bluuebunny/crossref_metadata_2025 huggingface dataset:
Reappraisal of Inhibition and Summation with a Single Conditioning Stimulus in Man
Authors: SAIHARA SHINICHIRO , INOUE HIROSHI , TODA IKU , USUI MASAHIRO , SUGIMOTO TSUNEAKI
Published: July 2006

A noncapturing conditioning stimulus is known to exert inhibitory effect on a subsequent supru‐threshold stimulus, while summation occurs rarely in man. The present study was conducted to revaluate whether conditioning stimulus at a relatively low intensity produced inhibition and summation in man. Thirteen patients with various arrhythmias, 47 ± 19 years old, were studied. Basic ventricular driving stimuli (S1S1= 600 msec), a conditioning stimulus (Sc), and extrastimulus (S2) were introduced from a catheter electrode. Sc at an intensity of twice the late diastolic threshold inhibited suprathreshold S2 from evoking a response in all 13 patients. The ScS2 interval producing inhibition was from 11 ± 4 to 38 ± 26 msec. When Sc preceded S2 by 5 msec, effective refractory period was shortened by 16 ± 7 msec in 7 of 23 patients, a phenomenon of summation. The present study demonstrates that inhibition and summation are common phenomena with a single conditioning stimulus at relatively low intensities.
Torsade de Pointes and T‐U Wave Alternans Associated with Arsenic Poisoning
Authors: LITTLE RANDALL E. , KAY G. NEAL , CAVENDER J. BRADLEY , EPSTEIN ANDREW E. , PLUMB VANCE J.
Published: July 2006

Arsenic intoxication is a common form of heavy metal poisoning. Although arsenic‐induced circulatory collapse, seizures, and syncope are well known, the potential for serious ventricular arrhythmias is Jess well recognized. Reported in this study are two cases of arsenic poisoning causing forsade de pointes. Furthermore, marked prolongation of the QT‐U interval and the rarely observed phenomenon of T‐U wave alternans are demonstrated. Thus, arsenic intoxication may be complicated by prolongation of the QT‐U interval and torsade de pointes. T‐U wave alternans occurs in the presence of a long QT‐U interval and may be an electrocardiographic warning sign of torsade de pointes.
Clinical Utility of Telemetered Intracardiac Electrograms in Diagnosing a Design Dependent Lead Malfunction
Authors: SARMIENTO JOSEPH J.
Published: July 2006

Inhibition of pacemakers due to false signals from malfunctioning pacing leads has been previously reported. Three cases are reported in which inappropriale pauses were observed shortly following implantation. In all three cases, active fixation leads with an electronically active screw and ring tip electrode were used. All leads were manufactured by Oscor Medical, St. Petersburg, Florida. In case one, models PY‐61 (ventricle) and PY‐51 (atrium) were used. In case two, models PY‐61 were used in the ventricle and the atrium. In case three, models PY‐52 were used both in the atrium and ventricle. Thresholds at the time of implantation were acceptable. In cases one and two, inappropriate pauses were noted following, paced ventricular beats. In case three, inappropriate inhibition of the ventricular output was noted intermittently after some of the paced atrial beats. Spurious signals were identified as the cause of the apparent oversensing problem by using electrocardiograms with annotated telemetry information and noninvasively telemetered intracardiac electrograms. The amplitude of the spurious signals varied between 2 and 14 mV. In all cases, the problems resolved with time. A mechanism for the generation of false transients is proposed and the value of telemetered intracardiac electrograms is discussed.
Propafenone‐Induced Torsade de Pointes: Cross‐Reactivity with Quinidine
Authors: HII JOHN T.Y. , WYSE D. GEORGE , GILLIS ANNE M. , COHEN JAMES M. , MITCHELL L. BRENT
Published: July 2006

A 77‐year‐oid/emale with new onset atrial fibrillation occurring in the absence of structural heart disease developed torsade de pointes during therapy with quinidine bisulfate 500 mg orally every 8 hours. Ten days after quinidine therapy had been discontinued she developed torsade de pointes while receiving propafenone 300 mg orally every 8 hours. This case demonstrates that propafenone may be associated with torsade de pointes and suggests a cross‐reactivity between this effect and prior occurrence of torsade de pointes on Class IA antiarrhythmic drug therapy.
Aortic Leaflet Perforation During Radiofrequency Ablation
Authors: SEIFERT MARK J. , MORADY FRED , CALKINS HUGH G. , LANGBERG JONATHAN J.
Published: July 2006

A 15‐year‐old girl underwent successful radio frequency ablation of an accessory pathway. Following ablation, a new III/VJ diastolic murmur was noted. Echocardiography revealed a perforated aortic leaflet, with a small amount of adherent valvular tissue and trivial aortic insufficiency fay color Doppler. The patient remains asymptomatic. We are not aware of any similar complication from electrophysiological study, catheter ablation, coronary angiography, or percutaneous transluminal coronary angioplasty. We speculate that the current state of catheter technology contributed significantly to this complication. This case illustrates the need for using care in crossing the valve, continued advances in catheter technology to reduce the incidence of complications, and careful physical examination prior to and following attempts at ablation.
Effect of Antiarrhythmic Drug Therapy on the Incidence of Shocks in Patients who Receive an Implantable Cardioverter Defibrillator after a Single Episode of Sustained Ventricular Tachycardia/Fibrillation
Authors: KOU WILLIAM H. , KIRSH MARVIN M. , BOLLING STEVE F. , STIRLING MACK , KADISH ALAN H. , DE BUITLEIR MICHAEL , CALKINS HUGH , LEWIS RUTH R.R. , MORADY FRED
Published: July 2006

Seventy‐four patients (16 women, 58 men, age 58 ± 21 years, mean ± standard deviation) who received an implantable Cardioverter de/ibrillator (ICD) after experiencing a single episode of ventricular tachycardia or ventricular fibrillation were followed to determine if antiarrhythmic drug therapy affects the incidence of ICD discharges. Thirty‐three patients (group A) were treated with an antiarrhythmic drug that was either untested or previously demonstrated during electropharmacological testing to be ineffective in suppressing the induction of ventricular tachycardia. Forty‐one patients (group B) were not treated with an antiarrhythmic drug. There were no significant differences between the two groups in regards to age, sex, incidence of coronary artery disease, left ventricular function or the type of ICD pulse generator used. During a mean follow‐up of 14 months for the entire cohort, 15 patients (46%) in group A and 18 patients (44%) in group B experienced at least one ICD shock. The time to the first appropriate shock (5 ± 5 months in both groups) and the frequency of ICD shocks (0.3 ± 0.2/month in group A vs 0.4 ± 0.5/month in group B) were similar in both groups. The incidence of syncope at the time of ICD discharge was higher in group A than group B patients (31% vs 5%, P < 0.05). In conclusion, antiarrhythmic drugs that are untested or have failed electropharmacological testing do not appear to reduce the probability of ICD discharge over a short‐term (mean 14 months) follow‐up in patients who have had only one clinical episode of VT/VF and may increase the risk of syncope during ICD discharge. Studies with a larger sample size and longer follow‐up period will be needed to confirm these findings.
Entrainment of Ventricular Tachycardia in Arrhythmogenic Right Ventricular Tachycardia
Authors: AIZAWA YOSHIFUSA , FUNAZAKI TOSHIKAZU , TAKAHASHI MASASHI , NAITOH NAOKI , MIYAJIMA TAKEFUMI , KUSANO YORIKO , SHIBATA AKIRA , MISAKI TAKURO
Published: July 2006

In two patients with arrhythrnogenic right ventricular dysplasia (ARVDJ, sustained ventricular tachycardia (VT) was induced by programmed stimulations during serial drug testings. One patient had five and the other had two VT morphologies, and the sites of origin were determined by endocardial catheter mappings. When overdrive pacing was performed, constant fusion in the QflS complex was observed in the two patients. Constant fusion of a different degree was also observed at different paced cycle lengths. Both patients had dilated right ventricles and wall‐motion abnormality, and the diagnosis of ARVD was further confirmed by the specimen resected at the site of origin of VT. Therefore, VT in ARVD can be entrained and reentry is the most likely mechanism of such VT.
Bidirectional Bundle Branch Reentry Tachycardia Associated with Ebstein's Anomaly: Cured by Extensive Cryoablation of the Right Bundle Branch
Authors: ANDRESS J. DANIEL , SALM THOMAS J. VANDER , HUANG SHOEI K. STEPHEN
Published: July 2006

A 30‐year‐old woman with Ebstein's anomaly presented with a sustained, wide QRS complex tachycardia exhibiting a left bundle branch block morphology. Serial electrophysiological studies revealed right and left bundle branch reentry tachycardias refractory to many conventional antiarrhyfhmic drugs, Radiofrequency and direct current catheter ablation of the right bundle branch failed to control the tachycardias. The patient subsequently underwent extensive endocardial cryoablation to the right bundle branch resulting in cure of her arrhythmia.
Termination of Reentrant Propagation By a Single Stimulus: A Model Study
Authors: QUAN WEILUN , RUDY YORAM
Published: July 2006

A computer model of a ring‐shaped one‐dimensional cardiac fiber was used to examine responses of reentrant propagation to premature stimuli applied under different degrees of head‐tail interaction. Two different types (type I and type II) of termination window (TW) were identified. The type I TW was generated by functional inhomogeneity created by reentrant propagation. The width of the type I TW was proportional to the degree of cellular uncoupling. In contrast, uniform reduction in sodium channel conductance decreased the width of type I TW. The type II TW was generated by electrical alternans created by the head‐tail interaction of the reentrant action potential. It was demonstrated that electrical alternans were most significant in medium degree head‐tail interaction. For stronger or weaker head‐tail interaction, the electrical alternans tended to decrease. The type II TW was located in excitable gups following reentrant action potentials of short duration. Its size was proportional to the degree of electrical alternans. The type II TW was usually much larger than the type I TW. A premature conditioning stimulus induced alternans and created a type II TW. This response implies that a conditioning stimulus could facilitate greatly the termination of clinical reentrant arrhythmias by programmed electrical stimulation.
Afterdepolarizations and Triggered Activity Develop in a Select Population of Cells (M Cells) in Canine Ventricular Myocardium: The Effects of Acetylstrophanthidin and Bay K 8644
Authors: SICOURI SERGE , ANTZELEVITCH CHARLES
Published: July 2006

Early afterdepolarizations (EADs) are membrane oscillations that interrupt or retard the repolarization phase of the cardiac action potential, whereas delayed afterdepolarizations (DADs) are oscillations that arise after full repolarization. When EADs and DADs are sufficiently large to depolarize the cell membrane to its voltage threshold, they give rise to triggered action potentials, which are believed to underlie some forms of extrasystolic activity and tachyarrhythmias. EAD‐ and DAD‐induced triggered activity have been described and well characterized in isolated Purkinje fibers exposed to a wide variety of drugs, but are rarely seen in syncytial preparations of ventricular myocardium. These results are inconsistent with those of in vivo studies or experiments involving enzymatically dissociated myocytes. In the present study, we used the cardiotonic agent acetylstrophanthidin (AcS) and the calcium channel agonist Bay K 8644 to provide evidence in support of the hypothesis that induction of prominent EADs, DADs, and triggered activity occurs in a select population of cells in ventricular myocardium. The data indicate that EADs, DADs, and triggered activity produced by digitalis and Bay K 8644 are limited to or more readily induced in the deep subepicardial cell layers of the canine ventricle (M cells). Afterdepolarization‐induced triggered activity was never observed in the epicardial or endocardial layers.
Atrial Membranes Contain Nucleoside Diphosphate Kinase (NDPK) Activity: Its Role in Regulation of Muscarinic K+ Channels
Authors: HEIDBÜCHEL HEIN , VEREECKE JOHAN , CARMELIET EDWARD
Published: July 2006

Guinea pig or rabbit atrial muscarinic K+ channels in cell‐free inside‐out patches ran be activated in the absence of extracellular agonist and cytoplasmic G nucleotides by intracellular ATP‐Mg2+,1,2 This ATP‐dependent activation is compatible with the existence of a membrane‐bound nudeos de diphosphate kinase (NDPK), which directly phosphorylates GK‐bound GDP. We show that this ATP‐dependent activation is also possible in frog atria] cells, and that atrail membranes of frog and guinea pig contain NDPK activity. The relative order of different nucleoside triphogphates (NTPs) as phosphate donors parallels the observed efficiency of these nucleotides in activation of the channels. Thus, atrial membranes contain NDPK activity, which can be responsible for the ATP‐dependent activation o/muscarinic K+ channels, seen in patches of atrial cells. Under physiological conditions, NDPK can act as a GTP supply in the immediate vicinity of the G protein to ensure reliable signal transduction.
Proarrhythmic and Antiarrhythmic Effects of Flecainide on Nonsustained Reentry Around the Canine Atrial Tricuspid Ring In Vitro
Authors: FRAME LAWRENCE H. , RHEE EDWARD K. , FEI HAILING , LUCHETTI WAYNE
Published: July 2006

The effect of flecainide, 0.3 mg/L and 1.0 mg/L, on inducible nonsustained reentry was studied, in vitro, in the canine tricuspid ring. Nonsustained reentry was engineered by cutting the ring and reconnecting it with an adjustabJe electronic delay. Delays were used that produced reentry lasting 1–3 beats (group A), 4–10 beats (group B), and 11–25 beats (group C). Reentry was initiated multiple times at each selected delay. A proarrhythmic effect, defined as a significant increase in the duration of reentry, was observed in all 14 trials at the low dose and in two of 15 trials at the high dose in seven experiments. In four more trials a transient proarrhythmic response was seen initially during exposure to the high dose. In five of seven experiments, reentry became sustained after at least one dose of flecainide. Proarrhythmic responses resulted when flecainide increased the tachycardia cycle length more than the effective refractory period and there was less cycle length oscillation after initiation. Antiarrhythmic responses resulted either from a marked increase in effective refractory period at the site of block or production affixed block.
Comparison of Two Antitachycardia Pacing Modes in Supraventricular Tachycardia
Authors: JUNG WERNER , MLETZKO RALPH , MANZ MATTHIAS , LÜDERITZ BERNDT
Published: July 2006

The comparative efficacy of two different antitachycardia pacing techniques was evaluated in 22 consecutive patients who received the pacemaker Intertach® with an atrial electrode for drug refractory, recurrent Supraventricular tachycardia (SVT). The Intertach® has two consecutive programmable primary and secondary termination modes. The termination programs investigated were adaptive autodecremental burst pacing and adaptive decremental scanning. Atrioventricular nodal reentrant tachycardia was present in 15 patients and atrioventricular reentrant tachycardia due to Wolff‐Parkinson‐White syndrome in seven patients. The prospective comparison was arranged in a randomized, cross‐over study over a period of 12 months. To assess long‐term efficacy, diagnostic data of the pacemakers were obtained in intervals of 3 months. In addition, noninvasive programmed stimulation was performed to compare the incidence of pacing‐induced atrial fibrillation with both termination programs. During a follow‐up of 12 months the overall success rate of autodecremental burst pacing and decremental scanning was 80% and 95%, respectively. Decremental scanning was more effective in 12 patients and less successful in two patients than autodecremental burst pacing. During noninvasive electrophysiological studies, pacing induced atrial fibrillation could be documented in three often patients (30%) using autodecremental burst pacing, compared to one often patients (10%) using decremental scanning. These data suggest that decremental scanning proved to be more successful in the long‐term management of patients with recurrent S VT than autodecremental burst pacing. Furthermore, the occurrence of pacing‐induced atrial fibrillation could be documented more frequently with autodecremental burst pacing compared to decremental scanning.
Active Fixation Leads—Long‐Term Threshold Reduction Using a Drug‐Infused Ceramic Collar
Authors: ANDERSON NEIL , MATHIVANAR RANJINI , SKALSKY MICHAEL , TUNSTELL ALISON , NG MICHAEL , HARMAN DEIRDRE
Published: July 2006

Previous investigators, including our group, have reported the threshold reduction benefits of Steroid‐releasing leads. To date, all published literature has been for the passive fixation versions. The application of steroids should also enhance the performance of active fixation leads. We have developed and tested an atrial and a ventricular Accufix lead with a dexamethasone acetate‐releasing, porous ceramic collar (DA DEC], A long‐term sheep study has shown a significant reduction in threholds (THR) when compared to standard Accufix leads without the collar (ACC) for atrial (ATR) and ventricular (VENT) versions (bipolar THR (0.5 msec) at 24 weeks: VENT DA DEC = 0.51 ± 0.07, VENT ACC = 1.49 ± 1.03; ATR DA DEC = 1.31 ± 1.14, ATR ACC = 2.99 ± 1.31). All other parameters tested, including pacing and sensing impedance as well as polarization overpntential, were similar for the two groups. The Accufix DEC leads therefore have excellent potential for low energy stimulation.
Determinants of Pace‐Terminable Ventricular Tachycardia: Implications for Implantable Antitachycardia Devices
Authors: IP JOHN H. , WINTERS STEPHEN L. , SCHWEITZER PAUL , LOTVIN ALAN , TEPPER DAVID , GOMES ANTHONY J.
Published: July 2006

The next generation of implantable antitachycardia devices incorporate anti‐tachycardia pacing for the treatment of ventricular tachycardia. To evaluate the potential determinants of pace terminability, we analyzed 62 episodes of induced monomorphic ventricular tachycardia. We found that the tachycardia cycle length and cycle length variability are the major determinants of pace terminability. These findings should be considered in the designing of ventricular tachycardia detection and termination algorithms.
Intrinsic Conduction Maximizes Cardiopulmonary Performance in Patients with Dual Chamber Pacemakers
Authors: HARPER GLENN R. , PINA ILEANA L. , KUTALEK STEVEN P.
Published: July 2006

Dual chamber pacemaker programmability allows the possibility of atriallytracked ventricular pacing in patients who would otherwise have intrinsic atrioventricular (AV) conduction. Thirteen patients with permanent AV sequential pacemakers (ages 50–79) were evaluated with paired exercise tests to determine the Cardiopulmonary effects of pacemaker induced right ventricular activation compared with normal AV and intraventricular conduction. Peak oxygen uptake (VO2), oxygen pulse (O2P), respiratory rate (RR), and respiratory exchange ratio (RER) were determined using breath by‐breath analysis of expired gases. Patients exercised to fatigue and exercise tests were performed in random sequence. For patients with intrinsic AV conduction (group I, n = 8) the AV delay was programmed to preserve intrinsic conduction during one study; the alternate test used AV delay programming to produce ventricular pacing. Five patients with chronic AV block (group II) acted as a control for the effects of a rate adaptive AV delay compared to a fixed AV delay. Paired t‐testing showed a significantly lower peak VO2 (P < 0.015) and O2P (P < 0.01) in patients with atrially‐tracked ventricular pacing compared to intrinsic conduction. In contrast, group II showed a significant improvement in peak VO2 with rate adaptive AV delay compared to fixed AV delay programming (P < 0.05). In conclusion, intrinsic conduction should be preserved in patients with dual chamber pacemakers whenever possible.
Long‐Term Pacing in Heart Transplant Recipients is Usually Unnecessary
Authors: SCOTT CHRISTOPHER D. , OMAR IRFAN , MCCOMB JANET M. , DARK JOHN H. , BEXTON RODNEY S.
Published: July 2006

The indications for and timing of permanent pacing were reviewed in all 17 of 154 adult heart transplant recipients at this center who have had permanent pacemakers implanted. Resting 12‐lead ECGs recorded during routine follow‐up were examined. A prospective study of pacing requirement was then undertaken. Holter monitoring was performed before and after reprogramming the pacemakers to VVI mode at 50 beats/min. Exercise responses in various pacing modes were then assessed in seven patients with rate responsive pacemakers using a standard Bruce protocol treadmill test. The indication for pacing was sinus node dysfunction in 59% (10/17) and atrioventricular (AV) block in 41% (7/17). The majority of pacemakers were implanted between seven and 21 days after transplantation. There was a progressive reduction in the frequency of pacing on 12‐Jead ECGs with time after transplantation. Eight of 14 patients with empirically selected programming paced during Holter monitoring. After reprogramming to 50 beats/ min VVI mode only three of 14 patients, all with sinus node dysfunction, paced. Rate responsive pacing made no difference to exercise time. The requirement for long‐term pacing in cardiac transplant recipients is small (3/154) and is limited lo patients with sinus node dysfunction. Rate responsive pacing did not increase exercise tolerance.
A New Algorithm for Minimizing Pacemaker Polarization Artifact: Universally Applicable in Permanent Pacing Systems
Authors: CURTIS ANNE B. , VANCE FRED , QUIST STEPHEN M. , DOMIJAN ALEXANDER , KEIM STEPHEN G. , DURAN AURELIO , MILLER KIM
Published: July 2006

Polarization artifacts that result from pacing may interfere with analysis of paced evoked responses during, e.g., automatic threshold tracking. We have developed a method for reduction of such artifacts that relies on the introduction of pacing stimuli during the refractory period of unipolar or bipolar paced captured beats after previous identification of a refractory period “template” or baseline. The refractory pacing stimuli cannot capture the heart, and thus any deviation from the template is due to polarization artifact alone. The artifact amplitude is measured and the precharge duration of the triphasic stimulus waveform is changed each time until artifact is minimized, as detected by repeated reversals in the polarily of the polarization artifact. In a series of 11 patients with unipolar and bipolar permanent pacing leads, mean initial artifact before balancing was 1.44 ± 0.84 mV, which was reduced to 0.44 ± 0.30 mV after balancing (P = 0.001). Initial precharge duration was 3.2 msec by design; mean final precharge duration was 3.30 ± 0,34 msec. This algorithm is universally applicable in permanent pacing systems, as it is valid in unipolar and bipolar pacing and it does not require an intrinsic cardiac rhythm.
Impact of Filtering Upon Ventricular Tachycardia Identification by Correlation Waveform Analysis
Authors: JENKINS JANICE M. , DICARLO LORENZO A. , CHIANG CHIH‐MING J.
Published: July 2006

Signal analysis of digitized waveforms has been postulated as a method for improving sensitivity and specificity of ventricular tachycardia (VTJ detection in implantable antitachycardia devices. Such improvement may alleviate the problem of unwarranted delivery of therapy by adding precision to the identification of the pathological VT. Morphological analysis could also allow distinct therapies to be initialized for multiple VTs in the same patient. Correlation waveform analysis (CWA) has been demon‐struted to be effective in separating benign rhythms from VT in wideband recordings (1–500 Hz) but the effect of filtering has not been previously examined. Bipolar (1 cm) intraventricular recordings (1–500 Hz) of sinus rhythm (SR) and 25 distinct VTs in 18 patients were analyzed by CWA using a signal‐averaged SR template. Passages contained 65.9 ± 19.8 VT depolarizations (range 45–108). Digital filtering was performed on all data passages with varying passbands. Results for passages with a bandwidth of 1–250 Hz were equivalent to wideband results, i.e., ≥92% paired sets of SR and VT were separable at a 95% confidence level. A bandwidth of 1–100 Hz decreased discrimination to 84%. At a bandwidth of 1–80 Hz, 80% of cases were successfully separated, but at 10–80 Hz these results improved to 88%. Bandwidths of 20–80 and 30–80 Hz reduced reliability of CWA performance to 72% and 60%, respectively. Filtering at typical pace‐maker/defibrillator passbands produced morphological analysis results equivalent to those yielded at wideband settings. Differences in the range between SR versus VT decreased in filtered recordings but overall detection of VT was not degraded.
Early Clinical Experience with a Minute Ventilation Sensor DDDR Pacemaker
Authors: VANERIO GABRIEL , PATEL SHAILESH , CHING ELIZABETH , TROHMAN RICHARD G. , WILKOFF BRUCE L. , CASTLE LON W. , MALONEY JAMES D. , SIMMONS TONY W.
Published: July 2006

The new DDDR pacemaker META DDDR utilizes a minute veritilation sensor based on transthoracic impedance measurements. The sensor determines the metabolic indicated interval, the atrioventricular (AV) delay and the postventricular atrial refractory period (PVARP). The baseline PVARP must be carefully selected to define nonphysiological tachycardias. If a Pwave falls within the PVARP the pacemaker will automatically switch to the VVIR mode. This behavior prevents tracking of paroxysmal atrial tachyarrhythmias (PAT). Twenty‐eight patients with sinus node dysfunction (n = 20), AV junction ablation (n = 5), complete or intermittent AV block (n = 3); who received a META DDDR pacemaker were studied. The mean age was 65 ± 13 years. Results: mode switching (reversion) to VVIR was observed in 57% of the patients. Forty‐two percent had episodes of mode switching to VVIR during a stress test four related to PAT, and seven to sinus tachycardia. Fifty percent had episodes of mode switching to VVIR during a 24‐hour Holter, four related to PAT, three to retrograde P wave sensing, and two to sinus tachycardia. At the last follow‐up, 20 of the 26 patients initially programmed to the DDDR mode remained in the DDDR mode, while five were reprogrammed to the DDD and one to the VVIR mode. Mode switching has a high sensitivity but a low specificity for PAT. It appears to be a useful approach to prevent rapid tracking of atrial tachyarrhythmias. Careful PVARP programming is critical to appropriate reversion behavior, but further modifications of the algorithm are needed to improve its performance.
Sensor for Right Ventricular Volumes Using the Trailing Edge Voltage of a Pulse Generator Output
Authors: CHIRIFE RAUL
Published: July 2006

Cardiac and thoracic volume (Vol) signals are useful for diagnosis and adaptive rate, pacing. Present systems need an AC or pulsed constant current carrier to measure conductivity (proportional to Vol), causing high battery drain and requiring complex detection algorithms or special leads. The aim of this study was to propose a new and simple sensor for cardiac volumes using standard pacing leads and no AC carrier signal. “Constant voltage” pulse generators (PG) deliver a square pulse to the lead via a capacitor (Cap). The signal resulting from the interaction between the PG and the tissues and blood is trapezoidal, with a leading edge voltage determined by PG output and a trailing edge voltage (TEV) dependent on electrode surface and Cap value (device constants), and patient load. The hypothesis that right ventricular (RV) and chest Vol variations could produce load‐related TEV changes was tested. Four PGs were connected to bipolar (Bip) leads within containers with 5–80 cc of saline, and TEV was measured with every 5 cc Vol change. Fifteen patients with previously implanted Bip PGs were studied during VOO pacing, scanning the intrinsic cardiac cycle. TEV was noninvasively measured as a function of time from onset of QRS. Results: (1) There was a nonlinear relationship between Vol and TEV, best expressed by exponential, power, or hyperbolic equations; (2) Cardiac cycle scanning revealed smaller TEV at end‐systole than at end‐diastole (mean difference = 88 mV [P < 0.001]); (3) Reconstruction of RV Vol curve by scanning‐rendered waveforms very similar to those obtained by the conventional impedance technique, end‐diastolic Vol, end‐systolic Vol, stroke Vol. and ejection fraction could thus be derived. Conclusion: TEV sensor provides a simple, reliable signal for hemodynamic diagnosis and for adaptive rate pacing in implantable devices, using conventional bipolar leads.
Pacing Threshold Spikes Months and Years After Implant
Authors: SHEPARD RICHARD B. , KIM JOHN , COLVIN EDWARD C. , SLABAUGH JANE , EPSTEIN ANDREW E. , BARGERON LIONEL M.
Published: July 2006

To determine patterns of variation in chronic pacing thresholds, we made 4,942 threshold measurements in 257 patients with 312 leads, at times from implant to 295 months (median 17 months) including 1,053 determinations in 46 children < 12 years old. Motivation was late sudden death in two single‐ventricle pacemaker‐dependent children with multiple possible death causes. At stimulus duration 0.5 ± 0.04 msec, mean of the thresholds, measured 1 month or more after implant, was 1.3 ± 0.66 volts (V) for endocardial electrodes and 2.8 ± 1.39 V for epicardially applied electrodes. Highest mean thresholds were in the 6 to 12‐year‐old age group. In 34 leads studied at implant, again within a month and for at least three years thereafter, time of maximum threshold occurred after one month in 59%, independent of lead type or patient age. Of 107 leads with five or more measurements after 3 months use, gradual increase in threshold continued after 3 months in 24%. An additional 21% had at least one threshold that exceeded the post‐three‐months individual patient lead mean by three standard deviations. Most striking was the occurrence of transient several‐volt increases and decreases in threshold as late as 8 years after lead implantation in at least three children. These temporary changes were detected initially transtelephonically by the vario method of threshold measurement. They occurred during minor illnesses such as summer colds, yet similar illnesses also occurred without threshold elevation. We suggest further study of pacing threshold variations in highly pacemaker‐dependent children whose cardiac anatomy makes use of epicardial electrodes necessary.
Clinical Efficacy of Low Energy Cardioversion in Automatic Implantable Cardioverter Defibrillator Patients
Authors: MCVEIGH KEVIN , MOWER MORTON M. , NISAM SEAH , VOSHAGE LYNNETT
Published: July 2006

The inclusion of low energy Cardioversion capability into modern implantable antiarrhythmic devices, although an appeahing idea, is nevertheless unproven with regard to its potential benefits. Moreover, since occasional reports have surfaced suggesting that ineffective application of low energy shocks may prejudice subsequent arrhythmia reversion, we examined the effectiveness and risks of this feature in a large series of patients performed as part of a US Food and Drug Administration clinical trial performed under an invesfigational device exemption. A total of 813 induced monomorphic ventricular tachycardias were studied in 244 patients. We found that many of the arrhythmias could be reverted to sinus rhythm with small amounts of energy. Cardioversion energy was ≤6 joules (J) for 84 (53.2%) and ≤14 joules in 105 (66.4%) of the 158 patients tested at implant and subsequently remained unchanged through ≥ 4 months follow up. The incidence of noncardioversion, acceleration or holh occurred in 12.7%, 5.7%, and 13.1%, respectively on a per patient basis. On a per episode basis, noncon‐version occurred in 51 (6.3%) and acceleration in 61 (7.5%) of the 813 inductions. There was no correlation between the occurrence of nonconversions and accelerations. The devices were allowed to recycle in the event the arrhythmia was not reverted. The subsequent shock was almost always effective, and in any event, no patient failed to be reverted by the second 30‐J rescue shock. Over the entire follow‐up period as long as 17 months, there were 17 deaths. Neither the incidence nor the mode of death was correlated with nonconversion or acceleration. We conclude that low energy Cardioversion is effective in treating monomorphic ventricular tachycardia and if unsuccessful, does not prejudice the success of subsequent higher energy therapy.
Improved Patient Surveillance and Data Acquisition with a Third Generation Implantable Cardioverter Defibrillator
Authors: LUCERI RICHARD M. , PUCHFERRAN RICHARD L. , BROWNSTEIN SHELDON L. , HABAL SALEM M. , DAVID IRVING B. , VARDEMAN LINDA L.
Published: July 2006

Thirteen patients were implanted with the Telectronics 4210 ATP implantable cardioverter defibrillator (ICD) for ventricular tachycardia or ventricular fibrillation. This device has multiprogrammable anfilachycardia pacing, bradycardia pacing, and shock therapies. In addition, there is extensive data Jogging and EGG snapshot capability for arrhythmia confirmation and response to therapy. These features permit easy retrieval of all detected and treated events, whatever the eventual outcome. In this study, the data logged at predischarge eleclrophysiological testing was compared to the data recorded in a standard manner. The bulk of the data, however, was derived from long‐term follow‐up of spontaneous events over a mean period of 203 days (range 154–257). During this period, a total of 6,193 arrhythmia detections were made: 20 were classified as ventricular fibrillation, and 6,173 as ventricular tachycardia. The vast majority of these (93%) terminated spontaneously without ICD intervention (5.738), underscoring the benefit of a standard second confirmation prior to therapy delivery (noncommitted system). There were 394 arrhythmia episodes treated with antitachycardia pacing; of these a total of 8.3% accelerated to either more rapid ventricular tachycardia or ventricular fibrillation (4.3% and 4.0%, respectively). Events were reported in an “episode log” format, listing all arrhythmia detections with time/date annotation; or in a “sense history” format, detailing each episode from start to conclusion. These data demonstrate that this advanced, “tiered” ICD with data recall contributes to better patient management, and permits a more tailored termination prescription for the individual patient.
Electroporation of Cardiac Cell Membranes with Monophasic or Biphasic Rectangular Pulses
Authors: TOVAR OSCAR , TUNG LESLIE
Published: July 2006

During defibrillation, cardioversion, and electrocution trauma, heart cells are exposed to potential gradients that increase the transmembrane potential (Vm). At sufficiently high Vm, pathological increases in cell permeability can occur. With enzymatically isolated frog heart cells (n = 29) we investigated the voltage and time sufficient for electroporation or cardiac cell membranes with rectangular voltage pulses, particularly with 5‐msec monophasic, and 5‐ or 10‐msec biphasic pulses. The rectangular voltage pulse (monophasic 0.1–1.5 V, 0.1–100 msec or symmetric biphasic 0.1–1 V, 0.4–10 msec [total duration]) was applied to the cell membrane using the cell‐attached patch clamp technique, and a low voltage pulse train was added so that membrane conductance could be monitored continuously. Step increases in membrane conductance (breakdown) were observed, indicative of electroporation, and occurred with different combinations of pulse amplitude and duration; for example, for monophasic square pulses: (1 V, 0.2 msec) or (0.5 V, 0.5 msec), and for biphasic pulses: (1 V, 0.4 msec total duration) or (0.5 V, 0.8 msec). Using 5‐ or 10‐msec rectangular pulses, breakdown occurred at a voltage around 0.4 V independent of polarity or waveform. The recovery of the permeabilized cell membrane after the voltage pulse was highly variable, in some cases not recovering at all while in other cases recovering after a lapse of seconds to minutes. These results suggest that monophasic and biphasic pulses of ∼1 V, 0.2–0.4 msec and ∼0.4 V, 5 msec can permeabilize the heart cell membrane even for minutes, time enough to cause an alteration in the cellular ionic composition leading to depressed or unexcitable tissue, a precursor for cardiac arrhythmia.
Long‐Term Follow‐Up of Patients with Nonischemic Dilated Cardiomyopathy and Ventricular Tachyarrhythmias Treated with Implantable Cardioverter Defibrillators
Authors: FAZIO GREGORY , VELTRI ENRICO P. , TOMASELLI GORDON , LEWIS RICHARD , GRIFFITH LAWRENCE S.C. , GUARNIERI THOMAS
Published: July 2006

We analyzed our 10‐year cumulative experience of 40 consecutive patients with idiopathic dilated Cardiomyopathy and associated ventricular tachyarrhythmias, treated with implantable Cardioverter defibrillators. Dilated Cardiomyopathy was defined as left ventricular ejection fraction (EF) ≤50% with no defineable etiology. Patient characteristics included: 24 male, mean age 52 years, mean EF = 33%, New York Heart Association Class I–III, presenting syndrome—cardiac arrest (n = 28), syncope/near syncope (n = 12). At 2.5 years mean follow‐up, there were 16 deaths: one operative, three sudden, two incessant ventricular tachycardia/ventricular fibrillation (VT/VF), six heart failure, and four noncardiac. The actuarial mortality at 1 and 4 years was 0% and 14% for sudden death, 11% and 34% for cardiac death. The projected mortality was 52% and 78% for same time intervals (P < 0.01). No useful baseline variable predicted who would or would not receive an ICD shock in follow‐up. ICD therapy appears effective in reducing sudden death mortality in this high risk population.
Accuracy of Rhythm Classification Using a Data Log System in Implantable Cardioverter Defibrillators
Authors: WANG PAUL J. , MANDALAKAS NICHOLAS , CLYNE CHRISTOPHER , BUTTS LAURIE , COLBURN CAROL , RASTEGAR HASSAN , ESTES N.A. MARK
Published: July 2006

Because the presence or absence of symptoms alone may be insufficient to correctly diagnose the rhythm for which implantable Cardioverter defibrillator therapy is delivered, we hypothesized that the addition of data Jog information available in Telectronics ATP 4210 may improve the accuracy of rhythm classification. With this system the recorded ventricular electrogram cycle length is reported on a beat‐to‐beat basis immediately before, during, and after the tachyarrhythmia is detected. Using this information recorded from the data log in 32 separate tachyarrhythmia episodes in 20 patients, we compared the sensitivity, specificity, and predictive accuracy of rhythm classification on the basis of symptoms alone, data Jog alone, and data Jog combined with symptoms. While classification based on symptoms alone is highly specific (10/10 episodes), it is insensitive and has an overall predictive accuracy of 53%. By contrast, data log is sensitive (90%) and specific (91%) with better predictive accuracy (94%) than symptoms alone (P = 0.002). The addition of symptoms to information on beat‐to‐beat cycle length from data log resulted in a slight increase in predictive accuracy.
Sustained Monomorphic Ventricular Tachycardia: A Single Electrocardiographic Expression of Different Patterns of Reentry
Authors: BRUGADA JOSEP , BOERSMA LUCAS , KIRCHHOF CHARLES , ZETELAKI ZOLTAN , ABDOLLAH HOSHIAR , KONINGS KAREN , ALLESSIE MAURITS
Published: July 2006

Sustained monomorphic ventricular tachycardia (SMVT) can be the electrocardiographic expression of a reentrant impulse in the ventricles. In this study we analyzed the different types of reentry that might lead to SMVT, Methods: The pattern of activation of 73 episodes of SMVT induced in thin sheets of epicardium in 50 Langendorff perfused rabbit hearts were visualized with high resolution epicardial mapping (248 points). Results: Five different patterns of reentry resulting in SMVT were identified: (1) Single‐loop reentry around a fixed obstacle (n = 40); (2) Single‐loop reentry around a functional arc of conduction block (n = 17); (3) Double‐wave reentry around a fixed obstacle (n = 9); (4) Figure‐of‐eight reentry around two areas of functional block (n = 5); and (5) Multiple synchronized circuits around multiple areas of functional block (n = 2), Conclusion: SMVT is a single electrocardiographic expression of different patterns of reentry. Accurate mopping is mandatory to identify the reentrant pathway and the pathophysiological substrate of the arrhythmia.
Histopathology of Monopolar Transcatheter Radiofrequency Ablation at the Mitral Valve Annulus
Authors: CHIN MICHAEL C. , SCHUENEMEYER TERRY , FINKEBEINER WALTER E. , STERN ROGER A. , SCHEINMAN MELVIN M. , LANGBERG JONATHAN J.
Published: July 2006

Although monopolar radiofrequency (RF) ecitheter ablation is being used to interrupt leftsided accessory pathways in patients with tachyarrhythrma, little is known of the histologic effects from this method of treatment. RF ablation at the mitral valve (MV) annulus was performed in ten dogs to examine the histology of the lesion area. A custom 6 French ablation catheter with a 4 mm distal electrode was positioned beneath the MV adjacent to the annulus. Mean preablation atrial to ventricular electrogram ratio (A/V ratio) was 0.26 ± 0.17. Thirty ± 1 watts of RF power were applied for 53 ± 13 seconds between the distal electrode and a large skin electrode. Nine dogs were sacrificed 6 weeks and one dog 2 days following ablation. Annular lesions were seen in eight of the ten dogs. Lesion volume was 136 ± 41 mm3 and correlated with (he A/V ratio (r2= 0.74, P = 0.006). Lesions consisted of necrosis of the left ventricle with extension into the atrioventricular groove and left atrium. No injury to the coronary sinus or circumflex artery was observed. A small area of injury was noticed on the mitral leaflet in one dog. Monopolar RF ablation creates lesions at the MV annulus without injury to adjacent vascular structures.
Differential Response of QTU Interval to Exercise, Isoproterenol, and Atrial Pacing in Patients with Congenital Long QT Syndrome
Authors: SHIMIZU WATARU , OHE TOHRU , KURITA TAKASHI , SHIMOMURA KATSURO
Published: July 2006

Sympathetic stimulation is well known to contribute to the genesis of QTU prolongation and ventricular lachyarrhythmias in patients with congenital long QT syndrome. In this study, we performed exercise treadmill testing, isoproterenol infusion (1–2 μg/min), and right atrial pacing (cycle length 500 msec) in 11 patients with congenital long QT (LQT) syndrome (LQT group) and in 12 age‐ and sex‐matched controls (control group). The responses of the corrected QT (QTc; Bazett's method) interval and the TU wave complex tvere evaluated. The QTc interval was prolonged from 482 ± 63 msec1/2 to 548 ± 28 msec1/2 by exercise in the LQT group (n = 11; P < 0.005), and this was associated with fusion of the T waves with enlarged U waves, whereas the QTc interval did not increase with exercise in the control group (n = 12; 402 ± 19 msec1/2 vs 409 ± 22 msec1/2). The QTc interval was also prolonged from 466 ± 50 msec1/2 to 556 ± 33 msec1/2 by isoproterenol in the LQT group (n = 7; P < 0.005) in association with morphological changes of the TU wave complex like those seen with exercise, whereas it was only slightly increased from 399 ± 10 msec1/2 to 436 ± 13 msec1/2 by isoproterenol in the control group (n = 77; P < 0.001). However, the QTc interval did not increase with atrial pacing in the LQT group (n = 8; 476 ± 57 msec1/2 vs 486 ± 59 msec1/2), whereas it was slightly increased from 400 ± 21 msec1/2 to 426 ± 18 msec1/2 by atrial paring in (he control group (n = 8; P < 0.005). These results suggest that sympathetic stimulation plays an important role in the QTU prolongation and marked TU wave complex abnormalities in patients with congenital long QT syndrome.
Multifactorial Prediction of Arrhythmic Events after Myocardial Infarction. Combination of Heart Rate Variability and Left Ventricular Ejection Fraction with Other Variables
Authors: ODEMUYIWA OLUSOLA , MALIK MAREK , FARRELL TOM , BASHIR YAVER , STAUNTON ANNE , POLONIECKI JAN , CAMM A. JOHN
Published: July 2006

Autonomic dysfunction has recently been shown to identify postinfarction patients at a high risk of arrhythmic events. Therefore, the predictive characteristics of heart rate variability and the left ventricular election fraction in combination with other prognostic variables—mean heart rate, late potentials, and ventricular ectopic beat frequency > 10/hour(VE10)—were examined in 417 postinfarction patients. The heart rate variability index was the most important factor for the stratification of patients at high risk of arrhythmic events after myocardial infarction and optimum stratification was based on the combination of the heart rate variability index with late potentials or with frequent ventricular ectopic beats.
Which Factors Determine the Development of Late Potentials After First Myocardial Infarction? A Multifactorial Analysis
Authors: MCCLEMENTS BRIAN , ADGEY A. A. JENNIFER , MACKENZIE GILBERT
Published: July 2006

A multifactorial analysis was performed to study the factors that contributed to the occurrence of late potentials on the signal‐averaged electrocardiogram in 106 consecutive patients with a first myocardial infarction. Ninety‐three (88%) patients received intravenous thrombolytic therapy within 6 hours of symptom onset. Thirty‐two (30%) patients had a late potential on the signal‐averaged electrocardiogram on day 6, including 17 of 31 (55%) in whom the infarct‐related artery was occluded and 15 of 75 (20%) in whom it was patent (P = 0.0004). Twenty‐three variables were analyzed by a multifactorial stepwise regression analysis. Predictors of a late potential were (1) an occluded infarct‐related coronary artery (t = ‐3.653, P = 0.0004) and (2) the extent of myocardial necrosis as indicated by the peak serum lactate dehydrogenase level (t = 3.094, P = 0.0025). The lower incidence of late potentials when the infarct‐related coronary artery was patent was independent of left ventricular election fraction and peak enzyme levels after infarction.