bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Architecture of the Atrial Musculature Between the Orifice of the Inferior Caval Vein and the Tricuspid Valve: The Anatomy of the Isthmus
Authors: CABRERA JOSE ANGEL , SANCHEZ‐QUINTANA DAMIAN , YEN HO SIEW , MEDINA ALEONSO , ANDERSON ROBERT H. 
Published: April 2007

Anatomy of Electrophysiologic Isthmus. Introduction: Electrophysiologists recognize a so‐called “isthmus” in the right atrium through which passes the reentrant circuit of common atrial flutter. Ablative lesions placed in this narrow channel have proved effective in breaking the circuit. To the best of our knowledge, however, no study has been performed to establish the arrangement and orientation of the atrial myocardial fibers in this crucial area. Methods and Results: We examined 28 normal heart specimens, identifying a quadrilateral area composed of three morphologic sectors between the inferior caval vein and the tricuspid valve confluent superiorly with the triangle of Koch. Within this quadrilateral, there are constant recesses, or sinuses, inferior and lateral to the orifice of the coronary sinus. The inferior isthmus measured an average of 31 ± 4 mm (range 19 to 40). Gross examination identified marked differences in the atrial wall forming the quadrilateral. A smooth anterior component forming the vestibule of the tricuspid valve was found in all the hearts, but variations in the remaining sectors were seen in ten specimens. The usually membranous posterior sector was noticeably muscular in three specimens, while the middle, trabecular sector was more membranous in five specimens. We demonstrated the orientation of the subendocardial atrial fibers by dissection in 14 specimens, revealing a relatively constant overall pattern in eight specimens and variations in fiber orientation in the remaining specimens. Conclusion: There are considerable anatomic variations in the atrial wall that comprises the so‐called isthmus. The presence of recesses and membranous areas in some hearts and the variations in arrangement of the subendocardial fibers are relevant in improving understanding of conduction in this area.
Comparison of Standard and Irrigated Radiofrequency Ablation in the Canine Ventricle
Authors: SKRUMEDA LISA L. , MEHRA RAHUL 
Published: April 2007

Standard and Irrigated RF Ablation Lesions. Introduction: radiofrequency ablation is successful for treating some arrhythmias but not for CAD‐VT, possibly due to insufficient lesion size. Irrigated electrodes were developed to apply higher power for longer duration to create larger lesions. Our objective was to characterize and compare irrigated and standard ablation in terms of lesion size, crater, and coagulum formation. Additionally, a method is proposed for creating large irrigated lesions without craters. Methods and Results: Three ablation protocols were conducted in canine ventricles. Protocol I: standard ablation was performed in power mode at 10, 20, 30, and 50 W, and electrode‐temperature mode at 70° and 90°C (120 sec). Protocol II: irrigated ablation was conducted with 30 and 50 W (30 and 120 sec). Protocol III: to create large lesions without craters, irrigated ablation was performed at 20 W (5 and 10 min). With a standard electrode, the largest lesions were created using 20 W (358 ± 194 mm3) and using 90°C (301 ± 130 mm2). Ablation duration decreased with power for the power mode standard ablations. The largest irrigated lesions were formed using 50 W (986 ± 357 mm2). Large lesions without craters were created with irrigation using 20 W for 10 minutes (602 ± 175 mm2). Coagulum was seen for most standard ablations but infrequently for irrigated ablations. Craters were observed with 30 and 50 W irrigated ablation but were not observed with 20 W irrigated ablation. Conclusion: Irrigated ablation created larger lesions than standard; large lesions may be created without craters using moderate power and long duration.
The Long QT Syndrome with Impaired Atrioventricular Conduction: A Malignant Variant in Infants
Authors: GORGELS ANTON P.M. , EADLEY FADEL AL , ZAMAN LIAQAT , KANTOCH MICHAL J. , HALEES ZOHAIR AL 
Published: April 2007

Distal Conduction Disease in the Long QT Syndrome. Introduction: The long QT syndrome (LQTS) is occasionally complicated by impaired AV conduction, mostly 2:1 AV block. This form of LQTS can manifest before birth or during neonatal life, and it is more sporadic than familial. It is usually an isolated disorder, although it can be accompanied by a variety of cardiovascular and other anomalies. In spite of different treatment modes, mortality is high. Methods and Results: The reported case presented not only with 2:1 AV conduction, but also with Wenckebach episodes with impaired right and left bundle branch conduction, and decremental conduction in the His‐Purkinje axis. We also observed sinus pauses and accelerated AV junctional escape beats. Conclusion: Our findings, and similar observations by others., suggest involvement of the sinus node and the distal conduction system in this form of the LQTS. Several histologic studies have documented abnormalities within the conduction system, including apoptosis. Because of the rare occurrence and poor prognosis of the LQTS with impaired AV conduction, international guidelines for diagnosis and treatment are needed. Development of an internal cardiac defibrillator for this young age group is necessary.
T Wave Alternans as a Predictor of Recurrent Ventricular Tachyarrhythmias in ICD Recipients: Prospective Comparison with Conventional Risk Markers
Authors: HOHNLOSER STEFAN H. , KLINGENHEBEN THOMAS , LI YI‐GANG , ZABEL MARKUS , PEETERMANS JOY , COHEN RICHARD J. 
Published: April 2007

T Wave Alternans for Risk Stratification. Introduction: The current standard for arrhythmic risk stratification is electrophysiologic (EP) testing, which, due to its invasive nature, is limited to patients already known to be at high risk. A number of noninvasive tests, such as determination of left ventricular ejection fraction (LVEF) or heart rate variability, have been evaluated as additional risk stratifiers. Microvolt T wave alternans (TWA) is a promising new risk marker. Prospective evaluation of noninvasive risk markers in low‐ or moderate‐risk populations requires studies involving very large numbers of patients, and in such studies, documentation of the occurrence of ventricular tachyarrhythmias is difficult. In the present study, we identified a high‐risk population, recipients of an implantable cardioverter defibrillator (ICD), and prospectively compared microvolt TWA with invasive EP testing and other risk markers with respect to their ability to predict recurrence of ventricular tachyarrhythmias as documented by ICD electrograms. Methods and Results: Ninety‐five patients with a history of ventricular tachyarrhythmias undergoing implantation of an ICD underwent EP testing, assessment of TWA, as well as determination of LVEF, baroreflex sensitivity, signal‐averaged ECG, analysis of 24‐hour Holter monitoring, and QT dispersion from the 12‐lead surface ECG. The endpoint of the study was first appropriate ICD therapy for electrogram‐documented ventricular fibrillation or tachycardia during follow‐up. Kaplan‐Meier survival analysis revealed that TWA (P < 0.006) and LVEF (P < 0.04) were the only significant univariate risk stratifiers. EP testing was not statistically significant (P < 0.2). Multivariate Cox regression analysis revealed that TWA was the only statistically significant independent risk factor. Conclusions: Measurement of microvolt TWA compared favorably with both invasive EP testing and other currently used noninvasive risk assessment methods in predicting recurrence of ventricular tachyarrhythmias in ICD recipients. This study suggests that TWA might also be a powerful tool for risk stratification in low‐ or moderate‐risk patients, and needs to he prospectively evaluated in such populations.
Comparison of ECG Variables of Dispersion of Ventricular Repolarization with Direct Myocardial Repolarization Measurements in the Human Heart
Authors: ZABEL MARKUS , LICHTLEN PAUL R. , HAVERICH AXEL , FRANZ MICHAEL R. 
Published: April 2007

Validation of ECG Variables of Dispersion. Introduction: QT dispersion (QTD) from the 12‐tead ECG has been widely adopted as a noninvasive index of dispersion of ventricular repolarization (DVR). QTD, however, has never been validated by direct comparison with myocardial DVR in the human heart. Methods and Results: Monophasic action potential (MAP) recordings obtained in an earlier study were retrospectively matched with 12‐lead ECGs available from within 24 hours of the invasive procedure. MAPs were available from an average of 8 ± 3 left endocardial sites in 4 patients with left ventricular hypertrophy (LVH) and 7 patients with normal ECGs, and 6 ± 2 epicardial sites in 3 patients of each group during normal ventricular activation. Local repolarization time (RT) was determined as MAP duration at 90% repolarization plus the local activation time. Dispersion of RT was calculated as the difference between the earliest and latest RT. ECGs were digitized and analyzed with recently described interactive QTD analysis software. In addition to standard QTD (defined as QTmax– QTmin), all currently proposed ECG dispersion variables were compared and correlated with the invasive measurements of DVR. QTD exhibited a reasonable correlation with dispersion of RT (R = 0.67; P < 0.01). Several other variables designed to measure DVR exhibited a similar, but not better, correlation. Among them, the QT peak/QT end ratio in V3 (R =−0.72; P < 0.01) and averaged over all analyzableleads (R =−0.59; P < 0.01) exhibited a good correlation with dispersion of RT, which was further improved when endocardial measurements were considered alone. T area measures did not correlate with dispersion of RT, but discriminated LVH. Conclusion: DVR can he assessed by means of a 12‐lead surface ECG. Several of the variables under study exhibit a similar accuracy in determination of true myocardial dispersion of repolarization. Variables involving the terminal part of repolarization, such as the QT peak/QT ratio, even from a single lead, may add to the determination of DVR from the human heart.
The Pediatric Radiofrequency Ablation Registry's Experience with Ebstein's Anomaly
Authors: REICH JONATHAN D. , AULD DEBBIE , HULSE EDWARD , SULLIVAN KEVIN , CAMPBELL ROBERT ,   FOR THE PEDIATRIC ELECTROPHYSIOLOGY SOCIETY
Published: April 2007

Radiofrequency Ablation in Pediatric Ebstein's Anomaly. Introduction: Abnormal anatomy and complex electrophysiology in patients with Ebstein's anomaly of the tricuspid valve may confound attempts at radiofrequency ablation (RFA). Methods and Results: Data for 65 pediatric Ebstein's patients (9.8 ± 5.4 years, 4 months to 20 years; 39 ± 25 kg, 5.1 to 108 kg) were obtained from the Pediatric Radiofrequency Ablation Registry. The degree of tricuspid regurgitation (DOTR) and the degree of Ebstein's anomaly were assessed with echocardiography/Doppler. Leading indications were drug refractoriness (24 [37%] of 65 patients) and life‐threatening arrhythmia (14 [22%] of 65 patients). For the 65 patients, 82 typical (nondecremental) accessory pathways (APs) (62% right free wall, 34% right septal, and 4% left sided), 17 other supraventricular tachycardias (1 ectopic atrial, 7 AV reentry, 5 Mahaim, and 4 intra‐atrial reentry tachycardias), and 1 ventricular mechanism were mapped. Thirty‐four (52%) of 65 patients had a single AP (21 right free wall, 10 septal, and 3 left); 19 (29%) of 65 patients multiple APs; 6 (9%) of 65 patients a single AP plus a non‐AP mechanism; and 6 (9%) of 65 patients non‐AP mechanism(s) only. REA acute success rates and recurrence rates for right free wall, right septal, and other mechanisms were 79%/32%, 89%/29%, and 75%/27%. Mild DOTR and a body surface area (BSA) ≤ 1.7 m2 independently predicted a better acute success rate. BSA ≤ 1.7 m2 also predicted long‐term success. Conclusion: In this patient subset, life‐threatening arrhythmias and multiple electrophysiologic mechanisms are commonly encountered during REA. Mild DOTR and a BSA ≥ 1.7 m2 predict a higher acute success rate. While acute success rates are relatively high, recurrence is frequent.
Shortening of the Intraventricular Conduction Time in Premature Ventricular Beats During Ventricular Extrastimulation: Possible Role of Dimensional Shortening of the Conducting Distance During Ventricular Systole
Authors: KASAI HIROI , KAWARA TOKUHIRO , HIEJIMA KAZUMASA , SUZUKI FUMIO 
Published: April 2007

Supernormal Intraventricular Conduction. Introduction: Conduction time (CT) is given by the formula: conducting distance divided by conduction velocity. Based on this formula, we hypothesized that CT shortening (i.e., supernormal conduction) may result from dimensional shortening of the distance of impulse propagation, which naturally occurs during ventricular systole. Methods and Results: To test the above, two separate groups of patients were studied, group A (14 patients) for electrophysiologic study and group B (12 patients) for echocardiographic study. In group A patients, CT from the stimulus artifact to the basal lateral wall of the left ventricle (LV) (S‐LV interval) was measured using right ventricular (RV) apical extrastimulus testing. S‐LV interval shortening in premature RV beats was demonstrated in all 14 patients. The maximum shortening was 20 ± 9 msec (range 10 to 40), and the maximum% shortening was 16%± 6% (7% to 27%). In group B patients with implanted pacemakers, the major (long) and minor (short) axis dimensions of the LV were measured with echocardiography. The major axis dimension was used as an approximate measure of the linear length from the RV apex to the basal lateral wall of LV. The maximum% shortening of the major axis dimensions was 15%± 4%, 16%± 2%, and 11%± 4% during VVI pacing, respectively, at paced cycle lengths of 1,000 (11 patients), 800 (5 patients), and 600 msec (12 patients). The maximum% shortening of the S‐LV intervals was comparable in magnitude with that of the major axis dimensions: 20% versus 15%± 4%, 15%± 7% versus 16%± 2% and 16%± 6% versus 11%± 4%, respectively, at paced cycle lengths of 1,000, 800, and 600 msec. There was also a good temporal correlation between the electrophysiologic (CT shortening) versus echocardiographic (dimensional shortening) parameters. Thus, the intraventricular CT and the major axis dimension of the LV were shortened in a similar magnitude and also at a similar timing in the cardiac cycle. Conclusion: These findings suggest the possibility that supernormal conduction may result, at least in part, from dimensional shortening of the pathway length of impulse propagation from the stimulating to recording electrodes, which naturally occurs during ventricular systole.
Ability of Activation Recovery Intervals to Assess Action Potential Duration During Acute No‐Flow Ischemia in the In Situ Porcine Heart
Authors: EJIMA JUNICHI , MARTIN DAVID , ENGLE CONNIE , SHERMAN ZOE , KUNIMOTO SATOSHI , GETTES LEONARD S. ,   for the EXPERIMENTAL CARDIOLOGY GROUP UNIVERSITY OE NORTH CAROLINA AT CHAPEL
Published: April 2007

Activation Recovery Intervals During No‐Flow Ischemia. Introduction: The ability to assess transmural changes in action potential duration during acute no‐flow ischemia is essential to an understanding of the tachyarrhythmias that occur in this setting. The purpose of this study was to determine if activation recovery intervals determined from unipolar electrograms would provide this information. Methods and Results: We recorded simultaneously transmembrane action potentials and unipolar electrograms from sites located as closely together as possible in the center and at the lateral margin of the ischemic zone during acute no‐flow ischemia and correlated the changes in activation recovery intervals obtained from the unipolar electrograms to the changes in action potential duration. We found that the activation recovery intervals provided an accurate measure of the changes in action potential duration during acute no‐flow ischemia provided the electrograms had a well‐defined, single negative component to the QRS complex with a maximum negative dV/dt > 10 V/sec and a single positive component to the T wave having a maximum positive dV/dt > 1.6 V/sec. Electrograms meeting these criteria comprised 90% of the electrograms recorded at the margin of the ischemic zone throughout 60 minutes of no‐flow ischemia. In the center of the ischemic zone, 75% of the recorded electrograms met these criteria for the first 20 minutes of no‐flow ischemia. Thereafter, the percentage declined and after 40 minutes of no‐flow ischemia, none of the electrograms recorded in the center of the ischemic zone met these criteria. Conclusion: Activation recovery intervals obtained from unipolar electrograms provide an accurate assessment of changes in action potential duration throughout the ischemic zone during acute no‐flow ischemia, provided the characteristics of the electrograms meet specific predetermined criteria.
Long‐Term Evaluation of the Ventricular Defibrillation Energy Requirement
Authors: TOKANO TAKASHI , PELOSI FRANK , ELEMMING MATTHEW , HORWOOD LAURA , SOUZA JOSEPH J. , ZIVIN ADAM , KNIGHT BRADLEY P. , GOYAL RAJIVA , MAN K. CHING , MORADY ERED , STRICKBERGER S. ADAM 
Published: April 2007

Defibrillation Energy Requirements. Introduction: Defibrillation energy requirements in patients with nonthoracotomy defibrillators may increase within several months after implantation. However, the stability of the defibrillation energy requirement beyond 1 year has not been reported. The purpose of this study was to characterize the defibrillation energy requirement during 2 years of clinical follow‐up. Methods and Results: Thirty‐one consecutive patients with a biphasic nonthoracotomy defibrillation system underwent defibrillation energy requirement testing using a step‐down technique (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, and 1 J) during defibrillator implantation, and then 24 hours, 2 months, 1 year, and 2 years after implantation. The mean defibrillation energy requirement during these evaluations was 10.9 ± 5.5 J, 12.3 ± 7.3 J, 11.7 ± 5.6 J, 10.2 ± 4.0 J, and 11.7 ± 7.4 J, respectively (P= 0.4). The defibrillation energy requirement was noted to have increased by 10 J or more after 2 years of follow‐up in five patients. In one of these patients, the defibrillation energy requirement was no longer associated with an adequate safety margin, necessitating revision of the defibrillation system. There were no identifiable clinical characteristics that distinguished patients who did and did not develop a 10‐J or more increase in the defibrillation energy requirement. Conclusion: The mean defibrillation energy requirement does not change significantly after 2 years of biphasic nonthoracotomy defibrillator system implantation. However, approximately 15% of patients develop a 10‐J or greater elevation in the defibrillation energy requirement, and 3% may require a defibrillation system revision. Therefore, a yearly evaluation of the defibrillation energy requirement may he appropriate.
Characteristics of Sinus Rhythm Electrograms at Sites of Ablation of Ventricular Tachycardia Relative to All Other Sites: A Noncontact Mapping Study of the Entire Left Ventricle
Authors: SCHILLING RICHARD JOHN , DAVIES D. WYN , PETERS NICHOLAS SIMON 
Published: April 2007

Noncontact Mappin g of VT During Sinus Rhythm. Introduction: Regions of the diseased ventricle that activate abnormally during sinus rhythm (SR) may be the areas of slow and disorganized conduction that form the diastolic pathway through which reentry may occur during ventricular tachycardia (VT). Methods and Results: We examined features of electrograms recorded during SR that might indicate a site suitable for ablation of VT using a noncontact mapping system, which enables reconstruction of > 3,000 electrograms. Preablation SR electrogram characteristics at sites of successful radiofrequency ablation (RFA) were examined in 13 patients with 53 VTs. Timing of onset, lateness of activity, electrogram duration, and number of baseline crossing events of reconstructed electrograms at the sites of successful RFA were compared with the electrograms of latest onset, latest activity, longest duration, and most baseline crossing events of all ventricular sites. Onset of activation at sites of successful RFA were 26.9 ± 25.2 msec (mean ± SD) earlier than (and 2.9 ± 1.7 cm away from) the site of latest onset of SR activation. Electrogram duration at sites of successful RFA was 83%± 14.6% of (and 4.3 ± 1.8 cm away from) the longest electrogram. The baseline crossing events at sites of successful RFA were 53%± 22% of (and 4.9 ± 1.9 cm away from) the most fractionated electrogram. The latest activity at sites of successful RFA was 21.6 ± 24.8 msec earlier than (and 4.3 ± 1.6 cm away from) the site of latest activity. Conclusion: Although the site of latest onset of endocardial activation during SR proved to be the most sensitive indicator, the characteristics of SR electrograms did not usefully predict successful ablation sites.
Acceleration‐Induced Action Potential Prolongation and Early Afterdepolarizations
Authors: BURASHNIKOV ALEXANDER , ANTZELEVITCH CHARLES 
Published: April 2007

Acceleration‐Induced Early Afterdepolarizations. Introduction: Precipitation of torsades de pointes (TdP) has been shown to he associated with acceleration of heart rate in both experimental and clinical studies. To gain insight into the cellular mechanism(s) responsible for the initiation of acceleration‐induced TdP, we studied the effect of acceleration of pacing rate in canine left ventricular epicardial, M region, endocardial, and Purkinje fiber preparations pretreated with E‐4031, an IKr blocker known to induce the long QT syndrome and TdP. Methods and Results: Standard microelectrode techniques were used. E‐4031 (1 to 2 μM) induced early afterdepolarization (EAD) activity in 31 of 36 M cell, 0 of 10 epicardial, 0 of 10 endocardial, and 9 of 12 Purkinje fiber preparations at basic cycle lengths (BCLs) ≥ 800 msec. In 30 of 36 M cells, sudden acceleration from a BCL range of 900 to 4,000 msec to a range of 500 to 1,500 msec induced transient EAD activity if none existed before or increased the amplitude of EADs if already present. Acceleration‐induced augmentation of EAD activity was far less impressive and less readily demonstrable in Purkinje fibers (4/12). In M cells, appearance of EAD activity during acceleration usually was accompanied by an abbreviation of action potential duration (APD). Within discrete ranges of rates in the physiologic range, acceleration caused a transient prolongation of APD in 38% of M cells, whether or not a distinct EAD was generated. Acceleration produced still more dramatic APD prolongation and EADs in M cells after the BCL was returned to the original slow rate. Epicardium and endocardium APD showed little change immediately after acceleration. A decrease of BCL as small as 10% and, in some cases, a single premature heat could promote EAD activity and APD prolongation in some M cells. Ryanodine (1 μM, 10/10), flunarizine (10 μM, 3/6), and low Na (97 vs 129 mM, 5/5) abolished the acceleration‐induced EAD activity and APD prolongation as well as the EAD activity observed at slow rates in M cells pretreated with E‐4031. Conclusion: Our results suggest that acceleration from an initially slow rate or a single premature beat can induce or facilitate transient EAD activity and APD prolongation in canine ventricular M cell preparations pretreated with an IKr blocker via a mechanism linked to intracellular calcium loading. Our data provide evidence in support of an important contribution of electrogenic Na/Ca exchange current to this process. These acceleration‐induced changes can result in the development of triggered activity as well as a marked dispersion of repolarization in ventricular myocardium and, thus, may contribute to the precipitation of TdP in patients with the congenital (HERG defect) and acquired (drug‐induced) long QT syndrome.