bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Simultaneous Atrioventricular Pacing on Atrial Refractoriness and Atrial Fibrillation Inducibility: Role of Atrial Mechanoelectrical Feedback
Authors: TSE HUNG‐FAT , PELOSI FRANK , ORAL HAKAN , KNIGHT BRADLEY P. , STRICKBERGER S. ADAM , MORADY FRED 
Published: August 2003

Atrial Mechanoelectrical Feedback.
Introduction: The purpose of this study was to evaluate the effects of an acute increase in atrial pressure on refractoriness (mechanoelectrical feedback) and the vulnerability to atrial fibrillation (AF) and to investigate the effects of autonomic blockade and verapamil on mechanoelectrical feedback in humans. Methods and Results: Right atrial pressure and effective refractory period (ERP) at the right atrial appendage (RAA) and high right atrial septum were measured during sinus rhythm, and during atrial and simultaneous AV pacing at a cycle length of 300 msec, either in the absence (n = 25) or presence (n = 22) of pharmacologic autonomic blockade. In another 15 patients, the protocol was performed before and after infusion of verapamil 0.15 mg/kg. In the absence of autonomic blockade, AV pacing resulted in a higher mean right atrial pressure (11.7 ± 3.3 vs 4.3 ± 3.0 mmHg, P < 0.001) and a shorter atrial RAA ERP (144 ± 23 msec vs 161 ± 21 msec; P < 0.001) compared with atrial pacing; AF was induced more often during AV pacing (87%) than during atrial pacing (20%) and was related directly to the right atrial pressure (r = 0.39, P = 0.004) and indirectly to the RAA ERP (r =−0.42, P < 0.001). The susceptibility to sustained AF was greatly enhanced by autonomic blockade. Verapamil markedly attenuated the shortening of ERP and the propensity for AF that occurred during simultaneous AV pacing. Conclusion: An acute increase in atrial pressure during tachycardia is associated with shortening of atrial refractoriness and a propensity for AF, i.e., atrial mechanoelectrical feedback, which may be enhanced by autonomic blockade and attenuated by calcium channel blockade.
Late Occurrence of Heart Block After Radiofrequency Catheter Ablation of the Septal Region: Clinical Follow‐Up and Outcome
Authors: PELARGONIO GEMMA , FOGEL RICHARD I. , KNILANS TIMOTHY K. , PRYSTOWSKY ERIC N. 
Published: August 2003

Late Occurrence of Heart Block.
Introduction: There are few data regarding the occurrence of delayed heart block at least 24 hours after radiofrequency catheter ablation (RFCA) of AV nodal reentry or posteroseptal accessory pathways (APs). We investigated the late occurrence of heart block in this population, the clinical outcome, and whether findings at electrophysiologic study could have predicted its development. Methods and Results: Two of 418 patients with AV nodal reentry undergoing RFCA using a posterior approach and 1 of 54 patients with RFCA of a posteroseptal AP developed late heart block. Anterograde and retrograde AV nodal conduction before and after RFCA were normal. Patients received 12, 15, and 32 RFCA lesions, respectively, using a mean maximum power of 44 W. The RFCA sites were the posterior septum for posteroseptal AP and the posterior and mid‐septum for patients with AV nodal reentry, with no His electrogram ever recorded at the ablation site. During RFCA, junctional tachycardia occurred with 1:1 VA conduction in the patient with a posteroseptal AP, but occasional intermittent single retrograde blocked complexes were present in both patients with AV nodal reentry. No rapid junctional tachycardia or > 1 consecutive retrograde blocked complex was ever observed during RFCA. Persistent high‐degree AV block with junctional escape developed 2 days after RFCA in the posteroseptal AP patient. A permanent pacemaker was implanted, and normal conduction was noted 16 days after RFCA. Both patients with AV nodal reentry complained of fatigue, mainly on exertion, 3 to 4 days after RFCA, and ECG‐documented exercise‐induced variable AV block was obtained. Because heart block resolved in our initial patient, a prolonged monitoring period was allowed. Symptoms disappeared at 13 and 8 days, and a follow‐up treadmill test showed normal PR interval and no heart block. No recurrence of heart block has been seen in any of these three patients. Conclusion: Late unexpected heart block after RFCA of AV nodal reentry and posteroseptal AP is rare, often resolves uneventfully in 1 to 2 weeks, and no specific electrophysiologic findings predicted its occurrence. Prolonged clinical observation is preferable to immediate pacemaker implantation in such patients.
Role of Structural Complexities of Septal Tissue in Maintaining Ventricular Fibrillation in Isolated, Perfused Canine Ventricle
Authors: IKEDA TAKANORI , KAWASE AYAKA , NAKAZAWA KAZUO , ASHIHARA TAKASHI , NAMBA TSUNETOYO , TAKAHASHI KEI , SUGI KAORU , YAMAGUCHI TETSU 
Published: August 2003

Tissue Structure and VF.
Introduction: It is unclear how the patterns of wavelet propagation during ventricular fibrillation (VF) vary between structurally different tissues. We hypothesized that the structural complexities of septal tissue influence the maintenance of reentrant wavelets in the ventricle. Methods and Results: Endocardial activation patterns during VF were analyzed in the isolated, perfused canine right ventricular (RV) free wall (n = 9), interventricular septum (n = 5), and left ventricular (LV) free wall (n = 6) using a computerized mapping system (2‐mm resolution) with 120‐msec consecutive windows. Each tissue sample was cut progressively to reduce the tissue mass until the VF was terminated. More wavelets were seen in the septa than in the RV and LV free walls at baseline (P = 0.004), and VF in the septa displayed a shorter cycle length than in the RV and LV free walls (P = 0.017). As the tissue mass decreased, VF became successively more organized in all regions: the number of wavelets decreased and the cycle length of VF lengthened. Single and “figure‐of‐eight” stationary, reentrant wavelets often were mapped after tissue mass reduction in the RV free walls and rarely in the LV free walls, but they were not observed in the septa. Less critical mass was required to maintain VF in the septa than in the RV and LV free walls (P = 0.0006). Gross anatomic and histologic examinations indicated that the tissue structure of the septa is more complex than that of the RV and LV free walls. Conclusion: VF activation patterns with progressive reduction of tissue mass differ for the septum and the ventricular free walls. The structural complexities of the septal tissue influence the maintenance of fibrillation in the ventricle.
Pacing During Ventricular Fibrillation: Factors Influencing the Ability to Capture
Authors: NEWTON JONATHAN C. , HUANG JIAN , ROGERS JACK M. , ROLLINS DENNIS L. , WALCOTT GREGORY P. , SMITH WILLIAM S. , IDEKER RAYMOND E. 
Published: August 2003

Pacing During Ventricular Fibrillation.
Introduction: Recent studies showed that pacing atrial and ventricular fibrillation (VF) is possible. The studies presented here determined which parameters influence the efficacy of a pacing train to capture fibrillating ventricular myocardium. Electrode type, current strength, order of pacing trains, polarity, and VF morphology preceding the pacing trains were investigated. Methods and Results: A 504‐electrode recording plaque sutured to the right ventricle of pig hearts was used to record the activations of VF and those resulting from the pacing stimulation. Capture of VF by pacing was determined by observing an animated display of the first temporal derivative of the electrograms. A series of electrodes in a line captured the heart more frequently during VF than did a point electrode. Increasing the current strength to 10× diastolic pacing threshold increased the incidence of capture, but increasing this strength further did not. The second or third train of 40 stimuli had greater capture rates than did the first train during the same VF episode. Anodal and cathodal unipolar, and bipolar stimulation were equally efficacious in capturing VF. VF activation during the 1‐second interval preceding pacing was more organized for pacing trains that captured than those that did not. The highest incidence of capture, 46% to 61% of pacing trains, occurred with a line of electrodes at 10× diastolic pacing threshold delivered by the second or third train. Conclusion: The probability of a pacing train capturing fibrillating myocardium can be influenced by the pacing protocol parameters.
Verapamil Prevents Stretch‐Induced Shortening of Atrial Effective Refractory Period in Langendorff‐Perfused Rabbit Heart
Authors: ZARSE MARKUS , STELLBRINK CHRISTOPH , ATHANATOU EVANGELIA , ROBERT JENS , SCHOTTEN ULRICH , HANRATH PETER 
Published: August 2003

Verapamil Prevents Stretch‐Induced AERP Shortening.
Introduction: Atrial dilation and rapid pacing reduce atrial effective refractory periods (AERPs), thereby increasing the susceptibility to sustained atrial fibrillation (AF) in Langendorff‐perfused rabbit hearts. It is unclear whether similar pathophysiologic mechanisms are operative in short‐term electrophysiologic changes caused by dilation and rapid pacing. Therefore, we analyzed whether both forms of short‐term electrophysiologic changes are similarly affected by pharmacologic interventions acting on different potential mechanisms underlying these changes. Methods and Results: Thirty Langendorff‐perfused rabbit hearts underwent a protocol with stepwise increase of intra‐atrial pressure from 0 to 12 cmH2O followed by 10 minutes of rapid pacing at 4 cmH2O. The protocol was repeated after addition of glibenclamide (10 μ mol/L, n = 7), cariporide (1 μ mol/L, n = 7), or verapamil (1 μ mol/L, n = 9). In the basal state, increase of intra‐atrial pressure from 0 to 12 cmH2O decreased AERPs from 85 ± 11 to 55 ± 9 msec (P < 0.01), rapid pacing at low intra‐atrial pressure (4 cmH2O) decreased AERP to a similar extent, from 81 ± 11 to 60 ± 10 (P < 0.01). At higher intra‐atrial pressure, decrease of AERP was more pronounced (10 cmH2O: 37 ± 2 msec) (n = 7). Addition of verapamil decreased basal AERP from 86 ± 10 msec to 68 ± 11 msec (P < 0.05). Short‐term electrophysiologic changes due to atrial dilation were abolished; changes due to rapid pacing were reduced but still present. Glibenclamide and cariporide had no significant effect. Conclusion: Langendorff‐perfused rabbit heart is a suitable model for studying short‐term electrophysiologic changes due to both rapid pacing and atrial dilation. AERPs are shortened to a similar extent by both mechanisms, whereas a combination of the two leads to more pronounced AERP reduction. Calcium overload plays a crucial role in short‐term electrophysiologic changes caused by atrial dilation, whereas atrial ischemia or acidosis has no significant impact.
Species Plays an Important Role in Drug‐Induced Prolongation of Action Potential Duration and Early Afterdepolarizations in Isolated Purkinje Fibers
Authors: LU HUA RONG , MARIËN ROGER , SAELS ANN , DE CLERCK FRED 
Published: August 2003

Species and Drug‐Induced Long APD and EADs.
Introduction: Although isolated Purkinje fibers (PFs) often are used to evaluate the electrophysiologic effects of new drugs in terms of prolongation of action potential duration (APD) and induction of early afterdepolarizations (EADs), species differences in this respect remain elusive. We evaluated potential species‐specific differences in drug‐induced prolongation of APD and EADs in isolated PF from various species. Methods and Results: Using a microelectrode technique, PFs (n = 7 to 11 per species) were isolated from hearts of rabbits, guinea pigs, dogs, swine, goats, or sheep, superperfused in Tyrode's solution with dofetilide (1 × 10−8 M) or quinidine (1 × 10−5 M) for 25 minutes, and stimulated at 1 Hz for 20 minutes and at 0.2 Hz for another 5 minutes. Dofetilide increased APD at 90% repolarization (APD90) at 1 Hz by 83% (rabbit), 24% (guinea pig), 65% (dogs), 18% (swine), 61% (goat), and 30% (sheep), and prolonged APD90 at 0.2 Hz by 187% (rabbit), 31% (guinea pig), 154% (dog), 17% (swine), 61% (goat), and 8% (sheep). Similarly, quinidine changed APD90by 93% (rabbit), 0% (guinea pig), 16% (dog), −3% (swine), 0% (goat), and −24% (sheep) at 1 Hz, and by 124% (rabbit), 15% (guinea pig), 53% (dog), 17% (swine), 11% (goat), and −39% (sheep) at 0.2 Hz in PF. During superfusion of dofetilide or quinidine, EADs occurred in most preparations in rabbit PFs at 0.2 Hz, but not in any of the PFs from other species at 0.2 Hz. Conclusion: Our study demonstrates that species plays an important role in the response of PF to drug‐induced prolongation of APD and EADs. Rabbit PFs constitute the most sensitive model for detecting drug‐induced, potential long APD and proarrhythmogenic effects in vitro.
Distribution of Patients′ Paroxysmal Atrial Tachyarrhythmia Episodes: Implications for Detection of Treatment Efficacy
Authors: KAEMMERER WILLIAM F. , ROSE M. SARAH , MEHRA RAHUL 
Published: August 2003

Distribution of Paroxysmal Atrial Tachyarrhythmia Episodes.
Introduction: Clinical trials of treatments for paroxysmal atrial tachyarrhythmia (pAT) often compare different treatment groups using the time to first episode recurrence. This approach assumes that the time to the first recurrence is representative of all times between successive episodes in a given patient. We subjected this assumption to an empiric test. Methods and Results: Records of pAT onsets from a chronologic series of 134 patients with dual chamber implantable defibrillators were analyzed; 14 had experienced > 10 pAT episodes, which is sufficient for meaningful statistical modeling of the time intervals between episodes. Episodes were independent and randomly distributed in 9 of 14 patients, but a fit of the data to an exponential distribution, required by the stated assumption, was rejected in 13 of 14. In contrast, a Weibull distribution yielded an adequate goodness of fit in 5 of the 9 cases with independent and randomly distributed data. Monte Carlo methods were used to determine the impact of violations of the exponential distribution assumption on clinical trials using time from cardioversion to first episode recurrence as the dependent measure. In a parallel groups design, substantial loss of power occurs with sample sizes < 500 patients per group. In a cross‐over design, there is insufficient power to detect a 30% reduction in episode frequency even with 300 patients. Conclusion: Clinical trials that rely on time to first episode recurrence may be considerably less able to detect efficacious treatments than may have been supposed. Analysis of multiple episode onsets recorded over time should be used to avoid this pitfall.
Do Current Dual Chamber Cardioverter Defibrillators Have Advantages Over Conventional Single Chamber Cardioverter Defibrillators in Reducing Inappropriate Therapies? A Randomized, Prospective Study
Authors: DEISENHOFER ISABEL , KOLB CHRISTOF , NDREPEPA GJIN , SCHREIECK JÜRGEN , KARCH MARTIN , SCHMIEDER SEBASTIAN , ZRENNER BERNHARD , SCHMITT CLAUS 
Published: August 2003

Dual Chamber vs Single Chamber Cardioverter Defibrillators.
Introduction: Supraventricular tachyarrhythmias are the main cause of inappropriate therapies in patients with conventional single chamber implantable cardioverter defibrillators (VVI‐ICD). It was anticipated that dual chamber cardioverter defibrillators (DDD‐ICD), with their capacity to analyze atrial and ventricular rhythm, could substantially reduce inappropriate therapies. Methods and Results: Our prospective study included 92 patients (87 men; mean age 61 ± 12.7 years) who were randomly assigned to a VVI‐ICD (45 patients) or a DDD‐ICD (47 patients). Both groups were followed for 7.5 ± 3.5 and 7.6 ± 4.1 months, respectively. During the follow‐up period, overall 725 ventricular tachycardia (VT)/ventricular fibrillation (VF) episodes were recorded in 45 (49%) of 92 patients. Of these episodes, 404 (56%) occurred in the VVI‐ICD group and 321 (44%) episodes occurred in the DDD‐ICD group. Twenty‐three (51%) patients in the VVI‐ICD group and 22 (47%) patients in the DDD‐ICD group (P = 0.8) developed VT/VF. Overall, 73 (10%) of 725 treated episodes were inappropriate in 6 (13%) patients in the VVI group and in 10 (21%) patients in the DDD‐ICD group (P = 0.2). There were 22 (31%) inappropriately treated episodes in the VVI‐ICD group and 51 (69%) in the DDD‐ICD group. Thirty‐two of the 51 inappropriate episodes in the DDD‐ICD patients resulted from intermittent atrial sensing problems that led to failure of the respective dual chamber algorithms. Nonfatal complications occurred in 6 (13%) patients in the VVI‐ICD group and in 3 (6%) patients in the DDD‐ICD group (P = 0.7). Conclusion: We conclude that the implanted DDD‐ICD and conventional VVI‐ICD are equally safe and effective for therapy of life‐threatening ventricular tachyarrhythmias. Although DDD‐ICDs allow better rhythm classification, the applied detection algorithms do not offer benefits in avoiding inappropriate therapies during supraventricular tachyarrhythmias.
Use of Correlation Waveform Analysis in Discrimination Between Anterograde and Retrograde Atrial Electrograms During Ventricular Tachycardia
Authors: SABA SAMIR , GORODESKI REVITAL , YANG SHAWN , MacADAM DAVID , LINK MARK S. , HOMOUD MUNTHER K. , ESTES N.A. MARK , WANG PAUL J. 
Published: August 2003

Correlation Waveform Analysis.
Introduction: Discriminating between ventricular tachycardia (VT) with 1:1 ventriculoatrial association and sinus tachycardia can be difficult, even when assisted by intracardiac tracings. In this study, we used a new computer algorithm to perform correlation waveform analyses on intracardiac atrial electrograms to help distinguish between VT and sinus tachycardia. Methods and Results: Electrophysiologic studies of 28 patients (22 men; age 66 ± 14 years) with inducible VT and mean ejection fraction of 37% ± 16% were analyzed. A template of an intracardiac high right atrial electrogram was obtained during sinus rhythm (SR). Atrial electrograms during SR and VT were compared with the template using the new algorithm, and correlation coefficients (ρ) were generated. The correlation coefficient of SR beats with the template was 96.4% ± 3.4%. During VT with AV dissociation and persistent SR, ρ was 94.5% ± 3.7% (P = NS). During VT with 1:1 retrograde conduction, ρ was 70.6% ± 11.3% (P < 0.0001). At a cutoff of 85%, ρ had positive and negative predictive values of 99% and 96%, respectively. Conclusion: Our findings indicate that the new algorithm can reliably separate between anterograde and retrograde atrial activation during VT. It can, therefore, discriminate between sinus tachycardia and VT with 1:1 ventriculoatrial conduction and may be useful in preventing inappropriate shocks from dual chamber defibrillators.
Use of a Saline‐Irrigated Tip Catheter for Ablation of Ventricular Tachycardia Resistant to Conventional Radiofrequency Ablation: Early Experience
Authors: NABAR ASHISH , RODRIGUEZ LUZ MARIA , TIMMERMANS CARL , WELLENS HEIN J. J. 
Published: August 2003

Irrigated Tip Catheter for Ablation of Resistant VT.
Introduction: Radiofrequency (RF) catheter ablation of ventricular tachycardia (VT) may fail if the critical isthmus is located intramyocardially or epicardially. The design of a saline‐irrigated tip (SIT) catheter (Thermo‐Cool™, Cordis‐Webster) involves active cooling of the tip electrode, which allows creation of larger ablation lesions. Methods and Results: Eight patients (6 men, age 59 ± 12 years) in whom the clinical target VT (cycle length 430 ± 97 msec) could not be ablated using a conventional 4‐mm tip RF ablation catheter underwent additional attempts to ablate this VT using a SIT catheter. Six patients had an old myocardial infarction, 1 patient had a dilated cardiomyopathy, and 1 patient had a structurally normal heart. Ablation of the clinical target VT using a SIT catheter was attempted from the left ventricle in 6 (septal, posterobasal, and inferior: 2 each) and from the right ventricle in 2 patients (both septal), by entrainment (n = 6), activation (n = 1), or pace mapping (n = 1). A mean of 6 ± 5 (range 2 to 15) pulses were delivered. Target VT ablation was successful in 5 patients (63%). After successful ablation, at a mean follow‐up of 6.5 ± 4 months and while taking antiarrhythmic drugs, all 5 patients were free of VT recurrences. Conclusion: The clinical target VT could be ablated using a SIT catheter in 5 (63%) of the 8 patients in whom ablation using a conventional RF catheter was unsuccessful. In the 2 patients with septal VT, a biventricular approach to mapping and ablation was required.
Role of Transisthmus Conduction Intervals in Predicting Bidirectional Block after Ablation of Typical Atrial Flutter
Authors: ORAL HAKAN , STICHERLING CHRISTIAN , TADA HIROSHI , CHOUGH STEVEN P. , BAKER ROBERT L. , WASMER KRISTINA , PELOSI FRANK , KNIGHT BRADLEY P. , MORADY FRED , STRICKBERGER S. ADAM 
Published: August 2003

Isthmus Block During Atrial Flutter Ablation.
Introduction: Complete bidirectional cavotricuspid isthmus block is the endpoint for ablation of typical atrial flutter. The purpose of this study was to determine whether the extent of prolongation of the transisthmus interval after ablation predicts complete bidirectional block. Methods and Results: Fifty‐seven consecutive patients underwent 60 ablation procedures for isthmus‐dependent atrial flutter. The clockwise and counterclockwise transisthmus intervals were determined before and after ablation during pacing from the low lateral right atrium and the coronary sinus. Bidirectional block was achieved with ablation in 55 (96%) of 57 patients. The transisthmus intervals before ablation and after complete transisthmus block were 100.3 ± 21.1 msec and 195.8 ± 30.1 msec, respectively, in the clockwise direction (P < 0.0001), and 98.2 ± 24.7 msec and 185.7 ± 33.9 msec, respectively, in the counterclockwise direction (P < 0.0001). An increase in the transisthmus interval by ≥ 50% in both directions after ablation predicted complete bidirectional block with 100% sensitivity and 80% specificity. The positive and negative predictive values were 89% and 100%, respectively. The diagnostic accuracy of ≥ 50% prolongation in the a transisthmus interval was 92%. Conclusion: Prolongation of the transisthmus interval by ≥ 50% in the clockwise and counte clockwise directions is associated with a high degree of diagnostic accuracy and an excellent negative predictive value in determining complete bidirectional transisthmus block. This may be a useful and simple adjunctive criterion for assessment of complete transisthmus conduction block.