bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of Heart Rate and Arterial Blood Pressure Control: Implications for the Pathophysiology of Neurocardiogenic Syncope
Authors: QUAN KARA J. , CARLSON MARK D. , THAMES MARC D.
Published: July 2006

Neurocardiogenic syncope is a general term that describes syncope resulting from altered autonomic activity, as manifested by abnormal regulation of peripheral vascular resistance and heart rate. Although there has been great interest in the contribution of heart rate to this form of syncope, the peripheral circulation plays the dominant role in the induction of neurocardiogenic syncope in most patients. We review in this brief article the physiology of cardiovascular reflexes, which are important for short‐term arterial pressure control, and their potential contribution to the pathophysiology of neurocardiogenic syncope. This type of syncope represents a profound failure of the normal mechanisms for short‐term regulation of arterial pressure. Any therapeutic strategies for the management of neurocardiogenic syncope must deal with alterations in vascular control, which contribute to its pathogenesis.
Vasovagal Syncope and Skeletal Muscle Vasodilatation: The Continuing Conundrum
Authors: DIETZ NIKI M. , JOYNER MICHAEL J. , SHEPHERD JOHN T.
Published: July 2006

During vasovagal syncope, profound bradycardia and hypotension occur. Atropine administration can prevent the bradycardia but not the hypotension, suggesting that marked peripheral vasodilation is a major cause of the fall in arterial pressure. This concept has been confirmed since vasovagal syncope can be seen in patients who have undergone heart transplantation and also in patients subject to cardiac pacing. In both cases, there is no bradycardia but hypotension during the syncopal attacks. The major site of the vasodilation is in skeletal muscle and muscle sympathetic nerve activity is suppressed just prior to and during vasovagal attacks, indicating that sympathetic withdrawal contributes to the dilation. However, the skeletal muscle vasodilation seen during syncope is greater than that caused by sympathetic withdrawal alone, and it is absent in limbs that have undergone surgical sympathectomy, or local anesthetic nerve block. These observations suggest a role for neurally mediated “active” vasodilation during syncope. The afferent neural pathways that evoke the profound vasodilation during vasovagal attacks remain the subject of debate. The neural pathways responsible for the active component of the dilation are also unknown. Recent evidence has demonstrated that cholinergic, β‐adrenergic, and nitroxidergic (nitric oxide) vasodilator mechanisms are not essential to observe the dilation, demonstrating that the mechanisms responsible for it remain a continuing conundrum.
The Impact of a Dedicated “Syncope and Falls” Clinic on Pacing Practice in Northeastern England
Authors: DEY A.B. , BEXTON R.S. , TYMAN M.M. , CHARLES R.G. , KENNY R.A.
Published: July 2006

This study examined whether the increased demand for pacemaker implants for carotid sinus syndrome (CSS) at the Regional Pacing Service in northeastern England was related to the establishment of a dedicated “syncope and falls” clinic or to the publication of NASPE and BPEG guidelines for pacing symptomatic bradycardia. To this end, pacemaker rates for various indications at this institution were compared with those of a comparable region (Liverpool), as well as with BPEG's national pacemaker database. Findings indicate a distinct impact of the Newcastle syncope and falls clinic on recognition and pacemaker treatment of CSS.
Cardiac Pacing for Vasovagal Syncope: A Reasonable Therapeutic Option?
Authors: PETERSEN MARK E.V. , SUTTON RICHARD
Published: July 2006

A number of studies have evaluated the effect of cardiac pacing for prevention of tilt induced vasovagal syncope. The findings are relatively consistent. Pacing does not prevent the onset of vasovagal syncope. This is predictable since hypotension (vasodepressor effect) typically occurs prior to bradycardia. However, dual chamber may prolong the presyncopal period in patients with a prominent cardioinhibitory component. Further, the relation of laboratory observations to spontaneous events is uncertain. In the largest retrospective assessment of pacing efficacy, 89% of patients reported improved symptoms and 62% remained free of symptom recurrence over 50 months.
First Steps Toward a Pacing Algorithm for Vasovagal Syncope
Authors: SUTTON RICHARD , PETERSEN MARK E.V.
Published: July 2006

Vasovagal syncope is commonly associated with an intermediate fall in heart rate. Consequently, it seemed possible that a pacemaker algorithm designed to detect intermediate heart rate falls might prove useful as a diagnostic tool to initiate pacing therapy. Subsequent experience suggests that with such an approach it is still difficult to avoid “false‐positive” detection of physiologic heart rate slowing (e.g., sleep). On the other hand, findings from several reports suggest that high rate pacing using this algorithm has proved clinically effective.
North American Vasovagal Pacemaker Study: Study Design and Organization
Authors: SHELDON ROBERT S. , GENT MICHAEL , ROBERTS ROBIN S. , CONNOLLY STUART J. ,   THE NAVPAC INVESTIGATORS
Published: July 2006

The North American Vasovagal Pacemaker Study is an ongoing multicenter randomized, clinical trial that assesses the efficacy of dual chamber pacing utilizing rate drop sensing in patients with frequent syncopal spells. Patients are eligible if they have had at least six syncopal spells and a positive tilt table test, or a recurrence of syncope within 6 months of a positive tilt test. The tilt table test must have provoked a relative bradycardia. Patients are randomized to receive a Medtronic Thera DR with rate drop sensing, or to continue on their usual therapy. All patients complete a log of their presyncopal and syncopal spells daily, and are contacted every 2 months. The primary outcome measure is the time to the first recurrence of syncope. The goal of the main study is to recruit 284 patients in 3 years with a final fourth year of follow‐up; this will result in an 80% chance of detecting a 30% reduction in the risk of syncope. A pilot study is under way with the aim to recruit 60 patients over a period of 2 years with a final third year of follow‐up. Recruitment began in July 1995 and 47 patients have been enrolled to date.
The Economics of Treating Vasovagal Syncope
Authors: SUTTON RICHARD , PETERSEN MARK E.V.
Published: July 2006

The economics of treating vasovagal syncope depends on the severity of attacks. In patients with syncope without warning in whom injury is a consideration, a correctly chosen cardiac pacemaker may be warranted. Based on a recent appraisal of the cost effectiveness of dual versus single chamber pacing, it is possible to estimate the economic value of cardiac pacemakers for vasovagal syncope. Findings indicate that an economic argument favors pacing patients with severe vasovagal syncope. However, prospective study examining syncope recurrence rates in paced and nonpaced patients is not currently available.
Impact of Programmed Sensitivity Safety Factor on Atrial Sensing in Children
Authors: CHIU CHRISTINE C. , GOW ROBERT M. , McCRINDLE BRIAN W. , HAMILTON ROBERT M.
Published: July 2006

The relationship between the pacemaker sensitivity safety factor (PSSF) and atrial under‐ or oversensing as documented by 24‐hour Holter monitoring was examined. Our study comprised 78 transvenous fixed atrial leads implanted between 1983–1995 in 71 children. Overall, 210 Holter reports identified 143 (68%) Holters with normal atrial sensing function, 31 (15%) with undersensing, 32 (15%) with oversensing, and 4 (2%) with both problems. From 161 Holter reports in which the PSSF was available, the incidence of undersensing at a PSSF of 2.0 (range 1.5–2.4) was 25% (14/57). There was a dramatic decline in undersensing when the PSSF was 3 (3%) compared to a FSSF < 3 (21 %) (P < 0.001). A PSSF cut‐off point of 2.0 best predicted occurrence of undersensing with a sensitivity of 79% and a specificity of 67%. Other variable were also examined by multiple logistic regression analysis, but only PSSF remained highly associated with undersensing (odds ratio [OR] = 0.6, P = 0.03). In contrast, PSSF did not have a significant role in predicting oversensing, but presence of sick sinus syndrome (OR = 10.5) or unipolar lead (OR = 5.6) were significantly associated with oversensing (P = 0.0001). The majority of undersensing problems can be avoided by routinely allowing for at least a threefold or more programmed sensitivity margin. Other factors may increase the risk of oversensing, regardless of the PSSF.
Use of an Orthogonal Electrode Array to Identify the Successful Ablation Site in Right Ventricular Outflow Tract Tachycardia
Authors: FISHER WESTBY G. , BACON MARTIN E. , SWARTZ JOHN F.
Published: July 2006

A novel approach to localize the origin of a right ventricular outflow tract tachycardia using an ablation catheter having an orthogonally oriented electrode array is described. Bipolar electrogram polarity reversal using minimally filtered (1–500 Hz) electrograms simultaneously acquired in two axes from the ablation catheter permitted accurate localization of the tachycardia focus. A single radiofrequency energy application at the site identified by this technique resulted in successful tachycardia ablation. This technique may facilitate mapping of any arrhythmia which can be modeled as arising from a point source.
Internal Cardioversion of Chronic Atrial Fibrillation in Patients
Authors: NERI ROBERTO , PALERMO PIERO , CESARIO ANTONIO SILVIO , BARAGLI DANIELA , AMICI ELISABETTA , GAMBELLI GIANCARLO
Published: July 2006

Transvenous internal cardioversion of chronic AF using a right atrium (RA) coronary sinus (CS) vector requires more energy than cardioversion of paroxysmal AF. Chronic AF is not terminated in 25% of patients using biphasic shocks up to 10 J. We therefore evaluated efficacy, safety, and tolerability of internal cardioversion using a “unipolar’ configuration (RA to skin patch) and biphasic shocks in patients with long‐lasting AF and different heart disease. In each patient, biphasic R have synchronous shocks were delivered between a large defibrillating surface area electrode in the RA and a skin patch in the left prepectoral position. Defibrillation protocol started with a test shock of 0.4 J. Shocks were repeated and increased until termination of AF or a maximum of 34 J. Sedation was used when the patient described the shock as painful. This study included 11 patients with a mean age of 67 ± 8 years (range 56–83). AF duration was ± 1 month in all patients with a mean duration of 11 ± 11 months (range 2–36). Underlying heart disease was present in all patients and the mean left atrial dimension was 43 ± 9 mm (range 26–57). AF was terminated in 10 of 11 patients (91 %) with a mean delivered energy of the successful shocks of 18.7 ± 8.7 J (median energy 16.9 J; range 7.3–32.5) and a mean leading edge voltage of 564 ± 129 V. The mean shock impedance at the defibrillation threshold was 71 ± 13 Ω, (range 59–103). A total of 131 shocks were delivered without any complication and proarrhythmia episodes. We conclude that low energy “unipolar” internal cardioversion is a simple, safe, and effective technique for termination of chronic AF in patients with heart disease. The procedure is often tolerated under light sedation.
Successful Management of an Infected Implantable Cardioverter Defibrillator with Oral Antibiotics and without Removal of the Device
Authors: TURKISHER VLADIMIR , PRIEL ISRAEL , DAN MICHAEL
Published: July 2006

Infection of an implantable cardioverter defibrillator developed 2 weeks after implantation, presenting with fever, swelling, redness, and tenderness of the skin above the generator site. A cloxacillin resistant coagulase‐negative staphylococcus was repeatedly cultured from the abdominal wall pocket fluid. The infection was successfully treated with a combination of two antibiotics, fusidic acid and rifampin, given orally for 3 months. Although the device was not removed, infection did not recur during a 24‐month follow‐up.
Inappropriate Pauses During Bradycardia Pacing in a Third‐Generation Implantable Cardioverter Defibrillator
Authors: COSSÚ SERGIO F. , HSIA HENRY H. , SIMSON MICHAEL B. , HANNA MICHAEL S. , CLYNE CHRISTOPHER A.
Published: July 2006

Many ICD devices have the capability for back up bradycardia pacing. Because of the use of a single sensing algorithm for both bradycardia and tachycardia functions, they may be prone to certain “sensing errors.” Following implantation of an ICD in a patient with long QT syndrome, “inappropriate” pauses were noted during bradycardia pacing, which were exactly twice the programmed pacing cycle length. This was due to an automatic increase in the device's sensitivity during pacing, a characteristic of the automatic gain control of this particular ICD. Proper recognition of this ICD's special features, known as “lower threshold crossing,” allowed noninvasive rectification of the problem and prevented these pauses.
Atrial Septal Pacing: A Method for Pacing Both Atria Simuhaneously
Authors: SPENCER WILLIAM H. , ZHU DENNIS W.X. , MARKOWITZ TOBY , BADRUDDIN SHAMIN M. , ZOGHBI WILLIAM A.
Published: July 2006

By pacing both atria simultaneously, one could reliably predict and optimize left‐sided AV timing without concern for IACT. With synchronous depolarization of the atria, reentrant arrhythmias might be suppressed. We studied four male patients (73 ± 3 years) with paroxysmal atrial fibrillation and symptomatic bradyarrhythmias using TEE and fluoroscopy as guides; a standard active fixation screw‐in lead (Medtronic model #4058) was attached to the interatrial septum and a standard tined lead was placed in the ventricle. The generators were Medtronic model 7960. The baseline ECG was compared to the paced ECG and the conduction time were measured to the high right atrium, distal coronary sinus and atrial septum in normal sinus rhytbm, atrial septal pacing, and AAT pacing. On the surface ECG, no acceleration or delay in A V conduction was noted during AAI pacing from the interatrial septum as compared with normal sinus rhythm. The mean interatrial conduction time for all 4 patients was 106 ± 2 ms; the interatrial conduction time measured during AAT pacing utilizing the atrial septal pacing lead was 97 ± 4 ms (P = NS). During atrial septal pacing, the mean conduction time to the high right atrium was 53 ± 2 ms. The mean conduction time to the lateral left atrium during atrial septal pacing, was likewise 53 ± 2 ms. We conclude that it is possible to pace both atria simultaneously from a single site using a standard active fixation lead guided by TEE and fluoroscopy. Such a pacing system allows accurate timing of the left‐sided AV delay.
Long QTc and Torsades de Pointes in Human Immunodeficiency Virus Disease
Authors: KOCHERIL ABRAHAM G. , BOKHARI S.A.J. , BATSFORD WILLIAM P. , SINUSAS ALBERT J.
Published: July 2006

Three patients with human immunodeficiency virus (HIV) infection presented with QTc prolongation (> 440 ms) and torsades de pointes. We sought to evaluate the etiology of the long QT syndrome in these patients without previously identified causes for QTc prolongation, and determine the prevalence among patients with HIV infection. The three index patients underwent: (1) left stellate ganglion block; (2) β‐blocker challenge; and (3) electrocardiographic stress testing. QTc interval was measured before and after intervention. We undertook a retrospective analysis of prevalence of QTc prolongation among all patients with computerized ECGs over a 6‐month period at one institution and compared it to the prevalence in hospitalized patients with HIV disease. Thirty‐four thousand one hundred eighty‐one patients with computerized ECGs were screened for QTc prolongation. Forty‐two hospitalized patients with HIV disease had computerized ECG during the same 6‐month period. In the three index patients, the QTc failed to shorten with left stellate ganglion blockade, β‐blocker challenge, or stress testing, suggesting an acquired form of the long QT syndrome in these patients with HIV disease. None had previously recognized acquired causes of QTc prolongation. Mexiletine hydrochloride was useful in preventing recurrences of torsades de pointes. We observed a 7.0% prevalence of QTc prolongation among all patients screened. Hospitalized patients with HIV disease (n = 42) during this same period, demonstrated an increased prevalence of QTc prolongation (28.6%, P = 0.002). Patients with HIV disease have a significantly higher prevalence of QTc prolongation than a general hospital‐based population, may have an unrecognized acquired form of the long QT syndrome, and are at risk for torsades de pointes.
Retroconduction Selective Recognition in Wide‐Dipole Floating Atrial Sensing
Authors: DI GREGORIO FRANCO , AL‐BUNNI MUHAMAD , BULLA VINCENZO , CROCE ADRIANO , MORACCHINI PIERVITTORIO , OCCHETTA ERALDO , ORLANDI MARIO , VINCENTI ANTONIO ,   THE MULTICENTER STUDY GROUP
Published: July 2006

Effective discrimination of retrogradely conducted P waves would allow distinguishing sinus tachycardia from supraventricular tachycardias due to A V or nodal reentry, and would prevent pacemaker‐mediated tachycardia in AV sequential pacing. This might be especially relevant in VDD implants, where retroconduction could be induced by escape ventricular stimulation. In order to analyze the respective waveform properties, anterograde and retrograde atrial signals were recorded by a wide floating electrode dipole, on the implantation of a permanent single‐pass lead for VDD pacing. Generally, bipolar recording did not allow reliable discrimination, while the signal nature could be readily diagnosed from the main features of the unipolar atrial electrograms. The unipolar waveform recorded under sinus rhythm in high right atrium, close to the superior vena cava opening (proximal EGM), started with a negative deflection in 88% of the patients. In 7% of the patients, the first deflection of the signal was positive in some cardiac cycles only, and, on the average, the amplitude of the positive phase was not higher than 5% of the signal peak‐to‐peak amplitude. Conversely, under retroconduction, the starting deflection attained higher positive values in 98% of the patients, being stably over 15% of the peak‐to‐peak amplitude in 86% of the cases. Furthermore, in 69% of the cases, the lag time between the onset of the negative deflection of proximal and distal (mid‐low atrium) unipolar EGM changed unambiguously when retroconduction occurred, exceeding the range of variation observed in each patient during sinus activity. The combined evaluation of unipolar EGM shape and lag time allowed specific retroconduction recognition in 95% of the patients. We suggest that this approach may yield useful information for the discrimination of retrograde atrial signals, provided that the recording dipole is sufficiently long and the proximal electrode is properly positioned in the high right atrium.
Graphical Representation of Complex Data—Diurnal Patterns of Initiations of Atrial Fibrillation Episodes
Authors: HNATKOVA KATERINA , MURGATROYD FRANCIS D. , GUO XIAOHUA , CAMM A. JOHN , MALIK MAREK
Published: July 2006

A construction of a purpose designed graphical display is demonstrated in a study investigating the circadian distribution of patterns of RR interval sequences preceding episodes of paroxysmal atrial fibrillation (PAF). Based on a comparison with a (80%, 120%) range around the median of preceding 10 RR intervals, each RR interval is classified as normal, short, or long. Classifications of RR intervals in n‐tuplets (n = 1, …, 5) preceding PAF episodes are used to compute probabilities of individual types of sequences occurnng within 4‐hour periods of the day (between 1 am, 5 am, 9 am, 1 pm, 5 pm, and 9 pm). Graphical representation of the data is proposed using a hierarchy of bar graphs. The graphical system has been filled with data of 327 atrial fibrillation episodes recorded in 46 24‐hour ECGs in PAF patients. The graphical analysis supports a link between PAF initiation and cardiac autonomic status.
Near Doubling of Heart Rate After Intravenous Verapamil for Treatment of Atrial Fibrillation Without Preexcitation
Authors: ORLOV YELENA S.K. , BRODSKY MICHAEL A. , ORLOV MICHAEL V. , ALLEN BYRON
Published: July 2006

Initial treatment of atrial fibrillation often involves pharmacological therapy to control ventricular response. While verapamil is usually safe and effective when used for this purpose, we report a proarrhythmic response. In this report a 30‐year‐old female presented with paipitations associated with atrial fibrillation and a ventricular response of 145 beats/min. Soon after she was given 5 mg of intravenous verapamil her ECG documented a regular wide QRS tachycardia at 290 beats/min. After 7 seconds the rhythm returned to an irregularly irregular narrow QRS tachycardia at 125–150 beats/min. At a later electropliysiology study there was neither evidence of preexcitation norinducible supraventricular or ventricular tachycardia. These data suggest that verapamil may have been associated with acceleration of the heart rate. The mechanism of proarrhythmia may be reiated to an aiteration in the atrial rhythm from atriaL fibrillation to atrial flutter, with additional factors as well.
Pectoral Muscle Stimulation After Falling Off a Ladder
Authors: NASH ANTONY , HALL SUSAN , MARSHALL ANDREW J.
Published: July 2006

A pacemaker that had been implanted correctly was found at follow‐up to have “flipped over” as a result of a fall from a ladder. Symptomatic pectoral muscle stimulation ceased immediately when the generator was manually flipped back into the correct position.
The Effects of Electrode‐Tissue Contact on Radiofrequency Lesion Generation
Authors: AVITALL BOAZ , MUGHAL KASHEF , HARE JOHN , HELMS RAY , KRUM DAVID
Published: July 2006

During the generation of radiofrequency (RF) lesions in the ventricular myocardium, the maintenance of adequate electrode‐tissue contact is critically important. In this study, lesion dimensions and temperature and impedance changes were evaluated while controlling electrode‐tissue contact levels (−5, 0, +1, and +3 mm) and power levels (10, 20, and 30 W). This data was used to assess the ability of impedance and temperature monitoring to provide useful information about the quality of electrode‐tissue contact. The results show that as the electrode‐tissue contact increases, so does the amount of temperature rise. Witb the electrode floating in blood (‐5 contact), the average maximum temperature increase with 20 and 30 W was only 7 ± 1 and 11 ± 2°C, respectively. At 20 and 30 W the temperature plateaued sbortly after the initiation of power application. With good electrode‐tissue contact (+1 mm or +3 mm), the temperature increase within the first 10 seconds was significantly greater than the temperature increase from baseline with poor contact (0 mm or −5 mm) and reached a maximum of 60 ± 1°C after 60 seconds of power application. As the electrode‐tissue contact increased, so did the rate and level of impedance decrease. However, the rate of impedance decrease was slower compared to the rate of temperature rise. With the electrode floating in blood, the maximum impedance decreases with 20 and 30 W were 6 ± 6 Ω and 9 ± 5 Ω, respectively. The impedances plateaued after a few seconds of power application. With the electrode in good contact, the maximum impedance decreases with 20 and 30 W were 25 ±2Ω and 20 ± 6 Ω, respectively. In these cases the rate of the impedance decrease plateaued after 40 seconds of power application.The increase in lesion diameter and depth correlate well with decreasing impedance and increasing temperature. However, lesion depth appears to correlate better with impedance than temperature. We conclude that, since the electrode‐tissue contact is not known prior to the application of power to the endocardium, in the absence of a temperature control system, the power should initially be set at a low level. The power sbould be increased slowly over 20–30 seconds, and then maintained at its final level for at least 90 seconds to allow for maximal lesion depth maturation. The power level should be lowered if the impedance drop exceeds 15 Ω.
Permanent Overdrive Atrial Pacing in the Chronic Management of Recurrent Postoperative Atrial Reentrant Tachycardia in Patients with Complex Congenital Heart Disease
Authors: RAGONESE PIETRO , DRAGO FABRIZIO , GUCCIONE PAOLO , SANTILLI ANTONELLA , SILVETTI MASSIMO STEFANO , AGOSTINO DOMENICO ANTONIO
Published: July 2006

This study investigated the value of permanent atrial pacing as an adjunct to the current therapy in the chronic management of recurrent postoperative atrial reentrant tachycardia in patients with complex congenital heart disease. We studied the postpacing clinical course in 18 patients with recurrent atrial reentrant tachycardias unresponsive to conventional therapy who had an implanted atrial pacemaker. The pacemaker was programmed at a lower pacing rate 20% faster than the spontaneous mean daily rate previously determined with 24‐hour Holter monitoring. Serial Holter recordings and pacemaker programming sessions were subsequently performed trying to mantain a paced atrial rhythm overdriving the spontaneous rhythm as long as possible. Twenty‐four hour Holter monitoring documented a prevalent (> 80%) paced rhythm during the daily hours in all patients during the follow‐up; all patients, however, required at least once a variation In programmed mode and pacing rate. Antiarrhythmic medications were discontinued after 6 months if the patient remained arrhythmia free while on pacing. Recurrences of atrial reentrant tachycardia occurred in five patients (29%) during the initial 6 months interval after the pacemaker implantation, while late recurrences occurred in only two patients (11 %). One patient died suddenly 10 months after the pacemaker implant. At the end of the follow‐up, 15 patients (83%) were arrhythmia‐free and only 2 of them were still on antiarrhythmic drugs. We conclude that permanent atrial overdrive pacing can be an important tool in the management of patients with atrial reentrant tachycardia following repair of congenital heart disease.
Heart Rate Variability in Patients with Familial Amyloid Polyneuropathy
Authors: KINOSHITA OSAMU , HONGO MINORU , SAIKAWA YUKO , KATSUYAMA TSUTOMU , TANAKA MASAO , TAKEDA MASASHI , YAMAMOTO HIROAKI , ISOBE MITSUAKI , SEKIGUCHI MORIE
Published: July 2006

The purpose of this study was to evaluate heart rate variability (HRV) in patients with familial amyloid polyneuropathy (FAP) using the time‐ and frequency‐domain analysis. The study population consisted of 19 patients with FAP, and 19 age and sex matched normal volunteers. The 24‐hour Holter recordings of all subjects in sinus rhythm and off medication were analyzed. Five time‐domain indices of HRV were computed. The frequency component of HRV was calculated by fast Fourier transform analysis of the RR intervals. The power spectrum of the low frequency (LF) between 0.04–0.15 Hz and high frequency (HF) between 0.15–0.40 Hz and the LF/HF ratio was calculated. Global measures of HRV including the standard deviation of the mean of RR intervals (SDNN) and the standard deviation of 5‐minute mean RR intervals (SDANN) were decreased in patients with FAP. Specific vagal influences on HRV including the proportion of RR intervals more than 50 milliseconds different (pNN50) and the HF power on spectral analysis were less in patients with FAP. LF power and LF/HF ratio were more decreased in patients with FAP at the advanced stage than at the early stage. In conclusion, HRV was significantly decreased in patients with FAP at the early stage, and sympathetic activity was more decreased in patients at the advanced stage. These findings suggest that the decrease of the HRV is an indicator of this disease and the power spectral analysis of the HRV is beneficial in assessing the severity of the autonomic dysfunction.
Diagnostic Approach to Narrow Complex Tachycardia with VA Block
Authors: HAMDAN MOHAMED H. , PAGE RICHARD L. , SCHEINMAN MELVIN M.
Published: July 2006

Narrow complex tachycardia with VA block is rare. The differential diagnosis usually consists of (1) junctional tachycardia (JT) with retrograde block: (2) AV nodal reentrant tachycardia (AVNRT) with proximal common pathway block; and finally (3) nodofascicular tachycardia using the His‐Purkinje system for antegrade conduction and a nodofascicular pathway for retrograde conduction. Analysis of tachycardia onset and termination, the effect of bundle branch block on tachycardia cycle length, and the response to atrial and ventricular premature depolarization must be carefully done. Making the correct diagnosis is crucial as the success rate in eliminating the tachycardia will depend on tachycardia mechanism.
Infections in Transvenous Cardiac Pacemakers: Two More Cases
Authors: MEZILIS NICK , HOUGH RACHAEL E. , OAKLEY G. DAVID G.
Published: July 2006

Two patients with metastatic pacemaker infections, one caused by Pseudomonas aeruginosa, 5 months after implantation, and the second by Streptococcus pneumoniae, 8 years after implantation, were treated successfully by removal of the pacemaker systems. Infection reoccurred in the patient with Pseudomonas aeruginosa, who initially underwent partial pacing system removal allowing the atrial lead to remain. Repeat partial atrial lead removal and contralateral pacemaker implantation was followed by clinical infection, which was resolved when both the implanted atrial lead fragment and the recently implanted pacemaker were both removed. Removal of all hardware is required for cure of pacemaker infection.
Hemodynamic Effects and Clinical Determinants of Defibrillation Threshold for Transvenous Atrial Defibrillation Using Biatrial Biphasic Shocks in Patients with Chronic Atrial Fibrillation
Authors: LOK NGAI‐SANG , LAU CHU‐PAK , HO DAVID SAI‐WAH , TANG YUEN‐WAI
Published: July 2006

We assessed the relationship between the hemodynamic changes and shock intensity in transvenous atrial defibrillation for chronic AF. The correlation between the clinical profile and atrial DFT and the factors predicting maintenance of SR after successful defibrillation were also investigated. Atrial defibrillation using entirely transvenoas leads has been investigated as an alternative means of managing patients with AF. However, the hemodynamic consequence of this technique and the clinical factors predicting defibrillation efficacy have not been evaluated. Thirty‐seven patients with chronic AF (4 weeks to 60 months) underwent transvenoas atrial defibrillation. Defibrillation was performed by delivering R wave synchronized, biphasic (3/3 ms) shocks with step‐up voltages (20–400 V) between defibrillation catheters in the anterolateral right atrium and the distal coronary sinus. Clinical profile of the patients, the DFT, arterial blood pressure, and RH interval during defibrillation and the 6‐month recurrence rate were determined. SR was restored in 33 (89%) of 37 patients and the DFT was 3.7 ± 1.4 J (317 ± 58 V). Transvenous atrial defibrillation resulted in a mild reduction in blood pressure (6 ± 10 mmHg), but substantial prolongation of longest postshock RR intervals (507 ± 546 ms), which were significantly related to the shock intensity (r = 0.5, P < 0.001). There was no ventricular proarrhythmia. The patients'age, body weight, duration of AF, left atrial diameter, and ejection fraction were not related to the success of defibrillation, not the 6‐month maintenance rate of SR (39%). However, the patients'age was related to DFT. Apart from transient reduction in blood pressure and shock related pauses that may require backup pacing, transvenous biatrial defibrillation was a highly effective and well‐tolerated technique. The absence of clinical determinant for successful defibrillation suggests that restoring SR by transvenous atrial defibrillation could be attempted in most patients with chronic AF.
Echographic Detection of Latent Severe Thrombotic Stenosis of the Superior Vena Cava and Innominate Vein in Patients with a Pacemaker: Integrated Diagnosis Using Sonography, Pulse Doppler, and Color Flow
Authors: NISHINO MASAMI , TANOUCHI JUN , ITO TATSUO , TANAKA KENJIRO , AOYAMA TSUKASA , KITAMURA MIWA , NAKAGAWA TAKAHIKO , KATO JUNJI , YAMADA YOSHIO
Published: July 2006

Thrombosis of the innominate vein and SVC is a serious complication in patients with pacemakers, inducing puhnonary embolism or SVC syndrome. Venography is the definitive method for its diagnosis; however, it is too invasive for related studies. The purpose of this study was to validate sonography, pulse Doppler, and color flow in detecting noninvasively innominate vein or SVC thrombosis in patients with pacemakers. In 53 patients with pacemakers, the 1 severe SVC stenosis and 18 severe innominate vein stenoses due to thrombosis were diagnosed by digital subtraction angiography. Sonography accurately showed the severe SVC stenosis due to thrombosis, but had limitations on the innominate vein thrombosis. Color flow demonstrated mosaic flow, indicating poststenotic turbulence due to stenosis of the innominate vein and SVC caused by thrombosis in 15 of 16 patients, and pulse Doppler disclosed absence of flow due to complete occlusion of the innominate vein in 2 of 2 patients. Sensitivity and specificity for detecting severe innominate vein stenosis due to thrombosis using combined color flow and pulse Doppler was 94% and 100%, respectively. In conclusion, sonography, pulse Doppler, and color flow allow accurate detection of severe innominate vein or SVC stenosis due to thrombosis, and are therefore useful for the follow‐up of patients with a pacemaker.
The Vanishing Defibrillator Syndrome: Incidence, Mechanism, and Clinical Relevance
Authors: LEONELLI FABIO M. , SALLEY ROBERT , SZABO TIBOR S. , KUO CHIEN SUU
Published: July 2006

Intraperitoneal migration of an abdominally implanted cardioverter defibrillator is a complication not yet fully described. In a consecutive series of 195 patients, migration occurred between I and 20 months in 5 (8%) of the 63 patients in whom a subrectus abdomini placement of the generator was chosen. It was unrelated to the patients'clinical characteristics or the defibrillator model. Dysuria and inability to interrogate the device were present in every subject, and the diagnosis was confirmed by the characteristic abdominal x‐ray appearance and the findings at the time of surgery. Adhesions involving the omentum, and in one case, the small bowels, were present in three patients and seem to be related to the length of intraabdominal permanence of the generator. Because this complication may be due to specific anatomical characteristics of the aponeurosis of the abdominal muscles, it is likely that its incidence will be unchanged by the use of smaller devices. A close follow‐up of the generators implanted deep to the rectus fascia is therefore advisable.
Pacemaker Induced Repetitive Nonreentrant Ventriculoatrial Synchrony: Initiation and Termination by Ventricular Extrasystole
Authors: BAROLD S. SERGE
Published: July 2006

During dual chamber pacing, repetitive ventriculoatrial (VA) synchrony secondary to retrograde conduction can occur whenever otherwise effectual atrial stimuli fall continually within the atrial myocardial refractory period generated by preceding unsensed retrograde atrial depolarization. The latter falls within the pacemaker atrial refractory period and cannot initiate endless loop tachycardia, another form of repetitive VA synchrony secondary to a reentrant process through the pacemaker and the heart. This report describes the usefulness of Holter recordings in the diagnosis of repetitive nonreentrant VA synchrony and documents initiation and termination of this process by a ventricular extrasystole.
Are Double Potentials Markers of a Specific Zone of the Atrioventricular Junction in the Isolated Rabbit Heart?
Authors: CHORRO FRANCISCO J. , SANGHIS JUAN , SUCH LUIS , CARCÍA‐CIVERA ROBERTO , LLAVADOR ESTEBAN , LLAVADOR JUAN J. , MONMENEU JOSÉ V. , LOṔEZ‐MERINO VICENTE
Published: July 2006

A study is made of the characteristics of the atrial potentials recorded in the Koch triangle and its proximity, their variations on modifying the site of cardiac pacing, and their usefulness as markers of a distinct zone of the AV junction. In 12 isolated and perfused rabbit heart preparations an analysis was made of the endocardial atrial electrograms recorded with a multiple electrode positioned in the AV junction. The electrograms were obtained during spontaneous rhythm and on pacing at the crista terminalis (CT), interatrial septum (IAS), left atrium, and right ventricle. Double potentials were frequently obtained. On pacing at the CT, high‐low double potentials (DP [H‐L]) were more frequent (P < 0.05) in the low CT (11%± 4% of the electrodes) and posterior zone of the Koch triangle (6%± 5%), than in the IAS (1 %± 2%) and anterior zone of the Koch triangle (2%± 3%). A similar tendency was observed either on pacing at the left atrium or during spontaneous rhythm. During pacing at the IAS the percentages of low‐high double potentials (DP[L‐H]) were significantly higher (P < 0.05) in the low CT (7%± 6%). DP (H‐L) were of low sensitivity in indicating a given zone; maximum sensitivity was 61 % in the low CT when pacing at the CT. DP (L‐H) proved even less seusitive in indicating a given zone, though their specificity was greater in the low CT (91%) during pacing at the IAS. The specific zones in which the highest percentages of DP (H‐L) or DP (L‐H) are obtained depend on the site of cardiac pacing. On pacing at the IAS. DP (L‐H) are more specific of the low CT. During pacing at both the CT and at the IAS. DP (H‐L) sensitivity in indicating a given zone is low.
Permanent Atrial Pacing in Cardiac Transplant Patients
Authors: WOODARD DAVID A. , CONTI JAMIE B. , JR ROGER M. MILLS , WILLIAMS ROGER A. , GURTIS ANNE B.
Published: July 2006

Thirteen out of 223 consecutive cardiac transplant patients required permanent pacemaker implantation; 11 for sinus node dysfunction and 2 for complete AV block. Patients with sinus node dysfunction were considered for AAIB mode pacemakers if they had intact AV conduction defined as a Wenckebach point of > 120 beats/min. Ten of 11 patients with sinus node dysfunction had a single atrial lead placed. Atrial lead placement was most easily accomplished with a straight, active fixation lead and the use of manually curved stylets to find an optimal position in the donor atrium, although active fixation leads with a preformed atrial J were used as well. Two leads dislodged requiring revision. In contrast, only 1 of 250 atrial leads implanted in nontranspianted hearts dislodged (P < 0.0001). Transvenous endomyocardial biopsies have not caused atrial lead dislodgment. Most transplant recipients requiring permanent pacing have intact AV nodal function and require only atrial pacing. Atrial lead dislodgment requiring lead revision occurs more frequently in heart transplant recipients than in native hearts. Use of a straight active fixation lead with a munually formed curve in the stylet is useful in order to find the optimal position for pacing.
Atrial Pacing Leads Following Open Heart Surgery: Active or Passive Fixation?
Authors: CONNELLY DEREK T. , STEINHAUS DAVID M. , HANDLIN LARRY , LEMERY ROBERT , MOUTRAY KELLY , FOLEY LAURA , DAVIE SCOTT , CARDINAL DEBBIE , LIPKE JANET
Published: July 2006

The right atrial appendage is often amputated at the time of cardiopulmonary bypass. Because of concerns regarding lead displacement, use of active fixation otrial leads has been recommended in patients who require permanent atrial or dual chamber pacing after open heart surgery. We evaluated the acute and chronic performance of active and passive fixation atrial leads implanted at our institution between 1985 and 1993 in patients with previous open heart surgery. Of 78 consecutive patients, 38 had an active fixation atrial lead, 28 had a passive fixation steroid‐eluting lead, and 12 had a passive fixation lead without steroid‐eluting properties. At implantation, sensed P wave amplitudes were similar in the three groups, but lead impedance and threshold were significantly higher for active fixation leads compared to all passive fixation leads. During follow‐up, atrial pacing thresholds were significantly higher, and sensed P wove amplitudes significantly lower, in the patients with active fixation leads compared to those with passive fixation leads. Loss of sensing occurred in 6 of 38 (16%) patients with active fixation leads and 1 of 40 (2.5%) patients with a passive fixation lead (P = 0.027). Atrial lead displacement occurred in two patients with active fixation leads and one with a passive fixation lead. Comparison with a parallel group of patients without previous open heart surgery demonstrated that atrial lead performance was similar in the two groups. We conclude that, when permanent atrial or dual chamber pacing is necessary in patients with prior open heart surgery, it is appropriate to implant a passive fixation atrial lead except on the infrequent occasions when a stable atrial position cannot be obtained.
A Comparison of Transvenous Atrial Defibrillation of Acute and Chronic Atrial Fibrillation and the Effect of Intravenous Sotalol on Human Atrial Defibrillation Threshold
Authors: LAU CHU‐PAK , LOK NGAI‐SANG
Published: July 2006

The comparative efficacy and safety of transvenous defibrillation for acute and chronic AF and the effect of antiarrhythmic agents on this therapy have not been evaluated. Transvenous atrial defibrillation was performed in 25 patients with chronic AF and 13 patients with acute AF by delivering R wave synchronized, biphasic shocks between the right atrium and coronary sinus. The lowest energy and voltage resulting in successful defibrillation were considered to be atrial defibrillation threshold (ADFT). Intravenous sotalol (1.5 mg/kg) was thengiven over 15 minutes and ADFT was determined again. The mean ADFT was 1.5 /and 3.6 J for acute and chronic AF, respectively, and the threshold was highly reproducible. Sotaloi reduced ADFT in patients with acute AF while the reduction in chronic AF group was not significant. There was no significant increase in creatinine kinase nor reduction in blood pressure, but prolonged pause after successful defibrillation required ventricular supporting pacing. We conclude that transvenous atrial defibrillation is a safe and effective means for defibrillating both acute and chronic AF. ADFT was lower in acute AF than in chronic AF. ADFT was highly reproducible during repeated defibrillation. Sotalol reduced ADFT in acute AF and to a lesser extent in chronic AF, and increased the defibrillation success rate. Ventricular pacing will often be required because of prolonged pause after successful defibrillation.
Supernormality with Cycle Length‐Dependent Intra‐His Alternans: A New Cause of Group Beating
Authors: TROHMAN RICHARD G. , PINSKI SERGIO L.
Published: July 2006

This article describes a patient with baseline infranodal conduction disease. Following the administration of intravenous procainamide, the patient developed group beating. Careful electrophysiological evaluation revealed that the group beating was due to alternating intra‐His conduction times. Systematic analysis of paced and spontaneous events provides strong evidence that the alternans results from supernormality within the His bundle.
Clinical Perspective on Risk Stratification
Authors: SLEIGHT PETER
Published: July 2006

Surveys show that subjective risk assessment or risk stratification is often widely inaccurate. Objective data from large observational studies or from clinical trials identifies a persons absolute risk of an event in a given time in order to assess the risk/benefit ratio of a given treatment. In general, the higher the risk the better the risk/benefit ratio. Relative risk reduction by a given treatment is often similar across subgroups divided by sex, age, blood pressure etc.; however if the absolute risk is low it may not e worth taking a treatment with serious side effects (e.g., cerebral haemorrhage). Risk stratification is also important in assessing the cost effectiveness of treatment (e.g,. cholesterol reduction by stotins for different groups of the population). Inappropriate surrogate end points should be avoided in cost benefit analysis (e.g., suppression of ventricular ectopic beats by antiorrhythmic drugs). A Bayesian approach should be adopted.
Risk Assessment and Risk Stratification in Sudden Cardiac Death: A Biostatistician's View
Authors: CHURCH TIMOTHY R.
Published: July 2006

Determining individual probabilities of developing lethal arrhythmia over time (risk assessment) and grouping individuals by that probability (risk stratification) are similar to, yet differ in purpose from, screening, diagnosis, risk factor identification, and prognostic staging. Methods of handling bias, use of multiple predictors, and evaluation of results provide challenges. A key purpose of risk assessment and stratification is examined. The role of operational definitions of predictors and events and of methods that account for multiple predictors and known confounding factors is analyzed. Constructed examples illustrate potential pitfalls in assessment and how multivariate techniques can deal with multiple predictors. A trial design to evaluate risk stratification for the identified purpose is elaborated and potential results are interpreted. Bias from predictors regressing to the mean can be minimized either by averaging a number of measurements or by equalizing the bias in comparison groups. An analysis of two predictors and two risk strata illustrates how the discrimination of combined predictors may be greater than the sum of the individual variables' discrimination. Risk stratification can be evaluated in trials that randomize competing interventions within different risk strata. Results of such trials indicate whether the risk strata adequately distinguish individuals by their responsiveness to particular intervention. Potential pitfalls, not easily recognized in risk stratification, can be avoided in the methods and in studies for evaluating those methods. Multivariate techniques maximize the discrimination of multiple predictors, but may increase complexity. Randomized trials of treatment provide evidence for utility of risk stratification.
Classification of Sudden and Arrhythmic Death
Authors: TORP‐PEDERSEN CHRISTIAN , KØBER LARS , ELMING HANNE , BURCHART HANS
Published: July 2006

Since all death is (eventually) sudden and associated with cardiac arrhythmias, the concept of sudden death is only meaningful if it is unexpected, while arrhythmic death is only meaningful if life could have continued had the arrhythmia been prevented or treated. Current classifications of death as being arrhythmic or sudden are all biased by the difficulty of having to decide on the degree of unexpectedness or the likelihood that life could continue without the arrhythmia. The uncertainties are enlarged by the fact that critical data (such as knowledge of arrhythmias at the time of death or autopsy) are available in only a few percent of cases. A main problem in using classifications is the lack of validation data. This situation has, with the MADIT trial, changed in the case of the Thaler and Hinkle classification of arrhythmic death. The MADIT trial demonstrated that arrhythmic death was nearly abolished by the implantable defibrillator, indicating that arrhythmic death by this classification is meaningful, at least in the population studied. For future investigations, a call is made for committees to present data in a way that allows the reader to examine the quality of the data used for evaluation.