continuous correct contextual diagnosis as indicator of successful arrhythmia detection, 2CRM obtained an accuracy of 34 out of 36 passages (94.4%).
Platelet Aggregability in Patients with a VVI Pacemaker
Authors: FAZIO SERAFINO , CITTADINI ANTONIO , SABATINI DOMENICO , SANTOMAURO MAURIZIO , COCOZZA MANLIO , OLIVIERO UGO , CHIARIELLO MASSIMO , SACCA LUIGI
Published: July 2006

Several studies have suggested an increased incidence of thromboembolic events in patients with VVI pacemaker (VVI patients); furthermore, other authors have demonstrated that a treatment with anticoagulants or antiplatelet drugs may be effective in reducing thromboembolic events, thus suggesting an increased formation of platelet thrombi in these patients. In this respect, platelet aggregability was investigated in ten VVI patients and ten age– and sex–matched subjects. β–thromboglobulin (β–Tg) and platelet factor 4 (PF4) plasma levels were determined as weJJ as platelet aggregation induced by ADP, collagen, epinephrine, and arachidonic acid. Plasma β–Tg JeveJs were increased in the patient group (86 ± 24 vs 24 ± 13 ng/mL; P < 0.001) in presence of normal PF4 values (14 ± 11 vs 13 ± 6 ng/mL; NS). Aggregation curves showed abnormal values of maximal amplitude, slope, and lag time. In particular, maximal amplitude was significantJy higher in VVI patients as compared with controls (ADP P < 0.01, collagen P < 0.001, adrenaline P < 0.01, arachidonic acid P < 0.05). These findings strongly suggest an increase of platelet activity in VVI patients.
Endocardial Pacemakers in Children: Lead Length and Allowance for Growth
Authors: O'SULLIVAN JOHN J. , JAMESON STUART , GOLD RONALD G. , WREN CHRISTOPHER
Published: July 2006

Permanent endocardial pacing in small children is feasible but is limited by two problems; sufficient extra lead has to be left within the heart to allow for growth and the excess has to be coiled behind the pacemaker, limiting the benefit from smailer generators. The required intravascuiar lead length in 120 children and aduits was measured on posteroanterior chest X ray and was correlated with standing height. Measurements were made from the mid‐point of the left ciavicle to the apex of the right ventricle in a curve simulating the usual endocardial lead position. In 60 children, aged 2.0–15.9 years, intravascular lead length (range 15.5–29.0 cm) correlated well with height (0.83–1.70 m), r = 0.91. in 60 adults, mean age 54.9 years, intravascular lead length (25.5–35.6 cm) also correlated well with height (1.45–1.85 m), r = 0.71. In 20 adults the excess extravascuiar lead length, measured during pacemaker impiantation via the subclavian route, was 15.1–33.7 cm and was inversely correlated with height. A child's eventual adult height can be predicted and, using our data, the extra length of lead necessary to allow for growth can be computed. Available endocardial pacing leads are usually 58‐ to 64‐cm long. The excess extravascular lead is a major practical difficulty in children. Shorter leads would avoid the problem of excess lead and facilitate long‐term pacing in small children.
Influence of External Defibrillator Electrode Polarity on Cardiac Resuscitation
Authors: WEAVER W. DOUGLAS , MARTIN JENNY S. , WIRKUS MARK J. , MORUD SUE , VINCENT STEPHEN , LITWIN PAUL E. , MORCAN CARL
Published: July 2006

Eight hundred forty‐seven consecutive patients discovered in cardiac arrest by first responding firefighters received initial defibrillation attempts using automatic external defibrillators. The effect of electrode polarity on defibrillation and resuscitation was delermined in the subset of 289 (34%) with ventricuiar fibrillation in a prospective, randomized trial. The ECG was recorded in 205 consecutive patients whose initial rhythm was ventricular fibrillation. Eighty‐seven of 114 patients (76%) in whom the apex chest electrode was positive were defibrillated with the first 200‐joule shock, compared to 70 of 91 patients (77%) in whom the apex eiectrode was negative. There was no difference in the type of rhythm established, e.g., organized versus brady‐asystole following defibrillation with either electrode polarity. Resuscitation was possible in 56% of patients in whom the apex electrode was positive and 60% of those in whom the apex electrode was of negative polarity. Hospital survival rates (26% vs 27%) were also similar for both treatment groups, Unlike results during experimental external defibrillation of animals or those obtained using implantoble defibrillators, this randomized trial of external defibrillation conducted during attempted out‐of‐hospital resuscitation showed no difference in outcomes related to electrode polarity.
Infected Endocardial Pacemaker Electrodes: Successful Open Intracardiac Removal
Authors: NIEDERHÅUSER URS , VON SEGESSER LUDWIG K. , CARREL THIERRY P. , LASKE ANDREAS , BAUER ERWIN , SCHÖNBEGK MARIETTE , TURINA MARKO
Published: July 2006

The long‐term results after open intracardiac removal of infected pacing electrodes are presented. Methods: between 1985 and 1990 open intracardiac removal of 19 infected pacing electrodes was performed in seven patients (six male and one femalel, with a mean age of 56 years. The indications were; persisting bacteremia in three; generator pocket infection in four; endocarditis in one; and ventricular tachycardia caused by retracted electrodes in one. All electrodes were fixed in the right heart and extraction by closed methods failed. Percutaneous catheter techniques were not applied in these seven patients. In five patients two ventricular electrodes had to be removed, and in two patients a single one. A total of seven atrial electrodes were removed in six patients (one electrode each in five patients; two electrodes in one patient). All atrial and two ventricular electrodes could be removed through a pursestring suture without use of a pump oxygenator. For the removal of ten ventricular electrodes in six patients (two electrodes each in four patients; 1 electrode each in two patients) a right‐sided atriotomy was necessary with cardiopulmonary bypass (CPB). Simultaneously, five new pacing systems were implanted. Results; there were no early or late mortalities. In January 1991, all seven patients are alive and in a mean New York Heart Association Class 1,3 of heart failure after a mean interval of 33 months. In all cases the infection could be controlled with a simultaneous antimicrobial chemotherapy and the postoperative period was free of major complications. Conclusion; open intracardiac removal of retained pacing electrodes with or without use of CPB is a safe procedure without major complications. It is mandatory for all infected pacing electrodes that cannot be extracted by closed methods.
The Effect of Bidisomide (SC‐40230), a New Class Ia/Ib Antiarrhythmic Agent, on Defihrillation Energy Requirements in Dogs with Healed Myocardial Infarctions
Authors: HACKETT AIMEE M. , GARDINER PETER , GARTHWAITE SUSAN M.
Published: July 2006

Bidisomide is a Class Ia/Ib antiarrhythmic agent with activity against ventricular and supraventricular arrhythmias. The potential for bidisomide to increase defibrillation threshold (DFT) was tested in anesthetized dogs with healed left ventricular infards (≥ 10 days). Defibrillation patches were attached to each ventricle and shocks were delivered via an external cardioverter/defibrillator. Three groups were studied: placebo (saline), canine therapeutic bidisomide (TB, 2–5 μg/mL plasma concentration) and supratherapeutic bidisomide (STB, 6–14 μg/mL). Each animal received only one treatment. An abbreviated DFT curve was determined before and after treatment. Heart rate, blood pressure, PR, QRS, infarct size, and hematocrit were also measured be/ore and after treatment. DFT was significantly increased (average + 3 to +5 joules [J], P < 0.05) by TB and STB. TB (5/5) did not increase DFT beyond 40 J. In 6/7 experiments, STB did not increase DFT beyond 40 J. Placebo (n = 6) had no significant effect on DFT. Infarct size (x = 11% of the left ventricle) was not significantly different between groups. Heart rate and QRS were not significantly altered but blood pressure was significantly decreased (16%‐31% systolic, 29%‐45% diastolic) and hematocrit was significantly increased (19% to 25%) in oil groups. PR was significantly increased by STB only. Conclusion: therapeutic and supratherapeutic doses of bidisomide slightly but significantly increased DFT (3–5 J) in a canine infarcted heart model.
Loss of “Pacemaker's Identity” Following Activation of the Emergency VVI Feature
Authors: SCHUCHERT ANDREAS , KUCK KARL‐HEINZ
Published: July 2006

Electromagnetic signals coming from the pacemaker programmer can permanently damage multiprogrammable pacemakers. At a follow‐up of a six fold programmable VVI pacemaker (Phoenix 251–6, Pacesetter), the emergency VVI button was activated on the programmer after the programming of the pacing impulse had induced a loss of capture. The next telemetrical interrogation revealed an alteration to a threefold programmable Programmalith III. The inadvertent programming of the model number occurred, because the programming head was removed at one very specific time in the programming sequence of the emergency VVI command.
Blind Cannulation of the Left Pericardiophrenic Vein: An Unusual Cause of Diaphragmatic Pacing
Authors: KOGAN ALAN D. , MALEK MICHAEL
Published: July 2006

Diaphragmatic stimulation as a complication of cardiac pacing due to right ventricular perforation of an endocardial lead or penetration of a screw‐in lead along the right atrial free wall, adjacent to the right phrenic nerve, has previously been described. A case of diaphragmatic pacing due to inadvertent insertion of a temporary pacing lead into the left pericardiophrenic vein via the left internal jugular vein is presented and anatomical considerations are discussed.
Radiofrequency Modification of Atrioventricular Conduction by Selective Ablation of the Low Posterior Septal Right Atrium in a Patient with Atrial Fibrillation and a Rapid Ventricular Response
Authors: FLECK R. PETER , CHEN PENG‐SHENG , BOYCE KER , ROSS ROBERT , DITTRICH HOWARD G. , FELD GREGORY K.
Published: July 2006

A case is presented of a 58‐year‐old woman with atrial fibrillation and uncontrolled ventricular responses up to 180 beats/min despite therapy with digoxin. Radiofrequency energy was applied to the low posteroseptai right atrium in an attempt to modify “slow fiber” conduction. This resulted in a decrease in ventricular rate from 125 to 50 beats/min. Follow‐up Holter monitor demonstrated an average heart rate of 64 beats/min (range 43–112). On exercise tolerance test, the maximum heart rate was 126. Modification of the low posterosepta right atrium may prove to be an alternative to AV node or His bundle ablation and pacemaker implantation in patients with poorly controlled atrial fibrillation and rapid ventricular response. The mechanism by which this approach was effective may be ablation of slow conducting AV nodal fibers with a short refractory period.
Malignant Ventricular Arrhythmias in Patients with Mitral Valve Prolapse and Mild Mitral Regurgitation
Authors: VOHRA JITU , SATHE SUNIL , WARREN RODERIC , TATOULIS JAMES , HUNT DAVID
Published: July 2006

Mitral valve prolapse (MVP) is a common disorder that, in general, has a good prognosis. Rare occasions of sudden death have been reported in patients with MVP and it is presumed that the basis of sudden death is arrhythmic. We report seven patients with moderate to severe MVP and malignant ventricular arrhythmias. All patients had trivial to mild mitral regurgitation and normal left ventricular function. Three patients presented with syncope, two with out‐of‐hospital cardiac arrest, and three with recurrent palpitations and presyncope. In a mean follow‐up period of 2.5 years (range 6 months to 5 years), two patients died suddenly despite successful control of their nonsustained ventricular tachycardia (VT) with sotalol as shown by ambulatory monitoring. Two patients, who had sustained VT despite antiarrhythmic drug therapy, had mitral valve surgery, however, monomorphic VT could be induced in both even after surgery. The arrhythmias in the remaining three patients are controlled on antiarrhythmic drugs. We conclude that a selected subset of patients with MVP, malignant ventricular arrhythmias, and miid mitral regurgitation are at risk of sudden death. Syncope, inferolateral repolarization changes, complex ventricular ectopy, and a markedly myxomatous valve may be pointers to higher risk of sudden death and mitral valve surgery may not provide control of ventricular arrhythmias.
Accelerometer‐Based Adaptive‐Rate Pacing: A Multicenter Study
Authors: CHARLES RICHARD G. , HEEMELS JAN P. , WESTRUM BARBARA L. ,   EUROPEAN EXCEL™ STUDY GROUP
Published: July 2006

A new adaptive rate pacemaker, using an acceleromeler to detect body motion as an indicator of metabolic demand, was evaluated in 13 centers located in five countries. During the study, 55 patients with a broad range of indications were implanted with the EXCEl™ VR single chamber pacemaker. One month evaluations were completed on a subgroup 0f 37 patients. The pacemaker response was optimized before discharge using a simple walking test. An “exercise test” recording feature in the programmer eliminated the need for ECG monitoring. At nominal settings, the mean (± SD) pacing rate increased 29 ± 9 ppm while walking slowly and 44 ± 11 ppm (n = 33) during a brisk walk. This information was used to optimize the parameter settings. Without further changes to the programmed settings the patients were subsequently tested 2–4 weeks postimplant with a symptom‐limited treadmill test using the chronotropic assessment exercise protocol (CAEP). Mean pacing rate increased from 74.5 ±2.5 ppm (n = 24) at rest to 118.6 ± 12.2 ppm (n = 21) at 3 mph/6% grade to 143.5 ± 3.5 ppm [n = 2) at 3.8 mph/8% grade. Conclusion: The individual responses were proportional to the physical exertion imposed on the patients. Pacing rates were considered to be appropriate using the chronotropic response zone as a criterion for appropriate rate modulation. A simple walking test utilizing the exercise test facility, results in appropriate optimization of the pulse generator to the individual patient.
The Rationale for Prophylactic Implantation of a Defibrillator in “High Risk” Patients
Authors: BRUGADA PEDRO , ANDRIES ERIK
Published: July 2006

The increasing technological developments have made it possible to have implantable defibrillators with a wide range of diagnostic and therapeutic capabilities, which can be implanted without the need for a thoracotomy. It is not surprising, therefore, that the indications for implantation of a defibrillator have rapidly evolved. Defining populations of patients in whom a true “prophylactic” implantation (before the first episode of ventricular tachycardia or ventricular fibrillation) may be justified is still difficult. However, the time has certainly come to provide a cardioverter defibrillator to all patients who have suffered from one episode of ventricular tachycardia or ventricular fibrillation and who are at real risk of sudden arrhythmic death. Identification of these patients is relatively easy. It can be done using simple variables from the clinical history. Results from an ongoing multicenter trial testing the hypothesis that clinical variables can indeed be used to stratify the risk of sudden death and to select candidates for a defibrillator have proven the validity of this approach. There is no medical justification to withhold implantation of a cardioverter defibrillator in the truly “high risk” patient. One has to realize, however, that the concept of “high risk” is relative, and that the indications for the implantable defibrillator will continue to broaden.
Should Radiofrequency Current Ablation be Performed in Asymptomatic Patients with the Wolff‐Parkinson‐White Syndrome?
Authors: STEINBECK GERHARD
Published: July 2006

The exiting new method of ablation of accessory pathways using radiofrequency current applied by catheters will dramatically change our therapeutic decisions in these patients in the near future. This brief survey reviews the existing literature about the risk of the disease as well as of the procedure of catheter ablation. From these data, the risk of sudden death appears to be extremely low in asymptomatic Wolff‐Parkinsan‐White (WPW) individuals. Side effects of catheter ablation may result from the invasive procedure as well as from radiation exposure (the latter to the patienl as well as to operating physicians). While the complication rate in experienced centers is extremely low, a multicenter registry of the success and complication rate is urgently needed in view of the many centers starting with catheter ablation. Based on a subjective benefit‐to‐risk analysis, asymptomatic WPW individuals should be offered catheter ablation only under special circumstances (high risk profession, athletes, family history of sudden death). On the other hand, catheter ablation need not be and should not be considered generally in asymptomatic individuals with WPW pattern. Finally, this author cannot imagine that the energy, time, and money spent for mass screening and eventual catheter ablation of asymptomatic WPW individuals with its attending risks can be outweighed by the potential benefits for these asymptomatic individuals.
Beep Detection Technique for Immediate Documentation of R Wave Sensing by an Implanted Defibrillator
Authors: BERNSTEIN ALAN D. , NEGLIA DONNA L. , PARSONNET VICTOR
Published: July 2006

A technique is described for follow‐up clinic evaluation and documentation of R wave detection by an implanted defibrillator that emits audible tones upon magnet application whenever an R wave or other signal is sensed. A circuit comprising an electrets microphone, an instrumentation amplifier, a high‐pass filter, and an envelope detector is used to generate a signal that may be plotted together with a surface‐lead electrocardiogram on a two‐channel strip‐chart recorder. The resulting plot documents the sensing function of the implanted device and serves as an indication of optimal magnet position. Alternatively, the beep detector output could be used to trigger the inscription of fiduciary markers on a single‐channel strip‐chart recorder equipped with an auxiliary input for this purpose.
Delayed Success Following Radiofrequency Catheter Ablation
Authors: STEIN KENNETH M. , LERMAN BRUCE B.
Published: July 2006

Two patients who underwent attempted radiofrequency catheter ablation of an atrioventhcular accessory pathway experienced delayed abolition of pathway conduction. During the procedures there was transient block in the accessory pathway following multiple ablotion attempts at closely spaced sites. Both patients showed evidence of preexcitation at the conclusion of the ablation session but neither showed evidence of accessory pathway conduction during a second electrophysiological study. These observations demonstrate that in patients in whom transient block of the accessory pathway is produced, continued evolution of radiofrequency energy lesions may result in the eventual success of an initially unsuccessful ablation session.
Choosing the Stimulation Rate in Patients with Intermittent Bradycardia and a Single Lead Pacemaker
Authors: ROSENQVIST MÅRTEN , EDHAG OLOF K. , LAGERGREN HANS , NORDLANDER ROLF , VALLIN HANS
Published: July 2006

In order to assess the prevalence of intermittent bradycardia in a pacemaker population, we retrospectively evaluated the occurrence of intrinsic heart activity in 229 patients with ventricular pacing. Spontaneous heart activity was recorded in 60% of the patients. However, the stimulation rate had been decreased in onJy 40% of the patients in order to allow for longer periods of intrinsic heart activity. In the second part of the study we prospectively assessed differences in pacemaker utilization in 19 patients with intermittent bradycardia and single lead pacemakers. All patients were observed over four periods of 14 days, with the following pacing modes: 70 heats/min, 50 beats/min, hysteresis sensing 50 beats/min, and pacing 70 heats/min; and search hysteresis sensing 50 beats/min and pacing 70 beats/min. Search hysteresis pacing is a new feature that theoretically allows for a shorter time of pacing than that of hysteresis pacing. A reduction in the stimulation rate from 70 beats/min to 50 beats/ min resulted in a 60% reduction in pacemaker utilization (P < 0.05). Search hysteresis decreased pacemaker utilization by 33% (P < 0.05) There was no statistical difference between conventional hysteresis and fixed rate pacing at 70 beats/min. Most patients found fixed rate pacing preferable to hysteresis pacing. In order to minimize battery consumption and to avoid unfavorable hemodynamics in patients with ventricular pacing, the stimulation mode and rate should be optimized in patients with intermittent bradycardia to allow for longer periods of intrinsic heart activity.
Radiofrequency Catheter Ablation for AV Nodal Reentry: A Technique for Rapid Transection of the Slow AV Nodal Pathway
Authors: MOULTON KRIEGH , MILLER BRIAN , SCOTT JANE , WOODS W.T.
Published: July 2006

Selective radiofrequency (RF) catheter ablation of the slow AV nodal puthway has shed new light on the anatomy and physiology of the atrioventricular junction. The recording of “slow pathway potentials” facilitates localization of the slow pathway and has led to a concept of multiple pathway components with atrial insertion sites covering a potentially broad region surrounding the coronary sinus os. The critical area for complete interruption of the slow pathway may be larger than lesion size produced by ablation at a single site, resulting in multiple RF applications with lengthy sessions and prolonged radiation exposure. Information from both old and recent literature suggests that the slow AV nodal pathway is represented by a group of fibers originating from the posteroinferior interatrial septum and coursing anterosuperiorly near the tricuspid annulus before converging upon the compact AV node. Based on this anatomical arrangement, the present study was conducted to evaluate a technique designed to transect the slow pathway by producing a linear RF lesion perpendicular to the orientation of the slow pathway within the mid‐portion of Koch's triangle. Using this technique, 30 of 30 patients with common AV nodal reentry ivere rendered noninducible using 1 to 3 RF applications. Total procedure time averaged 3.4 ± 1.1 hours and fluoroscopy time averaged 14.8 ± 4.6 minutes. As a marker of efficacy, episodic nonsustained atrial tachycardia (NSAT) during RF delivery occurred in 28 of 30 (93%) successful applications. Three patients experienced tachycardia recurrence and were successfully ablated by repeat procedure. Conduction characteristics and refractoriness of the fast pathway were unchanged in 23 of 23 patients reevaluated at a mean of 7.2 weeks postablation. Two of 30 (6%) patients experienced procedure related complications but there were no instances of AV block. We conclude that the technique of producing a linear lesion by continuous migratory RF application in the manner described safely and effectively eliminates AV nodal reentry, simplifies the procedure, and minimizes radiation exposure to the patient and the physician.
A Minimal Model of the Monophasic Defibrillation Pulse
Authors: KROLL MARK W.
Published: July 2006

A minimal model of the defibrillation capability of a monophasic capacitive discharge pulse is derived from the Weiss‐Lapicque strength duration model. The model suggests that present, empirically derived values of pulse durations and tilts are close to optimum for presently used values of capacitors and electrode resistances. The model suggests that neither the tilt nor fixed duration specification is universally superior to the other for dealing with electrode resistance changes. A tilt specification would appear to best handle resistance decreases while a fixed duration specification would best handle resistance increases. The model was used to study the effect of capacitance changes. It appears that the optimum tilt and pulse duration vary with the capacitance value. The model further suggests that decreasing the capacitance from presently used values may lower defibrillation thresholds.
Failure of One Conductor in a Nonthoracotomy Implantable Defibrillator Lead Causing Inappropriate Sensing and Potentially Ineffective Shock Delivery
Authors: EPSTEIN ANDREW E. , SHEPARD RICHARD B.
Published: July 2006

We describe how a single defect in a new model transvenous lead for an implantable curdiuverter defibrillator can result in malfunction of the sensing and defibrillation circuits. The patient had received shocks during atrial fibrillation without premonitory symptoms. At least one shock was delivered and not fell by the patient. In addition, late in the course, a shock was delivered during atrial fibrillation documented to be with a slow ventricular response. In the transvenous lead, a distal spring functions as the anode for rate sensing and the cathode for defibrillation. The wire from this spring bifurcates near the proximal end of the catheter. One wire from the bifurcation leads to the positive (anode) rate‐sensing socket of the pulse generator, and the other wire leads to the negative (cathode) high voltage output socket of the defibrillator for defibrillation and cardioversion. After the inappropriate and unperceived shocks were documented, intraoperative and postoperative electrical testing indicated that intermittent discontinuity of the distal spring system within the proximal yoke of the catheter caused faulty sensing and potentially unreliable defibrillation. This dual malfunction was possible because the distal spring of the lead functions in the high‐voitage output and the rate‐sensing iow‐vollage input circuits of the implantable defibrillator.
Maleficent Magnets and Mangled Megabytes
Authors: FYKE F. EARL
Published: July 2006

Personal computers have become commonplace in physicians' practices and their use in cardiac pacing for programming and follow‐up is increasing. The most commonly used media for mass data storage are ferromagnetic. That the toroidal and bar magnets used to activate reed switches pose a threat to such data is well known but the degree of care necessary in handling magnets around storage media, especially the vulnerable floppy diskettes, is not generally appreciated. The basic principles of magnetic data storage discussed herein elucidate the mechanism of data alteration by extraneous magnetic fields. The properties of the surface coatings, the requirements of applicable industry standards, and the field strengths of the pacemaker magnets suggest that data on diskettes should be secure if kept at least 6–7 cm fram an isolated pacemaker magnet. Experiments with typical bar and toroidal magnets demonstrated that data recorded on representative diskettes actually remained unaltered until the magnets were placed < 1 cm from the recording surfaces.
Beneficial Effects of Dextro‐Amphetamine in the Treatment of Vasodepressor Syncope
Authors: SUSMANO ARMANDO , VOLGMAN ANNABELLE S. , BUCKINGHAM THOMAS A.
Published: July 2006

Three patients with history of documented hypolension, near syncope, or syncope before or after the administration of isoproterenol during head‐up tilt table are reported. Severe bradycardia was also noted in one patient. All three patients responded to the administration of 2.5 mg of oral dextro‐amphetamine 45 minutes prior to a repeat head‐up tilt table study. The potent central and peripheral adrenergic agonist pharmacological properties of this drug permitted the prevention of severe vasodepressor syncope in these patients.
Radiofrequency Catheter Ablation of an Intraatrial Reentrant Tachycardia: Evidence of an Area of Slow Conduction
Authors: GIUDICI MICHAEL C. , GIMBEL MICHAEL J.
Published: July 2006

Radiofrequency catheter ablation for infraatrial reentrant tachycardia has not been previously reported. This article describes a patient with a demonstrable area of slowed conduction in ihe lateral right atrium that responded to radiofrequency catheter ablation in the area of the fractionated eiectrogram ivith elimination of the tachycardia. This patient also had the common form of atrioventricular nodal reentrant tachycardia, which was also successfully ablated.
The Epicardial Field Potential in Dog: Implications for Recording Site Density During Epicardial Mapping
Authors: PIEPER CARL F. , PACIFICO ANTONIO
Published: July 2006

Investigations into mechanisms and successful surgical therapy of ventricular tachycardia (VT) depend upon accurate endocardial/epicardial mapping. Deduction of local activation is based upon parameters derived from the field potentiai (FP) (monopolar recording) or its first spatial derivative (bipolar recording). Adequate electrode spacing is an assumption fundamental to the mapping process, but the electrode spacing required for accurate representation of the FP is unknown. The purpose of this work is to derive the electrode spacing necessary to accurately describe the FP on the epicardium. In 11 dogs, electrograms from vertical (V) (base to apex h) bands having 40 electrodes and horizontal (H) bands having 40 to 80 electrodes were sampled at I kHz. The spatial handwidths (BW) were computed according lo two criteria: (1) the frequency yielding 2% mean squared error (MSE) computed at the time of the greatest integrated magnitudes of the Fourier transform; and (2) the highest frequency bounding 95% power computed at each msec throughout the beat. Implied electrode spacings were defined according to the sampling theorem. The 5th percentiles of the implied electrode spacing distributions were used to define the widest interelectrode distance required to prevent spatial aliasing. H‐5th percentile and V‐5th percentile were, respectively; 2% MSE (3.5 mm, 2.3 mm); 95% power (3.6 mm, 2.3 mm). Thus, a typical 20‐kg dog requires more than 250 recording sites for accurate epicardial mapping. Extrapolating to man, these results suggest inadequate electrode density may partially be responsible for incomplete and ambiguous reentry patterns often observed during intraoperutive mapping.
The Ventricular‐Synchronous, Skeletal‐Muscle Ventricle: Preliminary Feasibility Studies
Authors: GEDDES L.A. , JANAS W. , HINDS M. , BADYLAK S.F. , COOK J.
Published: July 2006

The two requirements for the optimal use of skeletal muscle wrapped around a pouch used to pump blood are.(1) a low poucli diastolic pressure (to assure a iiigh musde capillary blood flow; and (2) a high pouch precontraction pressure (PCP) (to assure a forceful muscle contraction). Both requirements are satisfied with the pumping method described herein. This new type of skeletal‐muscle ventricle (SMV) consists of a rectus abdominis muscle wrapped around a pouch connected to the left ventricular apex (with no valve) and to the aorta via a one‐way valve. Consequently, the pressure in the SMV pouch is always equal to left ventricular pressure. The high PCP is obtained by stimulating the rectus muscle to contract tt the desired left ventricular pressure. The R (or P) wave of the cardiac electrogram initiates a delayed train of stimuli to cause the rectus muscle to contract tetanically and expel Wood from the pouch. We have designated this pumping configuration the ventricular‐synchronous SMV (VS‐SMV). In this study, eight ucute anesthetized dogs were used. The muscles were unconditioned and among the items investigated were the importance of the delay (d) between the R (or P) wave and the onset of the stimulus train, the optimal stimulus frequency and train duration, the VS‐SMV output with different ratios of VS‐SMV to left ventricular contractions, unloading of the left ventricle, Frank‐Starling curves for the VS‐SMV, pressure‐volume loopsforthe VS‐SMV with and without contraction of the rectus muscle, and washout characteristics of the VS‐SMV. It was found that a stimulus frequency of 40/sec. and a train duration of 250 msec is optimal. It was also found that choice of the proper delay from the R or P wave provided maximal augmentation in stroke volume, typically 20 to 40 mL. Pumping with a ratio of 1:2 provided VS‐SMV outputs ranging from 20 to 140 mL/min per kg of body weight. With this same pumping ratio, cardiac output increased by 28% and the post‐VS‐SMV contraction, left ventricular stroke volume was reduced. The Frank‐Starling curves showed that PCPs on the order of aortic pressure are needed for the most forceful muscle contraction. With this new pumping configuration, the left ventricle resembles an atrium which delivers blood to the VS‐SMV that is stimulated to contract when the desired PCP is reached. Studies were also conducted in which the VS‐SMV outlet (valve end) was closed and filling and emptying occurred through the left ventricle. Saline washout studies were performed to determine the emptying characteristics with and without pumping using the closed‐end pouch. A typical emptying was 50% for five VS‐SMV contractions with the muscle contracting. However, even without the muscle contracting, there was washout due to the compliant recoil of the pouch which was stretched during ventricular systole. Essentially the same pumping performance was obtained with the closed‐end mode of operation.
Actuarial Survival of Transvenous Pacing Leads in a Pediatric Population
Authors: LAU YUNG R. , GILLETTE PAUL C. , BUCKLES DAVID S. , ZEIGLER VICKI L.
Published: July 2006

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.
Total Pectoral Implantation: A New Technique for Implantation of Transvenous Defibrillator Lead Systems and Implantable Cardioverter Defibrillator
Authors: CAMUÑAS JORGE , MEHTA DAVENDRA , JOHN IP , ELANA PE , GOMES J. ANTHONY
Published: July 2006

We describe a new approach to tolal pectoral implantation of cardioverter defibrillators with an endocardial defibrillation lead system. Endocardial lead configuration used was an FDA approved right atrial‐superior vena cavo defibriliation spring electrode, right ventricular bipolar sensing electrode, and a pectoral patch. Endocardial leads were implanted via a cephalic or an axillary venesection. Pectoral patch was placed in a sabmuscular position. In case of failure to obtain satisfactory thresholds, a small intercostal thoracofomy was performed via fhe same skin incision and patch placed over the epicardium instead of submuscular position and used with Ihe right atrial spring electrode. The device was implanted in the pectoral region, submuscularly, over the patch. Sixteen consecutive patients underwent this approach. With a submascular patch, adequate defibrillation thresholds (< 15 joules [J]) were obtained in 14 (87.5%) patients. In the other two, defibrillation thresholds of ≤ 15) were obtained with a epicardial patch. Pectoral implantation of the device was feasible in all 16 patients and none needed repositioning. Average postimplant hospital stay was 5 days. During follow‐up period (average 5 months), none of the patients reported any major local symptoms and no problems have been encountered in device interrogation. Thus, total pectoral implantation of the cardioverter defibrillator including the patch, leads, and the device is feasible. Furthermore, in case of foilure to obtain adequate defibrillotjon thresholds with submuscular patch, an epicardial patch can easily be implanted and allows 100% successful defibrillation at energy levels of ≤ 15 J with right atrial patch configuration.
Oral Flecainide, Sotalol, and Verapamil for the Termination of Paroxysmal Supraventricular Tachycardia
Authors: HAMER ANGAS W.F. , STRATHMORE NEIL , VOHRA JITU K. , HUNT V. DAVID
Published: July 2006

The ability to terminate supraventricular tachycardia (SVT) acutely with an oral dose of flecainide (2.5–3.3 mg/kg). sotalol (2.0–2.9 mg/kg), and verapamil (3.3–3.7 mg/kg) was investigated in an observational study of six patients u'ith SVT normally controlled by an antitachycardia pacemaker. The pacemaker was programmed to induce SVT and the stahility of SVT was observed for 90 minutes as a baseline. Subsequent studies involved testing of the three antiarrhythmic drugs on separate occasions, given in random order as crushed tablets in orange juice during pacemaker induced SVT, with plasma drug levels collected every 15 minutes for 90 minutes post drug ingestion. Sotalol produced drug induced slowing of SVT in all six patients, with termination of SVT in three patients by 60–65 minutes, with maximum plasma levels of 0.76–2.09 μg/mL achieved by 90 minutes. Flecainide produced maximum plasma levels of 83–745 ng/mL, 60–90 minutes post ingestion, and slowed SVT in three patients, SVT was terminated in three patients after 45–85 minutes, but no effect on SVT was seen in two patients who had inodequate plasma levels (≤ 166 ng/mL) from doses < 3 mg/kg. Verapamil produced maximum plasma levels of 0 (undetectable) to 388 ng/mL, 45–90 minutes post ingestion, and slowed SVT in three patients, but only one of these patients reverted to sinus rhythm (at 40 min). No effect on SVT was seen in three patients due to undetecfable plasma levels. We concluded that sotalol (≤ 2 mg/kg) and flecainide (≤ 3 mg/kg) appeared to be suitable oral drugs for termination of SVT. Verapamil appeared unsuitable due to its unpredictable bioavailability, despite the use of high doses (> 3 mg/kg).
Is the Second Phase of a Biphasic Defibrillation Waveform the Defihrillating Phase?
Authors: HILLSLEY RUSSELL E. , WALKER ROBERT G. , SWANSON DAVID K. , ROLLINS DENNIS L. , WOLF PATRICK D. , SMITH WILLIAM M. , IDEKER RAYMOND E.
Published: July 2006

Why some biphasic waveforms defibrillate with lower energies than monophasic waveforms of similar duration is unknown. One hypothesis is that the first phase of a hiphasic waveform acts as a conditioning, hyperpolarizing prepulse to prepare for defihrillation by a second depolarizing phase. To test whether the second phase of a biphasic waveform is the defibrillating phase, three monophasic wavefarms, an ascending ramp (A), a square wove (S), and a descending ramp (D), were compared to three biphasic waveforms with A, S, or D in the first phase (biphasic first phase) and three hiphasic waveforms with A, S, or D in the second phase (biphasic second phase). Two defibrillation thresholds for each waveform were performed in 18 open chest pigs and mean defibrillation thresholds were compared. In nine pigs 16‐msec monophasic and 16/16‐msec biphasic waveforms were ranked by mean current and energy at defibrillation threshold. The ranks were the same for monophasic and biphasic second phase waveforms: for mean current A < S = D and for energy A < S < D. The ranks were different for the biphasic first phase ivaveforms: far mean current S < A = D and for energy S < A = D. Although ranks for the 16‐msec monophasic ivaveforms matched those for the 16/16‐msec biphasic second phase waveforms, the biphasic waveforms had higher mean currents and energies at defihrillation threshold. in nine pigs defibrillation thresholds for 6‐msec monophasic and 6/6‐msec biphasic ivaveforms were ranked. For mean current the ranks were monophasic: A < S = D: biphasic first phase: A = S = D; and biphasic second phase: S = D < A. For energy the ranks were monophasic: A = S < D; biphasic first phase: A = S = D: and biphasic second phase; S = D < A. Thus, ranks for the 6‐nisec monophasic waveforms differed from those for the 6/6‐msec biphasic second phase waveforms. For 16/16‐msec biphasic waveforms, less effective for defibrillation than corresponding 16‐msec monophasic waveforms, these results support the hypothesis that the second phase of a biphasic waveform defihrillates since the defibrillation efficacy of a 16/16‐msec biphasic waveform is reiated to the defibrillation efficacy of its second phase waveshape. However, for clinicaily useful 6/6‐msec biphasic waveforms, more effective for defibrillation than 6‐msec monophasic waveforms, the hypothesis is not supported because the ability of a 6/6‐msec biphasic waveform to defibrillate is unrelated to the defibrillation efficacy of its second phase waveshape.
A Subcutaneous Lead Array for Implantable Cardioverter Defibrillators
Authors: JORDAENS LUC , VERTONGEN PATRICK , van BELLEGHEM YVES
Published: July 2006

Two patients received an implantable cardioverter defibrillator with the combination of a transvenous lead and a subcutaneous lead array with three branches. This approach allowed us to find low defibrillation threshoids in both patients (≤10 and ≤ 15 joules [J], respectively], which was impossible with a transvenous catheter. In a third patient, a crinkled subcutaneous patch was replaced by an array. The defibrillation threshoid with the array was ≤ 20 J, as opposed to ≤24 J with the patch. No surgical problems occurred. The subcutaneous array is a technical improvement for tiie therapy with impiantable defibrillators, when a single catheter system is not sufficient to ensure a safety margin for defibrillation, or when surgicai or postsurgical problems occur with a subcutaneous patch.
High Rate of Late Dislodgements of an Active Fixation Atrial Lead
Authors: NOWAK BERND , VOIGTLAENDER THOMAS , BECKER HANS‐JUERGEN
Published: July 2006

Between May 1985 and May 1991 we implanted 115 DFH‐leads as unipolar atrial leads. The active fixation mechanism of this electrode consists of two sickle‐shaped anchoring hooks which are placed at a distance of 0.9 mm parallel to the distal flat end of the electrode. All leads were affixed to the free wall of the right atrium. One hundred eight leads (93.9%) were implanted for dual chamber pacing and seven leads (6.1%) for single chamber atrial pacing. Parameters measured at implantation were (mean values): stimulation threshold 1.06 ± 0.42 V at 0.5 msec pulse width, P wave amplitude 5.12 ± 2.04 mV, and lead impedance 560 ± 76.1 Ohms. Within the first week after implantation, three early dislodgements occurred (2.6%). The follow‐up period averaged 30.4 ± 16.2 months (range 2–76 months). During this time, 14 late macrodislodgements (12.2%) occurred after a mean period of 18.4 months (range 2–59 months). All of them required reoperation. The active fixation mechanism of the DEH‐lead appears to be unreliable, if implanted in the free wall of the right atrium for dual chamber pacing.
Exercise Chronotropy in Patients with Normal and Impaired Sinus Node Function After Cardiac Transplantation
Authors: HEINZ GOTTFRIED , RADOSZTICS SUSANNE , KRATOCHWILL CHRISTOPH , KREINER GERHARD , BUXBAUM PETER , GRIMM MIGHAEL , SUNDER‐PLASSMANN GERE , LAUFER GÜNTHER , LAGZKOVICS AXEL , GÖSSINGER HEINZ
Published: July 2006

The chronotropic response during graded, symptom limited exercise was investigoted in 32 cardiac transplant recipients a mean of 49 ± 18 days after transplantation. All patients had systematic evaluation of postoperative donor sinus node (SN) function and the cardioacceleratory response was compared according to the SN function. Twenty‐one patients had normal postoperative SN studies (corrected SN recovery time < 520 msec, group I) while the SN function was impaired postoperatively in the remainder (n = 11, group II; corrected SN recovery time 4,149 ± 6,283 msec in 5 patients, junctionai escape rhythm in 6 patients). All patients had regained sinus rhythm at time of the exercise test Patients in group II had lower basal sinus rates at the beginning of exercise (91.5 ± 11 vs 101.4 ± 7 beats/min, P < 0.02). This lower chronotropy was maintained over every incremental step (Frato between groups= 30, P = 0.0001, Frate vs workload= 15, P = 0.0001 by two‐way ANOVAJ and resulted in a significantly lower heart rate at individual peak exercise (108.3 ± 20 vs 124.2 ±13 beats/min, P < 0.02). A total of 14/16 patients in group I but only 2/16 patiejils in group 11 accomplished a peak heart rate ± 120 beats/min (P = 0.009). The workload achieved did not differ between the groups (107 ± 29 vs 102 ± 32 watts, P > 0.5). These data show a lower SN chronotropy during rest and at peak exercise in cardiac transplant recipients with postoperative SN deficiency and apparent normalization of SN fundion.