bluuebunny/crossref_metadata_2025 huggingface dataset:
Titration of Power Output During Radiofrequency Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia
Authors: LANGBERG JONATHAN J. , HARVEY MARK , CALKINS HUGH , EL‐ATASSI RAFEL , KALBELEISGH STEVEN J. , MORADY FRED
Published: July 2006

Radiofrequency lesions in the anterior, superior aspect of the tricuspid annulus result in selective elimination of fast pathway function in patients with typical atrioventricular (AV) nodal reentry tachycardia. This technique is simple and effective, but has been associated with a significant risk of inadvertent complete AV block. The purpose of this study was to compare the safety and effectiveness of two different techniques for radiofrequency catheter ablation of the fast AV nodal pathway. Initially, a fixed power output was used at each target site. This method was compared retrospectively to a newer technique where power output was gradually incremented at each site. Radiofrequency power was initially applied at 10 watts for 10–15 seconds. If no junctional ectopy or a change in PR intervoi was seen, power output was incremented by 2 to 4 watts every 10 to 15 seconds up to a maximum of 30 watts. Thirty seven of 38 (96%) patients treated using this incremental power output were cured of their AV nodal reentry tachycardia. None of these patients developed inadvertent complete AV block. In contrast, 92% of historic controls treated with a fixed power output between 20 and 30 watts achieved a primary success and nine of these 89 (10%) historic controls developed inadvertent complete AV block (P = 0.04). There was no difference in the amplitudes of atrial, His, or ventricular electrograms at the effective sites between the two groups. Conclusions: (1) the anterior approach to radiofrequency catheter ablation of typical AV nodal reentry is associated with a significant risk of inadvertent complete AV block if a fixed power output is used; (2) starting at low power and gradually incrementing the output during radiofrequency energy application reduces the risk of complete AV block; (3) this incremental technique does not compromise efficacy.
The Effect of Phase Separation on Biphasic Waveform Defibrillation
Authors: COOPER RANDOLPH A.S. , WALLENIUS STEVEN T. , SMITH WILLIAM M. , IDEKER RAYMOND E.
Published: July 2006

It has been hypothesized that the defibrillafion efficacy of a biphasic shock is caused hy the large change in voltage between the two phases. This study examined the effects of separating the two phases in time thus splifting in half the rapid voltage change at phase reversal. The study was performed in three parts each using six dogs. Part I determined defibrillation thresholds (DFTs) for two exponentially truncated biphasic waveforms (3.5/2 msec and 6/6 msec) with interphase time delays of 0, 1, 2, 3, 4, 6, 8, and 10 msec. In Part II, probability of success curves were generated using an up down method with 15 shocks for each delay for the 3.5/2 msec biphasic waveform with inferphase delays of 0, 2, 3, 4, and 5 msec. In Part III, DFTs were determined using a 3.5/2 msec and 6/6 msec biphasic as well as a fhird waveform that consisted of two sequential 6‐msec pulses of the same polarity with interphase delays of 0, 5, 10, 15, 20, 25. 50, and 100 msec. In all three parts the defibrillating cathode was a 6.17 cm2 transvenous spring electrode positioned in the RV apex and the anode was a 113 cm2 cutaneous left chest wall eiectrode patch. With all waveforms, the trailing edge voitage of the first phase was equal to the negative of the leading edge voltage of the second phase. There was no statistical difference in DFTs or in 50% successful defibriliation points for phase separations from 0 to 6 msec and 0 to 5 msec for Parts I and II, respectively. In Part I there was a significant increase in DFTs for phase separations of 8 and 10 msec compared to a phase separation of 0 msec. In Part III there was no significant difference for seporations of 0 and 5 msec; however, there was a significant increase in DFT requirements for separations from 5 to 50 msec, which then decreased with a separation of 100 msec for ail three waveforms tested. In conciusion, defibriilation efficacy was unchanged with phase separations up to 6 msec. With phase separation, the rapid voltage change during phase reversal is split in half and. thus, cannot explain the improved efficacy of biphasic waveforms.
Propranolol Induced Electrical and Mechanical Alternans in Orthodromic Reciprocating Tachycardia
Authors: CROSSON JANE E. , DUNNIGAN ANN
Published: July 2006

During an electrophysiological study in a patient with a concealed accessory connection, there was no evidence of eiectrical or mechanical alfernans during tachycardia until propranolol was adminislered, but both forms of alternans developed with tachycardia of a slower rate following propranolol. Echocardiographic. arterial pressure, and electrocardiographic data obtained prior to and following propranolol administration are presented.
Implantable Cardioverter Defibrillator for Prevention of Sudden Cardiac Deatb in Patients with Ventricular Tachycardia and Ventricular Fibrillation: ICD Therapy In Sudden Cardiac Death
Authors: AKHTAR MASOOD , JAZAYERI MOHAMMAD , SRA JASBIR , TCHOU PATRICK , ROVANG KAREN , BLANCK ZALMEN , DHALA ANWER , DESHPANDE SANJAY , AXTELL KATHI
Published: July 2006

Among the various therapy options for survivors of ventricular tachycardia‐ventricular fibrillation (VT‐VF), the implantable cardioverter defibrillator (ICD) seems most promising. It reliably terminates VT‐VF and thus significantly impacts sudden cardiac death (SCD) survival. It is more effective than any of the known antiarrhythmic drugs in prevention of SCD, particularly among survivors of cardiac arrest. Compared to VT surgery, the ICD therapy can be offered to a larger pool of patients and can be placed at a lower surgical risk. With proper patient selection, ICD therapy is of major benefits to its recipients since it markedly reduces the chances of VT‐VF relaled mortality; the main cause of premature death in this population. The ICD therapy is cost effective when compared to other medical interventions and could be more so if the implant is carried out early in the course of VT‐VF management.
ICD Data Storage: Value in Arrhythmia Management
Authors: MARCHLINSKI FRANCIS E. , GOTTLIEB CHARLES D. , SARTER BRIAN , FINKLE JOHN , HOOK BRUCE , CALLANS DAVID , SCHWARTZMAN DAVID
Published: July 2006

Sophisticated diagnos tic information is provided by the latest generation of implantable defibriliators. The success of therapy and the type of therapy successful in terminating ventricular arrhythmias is provided by interrogating the ICD device. In addition, R to R interval information can be retrieved. In selected devices, either locai bipolar electrograms from the rate sensing leads or wide bipolar electrograms from the energy delivering leads provide visual confirmation of the presence of ventricular tachyarrhythmic events loading to ther apy. The value and limilations of this sophisticated diagnostic information in providing insight into the electrical events triggering therapy and the events triggering ventricular arrhythmias are discussed.
The Importance of Antitachycardia Pacing for Patients Presenting with Ventricular Tachycardia
Authors: ALMENDRAL JESÚS , ARENAL ANGEL , VILLACASTIN JULIAN P. , ROMÁN DANIEL SAN , BUENO HECTOR , ALDAY JESÚS M. , PASTOR AGUSTÍN , DELCAN JUAN L.
Published: July 2006

The initial experience from electrophysiological studies showed that pacing induced termination of ventricular tachycardias is usually possible but requires a critical pacing sequence. Studies on the resetting phenomenon showed, in most instances of failure of termination, that the “limiting factor” to produce ventricular tachycardia termination is usually failure to produce block within the circuit rather than failure to access or interact with the ventricular tachycardia origin. The resetting response is related to tachycardia termination in a number of ways. Of note is that a steeply increasing resetting pattern usually predicts tachycardia termination. Between 50% and 90% of induced ventricular tachycardias will be terminated by trains of rapid ventricular pacing. The analysis of the pacing rate necessary for termination shows that it varies widely. Paced cycle lengths of < 80% of tachycardia cycle length are necessary in at least 20% of tachycardias. In contrast, the incidence of acceleration is closely related to the paced cycle length: it is negligible with paced cycle lengths over 80% of tachycardia cycle length and increases to 36% with paced cycle lengths below 76% of tachycardia cycle length. Present information about efficacy of antitachycardia pacing in spontaneous tachycardias suggests that it is extremely effective, with over 90% success. However, it is likely that these data correspond to a selected group of tachycardias.
Defibrillation Energy Requirements with Single Endocardial (Endotak™) Lead
Authors: WINTER JOACHIM , VESTER ERNST G. , KUHLS STEPHAN , KANTARTZIS MICHAEL , PERINGS CHRISTIAN , PAUSCHINGER MATTHIAS , STRAUER BODO E. , BIRGKS WOLFGANG
Published: July 2006

The need for thoracotomy in usually high risk patients has limited the use of the implantable cardioverter defibrillator. Initial clinical results with endocardial and subcutanous patch electrodes (SQPs) are en couraging. Using a single endocardial lead in the absence of a SQP for chronic implantation of the cardioverter defibrillator, the goal of the study was to obtain defibrillation thresholds (DFTs) of 15 Joules (J) or less and to investigate changes in DFT over time. We tested 19 consecutive patients (15 men, 4 women] age 62 ± 8.5 years with malignant ventricular arrhythmias (14 VT/5 VF). The underlying heart disease was coronary artery disease in 15 pafients, dilative cardiomyopathy in two patients, and primary electricaJ disease in two patients. Four patients had undergone previous cardiac surgery. Left ventricular ejection fraction ranged between 14% and 66% (39%± 12.6%). Pacing thresholds (0.54 ± 0.17 Vat 0.5 msec), R wave amplitude for pacemaker sensing (14.2 ± 7.0 mV), slew rate (2.12 ± 1.4 V/sec), and resistance (500.3 ± 73.9 W) were sufficient in all patients. Eighteen patients met our endocardial impiant criteria with a DFT ≤ 15 J (10.05 ± 4.03 J) using monophasic (14 patients) or biphasic (four patients) pulse wave forms. In the one remaining patient, with a DFT of 20 J, we implanted a SQP but there was no reduction of the DFT. All patients tested showed successful defibrillation prior to discharge. During follow‐up of 88 patient‐months (1–9 months), 114 spontaneous VT/VF episodes occurred in five patients and were all successfully terminated. Eleven patients with a minimum follow‐up of 2 months were reassessed. In seven out of 11 patients, termination of VF was achieved with the same minimal energy requirements obtained intraoperatively. In three patients, DFT increased by 5 J (one patient) and 10 J (two patients). In a further patient, X ray revealed dislocation of the endocardial lead. Our data suggest that effective defibrillation is feasible with a single endocardial lead for implantation of cardioverter defibrillator. In addition, we strongly recommend repetitive x‐ray control to detect asymptomatic lead dislocation. Despite stable DFTs in most of our patients, an energy difference of ≤ 15 J between acute DFT and cardioverter defibrillator energy rating seems to be currently desirable to ensure successful postoperative defibrillation.
Automatic Implantable Cardioverter Defibrillator: Cost Effectiveness
Authors: HAUER RICHARD N.W. , WEVER ERIC F.D. , CRIJNS HARRY J.C.M.
Published: July 2006

Unexpected out‐of‐hospital cardiac arrest is in most cases due to ventricular fibrillation or rapid ventricular tachycardia. The usual therapeutic strategy in survivors starts with drug treatment, in case of failure followed by nonpharmacological therapy, which may include catheter ablation, ablative surgery, and finally defibrillator implantation. In most cases, this strategy is long lasting and very expensive. Implantation of a defibrillator as a first choice therapy may be cost effective, especially if the probability of successful drug treatment is low. However, cost‐effective aspects have been studied only retrospectively and in models. In 1989 we started a prospective cost‐effectiveness analysis of implantation of the automatic implantable cardioverter defibrillator (AICD) as first choice therapy (“early” AICD implantation) in successfully resuscitated postinfarct patients. Evaluation is being done in a randomized way with one group having early AICD implantation and the other group following the usual conventional therapeutic strategy. We compare medical, economic, and quality‐of‐life aspects. As of June 1992, 46 patients have entered the study. Totally 60 patients will be included. Results are expected in 1993 and will be expressed as cost effectiveness ratios in both study arms.
The Biophysics of Radiofrequency Catheter Ablation in the Heart: The Importance of Temperature Monitoring
Authors: HAINES DAVID E.
Published: July 2006

Radiofrequency (RF) catheter ablation is a technique whereby high frequency alternating electrical current with frequencies of 350 kHz to 1 MHz is delivered through eiectrode catheters to myocardial tissue creating a thermal lesion. The mechanism by which RF current heats tissue is resistive (or ohmic) heating of a narrow rim (< 1 mm) of tissue that is in direct contact with the electrode Deeper tissue planes are then heated by conduction from the small region of volume heating. Heat is dissipated from the region by further heat conduction into normothermic tissue, and by heat convection via the circulating blood pool and larger coronary vessels. The lesion size is proportional to the temperature at the electrode‐tissue interface (which is also a function of power level if electrical factors remain constant), and to the size of the electrode. At temperatures above 100°C, boiling occurs at the electrode‐tissue contact point resulting in a rapid rise in electrical impedance. Therefore, a theoretical maximum lesion size exists for any given electrode geometry. Other factors that are important for RF lesion formation incude electrode‐tissue contact pressure and duration of RF delivery. Temperature rises monoexponentially, and duration of energy delivery should be at least 35 to 45 seconds to approach steady state.
Electrophysiological Behavior of Atrioventricular Node After Selective Fast or Slow Pathway Ablation in Patients with Atrioventricular Nodal Reentrant Tachycardia
Authors: JAZAYERI MOHAMMAD R. , AKHTAR MASOOD
Published: July 2006

One hundred twenty consecutive patients with symptomatic atrioventricular nodal reentrant tachycardia (AVNRT) underwent catheter ablation using radiofrequency energy. Fast pathway ablation was attempted in the first 16 consecutive patients by application of radiofrequency current in the anterior and superior aspect of the tricuspid annulus. Successful results were accomplished in 13 patients, complete atrioventricular (AV) block occurred in three. One hundred four patients underwent ablation of the slow pathway in the posterior and inferior aspect of the tricuspid annulus, which was successful in 98 patients. The remaining six patients subsequently underwent a fast pathway ablation with successful results in four and AV block in two. Therefore. 102 (98%) of the last 104 patients became free of AVNRT while maintaining intact AV conduction. This study characterizes the electrophysiological properties of the residual AV node following a selective fast or slow pathway ablation.
Catheter Ablation of Atrial Flutter Circuits
Authors: COSÍO FRANCISCO G. , GOICOLEA ANTONIO , LÓPEZ‐GIL MARÍA , ARRIBAS FERNANDO
Published: July 2006

Atrial flutter (AF) mapping has shown circular activation in the right atrium (RA), wilh a “counterclockwise” rotation in a frontal view. The myocardial isthmus between the inferior vena cava and the tricuspid valve (IVC‐T) closes the activation circuit in its caudal end. The reproducibility of this activafion pattern, and the fact that some “rare” AF with a “clockwise” rotation of activation use the same circuit, suggests that reentry is greatly facilitated by the anatomical arrangement of the caudal end of the RA. This suggested that ablation of the IVC‐T isthmus may interrupt AF and prevent its recurrence. We have applied radiofrequency (RF) current to the IVC‐T isthmus in nine patients, producing sudden interruption of activation at this point in five (all those treated with large surface electrode catheters). in three others, RF produced acceleration or disorganization, leading to interruption. Preliminary follow‐up data suggest a favorable effect on AF recurrence, either by preventing it, or by making antiarrhythmic drugs effective.
Supraventricular Tachycardias: The Role of Surgery
Authors: GUIRAUDON GERARD M. , KLEIN GEORGK J. , YEE RAYMOND
Published: July 2006

Because of its high efficacy and low morbidity radiofrequency energy catheter abiation techniques have toppled the hierarchy of choice in tiie electrophysiological intervention armamentum. This review assesses current role of surgery and its foreseeable future. Most accessory AV pathways can be attained by endocardial manipulation and ablated. Surgical dissection of accessory pathways on the beating heart had documented that most pathways were paraannular, although right‐sided pathways may be distant to the annulus. Results of accessory pathway ablation have shown that right‐sided pathways are difficult to approach and ablate. Surgical ablation may currently be considered after failed catheter ablation. AV nodal modification using catheter ablation also yields excellent results. Radiofrequency energy creates a discrete lesion associated with discrete electrophysiological alteration. Surgical dissection is associated with more diffuse and extensive anatomical and electrophysiological changes and is no longer used even after failed catheter ablation. The arrhythmogenic anatomical substrate associated with atrial flutter is not yet well delineated in the coronary sinus os region. How to extend tissue modification for uniform success here is not yet known. Further surgical approach combined with extensive intraoperative cardiac mapping may ultimately prove a valuable guide for subsequent catheter technique. Atrial fibrillation is the last surgical frontier unchallenged by catheter techniques. Arrhythmogenic anatomical substrate is diffuse spreading over the entire atrial myocardium without a discrete target. The associated pathology is diffuse, severe, and progressive and present even in the so‐called lone atrial fibrillation. Progression of underlying pathology can nullify the best designed surgical rationale in terms of sinus node chronotropic function, and atrial contractility. Currently used surgical techniques, i.e., the corridor and the Maze operations, have contributed to a better selection of patients. Surgery is still associated with significant morbidity and relative efficacy, and may be improved before becoming the electrophysiological intervention of choice for atrial fibrillation. In conclusion, atrial fibrillation is a greater surgical challenge, but has to be met with the same standard used for other supraventricular tachycardias.
First Lessons from Radiofrequency Catheter Ablation in Patients with Ventricular Tachycardia
Authors: GÜRSOY SINAN , CHILADAKIS IOANNIS , KUCK KARL‐HEINZ
Published: July 2006

Fourteen patients (12 men, 2 women; 61 ± 9 years) with ventricular tachycardia and underlying heart disease underwent an attempt at radiofrequency energy catheter ablation. Twelve patients had coronary disease and two patients had dilated cardiomyopathy. Two patients had two clinical tachycardias, the ejection fraction was 38%± 11%. All tachycardias were inducible and hemodynamically well tolerated (cycle length = 357 ± 56 msec). Ablation was initially successful in nine patients (no tachycardia inducible after ablation and before discharge). Two patients had recurrences (in‐hospital and 4 months) and one patient had a tachycardia of a different morphology, which was also successfully ablated. Ablation was overall successful in seven patients and unsuccessful in seven patients (including all patients with cardiomyopaihy). Mid‐diastolic potentials were observed in all the patients in whom ablation was successful but not observed in four of seven unsuccessful patients. The successful patients remain free of recurrences at 9 ± 8 months follow‐up. Conclusions: (1) in ventricular tachycardia following an old infarction radiofrequency energy ablation is possible with a high success rate if a critical component of the tachycardia circuit can be localized. Localizing isolated mid‐diastolic potentials and ensuring these potentials are part of the reentrant circuit with concealed entrainment can help to enhance the results. (2) A negative predischarge electrophysiological study may be predictive of success.
Head‐Up Tilt Testing With and Without Isoproterenol Infusion in Healthy Subjects of Different Ages
Authors: NEWMAN DAVID , LURIE KEITH , ROSENQVIST MÅRTEN , WASHINGTON CHERYL , SCHWARTZ JANICE , SCHEINMAN MELVIN M.
Published: July 2006

Passive head‐up tilt testing with or without infusion of isoproterenol is used in the investigation and management of patients with syncope. Twenty‐five healthy asymptomatic volunteers prospectively grouped according to age (young [28 ± 1.7 years]: n = 9; middle [51 ± 3.3 years]: n = 11; elderly [81 ± 2.4 years]; n = 5; mean ± SE) were studied during: (1) supine carotid sinus massage: (2) 60° head‐up tilt aione; and (3) infusion of isoproterenoJ to raise the heart rate 20% above supine baseline, prior to a 10‐minute repeat tilt. Symptoms occurred in three subjects (12%) and only occurred with passive tilting alone. Two young subjects had syncope with sinus pauses greater than 10 seconds, One elderly subject developed atrial flutter. No subject had symptoms or hypotension during tilt plus isoproterenol or a pause greater than 3 seconds with carotid sinus massage. With passive tilt, mean heart rate increased by 16 ± 6 beats/min and 18 ± 7.8 beats/min in the young and middle aged subjects (P < 0.05), but only by 6 ± 5 beats/min in the elderly (P = NS, supine vs 60° in each group). With head‐up tilt plus isoproterenol infusion, the mean heart rate elevation in response to tilt was 17 ± 9 beats/ min, 8 ± 3 beats/min, and 12 ± 4 beats/min for the young, middle, and elderly subjects, respectively (P < 0.05, supine vs 60° in each group). Supine serum norepinephrine concentration values were 229 ± 33 pg/mL, 374 ± 107 pg/mL, and 409 ± 41 pg/mL (mean ± SE) in the young, middle aged, and elderly groups, respectively (P = 0.05, young vs elderly). With head‐up tilt, these significantly rose in the three groups. With tilt, serum epinephrine tended to rise (P < 0.10) only in the young and middle aged groups. Serum dopamine did not significantly increase in response to tilt in any of the groups. These studies suggest that tilt testing protocols need to be assessed against age and protocol matched controls.
Do Steroid‐Eluting Electrodes Really Have Better Performance Than Other State‐of‐the‐Art Designs?
Authors: SANTINI MASSIMO , DE SETA FRANCESCO ,   THE ITALIAN MULTICENTER STUDY CROUP ON LOW OUTPUT STIMULATION
Published: July 2006

A multicenter study evaluated the performance of atrial and ventricular unipolar leads with porous steroid‐eluting and platinized grooved electrodes. A total of 563 leads were implanted in 451 patients. These included 311 ventricular and 97 atrial steroid‐eluting electrodes; and 112 ventricular and 43 atrial leads with platinized electrodes. Mean follow‐up was ± 1 year. At implant there were no significant differences in threshold parameters in either chamber. Chronically, however, the steroid eluting lead consistently had significantly lower pacing thresholds in both chambers. For example, after 360 days implant, steroid‐eluting electrodes had 0.23 ± 0.10 msec ventricular thresholds at 0.8 V compared to 0.45 ± 0.3 msec in the platinized group (P < 0.0001). In the atrium, the steroid‐eluting lead's 6‐month thresholds at 0.8 V were 0.15 ± 0.06 msec compared to 0.9 ± 0.8 msec for the platinized electrode (P < 0.01). The chronic ventricular QRS amplitudes were significantly greater for the steroideluting electrode (P < 0.0005). There were no significant differences in atrial sensing and no incidence of atrial undersensing in the study. The low and consistent thresholds of the steroid‐eluting electrodes would have permitted pacing in the ventricle at ± 2.5 V without compromising safety factor in 99.4% of the patients. The other 0.6% required 5 V temporarily. In the atrium, 100% of the patients could have been paced safely at reduced output. In spite of this, 63% of the implanters lacked the confidence to use reduced outputs.
Undesirable Mode Switching with a Dual Chamher Rate Responsive Pacemaker
Authors: PITNEY M.R. , MAY CD. , DAVIS MJ.
Published: July 2006

The Telectronics 1250 Meta MV DDDR pacemaker is a new device featuring automatic mode switching from DDDH to VVIR pacing in the event of an atrial arrhythmia. Although mode switching is a valuable feature, sinus tachycardia can cause an undesirable mode switch to occur. Of 24 implants at this institution, 11 have been for an AV conduction disorder. Eight of these 11 patients were specificalJy evaiuated for undesirable mode switching. During exercise testing and/or Holter monitoring, mode switching was repeatediy seen in seven of the eight at low levels of exercise. Factors precipitating mode switching were a low rate response factor, low upper rate setting, long base postventricular atrial refractory period (PVARP) and a long AV delay. During Holter monitoring, patients spent up to 50% of the time in VVIR pacing as opposed to DDDR pacing. It is concluded that patients with intact sinus node function are at risk of undesirable mode switching and should probably be programmed to the DDD mode unless there is a specific indication for DDDR pacing. If the DDDR mode is chosen, careful selection of the aforementioned pacing parameters is required.
Is Absolute Hypovolemia a Risk Factor for Vasovagal Response to Head‐Up Tilt?
Authors: JAEGER FREDRICK J. , MALONEY JAMES D. , CASTLE LON W. , FOUAD‐TARAZI FETNAT M.
Published: July 2006

To test the hypothesis that hypovolemia is associated with an increased incidence of vasovagal syncope during head‐up tilt (HUT) 45 patients with history of syncope or presyncope were studied. Blood volume (radio‐iodinated serum albumin) was determined, then subjects underwent a graded HUT (from 15°–60° HUT) with cuff blood pressure and ECG monitoring. All patients were kept on their own medications during evaluation. Thirty patients (12 male, 18 female, mean age 50 ± 19 [SD] years) had hypovolemia, defined as blood volume < 90% of lab normal for corresponding sex, while 15 patients (7 male, 8 female, mean age 52 ± 21 years) were normovolemic with blood volume ranging from 91%‐110% of sex‐matched normal subjects. The normovolemic patients served as controls. During HUT, a vasovagal response was elicited in 5 of the 30 hypovolemics and in 4 of the 15 normovoiemic (16.7% and 26.7%, respectively, P = NS). In those who developed vasovagal response, the changes of heart rate and blood pressure during HUT were not significantly different between hypovolemics and normovolemics, neither at the endpoint (vasovagal response) nor immediately before the development of the vasovagal response. In patienis with nonvasovagal events, four types of hemodynamic responses to tilt were observed; normal blood pressure response associated with normal heart rate increase, normal blood pressure response in association with accentuated increase in heart rate, orthostatic hypotension with normal acceleration of heart rate, and orthostatic hypotension with accelerated increase in heart rate. The percent distribution of these responses were 44%, 20%. 0%, and 36% in the 25 nonvasovagal hypovoiemics versus 73%, 0%, 18%, and 9% in the 11 nonvasovagal normovolemics. The results demonstrate that supine total blood volume does not predict the occurrence of vasovagal response to HUT. However, accentuated orthostatic tachycardia was more prevalent in hypovolemics as compared to normovolemics with nonvasovagal response to tilt.
Efficacy and Safety of Combination Therapy with Amiodarone and Type I Agents for Treatment of Inducible Ventricular Tachycardia
Authors: JUNG WERNER , MLETZKO RALPH , MANZ MATTHIAS , NITSCH JOBST , LÜDERITZ BERNDT
Published: July 2006

In a prospective study the efficacy of amiodarone in combinalion with the three Class I drugs mexiletine, fiecainide, orencainide was evaluated consecutively in 12 patients with recurrent venlriculav tachycardias (VT) by programmed stimulation. None of the tested drug combinations suppressed induction of sustained VT. The combination of amiodarone with Class IC drugs fJecainide and encainide prolonged the cycle length of VT significantly, whereas the combination with mexiletine did not hove the same degree of slowing on the VT cycle length. Several proarrhythmic effects occurred during the combination therapy with encainide: (1) frequent, spontaneous recurrences of hemodynamically well tolerated VT in four patients; (2) enhanced inducihilily of VT in three patients; (3) impaired termination of VT in three patients. Though a marked increase in QRS and QTc intervals was observed by combined treatment with encainide, no significant correlation could be established between aggravation of arrhythmia and plasma levels of encainide, degree of QRS widening, JT or QTc prolongation. The only predictor for the occurrence of proarrhythmic events was found in left ventricular ejection fraction. These findings suggest that in patients refractory to amiodarone alone or a combination with mexiletine, the combined treatment of amiodarone with other Class IC drugs prolongs the VT cycle length but does not suppress induction of VT during programmed stimulation. Combination therapy of amiodarone with encainide was associated with a high incidence of proarrhythmic effects.
Adaptive Rate Pacing Controlled by Right Ventricular Preejection Interval for Severe Refractory Orthostatic Hypotension
Authors: GRUBB BLAIR P. , WOLFE DOUGLAS A. , SAMOIL DANIELA , HAHN HARRY , ELLIOTT LAURA
Published: July 2006

A 72‐year‐old African‐American man with frequent recurrent syncope was found to have severe refractory orihostatic hypotension with concomitant supine hypertension. Pharmacotherupy was successful in controlling his supine hypertension but was unable to resolve his severe orihostatic hypotension. Temporary fixed rate tachypacing was only minimally effective in preventing syncope during upright tilt, while variable rate pacing based on degree of blood pressure fall was far superior. Following these observations, an adaptive rate pacing system controlled by right ventricular preejection interval was implanted (Precept DR Model 1200). The system adequately sensed the patient's fall in blood pressure when sitting or standing and augmented its rate accordingly, thus preventing syncope. While supine, the pacing rate fell to 60 ppm, thereby, avoiding an exacerbation of his concomitant supine hypertension. Over a 3‐nionth follow‐up period, he has had no further orthostatic or syncopal episodes. We conclude that adaptive rate pacing using right ventricular preejection interval may be an effective treatment for severe refractory orthostatic hypotension.
Pericardial Effusion Increases Defibrillation Energy Requirement
Authors: THAKUR RANJAN K. , SOUZA JOSEPH J. , TROUP PAUL J. , CHAPMAN PETER D. , WETHERBEE JULE N.
Published: July 2006

Pericardial effusion may increase defibrillation energy requirements. We examined the effect of pericardial effusion in seven pentobarbital anesthetized dogs (25.3 ± 3.4 kg) using monophasic and biphasic shock. A median sternotomy was performed and two 13.9 cm2 patch electrodes were sewn extrapericardially; 3 cc/kg of 0.9% NaCl was instilled through an intrapericardial catheter used to create a hemodynamically insignificant pericardial effusion. Four triais of five leading edge voltages (200–600 volts, in 100 volt increments) were performed for monophasic and biphasic shocks of 10 msec total duration and defibrillation efficacy curves were determined by logistic regression anaiysis. Baseline impedance was 68.1 and 66.2 Ohms for monophasic and biphasic waveforms, respectiveiy, and decreased to 52.9 and 49.9 Ohms, respectively, with pericardial effusion (P < 0.01). Energy associated with 80% probability of successful defibrillation (E80) for monophasic shock was 16.0 jou]es at baseline and increased to 18.5 joules with pericardial effusion (P < 0.016). Similarly, E80 for biphasic shocks increased from 10.6 joules to 13.0 joules (P < 0.016). Removal of pericardial effusion was associated with impedance and E80 returning to baseline. In this model, pericardial effusion increased defibrillation energy requirements and may expiain early postimplant defibrillator failure.
Acute and Long‐Term Ventricular Stimulation Thresholds with a New, Iridium Oxide‐Coated Electrode
Authors: DEL BUFALO ALESSANDRO G.A. , SCHLAEPFER JURG , FROMER MARTIN , KAPPENBERGER LUKAS
Published: July 2006

Efforts have been made to design electrodes that significantly reduce not only the acute and chronic stimulation thresholds, but also attenuate the early peaking phenomenon and polarization. At two voltage levels (2.7 V and 5.4 V, respectively), we evaluated the right ventricular stimulation thresholds obtained with a new, iridium oxide‐coated electrode in ten patients who received a VVI pacemaker. Measurements were mode at implant and at multiple intervals for 1 year. Pulse width stimulation thresholds at implant were as follow: 0.04 ± 0.008 msec at 2.7 V, 0.03 ± 0.004 msec at 5.4 V; values at 2 weeks were 0.14 ± 0.06 msec at 2.7 V, 0.07 ± 0.025 msec at 5.4 V; values at 3 months were 0.09 ± 0.03 msec at 2.7 V, 0.05 ± 0.01 msec at 5.4 V; values at 1 year were 0.08 ± 0.02 msec at 2.7 V, 0.04 ± 0.01 msec at 5.4 V, The maximal increase of 0.11 ± 0.05 msec occurred at 2.7 V, 2 weeks after implant. Our results indicate that this new electrode provides low acute and long‐term stimulation thresholds, as well as an attenuated early peaking phenomenon, being able to stimulate safely at 2.7 V even early after implant.
Effect of Extracorporeal Shock Wave Lithotripsy on Implantable Cardioverter Defibrillator
Authors: VASSOLAS GEORGE , ROTH ROBERT A. , VENDITTI FERDINAND J.
Published: July 2006

Extracorporeal shock wave Jithotripsy (ESWL) is frequently used for nephrolithiasis of the upper urinary tract. Because of the powerful shock wave and electromechanical forces created, this therapy has been contraindicated in the patient with an implantable cardioverter defibrillator (ICD). To determine whether or not ESWL affects ICD devices, we subjected ten devices to a full course of ESWL. The devices were then returned to the manufacturer to undergo bench analysis, which revealed no abnormalities in function. Additionally, one device was placed in the pathway of the shock wave, resulting in a discharge of the device despite a frequency of ESWL of 100 shocks/min (well below the rate cutoff of that device). Manufacturer analysis of this device, likewise, revealed no abnormalities even though the device had been exposed to the focal point of the shock wave. We conclude that contralateral ESWL is not contraindicated for the patient with an ICD. We do, however, recommend a postprocedure evaluation to ensure appropriate function of the ICD.
Effects on Cardiac Performance of Atrioventricular Node Catheter Ablation Using Radiofrequency Current for Drug‐Refractory Atrial Arrhythmias
Authors: TWIDALE NICHOLAS , SUTTON KAYE , BARTLETT LYN , DOOLEY ALISON , WINSTANLEY SUSAN , HEDDLE WILLIAM , HASSAM RHONDA , KOUTSOUNIS HARI
Published: July 2006

Patients with atrial fibrillation or atrial flutter (AF) are candidates for radiofrequency (RF) catheter ablation of the atrioventricular (AV) node with the aim being to control heart rate. As patients wilh AF can have markedly impaired ventricular function, information concerning the hemodynamic effects of AV node ablation using RF current would be valuable. Fourteen consecutive patients (mean age 65 ± 3 years) with drug‐resistant AF underwent AV node catheter ablation with RF current and had permanent pacemaker implantation. The mean left ventricular ejection fraction (FFJ by two‐dimensional echoeardiography immediately before ablation was 42 ± 3% (range 14%–54%) and their mean exercise time was 4.4 ± 0.4 minutes. Complete AV block was achieved in all 14 patients with 6 ± 2 RF applications (range 1–18). There was no evidence of any acute cardiodepressant effect associated with delivery of RF current, and EF 3 days after ablation was 44 ± 4%. By 6 weeks after ablation, the left ventricular EF was significantly improved compared to baseline (47 ± 4% postablation vs 42 ± 3% preahlation; P < 0.05), and this modest increase in EF was accompanied by an improvement in exercise time (5.4 ± 0.4 min). In conclusion, delivery of RF current for AV node catheter ablation in patients with AF and reduced ventricular function is not associated with any acute cardiodepressant effect. On the contrary, improved control of rapid heart rate following successful AV node ablation is associated with a modest and progressive improvement in cardiac performance.
Transesophageal Defibrillation: Animal Studies and Preliminary Clinical Observations
Authors: COHEN TODD J. , CHIN MICHAEL C. , OLIVER DIANE G. , SCHEINMAN MELVIN M. , GRIFFIN JERRY C.
Published: July 2006

Ventricular fibrillation (VF) that fails to respond to transthoracic defibrillation leaves the clinician with few alternatives. The purpose of this study was to develop a technique of rescue defibrillation by use of transesophageal electrodes. Fourteen anesthetized dogs (20 30 kg) were investigated in this study. Two electrodes (300 mm2) were mounted 8 cm apart on an esophageal probe and inserted approximately 40 cm from the mouth. VF was induced using AC current delivered to the myocardium. Defibrillation was then performed between the distal electrode (anode) and anterior skin patch (cathode). After 15 seconds of induced VF, transesophageal and transthoracic defibrillation thresholds (DFTs) were determined in random order. The esophageal DFT (90 ± 15 joules) tended to be lower than the transthoracic DFT (115 ± 35 joules), though this difference was not statistically significant. One dog could not be defibrillated by transthoracic defibrillation but responded to transesophageai defibrillation. Esophageal electrodes were also useful for arrhythmia discrimination and ventricular pacing (pacing threshold of 38 ± 5 mA at a pulse duration of 2.5 msec). Following transesophageal DFT determination, in ten dogs (total energy of 600 ± 150 joules), acute esophageal histopathology demonstrated mild to severe focal injury to the mucosa and/or muscular layers. However, esophagi in four chronic dogs (total energy of 470 ± 110 joules) showed no gross evidence of macosal damage, perforation, or stricture 4 weeks following defibrillation. Histopathology showed only focal myocyte atrophy and repair. As a last resort, transesophageal defibrillation was performed in the emergency room on four patients with out‐of‐hospital refractory VF who failed > 6 high energy transthoracic shocks. Transesophageal defibrillation successfully terminated VF in each patient in spite of ≥ 50 minutes of cardiac arrest, however, none of the patients survived the initial resuscitation, Jn conclusion, transesophageal defibrillation is as effective as transthoracic defibrillation in a canine model and safe up to a total energy of 600 joules. Preliminary clinical trials suggest that this method results in conversion from VF when trunsthoracic defibrillation fails.
Altered Cardiac Oxygen Extraction, Lactate Production and Coronary Blood Flow After Large Dose Transthoracic DC Countershocks
Authors: TROUTON T.G. , ALLEN J.D. , YOUNG I.S. , TRIMBLE E.R. , ADGEY A.A.J.
Published: July 2006

Although problems such as hypotension and pulmo‐nary edema complicate the use of trunsthorucic DC counlershocks, the mechanisms are not clear. In anesthetized dogs at 1 minute after only two defibrillator shocks there was a brief rise in coronary sinus lactate. exceeding arteriol concentrations. Larger rises in lactale were seen after five shocks, indicating myocardial production of lactate. By contrast in eight animals given dummy shocks the heart always extracted lactate. At 2 minutes after five shocks mean myocardial oxygen extraction (6.5 ± 0.6 mL/100 mL blood; n = 5) was significantly lower than in controls (11.1 ± 0.6 mL/100 mL blood: n = 4; P < 0.0001), and remained so until 3 minutes after shocks, without significant increase in the lipid pevoxidation product malondiaidehyde in coronary sinus or arterial blood. Great cardiac venous blood flow, measured hy thermodiiution, rose after five shocks, and the heart rate pressure product also increased at 1–2 minutes. This transient failure of oxygen extraction, in the presence of arterial normoxia. hyperemia, and increased cardiac work, is best accounted for by a central effect of countershocks on myocardial ceiluiar respiration.
A Severed Pacemaker Lead Entrapped in a Hepatic Vein
Authors: STORM C.J. , van MECHELEN R.
Published: July 2006

Complete lead fracture is a uncommon phenomenon in cardiac pacing. Recently we encountered a patient with a severed lead at routine pacemaker follow‐up visit. In this case report, the typical ECG changes and noninvasive pacemaker measurements are discussed. The chest roentgengram showed the position of the proximal part of the lead, but this technique could not establish the exact position of the distal part of the lead. Ultrasound recording of the upper abdomen demonstrated that the distal part of lead was entrapped in the great hepatic vein. Since this position was stable with one end in the right ventricular apex and the other end in a hepatic vein, no further action was undertaken to remove this part of lead. The proximal part of the lead and the pulse generator were explanted. So far the clinical course of the patient has been unevenfful. Strategies to remove severed leads are discussed based on a review of the literature.
A Unique Pulse Generator Safety Feature for Bipolar Lead Fracture
Authors: MAUSER JONATHAN F. , HUANG SHOEI K. STEPHEN , RISSER THOMAS , BONAVITA GREGORY J. , WAGSHAL ALAN B. , MITTLEMAN ROBERT S. , CUELLO CARLOS
Published: July 2006

In this report, we describe two pacemaker dependent patients with outer‐coil fractures in their bipolar ventncular leads who averted potentially calastrophic consequences because of a new safety feature incorporated into their puise generators (Intermedics Cosmos II, model 284–05). Both patients were asymptomatic; the malfunctions were discovered at routine pacemaker evaluation. Magnet application resulted in symptomatic loss of ventricular capture. In each instance, the pulse generator detected an outer‐coil fracture and reprogrammed itself from bipolar DDD to unipolar DOO pacing to prevent loss of capture. Subsequent lead replacement resulted in resumption of normal function. We suggest that this feature be incorporaled into all devices with programmable polarity.
Curative Radiofrequency Catheter Ablation for Permanent Junctional Reciprocating Tachycardia
Authors: YANG YANZONG , GRECO CESARE , CICCAGLIONI ANTONIO , QUAGLIONE RAFFAELE , CRITELLI GIUSEPPE
Published: July 2006

Two patients with the permanent form of junctional reciprocating tachycardia successfully treated with the radiofrequency catheter ablation technique are described. In both patients a reentrant tachycardia utilizing a conceoled slow conducting posterior septal accessory pathway for retrograde conduction was demonstrated. Radiofrequency current was delivered below the coronary sinus orifice. The procedure resulted in ablation of the accessory pathway conduction in both patients. During the follow‐up, both patients remained free from tachycardia on no medication. This report demonstrates that the arrhythmogenic substrate of the permanent junctional reciprocating tachycardio can be easily suppressed by means of the radiofrequency catheter technique.
Impedance Cardiography for Cardiac Output Estimation in Pacemaker Patients: Review of the Literature
Authors: OVSYSHCHER ILYA , FURMAN SEYMOUR
Published: July 2006

Impedance curdiogrciphy permits noninvasive beat‐to‐beat determination of cardiac output, the product of the amplitude of the first derivative of thonicic impedance signal (dZ/dt), the venfricular ejection time, and heart rate corrected by the distance between the measuring electrodes. Its use is based on: (1) the dZ/dt signal that originates from the upper thorax; (2) the ventricular ejection period measured by the dZ/dt curve that occurs between the opening and closing of the aortic vnlve: (3) the dZ/dt curve is similar in morphology and timing to the aortic flow curve measured by an electromagnetic flowmefer with a significant linear correlation (r = 0.9) between dZ/dt and peak aortic flow; (4) similarity of the linear correlation between stroke volume, determined by the flowmeter and the impedance signal; and (5) significant reduction of the dZ/dt signal by 90% follows simultaneous occlusion of the aorta and the pulmonary artery. The rapid systolic portion of the impedance signal occurs only when blood is ejected into the aorta and is independent of right ventricular ejection. Most studies comparing impedance cardiography results with standard cardiac output determination have shown a correlation of 0.7–0.9. While the accuracy of impedance cardiography remains controversial and can be affected by the inherent limitations of the technique and by low cardiac output, intracardiac shunts. and valvular regurgitation. the high reproducibility of the method is established and may be comparable or superior to other commonly used techniques. When accurate determination of cardiac output is crucial, impedance cardiography may be used in conjunction with a standard technique to establish a baseline reference, thereby permitting further analysis. If only the trend need be followed, the high reproducibility of impedance cardiography measurements allows small changes in cardiac output to be detected on a frequent and ongoing basis. The ease and precision of this technique warrants its more widespread use in the assessment of pacemaker patients. Further use of this promising technique will allow a better definition of its role in the assessment of a wide range of cardiac patients.
Radiofrequency Catheter Ablation of an Accessory Atrioventricular Connection in a Fontan Patient
Authors: CASE CHRISTOPHER L. , SCHAFFER MICHAEL S. , DHALA ANWER A. , GILLETTE PAUL C. , FLETCHER SCOTT E.
Published: July 2006

Radiofrequency catheter ablation is fast becoming the procedure of choice for the nonpharmacological treatment of atrioventricular connections that are responsible for debilitating tachycardias. We, herein, present a case of reentrant supraventricular tachycardia secondary to on otrioventricular connection in a Fontan patient that was successfully treated with radiofrequency catheter ablation.
Intraoperative Mapping and Radiofrequency Ablation of the His Bundle in a Patient with Complex Congenital Heart Disease and Intractable Atrial Arrhythmias Following the Fontan Operation
Authors: URCELAY GONZALO , II MACDONALD DICK , BOVE EDWARD L. , MOSCA RALPH , DOROSTKAR PARVIN C. , SERWER GERALD A. , CAMPBELL ROBERT M. , ARMSTRONG BRIAN
Published: July 2006

Intraoperative mapping and radiofrequency ablation of the His bundie (with epicardial ventriculor pacing) were performed in an 18‐year‐old woman with complex congenital heart disease and inlractable chronic atrial arrhythmias following the Fontan operation. The presence of complex intracardiac anafomy as well as the exclusion of tbe atrioventricular conduction tissue from the systemic venous circulation strongly influenced the technical approach.