bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accuracy of the Unipolar Electrogram for Identification of the Site of Origin of Ventricular Activation
Authors: MAN K. CHING , DAOUD EMILE G. , KNIGHT BRADLEY P. , BAHU MARWAN , WEISS RAUL , ZIVIN ADAM , SOUZA S. JOSEPH , GOYAL RAJIVA , STRICKBERGER S. ADAM , MORADY ERED 
Published: April 2007

Unipolar Electrogram. Introduction: The purpose of this study was to determine the accuracy of the unipolar electrogram for identifying the earliest site of ventricular activation. The earliest site of ventricular activation may be identified with the unipolar electrogram by the absence of an R wave. However, the accuracy of this technique is unknown. Methods and Results: A single ventricular premature complex was induced mechanically at the tip of an electrode catheter to simulate a ventricular premature depolarization site of origin. Unipolar electrograms were recorded from the right ventricular septum at the tip electrode and at 2, 5, 8, and 11 mm from the electrode tip in 20 patients. No R waves were detected at the ventricular premature depolarization site of origin. R waves were detected in 4 of 20 patients (20%) at 2 mm from the tip electrode and 7 of 20 patients (35%) at 5, 8, and 11 mm from the tip electrode. An R wave was not observed at distances ≤ 11 mm from the site of tachycardia origin in 13 of 20 patients (65%). Conclusions: While an R wave in the unipolar electrogram can he seen as close as 2 mm from the site of impulse origin, the absence of an R wave as an indicator of the site of impulse origin in the right ventricle is highly inaccurate. Therefore, the absence of an R wave in the unipolar electrogram is unlikely to be an adequate guide for identification of an effective target site for ablation of right ventricular tachycardia.
Epicardial Maps of Atrial Fibrillation After Linear Ablation Lesions
Authors: SIH HARIS J. , BERBARI EDWARD J. , ZIPES DOUGLAS R 
Published: April 2007

Maps of AF After Ablation. Introduction: The purpose of this study was to investigate the mechanisms by which atrial linear ablation lesions eliminate atrial fibrillation (AF). Methods and Results: With an array of 112 unipole, epicordial maps of electrically induced AF in 6 dogs (acute group), self‐sustained AF in 6 dogs (chronic group), and sinus rhythm and atrial pacing in 3 dogs (control group) were analyzed before and after creating linear radiofrequency ablation lesions in both atria that eliminated the AF. In the acute and chronic groups, activation maps showed multiple wavelets with complex patterns of activation and reentry during AF. Conduction velocity and the number, size, and complexity of wavelets did not change, whereas median fibrillatory cycle length increased with the number of linear lesions. In the control group, refractoriness and conduction velocity were unaffected by the number of lesions. Conclusions: In these models of AF, linear lesions that eliminate AF increase the cycle length of AF without changing conduction velocity, number or size of wavelets, or complexity of activation patterns.
Effect of Electrode Polarity on Internal Defibrillation with Monophasic and Biphasic Waveforms Using an Endocardial Lead System
Authors: HUANG JIAN , KENKNIGHT BRUCE H. , WALCOTT GREGORY P. , WALKER ROBERT G. , SMITH WILLIAM M. , IDEKER RAYMOND E. 
Published: April 2007

Defibrillation Electrode Polarity. introduction: To test the hypothesis that the effect of shock polarity on defibrillation depends on waveform duration, this study determined strength‐duration defibrillation curves of monophasic and biphasic truncated exponential waveforms for both polarities. Methods and Results: Defibrillation thresholds (DFTs) were obtained in 32 pigs for catheter electrodes in the right ventricle (RV) and superior vena cava (SVC) using a modified Purdue technique. Both electrode polarities were tested in five different protocols. In part 1, DFTs were determined with 1‐ to 14‐msec monophasic waveforms. In parts 2, 3, and 4, DFTs were determined with two different sizes of SVC electrodes for biphasic waveforms with a phase 1 of 4 or 6 msec and a phase 2 ranging from 1 to 10 msec. In part 5, DFTs were tested for monophasic waveforms ranging from 2 to 11 msec and for biphasic waveforms with a phase 1 duration corresponding to each monophasic waveform and a phase 2 held constant at 1 msec. Mean DFTs for monophasic waveforms were significantly lower when the RV electrode was an anode than when it was a cathode for waveform durations ≥ 3 msec. For biphasic waveforms in which phase 2 was ≤ phase 1 in duration, no significant difference in mean DFT was observed when polarity was reversed. Even a phase 2 as short as 1 msec could eliminate the DFT difference between polarities observed with monophasic shocks. When phase 2 was ≥ 2 msec longer than phase 1, polarity did affect the DFT of biphasic waveforms: it affected the DFT similarly to a monophasic waveform of the same polarity as phase 2. Phase 1 duration and electrode size also affected the difference in DFT produced by changing the electrode polarity. Conclusions: For phase durations most commonly used clinically because of their low DFTs. reversing polarity changed defibrillation efficacy for monophasic but not biphasic shocks. For inefficient biphasic waveforms with phase 2 ≥ 2 msec longer than phase 1, the DFT was lower when the RV electrode was an anode during phase 2, similar to the polarity difference for monopbasic waveforms, suggesting that a long second phase of biphasic waveforms defibrillates in a similar fashion to monophasic waveforms.
Automated Ventricular Tachyarrhythmia Recognition
Authors: IGEL DAVID A. , WILKOFK BRUCE L. 
Published: April 2007

Automated Ventricular Tachyarrhythmia Recognition.Introduction: Cardiac monitoring devices such as external cardioverter defibrillators and ICU computerized ECG monitoring systems sense individual QRS complexes to detect and subclassify ventricular tachyarrhythmias. Many algorithms that evaluate ECG morphology mark individual QKS complexes so that specific waveform characteristics can he measured. QRS sensors miss a percentage of electrogram events, especially during fibrillatory rhythms; thus, a morphology algorithm that helps subclassify arrhythmias without marking individual electrogram events may be more robust and improve arrhythmia detection accuracy.Methods and Results: Four nonlinear dynamics calculations were evaluated for detecting ventricular tachyarrhythmias and for subclassifying monomorphic ventricular tachycardia (MVT) and polymorphic ventricular tachycardia (PVT). Five‐second epochs of normal (NML, n = 48), MVT (n = 58), and PVT (n = 75) rhythms were presented to a statistical discriminant function based on cycle length (CL), and its performance was compared to two other discriminant functions, one consisting of the nonlinear dynamics calculations and one consisting of a combination of all variables. The discriminant function based on nonlinear dynamics calculations and CL detected 100% of the ventricular tachyarrhythmias, and subclassified more (P < 0.001) MVT and PVT arrhythmias (90%) than that based on CL alone (71%).Conclusions: The nonlinear dynamics measurements used in this study significantly increased the suhclassification accuracy of the CL‐based discriminant function, and they were calculated from ECG signals without marking individual QRS complexes. Therefore, arrhythmia detectors that use nonlinear dynamics measurements may commit fewer classification errors due to QRS undersensing and aid therapy decisions when circumstances suggest that QRS sensing is inaccurate.
Idiopathic Left Ventricular Tachycardia with Left and Right Bundle Branch Block Configurations
Authors: ZIVIN ADAM , GOYAL RAJIVA , DAOUD EMILE , MAN K. CHING , STRICKBERGER S. ADAM , MORADY FRED 
Published: April 2007

Fascicular Tachycardia. Introduction: Idiopathic left ventricular tachycardia typically has a right bundle branch block configuration. The purpose of this case report is to demonstrate that idiopathic ventricular tachycardia arising in or near the left posterior fascicle also may have a left bundle branch block configuration. Methods and Results: A 27‐year‐old woman underwent an electrophysiologic procedure because of recurrent, verapamil‐responsive, wide QRS complex tachycardia. Two types of ventricular tachycardia (cycle lengths 330 to 340 msec) were reproducibly inducible, one with a right bundle branch block configuration and left‐axis deviation that had been documented clinically, and the other with a left bundle branch block configuration and axis of zero. A Purkinje potential recorded at the junction of the left ventricular mid‐septum and inferior wall preceded the ventricular complex by 40 msec in both tachycardias. A single application of ra‐diofrequency energy at this site successfully ablated both ventricular tachycardias. Conclusion: The findings of this case report demonstrate that idiopathic ventricular tachycardia arising in or near the left posterior fascicle may have a left bundle branch block configuration
Tachycardia‐Induced Cardiomyopathy Secondary to Right Ventricular Outflow Tract Ventricular Tachycardia: Improvement of Left Ventricular Systolic Function After Radiofrequency Catheter Ablation of the Arrhythmia
Authors: VTJGEN JOHAN , HILL PHILIP , BIBLO LEE A. , CARLSON MARK D. 
Published: April 2007

Cardiomyopathy Secondary to RVOT VT. Introduction: Several reports describe development of cardiomyopathics secondary to supraventricular tachycardia. Few reports have described cardiomyopathies secondary to ventricular tachycardia. Methods and Results: We describe a patient who presented with dilated cardiomyopathy and repetitive nonsustained monomorphic ventricular tachycardia. Cardiac cathcterization showed hemodynamically insignificant coronary artery disease. Radiofrequency ablation of a right ventricular outflow tract ventricular tachycardia resulted in improvement of the left ventricular systolic function and resolution of heart failure symptoms. Conclusions: This report suggests that right ventricular outflow tract ventricular tachycardia may cause reversible tachycardia‐induced cardiomyopathy.
Comparison of the Rate‐Dependent Properties of the Class III Antiarrhythmic Agents Azimilide (NE‐10064) and E‐4031
Authors: GROH WILLIAM J. , GIBSON KEVIN J. , MAYLIE JAMES G. 
Published: April 2007

Rate Dependence of Azimilide and E‐4031. Introduction: Reverse rate‐dependence, a lessening in Class III antiarrhythmic agent action potential duration (APD) prolongation as heart rate is increased, has been proposed to be related to an incomplete deactivution of the slow component (IKs) of the delayed rectifier K+ current (IK). The rate‐dependent properties of block of IK by azimilide were compared to E‐4031, which selectively blocks the rapid component (IKr) of Ik, in guinea pig ventricular muscle. Methods and Results: Azimilide prolonged APD in isolated papillary muscles in a concentration‐dependent manner and to a greater degree than E‐4031. Both agents prolonged APD less at fast than slow rates, consistent with a similar reverse rate‐dependent effect. Isolation of azimilide block of IKs by subtraction of APD during E‐4031 plus azimilide from E‐4031 alone revealed rate‐independent prolongation of APD. In voltage clamp experiments on single ventricular myocytes, activation of Iks was similar following 30 seconds of conditioning pulses of physiological duration (125 to 200 msec) with either a fast (cycle length 250 msec) or slow (cycle length 2000 msec) rate. The block of IKs by azimilide 3 μM was greater after a fast conditioning pulse train. Conclusions: Selective block of Iks prolongs APD in a rate‐independent manner. In voltage clamped myocytes, no evidence of a rate‐dependent accumulation of IKs was observed. These findings support a mechanism of reverse rate‐dependent APD prolongation by Class III antiarrhythmic agents that block IKr independent of IKs.
Abnormal Action Potential Conduction in Isolated Human Hypertrophied Left Ventricular Myocardium
Authors: McINTYRE HUGH , FRY CHRISTOPHER H. 
Published: April 2007

AP Conduction in Hypertrophied Myocardium. Introduction: Cardiac hypertrophy is associated with an increased incidence of arrhythmias that result from altered action potential configuration or propagation velocity. These variables were measured in isolated preparations of human left ventricular myocardium and correlated with the degree of hypertrophy. Methods and Results: Cardiac mass was estimated by echocardiography and cell diameter was measured from fixed isolated specimens; the two variables correlated significantly. Action potential duration was measured under field stimulation but was independent of the degree of hypertrophy; however, the duration was longer in septal preparations (405 ± 12 msec, 37°C, 1‐Hz stimulation) than in papillary muscles (342 ± 11 msec). Conduction velocity decreased progressively as cell diameter increased both in septal and papillary muscle preparations. Cable analysis showed that the variation of conduction velocity could be accounted for adequately by an increase of the intracellular resistivity of the preparations. Conclusion: The data suggest that conduction defects occur in a progressive manner in human hypertrophy, which would provide an important substrate for dysrhythmias in human left ventricular hypertrophy and could result from a decrease of electrical coupling between adjacent myocardial cells.
Inappropriate Discharge of an Implantable Cardioverter Defibrillator During Atrial Flutter and Intermittent Ventricular Antibradycardia Pacing
Authors: PETERS WERNER , KOWALLIK PETER , WITTENBERG GÜNTER , SCHOLL CHRISTOPH , MEESMANN MALTE 
Published: April 2007

Inappropriate Discharge of an ICD. Introduction: Inappropriate discharses of an implantable cardioverter defibrillator (ICD) are troublesome to the patient and sometimes a difficult task for the physician trying; to identify and treat the cause. Methods and Results: For the first time, we report a mechanism of inappropriate ICD discharges during episodes of atrail flutter with a slow ventricular response and intermittent antibradycardia pacing. The episodes occurred in tow patients and were triggered by the unique sensing alogorithm of the Ventitex Cadence® V‐100 in combination with the tripolar CPI Endotak® 072 transvenous defibrillation lead, which provides integrated bipolar sensing. Conclusion: Besides treatment of the underlying arrhythmia, reprogramming of the device, an electrode position far away from the atria, and true bipolar sensing will enhance the performance of ICD systems with respect to the episodes described here. In addition, more flexible sensing algorithms may. in the future, prevent this overall rare complication.
Reproducibility of Ventricular Fibrillation Characteristics in Patients Undergoing Implantable Cardioverter Defibrillator Implantation
Authors: TANEJA TARESH , GOLDBBRGER JEFFREY , PARKER MICHELLE A. , JOHNSON DAVE , ROBINSON NIKKI , HORVATH GEORGE , KADISH ALAN H. 
Published: April 2007

Reproducibility of VF Characteristics. Introduction: The purpose of this study was to evaluate the immediate reproducibility of local electrogram characteristics recorded during repeated episodes of induced ventricular fibrillation (VF) in patients undergoing implantable cardioverter defibrillator (ICD) implantation. Methods and Results: Power spectral analysis (using a fast Fourier transform algorithm) of electrograms recorded during 3 seconds of VF were analyzed in 24 patients undergoing ICD implantation using a Medtronic Transvene lead. Patients had 2 to 7 episodes of VF that were induced during defibrillation threshold testing. VF was induced by burst pacing (n = 20) or T wave shock (n = 4). Simultaneous electrograms during VF were recorded from a Medtronic Transvene lead with the following configurations: (1) a narrow spaced (12 mm) dedicated bipole used clinically for sensing; (2) a unipolar electrogram from the right ventricular coil; and (3) a widely spaced (18.3 mm) integrated bipole using the distal tip and the coil. Intraclass correlation coefficients (ICCs) were determined to examine the reproducibility of these VF characteristics among VF episodes in each patient. Recordings from both bipolar configurations had ICCs from 0.40 to 0.55, whereas unipolar recordings ICCs were below 0.40. Reproducibility was similar for dedicated and integrated recordings. Conclusions: Frequency characteristics of repeated episodes of VF induced in the same subjects show fair‐to‐good but not excellent reproducibility. Bipolar recordings were far more reproducible than unipolar recordings, but both bipolar configurations had similar reproducibility. These findings have implications for both the pathophysiology of induced VF and the design of VF detection algorithms.
Three‐Dimensional Distribution of ST‐T Wave Alternans During Acute Ischemia
Authors: GREEN LARRY S. , FULLER MICHAEL P. , LUX ROBERT L. 
Published: April 2007

Repolarization Alternans in Ischemia. Introduction: A canine model of reversible ischemia was used to measure the magnitude and transmural distribution of repolarization alternans. Methods and Results: Twenty‐four multielectrode needles were inserted into a reversibly ischemic region created by 8 minutes of coronary occlusion. One hundred ninety‐two unipolar electrograms were simultaneously recorded at 1‐minute intervals for 8 minutes of ischemia and 3 minutes of reflow recovery. Beat‐to‐beat repolarization alternans was quantified for all electrograms using the standard deviation of QRST integrals. When alternans from animals that fibrillated was compared with alternans from animals that did not, the magnitude of alternans in the fibrillation group was an average standard deviation of 1125 ± 99.7 mV‐msec at the time of fibrillation and 409 ± 183 mV‐msec at 8 minutes of ischemia in the animals that did not fibrillate. The increase in alternans occurred mainly in the mid‐myocardial and epicardial regions in the animals that fibrillated. QRS morphology of sequential electrograms did not differ in beat‐to‐beat comparison, suggesting that repolarization alternans measured was not due to alternating conduction block in the region of reversible ischemia. Conclusion: During acute ischemia, the magnitude and distribution of repolarization alternans are greater and differ in hearts that experience ventricular fibrillation. This observation may have clinical utility in arrhythmia prediction. It also is consistent with the possibility there may be multiple mechanisms for repolarization alternans.
Differential Effect of β‐Adrenergic Stimulation on the Frequency‐Dependent Electrophysiologic Actions of the New Class III Antiarrhythmics Dofetilide, Ambasilide, and Chromanol 293.
Authors: SCHREIECK JÜRGEN , WANG YANGGAN , GJINI VIKTOR , KORTH MICHAEL , ZRENNER BERNHARD , SCHÖMIG ALBERT , SCHMITT CLAUS 
Published: April 2007

Class III Antiarrhythmics and β‐Adrenergic Stimulation. Introduction: Blockade of the rapid delayed rectifier potassium current (IKr) as an important mechanism for current Class III antiarrhythmics is less effective in action potential prolongation during β‐adrenergic activation. We hypothesized that blockade of the increased slow IK (IKs) current during β‐adrenergic stimulation could improve action potential prolongation and tested this hypothesis by comparison of three different IK blockers: dofetilide, a selective blocker of IKr; ambasilide, a nonselective blocker of IK; and chromanol 293B, a selective blocker of IKs. Methods and Results: Transmembrane action potential duration was determined in guinea pig papillary muscles. After equilibration with the potassium channel blockers (dofetilide 10 nM, amhasilide 10 μM, chromanol 293B 10 μM), isoproterenol (10 and 100 nM) was added. The action potential prolonging effect of dofetilide was reduced in the presence of increasing concentrations of isoproterenol whereas the effect of ambasilide was much less reduced. In contrast, the effect of chromanol 293B clearly was increased in the presence of both concentrations of isoproterenol. No afterdepolarizations were observed after application of isoproterenol in control. Following isoproterenol, but not before, dofetilide and chromanol 293B induced early afterdepolarizations in 20% and 17% of the papillary muscles, whereas ambasilide and chromanol 293B induced delayed afterdepolarizations in 27% and 17%, respectively. Conclusion: In contrast to dofetilide, the Class III effect of ambasilide is less reduced and the effect of chromanol 293B is enhanced during β‐adrenergic stimulation. Our data support the hypothesis that IKs blockade improves the efficacy of antiarrhythmics in action potential prolongation during β‐adrenergic activation; however, this effect may increase the risk of afterdepolarizations.
Long‐Term Results of Visually Guided Left Ventricular Reconstruction as Single Therapy to Treat Ventricular Tachycardia Associated with Postinfarction Anteroseptal Aneurysm
Authors: SOSA EDUARDO , SCANAVACCA MAURICIO , D'AVILA ANDRE , FUKUSHIMA JULIA , JATENE ADIB 
Published: April 2007

Visually Guided Left Ventricular Reconstruction for Recurrent VT. Introduction: Postinfarction ventricular tachycardia (VT), anteroseptal aneurysm. and ventricular dysfunction are commonly associated and predict a poor long‐term prognosis. Surgical left ventricular reconstruction, which includes double plication of the anterior and septal wall, can improve ventricular function. This article analyzes the long‐term efficacy of such a procedure to control recurrence of VT in a group of 50 consecutive patients. Methods and Results: The study group consisted of 50 consecutive patients operated on between December 1986 and December 1994. The group comprised 44 men and 6 women. The mean age was 56 ± 11 years. All patients had spontaneous VT following an anterior myocardial infarction. Twenty‐five patients had two or more episodes of VT (eight presented as cardiac arrest, nine as syncope). Coronary artery disease was limited to the left anterior descending artery in 27 patients. An anteroseptal aneurysm was present in 49 patients. All patients had VT induced by programmed ventricular stimulation before surgery, and left ventricular reconstruction was performed without intraoperative mapping in all cases. Total mortality, VT recurrence, and sudden death rate were the endpoints of the study. In‐hospital mortality was 8%. Postoperative left ventricular ejection fraction improved from 0.38 to 0.50 (P < 0.05). Only two patients had postoperative inducible VT. Overall survival, VT recurrence rate, and sudden death rate were 73%, 12%, and 10%, respectively, after a median follow‐up period of 6.25 years (0 to 8 years). Conclusion: Visually guided left ventricular reconstruction with septal and anterior wall plicature can he utilized effectively to treat recurrent VT associated with postinfarction anteroseptal aneurysm.