bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Atrial‐His Intervals During Tachycardia and Atrial Pacing in Patients with Long RP Tachycardia
Authors: MAN K. CHING , NIEBAUER MARK , DAOUD EMILE , STRICKBERGER S. ADAM , KOU WILLIAM , WILLIAMSON BRIAN D. , MORADY FRED 
Published: May 2007

Long RP Tachycardia. Introduction: The purpose of this study is to describe a simple and reliable diagnostic maneuver that allows for the rapid differentiation of atypical AV nodal reentrant tachycardia (AVNRT) from other causes of long KP tachycardia. Long RP tachycardias may he caused by atypical AVNRT, orthodromic reciprocating tachycardia (ORT) involving a slowly conducting retrograde accessory pathway, or atrial tachycardia. The differentiation of atypical AVNRT from ORT or atrial tachycardia may be difficult, especially when the differential diagnosis includes a posteroseptal accessory pathway or an atrial tachycardia arising in the posteroseptal right atrium. Methods and Results: Twelve patients with atypical AVNRT, 21 with ORT, and 12 with an atrial tachycardia diagnosed using conventional criteria were enrolled In this study. The atrial‐His (AH) interval was measured at the His‐bundle position during the tachycardia and during atrial pacing from the high right atrium at the tachycardia cycle length in the setting of sinus rhythm. In patients with atypical AVNRT, the mean AH interval was 69 msec ± 50 msec (± SD) longer during high right atrial pacing than during the tachycardia (P < 0.001). In 10 of 12 patients with atypical AVNRT, the AH interval during atrial pacing was more than 40 msec longer than the AH interval measured during the tachycardia. In contrast, in patients with ORT or atrial tachycardia, the differences in AH interval between atrial pacing and tachycardia were never more than 20 and 10 msec, respectively. Conclusion: The difference in the AH interval between atrial pacing and the tachycardia allows a simple and rapid means of differentiating atypical AVNRT from other types of long RP tachycardias.
Effects of Optical Enantiomers CK‐4000(S) and CK 4001(R) on Defibrillation and Enhancement of Shock‐ Induced Extension of Action Potential Duration
Authors: BEATCH GREGORY N. , DICKENSON DAVID R. , TANG ANTHONY S.‐L. 
Published: May 2007

Antiarrhythmic Drugs and DFT. Introduction: Class III antiarrhythmics have been reported to lower defibrillation threshold (DFT); however, the mechanism(s) of this effect is unknown. Recent evidence suggests that DFT strength DC shocks may terminate reentrant arrhythmias through prolongation of action potential duration and refractory periods. Since Class III antiarrhythmic drugs prolong repolarization, we examined the hypothesis that these drugs enhance shock‐induced action potential duration extension (APDE), which might contribute to lowering of DFT. Methods and Results: In order to investigate the specificity of drug effects on action potential repolarization following a shock, an optical enantiomer with mixed β‐blocking and Class III effects (CK‐4000) and its enantiomer with “pure” Class III antiarrhythmic effects (CK‐4001) were compared against placebo in a canine defibrillation model (n = 8 per group). At the 3 mg/kg dose, the enantiomers nonstereoselectively lowered DFT voltage by 19 ± 15% (CK‐4000, P < 0.05 compared to placebo) and 25 ± 12% (CK‐4001, P < 0.05 compared to placebo), indicating that Class III antiarrhythmic actions alone were sufficient for this effect. Similarly, CK‐4000 and CK‐4001 at 3 mg/kg enhanced APDE (P < 0.01 compared to placebo) by 20 ± 11% and 24 ± 17%, respectively. APDF prolongation significantly correlated with reduction in DFT voltage for both CK‐4000 (r = ‐0.55, P < 0.03) and CK4001 (r = ‐0.63, P < 0.01). At 3 mg/kg, the enantiomers stereoselectively prolonged action potential duration (APD75) by an average of 37 ± 14% (CK‐4000, P < 0.001) and 23 ± 14% (CK‐4001, P < 0.001), and ventricular effective refractory period (VERP) by 38 ± 15% (CK‐4000, P < 0.01) and 27 ± 13% (CK‐4001, P < 0.05). Prolongations of APD75 and VERP did not correlate with reductions of DFT in individual dogs. Conclusions: These results show that Class III antiarrhythmics and DFT strength shocks additively delay repolarization, which suggests that drug enhancement of APDE may contribute to their effects on DFT.
Serial Defibrillation Threshold Measures in Man: A Prospective Controlled Study
Authors: POOLE JEANNE E. , BARDY GUST H. , LEE DOLACK G. , KUDENCHUK PETER J. , ANDERSON JILL , JOHNSON GEORGE 
Published: May 2007

Serial DFT Measures in Man. Introduction; The defibrillation threshold (DFT) may change throughout the first year following implantation of a cardioverter defibrillator, but it remains uncertain if changes are a consequence of changes in clinical condition or are related to fundamental alterations at the electrode‐tissue interface. The purpose of this study was to evaluate the extent and time course of DFT changes over the first year following implantable cardioverter defibrillator (ICD) surgery when extraneous clinical and device variables potentially affecting the DFT were excluded. Methods and Results.: We prospectively enrolled 61 patients undergoing epicardial or non‐thoracotomy/transvenous ICD therapy into a series of follow‐up studies where the DFT was measured at implant and at 1, 6,12, and 52 weeks following implantation in a uniform manner. Stored energy DFT was measured and recorded for all patients. Patient exclusion criteria were: (1) inability to complete all five measures of the DFT; (2) institution of Class I or Class III antiarrhythmic drugs at any time during the study; (3) lead system changes (relocation or new leads) or programming changes in pulse width or current pathway; or (4) development of a significant change in their clinical status, such as decompensated congestive heart failure or acute ischemia. Only 20 of the 61 patients satisfied the criteria required to complete the study. Two of the excluded patients developed high DFTs, which required reprogramming of the current pathway. Eight patients had an epicardial lead system, and 12 had a nonthoracotomy lead system. The rise in DFT over the first 12 weeks was significant for the eight epicardial lead system patients (P = 0.05) and for the 12 nonthoracotomy lead system patients (P = 0.004). The peak rise in DFT occurred at 1 week for the patients with an epicardial lead system (3.4 ± 1.8 J to 7.9 ± 3.8 J) and at 12 weeks for the patients with a transvenous lead system (10.3 ± 5.3 J to 16.1 ± 7.4 J). Conclusions: This study confirms a transient significant rise in the DFT in the first 12 weeks following ICD surgery that partially returns to the implant value over the remainder of the year. Because specific clinical and technical variables were excluded from this study, the observations made in this patient population suggest that the rise in DFT may be a consequence of changes at the electrode‐tissue interface.
The Vulnerable Window for Unidirectional Block in Cardiac Tissue:
Authors: SHAW ROBIN M. , RUDY YORAM 
Published: May 2007

Vulnerable Window of Unidirectional Block. Introduction: Unidirectional block is a requisite event in the initiation of reentry in cardiac tissue, but its initiation and behavior in the presence of tissue pathologies remain poorly understood. Previous experimental and theoretical reports on vulnerability to unidirectional block under conditions of reduced cellular coupling and reduced membrane excitability have varied due to differences in experimental and simulation protocols. Methods and Results: We have addressed the issue of vulnerability to unidirectional block using the recent Luo‐Rudy membrane model and computer simulations of propagation in a one‐dimensional cardiac fiber. The vulnerable window (VW) of unidirectional block from premature stimulation is expressed in units of time, VWtime, and as a range of membrane potentials at the stimulus site, VWpot VWpot and VWtime, were quantified over a range of membrane excitability and gap junction resistances (intercellular coupling). With normal membrane excitability and intercellular coupling, VWpot, and VWtime, were small (VWPot, = 0.44 mV, VWtime, = 0.39 msec). A uniform reduction (0.25 ×) in the degree of intercellular coupling increased VWtime, and VWpot, by factors of 3.6 and 4.7, respectively, whereas a uniform decrease (0.25 ×) in membrane excitability (same resulting velocity) increased VWtime, by only a factor of 0.4 and decreased VWpot, to negligible levels. When inhomogeneities in fiber properties were introduced (intercellular coupling and membrane excitability), VWtime, increased more due to inhomogeneity in membrane excitability (VWtime= 4.5 msec) than to inhomogeneity in intercellular coupling (VWtime, = 1.5 msec). The simulations also clarify the dependence of the VW on the dimensions of the stimulating electrode. The length of the stimulating electrode added a factor, equal to the propagation time across the eiectrode length, to the intrinsic VW of the fiber. Conclusions: VWpot, and VWtime, are both important parameters for quantifying vulnerability to unidirectional block. In an environment with uniform distribution of fiber and membrane properties, reduced intercellular coupling bas a greater effect on the VW than reduced membrane excitability. Inhomogeneous reduction of membrane excitability can significantly enhance vulnerability to unidirectional block, much more so than inhomogeneous reduction of intercellular coupling. Theoretically, stimulation at a point should be used to define the VW. Finite electrode dimensions introduce a geometrical factor that affects the measurement of the VW.
Kinetics of Cycle Length Dependence of Ventricular Repolarization:
Authors: RAEDER ERNST A. , ALBRECHT PAUL , PERROTT MICHAEL , COHEN RICHARD J. 
Published: May 2007

Cycle Length Dependence of Repolarization. Introduction: Beat‐to‐beat adaptation of ventricular repolarization duration to cardiac cycle length and autonomic activity has not been previously characterized in the spontaneously beating human heart. Methods and Results: The ECG of 14 healthy subjects was recorded from the supine and upright positions. Autonomic blockade was accomplished by atropine and propranolol. RR and RT intervals were measured by a computer algorithm, and the impulse response (h) from RR to RT computed. In the supine position the maximal adjustment of the RT interval occurred in the first beat following a change in cycle length (hpeak= 17.8 ± 1.6 msec/sec), but continued to be detectable for 3.8 seconds (2.9–4.7 sec). Propranolol attenuated the peak impulse response to 15.8 ± 4.0 msec/sec (P = NS). In the standing position the peak impulse response was increased to 25.2 ± 5.0 msec/sec (P = 0.004 vs supine), and the impulse response duration (hdur) shortened to 1.4 seconds (1.3–1.6). This was reversed by beta blockade (hpeak= 10.7 ± 3.6 [P = 0.005 vs standing]; hdur= 5.5 sec [4.8–6.1]). Parasympathetic and combined autonomic blockade resulted in too little residual heart rate variability to estimate the impulse response accurately. The slope of the regression of δRT and δRR in the supine position was 0.0177 ± 0.0016, which was closely correlated with the peak impulse response (r = 0.91). Conclusions: System identification techniques can assist in characterizing the cycle dependence of veritricular repolarization and may provide new insights into conditions associated with abnormal repolarization.
Diagnostic Clues From the Surfaee ECG to Identify Idiopathic (Fascicular) Ventricular Tachycardia: Correlation with Electrophysiologic Findings
Authors: ANDRADE FERNANDO ROSAS , ESLAMI MASSOUD , ELIAS JORGE , KINOSHITA OSAMU , NAKAZATO YUJI , MARCUS FRANK I. , FRANK ROBERT , TONET JOELCI , FONTAINE GUY 
Published: May 2007

ECG in Idiopathic Fascicular VT. Introduction: An RS interval > 100 msec in precordial leads has been recently described for the diagnosis of ventricular tachycardia (VT). The aim of this study was to assess the value of this criterion when applied to patients with right bundle branch block pattern, left‐axis deviation (fascicular) VT sensitive to verapamil. Methods and Results: Eleven patients (mean age 31 ± 11 years; range 16 to 51) had a mean heart rate of 164 ± 37 beats/min (range 107 to 230) during VT, The QRS complex axis was ‐92°± ‐15° (range ‐80 to ‐115). The mean QRS duration was 121 ± 9 msec (range 105 to 140). The mean RS interval was 67 ± 9 msec (range 60 to 80). Fusion beats were present in 2 patients (18%), and AV dissociation confirmed by electrophysiologic study was found on ECG in 8 (73%) of 11. During tachycardia, the QRS‐H'interval was 19 ± 10 msec (range 10 to 30) in 6 of 11 patients. In seven patients, a fast, unique (or double) presystolic potential lasting 32 msec (range 12 to 40) occurring before the onset of the QRS complex was found at the site of origin of VT, localized in the inferior apical left ventricular septum. In all cases, VT was successfully treated by catheter ablation. Conclusion: A wide QRS complex tachycardia with right bundle branch block and left‐axis deviation sensitive to verapamil observed in a young patient without structural heart disease should not be confused with supraventricular tachycardia with aberrancy but rather suggests the presence of fascicular VT. As opposed to VT associated with structural heart disease, the RS interval is < 80 msec in all precordial leads in all cases. Independent of this parameter, AV dissociation detectable on surface ECG has a sensitivity of 73%, which increases to 82% in the presence of fusion beats.
Junction Potentials and Action Potentials of the Crayfish Myocardium
Authors: HERNANDEZ VICENTE , MENDEZ CARLOS 
Published: May 2007

Junction and Action Potentials. Introduction: The purpose of this investigation was to study the properties of junction and action potentials elicited by nerve stimulation in the absence of the cardiac ganglion in crayfish myocardium. Methods and Results: The cardiac ganglion was surgically removed in isolated crayfish hearts. Electrical stimulation of one of the peripheral anterolateral nerves provided isolated junction potentials and action potentials free of the usual postspike bursts of junction potentials. The single junction potentials displayed amplitudes of up to 25 mV and slow exponential decay; the mean time constant was 170 ± 13 msec (xT ± SD). In fully recovered tissue, the junction potentials triggered action potentials free of repetitive subthreshold discharges. Tetrodotoxin did not alter the amplitude or shape of action potentials initiated by direct electrical stimulation of the muscle cells. Calcium channel blocking agents such as Cd2+ and Ni2+ eliminated the action potentials but not the junction potentials. Tetraethylammonium markedly prolonged the action potential duration. Conclusions: Our data suggest that: (1) A slow decay of the junction potentials may result from the disappearance of the neurotransmitter; this process also accounts for the late slow repolarization of the final part of the action potentials; (2) The equilibrium potential of the junction potentials is close to 0 mV; (3) The upstroke of the action potentials is carried by calcium currents; (4) The fast repolarization phase of the action potentials is likely caused by the delayed rectifier; and (5) The refractory phase outlasts the duration of the action potential.
Endoscopy‐Assisted Radiofrequency Ablation Around the Coronary Sinus Ostium in Dogs:
Authors: TANAKA KAZUSHI , CHA YONG‐MEI , FUJIMURA OSAMU 
Published: May 2007

Endoscopy for Ablation Around the CS Ostium. Introduction: Radiofrequency ablation of the slow pathway can prolong atrioventricular (AV) nodal properties and RR intervals during atrial fibrillation (AF) in many patients with AV nodal reentrant tachycardia. However, it is not well elucidated whether these changes are related to the presence of dual AV nodal pathway physiology. The aim of this study was to evaluate changes of AV nodal properties and RR intervals during AF caused by ablation of two specific areas in dogs. Methods and Results: Assisted by fiberoptic endoscopy, linear lesions were created between the coronary sinus ostium and tricuspid valve annulus (area 1) or posterior to the ostium (area 2) in 15 dogs. Three additional dogs served as controls. The measurements were made under autonomic blockade. Catheter ablation could be assisted in all dogs by means of endoscopy. Linear lesions were confirmed at autopsy. AV nodal parameters and RR intervals showed no overall changes. Individual data showed that ablation of area I resulted in modification of AV nodal properties in 54.5% (facilitation in 363% and inhibition in 18.2%), whereas ablation of area 2 induced changes in 50% (facilitation in 10% and inhibition in 40%). The RR intervals were shortened in 33.3% and 20% and prolonged in 44.5% and 40% after ablation of areas 1 and 2, respectively. The RR intervals during AF correlated well with the Wenckebach cycle length and the AV node functional refractory period before and after ablation (r = 0.78 to 0.94, P < 0.01 for each). Conclusions: Ablation of the two specific areas around the coronary sinus ostium was equally effective in modifying AV nodal properties and the ventricular response during AF without dual AV nodal pathway physiology. The ventricular rate to AF after ablation correlated well with the residual AV nodal properties.
Radiofrequency Catheter Ablation of Idiopathic Ventricular Tachycardia Originating in the Anterior Fascicle of the Left Bundle Branch
Authors: RODRIGUEZ LUZ‐MARIA , SMEETS JOEP L.R.M. , TIMMERMANS CARL , TRAPPE HANS J. , WELLENS HEIN J.J. 
Published: May 2007

Ablation of an Anterior Fascicular Idiopathic VT. Introduction: Idiopathic ventricular tachycardia (VT) originating in or close to the anterior fascicle of the left bundle is rare. A patient with no structural heart disease and VT with a right bundle branch block configuration and right‐axis deviation underwent an electrophysiologic examination. Methods and Results: Both endocardial activation mapping during VT and pacemapping were performed via a transseptal approach to localize the site of origin of the VT. Endocardial recordings of the His bundle and the posterior and anterior fascicles of the left bundle branch revealed an origin of the VT in or close to the anterior fascicle. The Purkinje potential at that site preceded the QRS complex by 20 msec, with pacemapping showing an optimal match between the paced rhythm and the clinical VT. RF energy delivered at this site terminated the VT. A left anterior nemiblock appeared after RF ablation. Ten months later, the patient is free from recurrences of VT. Conclusions: Idiopathic VT originating in or close to the anterior fascicle was cured by RF ablation. A Purkinje potential preceding the QRS during tachycardia and an optimal pacemap were used to guide RF ablation.
PR/RR Interval Ratio During Rapid Atrial Pacing:
Authors: BAKER JAMES H. , PLUMB VANCE J. , EPSTEIN ANDREW E. , NEA KAY G. 
Published: May 2007

Method for Confirming Slow Pathway Conduction. Introduction: Although the AV conduction curve in patients with AV nodal reentrant tachycardia (AVNRT) is usually discontinuous, many patients with this arrhythmia do not demonstrate criteria for dual AV nodal pathways. During rapid atrial pacing, the PR interval often exceeds the pacing cycle length when there is anterograde conduction over the slow pathway and AVNRT is induced. The purpose of this prospective study was to determine the diagnostic value of the ratio of the PR interval to the RR interval during rapid atrial pacing as an indicator of anterograde slow pathway conduction in patients undergoing electrophysioiogic testing. Methods and Results: The PR and RR intervals were measured during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction in four study groups: (1) patients with inducible AV nodal reentry and the classical criterion for dual AV nodal pathways during atrial extrastimulus testing (AVNRT Group 1); (2) patients with inducible AV nodal reentry without dual AV nodal pathways (AVNRT Group 2); (3) control subjects ≤ 60 years of age without inducible AV nodal reentry; and (4) control subjects > 60 years of age without inducible AV nodal reentry. For both groups of patients with inducible AV nodal reentry, AV conduction was assessed before and after radiofrequency ablation of the slow AV nodal pathway. Before slow pathway ablation, the PR/RR ratio exceeded 1.0 in 12 of 13 AVNRT Group 1 patients (mean 1.27 ± 0.21) and 16 of 17 AVNRT Group 2 patients (mean 1.18 ± 0.15, P = NS Group 1 vs Group 2). After slow pathway ablation, the maximum PR/RR ratio was < 1.0 in all AVNRT patients (Group 1 = 0.59 ± 0.08, P < 0. 00001 vs before ablation: Group 2 = 0.67 ± 0.11; P < 0.00001 vs before ablation). Among both groups of control subjects, the PR/RR ratio was > 1.0 in only 3 of 27 patients with no relation to patient age. Conclusion: The ratio of the PR interval to the RR interval during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction provides a simple and clinically useful method for determining the presence of slow AV nodal pathway conduction. This finding may be particularly useful in patients with inducible AV nodal reentry without dual AV nodal physiology on atrial extrastimulus testing.
Retrograde Migration of the Site of Functional Block:
Authors: TCHOU PATRICK J. , TROHMAN RICHARD , KIDWELL GREGORY , MEHDIRAD ALI A. 
Published: May 2007

Retrograde Migration of Functional Block. Introduction: Functional bundle branch blocks during supraventricular tachycardia have been described, and their sustainment has been attributed to concealed conduction. Such blocks frequently resolve spontaneously, but the electrophysiologic mechanism of resolution bas not been well described. This report describes the resolution of functional bundle branch block through proximal migration of the site of block. Methods and Results: During electrophysiologic study of a patient with reentrant antidromic tachycardia via an atriofascicular accessory pathway, functional retrograde right bundle branch block could be readily induced following tachycardia initiation with right ventricular apical pacing. Resolution of this block was associated with shortening of the tachycardia cycle length. Electrogram recordings along the right bundle branch during tachycardia determined that resolution of the functional retrograde right bundle branch block was associated with migration of the site of block from the distal to the proximal right bundle. When the site of block was directly at the recording site, both anterograde and retrograde activation of the right bundle was demonstrated. Conclusion: Migration of the site of block is a mechanism of resolution for functional conduction blocks maintained by concealed conduction.
Catheter Ablation of Coexistent Bundle Branch and Interfasdcular Reentrant Ventricular Tachycardias
Authors: BERGER RONALD D. , ORIAS DAVID , KASPER EDWARD K. , CALKINS HUGH 
Published: May 2007

Bundle Branch and Interfascicular Reentry. Introduction: Bundle branch reentry and interfascicular reentry are potential mechanisms of ventricular tachycardia in the setting of a dilated cardiomyopathy. We report a patient with myotonic dystrophy who presented with near syncope, in whom both of these mechanisms were present, leading to two different wide complex tachycardias. Methods and Results: Electrophysiologic study demonstrated Infra‐Hisian conduction system disease and inducible bundle branch reentrant ventricular tachycardia. Catheter ablation of the right bundle eliminated bundle branch reentry. However, following this, the patient had inducible interfascicular reentry, which subsequently occurred spontaneously while still hospitalized. Catheter ablation of the left posterior fascicle successfully eliminated this second tachycardia, and the patient has had no further arrhythmias. Conclusions: This report is of an unusual patient with coexistent bundle branch reentry and interfascicular reentry producing two different forms of sustained ventricular tachycardia. This is the first report of catheter ablation of the left posterior fascicle for elimination of conduction system reentry.