bluuebunny/crossref_metadata_2025 huggingface dataset:
Determining Optimal Atrial Sensitivity Settings for Single Lead VDD Pacing: The Importance of the P Wave Histogram
Authors: LANGFORD EDWARD J. , SMITH RUSSELL E.A. , Mc CREA WILLIAM A. , WAINWRIGHT RAY J.
Published: July 2006

In order to provide atrioventricular synchrony, VDD pacing systems require reliable atrial sensing. Variations in atrial signals with exercise and daily activities may lead to undersensing, with loss of physiological pacing. The aim of this study was to determine, for a single lead VDD pacing system, the maximal variation in atrial signals in order to facilitate optimal programming of atrial sensitivity. Fifteen patients underwent implantation of a Vitatron Saphir VDD pacemaker with a Vitatron Brilliant electrode. At a mean (± SD) follow‐up of 67.3 ± 38.8 days, resting P wave amplitude was compared with the P wave amplitude histogram obtained from the pacemaker, which recorded atrial signals over the preceding 30 days. Resting P wave amplitude was also compared with P wave amplitudes during variations in posture, respiration, and during exercise. P wave amplitude showed great variation with changes in posture and respiration, but there was no consistent increase or reduction. During exercise, the mean P wave amplitude fell hy 36.6%± 31.3% compared with the resting value (P < 0.05). During daily activities, 22.6% of P wave amplitudes recorded on the P wave histogram were < 0.5 mV. The smallest P wave amplitudes were detected by the P wave histogram in 11 (79%) of 14 patients. These data suggest that atrial sensitivity may need to be programmed higher than that indicated by single readings or exercise. The P wave amplitude histogram is the most reliable indicator of the smallest atrial signal and should be used to opthnize atrial sensitivity settings.
Interactions Between Transvenous Nonthoracotomy Cardioverter Defibrillator Systems and Permanent Transvenous Endocardial Pacemakers
Authors: GEIGER MARY J. , O'NEILL PADRAIG , SHARMA ARJUN , SKADSEN ANNE , ZIMERMAN LEANDRO , GREENFIELD RUTH ANN , NEWBY KEITH H. , WHARTON J. MARCUS , KENT VIRGINIA , NATALE ANDREA
Published: July 2006

Limited information is available regardIng potential adverse Interactions between transvenous nonthoracotomy cardioverter defibrillators and pacemakers. We describe our experience with 37 patients who have undergone successful Implantation of both a transvenous defibrillator and pacemaker. The patients’mean age was 64 ± 12,9 years. Thirty‐three were male and four were female. The mean LVEF wos 30.8%±11.8%, The indications for pacemaker implantation included sick sinus syndrome in 13 patients, complete heart block in 15 patients, sinus brady‐cardia secondary to medications In 8 patients, and neurocardlogenlc syncope In 1 patient. The Indications for Insertion of a defibrillator Included medically refractory VT in 27 patients and sudden cardiac death in 10 patients. Twenty‐three patients received an Endotak lead and 14 patients received o Transvene lead. Eighteen patients had a pacemaker prior to an ICD, 14 patients had an ICD prior to a pacemaker, and 4 patients had both devices placed simultaneously. Interaction was evaluated at Implant of the second device and 1–3 days after both devices were placed. Detection of VF/VT was analyzed during asynchronous pacing (DOO/VOO) with maximum pacing output. In addition, in six patients, DFT was determined before and after pacemaker implantation. In 14 patients (38%), device interactions that could not always be optimally corrected were observed. In five patients, the pacemaker was reset to the “noise reversion” mode after high energy ICD discharge, Oversensing of atrial pacemaker stimuli resulted in inappropriate ICD firings in four patients. This wos observed only with a specific device ond could not be prevented by atriol leod repositioning in two of them, but required reprogramming of the pacemaker to the VVImode. An increase in DFT was observed in five patients who had a pacemaker implanted after on ICD. Compared with previously published studies, a greater frequency of tronsvenous ICD and pacemaker Interactions were observed. Considering that almost 50% of the patients already have o pacemaker ot the time of ICD Implant, the ovalloblllty of deflbrlllotors with dual chamber pocing capability will not eliminate the potential for this problem.
Refractory Period Extension During Ventricular Pacing at Fibrillatory Pacing Rates
Authors: GILL ROBERT M. , SWEENEY ROBERT J. , REID PHILIP R.
Published: July 2006

Refractory period extension (RPE) bas been proposed as a basic mechanism for defibrillation but it remains unclear if RPE exists at the fast rates associated with ventricular fibrillation. In 7 pentobarbital anesthetized dogs, we measured refractory periods with and without 8 ms rectangular transcardiac shocks at left ventricular pacing rates of 200–600 beats/min. To achieve these high rates, an incremental rate pacing method was used to produce pacing train timing sequences requiring 4.5–27 seconds. A variably timed premature stimulus followed the last stimulus in each pacing train. To determine refractoriness, a 128 electrode arrav (4 × 4 cm) was used to detect the presence, or absence of an activation sequence sweeping away from the pacing site. At each rate, a control refractory period (RPc) was measured and refractory periods were also measured for 8 and 12 V/cm shocks with coupling intervals of 60% to 90% of RPc. RPc decreased as the rate increased with a minimum RPc of 94 ms at a rate of 600 beats/min (100 ms cycle length). RPE/RPc versus shock coupling interval was similar at all pacing rates. RPE/RPc increased with increased coupling interval or higher shock intensity. We conclude that during ventricular pacing at fibrillatory rates tissue is nearly always in a refractory state: that RPE exists at fibrillatory activation rates; and that RPE/RPc versus shock coupling interval does not vary strongly with pacing rate. These findings support the hypothesis that RPE contributes to defibrillation.
The Conduction System in Sudden Death in Alaskan Sled Dogs During the Iditarod Race and/or During Training
Authors: BHARATI SAROJA , CANTOR GLENN H. , LEACH JAMES B. , SCHMIDT KARIN E. , BLAKE JOHN
Published: July 2006

Using serial section examination, we studied the conduction system in five Alaskan sled dogs that died suddenly: four during the Iditarod race and one during training. We compared our findings with the conduction system of three sled dogs of similar age that died of natural causes unrelated to the cardiovascular system. The conduction system of sudden death dogs revealed marked fibrosis of the sinoatrial (SA) node and/or its approaches and narrowing of the SA nodal artery in 3 dogs, fibrosis and marked fatty infiltration in and around the AV node in all 5, total isolation and/or tenuous connection of the AV node with its approaches in 4, fat and fibrosis in the A V bundle and bundle branches to a varying degree in all, and focal fibrotic scars in the left ventricle with fat and/or some disarray in 3. The control group revealed mild fibro‐fatty changes in the conduction system without fibrotic scar areas in the heart. These findings are similar to the pathological findings in and around the conduction system in cases of sudden death in humans, especially trained athletes. These changes may form an anatomical substrate for an arrhythmic event in susceptible dogs during an altered physiological state.
Comparison of Signal‐Averaged Electrocardiograms with Different Levels of Noise: Time‐Domain, Frequency‐Domain, and Spectrotemporal Analysis
Authors: MAOUNIS THEMISTOCLIS N. , KYROZI ELENA , CHILADAKIS IOANNIS , VASSILIKOS VASSILIOS P. , MANOLIS ANTONIS S. , COKKINOS DENNIS V.
Published: July 2006

In order tn test the effect of noise on the various parameters of the SAECG, 83 patients underwent three consecutive recordings at different noise levels. The high noise (HN) recordings had a noise level of 0.60–0.74 μV. the intermediate noise (IN) had 0.31–0.59 μV, and the low noise (LN) had ≤ 0.30 μV. For the calculation of noise we used the standard deviation of the mean noise of the composite lead high pass filtered at 40 Hz. The recordings were compared using time‐domain, frequency‐domain, and spectrotemporal analysis. The time‐domain parameters of the LN recordings, using 25‐Hz, 40‐Hz, and 60‐Hz high pass cutoffs, were significantly different from those of the HN or IN recordings (P < 0.05). In the frequency‐domain analysis, significant differences were found in some of the parameters of the LN compared to the HN. The spectrotemporal analysis of the X and Z leads also showed significant differences among the LN and the other recordings. In the time‐domain analysis, both at 40 Hz and 25 Hz, there were more abnormal LN compared to the HN recordings (P < 0.05). In the spectrotemporal analysis, there were significantly more abnormal HN and IN recordings compared to the LN (P < 0.001 and P < 0.01. respectively). Therefore, the level of noise, even within the acceptable range, can significantly affect the SAECG. In the time domain at the lower noise levels the parameters become more abnormal, while the opposite seems to occur in the spectral and the spectrotemporal analysis.
Early Afterdepolarizationlike Activity in Patients with Class IA Induced Long QT Syndrome and Torsades de Pointes
Authors: KURITA TAKASHI , OHE TOHRU , SHIMIZU WATARU , SUYAMA KAZUHIRO , AIHARA NAOHIKO , TAKAKI HIROSHI , KAMAKURA SHIRO , SHIMOMURA KATSURO
Published: July 2006

Early afterdepolarizations (EADs) have been linked to the mechanism of torsades de pointes in long QT syndrome. The purpose of this study was to investigate the role of EADs in Class IA induced torsades de pointes. We studied nine patients with Class IA induced torsades de pointes at the time this arrhythmia was present (acute period, n = 7) and after Class IA therapy was discontinued (chronic period, n = 6). ECCs and monophasic action potentials were recorded in both periods. In the chronic period, electrophysiological studies were performed before and after disopyramide infusion. In the acute period, QTc interval was markedly prolonged (655 ± 32 ms1/2), and EAD‐like activity was recorded in all patients. QTc interval returned to normal (428 ± 45 ms1/2) and EAD‐like activity disappeared after discontinuation of IA drug. Although, in the chronic period, disopyramide infusion prolonged QTc interval from 428 ± 48 ms1/2 to 479 ± 31 ms1/2 and induced EAD in three of six patients, the degree was not as marked as observed in the acute period. EADs may play an important role in the genesis of long QT and torsades de pointes. Disopyramide infusion in the chronic period could not reproduce marked repolarization ahnormalities and torsades de pointes.
Rise in Chronic Defibrillation Energy Requirements Necessitating Implantable Defibrillator Lead System Revision
Authors: DAOUD EMILE G. , MAN K. CHING , MORADY ERED , STRIGKBERGER S. ADAM
Published: July 2006

The chronic defibrillation energy requirement (DER) is believed to remain clinically stable in patients with defibrillators. Six patients (two with an epicardial and four with a nonthoracotomy system) were identified with a rise in their chronic DER, which eliminated a 10‐J safety margin, thus necessitating a defibrillator lead system revision. The mean increase in DER was 14.7 ± 4 J and was discovered at a mean of 16.0 ± 18 months (range 2‐41) following implantation. Management included placement of a defibrillator with a biphasic waveform, placement of an additional defibrillation electrode, or both. At 2 months following revision of the defibrillation system, a 10‐J DER safety margin was present in each patient. In some patients, there is a progressive increase in the chronic DER with elimination of a 10‐J safety margin necessitating revision of the defibrillation system. Routine reevaluation of the chronic DER, therefore, is necessary to identify these patients.
Ventricular Output Failure in a DDD Permanent Pacemaker Associated with Increased Atrial Output
Authors: SANTUCCI PETER A. , MITRA RAMAN L.
Published: July 2006

Previous reports have described the occurrence of ventricular output failure in a permanent DDD pacemaker system related to an increase in the atrial output in the presence of low atrial lead impedance (Medtronic Synergyst/Synergyst II). This phenomenon is seen exclusively following atrial paced events, and may potentially lead to significant bradyarrhythmia or ventricular asystole in a pacemaker dependent patient. We describe tbe occurrence of analogous behavior in a Medtronic Symbios 7006 generator.
Tilt Table Testing: Concepts and Limitations
Authors: GRUBB BLAIR P. , KOSINSKI DANIEL
Published: July 2006

Recurrent unexplained syncope is a common and often frustrating clinical problem. Over the last decade, bead upright tilt table testing bas emerged as an important diagnostic metbod far the identification of individuals whose syncope is likely to be neurocardiogenic in origin. At the same time, tilt table testing, by providing syncopal episodes in a controlled setting, has allowed for a much greater understanding of these disorders. This article reviews the concepts behind tilt table testing, as well as the uses and limitations of the evolving diagnostic modality.
Neural Monitoring of Vasovagal Syncope
Authors: ELLENBOGEN KENNETH A. , MORILLO CARLOS A. , WOOD MARK A. , GILLIGAN DAVID M. , ECKBERG DWAIN L. , SMITH MICHAEL L.
Published: July 2006

Head‐up tilt testing has become a valuable and widely accepted diagnostic tool for evaluation of patients with vasovagal syncope. This test has afforded clinical researchers the opportunity to focus on the hemodynamic, humoral, and neural changes that accompany syncope. We review the animal and clinical studies that provide insight into the possible pathophysiological mechanisms involved in vasovagal syncope. Hemodynamic measurements in patients with vasovagal syncope suggest that a relative decrease in ventricular size and increase in cardiac contractility may be seen in many patients with vasovagal syncope. Patients with vasovagal syncope have also demonstrated numerous “exaggerated” neurohumoral responses to syncope. Differential changes in plasma levels of epinephrine, renin, endothelin, vasopressin, cortisol, prolactin, beta endorphins, and substance P have been reported by some investigators either prior to or during a syncopal episode in patients with vasovagal syncope. The precise pathophysiological significance of these measurements is unknown at the present time. Measurements of autonomic tone may be accomplished indirectly with analysis of heart rate variability or baroreflex slope, or directly by sympathetic neural recordings of the peroneal nerve. We have demonstrated decreased baroreflex slopes in patients with vasovagal syncope. Using microneurography, we and others have demonstrated decreased sympathetic nerve activity occurring 11 ± 3 seconds prior to syncope during bead‐up tilt table testing. A variety of other abnormal reflexes, including blunted forearm blood flow responses during exercise, have been demonstrated by others. These observations suggest that pacing instituted after the event may not be as helpful as the use of a hemodynamic sensor that will result in the initiation of pacing prior to sympathetic withdrawal or modify the decrease in sympathetic tone that occurs prior to syncope.
Right Ventricular Pressure, dP/dt, and Preejection Interval During Tilt Induced Vasovagal Syncope
Authors: PETERSEN MARK E.V. , WILLIAMS T.R. , ERICKSON MARK , SUTTON RICHARD
Published: July 2006

This study examined the potential utility of monitoring right ventricular dP/dt as a means of detecting imminent vasovagal syncope. To assess this possibility, continuous right ventricular pressure measurements were recorded in nine patients during induction of syncope by head‐up tilt testing. Findings indicated that arterial pressure tended to fall prior to drop in heart rate. RV pressure exhibited a significant, but very small, fall during tilt. DP/dt max increased by 15–20% during tilt, then fell by a median of 30% from maximum value beginning aboutr 2 minutes prior to syncope. Thus, further investigation of dP/dt as a potential marker of impending vasovagal syncope is warranted.
Response of Neurocardiac Syncope to β‐Blocker Therapy: Interaction Between Age and Parasympathetic Tone
Authors: SLOTWINER DAVID J. , STEIN KENNETH M. , LIPPMAN NEAL , MARKOWITZ STEVEN M. , LERMAN BRUCE B.
Published: July 2006

Beta‐blockers are a first line therapy for neurocardiac syncope, but are not always effective. The purpose of this study was to determine whether differential autonomic responses to orthostasis predict the response of patients with neurocardiac syncope to β‐adrenergic blockade. We computed the RMS successive difference of the BB intervals (BMSSD: a measure of cardiac parasympathetic tone) during supine and upright phases of the initial tilt test in 28 patients with syncope and positive tilt tests who were treated with atenolol. Follow‐up tilt testing was performed to assess the efficacy of the drug in preventing tilt induced neurocardiac syncope. BMSSD did not differ at baseline (supine) between those who did (n = 20) and did not (n = 8) respond to β‐blockade. However, withdrawal of parasympathetic tone in response to tilt varied inversely with age (r =−0.69; P < 0.01). Reduced age adjusted parasympathetic withdrawal during orthostasis was associated with a 47% versus 8% risk of β‐blockade failure (odds ratio = 11; P = 0.01). Patients with diminished age adjusted parasympathetic withdrawal during orthostatic stress are less likely to respond to β‐blocker therapy of neurocardiac syncope than their counterparts. This may reflect a correspondingly greater sympathetic response to orthostasis in these patients, but the mechanism for this interaction is undetermined.
Cardiovascular Syncope Is the Most Common Cause of Drop Attacks in the Elderly
Authors: DEY A.B. , STOUT N.R. , KENNY R.A.
Published: July 2006

Drop attacks are defined as a sudden loss of postural tone without loss of consciousness. The mechanism is often unknown. This report examines findings in consecutive elderly patients with drop attacks referred to a dedicated “syncope and falls” center. Thirty‐five patients were included. A diagnosis was established in 25 (71 %); cardioinhibitory cartoid sinus syndrome (CSS) or mixed CSS in 15, vasodepressor CSS in 3, orthostatic hypotension in 5, vasovagal syncope in 1, and gait imbalance in 1. In 21%, more than one pathological diagnosis was present. In conclusion, absence of a history of syncope is unreliable in elderly patients, and these individuals should be routinely investigated for hemodynamic changes during carotid massage and standing.
Prevalence of Cardioinhibitory Carotid Sinus Hypersensitivity in Patients 50 Years or over Presenting to the Accident and Emergency Department with “Unexplained” or “Recurrent” Falls
Authors: RICHARDSON D.A. , BEXTON R.S. , SHAW F.E. , KENNY R.A.
Published: July 2006

To study the prevalence of Cardioinhibitory Carotid Sinus Hypersensitivity (CICSH) in patients 50 years or over presenting to casualty with “unexplained” or “recurrent” falls. The prospective study was from October 1, 1995 to April 30, 1996 in the Inner City Accident and Emergency Departments, Newcastle Upon Tyne, U.K. Ten thousand four hundred forty‐three patients 50 years and over presented, of which 4,051 (39%) were fallers. Fallers were excluded if they lived over 15 miles from the hospital (81), were registered blind (17), were unable to speak English (22), were unable to previously walk (27), if there was a history of only one accidental fall (1,659) or were cognitively impaired (776: Mini Mental State Examination < 24 [30]) or if there was a clear attributable medical diagnosis for the fall (871). Five hundred ninety‐eight “unexplained” or “recurrent” fallers (defined as three or more falls in the previous 12 months) were assessed for carotid sinus massage (CSM). One hundred forty‐five patients declined CSM (24%), 70 (12%) had relative contraindications to CSM and 13 already had pacemakers in situ (2%). Two hundred seventy‐nine underwent CSM, of whom 65 had CICSH (23%), which might be amenable to treatment with pacemakers. The prevalence of CICSH (a potentially treatable condition) in “unexplained” or “recurrent” fallers who present to the accident and emergency department is 23%. A randomized control study to assess benefit from pacemaker intervention in these patients is underway.
Clinical Experience with Thera DR Rate‐Drop Response Pacing Algorithm in Carotid Sinus Syndrome and Vasovagal Syncope
Authors: BENDITT DAVID G. , SUTTON RICHARD , GAMMAGE MICHAEL D. , MARKOWITZ TOBY , GORSKI JOANNE , NYGAARD GARY A. , FETTER JOSEPH ,   THE INTERNATIONAL RATE‐DROP INVESTIGATORS GROUP
Published: July 2006

This study examined the effectiveness of cardiac pacing using the Thera DR rate‐drop response algorithm for prevention of recurrent symptoms in patients with carotid sinus syndrome (CSS) or vasovagal syncope. The algorithm comprises both diagnostic and treatment elements. The diagnostic element consists of a programmable “window” used to identify heart rate changes compatible with an evolving neurally mediated syncopal episode. The treatment arm consists of pacing at a selectable rate and for a programmable duration. Forty‐three patients (mean age 53 ± 20.4 years) with CSS alone (n = 8), CSS in conjunction with vasovagal syncope (n = 4), or vasovagal syncope alone (n = 31) were included. Thirty‐nine had recurrent syncope, while the remaining four reported multiple presyncopal events. Prior to pacing, 40 ± 152 syncopal episodes (range from 1 to approximately 1,000 syncopal events) over the preceding 56 ± 84.5 months. Postpacing follow‐up duration was 204 ± 172 days. Three patients have been lost to follow‐up and in one patient the algorithm was disabled. Among the remaining 39 individuals, 31 (80%) indicated absence or diminished frequency of symptoms, or less severe symptoms. Twenty‐three patients (23/29, or 59%) were asymptomatic with respect to syncope or presyncope. Sixteen patients had symptom recurrences. Of these, seven experienced syncope (7/39, or 18%) and 9 (29%) had presyncope: the majority of patients with recurrences (6/7 syncope and 7/9 presyncope) were individuals with a history of vasovagal syncope. Consequently, although symptoms were observed during postpacing follow‐up, they appeared to be of reduced frequency and severity. Thus, our findings suggest that a transient period of high rate pacing triggered by the Thera DR rate‐drop response algorithm was beneficial in a large proportion of highly symptomatic patients with CSS or vasovagal syncope.
Rate‐Drop Response Programming
Authors: GAMMAGE MICHAEL DENNIS
Published: July 2006

Effective programming of the rate‐drop response algorithm requires careful attention to the heart rate and blood pressure responses seen during diagnostic tilt testing. In order to undertake effective programming, additional tilt testing procedures may be necessary, and it is vital that the protocol should be identical on each occasion and very careful note taken of exact times of onset of symptoms and relative timing of onset of changes in heart rate and blood pressure. The algorithm settings in the Thera DR generator as delivered (factory or “shelf” parameter settings) must be considered nontherapeutic (an unusual situation for a pacemaker algorithm) and will require adjustment for each individual patient. Effective therapeutic settings are likely to result in an excess of pacing interventions; these, however, tend to be less symptomatic than the syncope orpresyncope suffered by the patient and are generally well tolerated or not noticed.
The Effect of Variable Retrograde Penetration on Dual AV Nodal Pathways: Observations Before and After Slow Pathway Ablation LDD
Authors: LI HUAGUI , YEE RAYMOND , THAKUR RANJAN K. , KLEIN GEORGE J.
Published: July 2006

Retrograde VA conduction is usually over the fast pathway and rarely over the slow pathway in patients with dual AV nodal pathways. It is unknown whether this apparent unidirectional conduction of the slow pathway is due to the lack of its retrograde conducting ability or the result of concealment. The effect of variable retrograde AV nodal penetration on antegrade AV nodal conduction was determined in patients with typical AV nodal reentrant tachycardia before and after the slow pathway ablation. Variable retrograde penetration was produced by delivering a ventricular extrastimulus simultaneously with (VE‐0), 50 ms after (VE‐50), or 100 ms after (VE‐100) the last basic atrial stimulus, while atrial extrastimuli were used to determine changes of anterograde AV nodal effective refractory period (ERP) and A‐H interval. The AV nodal functions measured without the ventricular extrastimuli served as the baseline. Although the mean slow pathway ERP was not significantly different among the different stimulation protocols, a significant shortening of the slow pathway conduction time (A‐H from 348 ± 60 to 324 ±119 ms, P < 0.05) was observed with upper level retrograde penetration of the AV node (VE‐0). This facilitating effect became a prolonging effect when the retrograde penetration level moved to the lower level (VE‐100, A‐H from 324 ± 119 to 366 ± 122 ms, P < 0.05). The fast pathway ERP shortened with an upper level penetration (VE–0) but tended to prolong with a lower level retrograde penetration (VE‐100) both before and after the slow pathway ablation (preablation, from 348 ± 143 of the baseline to 302 ± 114 to 360 ± 143 ms, P < 0.05; postablation, from 314 ± 101 of the baseline to 274 ± 118 to 361 ± 143 ms, P < 0.05). The mean A2−H2 interval of the slow pathway was significantly shorter than the baseline (350 ± 44 ms) with VE‐0 (249 ± 48 ms, P < 0.05) and VE‐5O stimulation (285 ± 82 ms, P < 0.05) but not with VE‐100 stimulation (330 ± 83 ms, P = NS). Refore slow pathway ablation, the A2−H2 interval of the fast pathway at equal coupling intervals was shorter than the baseline (165 ± 53 ms) with VE‐0 (144 ± 47 ms, P < 0.01) and VE‐50 stimulation (152 ± 43 ms, P < 0.05) but tended to be longer with VE‐l00 stimulation (175 ± 47 ms, P = NS). After slow pathway ablation, the mean A2−H2 interval at the same coupling interval was shorter than the baseline (173 ± 39 ms) with VE‐0 (139 ± 35 ms, P < 0.05), VE‐50 (153 ± 32 ms, P = 0.05) but tended to be longer with VE‐100 stimulation (178 ± 49 ms, P = NS). We conclude that: (1) concealed retrograde conduction can be demonstrated in both the slow and the fast A V nodal pathways; and (2) concealed retrograde conduction may either shorten or prolong anterograde refractoriness and conduction time, depending on the level of retrograde penetration.
Biphasic Waveforms for Ventricular Defibrillation: Optimization of Total Pulse and Second Phase Durations
Authors: MATULA MARKUS H. , BROOKS MICHAEL J. , PAN QI , PLESS BEN D. , PROVINCE ROSE A. , ECHT DEBRA S.
Published: July 2006

Waveform parameters may affect the efficacy of ventricular defibrillation. Certain biphasic pulse waveforms are more effective for ventricular defibrillation than monophasic waveforms, but the optimal biphasic waveform parameters have not been identified. The purpose of this study was to investigate the effects of total pulse duration and the duration of the second (negative) phase on voltage and energy defibrillation requirements using biphasic waveforms. Defibrillation efficacy was evaluated in an isolated rabbit heart model using the Langendorff technique. The biphasic waveform was a truncated exponential with the initial voltage of the second phase equal to 50% of the final voltage of the first phase. An up/down protocol was used to determine the 50% probability‐of‐success levels (E50) for delivered energy and initial voltage. First, using pulse waveforms with equal positive and negative phase durations, test waveforms with total durations of 4 nw (2 ms positive + 2 ms negative), 6 ms (3 + 3 ms), and 16 ms (8 + 8 ms) were compared to the control waveform of 8 ms (4+4 ms) in 30 experiments. Defibrillation voltage requirements with 4 ms (174 ± 56 V) were higher (P = 0.001) compared to 8 ms (127 ± 49 V). Defibrillation voltage requirements for the 6‐ms and 16‐ms waveforms were similar to the 8‐ms control waveform. Delivered energies tended to be higher with the 4‐ms waveform. A second series of 40 experiments were performed to compare monophasic (4+0 ms) and three asymmetric biphasic waveforms (4+2 ms, 4 + 8 ms, and 4 + 16 ms) to the symmetric control waveform (4+4 ms). The monophasic (2.15 ± 1.21 J) and the 4 + 16 ms waveform (1.86 ± 1.09 J) required higher energies (P ± 0.05) than the control waveform (1.24 ± 0.41 J and 0.87 ± 0.7 J, respectively). The monophasic waveform also resulted in greater voltage requirements (223 ± 64 V) compared to the control waveform (160 ± 26 V) (P = 0.02). Energy and voltage requirements were similar for the 4+2 ms and 4+8 ms waveforms compared to the control. Defibrillation requirements with biphasic waveforms were affected by total and second phase duration. For waveforms with equal phase durations, total durations between 6–16 ms resulted in the lowest values for defibrillation. For waveforms with variable second (negative) phase durations, durations ranging from 50%‐200% of the first phase did not affect defibrillation efficacy.
Chronic Ventricular Pacing Using an Output Amplitude of 1.0 Volt
Authors: SCHWAAB BERNHARD , SCHWERDT HOLGER , HEISEL ARMIN , FRÖHLIG GERD , SCHIEFFER HERMANN
Published: July 2006

Thirty‐seven patients (21 male, 16 female, mean age 71 years) received identical DDD pacemakers. They also received the same bipolar ventricular passive fixation electrode, which has a microporous tip of platinum‐iridium, a surface area of 5.8 mm2, and steroid elution. Eighteen months after implantation the ventricular charge threshold [μC] was measured telemetrically at 0.5, 1.0, and 2.0 V, respectively. For the 1.0 and 2.0 V amplitudes the pulse duration was increased until the charge per pulse [μC] was twice the threshold value, thus giving a 100% safety margin in terms of charge (“safety charge”). Patients who had ventricular capture at 0.5 V were permanently programmed to 1.0 V (30/37 patients), while those who did not capture at 0.5 V were set to 2.0 V (7/37 patients). In both cases, the pulse duration was programmed according to the rationale of “safety charge.” During a routine follow‐up period of 6 months, no complications were observed and none of the patients suffered from symptoms indicating loss of ventricular capture. Twenty‐four‐hour Holter recordings, obtained from all patients at the end of the follow‐up with the output parameters unchanged, revealed constant ventricular capture. In patients with chronic stable pacing thresholds and steroid‐eluting low threshold leads who have capture at 0.5 V, chronic ventricular pacing at an output amplitude of 1.0 V is feasible, and it seems to be safe if the pacing threshold is measured as charge delivered per pulse and a 100% safety margin in terms of charge is programmed. Reducing the output amplitude to well below the battery voltage may increase pacemaker longevity.
Timing of the Upper Limit of Vulnerability is Different for Monophasic and Biphasic Shocks: Implications for the Determination of the Defibrillation Threshold
Authors: BEHRENS STEFFEN , LI CUILAN , FRANZ MICHAEL R.
Published: July 2006

The upper limit of vulnerability (ULV) has been used in clinical studies to predict the DFT in patients with ICDs. Despite the ULV‐DFT correlation, uncertainties about the optimal timing of the ULV determination remain. Previous studies using monophasic or biphasic shock waveforms reported differences in the ULV timing with respect to the electrocardiographic T wave. The purpose of this study was to directly compare the ULV timing for mono‐ versus biphasic T wave shocks. In ten isolated rabbit hearts, mono‐ and biphasic shocks were delivered randomly during the vulnerable window and at varying shock strengths to determine the ULV. The ULV timing was expressed as the coupling interval at the ULV, the myocardial repolarization state at the ULV measured by monophasic action potential recordings, and the relation between the ULV and the peak of the simultaneously recorded volume conducted T wave. The ULV for biphasic shocks occurred at longer coupling intervals than for monophasic shocks (188.0 ± 9.5 ms vs 173.5 ± 8.8 ms, P < 0.001). This resulted in a more repolarized myocardial state at the ULV for biphasic than for monophasic shocks (81.1%± 7.5% vs 66.9%± 9.0%, P = 0.002). The ULV for monophasic shocks occurred predominantly during the upslope of the T wave (8.0 ± 9.7 ms before the peak of the T wave) whereas the ULV for biphasic shocks occurred at or after the peak of the T wave (5.9 ± 9.3 ms after the peak of the T wave) (P < 0.001). Biphasic shocks delay the timing of the ULV as compared to monophasic shocks. This is important for the prediction of the DFT by ULV measurements.
Influence of Anodal Electrode Position on Transvenous Defibrillation Efficacy in Humans: A Prospective Randomized Comparison
Authors: MARKEWITZ ANDREAS , KAULBACH HANS , MATTKE SÖREN , MÜLLER DIETER , BERNUTZ CHRISTINE , HOFFMANN ELLEN , WEINHOLD CHRISTIAN , STEINBECK GERHARD , REICHART BRUNO
Published: July 2006

Nonthoracotomy lead systems for implantable cardioverter defibrillators (ICDs) have reduced operative mortality and morbidity as compared to epicardial lead systems but are usually associated with higher defibrillation thresholds (DFTs). The purpose of this prospective randomized trial was to investigate if the second defibrillation electrode in the left subclavian vein can increase defibrillation efficacy and decrease DFT as compared to the superior vena cava (SVC) position in nonthoracotomy lead systems for ICDs. Seventeen patients (mean age; 49.9 ± 11.3 years, mean ejection fraction; 46.1%± 15.8%) were implanted with an investigational unipolar electrode (Medtronic 13001) used as the defibrillation anode. DFT testing was started in the SVC (n = 10, group A) or the left subclavian vein (n = 7, group B), and repeated in the alternative position starting at the DFT of the initial position. Fifteen patients were eligible for analysis (group A: n = 9, group B: n = 6). With the electrode in the SVC, ventricular fibrillation could be successfully terminated in 9 out of 15 patients (60%). In the left subclavian vein the success rate was 100% (P < 0.01). Mean DFT in the SVC was 13.0 ± 5.2 J and in the left subclavian vein 10.2 ± 4.9 J. DFTs in the left subclavian vein were either lower (group A: n = 5/9, group B: n = 5/6) or equal to the results in the SVC position (P < 0.001). Thus, the left subclavian vein appears to be a superior alternative for positioning of the defibrillation anode as compared to the SVC for nonthoracotomy lead systems using two separate leads.
The Postural Orthostatic Tachycardia Syndrome: A Neurocardiogenic Variant Identified During Head‐Up Tilt Table Testing
Authors: GRUBB BLAIR P. , KOSINSKI DANIEL J. , BOEHM KATHY , KIP KATRINKA
Published: July 2006

Head upright tilt table testing has emerged as an accepted modality for identifying an Individual's predisposition to episodes of autonomically mediated hypotension and bradycardia that are sufficiently profound so that transient loss of consciousness ensues (neurocardiogenic syncope). However it has also become apparent that less dramatic falls in blood pressure, while not sufficient to cause full syncope, may produce symptoms such as near syncope, vertigo, dizziness, and TIA‐like episodes. We have identified a subgroup of individuals with a mild form ofautonomic dysfunction with symptoms of postural tachycardia and lightheadedness, disabling fatigue, exercise intolerance, dizziness, and near syncope. During baseline tilt table testing these patients demonstrated a heart rate increase of ± 30 beats/min (or a maximum heart rate of 120 beats/min) within the first 10 minutes upright (unassociated with profound hypotension), which reproduced their symptom complex. In addition these patients exhibit an exaggerated response to isoproterenol infusions. Similar observations have been made by others who have dubbed this entity the Postural Orthostatic Tachycardia Syndrome (POTS). We conclude that POTS represents a mild (and potentially treatable) form of autonomic dysfunction that can be readily diagnosed during head upright tilt table testing.
Radiofrequency Catheter Ablation for AV Nodal Reentrant Tachycardia Associated with Persistent Left Superior Vena Cava
Authors: OKISHIGE KAORU , FISHER JOHN D. , GOSEKI YOSHINARI , AZEGAMI KOUJI , SATOH TAKAKO , OHIRA HIROSHI , YAMASHITA KATSUHIRO , SATAKE SHUTARO
Published: July 2006

Slow A V nodal pathway ablation using RF is highly effective for patients with refractory A V nodal reentrant tachycardia (AVNRT). We report three catheter ablation cases using RF current in patients associated with persistent left superior vena cava (PLSVC). Three patients with drug refractory AVNHT of common variety were involved in this study. An electrode catheter introduced through the left subclavian vein inserted directly into the coronary sinus, a typical anatomical finding of PLSVC. The ablation procedure was initially performed at the posteroinferior region of Koch's triangle. A slow pathway potential could not be found from that area; nonsustained junctional tachycardia (NSJT) did not occur during the delivery of RF current; there was failure to eliminate slow AV nodal pathway conduction. The catheter then was moved into the bed of the proximal portion of the markedly enlarged coronary sinus. A slow AV nodal pathway potential was recorded through the ablation catheter, and the delivery of RF current caused NSJT in two patients. Complete elimination of slow AV nodal pathway conduction was accomplished in these two patients by this method. No adverse effects were provoked by this procedure. Catheter ablation of the slow A V nodal pathway guided by a slow pathway potential and the appearance of NSJT was feasible and safe in the area of the coronary sinus ostium in patients associated with PLSVC.
Serial Measures of Sinoatrial and Atrioventricular Nodal Function in Ambulatory Patients
Authors: LAHAYE STEPHEN , SHEAHAN RICHARD , DARLING DAVID , DORIAN PAUL , NEWMAN DAVID
Published: July 2006

We hypothesized that the outpatient assessment of SA and AV nodal (SAN, AVN) function could be a useful tool to determine the effectiveness of drugs and other treatments. We sought to examine the reproducibility, safety and ease of acquiring serial measurements of these parameters. Ten patients with permanent pacemakers underwent low current chest wall stimulation while their device was programmed to unipolar atrial triggered mode. Measurements at multiple conditioning drive train frequencies were obtained for: sinus nodal recovery time (SNRT); corrected sinus nodal recovery time (CSNRT); SA conduction time (SACT); AVN block cycle length (AVNBCL); and AVN effective refractory period (AVNERP). AVN function curves were also constructed. All studies were repeated after 2 weeks. Measures of sinus nodal and AVN function did not show significant differences between the two studies. The following coefficients of correlation were obtained: SNRT800, r = 0.79; CSNRT800, r = 0.71; SNRT600, r = 0.71; CSNRT600, r = 0.44; SACT, r = 0.75; AVNBCL, r = 0.98; AVNERP800, r = 0.55; and AVNERP600, r = 0.99. A VN function curves did not significantly differ between week 1 versus week 2 at conditioning drive trains of either 800 ms or 600 ms. These data suggest that serial noninvasive electrophysiological measures of AVN and SAN function are reproducible over 2 weeks. Using data in this study, estimates of the sample size necessary for the evaluation of the effects of investigational drugs on the SAN and AVN in future studies are possible.
The CB‐12L: A New Device for Transtelephonic Transmission of a 12‐Lead Electrocardiogram
Authors: ROTH ARIE , BLOCH YORAM , VILLA YAEL , SCHLESINGER ZWI , LANIADO SHLOMO , KAPLINSKY ELIESER
Published: July 2006

The value of transtelephonic transmission of ECG information is well established, and technological advances have continuously provided improved state‐of‐the‐art equipment. Shahal Medical Services provides professional care to subscribers who call the medical center and describe their symptoms, whereupon therapeutic measures are decided upon. A new 12‐lead patient controlled device for telephonically transmitting an ECG (CB‐12L) has become available; the aim of this study was to evaluate its accuracy and practicability. Forty tracings (20 standard ECG tracings obtained under medical supervision in the physician's office and 20 by the patient in his home using the new CB‐12L ECG device and transmitted by telephone to the center) from 20 subjects with various electrocardiographic pathologies were reviewed by 19 experienced physicians who were asked to interpret the results and identify the recording device. In 82% of the possibilities, the interpretation of the tracings was identical for both those recorded by the standard ECG recorder and the CB‐12L ECG. An equal number of physicians could not identify the means by which device the tracings were taken. Proper placement of the electrodes did not prove to be a problem for the patient. Thus, the CB‐12L ECG was found to be an easily operable and reliable tool which may be of value for early and prompt diagnosis of threatening cardiac situations in the prehospital setting.
Use of Intracardiac Echocardiography in Interventional Electrophysiology
Authors: KALMAN JONATHAN M. , OLGIN JEFFREY E. , KARCH MARTIN R. , LESH MICHAEL D.
Published: July 2006

Intracardiac echocardiography is emerging as a potentially useful tool during RF ablation procedures. There are a number of potential benefits of direct endocardial visualization during RF ablation including: (1) precise anatomical localization of the ablation catheter tip in relation to important endocardial structures, which cannot be visualized with fluoroscopy; (2) reduction in fluoroscopy time; (3) evaluation of catheter tip tissue contact; (4) confirmation of lesion formation and identification of lesion size and continuity; (5) immediate identification of complications; and (6) as a research tool to help in understanding the critical role played by specific endocardial structures in arrhythmogenesis. This article will review existing data and speculate as to possible future roles for intracardiac echocardiography in interventional electrophysiology.
Amiodarone Induced Torsades de Pointes with Excessive QT Dispersion Following Quinidine Induced Polymorphic Ventricular Tachycardia
Authors: TRAN HIEU T. , CHOW MOSES S.S. , KLUGER JEFFREY
Published: July 2006

We report a case of amiodarone induced torsades de pointes (TdP) associated with increase QT dispersion in a patient with a history of quinidine induced TdP. An increase in QT dispersion of > 100% was noted on the 12 lead surface ECG postamiodarone therapy. In summary, amiodarone has a potential to induce TdP in patients with a previous history of quinidine induced TdP. QT dispersion could be a potential marker of TdP in these patients.
Deglutition Syncope Associated with Carotid Sinus Hypersensitivity
Authors: ANTONELLI DANTE , ROSENFELD TIBERIO
Published: July 2006

A 78‐year‐old patient complained of syncope, near syncope, and dizziness when eating; complete atrioventricular block, with ventricular asystole for 3.6 seconds, was recorded on continuous electrocardiographic monitoring. Left and right carotid sinus masssage produces sinus arrest and ventricular asystole lasting 6.4 and 4.8 seconds, respectively. These phenomena were prevented by atropine administration. The symptoms were completely relieved by permanent pacing, but the patient died 6 months later because of large cell undifferentiated carcinoma of the lower third of the esophagus.
Radiofrequency Catheter Ablation of an Accessory Pathway in Dextrocardia
Authors: ABE HARUHIKO , ARAKI MASARU , NAGATOMO TOSHIHISA , MIURA YASUSHI , NAKASHIMA YASUHIDE
Published: July 2006

A 60‐year‐old woman with situs inversus and paroxysmal supraventricular tachycardias utilizing an AV accessory pathway underwent successful, uncomplicated RF ablation. Using biplane fluoroscopy, accessory pathway catheter ablation in dextrocardia is as safe, easy, and useful as that for normal heart structure cases, and does not require a lengthy procedure.
Analysis of the Intraventricular Electrogram for Differentiation of Distinct Monomorphic Ventricular Arrhythmias
Authors: STEVENSON SHELLY A. , JENKINS JANICE M. , DiCARLO LORENZO A.
Published: July 2006

This study investigated the effectiveness of correlation waveform analysis for identifying different ventricular electrogram morphologies of multiple VTs in the same patient. Patients with implantable antitachycardia devices are commonly subject to the occurrence of more than one distinct monomorphic VT. Each of these VTs may have unique therapeutic alternatives for termination. VTs with identical and different monomorphic configurations were recorded (1–500 Hz) using distal bipolar (1 cm) and distal unipolar electrograms from the right ventricular apex. Thirty‐six distinct monomorphic VTs induced in 15 patients were analyzed. Nine VTs with identical morphologies (12/12 surface ECGs) were induced twice and used as a control. A template was created for each VT induced. Correlation waveform analysis was used to compare eacb depolarization of all other VTs induced subsequently in tbe same patient. The mean correlation coefficient (pμ) of cycle‐by‐cycle analysis was used as a discriminant function: pμ≥ 0.95 was considered matched; and pμ < 0.95 was considered distinct. From the control population, VTs were successfully classified as identical in 9 of 9 cases (100%) using both bipolar and unipolar electrograms. VTs with different monomorphic configurations were successfully classified as being different in 31 of 33 cases (94%) using bipolar electrogram analysis and in 29 of 33 cases (88%) using the unipolar. Template matcbing is effective for detecting: (1) the recurrence of VTs, which are identical; and (2) the occurrence of a VT with a different configuration. This method appears effective using either unipolar or bipolar intracardiac waveforms.
Asystolic Cardiac Arrest During Head‐Up Tilt Test: Incidence and Therapeutic Implications
Authors: LACROIX DOMINIQUE , KOUAKAM CLAUDE , KLUG DIDIER , GUÉDON‐MOREAU LAURENCE , VAKSMANN GUY , KACET SALEM , LEKIEFFRE JEAN
Published: July 2006

Occasionally, the cardioinhibitory response may be profond during tilt induced syncope. Whether this response is associated with more severe symptoms or predicts a poor response to pharmacotherapy remains controversial. The aim of this study was to characterize patients with vasovagally mediated asystole occurring during head‐up tilt test and to evaluate the respective interests of sequential pacing and β‐blockers to treat them. We performed 60° tilt testing in 179 consecutive patients with unexplained syncope (91 women and 88 men, age 36.6 ± 20.1 years). Asystole was defined as a ventricular pause > 5 seconds. All patients with tilt induced asystole received therapy with either β‐blockers or sequential pacing, the efficacy of which was evaluated with serial tilt tests. Of 77 patients with positive tilt test, 10 developed syncope related to asystole (mean duration 11.9 ± 4.9 s), 2 with spontaneous recovery, and 8 with seizures needing a brief cardiopulmonary resuscitation. When compared with patients without asystole, asystolic patients had more severe symptoms (seizures: 6/10 vs 9/67, P = 0.05, injury: 9/10 vs 27/67, P = 0.0048). In the first six patients in whom cardiac pacing was considered, syncope or presyncope still occurred despite atrioventricular pacing at 45 beats/min. Five of these 6 patients, as well as the remaining 4 asystolic patients, were tilted with β‐biockers: 3 patients became tilt‐negative; 3 were significantly improved; and 3 did not respond. During follow‐up (mean 22.7 ± 11.7 months) with every patient taking β‐blockers and seven having a permanent pacemaker, no syncopal recurrence was observed. Tilt‐induced asystole that may require resuscitative maneuvers occurs especially in patients with a history of seizures or injury. Therapy with β‐blockers is often effective to prevent induction of syncope as well as recurrences.