bluuebunny/crossref_metadata_2025 huggingface dataset:
Spurious Discharges Due to Late Insulation Break in Endocardial Sensing Leads for Cardioverter Defibrillators
Authors: PETERS ROBERT W. , FOSTER ANDREW H. , SHOROFSKY STEPHEN R. , NOLAN DEBORAH A. , GOLD MICHAEL R.
Published: July 2006

Despite their similarity to permanent pacemaker leads, endocardial sensing leads for Cardioverter defibrillators have a relatively high failure rate. We describe four patients with endocardial rate sensing leads who developed inappropriate discharges 10–30 months after implantation due to small breaks in the lead insulation. This problem may become increasingly common as the number of Cardioverter defibrillator implants with transvenous leads continues to grow and should be considered in the differential diagnosis of late sensing failure or inappropriate device discharges.
Implantation of a Subcutaneous Lead Array in Combination with a Transvenous Defibrillation Electrode via a Single Infraclavicular Incision
Authors: KALL JOHN G. , KOPP DOUGLAS , LONCHYNA VASSYL , BLAKEMAN BRADFORD , CADMAN CHRISTOPHER , O'CONNOR MARK , KINDER CHARLES , GILKERSON JAMES , AVERY ROBERT , WILBER DAVID
Published: July 2006

Occasional patients have excessive defibrillation energy requirements despite appropriate transvenous defibrillation lead position and modification of defibrillation waveform and configuration. Preliminary data suggest that use of subcutaneous defibrillation electrode arrays with nonthoracotomy systems is associated with a substantial reduction in defibrillation threshold. The current operative approach to subcutaneous lead array implantation involves the use of a separate left chest incision. We present two cases in which implantation of a subcutaneous lead array in combination with a transvenous defibrillation electrode was performed via a single infraclavicular incision and associated with a reduction in defibrillation threshold. Such an approach simplifies implantation and avoids the potential morbidity of the additional incision required of a left lateral chest approach.
Ventricular Pacing Induced Ventricular Tachycardia in Patients with Implantable Cardioverter Defibrillators
Authors: ROELKE MARC , O'NUNAIN SEAN , OSSWALD STEFAN , TROUTON THOMAS G. , HARTHORNE J. WARREN , GARAN HASAN , RUSKIN JEREMY N.
Published: July 2006

Appropriately timed noncompetitive ventricular pacing potentially may initiate ventricular tachycardia in patients prone to these arrhythmias. The combination of bradycardia pacing and stored electrograms in a currently available cardioverter defibrillator provides an opportunity to evaluate the occurrence of such pacing induced ventricular tachycardia. During a surveillance period of 18.7 ± 11.4 months, stored electrograms documented 302 episodes of ventricular tachycardia in 77 patients. Five patients (6.5%) demonstrated 25 episodes (1–16 per patient) of ventricular tachycardia that were immediately preceded by an appropriately paced ventricular beat (8.3% of all episodes of ventricular tachycardia). All five patients had prior myocardial infarctions and a history of monomorphic ventricular tachycardia occurring both spontaneously and in response to programmed electrical stimulation. Antitachycardia pacing terminated pacing induced ventricular tachycardia in 22 episodes; in one episode antitachycardia pacing accelerated ventricular tachycardia. In two cases shock therapy was aborted for nonsustained ventricular tachycardia. We conclude that, in selected postinfarction patients with recurrent sustained monomorphic ventricular tachycardia treated with implantable cardioverter defibrillators, appropriately timed ventricular pacing may induce ventricular tachycardia.
Unmasking of Retrograde Conduction by Isoproterenol in a Concealed Accessory Pathway
Authors: FRAZIER DAVID W. , PACKER DOUGLAS L. , STANTON MARSHALL S.
Published: July 2006

A 52‐year‐old female with no structural heart disease presented with a right bundle branch block (RBBB)/right axis deviation tachycardia with a cycle length of 300 msec. P waves were not discernible on the surface ECG. Baseline electrophysiology study in the drug‐free state revealed no evidence for anterograde or retrograde conducting accessory pathways (APs) or for dual AV node physiology. Retrograde VA block with AV dissociation was present at a ventricular paced cycle length of 600 msec (sinus cycle length of 635–700 msec). AV nodal Wenckebach occurred during decremental atrial pacing at a cycle length of 300 msec. During isoproterenol administration, a left lateral AP with retrograde only conduction became manifest with 1:1 VA conduction to 380 msec. No anterograde AP conduction was present. Orthodromic reciprocating tachycardia with a cycle length of 285–315 msec was easily induced. We conclude that total functional conduction block can exist in APs, and unmasking of total conduction block can be accomplished with isoproterenol. All patients with undiagnosed tachycardias should have full repeat stimulation studies during adrenergic stimulation if the initial baseline evaluation is nondiagnostic.
Optimizing Defibrillation Through Improved Waveforms
Authors: BLOCK MICHAEL , BREITHARDT GÜNTER
Published: July 2006

Defibrillation of the heart is achieved if an electrical current depolarizes the majority of the unsynchronized fibrillating myocardial cells. The applied current or the corresponding voltage described as a function of time is called the waveform. In pacing, to stimulate myocardial cells close to the electrode, a relatively low voltage is needed for a relatively brief duration. However, in defibrillation, approximately a 100‐fold higher voltage is needed and achieved by the use of capacitors. The exponential voltage decay of a capacitor during its discharge determines the basic waveform for defibrillation. In an attempt to lower the energy needed for defibrillation, the steepness of the decay (different capacitances), the duration (fixed duration waveforms) or tilt (fixed tilt waveforms), or the initial polarity can be changed. Additionally, the polarity of the electrodes can be reversed during the discharge of the capacitor once (biphasic waveform) or twice (triphasic waveform). If two capacitors and defibrillation pathways are available, bidirectional defibrillation pulses can be delivered sequentially. In humans, the original standard waveform used with endocardial leads was a single monophasic pulse delivered by a 125‐μF capacitor using the endocardial right ventricular electrode as cathode. It is now known that a reversal of the initial polarity and a reversal of polarity during capacitor discharge may significantly lower the energy needed for defibrillation, thereby preventing formerly frequent failures of defibrillation with endocardial lead systems. The use of sequential pulses showed no or only slight reductions of energy requirements and was abandoned due to the additional electrode needed. The use of a smaller capacitance (60–90 μF) reduced maximum energy output but generally did not reduce energy requirements for defibrillation. However, with more efficient electrodes, smaller capacitances that will help to reduce the size of the defibrillator might be used. Thus, today defibrillation is optimized with respect to energy, capacitor size, and ease of implantation if an approximately 90‐μF capacitor is used to deliver a biphasic pulse via a bipolar lead system using the right ventricular electrode as anode.
Italian Multicenter Clinical Experience with Endocardial Defibrillation: Acute and Long‐Term Results in 307 Patients
Authors: RAVIELE ANTONIO , GASPARINI GIANNI ,   ITALIAN ENDOTAK INVESTIGATOR GROUP
Published: July 2006

This study presents the acute and long‐term results of 307 patients (267 men, mean age 57.5 years, 205 suffering from coronary artery disease, mean left ventricular ejection fraction 33.3%) with malignant ventricular tachyarrhythmias who underwent attempted transvenous ICD implantation with the CPI Endotak lead system in 37 Italian centers. Transvenous ICD implantation was ultimately accomplished in 306 (99.7%) patients. These included 19 subjects with high (< 10 J below output energy of implanted device) defibrillation threshold (DFT) at implant. One hundred sixty‐four patients (53%) were implanted with the endocardial lead alone, while 142 also received an SQ patch or SQ array. The mean DFT (not always step‐down DFT) at implant was 16.9 ± 5.7 joules; 15.3 ± 5.2 joules with biphasic shock and 19.6 ± 5.4 joules with monophasic shock; P < 0.0001. A significantly higher percentage of patients tested with a biphasic shock could be implanted with adequate safety margin and without an additional SQ patch or SQ array (98% and 81 %, respectively). No perioperative deaths occurred. During the mean follow‐up of 14.5 ± 10.2 months, 140 patients (52%) received at least one appropriate shock. An inappropriate shock was observed in 26% of episodes. The 1‐ and 3‐year actuarial incidence of sudden death was 2% and 4%, respectively, and that of total death was 10% and 20%, respectively. A pocket infection requiring ICD explantation occurred in 4 patients (1.4%) and an endocardial lead dislodgment in 11 patients (3.6%). Two patients (0.3%) showed a sensing pin disconnection and six patients (2.3%) had a lead insulation break. The results of this Italian multicenter trial indicate that the GPl Endotak lead system is a simple, safe, and reliable system for endocardial defibrillation. When compared to epicardial leads, it clearly reduces the perioperative mortality and morbidity, while maintaining a similar efficacy in preventing sudden death and terminating ventricular arrhythmias.
Cardioverter Defibrillator Therapy as a Bridge to Heart Transplantation
Authors: TRAPPE HANS‐JOACHIM , WENZLAFF PAUL
Published: July 2006

The prognosis of patients with severely impaired left ventricular function is poor, with an annual mortality rate of about 50%, and the majority die from sudden cardiac death. Heart transplantation is an accepted therapy for patients with end‐stage heart disease; however, about 30% of candidates for transplantation die from sudden cardiac death while on the waiting list. It has been shown that implantable Cardioverter defibrillator (ICD) therapy has a low surgical mortality and is highly effective in the prevention of sudden death. Therefore, prophylactic ICD implantation may prevent sudden death in patients with end‐stage heart disease while on the waiting list, and it is highly probable that patients with an ICD have a greater chance of survival until a donor heart becomes available. However, this hypothesis still has to be proven by prospective studies.
Prospective Randomized Comparison of Biphasic Waveform Tilt Using a Unipolar Defibrillation System
Authors: POOLE JEANNE E. , BARDY GUST H. , KUDENCHUK PETER J. , LEE DOLACK G. , RAITT MERRITT H. , MEHRA RAHUL , JOHNSON GEORGE
Published: July 2006

Background: A unipolar defihrillation system using a single right ventricular (RV) electrode and the active shell or container of an implantable cardioverter defibrillator situated in a left infraclavicular pocket has been shown to be as efficient in defibrillation as an epicardial lead system. Additional improvements in this system would have favorable practice implications and could derive from alterations in pulse waveform shape. The specific purpose of this study is to determine whether defibrillation efficacy can be improved further in humans by lowering biphasic waveform tilt. Methods: We prospectively and randomly compared the defibrillation efficacy of a 50% and a 65% tilt asymmetric biphasic waveform using the unipolar defibrillation system in 15 consecutive cardiac arrest survivors prior to implantation of a presently available standard transvenous defibrillation system. The RV defibrillation electrode has a 5‐cm coil located on a 10.5 French lead and was used as the anode. The system cathode was the active 108 cm2 surface area shell (or “CAN”) of a prototype titanium alloy pulse generator placed in the left infraclavicular pocket. The defibrillation pulse derived from a 120‐μF capacitor and was delivered from RV ± CAN, with RV positive with respect to the CAN during the initial portion of the cycle. Defibrillation threshold (DFT) stored energy, delivered energy, leading edge voltage and current, pulse resistance, and pulse width were measured for both tilts examined. Results: The unipolar single lead system, RV ± CAN, using a 65% tilt biphasic pulse resulted in a stored energy DFT of 8.7 ± 5.7 J and a delivered energy DFT of 7.6 ± 5.0 J. In ail 15 patients, stored and delivered energy DFTs were < 20 J. The 50% tilt biphasic pulse resulted in a stored energy DFT of 8.2 ± 5.4 J and a delivered energy DFT of 6.1 ± 4.0 J;P = 0.69 and 0.17, respectively. As with the 65% tilt pulse, all 15 patients had stored and delivered energy DFTs < 20 J. Conclusion: The unipolar single lead transvenous defibrillation system provides defibrillation at energy levels comparable to that reported with epicardial lead systems. This system is not improved by use of a 50% tilt biphasic waveform instead of a standard 65% tilt biphasic pulse. (PACE 1995; 18:1369–1373)
Continuous Heart Rate Variability Monitoring Through Complex Demodulation Implemented with the Fast Fourier Transform and Its Inverse
Authors: BURGUERA MIGUEL , GANDÍA RAFAEL , CHORRO FRANCISCO J. , GARCÍA‐CIVERA ROBERTO , RUIZ RICARDO , LÓPEZ‐MERINO VICENTE
Published: July 2006

A new method for the analysis of 24‐hour heart rate variability (HBV) using complex demodulation (CDM) implemented with the fast Fourier transform (FFT) and its inverse is described. In a control group with palpitations and dizzy spells (n = 30, 47.2 ± 16.7years) the relationship between HRV parameters and subject age was investigated, CDM was used to obtain the amplitude and frequency of the low frequency (LF) and high frequency (HF) oscillations for 8 diurnal hours and 4 nocturnal hours. Differences between the two periods were seen in the LF/HF ratio (2.2 ± 0.6 vs 1.5 ± 0.6; P <0.0001), HF amplitudes (12 ± 6 vs 17 ± 7 normalized units, P < 0.05). and in the mean frequency of the LF oscillations (0.078 ± 0.008 vs 0.073 ± 0.007 Hz, P < 0.01). During the daytime, age was inversely correlated to HF amplitude (r =−0.60), directly correlated to HF mean central frequency (r = 0.40), inversely correlated to LF amplitude (r =−0.55), and likewise inversely correlated to LF mean central frequency (r=−0.74, P < 0.001). At night, age was only inversely correlated to HF amplitude andtoLF mean central frequency.Conclusions: Continuous HRV monitoring through COM implemented with the FFT and its inverse differentiates the periods of diurnal activity and nocturnal rest as an expression of two different activity states of the autonomic nervous system. It allows nonstationary analysis, and separately provides mean and instantaneous oscillation amplitude and frequency. Subject age is not equally related to mean amplitude and frequency of a given oscillation.
The Impact of the Implantable Cardioverter Defibrillator on Quality‐of‐Life
Authors: MAY CATHERINE D. , SMITH PETA R. , MURDOCK CHALLON J. , DAVIS MICHAEL J.E.
Published: July 2006

The implantable Cardioverter defibrillator (ICD) is an established treatment for patients with life‐threatening ventricular arrhythmias. While it clearly reduces the incidence of death from recurrent arrhythmia, little is known about the impact on patients' quality‐of‐life. In this prospective study, quality‐of‐life was assessed by questionnaire before and after ICD implantation. The “Sickness Impact Profile” (SIP), which evaluates physical, psychosocial, and other activities, as well as functions of daily life, was used. Employment and rehospitalization rates were also examined. Twenty‐one of 23 consecutive patients, aged 58 ± 11 years, undergoing ICD implantation at Royal Perth Hospital were studied. During the 14 ± 8 month follow‐up, 4 patients died. Functional capacity was unchanged in all but one of the survivors in whom it improved from New York Heart Association Class III to II. Four of 8 survivors employed before implant have since retired. Six patients required rehospitalization on 13 occasions, problems related to arrhythmias or the ICD. Overall SIP scores preimplant (11.2 ± 9.3; P < 0.05) were significantly worse at 6‐month follow‐up (21.7 ± 18.2), but returned to preimplant levels by 12‐month follow‐up (8.8 ± 10.8; NS). This was primarily due to transient problems in the areas of emotional behavior, alertness, and social interaction. SIP psychosocial dimension scores: preimplant: 7.2 ± 9.0; 6‐month: 17.8 ± 18.1 (P < 0.05); and 12‐month: 8.6 ± 10.3 (NS). Early retirement and hospitalizations due to arrhythmias may still be expected even after implantation of an ICD; however, quality‐of‐life appears only to temporarily decline.
Relief of Left Ventricular Outflow Tract Obstruction Following Inadvertent Left Ventricular Apical Pacing in a Patient with Hypertrophic Cardiomyopathy
Authors: CHANG ANTHONY C. , ATIGA WALTER L. , McAREAVEY DOROTHEA , FANANAPAZIR LAMEH
Published: July 2006

Dual chamber (DDD) pacing improves symptoms and relieves left ventricular (LV) outflow obstruction in hypertrophic Cardiomyopathy. The ventricular lead is usually positioned at the right ventricular apex (RVA). We report a patient in whom the ventricular lead had inadvertently penetrated the septum, resulting in DDD pacing from the LV apex. However, after 3 months, obstruction was reduced and symptoms were improved. Pacing from LV apex and RVA resulted in comparable hemodynamic improvement. This case suggests that the asynchronous wave of septal contraction, originating from the apex, irrespective of ventricular site, accounts for the reduction in LV outflow obstruction.
An Approach in the Assessment of Pacing Hemodynamics: A Comparison of VVI and DDD
Authors: PAYNE GILLIAN E. , WILLIAMS HAZEL , SKEHAN J. DOUGLAS
Published: July 2006

Previous methods for assessment of pacemaker hemodynamics have been limited to a rigid hospital environment. An alternative is the ambulatory ventricular function monitor (C‐VEST±) that, with a single injection of technetium‐99m, permits the continuous measurement of relative ejection fraction (EF) and cardiac output (CO) during the activities of daily living, A study of reproducibility and a comparison of dual chamber (DDD) and fixed rate ventricular (VVI) pacing are presented. Reproducibility was assessed in six patients (4 males; mean age 58, range 27–78 years) with a mean EF of 48.5% (range 34%–62%) and DDD pacemakers, implanted for conduction abnormalities. In addition, 11 patients (7 males; mean age 55.5, range 34–75 years) with a mean EF of 48.5% (range 34%–65%). chronic complete heart block, and DDD pacemakers were used for the comparative study. After an initial multigated scan, the monitor was positioned over the left ventricle and kept in place with the plastic C‐VEST. The patients undergoing the reproducibility study performed three shuttle walking tests with 20 minutes of rest in between. The patients in the comparative study were randomized to either VVI or DDD mode and performed one shuttle walking test in each pacing mode. The results confirmed that the C‐VEST produces reproducible results with no significant difference in peak CO between the three shuttle walks. In addition, it confirmed previous hemodynamic studies showing that DDD pacing was superior to VVI pacing both at rest (P < 0.004) and at exercise (P < 0.002). These findings show the C‐VEST to be an extremely useful tool for the hemodynamic assessment of pacemaker patients.
Low Energy Endocardial Cardioversion of Atrial Arrhythmias in Humans
Authors: KALMAN JONATHAN M. , JONES ELIZABETH F. , DOOLAN LAURENCE , OLIVER LESLIE E. , POWER JOHN M. , TONKIN ANDREW M.
Published: July 2006

We assessed the feasibility of low energy endocardial defibrillation in patients with atrial fibrillation or atrial flutter who had failed a trial of pharmacological reversion with amiodarone. Low energy endocardial defibrillation under general anesthesia was attempted in 9 patients, 5 with atrial flutter and 4 with atrial fibrillation (median duration of arrhythmia 3.75 months). Two large surface area endocardial leads were introduced percutaneousiy and sited in the right atrial appendage and at the right ventricular apex. A cutaneous patch electrode was placed on the left thorax. Biphasic shocks synchronized to the ventricular electrogram were used to terminate atrial arrhythmias. Three electrode configurations were evaluated in the following sequence at each energy level: atrial cathode to ventricular anode; ventricular cathode to atrial anode; atrial cathode to a combined ventricular and cutaneous anode. If endocardial defibrillation failed (0.5–10 J), transthoracic defibrillation using 200 joules followed by 360 joules, if required, was performed. Endocardial defibrillation was successful in all five patients with atrial flutter (0.5 J, 1.0 J, 1.0 J, 4.0 J, and 10,0 J) but in only one patient with atrial fibrillation (10 J). On no occasion did successful defibrillation occur with one configuration when it had failed with an alternate configuration at that particular energy level. Ventricular fibrillation did not occur, and there were no other significant complications. Low energy endocardial defibrillation is feasible in patients with atrial flutter using large surface area electrodes. Although the success rate of atrial defibrillation was low, further work is required, particularly in patients with more recent onset of the arrhythmia and using a right to left electrode configuration.
Comparison of Sinus Node Response to Exercise with Responses From Two Different Activity‐Based Rate Adaptive Pacemakers in Healthy Subjects of Different Age Groups
Authors: ROBERTS DAVID H. , BAXTER SUSAN E. , BRENNAN PAULA T. , GAMMAGE MICHAEL D.
Published: July 2006

The pacing rates from accelerometer‐based (Excel™) and piezoelectric‐based (Legend™) activity sensing rate adaptive pacemakers, both strapped externally in the pectoral position, were compared with sinus rate response in normal volunteers of two different age groups (group 1, mean age 35 ± 16 years; group 2, mean age 72 ± 9 years) during various physical activities. Both pacemakers were programmed in manufacturers' nominal rate adaptive settings. Both types of activity sensing pacemakers programmed in this way showed chronotropic deficiencies to metabolic demand in healthy young subjects and in those matching the usual age of pacemaker implant, especially during “burst” activities. These data suggest that present recommended activity sensing rate response algorithms for accelerometer and piezoelectric pacemakers are inappropriate for many physical activities.
A Technique for Stable His‐Bundle Recording and Pacing: Electrophysiological and Hemodynamic Correlates
Authors: MABO PHILIPPE , SCHERLAG BENJAMIN J. , MUNSIF ANAND , OTOMO KENICHIRO , LAZZARA RALPH
Published: July 2006

His‐bundle electrograms recorded from intracardiac electrode catheters have been a mainstay of basic and clinical electrophysiology. However, consistent His‐bundle pacing has not been as readily achieved. In 13 dogs anesthetized with sodium pentobarbital (30 mg/kg), we recorded leads II and aVR as well as the His‐bundle electrogram from the aortic root. A deflectable tip multipolar catheter (4 rings, 5 mm apart) was introduced via the right jugular vein into the right ventricle (RV). In 7 dogs, using fluoroscopy, the tip was placed under the tricuspid septal leaflet. In the other 6, after thoracotomy, the same placement was made by palpation through the right atrial wall. Stable His‐bundle and right bundle (Rb) branch recordings were made from distal and proximal electrode pairs, respectively. H‐V intervals measured 35 ± 6 ms from the aortic root and 33 ± 5 ms from under the tricuspid leaflet (P = NS). Rb‐V measured 25 ± 4 ms. Consistent His‐bundle pacing was accomplished from the aortic root with an average stimulus intensity of 6 ± 10 mA and from the tricuspid leaflet at 16 ± 8 mA (P < 0.05). In 7 anesthetized dogs we compared the hemodynamic effects of A‐V sequential pacing at the same heart rates using the His‐bundle recording site under the septal leaflet of the tricuspid valve (A‐H pacing) or pacing from the RV apex (A‐RV pacing). Under normal conditions there was a significant depression of mean blood pressure when A‐RV pacing was compared with atrial pacing (AOO); but no difference was found between AOO and A‐H pacing. These same differences were found after hemodynamic depression with propranolol (1 mg/kg; 4 dogs) or combining the beta blocker and verapamil (0.5 mg/kg; 1 dog). Thus, this catheter positioning provides both stable recordings of the His‐bundle electrogram and consistent pacing from the common bundle.
Carotid Sinus Syndrome: Acute Hemodynamic Evaluation of a Dual Chamber Pacing Mode
Authors: BLANC JEAN‐JACQUES , CAZEAU SERGE , RITTER PHILIPPE , DELAY MARC , DJIANE PIERRE , GIRODO SYLVIE , LIMOUSIN MARCEL , VICTOR JACQUES
Published: July 2006

Cardiac pacing is the treatment of choice in patients with carotid sinus syndrome (CSS), Three different pacing modes were tested in 20 patients (16 males, 4 females; mean age 75 ± 9 years) with documented symptomatic CSS, Three carotid sinus massages (CSM) were performed in each supine patient successively paced in random order in: DDI—the reference pacing mode; DDD—automatic mode conversion (DDD/AMC) allowing automatic switching from AAI to DDD when AV block occurs; DDD/AMC plus a trial acceleration (DDD/AMC + ace); and OOO (CSM without pacing) to determine whether the vasodepressive effect was still present 10 minutes after the preceding CSM. Intraarterial blood pressure was continuously monitored. Results were expressed as the value of the mean systolic BP at TO + 3 s + 6 s … TO + 30 s divided by the value of the mean systolic blood pressure prior to onset of CSM. The drop in arterial blood pressure was more severe in the DDI mode than in DDD/AMC (P < 0,001) and DDD/AMC + acc (P < 0.0001) in 20 patients. In the OOO mode, the drop in arterial blood pressure was most marked and greater than in the DDI mode (P < 0.0001). The average time between start of the CSM and onset of the drop in blood pressure was the same in the three dual chamber modes. We conclude that the DDD/AMC mode significantly improves the vasodepressor response to CSM compared to the DDI mode. There is a current trend favoring DDD/AMC + acc over DDD/AMC.
Dynamic Relationship Between the Q‐aT Interval and Heart Rate in Patients with Long QT Syndrome During 24‐Hour Holter ECG Monitoring
Authors: EMORI TETSURO , OHE TOHRU , AIHARA NAOHIKO , KURITA TAKASHI , SHIMIZU WATARU , KAMAKURA SHIRO , SHIMOMURA KATSURO
Published: July 2006

The purpose of this study was to investigate the dynamic relationship between heart rate and the Q‐aT interval (the interval from the Q wave to the T wave apex) in patients with long QT syndrome. The QT to heart rate relation is useful for evaluating abnormalities of the ventricular repolarization, but its clinical application to the long QT syndrome requires accurate computer aided measurement of the QT interval and the sampling of a large number of beats. Therefore, the Q‐aT interval was used on the basis of some reports that the heart rate dependency of the QT interval was concentrated in the Q‐aT interval. Recent advances in the computer technology have allowed analysis of the relationship between the Q‐aT and RR intervals on Holter ECG recordings. However, in addition to a prolonged QT interval, most patients with long QT syndrome have bizarre and variable T waves and the influence of this T wave morphology on the Q‐aT to heart rate relation has not been clarified. We investigated the dynamic relationship between the Q‐aT interval and heart rate in 10 patients with long QT syndrome and 11 control subjects using our original computer algorithm for the analysis of 24‐hour Holter ECG recordings. The patients showed morphological T wave changes associated with heart rate changes during Holter recordings and these affected the Q‐aT interval. The patients showed the following characteristics in the relationship between the major T wave peak and the RR interval: (1) a modestly decreased correlation between Q‐aT and RR than in the control subjects (a median r value of 0.87 vs 0.93; P = 0.001); and (2) a steeper Q‐aT/RR slope than in controls (a median slope of 0.24 vs 0.16; P < 0.05). Abnormal and variable T wave morphology in the long QT patients was closely related to a modestly decreased correlation between Q‐aT and RR than in the control subjects. The steep Q‐aT/RR slope might reflect unstable repolarization of the ventricle, which could act as a substrate for ventricular tachyarrhythmias.
Emergent Radio frequency Ablation of the AV Node in a Neonate with Unstable, Refractory Supraventricular Tachycardia
Authors: ERICKSON CHRISTOPHER C. , CARR DARLENE , GREER G. STEPHEN , KIEL ERNEST A. , TRYKA A. FRANCINE
Published: July 2006

Supraventricular tachycardia due to accessory atrioventricular connections in infants is usually well‐tolerated. Rarely an infant can have Supraventricular tachycardia that is incessant and refractory to medical therapy. We describe a patient with Supraventricular tachycardia detected prenatally that caused severe cardiac dysfunction and hemodynamic instability after birth.
Pacemaker Inhibition and Asystole in a Pacemaker Dependent Patient
Authors: YEŞÌL MURAT , BAYATA SERDAR , POSTACI NURSEN , AYDIN ÇETIN
Published: July 2006

A 17‐year‐old female with Kearns Sayre syndrome, complete heart block, and an implanted single chamber (VVIR) pacemaker, underwent testing with a GSM cellular phone that was placed directly over the pacemaker site. The pacemaker was immediately inhibited when the phone began to operate. A 6.5‐second period of complete heart block with asystole occurred until the phone was switched off.
Migration of a Fractured Retention Wire in the Pulmonary Artery From an Active Fixation Atrial Lead
Authors: KAO HSIEN‐LI , WANG SHOEI‐SHEN , CHEN WEN‐JONE , HUANG SHOEI K. STEPHEN , LEE YUAN‐TEH
Published: July 2006

A fragment of fractured retention wire of an atrial J lead (Accufix) was found in the pulmonary artery in an asymptomatic patient by routine chest X ray, fluoroscopy, and pulmonary angiography. The lead itself looked normal in these imaging studies. Results after successful surgical removal was reported.
The Evolution of Platelet Aggregability in Patients Undergoing Catheter Ablation for Supraventricular Tachycardia with Radiofrequency Energy: The Role of Antiplatelet Therapy
Authors: WANG TZONG‐LUEN , LIN JIUNN‐LEE , HWANG JUEY‐JEN , TSENG CHUEN‐DEN , LO HUEY‐MIN , LIEN WEN‐PIN , TSENG YUNG‐ZU
Published: July 2006

Forty‐two consecutive patients were checked for profiles of platelet aggregability before, during, and 10 and 30 minutes after catheter ablation. They were randomized into Group A (n = 20) who accepted intravenous aspirin (in 0.015 g/kg body weight) and Group P (n = 22) who accepted only placebo treatment. Blood samples were drawn from ascending aorta (Ao) and main pulmonary artery (MPA) simultaneously at each time period. In Group P, the EC50 of substrate induced platelet aggregability decreases significantly during (for ADP, from 1.72 to 0.78/mol/L for samples from Ao, P ± 0.0001; and from 1.68 to 0.69 μmol/ Lfor MPA, P ± 0.0001; for collagen, from 2.26 to 1.34 μg/mLfor Ao, P ± 0.005, and from 2.40 to 1.64 μg/mL, P ± 0.0001) and 10 minutes after successful ablation (for ADP, to 0.70 μmol/L for Ao, P ± 0.000, and to 0.61 μmol/L for MPA, P ± 0.0001; for collagen, to 1.54 μg/mL for Ao, P ± 0.01, and to 1.63 μg/ mL, P ± 0.0001), and then returned to baseline levels 30 minutes later (all P = NS) compared with comparative baseline levels. The levels of thromboxane B2 (TXB2) had the similar evolution. The evolution of platelet aggregability profiles was not associated with total energy dose, duration of energy application, duration of procedure, impedance, and ablation site. However, there were moderate positive correlations between the TXB2 levels and tip temperatures (r = 0.56, P ± 0.05 for Ao and r = 0.65, P ± 0.01 for MPA). These results suggest that increased platelet aggregability can occur during and 10 minutes after radiofrequency current ablation and antiplatelet therapy can maintain “flat” response of platelet aggregability to radiofrequency energy, which may provide possible benefits in preventing the occurrence of the complication.
Reproducibility of Time and Frequency Domain Analysis of Heart Rate Variability in Patients with Chronic Stable Angina
Authors: KAMALESH MASOOR , BURGER ANDREW J. , KUMAR SHYLENDRA , NESTO RICHARD
Published: July 2006

Before heart rate variability (HRV) can be used to investigate the effects of drugs or other clinical interventions in chronic stable angina, it is important to establish the stability and reproducibility of HRV indices over time. HRV analysis was performed on two consecutive 24‐hour ambulatory ECG recordings in 19 patients with chronic stable angina. Time‐domain analysis included average heart rate, variance, SDNN, SDANN5, ASDNN5, and PNN50. The power spectral analysis was computed using fast Fourier transformation for the total power (0.003 and 0.40 Hz), low frequency (0.04–0.15 Hz), and high frequency (0.15–0.40 Hz) bands. No statistically significant differences in the time or frequency domains were found between the two ambulatory ECG recordings. HRV indices in the time and frequency domains are consistent and reproducible in patients with chronic stable angina. Thus, cardiac autonomic tone can be evaluated using HRV analyses, and any significant changes that occur after medical therapy or other clinical interventions can be ascribed to the intervention rather than the lability of cardiac autonomic tone.
Thermistor Guided Radiofrequency Ablation of Atrial Insertion Sites in Patients with Accessory Pathways
Authors: TRACY CYNTHIA M. , MOORE HANS J. , SOLOMON ALLEN J. , RODAK DAVID J. , FLETCHER ROSS D.
Published: July 2006

Radiofrequency ablation has gained acceptance in the treatment of patients with symptomatic Wolff‐Parkinson‐White syndrome. The purpose of this study was to characterize the relation between temperature and other electroconductive parameters in patients undergoing atrial insertion accessory pathway ablation utilizing a thermistor equipped catheter. The mean temperature and power at sites of atrial insertion ablation are lower than has been previously associated with creation of radiofrequency lesions in the ventricle. While high cavitary blood flow in the atrium may result in cooling, the thinner atrial tissue may require less energy to achieve adequate heating than ventricular myocardium.
Estimation of Temperature During Radiofrequency Catheter Ablation Using Impedance Measurements
Authors: HARTUNG WOLFGANG M. , BURTON M. ERICK , DEAM A. GREGORY , WALTER PAUL F. , McTEAGUE KEVIN , LANGBERG JONATHAN J.
Published: July 2006

Temperature monitoring during radiofrequency catheter ablation is useful but requires specialized equipment that is not generally available. Previous studies have shown that impedance characteristically decreases as the result of heating at the electrode‐tissue interface. The purpose of the current study was to determine if impedance changes during radiofrequency current application could be used to estimate endocardial temperature in patients undergoing catheter ablation. Data from 43 patients treated with a thermistor ablation catheter were retrospectively analyzed. The slope of the initial 2 seconds of the impedance curve and subsequent changes in impedance were incorporated into an equation for estimation of temperature in real‐time. The accuracy of this equation was assessed by prospectively comparing the calculated and measured temperatures in 19 patients. Of the 88% of energy applications that were suitable for analysis, the average difference between calculated and measured temperatures was 5.2 ± 5.6°C. The average error was ± 10° in 89% of applications. The results of this study suggest that impedance measurements can be used to quantify tissue temperature in real‐time during radiofrequency catheter ablation. This method is sufficiently accurate to allow titration of power output to produce temperatures in the useful range (50–80°C) while avoiding excessive heating (± 90°C).
Use of Double Ventricular Extrastimulation to Determine the Preexcitation Index in Atrioventricular Nodal Reentrant Tachycardia
Authors: WAGSHAL ALAN B. , HUANG SHOEI K. STEPHEN , PIRES LUIS A. , MITTLEMAN ROBERT S. , GREENE TREVOR O. , SCHUGER CLAUDIO D.
Published: July 2006

The ability of single paced ventricular beats during tachycardia to penetrate the tachycardia circuit and reset the subsequent atrial depolarization (atrial preexcitation), enabling calculation of the “preexcitation index,” can be helpful in analyzing supraventricular tachycardias, However, the ventricular refractory period often prevents ventricular capture of beats with the necessary prematurity to demonstrate atrial preexcitation, particularly in atrioventricular nodal reentrant tachycardia (AVNRT). We hypothesized that the use of double premature stimuli could overcome this limitation. In 25 consecutive patients with either AVNRT or atrioventricular reciprocating tachycardia (AVRT) we attempted to demonstrate atrial preexcitation with single and double ventricular extrastimuli. Whereas atrial preexcitation with a single extrastimulus could only be achieved in 3 of 11 patients with AVNRT, all but 1 patient demonstrated atrial preexcitation with the use of double ventricular extrastimuli. On the other hand, in all but 1 patient with AVRT, atrial preexcitation could be achieved with single and double extrastimuli. A formula was derived for obtaining a preexcitation index with double extrastimuli and shown to correspond closely with the preexcitation index obtained with a single extrastimulus in the 16 patients in whom atrial preexcitation could be achieved with single and double extrastimuli. Thus, this technique significantly enhances the ability to achieve atrial preexcitation and to calculate the preexcitation index in patients with AVNRT, and thus may be useful in deciphering tachycardia mechanism in some patients, as well as being a useful technique in studying the electrophysiological properties of the antegrade and retrograde limbs of AVNRT.
Impedance to Defibrillation Countershock: Does an Optimal Impedance Exist?
Authors: KENKNIGHT BRUCE H. , MURAT EYÜBOG̀RLU B. , IDEKER RAYMOND E.
Published: July 2006

Defibrillation is thought to occur because of changes in the transmembrane potential that are caused by current flow through the heart tissue. Impedance to electric countershock is an important parameter because it is determined by the magnitude and distribution of the current that flows for a specific shock voltage. The impedance is comprised of resistive contributions from: (Ij extra‐tissue sources, which include the defibrillator, leads, and electrodes; (2) tissue sources, which include intracardiac and extra‐cardiac tissue; and (3) the interface between electrode and tissue. Tissue sources dominate the impedance and probably contribute to the wide range of impedance values presented to the defibrillation pulse. Hucause impedance is not constant within or between subjects, defibrillators must be designed to accommodate these differences without compromising patient safety or therapeutic efficacy. Experimental investigations in animals and humans suggest that impedance changes at several different time scales ranging from milliseconds to years. These alterations are believed to be a result of both electrochemical and physiological mechanisms. It is commonly thought that impedance is optimized when it has been decreased to a minimum, since this allows the most current flow for a given voltage shock. However, if the impedance is lowered by changing the location or size of the electrodes in such a way that current flow is decreased in part of the heart even though current flow is increased elsewhere, then the total voltage, current, and energy needed for defibrillation may increase, not decrease, even though impedance is decreased. A simple boundary element computer model suggests that the most even distribution of current flow through the heart is achieved for those electrode locations in which the impedance across the heart is at or near the maximum cardiac impedance for any location of these particular electrodes. Thus, the optimum shock impedance is achieved when impedance is minimized for extra‐tissue and extra‐cardiac tissue sources and is at or near a maximum for intracardiac tissue sources.
Wide Complex Tachycardia Due to Automaticity in an Accessory Pathway
Authors: DEAM A. GREGORY , BURTON M. ERICK , WALTER PAUL F. , LANGBERG JONATHAN J.
Published: July 2006

Patients with the Wolff‐Parkinson‐White (WPW) syndrome have preexcited tachycardia as the result of atrial arrhythmias or antidromic reentry. This article describes a patient with persistent wide complex tachycardia due to abnormal automaticity in the accessory pathway. Radiofrequency catheter ablation resulted in simultaneous elimination of accessory pathway conduction and automaticity. Accessory pathway automaticity may be an infrequent cause of preexcited tachycardia in patients with the WPW syndrome.
Determinants of Dual Chamber Pulse Generators Longevity
Authors: MARKEWITZ ANDREAS , KRONSKI DIETER , KAMMEYER AGNETA , KAULBACH HANS , WEINHOLD CHRISTIAN , DOERING WITTICH , REIGHART BRUNO
Published: July 2006

The aim of tbis study was to investigate the effect of battery capacity, internal current drain, and stimulation energy on pulse generators longevity, and if battery impedance measurements can reliably predict pulse generators end‐of‐life. For this purpose, the records of 577 patients with a mean age of 65 ± 14 years who had undergone implantation of two different dual chamber pulse generators (PGl: 409; PG2:168) were retro‐spectively reviewed. Battery capacity were 2.3 Ah (PGl) and 3.0 Ah (PG2) while current drain at compara‐ble nominal settings was 20 μA (PGl) and 30 μA (PG2) indicating a higher internal current drain of PG2. After a mean follow‐up of 46 ± 23 months, stimulation energy at reprogrammed output settings was significantly higher in PGl as compared to PG2 (17.1 ± 0.14 J vs 15.5 ± 0.24 f). Three PGl (0.7%) and 12 PG2 (7.1%) (P < 0.01) had to be exchanged after a mean of 77.3 ± 5.3 months (PGl) and 75 ± 13.5 months (PG2) (P = NS) due to end‐of‐life being reached. The difference in battery impedances of PGl and PG2 gained statistical significance 5 years after implantation (1.0 kΩ vs 2.4 ± 6.7 kΩ) preceding the significant difference in PG survival after 6 years (98.7 ± 1.3% vs 90.7 ± 4.8%). These results indicate that internal current drain is the most important determinant of the pulse generators longevity and that battery impedance can reliably predict end‐of‐life. Therefore, the essential information about internal current drain should be available for each pacemaker, since it is required for adequate pulse generator selection. Diagnostic functions of dual chamber pulse generators should include measurement of battery impedance.
Influence of Exercise Induced Myocardial Ischemia on Right Ventricular dP/dt: Potential Implications for Rate Responsive Pacing
Authors: CANDINAS RETO , MAYER ISABELLE V. , HEYWOOD J. THOMAS , HU ZHIHUA , HESS OTTO M.
Published: July 2006

Background: Right ventricular (RV) dP/dtmax has been used as a simple parameter for rate responsive pacing to simulate the normal sinus node function. However, the effect of acute myocardial ischemia on RV dP/dtmax has not yet been evaluated. Methods: RV high fidelity pressure was measured in 21 patients at rest and during supine bicycle exercise. Nine patients (Group 1 = controls) had no or only minimal alterations of the coronary arteries and 12 (Group 2 =CAD) had significant coronary artery disease with exercise induced left ventricular (LV) wall‐motion abnormalities (n = 10) and/or angina pectoris (n = 6). RV pressure and its first derivative (RV dP/dtj were determined by an 8 French micromanometer catheter. The time constant of RV pressure decay (Tau) was calculated from the negative reciprocal of RV pressure versus negative dP/dt during isovolumic relaxation. RV volumes and ejection fraction were calculated from RV biplane angiograms (multiple slice method) at rest and during exercise. Results: Heart rate (HR), RV dP/dtmax and dP/dtmin increased significantly during exercise, whereas Tau decreased. There were no significant differences between the two groups, although RV ejection fraction increased from 67% to 72% in the control group but decreased from 63% to 51% in the CAD group (P < 0.05). An exponential relationship was found between HR and dP/dtmax with a correlation coefficient of 0.82 (P < 0.01; SEE = 7% of the mean value). Conclusions: Acute exercise induced myocardial ischemia does not significantly influence RV dP/dtmax during sinus rhythm. Consequently, this index of RV contractility may be used in patients with coronary artery disease as a simple parameter for rate responsive pacing.
A Randomized Controlled Clinical Study to Quantify the Effect of Small Changes in the Design of Pacing Electrodes on Threshold Voltages
Authors: MURRAY ALAN , JAMESON STUART , GOLD RONALD G.
Published: July 2006

A double‐blind randomized study of three pacing leads, identical in all ways except for the surface of their electrodes, is presented. The leads were implanted in 30 patients. Ten patients (Group A) received a standard Laserdish lead (dish electrode with laser pores), 10 patients (Group B) received a platinum‐iridium coated modified Laserdish electrode, and 10 patients (Group C) received a platinum‐iridium coated dish electrode identical to that in Group B except for the absence of laser pores. All leads were implanted by the same operator via the subclavian vein and all patients received an Optima MPT pulse generator. Direct measurement at implantation of pacing threshold and endocardial electrograms showed no significant difference between the three groups (mean ± standard deviation voltage thresholds 0.30 ± 0.06 V at 0.5 ms and 0.21 ± 0.05 V at 1.0‐ms pulse durations, R wave amplitude 7.6 ± 3.2 mV). Significant differences (P = 0.001) were found in threshold impedances at implant (Group A 940 Ω, Group B 782 Ω, Group C 673 Ω). Ten further measurements of voltage threshold were made over the next 2 years. Overall, at a pulse duration of 1.0 ms, a significantly reduced (P < 0.025) threshold voltage was found for both the electrode with pores and platinum‐iridium coating compared with pores alone (20%), and with pores and platinum‐iridium coating compared with the coating alone (18%). There was no significant difference between using platinum‐iridium alone or pores alone. We have shown that a controlled randomized study, using electrodes that are identical except for the characteristics being assessed, can enable effects of small differences in electrode design to be quantified.