bluuebunny/crossref_metadata_2025 huggingface dataset:
U Wave: Facts, Hypotheses, Misconceptions, and Misnomers
Authors: SURAWICZ BORYS
Published: April 2007

U Wave. The clinical significance of U wave is limited to the occasional obfuscation of the end of T wave and an inadequately explained U wave inversion associated with myocardial ischemia, infarction, and ventricular hypertrophy and dilatation. Lengthening of QT interval often interferes with the recognition of U wave. The characteristics of U wave are not compatible with the Purkinje or ventricular muscle repolarization hypotheses. The timing of the U wave during ventricular relaxation and the links between U wave and mechanical events favor the mechanoelectrical hypothesis of U wave genesis. Unfortunately, little research has been done to test this hypothesis.
Immediate Reinitiation of Atrial Fibrillation Following Internal Atrial Defibrillation
Authors: TIMMERMANS CARL , RODRIGUEZ LUZ‐MARIA , SMEETS JOEP L.R.M. , WELLENS HEIN J.J.
Published: April 2007

Immediate Reinitiation of AF. Introduction: Although the recurrence rate of atrial fibrillation has been reported to be similar to that after external and internal cardioversion, little is known about immediate reinitiation of atrial fibrillation (IRAF) following internal cardioversion.

Methods and Results: Thirty‐eight patients (24 men; mean age 63 ± 13 years) underwent internal atrial defibrillation. Catheter‐based defibrillation electrodes were positioned in the anterolateral right atrium and the coronary sinus. All patients were cardioverted at a mean threshold of 4.6 ± 3.4 J. Five of 38 patients (13%) had 1 to 4 episodes of IRAF. No difference in clinical and echocardiographic characteristics were observed when patients with and without IRAF were compared. Atrial fibrillation was always reinitiated by an atrial premature beat. When the earliest atrial endocardial activation time on the defibrillation catheters was analyzed, these atrial premature heats did not seem to originate from the defibrillation catheters. Twenty‐one patients had atrial premature heats without IRAF. When the coupling intervals of the first atrial premature heat in patients without and with IRAF after conversion were compared, a significant difference was found (661 ± 229 vs 418 ± 79 msec, P < 0.05). IRAF was successfully treated with repeated shock delivery after the administration of atropine in 1 patient and intravenous flecainide in 2. Only repeated shock delivery was sufficient to treat IRAF in another 2 patients. Late recurrences of atrial fibrillation occurred in 3 of 5 with IRAK and in 19 of 33 patients without IRAF (P = NS).

Conclusion: IRAF after internal atrial defibrillation occurred in 13% of patients, was always initiated by an atrial premature heat having a short coupling interval not originating from the defibrillation catheters, and was prevented by repeated shock delivery with or without preceding administration of pharmacologic agents. IRAF did not predict early recurrences of the arrhythmia after discharge from the hospital, emphasizing the necessity to treat immediate reinitiation promptly to achieve a successful cardioversion.
Hypoxia and Hypothermia Enhance Spatial Heterogeneities of Repolarization in Guinea Pig Hearts:
Authors: SALAMA GUY , KANAI ANTHONY J. , HUANG DAVID , EFIMOV IGOR R. , GIROUARD STEVEN D. , ROSENBAUM DAVID S.
Published: April 2007

Spatial Autocorrelation of APDs During Arrhythmogenic Insults. Introduction: Regional dispersions of repolarization (DOR) are arrhythmogenic perturbations that are closely associated with reentry. However, the characteristics of DOR have not been well defined or adequately analyzed because previous algorithms did not take into account spatial heterogeneities of action potential durations (APDs). Earlier simulations proposed that pathologic conditions enhance DOR by decreasing electrical coupling between cells, thereby unmasking differences in cellular repolarization between neighboring cells. Optical mapping indicated that gradients of APD and DOR are associated with fiber structure and are largely independent of activation. We developed an approach to quantitatively characterize APD gradients and DOR to determine how they are influenced by tissue anisotropy and cell coupling during diverse arrhythmogenic insults such as hypoxia and hypothermia.

Methods and Results: Voltage‐sensitive dyes were used to map APs from 124 sites on the epicardium of Langendorff‐perfused guinea pig hearts during (1) cycles of hypoxia and reoxygenation and (2) after 30 minutes of hypothermia (32° to 25°C). We introduce an approach to quantitate DOR by analyzing two‐dimensional spatial autocorrelation of APDs along directions perpendicular and parallel to the longitudinal axis of epicardial fibers. A spatial correlation length l was derived as a statistical measure of DOR. It corresponds to the distance over which APDs had comparable values, where l is inversely related to DOR. Hypoxia (30 min) caused a negligible decrease in longitudinal θL (from 0.530 ± 0.138 to 0.478 ± 0.052 m/sec) and transverse θT (from 0.225 ± 0.034 to 0.204 ± 0.021 m/sec) conduction velocities and did not alter θL/θT or activation patterns. In paced hearts (cycle length [CL] = 300 msec), hypoxia decreased APDs (123 ± 18.2 to 46 ± 0.6 msec; P < 0.001) within 10 to 15 minutes and enhanced DOR, as indicated by reductions of l from 1.8 ± 0.9 to 1.1 ± 0.5 mm (P < 0.005). Hypothermia caused marked reductions of θL, (0.53 ± 0.138 to 0.298 ± 0.104 m/sec) and θT (0.225 ± 0.034 to 0.138 ± 0.027 m/sec), increased APDs (128 ± 4.4 to 148 ± 14.5 msec), and reduced l from 2.0 ± 0.3 to 1.3 ± 0.6 mm (P < 0.05). l decreased with increased time of hypoxia and recovered upon reoxygenation. Hypoxia and hypothermia reduced l measured along the longitudinal (l1) and transverse (lT) axes of cardiac fibers while the ratio lL/lT remained constant.
Radiofrequency Catheter Ablation of Left Ventricular Outflow Tract Tachycardia:
Authors: SHIMOIKE EIMEI , OHBA YURIKA , YANAGI NOBUHITO , HIRAMATSU SHIN‐ICHI , UEDA NORIHIRO , MARUYAMA TORU , KAJI YOSHIKAZU , KANAYA SHOZO , FUJINO TAKEHIKO , NIHO YOSHIYUKI
Published: April 2007

Left Ventricular Outflow Tract Tachycardia. Idiopathic ventricular tachycardia (VT) originating from the left ventricular outflow tract (LVOT) is rare. We report two patients whose QRS configuration during VT commonly showed an inferior axis and monophasic R waves in all the precordial leads. The mechanism of these VTs appeared to be triggered activity. From mapping and ablation, the origin of these VTs was determined to be in the most posterior LVOT, corresponding to the aortomitral continuity (left fibrous trigone).
Intracardiac Stimulation of Human Parasympathetic Nerve Fibers Induces Negative Dromotropic Effects:
Authors: CHEN SHIH‐ANN , CHIANG CHERN‐EN , TAI TAI CHING , WEN ZU‐CHI , LEE SHIH‐HUANG , CHIOU CHUEN‐WANG , ANN DING YU , CHANG SONG
Published: April 2007

Intracardiac Stimulation and Dromotropic Effect. Introduction: The dromotropic effects of intracardiac parasympathetic nerve stimulation have not been well studied; furthermore, the effects of radiofrequency ablation lesions on parasympathetic nerve stimulation are not clear.

Methods and Results: Group I: intracardiac electrical stimulation in the right posteroseptal and anteroseptal areas under different stimulation strengths; group II: intracardiac electrical stimulation before and 10 minutes after intravenous propranolol; group III; intracardiac electrical stimulation before and 5 minutes after intravenous atropine. Among the 10 patients with AV nodal reentrant tachycardia (group IV) and the 10 patients with atrial flutter (group V), atrial fibrillation was induced before and after successful ablation, and intracardiac electrical stimulation in the right posteroseptal area was performed before and after successful ablation. The maximal response and complete decay of the response occurred within 2 to 6 seconds of initiation or termination of parasympathetic nerve stimulation. This negative dromotropic effect disappeared after atropine was administered, but not after propranolol. After successful ablation, parasympathetic stimulation still induced negative dromotropic effects.

Conclusion: Electrical stimulation of parasympathetic nerve fibers near the posteroseptal and anteroseptal areas could induce a negative dromotropic effect, and this effect was preserved after successful radiofrequency ablation of slow pathway and isthmus conduction.
Changes in Cardiac Repolarization Following Short Periods of Ventricular Pacing
Authors: GOYAL RAJIVA , SYED ZAFFER A. , MUKHOPADHYAY PARTHA S. , SOUZA JOSEPH , ZIVIN ADAM , KNIGHT BRADLEY P , MAN K. CHING , STRICKBERGER S. ADAM , MORADY FRED
Published: April 2007

Cardiac Memory. Introduction: “Cardiac memory” (primary T wave change) is thought to occur after 15 minutes to several hours of right ventricular (RV) pacing. The two components of the temporal change in repolarization are memory and accumulation. The purpose of this study was to examine quantitatively the effect of short periods of ventricular pacing on the human cardiac action potential, using monophasic action potential (MAP) recordings.

Methods and Results: Thirty‐one patients (ages 43 ± 14 years) with structurally normal hearts undergoing a clinically indicated electrophysiologic procedure were enrolled. Catheters were placed in the right atrium (RA) and RV, and a MAP catheter was positioned at the RV septum. APD90 was calculated from digitized MAP recordings. MAP morphology comparisons were performed using the root mean square (RMS) of the difference between complexes. All pacing was at 500‐msec cycle length. There were four pacing protocols: (1) RA pacing was performed for approximately 15 minutes to evaluate temporal stability of the MAP recordings (5 pts); (2) to evaluate the memory phenomenon, four successive 1‐minute episodes of RV pacing were interspersed with 2 minutes of RA pacing (5 pts); (3) the accumulation phenomenon was evaluated by assessing the effects of 1, 5, 10, and 15 minutes of RV pacing on the MAP during RA pacing (16 pts); and (4) 20 minutes of RV pacing was followed by 10 minutes of RA pacing to correlate visually apparent T wave changes with changes in MAP recordings (5 pts). In the control patients, no changes in APD90 or RMS analysis were noted during 14.9 ± 1.4 minutes of RA pacing. In the second protocol, RMS of the difference between the baseline MAP complexes and the signal average of the first 50 beats following each of four 1‐minute RV pacing trains demonstrated progressively greater differences in morphology after successive episodes of RV pacing. In protocol 3, RMS analysis identified a progressively greater difference between the baseline MAP recording and the average of the first 50 beats after 1,5, 10, and 15 minutes of RV pacing. In protocol 4, visually apparent changes in T waves occurred in parallel with the RMS of the difference between the baseline MAP recordings and the average of the first 50 beats after 20 minutes of RV pacing. Similar changes also were demonstrated by APD90 analysis.

Conclusion: This study is the first to demonstrate that episodes of abnormal ventricular activation as short as 1 minute in duration may exert lingering effects on the repolarization process once normal ventricular activation resumes.
Differential Role of Epicardial and Endocardial KATP Channels in Potassium Accumulation During Regional Ischemia Induced by Embolization of a Coronary Artery with Latex
Authors: MIYOSHI SHUNICHIRO , MIYAZAKT TOSHTHISA , ASANAGI MIKA , MORITANI KAZUNORI , OGAWA SATOSHI
Published: April 2007

Epicardial and and Endocardial [K+]0 Rise and KATP Channels. Introduction: KATP channels are activated predominantly in the epicardium during regional ischemia. Therefore, the role of KATP channels in ischemia‐induced rise of extracellular potassium concentration ([K+]o) might he greater in the epicardium.

Methods and Results: In 18 anesthetized dogs, the left anterior descending coronary artery (LAD) was ligated, followed by injection of 23‐μm latex heads into the occluded artery to interrupt collateral flow, by which accumulated [K+]o might wash out. Epicardial and endocardial [K+]o were measured during a 20‐minute period of ischemia using a valinomycin membrane. The dogs were divided into three groups: 6 control dogs (CTRL); 7 dogs pretreated with intravenous glibenclamide (0.3 mg/kg [GLIB]), a blocker of KATP channels: and 5 dogs pretreated with intravenous nicorandil (0.2 to 0.25 mg/kg [NCR]), a KATP channel opener. Before LAD occlusion, there was no difference in [K+]o among the three groups. In the control group, epicardial and endocardial [K+]o were increased to a similar level as a function of time after occlusion (CTRL) at both layers. Ischemia‐induced epicardial [K+]o rise was suppressed by GLIB (8.4 ± 0.4 vs 6.7 ± 0.5 mM, P < 0.05) but augmented by NCR (12.9 ± 2.0 mM, P < 0.05). In contrast, endocardial [K+]o, rise remained unaffected (7.6 ± 0.2 mM CTRL, 7.6 ± 1.3 mM GLIB, and 9.4 ± 2.2 mM NCR, P = NS).

Conclusion: Activation of KATP channels plays an important role in epicardial [K+]o rise, but not in endocardial [K+]o rise, during regional ischemia. Another mechanism(s) may he important for endocardial [K+]o accumulation.
Effect of Shock Waveform on Relationship Between Upper Limit of Vulnerability and Defibrillation Threshold
Authors: SWERDLOW CHARLES D. , KASS ROBERT M. , O'CONNOR MARK E. , CHEN PEKG‐SHENG
Published: April 2007

ULV‐DFT Waveform. Introduction: The upper limit of vulnerability (ULV) correlates with the defibrillation threshold (DFT). The ULV can he determined with a single episode of ventricular fibrillation and is more reproducible than the single‐point DFT. The critical‐point hypothesis of defibrillation predicts that the relation between the ULV and the DFT is independent of shock waveform. The principal goal of this study was to test this prediction.

Methods and Results: We studied 45 patients at implants of pectoral cardioverter defibrillators. In the monophasic‐biphasic group (n = 15), DFT and ULV were determined for monophasic and biphasic pulses from a 120‐μF capacitor. In the 60‐ to 110‐μF group (n = 30), DFT and ULV were compared for a clinically used 110‐μF waveform and a novel 60‐μF waveform with 70% phase 1 tilt and 7‐msec phase 2 duration. In the monophasic‐biphasic group, all measures of ULV and DFT were greater for monophasic than biphasic waveforms (P < 0.0001). In the 60‐ to 110‐/tF group, the current and voltage at the ULV and DFT were higher for the 60‐μF waveform (P < 0.0001), hut stored energy was lower (ULV 17%, P < 0.0001; DFT 19%, P = 0.03). There was a close correlation between ULV and DFT for both the monophasic‐biphasic group (monophasic r2= 0.75, P < 0.001; hiphasic r2= 0.82, P < 0.001) and the 60‐ to 110‐μF group (60 μF r2= 0.81 P < 0.001; 110 μF r2= 0.75, P < 0.001). The ratio of ULV to DFT was not significantly different for monophasic versus biphasic pulses (1.17 ± 0.12 vs 1.14 ± 0.19, P = 0.19) or 60‐μF versus 110‐μF pulses (1.15 ± 0.16 vs 1.11 ± 0.14, P = 0.82). The slopes of the ULV versus DFT regression lines also were not significantly different (monophasic vs biphasic pulses, P = 0.46; 60‐μF vs UO‐μF pulses, P = 0.99). The sample sizes required to detect the observed differences between experimental conditions (P < 0.05) were 4 for ULV versus 6 for DFT in the monophasic‐biphasic group (95% power) and 11 for ULV versus 31 for DFT in the 60‐ to 110‐μF group (75% power).

Conclusion: The relation between ULV and DFT is independent of shock waveform. Fewer patients are required to detect a moderate difference in efficacy of defibrillation waveforms by ULV than by DFT. A small‐capacitor biphasic waveform with a long second phase defibrillates with lower stored energy than a clinically used waveform.
Effect of Shock Polarity on Biphasic Defibrillation Thresholds Using an Active Pectoral Lead System
Authors: OLSOVSKY MARY R. , SHOROFSKY STEPHEN R. , GOLD MICHAEL R.
Published: April 2007

Polarity and Biphasic Defibrillation Thresholds. Introduction: The downsizing of implantable defibrillator pulse generators has made pectoral placement routine. A further reduction of defibrillation thresholds (DFTs) may simplify implantation defibrillation testing and allow for smaller, lower output pulse generators while maintaining an adequate defibrillation safety margin. One factor that may affect defibrillation efficacy is shock polarity.

Methods and Results: Sixty consecutive patients undergoing dual‐coil, active left pectoral defibrillator implantation were evaluated. Paired, biphasic DFTs were measured in normal (RV apex = cathode) and reverse (RV apex = anode) polarity with order of testing randomized. Reverse polarity conferred a 15% reduction of mean DFTs (8.5 ± 5.0 J normal. 7.2 ± 4.6 J reverse polarity. P = 0.02). The effect of polarity appeared most pronounced among the patients with a high DFT (> 15 J) resulting in a 31% reduction with reverse polarity (16.7 ± 2.5 J normal, 11.5 ± 5.9 J reverse, P = 0.03).

Conclusion: Reversing shock polarity results in significantly lower biphasic DFTs with an active pectoral lead system, particularly in the subgroup of patients with a high normal polarity threshold. Reversing polarity in these patients may simplify acute defibrillation testing and allow for lower output devices.
Focal Atrial Tachycardia:
Authors: CHEN SHIH‐ANN , TAI CHING‐TAI , CHIANG CHERN‐EN , DING YU‐AN , CHANG MAU SONG
Published: April 2007

Atrial Tachycardia. Introduction: Reports about the clinical and electrophysiologic characteristics of focal atrial tachycardia vary widely. Furthermore, the impact of age, gender, associated cardiac diseases, mechanism, location of atrial tachycardia, and the prediction of results of radiofrequency catheter ablation was not clear. The purpose of this study was to further understand the clinical and electrophysiologic characteristics of focal atrial tachycardia and the prediction of results of radiofrequency ablation.

Methods and Results: We searched the literature published between January 1969 and July 1997 using the key word “atrial tachycardia” from the MEDLINE and National Library of Medicine systems. The items analyzed were age, sex, cardiac disease, mechanism, attack pattern, cycle length, location, number of atrial tachycardias, results of ablation, and recurrence after ablation. Multivariate analysis showed that age and paroxysmal type of tachycardia were independent predictors of nonautomatic mechanism; age and presence of other cardiac diseases were independent predictors of multiple atrial tachycardias, and age also was the independent predictor of right‐sided atrial tachycardia. Atrial tachycardia located in the right atrium was the only significant predictor of successful radiofrequency catheter ablation. Other cardiac diseases and multiple atrial tachycardias were the significant predictors of recurrence after initial successful radiofrequency catheter ablation.

Conclusion: Patient age is closely related to the clinical and electrophysiologic characteristics of atrial tachycardia based on our reanalysis, which found that patient age is an independent predictor of nonautomatic mechanism, right atrial location, existence of multiple atrial tachycardias, and recurrence of atrial tachycardia after initial successful ablation.
Evidence for Multiple Atrio‐AV Nodal Inputs in the Normal Dog Heart
Authors: ANTZ MATTHIAS , SCHERLAG BENJAMIN J. , OTOMO KENICHIRO , PITHA JAN , TONDO CLAUDIO , PATTERSON EUGENE , JACKMAN WARREN M. , LAZZARA RALPH
Published: April 2007

Multiple Atrio‐AVN Inputs in Dog Heart. Introduction: Complete AV block after combined fast pathway (FP) and slow pathway (SP) ablation is uncommon. The purpose of this study was to interrupt activation of these and additional inputs by placing a radiofrequency lesion across the interatrial septum between the FP and SP ablation sites.

Methods and Results: In eight anesthetized open chest dogs, FP ablation induced significant A‐H prolongation (δA‐H: 51±14 msec; P < 0.001) and a shift of earliest retrograde atrial activation from the anterior septum to the region of the coronary sinus (CS) os. Subsequently, ablation of the interatrial septum across the fossa ovalis was successful in 5 of 8 dogs, changing the sequence of atrial activation (A) so that A at the His‐bundle electrogram, which initially preceded A at the CS os (18 ± 4 msec vs 46 ± 7 msec, P < 0.01), now followed CS os A (81 ± 31 msec vs 59 ± 20 msec, P < 0.05). Additional ablation of the SP caused a type II Mobitz AV block or complete AV block in 5 of 8 dogs. The four dogs with complete AV block sbowed a stable, high junctional escape rhytbm at a rate of 64 ± 16 beats/min. Pacing between the ablation lesions and the AV node in one dog showed 1:1 AV conduction and Wenckebach‐type AV block indicating preserved AV nodal function. Histology showed necrotic changes in the FP and SP transitional cell zones and in the atrial tissue of the interatrial septum. However, the compact AV node. His bundle, and adjacent atria and transitional cells were undamaged.

Conclusion: There are additional AV nodal inputs in the interatrial septum in addition to the anterior FP and posterior SP inputs. Ablation of all of these may be required, if the aim is production of complete AV block proximal to the AV node with a high Junctional escape rhythm.
Selected Slow Pathway Ablation in a Patient with Corrected Transposition of the Great Arteries and Atrioventricular Nodal Reentrant Tachycardia
Authors: TADA HIROSHJ , NOGAMI AKIHIKO , NAITO SHIGETO , SUGUTA MASAHIKO , HOSHIZAKI HIROSHI , OSHIMA SHIGERU , TANIGUCHI KOICHI
Published: April 2007

AVNRT in Corrected TGA. We report the first known case of AV nodal reentrant tachycardia (AVNRT) associated with a corrected transposition of the great arteries to be treated successfully by ablation of the slow pathway. Triple AV nodal pathways were observed in the anterograde direction and two types of AVNRT were induced. Input of the fast pathway to the AV node was located at the anterior portion of the left‐sided A V annulus, while the input of the intermediate and slow pathways was located at the anteroseptal portion of the right‐sided AV annulus. Radiofrequency energy ablation at the right anteroseptal site eliminated the intermediate and slow pathways.
Recurrent Supine Syncope:
Authors: ISKOS DEMOSTHENES , SHULTZ JEFFREY J. , BENDITT DAVID G.
Published: April 2007

Supine Syncope. Introduction: Syncope occasionally may occur in the supine patient due to severe brady‐ or tachyarrhythmia. However, recurrent syncope upon assumption of the supine position as a result of a neurally mediated reflex mechanism has not been reported previously.

Methods and Results: Two young patients, both of whom had significant systemic illnesses, experienced recurrent episodes of presyncope and/or syncope shortly after assuming the supine position. During ambulatory ECG monitoring, symptoms were provoked only by lying down and were associated with transient bradycardia. Head‐up tilt table testing was undertaken as part of the syncope evaluation and was nondiagnostic in both cases. However, both patients exhibited a transient cardioinhibitory response with reproduction of typical symptoms upon return of the table to the supine position (“reverse tilt”). During follow‐up (8 and 14 months), both patients improved with pharmacologic treatment (disopyramide in one case and midodrine in the other).

Conclusion: Presyncope or syncope upon lying down can he an unusual manifestation of the neurally mediated faint.
Effect of Electrode Length on Atrial Defibrillation Thresholds
Authors: TIMMERMANS CARL , RODRIGUEZ LUZ‐MARIA , AYERS GREGORY M. , LAMBERT HENDRIK , SMEETS JOEP , WELLENS HEIN J.J.
Published: April 2007

Electrode Length for Atrial Defibrillation. Introduction: Catheter‐based electrodes have been used previously to terminate episodes of atrial fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electrodes are positioned in the distal coronary sinus and in the right atrium. The purpose of this study was to evaluate the use of longer electrode lengths for atrial defibrillation.

Methods and Results: In 15 patients, two decapolar catheters were inserted, one into the distal coronary sinus and one in the right atrium. To provide longer electrodes lengths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6‐cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecutive electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting consecutive, nonoverlapping rings of the third catheter with the 10 rings of the initial right atrial or coronary sinus catheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations of electrode lengths. All 15 patients could he successfully converted to sinus rhythm without complications; however, one patient could be converted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 ± 102 V, 5.9 ± 4.0 J for the 6 cm/6 cm electrode length combination with an impedance of 72 ± 18 ω. For the electrode combination using the 11‐cm electrode in the right atrium, the defibrillation threshold was 296 ± 107 V, 5.8 ± 3.9 J with an impedance of 61 ± 17 ω and was 294 ± 91 V, 5.6 ± 3.6 J with an impedance of 55 ± 11 ω for the 11‐cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P > 0.05) associated with the longer electrode lengths; however, the longer electrode lengths did significantly lower shock impedance (P < 0.05).

Conclusion: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the defibrillation requirements for restoration of sinus rhythm.
Immediate Reproducibility of Upper Limit of Vulnerability Measurements in Patients Undergoing Transvenous Implantable Cardioverter Defibrillator Implantation
Authors: ELLENBOGEN KENNETH A. , WOOD MARK A. , GILLIGAN DAVID M. , CROFTS THERESA , LONDON WENDY , McCLISH DONNA
Published: April 2007

Reproducibility of ULV. Introduction: Measurement of the upper limit of vulnerability (ULV) with monophasic T wave shocks has been proposed as a patient‐specific measurement of defibrillation efficacy that results in fewer episodes of ventricular fibrillation (VF) than measurement of a defibrillation efficacy curve.

Methods and Results: We sought to determine the magnitude of variance in ULV in 63 consecutive patients undergoing implantation of an implantable cardioverter defibrillator (ICD). We measured ULV as the strength at or above which VF is not induced when a stimulus is delivered at 310 msec after an 8‐beat ventricular pacing drive at 400 msec. Defibrillation threshold (DFT) was measured in patients with an active can device using a biphasic waveform and the binary search method beginning at 12 J. Sixty‐three patients were studied; they bad a mean age of 62 × 12 years and a mean ejection fraction of 35%± 15%. Three quarters of patients bad an ischemic cardiomyopathy. Each patient underwent 4.5 ± 0.8 measurements f ULV. Monophasic ULV correlated poorly with biphasic DFT (R between 0.19 and 0.28, P = 0.04 to 0.17). There was no change in ULV between second to third, third to fourth, and first to last measurement in 22% to 41% of patients. The reliability coefficient was 0.87. A ULV ≥ 20 J was found in eight patients. The only predictor of high ULV was a high DFT.

Conclusion: Monophasic ULVs do not closely predict biphasic active can DFTs using a standard protocol. High DFTs were predicted by high ULVs. There was little variation in the acute measurement of ULV between trials. These findings have important implications for using ULV measurements to determine changes in DFTs after interventions. The methodology of determining ULV is critical to its use for predicting DFTs and programming ICDs.
Altered Pattern of Connexin40 Distribution in Persistent Atrial Fibrillation in the Goat
Authors: van der VELDEN HUUB M.W. , van KEMPEN MARJAN J.A. , WIJEFELS MAURITS C.E.E , van ZIJVERDEN MAAIKE , GROENEWEGEN W. ANTOINETTE , ALLESSIE MAURITS A. , JONGSMA HABO J.
Published: April 2007

Cx40 Distribution in Goat Atrial Fibrillation. Introduction: Since altered expression of gap junction proteins (connexins) in diseased myocardial tissue may lead to abnormal electrical coupling between cardiomyocytes and hence contribute to arrhythmogenesis, the expression of connexin(Cx)40 and Cx43 was studied in atrial appendage from goats in sinus rhythm (SR) and persistent atrial fibrillation (AF).

Methods and Results: Biopsies were taken from the left and right atrial appendages from goats in SR or after pacing‐induced persistent AF. Analyses of Cx40 and Cx43 mRNA and protein levels, using quantitative (competitive) polymerase chain reaction and western blotting, respectively, revealed no significant changes in the overall expression of Cx40 and Cx43 as a result of persistent AF. At the cellular level, immunohistochemistry and confocal laser canning microscopy showed a homogeneous distribution of either connexin in atrial sections taken during SR. After induction of AF, the distribution of Cx43 gap Junctions was unchanged whereas the Cx40 pattern showed marked inhomogeneities with small areas (0.15 to 0.6 mm in diameter, 25% of section surface area) of low‐density Cx40 located between larger areas of normal (unchanged) Cx40 density. Activation mapping (244 electrodes, spatial resolution 2.25 mm) of the right atrial wall did not reveal changes in atrial conduction velocity.

Conclusion: Pacing‐induced persistent AF in the goat gave rise to changes in the spatial organization of Cx40 gap junctions. Although the overall conduction velocity appeared not to have changed, microheterogeneities in conduction due to the local redistribution of Cx40 gap junctions might have contributed to the initiation and maintenance of AF.
Nonfluoroscopic Transseptal Catheterization:
Authors: EPSTEIN LAURENCE M. , SMITH TIMIOTHY , HOFF HARM Ten
Published: April 2007

ICE‐Guided Transseptal Catheterization. Introduction: Recently, there has been a revival in the use of transseptal catheterization due to the development of balloon mitral valvuloplasty and radiofrequency catheter ablation. Complications of transseptal puncture, although rare, can be serious and life‐threatening. In the present study, we evaluated the use of intracardiac echocardiography (ICE) as the sole imaging modality to guide transseptal puncture and catheterization.

Methods and Results: In each animal. 10 transseptal punctures were performed guided solely by ICE. The standard approach to transseptal catheterization using a Brockenbrough needle and long vascular sheath was used except for the use of ICE instead of fluoroscopy. A 6.2‐French/12.5‐MHz and 9‐Frencb/9‐MH7, ICE catheter was used for imaging. At the end of each study, pathologic evaluation was performed. Transseptal puncture was performed safely, guided solely by ICE, in each of 100 attempts (five attempts guided by each ICE catheter in 10 dogs). While the fossa ovalis was easily visualized with both ICE catheters, the 9‐Frcnch/9‐MHz catheter offered an enhanced field of view. On pathologic evaluation, there was no evidence of perforation of either the right or left atrium outside of the fossa ovalis.

Conclusion: Both ICE catheters used in this trial allowed for excellent visualization of the fossa ovalis and safe transseptal puncture. Intracardiac echocardiography may be a better imaging modality than fluoroscopy for guiding transseptal atheterization, especially in less experienced hands.
Familial Sudden Cardiac Death Associated with a Terminal QRS Abnormality on Surface 12‐Lead Electrocardiogram in the Index Case
Authors: GARG ASHOK , FTNNERAN WILLIAM , FELD GREGORY K.
Published: April 2007

Familial Sudden Death and ECG Abnormalities. A case is presented of an 18‐year‐old male who had been resuscitated following an episode of sudden death due to ventricular fibrillation. The patient was noted to have an abnormal deflection in the terminal QRS on surface ECG and an abnormal signal‐averaged KCG demonstrating a late potential coincident with the terminal QRS abnormality on the ECG. The patient had easily inducible polymorphic ventricular tachycardia during electrophysiologic study, which was suppressed by quinidine but not by procainamide or beta blockers. The surface ECG and signal‐averaged ECG also were normalized by quinidine but not by procainamide or beta blockers. The patient had no further arrhythmias on quinidine for 6 years until he inexplicably discontinued his medication and died suddenly shortly thereafter. The present case may represent a unique familial sudden death syndrome or possibly a variant of the sudden death syndrome associated with right bundle branch block and ST elevation in V1, through V3, Currently available data suggest that, in such patients, an implantable cardioverter defibrillator may provide better protection from sudden death than does antiarrhythmic drug therapy.
Emergence of Bidirectional Accessory Pathway Conduction in Adulthood
Authors: NABAR ASHISH , VORA AMIT , LOKHANDWALA YASH
Published: April 2007

Emergence of AP Conduction in Adulthood. A 30‐year‐old woman presented with tachycardiomyopathy due to atrial flutter‐fibrillation and underwent radiofrequency ablation of the AV node and VVIR pacemaker implantation. There was no evidence of any accessory pathway (AP) conduction during the AV nodal ablation or during chronic ventricular pacing. One year later, she had a transient preexcited tachycardia. A year after this, her ECG showed 1:1 AV conduction with preexcitation. Electrophysiologic study revealed a left lateral AP with anterograde and retrograde refractory periods of 280 and 240 msec, respectively. Successful radiofrequency ablation of the AP was performed. This case highlights a unique emergence of an AP in adult life.
Becker Muscular Dystrophy with Bundle Branch Reentry Ventricular Tachycardia
Authors: NEGRI SUSAN M. , COWAN MARK D.
Published: April 2007

Muscular Dystrophy with Ventricular Tachycardia. This report describes a case of Becker muscular dystrophy presenting with recurrent symptomatic wide complex tachycardia. Electrophysiologic testing demonstrated the mechanism to be bundle branch reentry ventricular tachycardia. It is important to consider this potential mechanism in patients with ventricular arrhythmias who have this particular clinical entity, since radiofrequency catheter ablation can represent a curative treatment.
Effects of Gender on Cardiac Arrhythmias
Authors: LARSEN JENNIFER A. , KADISH ALAN H.
Published: April 2007

Gender Effects on Cardiac Arrhythmias. The purpose of this study is to review published data regarding gender differences in cardiac electrophysiology and in the occurrence of clinical arrhythmias. ECG differences between men and women include a faster resting heart rate in women, a longer corrected QT interval, and a lower QT dispersion than in men. The faster resting heart rate in women appears to be primarily related to differences in physical conditioning. The mechanism for the longer corrected QT interval in women is not completely known, but does not appear to be related to acute effects of estrogen or progesterone or differences in autonomic innervation. Women also appear to have a lower incidence of atrial fibrillation, a difference in the age distribution of supraventricular tachycardia, and a lower incidence of sudden death than men. Much of the lower incidence of sudden death in women may relate to a difference in the prevalence of coronary artery disease, but other factors such as inherent differences in repolarization, which may be reflected by a gender difference in the corrected QT interval, also may be operative. The paradox of a longer corrected QT interval and higher incidence of torsades de pointes, but lower population‐based incidence of sudden death in women, has not been completely resolved. Further studies will be required to help better understand the basic mechanisms involved in gender differences in electrophysiology and arrhythmias and determine the extent to which these differences have implications for clinical management of cardiac arrhythmias.
Influence of Body Position on Defibrillation Thresholds of Nonthoracotomy Implantable Defibrillators:
Authors: SCHAUERTE PATRICK , DIEM BJÖRN , ZIEGERT KATHRIN , FRANKE ANDREAS , HANRATH PETER , STELLBRINK CHRISTOPH
Published: April 2007

DFT of Nonthoracotomy Defibrillators. Introduction: Defibrillation thresholds (DFTs) usually are determined with the patient in the supine position. However, patients may be in the upright position when a shock is delivered during follow‐up, which may explain some first shock failures observed clinically. This study investigated whether body posture affects defibrillation energy requirements of nonthoracotomy implantable cardioverter defibrillators with biphasic shocks.

Methods and Results: Using a step up‐down protocol, DFTs were compared intraindividually in 52 patients (“active‐can” systems in 41 patients, two‐lead systems in II patients) for the supine and upright positions as achieved by a tilt table. The mean DFT was 7.3 ± 4.2 J in the supine versus 9.2 ± 4.8 J in the upright position (P = 0.002). Repeated comparison in reversed order 3 months after implantation in 22 patients revealed thresholds of 6.2 ± 2.5 J (supine) versus 8.4 ± 3.7 J (upright; P < 0.03) 1 week and 4.4 ± 2.4 J (supine) versus 6.2 ± 4.1 J (upright; P < 0.04) 3 months after implantation. DFTs decreased significantly for both body positions from 1 week to 3 months after implantation (P < 0.04).

Conclusion:(I) DFTs for biphasic shocks delivered by nonthoracotomy defibrillators are higher in the upright compared to the supine body position. (2) Differences remain significant 3 months after implantation. For both body positions, DFT decreases significantly from 1 week to 3 months after implantation. These findings have important implications for programming first shock energy to lower than maximal values or for development of devices with lower maximal stored energy.
Differential Effects of Bupivacaine on Cardiac K Channels: Role of Channel Inactivation and Subunit Composition in Drug—Channel Interaction
Authors: LIPKA LESLIE J. , JIANG MIN , TSENG GEA‐NY
Published: April 2007

Mechanisms of Bupivacaine's Actions on K Channels.Introduction: We examined the effects of a nonspecific ion channel blocker, bupivacaine, on K channels encoded by hERG, rKvl.4, rKv4.3, and hKvLQTI along with hIsK. Their native counterparts in the heart are important for the function of IKr, Ito, and IKsand, thus, play an important role in repolarization.

Methods and Results: To elucidate the mechanisms and sites of bupivacaine's actions, we correlated the voltage and time dependencies of drug effects with those of channel gating. We also studied the effects of altering the C‐type (hERG) or N‐type (rKvl.4) inactivation process or the subunit composition (hKvLQT1 with or without hIsK) on bupivacaine's actions. The results suggest that, except for hKvLQT1 co‐expressed with hIsK, bupivacaine binding occurred at depolarized voltages coinciding with channel activation. With hKvLQT1 co‐expressed with hIsK, bupivacaine bound preferentially at negative voltages when channels were in the closed state, and unbound at depolarized voltages when channels opened. The C‐type inactivation of hERG enhanced, whereas the N‐type inactivation of rKv1.4 hindered, bupivacaine's effects.

Conclusion: We propose that bupivacaine's actions on these K channels can be described as a nonspecific pore blockade in the inner mouth region. However, the apparent binding affinity and voltage dependence of binding can be differentially influenced by the inactivation processes occurring at two ends of the pore (C‐type inactivation at the outer end and N‐type inactivation at the inner end), or by the interaction between hIsK and hKvLQT1 subunits.
Left‐Sided Atrioventricular Nodal Ablation Using the Transseptal Approach:
Authors: FENRICH ARNOLD L. , FRIEDMAN RICHARD A. , CECCHIN FRANK C. , KEARNEY DEBRA
Published: April 2007

Transseptal Atrioventricular Nodal Ablation. To our knowledge, prograde access to the left ventricle to perform a left‐sided AV node (AVN) ablation has not been reported. We present the case of a patient with Noonan's syndrome and supravalve aortic stenosis who required aortic valve replacement with a mechanical valve. Due to chronic atrial fibrillation, a transvenons pacing system was implanted and transcatheter radiofrequency ablation of the AVN was performed. Attempts at right‐sided AVN ablation were unsuccessful. Due to the presence of the mechanical aortic valve, a left‐sided AVN ablation was performed successfully using the transseptal approach. The patient died suddenly 6 months after the procedure, and the histologic study of the heart is reported.
Myopotential Sensing by a Dual Chamber Implantable Cardioverter Defibrillator:
Authors: DESHMUKH PRAMOD , ANDERSON KATHY
Published: April 2007

Myopotential Oversensing by a Dual Chamber ICD. Introduction: Inappropriate discharges and/or improper inhibition of bradycardia pacing due to oversensing of extraneous signals in implantable cardioverter defibrillators (ICDs) have been described. With one exception, no previous report involving an intact lead system bas cited myopotential oversensing as the cause.

Methods and Results: Two case reports of myopotential oversensing by a dual chamber ICD system are reported. In the first patient suffering from chronic pulmonary obstructive disease, intermittent myopotential seasing during labored respiration resulted in episodic inhibition of bradycardia pacing. In the second patient, oversensing of sustained myopotentials generated during strenuous isometric activity resulted in an inappropriate ICD discharge. For both, the ICD system consisted of a CPI model 1810 Ventak AV used in conjunction with a model 0125 Endotak lead, incorporating integrated bipolar sensing.

Conclusion: Although modern ICDs have proven to be highly effective in detecting and terminating malignant tachyarrhythmias, the opportunity for improving their detection specificity remains.
Dynamic Changes of 12‐Lead Electrocardiograms in a Patient with Brugada Syndrome
Authors: MATSUO KIYOTAKA , SHIMIZU WATARU , KURITA TAKASHI , INAGAKI MASASHI , AIHARA NAOHIKO , KAMAKURA SHIRO
Published: April 2007

Dynamic ECG Changes in Brugada Syndrome. We present a patient with Brugada syndrome in whom 12‐lead ECXis were recorded just before and after an episode of ventricular fibrillation (VF). A progressive elevation of both the RS‐T segment and J waves just preceding and following the VF, and a close relationship between the amplitude of the RS‐T segment and the preceding R‐R intervals during atrial fibrillation, were documented. These findings support the hypothesis that RS‐T elevation and a subsequent VF are related to a transient outward current‐mediated spike‐and‐dome morphology of the epicardial action potential.
Progressive Depolarization: A Unified Hypothesis for Defibrillation and Fibrillation Induction by Shocks
Authors: DILLON STEPHEN M. , KWAKU KEVIN F.
Published: April 2007

Progressive Depolarization Defibrillation Hypothesis Experimental studies of defibrillation have burgeoned since the introduction of the upper limit of vulnerability (ULV) hypothesis for defibrillation. Much of this progress is due to the valuable work carried out in pursuit of this hypothesis. Tbe ULV hypothesis presented a unified electrophysiologic scheme for linking the processes of defibrillation and shock‐induced fibrillation. In addition to its scientific ramifications, this work also raised the possibility of simpler and safer means for clinical defibrillation threshold testing. Recent results from an optical mapping study of defibrillation suggest, however, tbat the experimental data supporting the ULV hypothesis could instead be interpreted in a manner consistent with traditional views of defibrillation such as the critical mass hypothesis. This review will describe the evidence calling for such a reinterpretation. In one regard the ULV hypothesis superseded the critical mass hypothesis by linking the defibrillation and shock‐induced fibrillation processes. Therefore, this review also will discuss the rationale for developing a new defibrillation hypothesis. This new hypothesis, progressive depolarization, uses traditional defibrillation concepts to cover the same ground as the ULV hypothesis in mechanistically unifying defibrillation and shock‐induced fibrillation. It does so in a manner consistent with experimental data supporting the ULV hypothesis but which also takes advantage of what has been learned from optical studies of defibrillation. This review will briefly deseribe how this new hypothesis relates to other contemporary viewpoints and related experimental results.
Current Concepts of Ventricular Defibrillation
Authors: CHEN PENG‐SHENG , SWERDLOW CHARLES D. , HWANG CHUN , KARAGUEUZIAN HRAYR S.
Published: April 2007

Mechanisms of Deflbhllation. The aim of this article is to review the current concepts of ventricular defibrillation. We studied the interaction between strong electrical stimulas and cardiac responses in both animal models and in humans. We found that a premature stimulus (S2) of appropriate strength results in figure‐eight reentry in vitro by inducing propagated graded responses. The same stimulation protocol induces figure‐eight reentry and ventricular fibrillation (VF) in vivo. When the S2 strength and the magnitude of graded responses increase beyond a critical level, the increase in refractoriness at the site of the stimulus becomes so long that the unidirectional block becomes bidirectional block, preventing the formation of reentry (upper limit of vulnerability [DLV]). In other studies, we found that the effects of an electrical stimulation on reentry is in part determined by the timing of the stimulus. A protective zone is present after the induction of VF and after an unsuccessful defibrillation shock during which an electrical stimulus can terminate reentry and protect the heart from VF. These results indicate that the effects of a defibrillation shock is dependent on both the strength and the timing of the shock. Timing is not important in areas where the shock field strength is < ULV because the shock terminates all reentry hut cannot reinitiate new ones. However, in areas where shock field strength is < ULV, the effects of the shock are determined by the timing of the shock relative to local VF activations. This ULV hypothesis of defibrillation explains the probablistic nature of ventricular defibrillation. It also indicates that, to achieve a high probability of successful defibrillation, a shock must result in a shock field strength of < ULV throughout the ventricles.