bluuebunny/crossref_metadata_2025 huggingface dataset:
Unipolar Mapping and Magnetic Resonance Imaging of “Idiopathic” Right Ventricular Outflow Tract Ectopy
Authors: MERINO JOSE L. , JIMENEZ‐BORREGUERO JESUS , PEINADO RAEAEL , MERINO SYLVIA V. , SOBRINO JOSE A.
Published: April 2007

Unipolar Mapping and MRI of Ventricular Ectopy. Radiofrequency catheter ablation of symptomatic ventricular ectopy guided by bipolar mapping was successfully accomplished at the right ventricular outflow tract in a patient who did not exhibit apparent structural heart disease. A “QS” morphology with a fast slope of the downstroke deflection at the successful ablation site was observed on the unipolar electrogram. Focal thinning of the lateral wall of the right ventricular outflow tract was shown in the magnetic resonance image, similar to that reported in patients with “idiopathic” right ventricular outflow tract tachycardia.
New Evidence that AV Node Slow Pathway Conduction Directly Influences Fast Pathway Function
Authors: GELLER J. CHRISTOPH , BIBLO LEE A. , CARLSON MARK D.
Published: April 2007

Interaction Between the Slow and Fast Pathway. Introduction: Shortening of the AV node fast pathway effective refractory period (ERP) following successful slow pathway ablation may be a nonspecific effect of energy application at the AV junction or may be due to elimination of a direct effect of slow pathway conduction on the fast pathway.

Methods and Results: Twenty‐six consecutive patients (20 women and 6 men; mean age 45 ± 3 years) with typical AV nodal reentrant tachycardia who underwent successful slow pathway ablation (defined as complete elimination of dual AV node physiology) were studied. The fast pathway ERP (at a drive train cycle length of 600 msec) was determined prior to ablation (baseline) and following unsuccessful and successful ablation attempts. Successful slow pathway ablation shortened the fast pathway ERP significantly (317 ± 9 msec; P < 0.001) compared to baseline (386 ± 12 msec), whereas unsuccessful ablations bad no effect (376 ± 11 msec). Sinus cycle length, the AH interval, and blood pressure were unchanged following successful ablation. Shortening of the fast pathway ERP did not correlate with the number of energy applications or with two measures of the proximity between the slow and the fast pathway.

Conclusion: These results support the hypothesis that shortening of the fast pathway ERP following slow pathway ablation is due to elimination of a direct effect of slow pathway conduction on fast pathway function rather than a nonspecific effect of repeated energy delivery at the AV junction.
Short‐Term Rapid Ventricular Pacing Prolongs Ventricular Refractoriness in Patients
Authors: KREBS MARK E. , SZWED JOSEPH M. , SHINN TIMOTHY , MILES WILLIAM M. , ZIPES DOUGLAS P.
Published: April 2007

Rapid Ventricular Rates Prolong VERP. Background: Traditional concepts suggest that ventricular refractoriness should gradually shorten during rapid pacing and gradually return to baseline after termination of pacing. Animal data, however, have shown that under certain circumstances sustained rapid ventricular rates can prolong refractoriness and action potential duration and, thereby, promote ventricular arrhythmias.

Methods and Results: In humans we evaluated the effect of rapid pacing (cycle length 400 msec for 30 min from either the right ventricular apex IRVA, 13 patients] or high right atrium [HRA, II patients]) on the ventricular effective refractory period (VERP) as measured from the RVA, using the extrastimulus method (drive train 500 msec). A control group of seven patients had serial measurements of VERPs in the absence of pacing. For a given patient, all VERPs were measured at constant stimulus output (twice diastolic threshold) from the same ventricular site and at the same drive train cycle length. VERPs obtained immediately following rapid pacing did not differ from those at baseline (P = 0.46); however, VERPs obtained 15 minutes post pacing were prolonged compared with baseline VERPs (231 ± 20 msec vs 246 ± 23 msec. P < 0.0026). Pacing site has no impact on VERP prolongation. There was no effect of time on VERP in the absence of pacing.

Conclusion: In contrast to traditional concepts of refractoriness, after the termination of sustained rapid ventricular rates, VERP prolonged. This phenomenon could help explain the observation of torsades de pointes in some patients after atrioventricular junction ablation or the administration of a Class IA antiarrhythmic agent to convert atrial fibrillation with rapid ventricular response to sinus rhythm.
Atrial Macroreentry Involving the Myocardium of the Coronary Sinus: A Unique Mechanism for Atypical Flutter
Authors: OLGIN JEFFREY E. , JAYACHANDRAN J. VIJAY , ENGESSTEIN ERICA , GROH WILLIAM , ZIPES DOUGLAS P.
Published: April 2007

Macroreentry Involving the Coronary Sinus. Atrial flutter involving either clockwise or counterclockwise rotation around the tricuspid annulus utilizing the subeustachian isthmus has been well described. However, macroreentrant atrial circuits in atypical atrial flutter in patients who have not undergone previous surgery or without atrial disease are not well defined. We describe a patient without structural heart disease who presented with an atrial macroreentrant rhythm. Entrainment mapping demonstrated a critical isthmus within the coronary sinus. Activation mapping demonstrated double potential throughout the length of the coronary sinus with disparate activation sequences. A circuit involving the myocardium of the coronary sinus, exiting in the lateral left atrium, down the interatrial septum, and reentering into the coronary sinus was identified. Successful ablation of the rhythm was accomplished by a circumferential radiofrequency application within the coronary sinus.
Cisapride‐Induced Torsades de Pointes
Authors: VITOLA JOÃO , VUKANOVIC JASMINKA , RODEN DAN M.
Published: April 2007

Cisapride‐Induced Torsades de Pointes. Two cases of torsades de pointes associated with cisapride are presented, both in association with concomitant drug therapy that inhibits cisapride biotransformation. In one case, plasma cisapride was elevated days after the event, strongly supporting a role for accumulation of the drug in causing the arrhythmia. It is emphasized that these adverse drug reactions are not idiosyncratic, hut rather are predictable based on an understanding of the underlying mechanisms.
Multiple Atrioventricular Nodal Pathways in Humans:
Authors: LEE KATHY L. , CHUN HINGSON M. , LIEM L. BING , LAUER MICHAEL R. , YOUNG CHARLIE , SUNG RUEY J.
Published: April 2007

Multiple AV Nodal Pathways. Introduction: Multiple AV nodal pathway physiology can be demonstrated in certain patients with clinical AV reentrant tachycardia.

Methods and Results: Evidence suggesting multiple AV nodal pathway conduction was present in seven (two males; age range 15 to 75 years) of 78 patients (9%) who underwent electrophysiologic studies for AV nodal tachycardia. The presence of two discrete discontinuities in the AV nodal conduction curves suggested triple AV nodal pathway conduction. Detailed mapping of their retrograde atrial activation sequence was performed along the tricuspid annulus from the coronary sinus ostium to the His‐bundle electrogram recording site. Three zones (anterior, middle, and posterior) correspond to the upper, middle, and lower third of the triangle of Koch, respectively. The fast pathway exits were determined as anterior (4/7) or middle (3/7), the intermediate pathway exits as middle (4/7) or posterior (3/7), and the slow pathway exits as middle (1/7) or posterior (6/7). Other evidence suggesting multiple AV nodal pathway conduction includes: (1) triple ventricular depolarizations from a single atrial impulse; (2) sequential dual ventricular echoes; (3) spontaneous transformation between the slow‐fast and fast‐slow forms of AV nodal reentrant tachycardia; and (4) persistent cycle length alternans during AV nodal reentrant tachycardia. In four patients, all three pathways were shown to be involved in AV nodal echoes or reentrant tachycardia.

Conclusion: Multiple AV nodal pathways are not uncommon and can be identified by careful electrophysiologic elucidation and mapping technique.
Retrograde Multiple and Multifiber Accessory Pathway Conduction in the Wolff‐Parkinson‐White Syndrome:
Authors: IESAKA YOSHITO , YAMANE TEIICHI , TAKAHASHI ATSUSHI , GOYA MASAHIKO , KOJIMA SHIGEYUKI , SOEJIMA YOHKOH , OKAMOTO YOSHIHIRO , FUJIWARA HIDEOMI , AONUMA KAZUTAKA , NOGAMI AKIHIKO , HIROE MICHIAKI , MARUMO FUMIAKI , HIRAOKA MASAYASU
Published: April 2007

Retrograde Multiple Accessory Pathway Precipitating AF. Introduction: The determinants of susceptibility to atrial fibrillation (AF) and the existence of accessory pathway conduction have remained unidentified in the Wolff‐Parkinson‐White (WPW) syndrome. We tested the hypothesis that excitation inputs into the atrium over a retrograde multiple or multifiber accessory pathway during AV reentrant tachycardia (AVRT) could precipitate initiation of AF.

Methods and Results: Two hundred fifty consecutive patients with WPW syndrome underwent electrophysiologic study and radiofrequency catheter ablation. The patients were classified into two groups according to the study results: 29 with retrograde multiple or multifiber accessory pathway (MP) and 221 with retrograde single accessory pathway (SP). Compared with the SP patients, the MP patients showed a significantly higher incidence of clinical AF (MP vs SP: 19/29 vs 51/221, P < 0.01), induced AF (12/29 vs 32/221, P < 0.01), and initiated AF during ventricular pacing and AVRT (10/12 vs 17/32, P < 0.05). There were no differences between the two groups in incidence of clinical and induced AVRT (24/29 vs 200/221 and 25/29 vs 206/221, respectively), mean cycle length of induced AVRT, or electrophysiologic parameters of the accessory pathway. AF inducibility during AVRT or ventricular pacing was eliminated by partial ablation in 7 of 10 patients with MP. After total ablation, the incidence of induced AF was similar between the two groups (MP vs SP: 1/29 vs 11/221).

Conclusion: The existence of a retrograde multiple or multifiber accessory pathway in patients with WPW syndrome is associated with a higher incidence of clinical and induced AF. Successful ablation of the retrograde multiple or multifiber accessory pathway can eliminate the induction of both AVRT and AF.
Acute and Long‐Term Effects of Consecutive Radiofrequency Applications on Conduction Properties of the Subeustachian Isthmus in Type I Atrial Flutter
Authors: SCHUMACHER BURGHARD , PFEIFFER DIETRICH , TEBBENJOHANNS JÜRGEN , LEWALTER THORSTEN , JUNG WERNER , LÜDERITZ BERNDT
Published: April 2007

Effects of Atrial Flutter Ablation. Introduction: Bidirectional conduction block at the subeustachian isthmus predicts long‐term efficacy of atrial flutter ablation. Limited data are available on the incidence and outcome of minor conduction changes such as unidirectional or incomplete block. This prospective study sought to systematically assess discrete acute and long‐term alterations of bidirectional conduction prior to a complete conduction block.

Methods and Results: In 41 patients with type I atrial flutter, pulse propagation through the subeustachian isthmus during low lateral and proximal coronary sinus pacing was documented and analyzed following each consecutive radiofrequency (RF) application. In cases of altered conduction properties and noninducibility of atrial flutter, patients were followed‐up for 12 months. Three sets of results were found. First, following RF application. 23 patients presented a progressive conduction delay prior to a complete conduction block. Second, RF application did not always affect counterclockwise and clockwise conduction simultaneously or to the same extent. In 13 patients, an initial alteration of counterclockwise conduction was present before an alteration of clockwise conduction; in 5 patients, clockwise conduction was primarily affected. Third, the recurrence rate of typical atrial flutter was 9% (2/22) in patients with a complete bidirectional conduction block, 54% (7/13) in patients with unidirectional conduction block, and 100% (6/6) in patients with sole bidirectional conduction delay.

Conclusion: In 50% of the patients, consecutive RF applications resulted primarily in a progressive conduction delay rather than a sudden conduction block. Since counterclockwise and clockwise conduction were not always affected simultaneously or to the same extent, lateral as well as septal pacing is recommended for improvement of bidirectional conduction block. Normalization of primarily altered conduction and, therefore, recurrence of atrial flutter are high in all patients without bidirectional block.
Mechanisms of Arrhythmias in Heart Failure
Authors: VERMEULEN JESSICA T.
Published: April 2007

Mechanisms of Arrhythmias in Heart Failure. The diagnosis of heart failure infers a bad prognosis. Mortality is high and many patients die suddenly. Ventricular arrhythmias, commonly observed in patients with heart failure, are thought to underlie at least some of these sudden deaths. The mechanism of arrhythmias occurring in the setting of heart failure is still unclear. Experimental evidence points to a higher tendency for failing myocardium to develop delayed and early afterdepolarization‐induced triggered activity and automaticity. Conditions favoring reentry also have been described in failing hearts. Modulating factors such as sympathetic activation, electrolyte disturbances, and chronic stretch are present in the setting of heart failure and may favor all of the mentioned mechanisms of arrhythmias. Clinical evaluation of arrhythmias in patients and animals with heart failure and the effects of pharmacologic treatment of ventricular arrhythmias in patients with depressed left ventricular function further accentuate that more than one mechanism of arrhythmia may he operating in heart failure and underscore the importance of modulating factors such as sympathetic activation and stretch.
Endocardial and Epicardial Ablation Guided by Nonsurgical Transthoracic Epicardial Mapping to Treat Recurrent Ventricular Tachycardia
Authors: SOSA EDUARDO , SCANAVACCA MAURICIO , D'AVILA ANDRE , PICCIONI JOÃO , SANCHEZ OSVALDO , VELARDE JOSÉ L. , SILVA MARCIO , REOLÃO BASILEO
Published: April 2007

Nonsurgical Epicardial Ablation. Introduction: An epicardial site of origin of ventricular tachycardia (VT) may explain unsuccessful endocardial radiofrequency (RF) catheter ablation. A new technique to map the epicardial surface of the heart through pericardial puncture was presented recently and opened the possibility of using epicardial mapping to guide endocardial ablation or epicardial catheter ablation. We report the efficacy and safety of these two approaches to treat 10 consecutive patients with VT and Chagas’ disease.

Methods and Results: Epicardial mapping was carried out with a regular steerable catheter introduced into the pericardial space. An epicardial circuit was found in 14 of 18 mapable VTs induced in 10 patients. Epicardial mapping was used to guide endocardial ablation in 4 patients and epicardial ablation in 6. The epicardial earliest activation site occurred 107 ± 60 msec earlier than the onset of the QRS complex. At the epicardial site used to guide endocardial ablation, earliest activation occurred 75 ± 55 msec before the QRS complex. Epicardial mid‐diastolic potentials and/or continuous electrical activity were seen in 7 patients. After 4.8 ± 2.9 seconds of epicardial RF applications, VT was rendered noninducible. Hemopericardium requiring drainage occurred in 1 patient; 3 others developed pericardial friction without hemopericardium. Patients remain asymptomatic 5 to 9 months after the procedure. Interruption during endocardial pulses occurred after 20.2 ± 14 seconds (P = 0.004), hut VT was always reinducible and the patients experienced a poor outcome.

Conclusion: Epicardial mapping does not enhance the effectiveness of endocardial pulses of RF. Epicardial applications of RF energy can safely and effectively treat patients with VT and Chagas’ disease.
Temporal Stability of Defibrillation Thresholds with an Active Pectoral Lead System
Authors: OLSOVSKY MARY R. , PELTNI MICHAEL A. , SHOROESKY STEPHEN R. , GOLD MICHAEL R.
Published: April 2007

Stability of Defibrillation Thresholds. Introduction: Monophasic defibrillation thresholds rise over time with a variety of lead systems. These chronic changes are attenuated or eliminated by biphasic waveforms, although the effect appears dependent upon the lead system. With the downsizing of pulse generator size to allow for routine pectoral implantation, active can lead systems have now become standard. However, the temporal stability of such lead systems has not been evaluated previously.

Methods and Results: This study was a prospective assessment of the changes of active pectoral defibrillation thresholds over time. Thresholds were measured at implant, predischarge, and at a mean follow‐up of 50 days in 46 patients with a uniform testing protocol and shock polarity. The lead system was a dual‐coil Endotak DSP lead with an active pectoral pulse generator. Defibrillation thresholds were 9.9 ± 5.5 J at implantation, 8.5 ± 6.0 J predischarge, and 7.6 ± 5.5 J at follow‐up (ANOVA, P = 0.007). Moreover, only two patients developed an increased threshold > 5 J, and no patient had an inadequate safety margin at follow‐up.

Conclusion: These results indicate that active pectoral defibirillation thresholds are stable over the first 2 months postimplantation and question the need for routine serial defibrillation threshold testing.
Enhanced Detection Criteria in Implantable Defibrillators
Authors: BRUGADA JOSEP , MONT LLUIS , FTGUEIREDO MARCIO , VALENTINO MARIANA , MATAS MARIONA , NAVARRO‐LÓPEZ FRANCISCO
Published: April 2007

Enhanced Tachycardia Detection Algorithm introduction: Enhanced detection criteria in third‐generation implantable defibrillators have been implemented to avoid inappropriate therapy of fast supraventricular arrhythmias. We prospectively analyzed the use of these criteria in patients with an implantable defibrillator with electrogram storing capability.

Methods and Results: In 82 consecutive patients with a Guidant‐CPI implantable defibrillator, sudden onset > 9% and stability < 40 msec were systematically programmed in zone 1 of therapy together with a sustained rate duration security mechanism. All detected tachycardia episodes were analyzed. The study population consisted of 59 patients who had at least one episode of tachycardia detected in zone 1 during follow‐up. The tachycardia rate in zone 1 never exceeded 210 beats/min. Twenty patients had no episodes during follow‐up, and three patients had episodes detected exclusively in zone 2 of therapy. Supraventricular arrhythmias were detected frequently in the ventricular tachycardia zone (193 of 690 tachycardia episodes in 23 of 59 patients). Use of sudden onset was very effective in detecting sinus tachycardias (65 of 67 episodes), and stability was very useful in detecting atrial fibrillation (31 of 32 episodes). However, sensitivity in detecting ventricular tachycardia was only 90% (451 of 497 episodes). Application of the sustained rate duration criterion allowed appropriate treatment of all ventricular tachycardia episodes, increasing sensitivity to 100%; however, specificity in appropriate non‐treatment of supraventricular decreased from 96% to 83%. Subsequent analysis of different algorithms applied to our data showed that sudden onset > 9% and stability < 40 msec was the algorithm with the best specificity and sensitivity.

Conclusion: Programming sudden onset and stability detection criteria with a sustained rate duration safety net for triggering tachycardia therapy results in appropriate device management in most patients with supraventricular and slow (< 210 beats/min) ventricular tachycardias.
Mechanisms of Induction of Typical and Reversed Atrial Flutter
Authors: COSÍO FRANCISCO G. , LÓPEZ‐GIL MARÍA , ARRIBAS FERNANDO , GONZÁLEZ H. DANIEL
Published: April 2007

Mechanisms of Flutter Induction. Introduction: Typical flutter is due to reentry around caval veins and terminal crest. In patients with typical flutter, reversed (clockwise) reentry can be induced. We studied mechanisms of typical and reversed flutter induction.

Methods and Results: Thirteen patients (11 men) underwent 16 radiofrequency (RF) ablation procedures for typical (12) or reversed flutter (1), High right atrium (RA) stimulation included 1 to 3 extrastimuli over cycle lengths 6(M) to 250 msec, and burst. We recorded simultaneously from three levels of septal and anterior RA. RF was delivered to the inferior vena cava‐tricuspid isthmus (CTI). Of 25 inductions, 4 were a result of single, 9 double, and 11 triple extrastimuli, and 1 burst. Clinical basal flutter was induced (7 typical, 1 reversed). After RF, typical flutter was reinduced in 9 cases and reversed flutter in 7, with only typical flutter seen clinically. All flutters were interrupted by ablation or catheter pressure on the CTI. Typical flutter began by low RA septal activation block, preceded by repetitive responses in 12 instances, atypical flutter in 1, and directly from stimuli in 4. Reversed flutter started in 8 instances by low RA block of a stimulated front descending the anterior wall and in 1 by repetitive responses.

Conclusion: Septal activation block was the usual mechanism of typical flutter induction by RA extrastimuli. Facilitation of reversed flutter after RF application is probably due to a new area of block in the CTI. Flutter induction without intermediate rhythms confirms the presence of block at the terminal crest at baseline.
Reduced Inward Rectifying and Increased E‐4031‐Sensitive K+ Current Density in Arrhythmogenic Subendocardial Purkinje Myocytes from the Infarcted Heart
Authors: PINTO JUDITH M.B. , BOYDEN PENELOPE A.
Published: April 2007

Outward Currents in Purkinje Cells from 48‐Hour Infarcted Heart. Introduction: Subendocardial Purkinje myocytes from the 4K‐hour infarcted heart (IZPCs) have reduced resting potentials, possibly due to altered inwardly rectifying K+ currents IKI. Abnormal depolarization‐activated outward K+ currents could contribute to long triangularly shaped action potentials of IZPCs.

Methods and Results: We used whole cell patch recordings to compare cesium‐sensitive IKI and 4‐aminopyridine (4‐AP)‐resistant, noninactivating sustained IK between normal Purkinje myocytes (NZPCs) and IZPCs. IZPCs showed decreased net membrane currents. Two IZPC groups were distinguished, based on 4‐AP‐resistant outward K+ currents. IZPC‐I had isochronal IKI current‐voltage relations similar to NZPCs whereas IZPC‐II showed significantly reduced IKI and increased outward plateau currents. To study the sustained IK in the presence of the Class III antiarrhythmic agent E‐4031, a two‐pulse protocol was used to inactivate transient outward currents, followed by step depolarizations. E‐4031‐sensitive currents were significantly greater in IZPCs at depolarized potentials (> 0 mV). Similar to NZPCs, IZPC E‐4031 currents showed time dependence during depolarization, lack of rectification at positive steps, and voltage‐dependent recovery from block.

Conclusion: Decreased IKI may account for reduced resting potentials in IZPCs. E‐4031‐sensitive currents in NZPCs, unlike those in canine ventricular myocytes, are sensitive to 4‐AP and are larger in IZPCs.
Lidocaine's Effect on Defibrillation Threshold are Dependent on the Defibrillation Electrode System: Epicardial Versus Endocardial
Authors: MILLER ALLISON P. WINECOFF , SIMS J. JASON , McSWAIN ROBERT , UJHELYI MICHAEL R.
Published: April 2007

Lidocaine's Effect on Defibrillation Depends on Lead System. Introduction: Epicardial and endocardial defibrillation electrode systems affect myocardial electrophysiology and sympathetic function differently. Thus, we postulate that antiarrhythmic drugs will interact with these electrode systems differently.

Methods and Results: Defibrillation energy requirements (DER) at 20% (ED20), 50% (ED50), and 80% (ED80), success were measured at baseline and during lidocaine (10 mg/kg per hour) or D5W treatment for epicardial and endocardial electrodes. Pigs were randomized to treatment (lidocaine or D5W) and electrode system, which resulted in four experimental groups: (1) epicardial electrode + D5W; (2) epicardial electrode + lidocaine; (3) endocardial electrode + D5W; and (4) endocardial electrode + lidocaine. ED50 DER (mean ± SEM) values at baseline for groups 1–4 were 10.6 ± 1, 8.5 ± 1, 12.6 ± 1, and 12.3 ± 1 J, respectively. DER values for groups 1 and 3 during D5W were similar to baseline. Conversely, lidocaine increased ED50 DER values from 8.5 ± 1 to 13.5 ± 2 J (P < 0.05) in group 2 animals (epicardial electrodes). When lidocaine was administered to group 4 animals (endocardial electrodes), however, ED50 DER values remained similar to baseline values (12.3 ± 1 to 14.3 ± 2 J, P = NS). Lidocaine increased ED50 DER values by 59% with the epicardial electrode system, which was significantly greater than the 16% increase with the endocardial electrode system (P < 0.05). Electrophysiologic response and electrode impedance were similar between electrode systems.

Conclusion: Lidocaine increases DER values to a greater extent when using epicardial versus endocardial electrode system. Thus, drug‐device interactions are dependent on the electrode system. These data suggest that the electrophysiologic milieu created by endocardial defibrillation mitigates the effects that lidocaine has on DER values.
Syncytial Heterogeneity as a Mechanism Underlying Cardiac Far‐Field Stimulation During Defibrillation‐Level Shocks
Authors: FISHLER MATTHEW G.
Published: April 2007

Far‐Field Stimulation via Syncytial Heterogeneities. Introduction: The mechanisms by which a defibrillation shock directly stimulates regions of cardiac tissue distal to the stimulus electrodes (“far‐field” stimulation) are still not well understood. Existing hypotheses have proposed that intercellular discontinuities and/or fiber curvatures induce the requisite membrane polarizations. This article hypothesizes a third potential mechanism: one based on the existence and influences of syncytial (anatomic) heterogeneities inherent throughout the bulk myocardium itself.

Methods and Results: We simulated the effects of such heterogeneities in a model of a two‐dimensional region of passive cardiac tissue subjected to uniform 1 V/cm longitudinal or transverse field stimuli. Heterogeneities were manifested via random spatial variations of intracellular volume fractions (fi) over multiple length scales, with mean of 80% and standard deviation ofi (σfi) ranging from 0% to 10%. During field stimulation, many interspersed and variously shaped and sized islands of hyperpolarization and depolarization developed across the tissue, with their locations and extents correlated to the spatial gradients of the underlying heterogeneities. Increases in σfi correspondingly increased the shock‐induced magnitudes of resulting membrane polarizations. The ratio of maximal polarizations for equivalent longitudinal and transverse shocks approximated 2:1 across all σfi tested. At σfi= 5%, these maximal induced polarizations were 17.4 ± 2.4 mV and 8.18 ± 1.5 mV, respectively. Assuming an excitation threshold of 25 mV, these data suggest corresponding diastolic thresholds of 1.47 ± 0.20 V/cm and 3.14 ± 0.50 V/cm, respectively.

Conclusion: This study predicts that syncytial heterogeneities inherent within cardiac tissue could represent a significant—and heretofore unappreciated—mechanism underlying field‐induced polarizations throughout the bulk myocardium.
Temperature‐Controlled Irrigated Tip Radiofrequency Catheter Ablation:
Authors: PETERSEN HELEN HØGH , CHEN XU , PIETERSEN ADRIAN , SVENDSEN JESPER HASTRUP , HAUNSØ STIG
Published: April 2007

Temperature‐Controlled Irrigated Tip Ablation. Introduction: In patients with ventricular tachycardias due to structural heart disease, catheter ablation cures < 60% partly due to the limited lesion size after conventional radiofrequency ablation. Irrigated tip radiofrequency ablation using power control and high infusion rates enlarges lesion size, hut has increased risk of cratering. The present study explores irrigated tip catheter ablation in temperature‐ controlled mode, target temperature 60°C, using an irrigation rate of 1 mL/min, comparing this to conventional catheter technique, target temperature 80°C.

Methods and Results: In vivo anesthetized pigs were ablated in the left ventricle. In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Lesion volume was significantly larger after irrigated tip ablation both in vivo (544 ± 218 vs 325 ± 194 mm3, P < 0.01) and in vitro (286 ± 113 vs 179 ± 23 mm3, P < 0.01). The incidence of cratering was not significantly different between the two groups. In vivo, no coagulum formation on part of the catheter tip was seen after irrigated tip ablation as opposed to 52% of the applications with conventional ablation (P < 0.05).

Conclusion: We conclude that temperature‐controlled radiofrequency ablation with irrigated tip catheters using low target temperature and low infusion rate enlarges lesion size without increasing the incidence of cratering and reduces coagulum formation of the tip.
Susceptibility to Atrial Fibrillation:
Authors: POWER JOHN M. , BEACOM GRAHAM A. , ALEERNESS CUE A. , RAMAN JAI , WUEEELS MAURITS , EARISH STEPHEN J. , BURRELL LOUISE M. , TONKIN ANDREW M.
Published: April 2007

Propensity for Extrastimulus to Induce AF. Introduction: The development of susceptibility to atrial fibrillation (AF) is a common consequence of many forms of cardiovascular disease, especially heart failure. In this study we used a sheep model of pacing‐induced stable early heart failure to describe, quantify, and relate the level of susceptibility to AF to changes in structural and electrophysiologic parameters.

Methods and Results: Epicardial electrodes were implanted on the atria and right ventricles of nine sheep. The AF thresbold, atrial vulnerability period, atrial effective refractory period (ERP), and interatrial conduction time were examined during control and over a 6‐week period of ventricular pacing at 190 beats/min. Left atrial (LA) area and left ventricular (LV) fractional shortening were monitored using echocardiography. There were significant increases in LA susceptibility to AF (P < 0.0003), LA area (P < 0.0002), and LA FRP400 (P < 0.0002). Rate of increase in LA area was related positively to AF susceptibility (P = 0.02) and inversely to LA ERP400 (P = 0.002). LV fractional shortening decreased to approximately 50% of control value (P < 0.00001). No changes were observed in right atrial electrophysiology.

Conclusion: In this study, susceptibility (the ability of an extrastimulus to induce AF) was rigorously measured within a predetermined format. Significant relationships were found to exist between susceptibility, certain of the observed changes in atrial electrophysiology and structure.
Preserved Autonomic Modulation of the Sinus and Atrioventricular Nodes Following Posteroseptal Ablation for Treatment of Atrioventricular Nodal Reentrant Tachycardia
Authors: KOWALLIK PETER , ESCHER SILKE , PETERS WERNER , BRAUN CHRISTIAN , MEESMANN MALTE
Published: April 2007

Autonomic Control of the AV Node. Introduction: Following radiofrequency catheter ablation of AV nodal reentrant tachycardia (AVNRT), inappropriate sinus tachycardia may occur, possibly due to damage to autonomic cardiac nerve fibers. Furthermore, inducibility of AVNRT is often critically dependent on the autonomic balance. We investigated whether successful ablation of AVNRT is associated with an alteration of autonomic input to the sinus and AV nodes.

Methods and Results: To estimate changes in the automatic modulation of the sinus and AV nodes, power spectra of beat‐to‐beat PP and PR intervals were analyzed from high‐quality nighttime ECG recordings of 11 patients before and after radiofrequency application. Normalized HF power (nHF) of PP and PR intervals was used as an index of efferent vagal modulation and the LF/HF ratio as an index of sympathovagal balance of the sinus node (PP) and AV node (PR). Before ablation, LF/HFPP was 3.2 and nHFPP was 0.3 in the sinus node, For the A/V node, LF/HFPR was 1.2 and nHFPR was 0.5. Following ablation. LF/HFPP (3.5) and nHFPP (0.3) of the PP intervals did not change. Similarly to the sinus node, there were no changes in the autonomic modulation of the AV node, as both LF/HFPR (1.2) and nHFPR (0.5) remained unchanged.

Conclusion: Our results indicate that autonomic control of the sinus und AV nodes is preserved following successful radiofrequency ablation of AVNRT. The effects of posteroseptal radiofrequency current application are not necessarily mediated by changes in the autonomic input to the AV node.
Novel Donor Splice Site Mutation in the KVLQT1 Gene is Associated with Long QT Syndrome
Authors: KANTERS JØRGEN K. , LARSEN LARS ALLAN , ORHOLM MARIANNE , AGNER ERIK , ANDERSEN PAAL SKYTT , VUUST JENS , CHRISTIANSEN MICHAEL
Published: April 2007

KVLQT1 Gene Mutation and LQTS. Introduction: Inherited long QT syndrome (LQTS) recently has been associated with mutations in genes coding for potassium (KVLQTI, KCNEI, and HERG) or sodium (SCN5A) ion channels involved in regulating either sodium inward or potassium outward currents of heart cells, resulting in prolongation of the repolarization period. We describe a new mutation, a‐1 donor splice site mutation in a kindred with two affected members (QTc = 0.61 and 0.54 sec).

Methods and Results: Single stranded conformation polymorphism (SSCP) analyses were performed on DNA fragments amplified by polymerase chain reaction from DNA extracted from whole blood. Aberrant conformers were analyzed by DNA sequencing. SSCP analysis of the KVLQTI gene revealed an aberrant conformer in the affected family members. DNA sequencing confirmed the presence of a G→A change in the last nucleotide of codon 344. This mutation does not cause an amino acid change, but a change of the splice site characteristics at the 3’end of exon 6. The mutation may affect, through deficient splicing, the putative sixth transmembrane segment of the K+ channel, and this type of mutation has not previously been described in KVLQTI.

Conclusion: The clinical course of LQTS in the affected family members, in whom no deaths occurred despite 20 to 30 syncopes, can he explained by the ability of the cellular machinery to perform partial correct splicing in the mutant allele. This type of mutation may be misinterpreted as a normal variant, since it is a point mutation causing neither an amino acid change nor the introduction of a stop codon.
Origin of Heat‐Induced Accelerated Junctional Rhythm
Authors: THIBAULT BERNARD , de BAKKER JACQUES M.T. , HOCINI MÉLÈZE , LOH PETER , WITTKAMPF FRED H.M. , JANSE MICHIEL J.
Published: April 2007

Accelerated Junctional Rhythm. Introduction: The application of high‐frequency current to the AV junctional area results in a temperature rise in the myocardium and may cause accelerated junctional rhythm (AJR). The aim of the study was to characterize heat‐induced AJR in an in vitro animal model.

Methods and Results: Studies were performed in isolated perfused pig and rabbit hearts. Using a small heating probe, we could induce AJR from a discrete area located in the middle of the triangle of Koch, which was smaller than the area from which RF energy application could elicit AJR. Histology showed that the heat‐sensitive area was located over, or close to, the compact AV node. It did not correspond with the areas where double potentials were found or with the site(s) of earliest atrial activation during VA conduction. Microelectrode recordings revealed that AJR arose in nodal‐type cells. Heat increased the slope of the phase 4 depolarization and shortened the action potential duration. Two types of AJR were observed: the first one was regular and the second one showed irregularity in the intervals. Interaction of multiple foci and the presence of conduction block between the foci and the His bundle caused the irregularity of the His‐His intervals during the second type of AJR.

Conclusion: AJR observed during heat and RF application in the AV nodal area results from the effect of heat on AV nodal cells with underlying pacemaker activity. The heat‐sensitive area is located over, or very close to, the compact AV node.
Management of Patients with the Hereditary Long QT Syndrome
Authors: MOSS ARTHUR J.
Published: April 2007

Long QT Syndrome. The hereditary long QT syndrome is an inherited ion channel disorder with QT prolongation, morphologic changes in the T waves, and a relatively high frequency of syncope, T wave alternans, torsades de pointes‐type ventricular tachycardia, and sudden death. Monotherapy with beta blockers is the treatment of first choice. In patients with recurrent syncope despite therapy with beta blockers, pacemakers and/or ganglionectomy may be useful in selected cases, with an implantable cardioverter defibrillator used as a fail‐safe approach in high‐risk patients.
Detection of Ventricular Fibrillation by Transvenous Defibrillating Leads:
Authors: GOLDBERGER JEFFREY J. , HORVATH GEORGE , DONOVAN DORIS , JOHNSON DAVID , CHALLAPALLI RAM , KADISH ALAN H.
Published: April 2007

Integrated Versus Dedicated Bipolar Sensing of VF. Introduction: Dedicated bipolar sensing has been suggested to be safer than integrated bipolar sensing due to an increased incidence of failure to redetect ventricular fibrillation after an unsuccessful shock with leads that use integrated bipolar sensing. We compared sensing charactersitics during ventricular fibrillation of simultaneously recorded dedicated and integrated bipolar electrograms.

Methods and Results: Thirty patients undergoing transvenous defibrillator implantation with a Transvene lead were studied. Simultaneous recordings were made from the dedicated bipole and the integrated bipole from the distal tip to the coil (interelectrode distance 18.3 mm). The mean detection time and number of undetected beats for the initial episode of ventricular fibrillation were 2804 ± 569 msec and 0.9 ± 0.8 using the dedicated recordings and 2938 ± 546 msec and 1.4 ± 1.1 (P = 0.026) using the integrated recordings. The mean redetection times and number of undetected beats following a failed first shock (n = 13) were 2468 ± 225 msec and 0.8 ± 1.1 for the dedicated recordings and 3042 ± 498 msec (P < 0.0003) and 4.2 ± 4.2 (P < 0.005) for the integrated recordings. Frequency analysis of the ventricular fibrillation electrograms demonstrated that the signal energy in the dedicated electrograms was significantly greater than the energy in the integrated electrograms (P < 0.0001). There was a significant negative relationship between detection times and the ventricular fibrillation signal energy. There was no independent effect of recording type (dedicated versus integrated).

Conclusion: There are only minor differences in detection/redetection of ventricular fibrillation between dedicated and integrated (with tip to coil spacing of 18.3 mm) recording configurations. Detection times during ventricular fibrillation are related to the signal variance or energy recorded. Differences in the sensing performance of the two recording configurations can be explained by the differences in signal energy between the dedicated and integrated recordings that occur during ventricular fibrillation.
Effect of Heart Rate on T Wave Alternans
Authors: KAVESH NEAL G. , SHOROFSKY STEPHEN R. , SARANG SAMANTHA E. , GOLD MICHAEL R.
Published: April 2007

Heart Rate and T Wave Alternans. Introduction: T wave alternans (TWA) is a promising technique for detecting arrhythmia vulnerability. Previous studies in animals demonstrated that the magnitude of TWA is dependent on heart rate. However, the effects of heart rate on TWA in humans and the clinical relevance of this effect remain controversial.

Methods and Results: This was a prospective evaluation of pacing rate and monitoring lead configuration on TWA in subjects undergoing electrophysiologic study. Measurements of TWA were performed on 45 patients in the absence of antiarrhythmic drugs. Recordings were made in normal sinus rhythm and during atrial pacing at 100 and 120 beats/min. Sustained monomorphic ventricular tachycardia (VT) was induced in 29 patients with programmed stimulation. TWA in the vector magnitude lead increased with heart rate, independent of VT inducibility (0.4 ± 0.7 μ V, 1.6 ± 1.9 μ V, and 2.4 ± 2.1 μ V in sinus rhythm and at 100 and at 120 beats/min, respectively; P < 0.001). In addition, the diagnostic performance of TWA for inducible VT was dependent on heart rate (sensitivity 4%, 42%, and 65%, and specificity 100%, 93%, and 63% at 77, 100, and 120 beats/min, respectively). By analyzing orthogonal leads rather than the vector magnitude lead, the sensitivity is increased from 42% to 59% at 100 beats/min, but the specificity is reduced from 93% to 72%.

Conclusion: These results indicate that TWA in humans is strongly dependent on heart rate with regard to both magnitude and diagnostic performance. The optimal heart rate for the measurement of TWA is between 100 and 120 beats/min and multiple leads should be monitored.
Radiofrequency Modification of the Atrioventricular Node in Patients with Chronic Atrial Fibrillation:
Authors: STABILE GIUSEPPE , TURCO PIETRO , DE SIMONE ANTONIO , COLTORTI FERNANDO , DE MATTEIS CARMINE
Published: April 2007

RF Modification of AVN in AF. Introduction: We compared, in a prospective and randomized fashion with a cross‐over design, the anterior and posterior approaches to radiofrequency (RF) modification of the AV node in patients with chronic atrial fibrillation.

Methods and Results: Thirty‐three patients were randomized to receive first an anterior (group I) or posterior (group II) approach for RF modification of AV nodal conduction. Patients who did not fill the endpoint ventricular rate (< 90 beats/min) were crossed over to the alternative approach. After the anterior approach in group I patients, mean ventricular rate was significantly lower than in group II patients after the posterior approach (79.6 ± 18.8 beats/min vs 110.8 ± 16.2 beats/min, P < 0.001). In group I, 14 (82%) of 17 patients fulfilled the endpoint, 1 (6%) had complete AV block, and 2 (12%) were crossed over to the posterior approach fulfilling the endpoint. In group II, 4 (25%) of 16 patients fulfilled the endpoint. No transient or permanent high‐degree AV block was observed. Among the 12 patients who were crossed over to the anterior approach, 8 fulfilled the endpoint, whereas 4 had permanent high‐degree AV block. RF ablation carried out only in the anterior region was safer than a stepwise approach (6% vs 33% incidence of AV block), even though the difference did not reach statistical significance (P = 0.09).

Conclusion: Posterior AV nodal modification is less effective but safer than anterior AV nodal modification. However, to reduce the incidence of AV block, the anterior approach is preferable to a stepwise approach from the posterior to the anterior zone.
Potentiating Effect of Acetylcholine on Stimulation by Isoproterenol of L‐Type Ca2+ Current and Arrhythmogenic Triggered Activity in Guinea Pig Ventricular Myocytes
Authors: SONG YEJIA , SHRYOCK JOHN C. , BELARDINELLI LUIZ
Published: April 2007

ACh Facilitation of Triggered Activity. Introduction: The objective of this study was to determine whether the effect of isoproterenol (Iso) to increase L‐type Ca2+ current [Ica(L)] and action potential duration (APD) was potentiated in ventricular myocytes following termination of an exposure of these cells to acetylcholine (ACh), and whether this potentiating effect of Ach could he arrhythmogenic.

Methods and Results: Transmembrane currents and potentials of guinea pig Isolated ventricular myocytes were measured using the whole cell, patch clamp technique. Stimulation of Ica(L) and prolongation of APD caused by Iso (10 nmol/L) were attenuated in the presence of Ach (10 μ mol/L), but were transiently enhanced by 111%± 20% and 214%± 44%, respectively, following termination of a 2‐ to 4‐minute exposure of myocytes to ACh. No changes were observed in the absence of Iso. Both the amplitude and incidence of isoinduced transient inward current, afterdepolarizations, and sustained triggered activity were greater immediately after termination of exposure to ACh than before application of ACh.

Conclusion: Stimulation by Iso of Ica(L) is transiently enhanced in guinea pig ventricular myocytes following termination of exposure of these cells to ACh. The rebound increase of Iso‐stimulated Ica(L) is associated with an increase of APD and induction of arrhythmogenic triggered activity.
Postshock Potential Gradients and Dispersion of Repolarization in Cells Stimulated with Monophasic and Biphasic Waveforms
Authors: SOBIE ERIC A. , TUNG LESLIE
Published: April 2007

Effects of Monophasic and Biphasic Stimuli. Introduction: Even though the clinical advantage of biphasic defibrillation waveforms is well documented, the mechanisms that underlie this greater efficacy remain incompletely understood. It is established, though, that the response of relatively refractory cells to the shock is important in determining defibrillation success or failure. We used two computer models of an isolated ventricular cell to test the hypothesis that biphasic stimuli cause a more uniform response than the equivalent monophasic shocks, decreasing the likelihood that fibrillation will be reinduced.

Methods and Results: Models of reciprocally polarized and uniformly polarized cells were used. Rapid pacing and elevated [K]o were simulated, and either 10‐nisec rectangular monophasic or 5‐msec/5‐msec symmetric biphasic stimuli were delivered in the relative refractory period. The effects of stimulus intensity and coupling interval on response duration and postshock transmembrane potential (Vm) were quantified for each waveform. With reciprocal polarization, biphasic stimuli caused a more uniform response than monophasic stimuli, resulting in fewer large gradients of Vm (only for shock strengths ≤ 1.25× threshold vs ≤ 2.125× threshold) and a smaller dispersion of repolarization (1611 msec2 vs 1835 msec2). The reverse was observed with uniform polarization: monophasic pulses caused a more uniform response than did biphasic stimuli.

Conclusion: These results show that the response of relatively refractory cardiac cells to biphasic stimuli is less dependent on the coupling interval and stimulus strength than the response to monophasic stimuli under conditions of reciprocal polarization. Because this may lead to fewer and smaller spatial gradients in Vm, these data support the hypothesis that biphasic defibrillation waveforms will be less likely to reinduce fibrillation. Further, published experimental results correlate to a greater degree with conditions of reciprocal polarization than of uniform polarization, providing indirect evidence that interactions between depolarized and hyper polarized regions play a role in determining the effects of defibrillation shocks on cardiac tissue.
Type I Atrial Flutter Ablation Guided by a Basket Catheter
Authors: RODRIGUEZ ENRIQUE , MAN DAVID C. , COYNE ROBERT F. , CALLANS DAVID J. , GOTTLIES CHARLES D. , MARCHLINSKI FRANCIS E.
Published: April 2007

Atrial Flutter Ablation. Bidirectional isthmus conduction block has been associated with a low recurrence rate after atrial flutter ablation. We present the ease of a type I, typical or “counterclockwise” atrial flutter ablation guided by stimulation and recordings obtained from a basket catheter, which allowed for constant electrogram recording from splines positioned along the right lateral free wall and septum. After atrial flutter termination with radiofrequency application, the ability to record and stimulate from multiple sites in the atrium using the basket catheter was useful to detect residual bidirectional slow conduction through the isthmus. Complete isthmus block could be documented after additional radiofrequency energy applications.