bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Potentials Are Unaffected by Radiofrequency Catheter Ablation in Patients with Ventricular Tachycardia
Authors: TWIDALE NICHOLAS , HAZLITT H. ANDREW , BERBARI EDWARD J. , BECKMAN KAREN J. , McCLELLAND JAMES H. , MOULTON KRIEGH P. , PRIOR MICHAEL I. , LAZZARA RALPH , JACKMAN WARREN M.
Published: July 2006

Reentrant ventricular tachycardia is dependent on an area of myofibers, embedded in scar tissue, which exhibit slow conduction. Late potentials recorded by signal‐averaged electrocardiography appear to correspond to these zones of slow conduction and frequently are present in patients with VT. We hypothesized that elimination of inducible VT by catheter‐mediated ablation of critical areas of slow conduction would alter late potentials. Four patients underwent catheter ablation in which radiofrequency current was delivered to zones of slow conduction exhibiting isolated mid‐diastolic potentials that could not be dissociated from the tachycardia. The four patients had developed VT (cycle length 382 ± 50 msec; mean ± SEM) 13–180 months after inferior myocardial infarction. Late potentials were present in each patient before catheter ablation was attempted. Although VT was not inducible in any patient immediately after ablation, late potentials were still present in all four patients and there was no significant difference in the QRS duration (136.5 ± 4.0 msec postablation; 135.7 ± 4.5 msec preablation), root mean square voltage in the terminal 40 msec of the QRS (10.0 ± 1.0 μV postablation; 5.9 ± 0.4 μV preablation). or in the duration of the low amplitude signal (69.2 ± 2.0 msec postablation; 62.7 ± 3.4 msec preablation). At follow‐up electrophysiology study performed 14 ± 7 days after ablation, one of the four patients had inducible VT. In conclusion, late potentials persist even after successful radiofrequency catheter ablation and do not appear to be useful for predicting results of follow‐up electrophysiology study.
Comparison of Ventricular Function in Atrial Rate Adaptive Versus Dual Chamber Rate Adaptive Pacing During Exercise
Authors: GALLIK DONNA M. , GUIDRY GERALD W. , MAHMARIAN JOHN J. , VERANI MARIO S. , SPENCER WILLIAM H.
Published: July 2006

The hemodynamic effects of two different pacing modes—rate adaptive atrial (AAIR) versus dual chamber (DDDR) pacing—were assessed in 12 patients with DDDR pacemakers during upright bicycle exercise first‐pass radionuclide angiography using a multiwire gamma camera with tantalum‐178 as a tracer. All patients had sinus node disease with intact AV conduction. Patients exercised to the same heart rate in random order in these two different pacing modes, AAIR and DDDR with AV delay (of 100 msec) selected to maintain 100% ventricular capture. Cardiac output in creased significantly above baseline values during exercise in both pacing modes: 154 ± 41% (mean ± SEM, P = 0.002) with AAIR, versus 95 ± 24% (P = 0.004) with DDDR (P = NS between the two modes). The peak filling rate, likewise, increased in both pacing modes (2.3 ± 0.21 end‐diastolic volumes/sec to 3.8 ± 0.31 end‐diastolic volumes/sec in AAIR [P = 0.0004] and 2.2 ± 0.18 end‐diastolic volumes/sec to 3.4 ± 0.27 end‐diastolic volumes/sec in DDDR [P = 0.0008]). LV ejection fraction was normal at rest (60 ± 4%, SEM) and did not significantly change with submaximal exercise in either pacing mode (both 56%, P = NS). No significant changes in end‐diastolic volume or stroke volume indexes occurred with exercise in either pacing mode. Our study demonstrates that in patients with normal resting LV function, AAIR and DDDR pacing are equally effective in attaining appropriate increases in cardiac output and LV filling during exercise.
Alteration of the QT/RR Relationship in Patients with Idiopathic Ventricular Tachycardia
Authors: FEI LÜ , STATTERS DEBORAH J. , GILL JASWINDER S. , KATRITSIS DEMOSTHENES , CAMM A. JOHN
Published: July 2006

It has been shown that alterations in QT/RR relationship may be associated with arrhythmogenesis in several clinical settings. In the present study the QT/RR relationship was studied in 20 patients with idiopathic ventricular tachycardia (12 men and 8 women, aged 41±14 years) compared to 20 normal subjects (9 men and 11 women, aged 39 ± 13 years). All the patients were off any antiarrhythmic drugs and had no evidence of intraventricular conduction defects. The QT intervals and their preceding RR intervals were measured on electrocardiogram strips from 24‐hour Holter tapes at hourly intervals. The differences in the maximum, minimum, and mean of either the QT interval or its corrected values between patients with idiopathic ventricular tachycardia and normal subjects were not statistically significant. There was a significant correlation between the QT and RR intervals in normal subjects (γ= 0.73 ± 0.12, P < 0.05) and in patients with idiopathic ventricular tachycardia (γ= 0.80 ± 0.10, P < 0.05). However, the linear regression line of the QT interval against the RR interval were significantly (P < 0.001) altered in patients with idiopathic ventricular tachycardia (QT = 0.24 + 0.18 RR) compared to normal subjects (QT = 0.27 ± 0.12 RR). We conclude that although there is no significant change in the QT interval and its corrected values, the QT/RR relationship is significantly altered in patients with idiopathic ventricular tachycardia as compared to normal subjects. This may be of importance in the pathogenesis of idiopathic ventricular tachycardia in these patients.
The Effect of Overdrive Pacing Rate and Duration on Ventricular Escape Rhythms in Patients with Chronic Complete Atrioventricular Block
Authors: ROSENHECK SHIMON , BONDY CHAVA , WEISS AVRAHAM T. , COTSMAN MERVYN S.
Published: July 2006

The effect of overdrive (OD) pacing rate and duration on subsidiary pacemakers was evaluated in 54 patients with third‐degree AV block. They had a permanent pacemaker implanted 61 ± 56 months earlier because of complete AV block in 38 patients and, in 16 patients because of second‐degree AV block, which in the interim advanced to complete AV block. The patients had a reliable infranodal escape rhythm, with a mean cycle length of 2,022 ± 603 msec, upon discontinuation of the ventricular OD pacing, at a rate of 40 beats/min. The escape interval and escape rhythm cycle length was evaluated after OD pacing at 40, 50, 60, 70, 80, 90, and 100 beats/ min for 30 seconds, at each rate. In 100% of the patients the subsidiary pacemaker recovered after OD pacing at 40 and 50 beats/min and the number decreased to 59% at a rate of 100 beats/min. The escape interval prolonged gradually between OD pacing at 40 and 100 beats/min, by 56%. The effect of OD pacing duration at 50 and 70 beats/min was evaluated. At an OD pacing rate of 70 beats/min there was a significant effect of the pacing duration on the escape interval. There were significant differences in the escape interval duration and escape rhythm cycle length between males and females, patients with or without coronary artery disease, and patients with narrow or wide QBS escape. However, the increase in the OD pacing rate had a similar effect on the escape interval in the above mentioned groups. There was no effect on the paced QRS duration and sinus cycle length at each OD pacing rate. In nine patients premature escape beats were present after OD pacing at 80 and 90 beats/min. In conclusion, OD pacing may suppress the infranodal subsidiary pacemakers originating at the proximal conduction system or from a ventricular site and this effect depends on the pacing rate and duration. An OD pacing at a rate of 50 beats/min or less has minimal or no effect on these inherent pacemakers. Overdrive stimulation in the form of premature escape beats is present in 17% of the patients.
Why Do Some Patients Have High Defibrillation Thresholds at Defibrillator Implantation?
Authors: HILLSLEY RUSSELL E. , WHARTON J. MARCUS , CATES ADAM W. , WOLF PATRICK D. , IDEKER RAYMOND E.
Published: July 2006

Implantable cardioverter defibrillators reduce the risk of sudden cardiac death in patients with ventricular tachyarrhythmias. However, for the few patients with unacceptably high defibrillation thresholds at implantation the risk of sudden death may remain high. If a small number of defibrillation attempts are used to determine a defibrillation threshold, then a high defibrillation threshold may occur in some patients due to the probabilistic nature of defibrillation: a small percentage of shocks will fail even at optimal shock strengths. Basic investigations have suggested mechanisms for high defibrillation thresholds in other patients. The extracellular potential gradients produced by a shock correlate with ability to defibrillate and may be used to classify mechanisms for high defibrillation thresholds. Computerized mapping studies have demonstrated that extracellular potential gradient fields produced by defibrillation shocks are uneven with high gradient areas close to the electrodes and low gradient areas distant from the electrodes. A high defibrillation threshold may occur because: (1) a shock creates a subthreshold potential gradient in the low gradient areas; (2) a patient has a higher minimum potential gradient threshold than other patients; or (3) a shock leads to refibrillation in the high gradient areas. This article reviews experimental evidence to support each of these three possibilities then suggests experimental and clinical investigations that may clarify the causes of high defibrillation thresholds in patients.
Pacemaker Failure Induced by Radiotherapy
Authors: SOULIMAN S.K. , CHRISTIE J.
Published: July 2006

It is well documented that radiation therapy can have significant transitory and permanent effects on the function of cardiac pacemakers. In this study 18 multiprogrammable pacemakers were tested to establish any pattern by which these pacemakers are affected. The results confirm previous predictions on how pacemakers are damaged. The damage could be divided essentially into three types: (1) temporary change to interference or safety mode pacing lasting for the duration of the irradiation only; (2) change to interference mode pacing—from which recovery may occur after reprogramming the pacemaker; and (3) severe damage; in this case the pacemaker stops generating pulses. Recovery from this may occur a long time after the end of the treatment, but this recovery is mostly incomplete and the pacemaker cannot be used reliably thereafter. Therefore it is essential that patients with implanted pacemakers undergoing radiation therapy, should be monitored closely during the course of the treatment and for a few weeks thereafter.
DDI Pacing: Indications, Expectations, and Follow‐Up
Authors: IRWIN MARLEEN , HARRIS LOUISE , CAMERON DOUGLAS , LOUIS CICELY , RADVANSZKY EVA , GOLDMAN BERNARD
Published: July 2006

The DDI mode of pacing that permits noncompetitive atrioventricular sequential bradycardia support was chosen in 65 of 480 (14%) patients selected for dual chamber pacing between February 1985 and March 1990. All patients were implanted with Pacesetter 283 or 285 pulse generators and programmed to DDI. The indications for pacing were sick sinus syndrome (n = 52), combined sinus node dysfunction and AV block (n = 13). Forty‐two of these patients had a history of paroxysmal atrial arrhythmias. All patients received passive fixation atrial and ventricular leads. Follow‐up thereafter was performed predischarge, and at 6 weeks, 3 and 6 months after discharge. The duration of follow‐up ranged from 1‐61 months (mean 31 months). Fifty‐four of 65 (83%) patients chosen for DDI remain programmed in the DDI mode. Three patients were reprogrammed to VVI and eight to DDD. During the course of follow‐up, six patients presented with effective VVI pacing with consistent ventriculoatrial conduction that was appropriately sensed by the atrial circuit with atrial output inhibition. A further four patients presented with “functional undersensing” due to ventricular blanking period (VBP) characteristics in these pulse generators and in this mode. Functional undersensing was eliminated in all but one patient by reprogramming the VBP to 13 msec with no subsequent episodes of provoked crosstalk inhibition. Effective VVI pacing was observed in patients with AV block during times of sinus acceleration. While DDI mode is an effective form of pacing, permitting non‐competitive atrioventricular sequential pacing, potential limitations include: effective VVI pacing during intact ventriculoatrial conduction, functional undersensing when long VBP are programmed, and effective VI pacing with sinus node acceleration during AV block.
A Pilot Study: Defibrillation Thresholds in Dogs are Similar with Isoflurane, Halothane, and Pentobarbital
Authors: JARVIS ALISON S. , LAHTINEN STUART P.
Published: July 2006

The objective of this pilot study was to determine if three common anesthetic drugs have differing effects on the measurement of defibrillation thresholds (DFT) in dogs. The drugs compared were pentobarbital, isoflurane, and halothane. We used six dogs, which were surgically instrumented, in a chronic study design. Each dog had two internal defibrillation patches placed on its heart, which were used to deliver the defibrillation energy. DFT was determined while each dog was anesthetized under each of the listed drugs in a crossover design. This pilot study suggests that differences in DFT due to the anesthetic drugs is not significant in studies with low numbers of animals (halothane 14.5 ± 1.0, isoflurane 14.2 ± 1.0, pentobarbital 12.8 ± 1.0;P = NS; mean ± SE). Tbe variation in DFT between individual animals is much larger than the difference in DFT due to the drugs.
A Selective, Non‐lschemic, Non‐Pharmacological Left Ventricular Failure Animal Model
Authors: GEDDES L.A. , RAGHEB A.O. , JANAS W.
Published: July 2006

Selective left ventricular failure was induced in 13 acute anesthetized, closed chest dogs ranging in weight from 18–26 kg. Failure was induced by passing a single, high intensity pulse of current from a defibrillator connected to a left ventricular catheter electrode and a left chest electrode. The intensity of the myocardial damaging shock was related to the predicted current required for transventricular defibrillation, based on heart weight. Thermodilution cardiac output, left ventricular pressure, impedance stroke volume, the cardiac electrogram, and lead IIECG were recorded, along with the pressure impedance (volume) loop, which is a measure of stroke work. It was found that the cardiac output decreased with increasing current intensity. Immediately following the high current shock, cardiac output, and stroke work decreased. In some animals, with a moderate intensity shock, there was a transient increase in cardiac output, followed by a decrease. In the five animals that were monitored continuously for 4 hours, the average percent reduction in cardiac output at this time was 42.5% for an average current overdose ratio of 5.39. The energy setting on the defibrillator to obtain this range of reduction in cardiac output was 175–350 joules. The method described herein is easily applied to the closed chest animal and will allow evaluation af the pumping capabilities of cardiac augmentation techniques, such as dynamic cardiomyoplasty and the skeletal muscle ventricle.
Apparent Extension of the Atrioventricular Interval Due to Sensor‐Based Algorithm Against Supraventricuiar Tachyarrhythmias
Authors: LEUNG SUM‐KIN , LAU CHU‐PAK , LEUNG WING‐HUNG , TAI YAU‐TING , CHUNG FELSA , CHOW YUEN‐HA
Published: July 2006

Rapid ventricular tracking response to supraventricular tachyarrhythmia is one major limitation to DDD pacing. In a DDDR pacemaker, sensor‐based algorithms have been used to control these arrhythmias. These include the use of an interim rate limit (conditional ventricular tracking limit) or a separate maximum tracking and sensor rate limits (discrepant upper rate). These algorithms limit inappropriate ventricular pacing rate during tracking of pathological supraventricuiar tachyarrhythmia and atrial flutter by Wenckebach‐like prolongation of the AV interval. We observed that this may cause an unexpected extension of the AV interval in patients with high atrial rate and intact AV nodal conduction. This was due to P wave rate above the conditional ventricular tracking limit or maximum tracking limit, but AV paced interval prolongation was avoided by the occurrence of intrinsic conduction, albeit at an AV interval longer than the programmed AV interval. This might appear as failure of ventricular pacing on the ECG. This phenomenon is a modified form of “upper rate” behavior occurring in the AV interval, and should be recognized as a normal behavior rather than pacemaker malfunction.
Detection of Atrial Fusion Systole in Patients with Dual Chamber Pacemakers by 24‐Hour Esophagus ECG
Authors: GRILLE WERNER , HOLST THOMAS , LAESSING CLAUS , SCHRÖDER EBERHARD , ASBECK FRANK
Published: July 2006

We performed ambulatory 24‐hour esophagus ECG in nine patients with dual chamber pacemakers suspect of transient arrhythnias in order to achieve correct and reliable P wave identification during daily life activities. In all patients episodes were observed with varying atrial artifact to left atrial depolarization sequences. These episodes probably reflected presence of atrial fusion systole, an ECG phenomenon which should be taken into account when analyzing ambulatory esophagus ECC. Thus, the ambulatory esophagus ECG revealed its ability to detect spontaneous atrial depolarization in the presence of pacemaker artifact in patients with DDD(R) pacemakers.
Modification of Atrioventricular Conduction Using a Combined Laser‐Electrode Catheter
Authors: CURTIS ANNE B. , MANSOUR MICHAEL , FRIEDL STEPHAN E. , TOMARU TAKANOBU , BARBEAU GERALD R. , NORMANN SIGURD J. , ABELA GEORGE S.
Published: July 2006

Ablation of the AV junction is an accepted technique for the management of selected supraventricular tachyarrhythmias. Radiofrequency ablation appears to be safe and effective for AV junction ablation in most patients, but the need for firm tissue contact may make it less effective for ventricular tachycardia and certain ectopic atrial tachycardias. Laser energy can also be delivered through a catheter, and thus it may be an attractive alternative energy source for ablation. A new laser‐electrode catheter was developed for modification of conduction through the AV node as a model for ablation of an arrhythmia substrate. A window for delivery of continuous‐wave Nd:YAG laser energy was placed between the two electrodes of a bipolar electrode catheter. In vitro studies using a matrix of power versus time were performed to determine the energy that would create lesions of the appropriate size in vivo. Using this information, advanced AV block was successfully created in 16 of 17 dogs (94%) with the laser‐electrode catheter. Advanced AV block was successfully created in all four dogs in the chronic study, and it persisted for 1‐24 weeks of follow‐up until sacrifice of the animals. Histologic examination demonstrated discrete thermal damage at the AV junction with no instances of septal perforation in the acute studies or progressive necrosis in chronically maintained dogs. Advanced AV block may be produced consistently and safely in dogs using a combined laser‐electrode catheter.
Sustained Left Ventricular Tachycardia Terminated by Dipyridamole: Cyclic AMPMediated Triggered Activity as a Possible Mechanism
Authors: KOBAYASHI YOUICHI , KIKUSHIMA SHUJI , TANNO KAORU , KURANO KOZO , BABA TAKAO , KATAGIRI TAKASHI
Published: July 2006

Sustained VT in two patients was terminated by intravenous administration of dipyridamole, an adenosine transport inhibitor. VT was induced by rapid atrial or ventricular pacing, isoproterenol, or dibutyryl cyclic AMP infusion, or exercise. VT also was aborted by adenosine triphosphate or acetylcholine injection, or by vagal stimulation. VT was terminated or prevented by verapamil or propranolol. In addition, arrhythmias were prevented by oral administration of dipyridamole. These results suggest that VT is due to cyclic AMP‐mediated triggered activity and that inhibition by dipyridamole may be due to a reduction in the intracellular concentration of cyclic AMP.
Insights Into the Pathogenesis of Sudden Cardiac Death From Analysis of Circadian Fluctuations of Potential Triggering Factors
Authors: HOHNLOSER STEFAN H. , KLINGENHEBEN THOMAS
Published: July 2006

Sudden cardiac death continues to be a poorly understood event in terms of its underlying pathophysiological mechanisms. The observation of a circadian variability in the incidence of this catastrophic event with a prominent peak in the early morning hours provides an opporfunity to study triggering factors that may play a causative role in the genesis of sudden cardiac death. As reviewed in this article, there is convincing evidence that transient disturbances in autonomic tone and the resulting consequences may predispose the heart to increased electrical vulnerability. This evidence is based for instance on circadian fluctuations of spontaneous ventricular ectopic activity and transient ischemia, which may serve as trigger factors for the genesis of sustained ventricular tachyarrhythmias. Analysis of heart rate variability provides further evidence of reduced vagal and elevated sympathetic tone during the morning hours particularly in patients with compromised left ventricuiar function. Diurnal variations in ventricular repolarization as indicated by QT interval changes in the surface ECG also support the concept of triggering factors in the genesis of sudden cardiac death. Therapeutic measures aiming at a reduction in sympathetic input to the heart have been successful in preventing ventricular fibrillation and thus indicate the importance of unbalanced sympathetic tone in patients prone to sudden cardiac death.
Results of Holter ECG Guided Therapy for Ventricular Arrhythmias: The ESVEM Trial
Authors: LAZZARA RALPH
Published: July 2006

The Electrophysiological Study Versus Electrocardiographic Monitoring (ESVEM) trial randomized 486 patients with spontaneous sustained ventricular tachycardia (VT), ventricular fibrillation (VF) or unmonitored syncope, who manifested reproducibly inducible sustained ventricular arrhythmias by provocative stimulation and 10 or more premature ventricular contractions per hour on Holter monitoring, to two groups treated with pharmacotherapy guided by suppression of stimulation‐inducible VT/VF or suppression of spontaneous or exercise induced ventricular arrhythmias. There was no difference over four years of follow‐up in the rates of recurrence of arrhythmias, arrhythmic mortality, cardiac mortality, or mortality from any cause between the two groups of patients but more patients [77%) received pharmacotherapy in ihe group treated on the basis of suppression of spontaneous arrhythmias than the group treated on the basis of electrophysiological study. In this trial, rates of recurrence of arrhythmias were higher (37% at one year and 66% at four years) than generally reported, but cardiac and arrhythmia mortality were comparable or lower than generally reported. Of the seven agents tested, six were sodium channel blockers (imipramine, mexiletine, procainamide, propafenone, pirmenol, and quinidine) and the other was sotalol. Sotalol had a significantly higher rate of efficacy predictions by EPS (35%) than the others (15%) and a comparable rate by Holter monitor. Sotalol was significantly more efficacious in preventing recurrences, arrhythmic mortality, cardiac mortality, and total mortality than the other agents and it was better tolerated. Probability of successful long term therapy with a sodium channel blocker tested by electro‐physiological study was low (5% at one year). These results indicate sotalol is a reasonable first option for pharmacotherapy io prevent recurrent VT/VF in patients comparable to the patients included in ESVEM and that Holter monitoring is an acceptable mode of guiding therapy.
Magnetocardiographic Localization of the Origin of Ventricular Ectopic Beats
Authors: OEFF MICHAEL , BURGHOFF MARTIN
Published: July 2006

Magnetocardiogruphic mapping opens new perspectives for three‐dimensional localization of cardiac electrical activation. Using a 37‐channel SQUID magnetometer equipment with high shielding, the origin of abnormal ventricular aclivalion was investigated in 18 patients ivith Wolff‐Parkinson‐White syndrome prior to catheter ablation and in 5 of 31 patients with coronary artery disease having a sufficient number of monomorphic ventricular extrasystoies to enable evaluation. In ali WPW‐patients, the site of the earliest dello‐wave activation was projected onto the AV‐valve plane in accordance with the MR images. The result of magnetocardiographic localization was then compared to the site of successful catheter oblation delermined by digital imaging processing. After optimization of the algorithms, both sites were in the various planes at the foliowing distance from each other; X‐plane; 0.8 ± 0.9 cm, Y‐pIane; 1.1 ± 1.0 cm and Z‐piane; 1.5 ± 1.0 cm. In three‐dimensional projection, the mean difference in space between both positions was calculated to be 2.1 ± 1.7 cm. After this vahdofion ventricular premature beats were localized in another group of patients. In 4 of 5 palienfs their origin was found at the border of infarct areas. In each case, the progression of the ventricular activation couid be pursued. The detected structure of the magnetic field distribution of the VBP's exhibited a stable bipolar patlern, which is comparable to that of venlricuiar tachycardia, and its algorithms may be used to localize the origin of ventricular lachycardia. Thus, non‐invasive magnetocardiographic mapping localizes abnormal ventricuiar activations with fair accuracy, which makes it an useful adjunct for invasive investigations as well as studies of the pathophysiology of arrhythmias.
In Vivo Ventricular Lesion Growth in Radiofrequency Catheter Ablation
Authors: SIMMERS TIMOTHY A. , WITTKAMPF FRED H.M. , HAUER RICHARD N.W. , DE MEDINA ETIENNE O. ROBLES
Published: July 2006

While radiofrequency catheter ablation has proved highly effective in the treafment of various supravenfricular tQchyarrhythmias, resulls in the trentment of ventricular tachycardia invite improvement. Knowledge of lesion growth in vivo might improve understanding of this discrepancy. So far only information from in vitro and in vivo studies using a small 2 mm tip eiectrode is available. Growlh of ventricular radiofrequency lesions created with a 4 mm ahlalion electrode was studied in 11 closed‐chest dogs. Endocardia] ablations were performed at 31 left and 35 right ventricuiar sites at a power setting of 25 Watts and 5, 10, 20, 30 or 60 seconds pulse duration. Macroscopic and histopathologic lesion examination were performed after one week survival. Mean lesion volume increased from 52 mm3 after 5 seconds pulse duration to a maximum 388 mm3 and approximately 7 mm depth after 30 seconds. Lesions were prolate spheroid in form, with a sparing of subendocardial myocardium and maximum lesion diameter at some millimeters depth. Results indicate that catheter positioning at no more tlian 7 mm from the target is required for successful ablation. Due to lesion geometry, subendocardial targets demand even more exact catheter positioning, while subepicardial substrates may not be ammenable to ablation if ventricular wall thickness exceeds 7 mm at the ablation site. Repeated pulses at adjacent sites may be required for ablation of extended arrhytbmogenic areas. Volume at 5 seconds was only approximately 15% of mature lesions. Therefore, the use of a short‘test pulse after careful mapping may be useful to pinpoint the most appropriate site for ablation in discrete pathways.
Catheter Ablation of Ventricular Tachycardia Occurring Late After Myocardial Infarction: A Point‐of‐View
Authors: D'AVILA ANDRÉ , NELLENS PAUL , ANDRIES ERIK , BRUGADA PEDRO
Published: July 2006

A Point‐of‐View. Venfricular tachycardia can be cuntwUed by radiofrequency or chemical ablation of the site of origin of the arrhythmia. However, these techniques are far from being accepted as routine treatment for this problem. This article describes the theoretical and practical background of catheter ablation of ventricuiar tachycardia occurring late after myocardial infarction.
Management of Patients After Catheter Ablation of Ventricular Tachycardia
Authors: GONSKA BERND‐DIETER , CAO KEJIANG , SCHAUMANN ANSELM , DORSZEWSKI AXEL , von zur MÜHLEN FRIEDERIKE , KREUZER HEINRICH
Published: July 2006

The management of patients after catheter ablation of ventricular tachycardia is not well defined. In this article we summarize recently published results and report our own experience. Factors influencing the clinical outcome of these patients and methods to identify patients with an increased risk of recurrence of ventricular tachycardia are discussed. Furthermore, a review is given on current concomitant therapeutic tools including antiarrhythmic drugs and the implantation of an automatic cardioverter defibrillator.
The Effect of Coronary Bypass Graft Surgery for the Prevention of Sudden Cardiac Death: Recurrent Episodes After ICD Implantation and Review of Literature
Authors: AUTSCHBACH RÜDIGER , FALK VOLKMAR , CONSKA BERND‐DIETER , DALICHAU HARALD
Published: July 2006

Sudden cardiac death (SCD) accounts for at least 50% of the mortality of patients with ischemic heart failure. Ventricular arrhythmias are responsible for most cases of sudden cardiac death. There is some evidence that coronary artery bypass graft (CABG) surgery may reduce the incidence of recurrent episodes of SCD by prevention of myocardial ischemia. To test the hypothesis that CABG surgery is effective in the prevention of SCD, we compared the recordings of implantable cardioverter defibrillators (ICD) in patients who underwent ICD implantation alone (n = 64) or ICD implantation and concomitant CABG surgery respectively (n = 11). All patients had experienced out of hospital cardiac arrest. ICD recordings were obtained every 3 months and the number of recurrent episodes of ventricular tachycardia (VT) for each time period was noted. Three months foilowing ICD implantation patients in the surgically treated group had an average of one episode of VT per patient as compared to 2.7 episodes in the nonsurgical group. This difference was observed during the following months as well. However, at nlo time (up to 18 months of follow‐up) this difference reached statistical significance. There were no deaths in the surgically treated group. Although we could not demonstrate a statistical significant difference between the two groups, there was a tendency in the surgically treated group to have less episodes of recurrent VT than in the medically treated group. We, therefore, conclude that survivors of SCD presenting with multivessel coronary artery disease (CAD) should undergo coronary artery bypass grafting to prevent myocardial ischemia as the triggering event for lethal ventricular arrhythmias.
Comparison of Spectral Temporal Mapping to the Time Domain Signal‐Averaged Electrocardiogram in Normal Subjects and in Patients with Coronary Artery Disease and Sustained Ventricular Tachycardia
Authors: MITTLEMAN ROBERT S. , CANDINAS RETO , COLLETT‐WILLEY PAMELA , HUANG S.K. STEPHEN
Published: July 2006

Spectral temporal mapping is a new form of analysis for signal‐averaged electro‐cardiography, which has the goal of improving the sensitivity and specificity of traditional time domain analysis. Our objective in this study was to determine the effectiveness of one form of spectral temporal mapping, in the face of conflicting results that have so far been reported with this approach. We prospec‐tively performed both spectral temporal mapping and time domain analysis on 50 patients with a history of coronary artery disease and inducible sustained monomorphic ventricular tachycardia (Group 1) and on 25 normal subjects with normal electrocardiograms and no history of heart disease (Group 2). We found that for the 40 Group 1 patients without bundle branch block (Group lA), the sensitivity of spectral temporal mapping was lower than that for time domain analysis (45% vs 80%, P < 0.005). The results of spectral temporal mapping for Group lA patients were similar to that for all of Group 1. The sensitivity of spectral temporal mapping was 60% (n = 10) for patients with bundle branch block (Group IB). The specificity noted in Group 2 was 88% by each means of analysis; however, no one In Group 2 had an abnormal finding by time domain and spectral temporal mapping. Attempts to optimize the criteria for an abnormal spectral analysis did not identify criteria that were superior to those currently in use. We conclude that spectral temporal mapping using Haberl's method is inferior to time domain analysis in identifying patients with sustained ventricular tachycardia, but may be of value in conjunction with the traditional approach in identifying normal subjects.
The Anatomical Determinants for the Design of Intracardiac Mapping and Ablation Catheters
Authors: AVITALL BOAZ , HARE JOHN , KRUM DAVID , DHALA ANWER
Published: July 2006

An important factor in the efficient and successful completion of the ablation procedure is the design characteristics of the mapping/ablation catheters. These procedures are often hampered by the inability to maneuver the catheter to the desired location, in part because the catheters only have a single plane deflection capability and are not designed for the specific cardiac anatomical structures that contain the arrhythmogenic substrate. Single and Biplane Deflectable Catheters: Using measurements taken from six normal human cadaver hearts, ablation catheter design characteristics are presented for posterior, posterior septal, lateral, and posterior lateral pathways for retrograde and transseptal approaches. Three catheter designs based on anatomical characteristics were also evaluated. Pigtail Catheter: This catheter adapts to the atrial side of the mitral ring and improves positioning and stability for mapping and ablation of left‐sided accessory pathways. Loop Catheter: This catheter is positioned at the perivalvular tricuspid ring and provides simultaneous mapping and aNation capabilities without the need to move the catheter or the need for additional catheters. Rotating Tip Catheter: The tip of this catheter is made up of three elongated teeth, which were curved 120° apart into the rotating tip electrode. This electrode was designed to negotiate the surfaces of the atrial and intraventricular chambers. It is capable of discrete movements and has a large electrode‐tissue contact area for the ablation of atrial and ventricular arrhythmias. Catheter designs presented in this article are based on the ability of the catheter to adapt to the anatomical location of the arrhythmogenic tissue as well as the maneuverability of the catheter's mapping and ablation elec‐trodes. An anatomical approach to the design of ablation catheter technology is likely to reduce the x‐ray radiation exposure for patient and operator, and may further increase the success rate of the procedure.
Electrode Polarity Is an Important Determinant of Defibrillation Efficacy Using a Nonthoracotomy System
Authors: THAKUR RANJAN K. , SOUZA JOSEPH J. , CHAPMAN PETER D. , TROUP PAUL J. , WETHERBEE JULE N.
Published: July 2006

Experimental and clinical data using epicardial patch electrodes and monophasic waveform suggest that electrode polarity may be an important determinant of defibrillation efficacy. Our objective was to examine the effect of electrode polarity in an animal model using a nonthoracotomy system and monophasic and biphasic waveforms for defibrillation. We examined the effect of lead polarity in 14 pentobarbital anesthetized dogs (21.1 ± 2.4 kg) using monophasic and biphasic shocks and a nonthoracotomy system. Monophasic and single capacitor biphasic shocks of 10‐msec total duration were used. The lead system consisted of a right ventricular catheter electrode with 4‐cm2 surface area and a left chest wall subcutaneous patch electrode with 13.9‐cm2 surface area. Electrode polarities RV(−)‐Patch(+) and RV(+)Patch(−) were tested using both monophasic and biphasic waveforms. Alternating current was used to induce ventricular fibrillation and test shocks were delivered after 10 seconds of ventricular fibrillation. Each polarity configuration for monophasic and biphasic waveforms was tested four times at five different capacitor voltage levels (200–600 V, in 100‐V increments). Defibrillation efficacy curves were constructed using logistic regression analysis for each animal and energies associated with 80% probability of successful defibrillation (E80) were determined. The mean E80 ± SD values were as follows. Monophasic waveform: RV(−)Patch(+) 23.4 ± 7.5 J; RV(+)Patch(−) 20.9 ± 7.9 J(P <0.03). Biphasic waveform: RV(−)Patch(+) 15.8 ± 6.8 J; RV(+)Patch(−) 12.5 ± 6.0 J (P < 0.03). The mean impedance values for both waveforms using either polarity ranged from 65.4 to 67 ohms and were not significantly different. Biphasic waveforms were superior to monophasic (P < 0.01), regardless of lead polarity. For either waveform, reversal of lead polarity in some animals resulted in improved defibrillation efficacy and worsening in others, butasagroup, the RV(+)Patch(−) electrode configuration was superior. Conclusions: These observations suggest that electrode polarity is an important determinant of defibrillation efficacy for nonthoracotomy defibrillation. The optimal electrode configuration cannot be determined a priori, suggesting that alternate polarity configurations should be tested to maximize the defibrillation safety margin.
Short‐and Long‐Term Reproducibility of QT, QTc, and QT Dispersion Measurement in Healthy Subjects
Authors: KAUTZNER JOSEF , YI GANG , CAMM A. JOHN , MALIK MAREK
Published: July 2006

The study investigated interobserver and intrasubject reproducibility of QT interval duration and dispersion measured in standard 12‐lead ECGs recorded at 25 mm/sec. Twenty‐eight healthy volunteers were studied. Each undenvent four ECG recordings, which were performed 1, 7, and 30 days apart. Two independent observers analyzed each ECG record. In each lead with a distinguishable T wave pattern, the RR interval, Q‐peak of T interval, and Q‐end of T interval were measured using a digitizing board with a 0.1‐mm resolution. From each recording the following measures were derived: the maximum, minimum, and mean QT interval; maximum, minimum, and mean heart rate corrected QT interval (QTc); QT and QTc dispersion (the difference between the maximum and minimum QT interval among the 12 leads); and adjusted QT and QTc dispersion (dispersion divided by the square root of the number of leads measured). The interobserver and short‐term (1 day) and long‐term (1 week and 1 month) reproducibility of individual indices was assessed by computing the relative errors and comparing them by a standard sign test. In addition, the distributions of maximum and minimum QTc values among electrocardiographicleads, and the differences between QT‐end and QT‐peak based measurements were investigated. The results showed that: (1) the measurement of the QT interval from standard ECG recordings is feasible and not operator dependent (interobserver relative error <4%); (2) the duration of the QT interval in healthy volunteers is stable and its short‐ and long‐term reproducibility is high (intrasubject relative error < 6%); (3) parameters that characterize dispersion of the QT interval in the 12‐lead ECG are highly nonreproducible, both between subsequent recording (relative error of 25%–35%) and between observers (relative errar 28%–33%), the reproducibility of QT dispersion is significantly lower than that of QT duration (P < 0.01); and (4) the duration of the entire QT interval correlates only weakly with the duration of the Q‐peak of T interval.
Spiral Waves in a Computer Model of Cardiac Excitation
Authors: ABILDSKOV J.A. , LUX ROBERT L.
Published: July 2006

Spiral excitation fronts have been demonstrated in association with reentry in a computer model of propagated excitation. Fronts were initiated by the reentrant circuits but the spiral configurations themselves occurred outside the circuits. Excitation initiated near the initial portion of reentrant circuits propagated greater distances during a particular time period than excitation initiated from later portions of the circuit. This resulted in spiral configuration of excitation fronts in which the front was located at increasing distance from the latest initiating event. Excitation fronts that did not themselves have spiral configurations in certain matrices were identifiable as parts of spiral configurations that occurred when the same reentrant events were present in other matrices. Spiral waves were initiated by either leading circle reentry associated with functional block to propagation or reentry associated with structural obstacles. They also occurred in the presence of initially uniform refractory periods and resulted in self‐sustained reentrant excitation. This however, required particular conditions of excitation such that recovery times constituted a functional block permitting leading circle reentry.
VDD Pacing at Short Atrioventricular Intervals Does Not Improve Cardiac Output in Patients with Dilated Heart Failure
Authors: INNES DONALD , LEITCH JAMES W. , FLETCHER PETER J.
Published: July 2006

Atrial synchronous pacing with short, nonphysiologicai atrioventricular (AV) intervals has been reported to increase cardiac output in selected patients with severe dilated heart failure. The aim of this study was to determine the acute effect of atrial synchronous pacing with short AV intervals in a consecutive series of patients with dilated heart failure. Twelve patients with a mean ejection fraction of 21 %± standard error 2.5% were studied. Pacing catheters were placed in the high right atrium and right ventricular apex and a balloon flotation catheter in the pulmonary artery for measurement of cardiac output. Simultaneous transthoracic echocardiography was performed for measurement of left ventricular filling time and mitral regurgitation. In a randomized crossover design, measurements were made during VDD pacing at programmed AV intervals of 100 and 60 msec and during a control period in sinus rhythm. Left ventricular filling time increased at AV intervals of 100 and 60 msec (mean difference 37 ± 9 and 34 ± 11 msec, respectively, both P < 0.01 compared to control). Despite increases in ventricular filling time, stroke, and cardiac index declined with short atrioventricular intervals (at an AV interval of 60 msec, stroke index fell by 2.1 ± 0.5 mL/m2, P < 0.05 and cardiac index by 125 ± 45 mL/m2; P = NS). Heart rate was unchanged at both AV intervals (78 ± 4.9 at control, 78 ± 5.2 at 100 msec and 79 ± 4.9 beats/min at 60 msec; P = NS). The decrease in stroke index at an AV Interval of 60 msec was inversely related to control left ventricular filling time (r = 0.74; P = 0.01) and ejection fraction (r = 0.69; P = 0.02) and directly related to heart rate (r = 0.77; P < 0.01). The change in stroke index at an AV delay of 60 msec was also inversely related to the change in mitral regurgitation induced by pacing (r = 0.84; P = 0.01). Thus, in a group of patients with stable dilated heart failure, atrial synchronous pacing with short AV intervals did not improve cardiac output. The change in cardiac output with pacing was inversely related to baseline left ventricular function and to the change in mitral regurgitation induced by pacing.
Radiofrequency Ablation of an Accessory Pathway in a Patient with Corrected Ebstein's Anomaly
Authors: KOCHERIL ABRAHAM G. , ROSENFELD LYNDA E.
Published: July 2006

Ebstein's anomaly of the tricuspid valve has a known association with the Wolff‐Parkinson‐White syndrome. Radiofrequency ablation has become the treatment of choice for the latter, but there have been no reports of the feasibility of this procedure after tricuspid valve replacement. We present a patient who first exhibited evidence of intermittent preexcitation and associated symptomatic arrhythmia 9 years after tricuspid valve replacement for Ebstein's anomaly, and describe the challenges posed by this case.
Atrial Late Potentials in Patients with Paroxysmal Atrial Fibrillation Detected Using a High Gain, Signal‐Averaged Esophageal Lead
Authors: VILLANI GIOVANNI Q. , PIEPOLI MASSIMO , CRIPPS TIM , ROSI ALESSANDRO , GAZZOLA UGO
Published: July 2006

High gain, signal‐averaged ECGs using conventional surface lead technique and a transesophageal lead technique were performed in 45 idiopathic paroxysmal atrial fibrillation patients and in 33 normal controls. Both techniques showed increased P wave duration in patients compared with the controls (P < 0.001), but higher P wave amplitudes were obtained using the transesophageal technique compared with surface leads (patients: 169.8 ± 81.7 μV vs 15.8 ± 7.3 μV; P < 0.0005; controls: 163.5 ± 22.1 μV vs 18.5 ± 5.2 μV; P < 0.0005). The signal‐averaged transesophageal lead, but not the surface recordings, identified the presence of atrial late potentials evidenced by lower root wean square voltages in the terminal portion of the P wave: in last 10 seconds, 4.4 ±1.3 μV versus 8.5 ± 3.0 μV; P < 0.001; in last 20 seconds, 7.0 ± 2.3 μV versus 16.0 ± 7.9 μV; P < 0.001; in last 30 seconds, 12.5 ± 5.3 μV versus 23.8 ± 12.8 μV; P < 0.001, in patients with respect to controls. The criterion P wave duration ≥ 110 msec had 85% sensitivity. 100% specificity, and 100% positive predictive value in identifying the patients; the combined criteria P wave duration ≥ 110 msec and root mean square for the last 10 msec ≤ 6.5 showed 80% sensitivity, 100% specificity, and 100% predictive value. The signal‐averaged transesophageal lead produces a higher amplitude signal, which reveals fractionation of atrial activation in atrial fibrillation and allows identification of individuals predisposed to this arrhythmia.
Variability of Left Atrial Bloodflow Predicts Intolerance of Ventricular Demand Pacing and May Cause Pacemaker Syndrome
Authors: SULKE NEIL , CHAMBERS JOHN , SOWTON EDGAR
Published: July 2006

Variability of left and right atrial and left ventncular bloodflow was studied using transthoracic and transesophageal Doppler echocardiography and related to pacemaker mode preference during everyday activity. Bloodflow variability was less at all sites during dual chamber pacing compared to single chamber pacing. However, in patients suffering from pacemaker syndrome and whom prefer DDDR pacing, significantly increased variability of left atrial antegrade (but not retrograde) bloodflow during VVIR pacing compared to DDDR pacing was noted, which was not evident in patients tolerating VVIR mode pacing. This effect was not detected at any other site and suggests that adverse left atrial hemodynamics may result in intolerence to VVI/R mode pacing and might cause pacemaker syndrome.