bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Ventricular Pacing in a Pacemaker Patient Undergoing Magnetic Resonance Imaging
Authors: FONTAINE JOHN M. , MOHAMED FEROZE B. , GOTTLIEB CHARLES , CALLANS DAVID J. , MARCHLINSKI FRANCIS E.
Published: July 2006

Magnetic resonance imaging (MRI) generates potent electromagnetic forces in the form of a static, gradient, or pulsed radiofrequency magnetic field that can result in pacemaker malfunction. This report documents a case of rapid cardiac pacing during MRI in a patient with a dual chamber pacemaker. Although the mechanism of rapid cardiac pacing is unclear, it was directly related to radiofrequency pulsing. We postulated that the lead acts as an antenna for radiofrequency energy that interacts with the pacemaker's output circuit, thus, causing cardiac pacing at a cycle length representing a multiple of the repetition time; or perhaps rapid pacing is related to induced currents generated between the MRI unit and the pacing lead.
ICD Trials: An Extraordinary Means of Determining Patient Risk?
Authors: NISAM SEAH , MOWER MORTON
Published: July 2006

Extensive clinical experience with the implantable cardioverter defibrillator (ICD) combined with recently completed prospective, randomized trials like MADIT and AVID, have demonstrated the lifesaving efficacy of this therapy and its superiority compared to conventional medical management in treating patients at high risk of sudden arrhythmic death. This evidence has in turn spurred great interest in further ICD studies. Since the ability of the ICD to save lives is no longer in question, there is a need to reexamine the real objectives of these new studies.
Prospective Evaluation of New and Old Criteria to Discriminate Between Supraventricular and Ventricular Tachycardia in Implantable Defibrillators
Authors: BAROLD HELEN S. , NEWBY KEITH H. , TOMASSONI GERY , KEARNEY MARGARET , BRANDON JOAN , NATALE ANDREA
Published: July 2006

This study was designed to evaluate the ability to distinguish between supraventricular tachycardias (SVTs) and ventricular tachycardias (VTs) based on onset, stability, and width criteria in an implantable defibrillator. Inappropriate detection of atrial fibrillation and sinus tachycardia is a common problem in patients with implantable defibrillators. The onset, stability, and width criteria were studied in 17 patients who underwent implantation of a Medtronic 7218C implantable defibrillator by inducing sinus tachycardia and atrial fibrillation. Additional data on the width criteria was obtained by pacing at separate sites in both the left and right ventricle. Patients were studied at different times for up to 6 months to determine any changes in the criteria. The onset and stability criteria caused inappropriate detections in 36% and 12% of the episodes, respectively. The addition of the width criteria decreased the inappropriate detection using the onset and stability criteria to 5% and 2%, respectively. Pacing from the RV apex, RV outflow tract, and LV apex was appropriately detected as wide in 76%, 41%, and 94%, respectively. The width criteria changed over time in individual patients, but was stable by 6 months in all but one patient. No single criterion is satisfactory for distinguishing between SVT and VT in this patient population, but the combination of criteria seems to provide better discrimination. The width criteria can change dramatically over time and needs to be monitored carefully. Newer algorithms will need to be developed to allow better detection of supraventricular tachycardias.
Pacing Impedance Variability in Tined Steroid Eluting Leads
Authors: DANILOVIC DEJAN , OHM OLE‐JØRGEN
Published: July 2006

The aim of the study was to investigate pacing impedance (PI) behavior in ambulatory patients. Eighteen atrial and 18 ventricular tined steroid eluting leads with 1.2‐mm2 and 5.6‐mm2 electrodes were implanted in 20 patients. At 9–27 months after implantation PI was measured automatically by means of additional algorithms downloaded via telemetry links into implanted Thera® pulse generators. PI was determined based on the voltage drop on the output capacitor during the 5 V‐1 ms pacing impulse, at the programmable sampling rates from 1 second to 30 minutes. The study examined in particular: (1) PI trends and variations associated with different breathing patterns, body postures, provocative maneuvers, bike exercise, and during 24 hours; (2) impact of pacing rate and AV‐delay on PI; (3) correlation between PI variability and pacing threshold, lead configuration, absolute PI value, age, gender, disease, and cardiac chamber. The most important findings were: (1) large PI variations of up to 450 Ω were observed in properly functioning leads, (2) PI variability exhibited a weak negative correlation with pacing thresholds as if electrode positional stability was not a major factor underlying PI variations, (3) unipolar and bipolar PI variations were equivalent to each other (correlation factor = 0.93) implying that PI was mostly dependent on the circumstances around the lead tip.
Prospective Comparison of Temperature Guided Microwave and Radiofrequency Catheter Ablation in the Swine Heart
Authors: JUMRUSSIRIKUL PITAYADET , CHEN JUNG‐TA , JENKINS MARK , HUI RICHARD , TAYLOR KEVIN , WANG PAUL J. , HUTCHINS GROVER M. , CALKINS HUGH
Published: July 2006

Microwave energy has been proposed as an alternative to radiofrequency energy for use during catheter ablation procedures. The purpose of this study was to prospectively compare, in an animal model, the lesion size associated with temperature guided catheter ablation using either microwave or radiofrequency energy. Eleven swine underwent catheter ablation with either radiofrequency (N = 4) or microwave energy (N = 7). In each animal catheter ablation was performed at 7–15 sites. At each site energy was delivered for 60 seconds using closed loop feedback temperature control to achieve a target temperature of 70°C. Cardiac catheterization was performed before and after ablation. Animals were sacrificed approximately one month following the ablation procedure. Analysis of lesion size demonstrated that overall lesions created using radiofrequency energy were larger than those created using microwave energy. In the ventricle, lesions created using microwave energy were longer, but had a similar width and depth as those created using radiofrequency energy. An important relation was observed between tbe depth of lesions created using microwave energy and catheter stability, as evidenced by the temperature profile. Overall, lesions created using microwave energy are smaller than those created using radiofrequency energy. Catheter stability has an important impact on lesion size.
Noise Detection During Bradycardia Pacing with a Hybrid Nonthoracotomy Implantable Cardioverter Defibrillator System: Incidence and Clinical Significance
Authors: ROSENTHAL MARK E. , PASKMAN CHARLOTTE
Published: July 2006

The purpose of this study was to prospectively evaluate the incidence of noise detection during bradycardia pacing by an FDA approved hybrid nonthoracotomy ICD system. An illustrative case report which prompted this investigation is provided. Backup bradycardia pacing by tiered therapy cardioverter defibrillators has been useful in preventing postshock bradycardia and occasionally for chronic rate support in bradycardic patients. Unexplained “noise” detected by real‐time telemetry has been previously described during bradycardia pacing by a device utilizing automatic gain control for sensing. Eighteen patients were prospectively evaluated for noise detection during ventricular pacing by the ICD. Real‐time telemetry was analyzed with each patient: (1) supine, (2) supine with deep inspiration/expiration, (3) supine during Valsalva, and (4) during a change in position from supine to sitting. Analysis of pacing threshold and lead impedance was made in each patient. Eleven of 18 patients bad noise detected on real‐time telemetry during bradycardia pacing. In 10 patients this was noted during deep inspiration/expiration, in 2 during Valsalva maneuver, and in 5 with position change. There was no evidence in any patient of lead malfunction nor any difference in pacing threshold or lead impedance between patients with noise detected versus those without it. Noise detection by an approved hybrid ICD system is common and may be due to the automatic gain control which maximizes sensitivity during bradycardia pacing. This may lead to clinically significant events, with both suppression of bradycardia pacing and triggering of tachycardia therapy in the absence of ventricular tachyarrhythmias in pacemaker‐dependent patients.
Prediction of Maintenance of Sinus Rhythm after Cardioversion of Atrial Fibrillation by Analysis of Serial Signal‐Averaged P Waves
Authors: STAFFORD PETER J. , KAMALVAND KAVAN , TAN KIM , VINCENT RICHARD , SULKE NEIL
Published: July 2006

After cardioversion from atrial fibrillation (AF) many patients develop early recurrence of the arrhythmia. While these patients may be appropriate for immediate prophylaxis against AF recurrence their identification at the time of cardioversion is not possible. Since the signal‐averaged P wave (SAPW) is abnormal in individuals with atrial arrhythmia, we assessed its utility for predicting early AF recurrence after cardioversion. Seventy‐five cardioversions in 31 patients were evaluated. The mean age was 59 (range 28–79) years; 26 were male. Fifty‐eight cardioversions were internal using low energy biphasic DC shocks delivered via electrodes placed in the right atrial appendage and coronary sinus. P wave specific signal averaging was performed at 3 and 24 hours after each cardioversion to estimate filtered P wave duration and energy from 20, 40, and 60 to 150 Hz. Follow‐up was by regular clinic visits and transtelephonic ECG monitoring. Early recurrence of AF (prospectively defined as sinus rhythm duration < 1 week) occurred after 30 cardioversions. No differences were found in any P wave variable measured at 3 hours between these cardioversions and those that resulted in a longer duration of sinus rhythm. Paired 3‐ and 24‐hour signal‐averaged data were available in 47 cardioversions. There were significant falls in P wave energy from 3 to 24 hours after 31 cardioversions that resulted in sinus rhythm for > 1 week, (P40: 3 hours 11.2 [±1.5] μV2· s, 24 hours 8.6 [±1.2] μV2· s, P < 0.001), but not following the 16 after which AF returned within 1 week (P40: 3 hours 9.0 [±1.2] μV2· s, 24 hours 8.5 [±1.2] μV2· s, P = NS). A fall in P40 of > 25% had a positive predictive accuracy for maintenance of sinus rhythm of 87%; negative predictive accuracy was only 37%. Similar falls in P wave energy occurred after cardioversions that resulted in longer term (> 4 weeks) sinus rhythm, but not in those that did not. However, the predictive accuracy of a fall in P40 was less (positive predictive accuracy 38%, negative predictive accuracy 62%). Patients with relapsing permanent AF who remain in sinus rhythm for at least 1 week after cardioversion show a fall in P wave energy within the first 24 hours. However, in these patients the technique does not predict recurrent AF within 1 week nor sinus rhythm > 4 weeks. These observations suggest persistent disordered atrial activation as a mechanism for early recurrence of AF after cardioversion.
Influence of Polarity Reversal on de‐fibrillation Success with Biphasic Shocks and a Transvenous/Subcutaneous Defibrillator System in a Porcine Animal Model
Authors: STELLBRINK CHRISTOPH , SCHAUERTE PATRICK , LOESER HOLGER , ROSENBAUM CHRISTOPH , KUCKERTZ EDITH , VOGEL MARTINA , MESSMER BRUNO J. , HANRATH PETER , SCHOENDUBE FRIEDRICH A.
Published: July 2006

Clinical studies show that polarity reversal affects de‐fibrillation success in transvenous monophasic defibrillators. Current devices use biphasic shocks for de‐fibrillation. We investigated in a porcine animal model whether polarity reversal influences de‐fibrillation success with biphasic shocks. In nine anesthetized, ventilated pigs, the de‐fibrillation efficacy of biphasic shocks (14.3 ms and 10.8 ms pulse duration) with “initial polarity” (IP, distal electrode = cathode) and “reversed polarity” (RP, distal electrode = anode) delivered via a transvenous/subcutaneous lead system was compared. Voltage and current of each defibrillating pulse were recorded on an oscilloscope and impedance calculated as voltage divided by current. Cumulative de‐fibrillation success was significantly higher for RP than for IP for both pulse durations (55% vs 44%, P = 0.019) for 14.3 ms (57% vs 45%, P < 0.05) and insignificantly higher for 10.8 ms (52% vs 42%, P = n.s.). Impedance was significantly lower with RP at the trailing edge of pulse 1 (IP: 44 ± 8.4 vs RP: 37 ± 9.3 with 14.3 ms, P < 0.001 and IP: 44 ± 6.2 vs RP: 41 ± 7.6 Ω with 10.8 ms, P < 0.001) and the leading edge of pulse 2 (IP: 37 ± 5 vs RP: 35 ± 4.2 Ω with 14.3 ms, P = 0.05 and IP: 37.5 ± 3.7 vs RP: 36 ± 5 Ω with 10.8 ms, P = 0.02). In conclusion, in this animal model, internal de‐fibrillation using the distal coil as anode results in higher de‐fibrillation efficacy than using the distal coil as cathode. Calculated impedances show different courses throughout the shock pulses suggesting differences in current flow during the shock.
A Nonfluoroscopic Catheter‐Based Mapping Technique to Ablate Focal Ventricular Tachycardia
Authors: NADEMANEE KOONLAWEE , KOSAR EROL M.
Published: July 2006

The recent introduction of a nonfluoroscopic electroanatomical cardiac mapping system (CARTO) is an exciting development in catheter ablation treatment of cardiac arrhythmias. The system uses ultralow magnetic fields to locate a sensor positioned near the tip of a regular mapping and ablation catheter. The catheter location and electrograms are recorded and reconstructed in real‐time and presented as a three‐dimensional geometrical mapped color coded with the electrophysiological information. The CARTO represents an important tool to guide the ablation of patients who have focal tachycardia (e.g., right ventricular outflow tract [RVOT] tachycardia and idiopathic left ventricular [ILV] tachycardia). This study describes how the CARTO system is useful in mapping and ablating these arrhythmias. Two case illustrations, one patient with RVOT tachycardia and another with ILV tachycardia, are described in this article. The tachycardia was mapped and ablated using the new electromagnetic catheter technology creating an electroanatomical map of the arrhythmia focus for each tachycardia without fluoroscopy; both tachycardias were successfully ablated, terminated, and rendered noninducible. The CARTO system is useful in mapping and guiding the ablation of focal tachycardia and merits further study.
Treatment of Malignant Neurocardiogenic Vasovagal Syncope with a Rate Drop Algorithm in Dual Chamber Cardiac Pacing
Authors: ABE HARUHIKO , IWAMI YASUYO , NAGATOMO TOSHIHISA , MIURA YASUSHI , NAKASHIMA YASUHIDE
Published: July 2006

A 29‐year‐old man with malignant vasovagal syncope presented with episodes of abrupt loss of consciousness associated with an aura, totaling more than 10 episodes over 3 months. Holter monitoring showed cardiac arrest with a duration of 15 seconds. Oral propranolol and disopyramide therapy failed to prevent the syncope. A dual chamber pacemaker with a rate drop response algorithm successfully prevented the syncope but not the aura. There may be multifactors involved in the mechanism of this syndrome. The patient has returned to a normal active life. This rate drop algorithm is an effective therapy for the prevention of syncope in malignant vasovagal syncope.
QT Dependent T Wave Sensing
Authors: BÖHM ÁDÁM , PINTÉR ARNOLD , PRÉDA ISTVÁN
Published: July 2006

A case of QT duration dependent T wave oversensing mimicking QRS undersensing and pacemaker malfunction is presented. This example indicates that interpretation of pacemaker ECG may be difficult, even in case of WI pacemaker.
Effects of Postmyocardial Infarction Scar Size, Cardiac Function, and Severity of Coronary Artery Disease on QT Interval Dispersion as a Risk Factor for Complex Ventricular Arrhythmia
Authors: PULJEVIC DAVOR , SMALCELJ ANTON , DURAKOVIC ZIJAD , GOLDNER VLADIMIR
Published: July 2006

The aim of the study was to determine the relation between QT dispersion and ventricular arrhythmia after myocardial infarction, as well as the effects of postinfarction scar size, cardiac function, and severity of coronary artery disease on QT dispersion. Three hundred three patients, 3 months after myocardial infarction, and a group of 21 healthy subjects were evaluated. QT dispersion was the difference between maximal and minimal QT interval in 12‐ECG leads. Postinfarction scar size was determined by Selvester's QRS scoring system. Cardiac function was evaluated by echocardiography and exercise stress test, and the severity of coronary artery disease by the number and degree of coronary artery stenoses. QT dispersion increased significantly in relation to the severity of arrhythmia (< 50 premature ventricular complexes vs ventricular tachycardia; 61.6 [± 12.3] vs 84.8 [± 16.4] ms, P < 0. 001). QT dispersion > 80 ms was associated with ventricular tachycardia with the sensitivity of 68% and specificity of 88%. QT dispersion also increased significantly, dependent on the postinfarction scar size (0% vs ± 33% of left ventricular myocardium; 61.8 [± 16.4] vs 74.7 [± 16] ms, P < 0. 001), as well as in the case of significantly impaired cardiac function. Although QT dispersion increased with the number of diseased vessels and the degree of stenoses, the differences were not significant (P > 0. 05). In conclusion, QT dispersion is a risk marker of complex ventricular arrhythmia in the chronic stage of myocardial infarction. Multiple regression analysis indicates that only the postinfarction scar size has an independent effect on QT dispersion (R2= 0. 39, P < 0. 05).
Stent Dilation of Superior Vena Cava and Innominate Vein Obstructions Permits Transvenous Pacing Lead Implantation
Authors: ING FRANK F. , MULLINS CHARLES E. , GRIFKA RONALD G. , NIHILL MICHAEL R. , FENRICH ARNOLD L. , COLLINS ELIZABETH L. , FRIEDMAN RICHARD A.
Published: July 2006

The purpose of this study was to assess the feasibility of stent dilation of venous obstructions/occlusions to permit transvenous pacing lead implantation. Innominate vein or superior vena cava (SVC) obstruction may preclude the implantation of transvenous pacing leads. Patients with d‐transposition of the great arteries, after a Mustard or Senning procedure, and children with previously placed transvenous pacing leads are at higher risk for this vascular complication. From May 1993 to January 1996, eight pediatric patients who underwent transvenous pacing lead implantation or replacement were found to have significant innominate vein or SVC obstruction or occlusion. Utilizing in‐travascular stents, a combined interventional and electrophysiological approach was used to relieve the venous obstruction and to permit implantation of a new transvenous pacing lead. Two patients had complete SVC occlusion requiring puncture through the obstruction with a transseptal needle. Vessel recanalization was achieved with balloon dilation and stent implantation. The remaining six patients had severe venous obstruction with a mean minimum diameter of 3.1 ± 3.3 mm. The mean pressure gradient across the obstructed veins was 8.6 ± 7.3 mmHg. Following implantation of 15 Palmaz P308 stents in eight vessels, the mean diameter increased to 14.2 ± 1.9 mm and the mean pressure gradient across the stented vessels decreased to 1.0 ± 2.0 mmHg, A transvenous pacing lead was implanted successfully through the stent (s) immediately or 6–8 weeks later. Innominate vein and SVC obstruction can be safely and effectively relieved with intravascular stents and permit immediate or subsequent transvenous pacing lead implantation.
Atrial Lead Implantation During Atrial Flutter or Fibrillation?
Authors: KINDERMANN MICHAEL , FRÖHLIG GERD , BERG MONIKA , LA WALL PETER , SCHIEFFER HERMANN
Published: July 2006

In patients with sinoatrial disease, unexpected atrial flutter (Af) or fibrillation (AF) is a common problem during implantation of atrial‐based pacing systems. As an alternative approach to blind atrial lead placement, lead positioning could be optimized by atrial electrogram mapping. It was the object of this study to evaluate if atrial lead implantation according to this approach and during ongoing arrhythmia is reasonable or if it should be postponed until restoration of sinus rhythm (SR). Twenty‐nine consecutive patients (group I) with sick sinus syndrome received a dual‐chamber pacemaker during an episode of Af (n = 11) or AF (n = 18). All but two atrial leads were of the screw‐in type and had bipolar sensing. Atrial lead position was optimized by mapping the electrogram under fluoroscopy to find locations with high potential amplitudes. The patients were followed for 15.1 ± 9.8 months, and atrial sensing threshold (AST), atrial pulse width threshold (PWT) at 2.0 V, the pacing mode programmed, and the clinical outcome (OUT) were recorded. The control group consisted of 30 patients (group II) who equally had a history of AF or Af, but were in SR during implantation. The atrial peak‐to‐peak potential (APEAK) after final lead placement was lower for AF (median value 2.5 mV, lower‐upper quartile: 1.7–3.1 mV) as compared to Af (3.8 mV, 2.7–4.9 mV, P < 0.05) and SR (4.1 mV, 3.3–6.2 mV, P < 0.001). There was a correlation (P < 0.01) between APEAK during Af/AF and the postoperative AST immediately after restoration of SR. No lead in any group had to be corrected due to improper sensing in the postoperative course. Median chronic AST was 2.8 mV (2.0–4.0 mV) in group I and 4.0 mV (2.8–4.0 mV) in group II. Median chronic PWT at 2.0 V was 0.15 ms (0.12–0.26 ms) in group I and 0.15 ms (0.09–0.20 ms) in group II. There was no significant difference in chronic AST and PWT between both groups. All but two patients in group I preserved SR as the basic rhythm. A stable SR was observed in 10 of 29 patients, intermittent Af/AF was documented in 17 of 29 patients, seven of whom were asymptomatic. There was no significant difference in OUT between group I and II. Hence, sinus rhythm is not a prerequisite of atrial lead implantation. Mapping the Af or AF waves appears to be useful to guide lead placement and to achieve sufficient sensing and pacing conditions after conversion to sinus rhythm.
An Integrated Dual Sensor System Automatically Optimized by Target Rate Histogram
Authors: LEUNG SUM‐KIN , LAU CHU‐PAK , TANG MAN‐OI , LEUNG ZOE , YAKIMOW KRISTIN
Published: July 2006

The use of combined sensors and advanced algorithms using different principles can improve rate performance over a single sensor system. Combinations of sensors and more sophisticated algorithms, however, invariably increase the complexity of pacemaker programming. An automatically optimized combined minute ventilation and activity DDDR pacemaker was developed to minimize repeated sensor adjustment. The device used subthreshold (below cardiac stimulation threshold) lead impedance to detect lead configuration at implantation automatically, followed by “implant management,” including setting of lead polarity and initiation of DDDR pacing. Automatic sensor adaptation was achieved by programming a “target rate histogram” based on the patient's activity level and frequency of exertion, and the rate profile optimization process matched the recorded integrated sensor response to the target rate histogram profile. In nine patients implanted with the DX2 pacemakers, the implant management gave 100% accuracy in the detection of lead polarity. Rate profile optinuzation automatically increased the pacing rate during exercise between discharge and 3‐month follow‐up (hall walk: 78 ± 3 vs 98 ± 3 beats/min, and maximal treadmill exercise: 89 ± 6 vs 115 ± 5 beats/min, P < 0.001) with a significant increase in exercise duration during maximal exercise (7.18 ± 1 min vs 9.56 ± 2 min, P = 0.05). The accuracy of rate profile optimization versus manual programming was assessed at 1 month, and there was no significant difference between pacing rate kinetics and maximal pacing rate between the two methods of programming. In conclusion, pacemaker automaticity can be initiated at implantation and the self‐optimized rate adaptive response appeared to be comparable to that derived from a manual programming procedure, which may reduce the need to perform time consuming sensor programming.
Automatic Adjustment of Pacemaker Stimulation Output Correlated with Continuously Monitored Capture Thresholds: A Multicenter Study
Authors: CLARKE MALCOLM , LIU BO , SCHÜLLER HANS , BINNER LUDWIG , KENNERGREN CHARLES , GUEROLA MODESTO , WEINMANN PETER , OHM OLE‐JØRGEN ,   on behalf of the European Microny Study Group
Published: July 2006

Pacing threshold is affected by many factors. A pacing system able to confirm capture at each beat and automatically adjust its output close to the actual pacing threshold is highly desirable. This study evaluates the safety and efficacy of the Autocapture function of the Pacesetter Microny SR+. One hundred thirteen patients were recruited from 16 centers in 7 European countries and followed up for 1 year. All pacemakers were implanted with Pacesetter's low polarization, bipolar leads. The key feature of Autocapture is the immediate delivery of a 4.5 V safety backup pulse 62.5 ms after any ineffective ongoing low output pulse. Holter recordings confirmed total reliability of this feature without any exit block. The measured evoked response (ER) signal was stable over time. Acute and chronic pacing thresholds measured by VARIO and Autocapture tests correlated (r > 0.79) over the period of the study. The incidence of backup pulses was 1.1% during pacing. With Autocapture programmed ON, the overall total current consumption was 4.1 μA for VVI and 5.0 μA for VVIR pacing. Tbis study proved that the Autocapture safely and reliably regulates the pacemaker's output according to the prevailing threshold thus providing maximum patient safety and prolonging service life.
Sudden Wenckebach Periods and Their Relationship to Neurocardiogenic Syncope
Authors: CASTELLANOS AGUSTIN , MOLEIRO FEDERICO , ACOSTA HELBERT , FERREIRA ALEXANDRE , COX MARILYN M. , INTERIAN ALBERTO , MYERBURG ROBERT J.
Published: July 2006

Throughout a 9‐month period during which 1, 125 Hoiter tapes were reviewed prospectively we identified 13 non medicated patients with an arrhythmia, which for the purposes of this presentation was categorized, because of their mode of initiation, as sudden Wenckebach periods (WP). The episodes emerged abruptly from a normal (± 200 ms) PR interval with sudden prolongation of PR and PP intervals (and reversed PR‐RP relationship that took place over 1–8 cycles. The postpaced PR interval was shorter than that of the last conducted beat. The episodes were separated into two groups. Group I included 11 patients with symptoms other than syncope and Group 11 included 2 patients with syncope. There were 26 episodes of sudden WP in Group 1. Twenty‐five terminated in a single (and one in double) blocked P waves. Most episodes occurred between 10 PM and 7 AM. Symptoms did not correlate with the episodes. Mean 24‐hour rates were < 90. In Group II there were 22 episodes, all occurring between 6 AM and 10 PM. The mean sinus cycle lengths before the phenomenon started to occur in Group I (861 ± 185 ms) as well as the cycle lengths at the onset of block (1,096 ± 215 ms) were statistically longer than those in Group II (591 ± 40 ms and 747 ± 63 ms, respectively, P < 0.0001). Although the mode of onset in the episodes in Group II was similar to Group I, 16 episodes terminated in 2–6 blocked P waves. Thus, the entire number of episodes could be categorized as an unusual type (because of the PR prolongation) of paroxysmal, or advanced second degree A V block. Because these patients had negative electrophysiological studies, positive tilt tests, and absent syncope after oral propranolol therapy, they were considered as having neurocardiogenic syncope. In addition, the faster than normal (> 100) mean 24‐hour rates) suggested that they also had so‐called inappropriate sinus tachycardia. In summary. Group I consisted of patients with a normal, benign, vagal‐induced second‐degree AV block, whereas the Hoiter findings in Group II appeared to refiect unusual (but natural, i.e., nonprovoked) electrocardiographic manifestations of certain patients with neurocardiogenic syncope.
Effects of Left Atrial Dilatation on the Endocardial Atrial Defibrillation Threshold: A Study in an Ovine Model of Pacing Induced Dilated Cardiomyopathy
Authors: POWER JOHN M. , BEACOM GRAHAM A. , ALFERNESS CLIF A. , RAMAN JAI , FARISH STEPHEN J. , TONKIN ANDREW M.
Published: July 2006

Left atrial (LA) dilatation is a common finding in patients with chronic atrial fibrillation (AF). Progressive dilatation may alter the atrial defibrillation threshold (ADFT). In our study, epicardial electrodes were implanted on the LA free wall and right ventricular apex of eight adult sheep. Large surface area, coiled endocardial electrodes were positioned in the coronary sinus and right atrium (RA). LA dilatation was induced by rapid ventricular pacing (190 beats/min) for 6 weeks and echocardiographically assessed weekly along with the ADFT (under propofol anesthesia). LA effective refractory period (ERP) was measured every 2–3 days using a standard extra stimulus technique and 400 ms drive. The AF cycle length (AFCL) was assessed from LA electrograms. During the 6 weeks of pacing the mean LA area increased from 6.1 ± 1.5 to 21.3 ± 2.4 cm2. There were no significant changes in the mean ADFT (122 ± 15 V), circuit impedance (46 ± 5 Ω), or LA AFCL (136 ± 23 ms). There was a significant increase in the mean LA ERP (106 ± 10 ms at day 0, and 120 ± 13 ms at day 42 of pacing). In this study, using chronically implanted defibrillation leads, the minimal energy requirements for successful AF were not significantly altered by ongoing left atrial dilatation. This finding is a further endorsement of the efficiency of the coronary sinus/RA shock vector. Furthermore, the apparent stability of the AF present may be a further indication of a link between the type of AF and the ADFT.
Should Unipolar Leads Be Implanted in the Atrium? A Holter Electrocardiographic Comparison of Threshold Adapted Unipolar and High Sensitive Bipolar Sensing
Authors: WIEGAND UWE K.H. , SCHIER HELMUT , BODE FRANK , BRANDES AXEL , POTRATZ JORGEN
Published: July 2006

The accuracy ofatrial sensing plays a central role in dual chamber pacing. Recent Holter electrocardiographic studies showed a high incidence of atrial malsensing. We investigated the efficacy of bipolar atrial sensing at high sensitivity compared to threshold adapted unipolar sensing. One h undred consecutive patients with identical dual chamber pacemakers and bipolar atrial leads were investigated. Mean and individual range of 40 unipolar and bipolar telemetered atrial potentials were calculated; sensing threshold was determined by a semiautomatic sensing test. Oversensing was investigated with the help of a muscle provocation test. Twenty‐four‐hour Holter monitoring was performed at the highest bipolar sensitivity as well as at a unipolar sensitivity of half the measured sensing threshold. Mean atrial potential was significantly lower during bipolar mode compared to the unipolar sensing configuration, 3.66 ± 1.75 versus 3.85 ± 1.62 mV, P = 0.02. The bipolar atrial potentials showed a higher individual range than the unipolar signals, 2.44 ± 2.62 versus 1.79 ± 0.92 mV, P < 0.01. Sensing threshold did not differ significantly, 2.76 ± 1.33 versus 2.67 ± 1.29 mV. Mean oversensing threshold was 1.21 mV at unipolar configuration, whereas oversensing could not be provoked at a bipolar sensitivity of 0.5 mV. The incidence of atrial undersensing was significantly higher at threshold adapted unipolar sensing compared to bipolar sensing at highest atrial sensitivity, 35% versus 22%, P = 0.04. Oversensing did not occur at bipolar sensing, but was observed in 56% of patients at unipolar mode. Thirty‐two percent of patients showed both atrial undersensing and over‐ sensing at the unipolar sensing configuration. The muscle provocation test reached a sensitivity of 89% and a specificity of 95% in prediction of atrial oversensing during daily life. In conclusion, unipolar atrial potentials are more stable than bipolar ones. On the other hand, bipolar atrial sensing is less prone to the perception of myopotentials. Programming a high bipolar sensitivity significantly improves atrial sensing. Th us, bipolar leads should generally be implanted in the atrium.
Intracardiac QRS Electrogram Width—An Arrhythmia Detection Feature for Implantable Cardioverter Defibrillators: Exercise Induced Variation as a Base for Device Programming
Authors: KLINGENHEBEN THOMAS , STICHERLING CHRISTIAN , SKUPIN MANFRED , HOHNLOSER STEFAN H.
Published: July 2006

Delivery of inappropriate therapy of implantahle cardioverter defibrillators (ICD) due to inaccurate arrhythmia detection represents a major clinical problem. Different arrhythmia detection criteria such as the “stability” of the cycle length or the suddenness of “onset” of tachycardia have been implemented in ICD software to prevent inappropriate therapy. The new Medtronic model 7223Cx ICD offers an additional detection parameter (QHS width), which reflects changes in the duration of ventricular depolarization as a tool to distinguish supraventricular from ventricular tachycardias. Although this criterion can be programmed based on ECG parameters derived from resting ECGs, this may not be sufficient since QRS width is subject to considerable changes due to transient myocardial ischemia, changes in autonomic tone, or frequency dependent effects of antiarrhythmic drugs. The present study aimed to determine frequency dependent changes in QRS width in individual patients at rest and during symptom‐limited exercise testing in 16 patients with documented ventricular tachycardia (N = 13) or ventricular fibrillation (N = 3). The optimal EGM slew threshold and the individual variation of QRS width were determined. Measurements obtained at the end of the implantation procedure were compared to those performed at hospital discharge. The majority of patients showed a wider variation in QRS duration as measured from 30 consecutive cycles during exercise as compared to rest. For example, the QRS range (i.e., the difference between the maximal and the minimal QRS width measured) averaged 7 ± 3 ms at rest and increased to 11 ±3 ms during exercise (P = 0.004) with an increase of ≥ 4 ms observed in 11 (69%) of 16 patients. In 13 (81%) of 16 patients a reprogramming of at least one QRS width parameter from its value at the time of implantation was necessary. Thus, the QRS width measured from the intracardiac EGM shows significant intra‐individual variations in different physiological conditions. Eor optimal programming of the QRS width parameter, measurements obtained during exercise are important.
Magnetic Electroanatomical Mapping for Ablation of Focal Atrial Tachycardias
Authors: MARCHLINSKI FRANCIS , CALLANS DAVID , GOTTLIEB CHARLES , RODRIGUEZ ENRIQUE , COYNE ROBERT , KLEINMAN DAVID
Published: July 2006

Uniform success for ablation of focal athaJ tachycardias has been difficult to achieve using standard catheter mapping and ablation techniques. In addition, our understanding of the complex relationship between atrial anatomy, electrophysiology. and surface ECG P wave morphology remains primitive. The magnetic electroanatomical mapping and display system (CARTO) offers an on‐line display of electrical activation and/or signal amplitude related to the anatomical location of the recorded sites in the mapped chamber. A window of electrical interest is established based on signals timed from an electrical reference that usually represents a fixed electrogram recording from the coronary sinus or the atrial appendage. This window of electrical interest is established to include atrial activation prior to the onset of the P wave activity associated with the site of origin of a focal atrial tachycardia. Anatomical and electrical landmarks are defined with limited fluoroscopic imaging support and more detailed global chamber and more focal atrial mapping can be performed with minimal fluoroscopic guidance. A three‐dimensional color map representing atrial activation or voltage amplitude at the magnetically defined anatomical sites is displayed with on‐line data acquisition. This display can be manipulated to facilitate viewing from any angle. Altering the zoom control, triangle fill threshold, clipping plane, or color range can all enhance the display of a more focal area of interest. We documented the feasibility of using this single mapping catheter technique for localizing and ablating focal atrial tachycardias. In a consecutive series of 8 patients with 9 focal atrial tachycardias, the use of the single catheter CARTO mapping system was associated with ablation success in all but one patient who had a left atrial tachycardia localized to the medial aspect of the orifice of the left atrial appendage. Only low power energy deHvery was used in this patient because of the unavaHahiHty of temperature monitoring in the early version of the Navistar catheter, the location of the arrhythmia, and the history of arrhythmia control with flecainide. No attempt was made to Umit fluoroscopy time in our study population. Nevertheless, despite data acquisition from 120–320 anatomically distinct sites during global and more detaHed focal atrial mapping, total fluoroscopy exposure was typically < 30 minutes and was as little as 12 minutes. The detailed display capabilities of the CARTO system appear to offer the potential of enhancing our understanding of atrial anatomy, atrial activation, and their relationship to surface ECC P wave morphology during focal atrial tachycardias.
Use of a Real‐Time Three‐Dimensional Magnetic Navigation System for Radiofrequency Ablation of Accessory Pathways
Authors: WORLEY SETH J.
Published: July 2006

Using conventional technology, accessory pathway abiation often requires prolonged exposure of the team and patient to ionizing radiation. Further, although the primary success rate (approximately 90%) and the rate of recurrence (approximately 10%) are acceptable, there is room for improvement. Finally, inadvertent ablation of the compact node and A V/His‐Purkinje system still occurs particularly with septal accessory pathways. The Biosense CAHTO Nonfluoroscopic Mapping and Navigation System (CARTO® System) when used to locate the accessory pathway and guide delivery of radio frequency energy lo the accessory pathway, has the potential to reduce radiation exposure, improve primary ablation success, and reduce the rate of recurrence and improve safety. This article describes our experience with the CARTO Biosense System relating to setting up the CARTO System specifically for WPW mapping/ablation, and features of the CARTO System, which are particularly advantageous for mapping and ablation of accessory pathways.
Amiodarone Induced Pulmonary Fibrosis in Infancy
Authors: BOWERS PETER N. , FIELDS JONATHAN , SCHWARTZ DANA , ROSENFELD LYNDA E. , NEHGME RODRIGO
Published: July 2006

We report a case of pulmonary fibrosis in an infant receiving amiodarone for treatment of intractable atrioventricular reentrant tachycardia secondary to Wolff‐Parkinson‐White syndrome. At 9 months, a screening chest radiograph showed a diffuse interstitial infiltrate in an asymptomatic, thriving infant. Amiodarone was discontinued and the pulmonary fibrosis resolved gradually over 6 months. This case documents the first report of amiodarone induced pulmonary fibrosis in the pediatric age group. We speculate that as amiodarone is used more frequently to manage pediatric arrhythmias, pulmonary fibrosis, a known complication of this antiarrhythmia in adults may be seen with increasing frequency in children.
The Use of the Block Cycle Length as a Safe and Efficient Means of Interrupting Sustained Ventricular Tachycardia and Its Pharmacological Modification
Authors: OHIRA KOJI , NIWANO SHINICHI , FURUSHIMA HIROSHI , TANEDA KOJI , CHINUSHI MASAOMI , AIZAWA YOSHIFUSA
Published: July 2006

In nine patients who had inducible monomorphic sustained ventricular tachycardia (VT), rapid pacing was performed in 11 episodes of morphologically distinct VT at progressively shorter cycle lengths and VT was interrupted at a critical cycle length. The VT interrupting critical cycle length was defined as the block cycle length (BCL) and the effect of Class I antiarrhythmic drugs were examined. Both the VT cycle length (VTCL) and the BCL were prolonged after administration of either drug. The overall mean ratio of the BCL to the VTCL was unchanged after procainamide administration, but increased after the use of mexiletine. The ratio, however, varied in individual VTs and the BCL after treatment with Class I antiarrhythmic drugs could not be predicted from the ratio baseline value, although the ratio was always > 60% and the hazard of VT acceleration might be avoided if the BCL is used.
Radiofrequency Catheter Ablation of Concealed Atrioventricular Accessory Pathways Using a “Simultaneous Pacing Method”
Authors: SUYAMA KAZUHIRO , KURITA TAKASHI , SHIMIZU WATARU , MATSUO KIYOTAKA , TAGUCHI ATSUSHI , AIHARA NAOHIKO , KAMAKURA SHIRO , SHIMOMURA KATSURO
Published: July 2006

The retrograde atrial potential at a successful ablation site is usually obscured by the wide and large ventricular potential during atrioventricular reentrant tachycardia or ventricular pacing, which makes it difficult to determine the appropriate ablation site for concealed accessory pathway. A pacing maneuver named the “simultaneous pacing method” is proposed herein to differentiate the retrograde atrial potential from the ventricular potential for a successful ablation of the concealed accessory pathway. Catheter ablation was performed in 12 patients with a single left free‐wall concealed accessory pathway. The atrial insertion site was determined by the simultaneous pacing method in six patients (group I) and by ventricular pacing in six patients (group II), In the simultaneous pacing method, electrograms recorded during ventricular pacing in the earliest retrograde atrial activation site are a fusion of the ventricular potential and the following retrograde atrial potential. When atrial and ventricular pacings are performed simultaneously (simultaneous pacing), the end portion of the electrograms recorded at the same site is solely the ventricular component, because atrial is activated earlier. The atrial potential can be confirmed during ventricular pacing in comparison with the electrograms during the “simultaneous pacing.” Radiofrequency catheter ablation was successful in eliminating conduction through the accessory pathway in all 12 patients. The radiofrequency applications in group I were significantly fewer than those in group II (1.7 ± 1.0 in group I, 5.3 ± 3.2 in group II, P < 0.05). The total procedure time in group I was significantly shorter than in group II (57.8± 15.7 vs 106.7 ± 41.6 mins in group II. respectively, P < 0.05). The fluoroscopy time in group I was significantly shorter than in group II (54.0 ± 7.9 vs 81.3± 26.3 mins, respectively, P < O.05). We were able to determine the atrial insertion site of accessory pathways by the simultaneous pacing method. The simultaneous pacing method was useful in eliminating concealed left free‐wall accessory pathways.
Effects of Sensor Selection on Exercise Stroke Volume in Pacemaker Dependent Patients
Authors: HAENNEL ROBERT G. , LOGAN TRINA , DUNNE CATHERINE , BURGESS JOHN , BUSSE EDWARD
Published: July 2006

The effects of sensor selection and sensor blending on the cardiovascular response to graded exercise was evaluated in 10 patients (age 74 ± 2 yrs; 7 men and 3 women) implanted with a dual sensor rate adaptive VVIR pacemaker (Vitatron Topaz(tm) model 515). Patients underwent three graded exercise tests (GXT) with sensor programming randomly assigned. For a given graded exercise text the pacemaker was programmed into activity sensing (ACT), QT sensing, or dual sensing (ACT = QT). Data were recorded at rest and during each stage of the graded exercise text. Oxygen uptake (VO2) was measured continuously using a Q Plex I system. Heart rate (HR), stroke volume (SV), and cardiac output (Qc) were measured by impedance cardiography. Systolic time intervals were calculated from simultaneous recordings of the ECG. phonocardiogram, and the impedance cardiogram. In response to the GXT no differences in peak VO2 were observed across the three sensor settings. Regardless of the sensor setting Qc increased linearly with each increment in VO2. The HR response to ACT only pacing was significantly higher than in the other two pacing conditions. During ACT only pacing SV failed to rise in response to exercise. The increased exercise Qc during QT and ACT = QT pacing were mediated by significant increases in both HR and SV. The QT and dual pacing conditions were also associated with longer diastolic filling times. The data indicate that the mechanisms responsible for the increase Qc during exercise were different for ACT versus ACT = QT or QT sensor‐driven pacing.
Cellular Phone Interference Testing of Implantable Cardiac Defibrillators In Vitro
Authors: BASSEN HOWARD I. , MOORE HANS J. , RUGGERA PAUL S
Published: July 2006

An in vitro study was undertaken to investigate the potential for cellular telephones to interfere with representative models of presently used ICDs. Digital cellular phones (DCPs) generate strong, amplitude modulated fields with pulse repetition rates near the physiological range sensed by the 1CD as an arrhythmia. DCPs with Time Division Multiple Access (TDMA) pulsed amplitude modulation caused the most pronounced effect—high voltage firing or inhibition of pacing output of the ICDs. This electromagnetic interference (EMI) occurred only when the phones were within 2.3–5.8 cm of the ICD pulse generator that was submerged 0.5 cm in 0.18% saline. ICD performance always reverted to baseline when the cellular phones were removed from the immediate proximity of the ICD. Three models of ICDs were subjected to EMI susceptibility testing using two types of digital phones and one analog cellular phone, each operating at their respective maximum output power. EMI was observed in varying degrees from all DCPs. Inhibition of pacer output occurred in one ICD. and high voltage firing occurred in the two other ICDs. when a TDMA11 Hz DCP was placed within 2.3 cm of the ICD. For the ICD that was most sensitive to delivering unintended therapy, inhibition followed by firing occurred at distances up to 5.8 cm. When a TDMA‐50 Hz phone was placed at the minimum test distance of 2.3 cm. inhibition followed by firing was observed in one of the ICDs. EMI occurred most frequently when the lower portion of the monopole antenna of the cellular phone was placed over the ICD header.