bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiofrequency Catheter Ablation Versus Modification of the AV Node for Control of Rapid Ventricular Response in Atrial Fibrillation
Authors: FELD GREGORY K.
Published: May 2007

AV Node Modification vs Ablation in AF. Atrial fibrillation is a common arrhythmia, which is frequently difficult to control. Symptoms and ventricular dysfunction may be caused by a rapid ventricular response to atrial fibrillation. Radiofrequency catheter ablation techniques for ventricular rate control have been developed, including AV node modification and AV node ablation with pacemaker implantation. For both AV node modification and ablation, radiofrequency energy is applied via a 4‐mm tipped electrode catheter. For AV node ablation radiofreqnency energy is applied near the compact AV node or His bundle via the right atrium, or occasionally at the His bundle via the left ventricle. For AV node modification radiofrequency energy is applied in the low middle or posterior septal right atrium near the tricuspid valve annulus. Both techniques can effectively control ventricular response to atrial fibrillation and the associated symptoms, although AV node modification is effective in only about 70% of patients compared to AV node ablation, which is effective in nearly 100%. In patients responding to AV node modification, maximal and mean ventricular response to atrial fibrillation is reduced by 25% to 35% chronically. Inadvertent AV block may occur during attempted AV node modification. It seems appropriate to attempt AV node modification prior to AV node ablation in patients with refractory atrial fibrillation and rapid ventricular response, in order to avoid the need for permanent pacemaker implantation. Although unproven, studies suggest that the mechanism by which AV node modification achieves ventricular rate control may he slow‐pathway ablation in the low posterior septal right atrium.
Insights into the Electrophysiology of Atrial Arrhythmias Gained by the Catheter Ablation Experience:
Authors: CALLANS DAVID J. , SCHWARTZMAN DAVID , GOTTLIEB CHARLES D. , MARCHLINSKl FRANCIS B.
Published: May 2007

Catheter Ablation of Atrial Arrhythmias. Although the development and wide‐scale application of catheter ablative techniques has drastically changed the practice of electrophysiology, catheter ablation does not preclude physiologic investigation. On the contrary, given the precise and directed nature of this technique and the increased attention to detailed cardiac mapping that it requires, catheter ablation may be viewed as a tool to provide unique information about arrhythmia substrates. In this article, the insights provided by the catheter ablation experience into the pathophysiology of the focal atrial arrhythmias, atrial tachycardia, sinus node reentrant tachycardia, and inappropriate sinus tachycardia will be reviewed. Atrial arrhythmias were initially difficult to treat with ablative therapy, particularly because they can occur anywhere within the atria and the experience with mapping for surgical ablation was quite limited. A number of novel approaches to atrial mapping have been developed in response to this challenge, and presently, catheter ablation provides effective therapy for the majority of patients with focal atrial arrhythmias. In addition, deliberate attempts at “learning while burning” have already begun to enhance our understanding of the interaction of the structural and electrophysiologic aspects of the substrate for atrial arrhythmias.
Diagnostic Clues From the Surfaee ECG to Identify Idiopathic (Fascicular) Ventricular Tachycardia: Correlation with Electrophysiologic Findings
Authors: ANDRADE FERNANDO ROSAS , ESLAMI MASSOUD , ELIAS JORGE , KINOSHITA OSAMU , NAKAZATO YUJI , MARCUS FRANK I. , FRANK ROBERT , TONET JOELCI , FONTAINE GUY
Published: May 2007

ECG in Idiopathic Fascicular VT. Introduction: An RS interval > 100 msec in precordial leads has been recently described for the diagnosis of ventricular tachycardia (VT). The aim of this study was to assess the value of this criterion when applied to patients with right bundle branch block pattern, left‐axis deviation (fascicular) VT sensitive to verapamil.

Methods and Results: Eleven patients (mean age 31 ± 11 years; range 16 to 51) had a mean heart rate of 164 ± 37 beats/min (range 107 to 230) during VT, The QRS complex axis was ‐92°± ‐15° (range ‐80 to ‐115). The mean QRS duration was 121 ± 9 msec (range 105 to 140). The mean RS interval was 67 ± 9 msec (range 60 to 80). Fusion beats were present in 2 patients (18%), and AV dissociation confirmed by electrophysiologic study was found on ECG in 8 (73%) of 11. During tachycardia, the QRS‐H'interval was 19 ± 10 msec (range 10 to 30) in 6 of 11 patients. In seven patients, a fast, unique (or double) presystolic potential lasting 32 msec (range 12 to 40) occurring before the onset of the QRS complex was found at the site of origin of VT, localized in the inferior apical left ventricular septum. In all cases, VT was successfully treated by catheter ablation.

Conclusion: A wide QRS complex tachycardia with right bundle branch block and left‐axis deviation sensitive to verapamil observed in a young patient without structural heart disease should not be confused with supraventricular tachycardia with aberrancy but rather suggests the presence of fascicular VT. As opposed to VT associated with structural heart disease, the RS interval is < 80 msec in all precordial leads in all cases. Independent of this parameter, AV dissociation detectable on surface ECG has a sensitivity of 73%, which increases to 82% in the presence of fusion beats.
Altered Pharmacologic Responsiveness of Reduced L‐Type Calcium Currents in Myocytes Surviving in the Infarcted Heart
Authors: AGGARWAL RAJESH , BOYDEN PENELOPE A.
Published: May 2007

Altered Pharmacology of Ica,L in Myocytes From Infarcted Heart. The pharmacologic responses of macroscopic L‐type calcium channel currents to the dihydropyridine agonist, Bay K 8644, and β‐adrenergic receptor stimulation by isoproterenol were studied in myocytes enzymatically dissociated from the epicardial border zone of the arrhythmic 5‐day infarcted canine heart (IZs). Calcium currents were recorded at 36° to 37° C using the whole cell, patch clamp method and elicited by applying step depolarizations from a holding potential of ‐40 mV to various test potentials for 250‐msec duration at 8‐second intervals. A Cs+ ‐rich and 10 mM EGTA‐containing pipette solution and a Na+‐and K+‐free external solutions were used to isolate calcium currents from other contaminating currents. During control, peak Ica,L, density was found to be significantly less in IZs (4.0 ± 1.1 pA/pF) than in myocytes dispersed from the epicardium of the normal noninfarcted heart (NZs; 6.5 ± 1.8 pA/pF). Bay K 8644 (I μM) significantly increased peak Ica,L density 3.5‐fold above control levels in both NZs (to 22.5 ± 6.2 pA/pF; n = 7) and IZs (to 12.8 ± 3.0 pA/pF; n = 5), yet peak Ica,L density in the presence of drug was significantly less in IZs than NZs. The effects of Bay K 8644 on kinetics of current decay and steady‐state inactivation relations of peak Ica,L were similar in the two cell types. In contrast, the response of peak L‐type current density to isoproterenol (1 μM) was significantly diminished in IZs compared to NZs regardless of whether Ba2+ or Ca2+ ions carried the current. Thus, these results indicate an altered responsiveness to β‐adrenergic stimulation in cells that survive in the infarcted heart. Furthermore, application of forskolin (1 μM and 10 μM) or intracellular cAMP (200 μM), agents known to act downstream of the β‐receptor, also produced a smaller increase in peak IBa density in IZs versus NZs, suggesting that multiple defects exist in the β‐adrenergic signaling pathway of IZs. In conclusion, these studies illustrate that reduced macroscopic calcium currents of cells in the infracted heart exhibit an altered pharmacologic profile that has important implications in the development of drugs for the diseased heart.
Junction Potentials and Action Potentials of the Crayfish Myocardium
Authors: HERNANDEZ VICENTE , MENDEZ CARLOS
Published: May 2007

Junction and Action Potentials. Introduction: The purpose of this investigation was to study the properties of junction and action potentials elicited by nerve stimulation in the absence of the cardiac ganglion in crayfish myocardium.

Methods and Results: The cardiac ganglion was surgically removed in isolated crayfish hearts. Electrical stimulation of one of the peripheral anterolateral nerves provided isolated junction potentials and action potentials free of the usual postspike bursts of junction potentials. The single junction potentials displayed amplitudes of up to 25 mV and slow exponential decay; the mean time constant was 170 ± 13 msec (xT ± SD). In fully recovered tissue, the junction potentials triggered action potentials free of repetitive subthreshold discharges. Tetrodotoxin did not alter the amplitude or shape of action potentials initiated by direct electrical stimulation of the muscle cells. Calcium channel blocking agents such as Cd2+ and Ni2+ eliminated the action potentials but not the junction potentials. Tetraethylammonium markedly prolonged the action potential duration.

Conclusions: Our data suggest that: (1) A slow decay of the junction potentials may result from the disappearance of the neurotransmitter; this process also accounts for the late slow repolarization of the final part of the action potentials; (2) The equilibrium potential of the junction potentials is close to 0 mV; (3) The upstroke of the action potentials is carried by calcium currents; (4) The fast repolarization phase of the action potentials is likely caused by the delayed rectifier; and (5) The refractory phase outlasts the duration of the action potential.
Atrial Flutter in the Human Fetus:
Authors: SOYEUR DANIEL J.
Published: May 2007

Fetal Atrial Flutter. In the context of a large program of prenatal echocardiographic detection of fetal heart disease, special attention was paid to the in utero detection and identification of fetal heart rate disorders. This article focuses on 18 cases of tachycardiac fetuses. It provides information on how to identify the nature of the detected tachycardia, the hemodynamic consequences of tachycardia, the particular characteristics of fetal atrial flutter. and the efficacy of the transmaternal treatment of fetal tachycardia. U also describes an original way to grade and score the degree of fetal heart failure that proved useful for the assessment and monitoring of in utero therapeutic procedures. The results presented stress the efficacy of digoxin for fetal atrial flutter as well as the usefulness of prenatal echocardiography in the assessment of anatomical, functional, and rhythmic conditions of the fetal heart.
Pharmacologic Therapy of Atrial Flutter
Authors: CAMPBELL RONALD W.F.
Published: May 2007

Pharmacologic Therapy of Atrial Flutter. Atrial flutter is a relatively rare but nonetheless important arrhythmia. Its mechanism and anatomy have been defined as right atrial macroreentry. It responds to treatment with a variety of antiarrhythmic agents but, in general, drug efficacy for acute termination is low. The addition of pacing to drug therapy markedly improves the success rate for restoration of sinus rhythm. Useful antiarrhythmic agents include amiodarone, sotalol, disopyramide, flecainide, and propafenone, but definitive efficacy studies have not been performed. The risk of provoking 1:1 AV conduction and a marked increase in ventricular response rate is always present. AV nodal blocking drugs (digoxin and verapamil) probably offer protection from this unwanted effect, but the prevalence of 1:1 conduction and the efficacy of AV nodal blockade remain to be established. When drug management fails, there is a place for radiofrequency ablation. Little is known about the thromboembolic risk of atrial flutter. As a consequence, the role of prophylactic anticoagulation is uncertain. Current interest in atrial flutter will ensure that these and other clinical questions are answered in the near future.
Endoscopy‐Assisted Radiofrequency Ablation Around the Coronary Sinus Ostium in Dogs:
Authors: TANAKA KAZUSHI , CHA YONG‐MEI , FUJIMURA OSAMU
Published: May 2007

Endoscopy for Ablation Around the CS Ostium. Introduction: Radiofrequency ablation of the slow pathway can prolong atrioventricular (AV) nodal properties and RR intervals during atrial fibrillation (AF) in many patients with AV nodal reentrant tachycardia. However, it is not well elucidated whether these changes are related to the presence of dual AV nodal pathway physiology. The aim of this study was to evaluate changes of AV nodal properties and RR intervals during AF caused by ablation of two specific areas in dogs.

Methods and Results: Assisted by fiberoptic endoscopy, linear lesions were created between the coronary sinus ostium and tricuspid valve annulus (area 1) or posterior to the ostium (area 2) in 15 dogs. Three additional dogs served as controls. The measurements were made under autonomic blockade. Catheter ablation could be assisted in all dogs by means of endoscopy. Linear lesions were confirmed at autopsy. AV nodal parameters and RR intervals showed no overall changes. Individual data showed that ablation of area I resulted in modification of AV nodal properties in 54.5% (facilitation in 363% and inhibition in 18.2%), whereas ablation of area 2 induced changes in 50% (facilitation in 10% and inhibition in 40%). The RR intervals were shortened in 33.3% and 20% and prolonged in 44.5% and 40% after ablation of areas 1 and 2, respectively. The RR intervals during AF correlated well with the Wenckebach cycle length and the AV node functional refractory period before and after ablation (r = 0.78 to 0.94, P < 0.01 for each).

Conclusions: Ablation of the two specific areas around the coronary sinus ostium was equally effective in modifying AV nodal properties and the ventricular response during AF without dual AV nodal pathway physiology. The ventricular rate to AF after ablation correlated well with the residual AV nodal properties.
Predicting Sudden Cardiac Death From T Wave Alternans of the Surface Electrocardiogram:
Authors: ROSENBAUM DAVID S. , ALBRECHT PAUL , COHEN RICHARD J.
Published: May 2007

T Wave Alternans and Sudden Cardiac Death. Sudden cardiac death remains a preeminent public health problem. Despite advances in preventative treatment for patients known to be at risk, to date we have been able to identify, and thus treat, only a small minority of these patients. Therefore, there is a major need to develop noninvasive diagnostic technologies to identify patients at risk. Recent studies have demonstrated that measurement of microvolt‐level T wave alternans is a promising technique for the accurate identification of patients at risk for ventricular arrhythmias and sudden cardiac death. In this article, we review the clinical data establishing the relationship between microvolt T wave alternans and susceptibility to ventricular arrhythmias. We also review the methods and technology that have been developed to measure microvolt levels of T wave alternans noninvasively in broad populations of ambulatory patients. In particular, we examine techniques that permit the accurate measurement of T wave alternans during exercise stress testing.
Conduction Barriers in Human Atrial Flutter:
Authors: OLGIN JEFFREY E. , KALMAN JONATHAN M. , LESH MICHAEL D.
Published: May 2007

Barriers in Atrial Flutter. Animal models of atrial flutter and early mapping studies of human atrial flutter have suggested the importance of barriers in this reentrant arrhythmia. The consistency of rate and morphology of typical atrial flutter suggest a common anatomic substrate for this arrhythmia. The unique endocardial architecture of the right atrium provides anatomic barriers around which reentry occurs. In typical human atrial flutter, the crista terminalis, eustachian ridge, and tricuspid annulus have been identified as barriers to conduction. The importance of conduction barriers, methodology for defining barriers, the anatomic substrate for these barriers, and the role of these barriers in other atrial arrhythmias are discussed.
Response to Beta Blockers in Patients with Neurocardiogenic Syncope: How to Predict Beneficial Effects
Authors: NATALE ANDREA , NEWBY KEITH H. , DHALA ANWER , AKHTAR MASOOD , SRA JASBIR
Published: May 2007

Beta‐Blocker Therapy for Neurocardiogenic Syncope. No definitive data are available about the possibility of predicting improvement in patients with neurocardiogenic syncope treated with beta blockers. Among 112 patients with syncope and a positive bead‐up tilt test (HUT), independent predictors for prevention of symptoms with beta blockers were determined using the Cox proportional hazards model. Each patient underwent HUT at 70° for 20 minutes both in the drug‐free state and during isoproterenol infusion given to increase the heart rate by at least 25%. Fifty‐nine patients bad a positive HUT during isoproterenol infusion and 53 in the drug‐free state. All patients were then given esmolol infusion at 500 μg/kg per minute for 3 minutes followed by 300 μg/kg per minute maintenance dose. HUT was then repeated as previously described with or without isoproterenol, depending upon the initial positive response. Regardless of the response during esmolol, all patients were treated with metoprolol 50 to 100 mg twice daily. At follow‐up, 36 patients experienced symptom relapse. Four of them bad negative HUT on esmolol, whereas the remaining 32 did not respond to the acute infusion of esmolol. Only four patients with positive HUT on esmolol had a favorable response to metoprolol. Patients responding to metoprolol were older (55 ± 12 years vs 42 ± 15 years, P < 0.05). Response to metoprolol was predicted by a negative test on esmolol (P < 0.0001) and a positive HUT on isoproterenol (P < 0.001). Age older than 42 years was also associated with a higher likelihood of metoprolol success (P < 0.02). Conclusion: Acute challenge with esmolol infusion appears to be an accurate predictor of response to chronic beta blockers, together with age and a positive HUT during low‐dose isoproterenol infusion.
Radiofrequency Catheter Ablation of Idiopathic Ventricular Tachycardia Originating in the Anterior Fascicle of the Left Bundle Branch
Authors: RODRIGUEZ LUZ‐MARIA , SMEETS JOEP L.R.M. , TIMMERMANS CARL , TRAPPE HANS J. , WELLENS HEIN J.J.
Published: May 2007

Ablation of an Anterior Fascicular Idiopathic VT. Introduction: Idiopathic ventricular tachycardia (VT) originating in or close to the anterior fascicle of the left bundle is rare. A patient with no structural heart disease and VT with a right bundle branch block configuration and right‐axis deviation underwent an electrophysiologic examination.

Methods and Results: Both endocardial activation mapping during VT and pacemapping were performed via a transseptal approach to localize the site of origin of the VT. Endocardial recordings of the His bundle and the posterior and anterior fascicles of the left bundle branch revealed an origin of the VT in or close to the anterior fascicle. The Purkinje potential at that site preceded the QRS complex by 20 msec, with pacemapping showing an optimal match between the paced rhythm and the clinical VT. RF energy delivered at this site terminated the VT. A left anterior nemiblock appeared after RF ablation. Ten months later, the patient is free from recurrences of VT.

Conclusions: Idiopathic VT originating in or close to the anterior fascicle was cured by RF ablation. A Purkinje potential preceding the QRS during tachycardia and an optimal pacemap were used to guide RF ablation.
Is the Automatic Atrial Defibrillator a Promising Approach?
Authors: GRIFFIN JERRY C. , AYERS GREGORY M. , ADAMS JOHN , ALFERNESS CLIF A. , INFINGER ROSS , ADLER STEVE , CHEN VICTOR
Published: May 2007

Automatic Atrial Defibrillator. Atrial fibrillation is a common arrhythmia, accounting for more consumption of medical resources than any other arrhythmia. The impact of the disease results from the combination of a loss of atrial contraction, and atrial control over cardiac rate. Studies in animals demonstrated the basic feasibility of atrial defibrillation using electrodes passed intravenously. Subsequent studies in patients confirmed that low‐energy shocks were effective in converting atrial fibrillation and were safe if delivered synchronous to the R wave in the absence of a short preceding RR interval. Preliminary experience suggests that a small implanted device might provide beneficial therapy for patients with recurring episodes of persistent, drug‐refractory, atrial fibrillation.
Sinus Node Recovery Time Assessment Revisited: Role of Pharmacologic Blockade of the Autonomic Nervous System
Authors: BERGFELDT LENNART , VALLIN HANS , ROSENQVIST MÅRTEN , INSULANDER PER , NORDLANDER ROLF , ÅSTRÖM HANS
Published: May 2007

Sinus Node Recovery and Autonomic Blockade. Sinus node recovery time assessment is used to diagnose clinically significant sinus node dysfunction (SND) when Holter has failed to prove a relationship between sinus bradyarrhythmias and symptoms, but consensus has not been reached as to the value of including assessment after pharmacologic blockade of the autonomic nervous system. This issue was addressed in the present study performed on 52 patients with syncope or presyncope/dizziness (n = 48), sinus bradyarrhythmias (n = 45), or both (n = 41). Group 1 consisted of 13 patients with a proven relationship between symptoms and sinus bradyarrhythmias. Group 2 consisted of 39 patients with suspected SND. The protocol included three pacing periods at two pacing rates and was performed at baseline (n = 52), after single doses of atropine and propranolol (0.02 mg/kg and 0.1 mg/kg, respectively) (n = 41), and again after a second dose (n = 29). The sensitivity of prolonged recovery times was 77% in group 1. Among group 2 patients, 56% had prolonged recovery times at baseline (79% when including the results after the first dose of drugs). The second dose did not contribute diagnostic information, but it caused significant adverse reactions in 7 of 29 patients (P < 0.001). These 7 patients were all older than 60 years. Assessment of sinus node recovery time after pharmacologic blockade of the autonomic nervous system thus increases the sensitivity of the method in patients with suspected SND and normal baseline results. However, only 50% of the initially suggested doses of atropine and propranolol is sufficient and eliminates the risk for significant adverse reactions.
Occult T Wave Alternans in Long QT Syndrome
Authors: PLATT SIMIE B. , VIJGEN JOHAN M. , ALBRECHT PAUL , VAN HARE GEORGE F. , CARLSON MARK D. , ROSENBAUM DAVID S.
Published: May 2007

T Wave Alternans in LQTS. T wave alternans that is visually apparent on the ECG is a known risk factor for sudden death in idiopathic long QT syndrome (LQTS). To determine if occult and visually undetectable forms of T wave alternans are also present in LQTS, we measured T wave alternans from a 16‐year‐old girl with LQTS during exercise using spectral analysis methods and a recording system designed to minimize exercise‐related noise. While there was no alternans at rest, statistically significant, yet visually inapparent T wave alternans were measured both during exercise and recovery. Using identical recording techniques, no significant T wave alternans was detected from the subject's mother, who had a prolonged QT interval but was not experiencing arrhythmias, nor from five healthy volunteers with normal QT intervals. This report suggests that electrocardiographically occult, yet prognostically important forms of T wave alternans may be present in patients with LQTS.
PR/RR Interval Ratio During Rapid Atrial Pacing:
Authors: BAKER JAMES H. , PLUMB VANCE J. , EPSTEIN ANDREW E. , NEA KAY G.
Published: May 2007

Method for Confirming Slow Pathway Conduction. Introduction: Although the AV conduction curve in patients with AV nodal reentrant tachycardia (AVNRT) is usually discontinuous, many patients with this arrhythmia do not demonstrate criteria for dual AV nodal pathways. During rapid atrial pacing, the PR interval often exceeds the pacing cycle length when there is anterograde conduction over the slow pathway and AVNRT is induced. The purpose of this prospective study was to determine the diagnostic value of the ratio of the PR interval to the RR interval during rapid atrial pacing as an indicator of anterograde slow pathway conduction in patients undergoing electrophysioiogic testing.

Methods and Results: The PR and RR intervals were measured during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction in four study groups: (1) patients with inducible AV nodal reentry and the classical criterion for dual AV nodal pathways during atrial extrastimulus testing (AVNRT Group 1); (2) patients with inducible AV nodal reentry without dual AV nodal pathways (AVNRT Group 2); (3) control subjects ≤ 60 years of age without inducible AV nodal reentry; and (4) control subjects > 60 years of age without inducible AV nodal reentry. For both groups of patients with inducible AV nodal reentry, AV conduction was assessed before and after radiofrequency ablation of the slow AV nodal pathway. Before slow pathway ablation, the PR/RR ratio exceeded 1.0 in 12 of 13 AVNRT Group 1 patients (mean 1.27 ± 0.21) and 16 of 17 AVNRT Group 2 patients (mean 1.18 ± 0.15, P = NS Group 1 vs Group 2). After slow pathway ablation, the maximum PR/RR ratio was < 1.0 in all AVNRT patients (Group 1 = 0.59 ± 0.08, P < 0. 00001 vs before ablation: Group 2 = 0.67 ± 0.11; P < 0.00001 vs before ablation). Among both groups of control subjects, the PR/RR ratio was > 1.0 in only 3 of 27 patients with no relation to patient age.

Conclusion: The ratio of the PR interval to the RR interval during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction provides a simple and clinically useful method for determining the presence of slow AV nodal pathway conduction. This finding may be particularly useful in patients with inducible AV nodal reentry without dual AV nodal physiology on atrial extrastimulus testing.
Retrograde Migration of the Site of Functional Block:
Authors: TCHOU PATRICK J. , TROHMAN RICHARD , KIDWELL GREGORY , MEHDIRAD ALI A.
Published: May 2007

Retrograde Migration of Functional Block. Introduction: Functional bundle branch blocks during supraventricular tachycardia have been described, and their sustainment has been attributed to concealed conduction. Such blocks frequently resolve spontaneously, but the electrophysiologic mechanism of resolution bas not been well described. This report describes the resolution of functional bundle branch block through proximal migration of the site of block.

Methods and Results: During electrophysiologic study of a patient with reentrant antidromic tachycardia via an atriofascicular accessory pathway, functional retrograde right bundle branch block could be readily induced following tachycardia initiation with right ventricular apical pacing. Resolution of this block was associated with shortening of the tachycardia cycle length. Electrogram recordings along the right bundle branch during tachycardia determined that resolution of the functional retrograde right bundle branch block was associated with migration of the site of block from the distal to the proximal right bundle. When the site of block was directly at the recording site, both anterograde and retrograde activation of the right bundle was demonstrated.

Conclusion: Migration of the site of block is a mechanism of resolution for functional conduction blocks maintained by concealed conduction.
Catheter Ablation of Coexistent Bundle Branch and Interfasdcular Reentrant Ventricular Tachycardias
Authors: BERGER RONALD D. , ORIAS DAVID , KASPER EDWARD K. , CALKINS HUGH
Published: May 2007

Bundle Branch and Interfascicular Reentry. Introduction: Bundle branch reentry and interfascicular reentry are potential mechanisms of ventricular tachycardia in the setting of a dilated cardiomyopathy. We report a patient with myotonic dystrophy who presented with near syncope, in whom both of these mechanisms were present, leading to two different wide complex tachycardias.

Methods and Results: Electrophysiologic study demonstrated Infra‐Hisian conduction system disease and inducible bundle branch reentrant ventricular tachycardia. Catheter ablation of the right bundle eliminated bundle branch reentry. However, following this, the patient had inducible interfascicular reentry, which subsequently occurred spontaneously while still hospitalized. Catheter ablation of the left posterior fascicle successfully eliminated this second tachycardia, and the patient has had no further arrhythmias.

Conclusions: This report is of an unusual patient with coexistent bundle branch reentry and interfascicular reentry producing two different forms of sustained ventricular tachycardia. This is the first report of catheter ablation of the left posterior fascicle for elimination of conduction system reentry.
Local Electrogram Changes in Response to a High‐Voltage Intracardiac Shock in Humans
Authors: SMITH JEFFREY R. , KADISH ALAN H. , INBAR SHMUEL , YE DINGZHONG , GOLDBERGER JEFFREY J.
Published: May 2007

Electrogram Changes Following ICD Shocks. Introduction: Transvenous defibrillators may have difficulty sensing ventricular fibrillation following an unsuccessful shock. This study was undertaken to characterize the changes that occur in intracardiac electrograms following a defibrillator shock that may contribute to the failure to redetect arrhythmias.

Methods and Results: Unipolar and bipolar electrogram recordings were made during sinus rhythm before and following monophasic and biphasic test shocks delivered in random order through a single lead defibrillator system in 15 patients. An additional 14 patients received only a biphasic shock. Electrogram amplitude, dV/dt, and activation recovery time were determined. Following biphasic shocks, unipolar electrogram amplitude decreased by a mean of 19.6% and the bipolar amplitude by a mean of 20.8% (P = NS). The mean dV/dt in the unipolar recordings decreased by 30.7% and in the bipolar recordings decreased by 33.0% (P = NS). Time constants for recovery were approximately 60 seconds. Reduction in dV/dt was greater when the shocking coil was closer to the distal sensing electrode. There was no significant influence of shock waveform (monophasic vs biphasic), recording type (unipolar vs bipolar), or clinical variables on the change in electrogram characteristics.

Conclusion: Changes in intracardiac electrograms following defibrillator shocks through transvenous leads are seen with shocks delivered in sinus rhythm and may be related to the proximity of the shocking coil to the distal sensing electrode.
Autonomic Dysfunction After Catheter Ablation
Authors: FRIEDMAN PETER L. , STEVENSON WILLIAM G. , KOCOVIC DUSAN Z.
Published: May 2007

Autonomic Dysfunction After Catheter Ablation. Autonomic dysfunction may occur as a consequence of radiofrequency (RF) catheter ablation of a variety of supraventricular tachycardias, Effects suggestive of autonomic dysfunction that may be seen acutely during the ablation procedure include sudden profound slowing of the sinus rate or transient AV block. These abnormalities may occur during application of RF current, typically along the tricuspid or mitral annulus, at sites distant from both the sinus and AV nodes; they resolve quickly when RF current delivery is terminated. The most common long‐term indication of autonomic dysfunction after ablation is inappropriate sinus tachycardia. This complication, rarely a lasting significant clinical problem, is seen after AV node modification and after ablation of accessory pathways. It usually resolves within several months. The mechanism appears to be loss of parasympathetic influence on the sinus node. Autonomic dysfunction after ablation of ventricular tachycardia bas not yet been described, but could occur as newer catheter technologies capable of producing larger lesions are perfected.
Late Diagnosis of Pericardial Constriction Associated with Defibrillator Patches and Deformation of the Left Ventricle
Authors: LE TOURNEAU THIERRY , KLUG DIDIER , LACROIX DOMINIQUE , KACET SALEM , LEKIEFFRE JEAN
Published: May 2007

Pericardial Constriction Associated with AICD Patches. We report a case of pericardial constriction associated with defibrillator patches developing 4.5 years after implantation. This constriction was related to the presence of a large pericardial mass that had developed above the defibrillator patch. This mass, which bad a calcified superior border, suggested former hematoma associated with pericardial fibrosis. It induced significant compression of the right ventricle and a dumb‐bell deformity of the left ventricle. The hemodynamic picture was of elastic‐form constrictive pericarditis. Because of previous cerebral stroke during cardiac surgery, the patient was discharged on pharmacologic treatment after improvement of his functional status. Since removal of epicardial patches is an effective treatment of constriction, constrictive pericarditis should be systematically considered in patients with epicardial patch electrodes and impairment of functional status.
Sensing and Tachyarrhythmia Detection Problems in Implantable Cardioverter Defibrillators
Authors: REITER MICHAEL J. , MANN DAVID E.
Published: May 2007

ICD Sensing‐Detection Errors. Sensing of cardiac activity and detection of tachyarrhythmias in implantable cardioverter defibrillators (ICDs) are complex functions and errors occur. Sources of sensing‐detection errors include the variable nature of intracardiac electrograms, the occasional inability of automatically adjusting signal amplifiers to cope with this variability, problems with sensing leads, inappropriate programming, and limitations of tachyarrhythmia detection algorithms, which are optimized to avoid underdetection of ventricular tachyarrhythmias. Current ICDs vary considerably in details of sensing and detection function, programmability, and diagnostic data, so that a thorough knowledge of each device is necessary to diagnose and correct these problems. Stored intracardiac electrograms and/or marker channels available in most of these devices have contributed much to our understanding of sensing‐detection errors. Undersensing of individual signals, most frequently due to signal variability and/or inability of the amplifier to adjust adequately, can lead to delay or failure of tachyarrhythmia detection. Delay or failure of tachyarrhythmia detection can also occur if algorithms to enhance specificity, such as sudden onset or rate stability, are utilized. Oversensing of T waves or noise can lead to false detection; however, the most common cause of false detection is the inability of current detection algorithms to distinguish supraventricular from ventricular tachyarrhythmias. New algorithms that incorporate atrial sensing, electrogram morphology analysis, or hemodynamic monitoring may result in improved detection accuracy of ICDs in the future.
Adenosine‐Sensitive Ventricular Tachycardia:
Authors: LERMAN BRUCE B. , STEIN KENNETH M. , MARKOWITZ STEVEN M.
Published: May 2007

Adenosine‐Sensitive VT. Idiopathic ventricular tachycardia (VT) is a term that refers to tachycardia that arises from ventricles devoid of apparent structural abnormalities. This form of VT is now recognized to be related to several distinct entities and includes a reentrant form typically located in the region of the left posterior fascicle, an automatic form that may originate from either ventricle, and a form that originates from the right ventricular outflow tract. This last type can account for up to 80% of cases of idiopathic VT and with few exceptions can be further subdivided into repetitive monomorphic VT and paroxysmal stress‐induced VT, Evidence has accumulated suggesting that both forms of VT are related to cAMP‐mediated triggered activity. The experimental underpinnings of this conclusion as well as the clinical characteristics of this form of idiopathic VT are elucidated in this review.
Atomic (Scanning) Force Microscopy in Cardiovascular Research
Authors: ARNSDORF MORTON F. , XU SHAOHUA
Published: May 2007

Atomic Force Microscopy. The promise of atomic (scanning) force microscopy (AFM) for cardiovascular research is enormous. The AFM images by using a sharp cantilever tip to sense the repulsive and attractive forces between the tip and the sample surface. The force of interaction is kept constant while raster scanning, resulting in images of the surface contours with molecular and, on hard inorganic surfaces, even atomic resolution. Movement of the cantilever in the Z plane is detected by a laser beam reflected off the cantilever to a photodiode system, a piezotube allows an X and Y raster, and a three‐dimensional image results. Its capabilities include: (1) the three‐dimensional imaging of membranes and biomolecules with molecular and submolecular resolution; (2) such imaging not only of dry specimens but of specimens in a physiologic solution, thereby allowing the investigation of dynamic processes in both viable biomolecules and living cells; (3) the sensing of charge and intermolecular interaction forces; (4) the chemical or biochemical modification of the cantilever tip, which allows the identification of specific structures and the measurement of specific interactions (e.g., a ligand‐receptor interaction); (5) nanometer control of the position and force of the cantilever, which, in turn, allows the physical manipulation of biomolecules, the dissection of biological structures (e.g., the separation of one gap junctional hemichannel from its neighbor, thereby revealing normally inaccessible surfaces), the delivery of ligands, drugs, or other materials to specific locations, and the precise measurement of interacting forces at specific sites; and (6) the modification of the apparatus by adding complementary methodologies (e.g., magnetic resonance imaging, fluorescence microscopy, confocal microscopy, and perhaps electrophysiology). AFM, however, is only now being applied to biological research, many technical and methodologic problems exist, and a number of them are considered in this review. Little work has been done in cardiovascular research, and the purpose of this review is to introduce this new and exciting approach to investigation.
Recurrence of Conduction Following Radiofrequency Catheter Ablation Procedures:
Authors: CALKINS HUGH , PRYSTOWSKY ERIC , BERGER RONALD D. , SAUL J. PHILI , KLEIN LAWRENCE S. , BIN LIEM L. , STEPHEN HUANG S.K. , GILLETTE PAUL , YONG PATRICK , CARLSON MARK ,   THE ATAKR MULTICENTER INVESTIGATORS GROUP
Published: May 2007

Recurrence of Conduction Following RF Catheter Ablation. Introduction: More than 1 in 10 patients may develop recurrence of conduction after undergoing a successful radiofrequency catheter ablation procedure. The physiologic basis for recurrence following successful ablation procedures remains uncertain. The purpose of this study was to evaluate the role of electrode temperature as a predictor of recurrence following radiofrequency catheter ablation procedures.

Methods and Results: The subjects of this study were 538 patients who underwent a successful attempt at radiofrequency catheter ablation of AV nodal reentrant tachycardia, an accessory pathway, and/or the AV junction. Patients were followed for a mean of 215 ± 138 days. Conduction recurred in 35 (6.5%) of the 538 patients. Recurrence of conduction occurred in 25 (9.3%) of 270 patients undergoing ablation of an accessory pathway, 7 (3.5%) of 201 patients undergoing ablation of AV nodal reentrant tachycardia, and in 3 (4.5%) of 67 patients undergoing ablation of the AV junction. The electrode temperature achieved at successful sites associated with recurrence was not different from the temperature achieved at successful sites without recurrence (61.1 ± 8.9 vs 61.6 ± 9.1; P = 0.8). The likelihood of developing a recurrence was higher following ablation of accessory pathways than following ablation of A V nodal reentrant tachycardia or the AV junction (P = 0.03). Patients experiencing a recurrence following ablation of an accessory pathway had longer procedure durations (P = 0.0001). Ablation of left free‐wall pathways was associated with a lower incidence of recurrence as compared with all other locations (P = 0.008).

Conclusion: The results of this study suggest that electrode temperature at the successful ablation site cannot be used to identify patients at highest risk of recurrence.
Amiodarone Instilled Into the Canine Pericardial Sac Migrates Transmurally to Produce Electrophysiologic Effects and Suppress Atrial Fibrillation
Authors: AYERS GREGORY M. , RHO TAI H. , BEN‐DAVID JOSEPH , BESCH HENRY R. , ZIPES DOUGLAS P.
Published: May 2007

Pericardial Sac as Amiodarone Reservoir. Introduction: We investigated whether amiodarone delivered into the pericardial sac exerted an effect on atrial and ventricular refractoriness, impulse generation, and conduction and on induced atrial fibrillation.

Methods and Results: All animals were anesthetized with α‐chloralose. After a sternotomy, the pericardium was opened and cradled to produce a “container” of approximately 75 mL. Part 1 experimental animals received amiodarone, 0.5, 1.0, or 5.0 mg/mL, dissolved in 3 mL polysorbate 80 and 5% dextrose in water (D5W) instilled into their pericardial sac for 3‐hour intervals. Part II experimental animals received either 1.0 or 5.0 mg/mL of amiodarone. Control dogs received a pericardial solution of 3 mL polysorhate 80 in D5W. Pre‐ and postinstillation electrophysiologic studies were performed. In part I, the increase in sinus cycle length, 1:1 AV conduction, and effective refractory period (ERP) of atrium, right ventricular (RV) and left ventricular epicardium, and RV endocardium were significantly greater in animals receiving amiodarone compared with controls. Amiodarone concentrations in the tissue samples were highest in the superficial sites of the atria, sinoatrial node, and ventricular epicardial samples and lowest in the interventricular septum. Only trace concentrations of amiodarone and no desethylamiodarone were found in the blood samples. In part II, atrial ERP significantly increased in the animals receiving amiodarone, and the number of episodes of sustained atrial fibrillation that could he induced decreased.

Conclusions: Amiodarone instilled into the pericardial sac migrates transmurally to produce significant electrophysiologic effects at superficial sites and appears to suppress electrically induced atrial fibrillation.
Will QT Dispersion Play a Role in Clinical Decision‐Making?
Authors: SURAWICZ BORYS
Published: May 2007

Role of QT Dispersion, (1) Dispersion of QT intervals is the difference between the longest and the shortest QT interval in the ECG. Owing to the relative ease of measurement and the perceived need for new markers of arrhythmogenicity, the method has attracted the interest of clinical investigators hut has not reached the level of practical utility. (2) It is postulated that to pass the test of practical utility, the method must meet the following criteria: (a) standardization; (b) establishment of normal values; (c) established sensitivity and/or specificity for diagnosis and/or prognosis; and (d) uniqueness of relevant information. (3) Analysis of the data from the literature suggests that standardization of the method and the range of normal values have not been established, and that the method lacks specificity for separating healthy persons from patients with heart disease. (4) Large values, such as average QT dispersion > 65 msec, have been found predominantly in patients with serious, life‐threatening ventricular tachyarrhythmias, and the largest values, i.e., > 110 msec in patients with congenital long QT syndrome. (5) The prognostic value of QT dispersion has been disputed, and the uniqueness of the relevant information has not been tested. (6) It is concluded that the acceptance of QT dispersion as a useful test in practice faces manifold and serious obstacles. It remains to be established whether these obstacles are insurmountable.
Randomized Comparison of Two Techniques for Titrating Power During Radiofrequency Ablation of Accessory Pathways
Authors: ADA STRICKBERGER S. , WEISS RAUL , KNIGHT BRADLEY P. , BAJU MARWAN , BOGUN FRANK , BRINKMAN KAREN , HARVEY MARK , GOYAL RAJIVA , DAOUD EMILE , MAN K. CHIN , MORADY FRED
Published: May 2007

Impedance Versus Temperature Monitoring. Introduction: The purpose of this study was to prospectively compare the value of impedance and temperature monitoring during accessory pathway ablation. Temperature and impedance monitoring can be used during radiofrequency ablation of accessory pathways to titrate power to achieve adequate but not excessive tissue beating.

Methods and Results: One hundred thirty‐two patients with a single accessory pathway were randomly assigned to undergo ablation using either impedance monitoring or temperature monitoring. During impedance monitoring, the endpoint for titration of power was a 5‐to 10‐Ω decrease in the measured impedance while for temperature monitoring the endpoint was to achieve a temperature of 58° to 62°C. Two protocols were used. In protocol 1 (90 patients), impedance monitoring was performed with a nonthermistor catheter and temperature monitoring was performed with a thermistor catheter. In protocol 2 (42 patients), a thermistor catheter was used in all patients. In protocol 1, the success rate (93% vs 93%; P = 1.0), ablation procedure duration (57 ± 56 vs 41 ± 41 min), fluoroscopy time (48 ± 29 vs 41 ± 23 min; P = 0.3), number of applications (6.2 ± 4.7 vs 5.7 ± 4.6; P = 0.8), and the number of applications associated with coagulum formation (0.1 ± 0.3 vs 0.3 ± 0.6; P = 0.1) were similar in the two groups. In protocol 2, as in protocol 1, there were no differences in the success rate (91% vs 95%; P = 1.0), ablation procedure duration (49 ± 37 vs 62 ± 55 min; P = 0.4), fluoroscopy time (46 ± 24 vs 49 ± 36 min; P = 0.8), number of applications (6.8 ± 7.0 vs 7.8 ± 12.1; P = 0.7), or number of applications associated witb coagulum formation (0.3 ± 0.6 vs 0.2 ± 0.7; P = 0.6) between the impedance and temperature monitoring groups.

Conclusion: Temperature and impedance monitoring are equally effective in optimizing the results of accessory pathway ablation.
Changes in Plasma Epinephrine Concentration and in Heart Rate During Head‐Up Tilt Testing in Patients with Neurocardiogenic Syncope:
Authors: KLINGENHEBEN THOMAS , KALUSCHE DIETRICH , LI YI‐GANG , SCHÖPPERL MATTHIAS , HOHNLOSER STEFAN H.
Published: May 2007

Sympathetic Activation in Neurocardiogenic Syncope. Introduction: Tilt table testing is widely used in the management of patients with neurocardiogenic syncope. However, the exact pathophysiologic mechanism of this disorder is still under debate. Likewise, therapy of these patients continues to represent a challenge in many cases. Therefore, the present study aimed to gain further insight into the pathophysiology of this syndrome and to examine easily accessible clinical parameters that can improve therapy selection.

Methods and Results: In 16 patients with neurocardiogenic syncope, changes in endogenous catecholamine concentrations were determined during repeated tilt table testing before and during treatment with metoprolol. Tachycardia preceded syncope in 8 of 10 responders compared to only 1 of 6 nonresponders (P < 0.05). In responders, the relative increase in epinephrine levels averaged 197%± 51% during drug‐free tilting and 75%± 33% during repeated testing while on β‐blocker therapy (P < 0.05). In nonresponders, there was a smaller relative increase in epinephrine averaging 137%± 35% at baseline tilt. During repeated tilt testing, a similar increase was observed in these patients with recurrent syncope (156%± 104%; P = NS compared to baseline).

Conclusion: In patients with neurocardiogenic syncope who show both an increase in epinephrine concentration during tilt test and sinus tachycardia prior to the onset of symptoms, β‐blocker treatment is very effective. These findings confirm the major role of sympathetic activation as a trigger of syncope. Particularly, heart rate changes at the onset of syncope may allow early identification of patients responding to antiadrenergic therapy.