bluuebunny/crossref_metadata_2025 huggingface dataset:
Programmed Electrical Stimulation Protocols: Variations on a Theme
Authors: FISHER JOHN D. , KIM SOO G. , FERRICK KEVIN J. , ROTH JAMES
Published: July 2006

A series of prospective protocols were designed to determine the yield ratio (true positives vs. false positives = nonclinical) in various patient groups using a variety of programmed electrical stimulation (PES) variables. First, a PES protocol was used in 772 patients. Single, double, and triple extrastimuli were delivered in sequence (leaving each successive extrastimulus just beyond its refractory period before moving to the next extrastimulus) during sinus rhythm and two ventricular paced rates at the RV apex, before moving to the outflow tract and repeating the sequence and then moving on to isoproterenol infusion with the PES sequence repeated at the apex. This protocol met NASPE standards for induction of VT in patients with coronary artery disease and a history of VT, while failing to induce monomorphic VT in any control patient. The best yield ratios combined with the greatest likelihood of inducing clinical tachycardia were achieved with sinus rhythm and three extrastimuli, and pacing at the lower rate and three extrastimuli. Pacing at the faster rate and triple extrastimuli was highly inductive of clinical arrhythmias, but had a low yield ratio due to induction of more nonclinical arrhythmias than other steps. The next protocol was performed in 61 patients with inducible ventricular tachycardia. In each case, the protocol described above was completed at the RV apex, even if tachycardia was also induced at an earlier point in the protocol. This allowed for more accurate yield ratios to be established for each step in the protocol, since each patient was exposed to each of these steps. The results confirmed those of the first protocol described above. The next protocol compared extrastimuli delivered (1) in a straight sequential fashion (each extrastimulus decremented to its refractory period and then left just late enough to capture while the next extrastimulus was added and decremented in a similar fashion); versus (2) the tandem method, in which after reaching refractoriness, each extrastimulus was moved 50 msec beyond the refractory period and then decremented in tandem with the next extrastimulus. Preliminary analysis of this protocol in > 30 subjects indicates no significant difference in the number of clinical or nonclinical arrhythmias induced with these methods, although the tandem method was much more time consuming. We conclude that a simple sequential PES protocol, taken to refractoriness, is efficient and effective, and is not at a disadvantage compared to more complex or cumbersome protocols.
Phase Plane Plot of Electrograms as a Marker of Ventricular Electrical Instability During Acute Ischemia: Initial Experimental Results and Potential Clinical Applications
Authors: KARAGUEUZIAN HRAYR S. , KHAN STEVEN S. , DENTON TIMOTHY A. , GOTOH MASAMICHI , MANDEL WILLIAM J. , DIAMOND GEORGE A.
Published: July 2006

We used a phase plane plots method (a plot of voltage [V(t)] vs rate of change of voltage [dV/dt]) derived from nonlinear dynamics to transform a sinus rhythm strip into a geometric form. The geometric form thus obtained detects variations in the ECG over time and therefore may aid in identifying patterns of vulnerability to ventricular fibrillation (VF). The tralectories of consecutive ventricular depolarizations and repolarizations of sinus rhythm in dogs that evolve to VF showed characteristic differential band thickening (inhomogeneities) that were absent in the dogs that did not develop VF. This method of analysis can be a useful complementary tool to detect cardiac electrical instability, and with simple hardware, can easily be displayed in real time.
Increased Temporo‐Spatial Dispersion of Repolarization During Double Premature Stimulation in the Intact Ventricle
Authors: KOBAYASHI YOSHINORI , GOTOH MASAMICHI , MANDEL W.J. , KARAGUEUZIAN HRAYR S.
Published: July 2006

The degree of temporo‐spatial variation of repolarization during single (S2) and double (S3) premature stimulation was evaluated in five closed‐chest anesthetized dogs. Monophasic action potentials (MAP) were simultaneously recorded with contact electrode and MAP duration (MAPD) restitution curves constructed from right ventricular (RV) and left ventricular (LV) endocardial sites. At a given coupling interval, S3 was associated with significantly greater dispersion of MAPD then S2 spatial dispersion, i.e., between RV and LV). Similarly, at a given diastolic interval, S3 at RV and LV sites, was associated with significantly greater dispersion of MAPD then S2 (temporal dispersion). It is concluded that S3 is associated with greater temporo‐spatial dispersion of repolarization then S2.
Intraindividual Reproducibility of Heart Rate Variability
Authors: HOHNLOSER STEFAN H. , KLINGENHEBEN THOMAS , ZABEL MARKUS , SCHRÖDER FRANK , JUST HANJÖRG
Published: July 2006

Heart rate variability was determined from three consecutive Holter recordings performed on days 1, 7, and 28 in 17 normal subjects, in 13 patients with angiographically normal coronary arteries, and in 9 patients with remote myocardial infarctions. Group data of several time and frequency domain measures of heart rate variability were highly reproducible (correlation coefficients 0.629–0.894). However, some individuals exhibited considerably larger day‐to‐day variations in heart rate variability. Single heart rate indices differed by up to 50% between two Holter recordings. Such potential differences must be considered when repeated heart rate variability determinations are used to assess changes in neurocardiac reflex regulation or effects of therapeutic interventions.
Prognostic Value of Heart Rate Variability in Patients Awaiting Cardiac Transplantation
Authors: BINDER T. , FREY B. , PORENTA G. , HEINZ G. , WUTTE M. , KREINER G. , GÖSSINGER H. , SCHMIDINGER H. , PACKER R. , WEBER H.
Published: July 2006

Time and frequency domain parameters of heart rate variability (HRV) were determined in patients with severe end stage heart failure awaiting cardiac transplantation (HTX). These parameters were then correlated with mortality to investigate the performance of HRV in discriminating between groups with high and low risk of death. The standard deviation of five consecutive RR intervals (SDANN) was found to be the parameter with the greatest sensitivity (90%) and specificity (91%). Patients with SDANN values of < 55 msec had a twenty‐fold increased risk of death (90% confidence limits: 4–118, P < 0.001). The results furthermore suggest that measurements of HRV are superior to other prognostic markers such as left ventricular ejection fraction, pulmonary artery wedge pressure, cardiac index, and serum sodium levels. We conclude that HRV is a powerful, noninvasive tool to assess the risk of death in candidates for HTX. HRV measurements can therefore be used as a supplement to other markers of risk to determine the optimal therapeutic strategy in patients with severe congestive heart failure.
Heart Rate Variability in Patients with Vasovagal Syndrome
Authors: THEODORAKIS GEORGE N. , KREMASTINOS DIMITRIOS T. , AVRAMBOS GEORGE T. , STEFANAKIS GEORGE S. , KARAVOLIAS GEORGE K. , TOUTOUZAS PAVLOS K.
Published: July 2006

The aim of this study was to assess the heart rate variability in patients with vasovagal syndrome (WS). Heart rate variability was expressed as: (1) the standard deviation (SD) of the mean RR interval; and (2) the SD as a percentage of the mean RR interval (%SD). Heart rate variability was measured in VVS patients and compared with control individuals. Eighteen patients (mean age 50 ± 14 years) with a history of recurrent syncope and positive tilt testing were included in the study. Fifteen asymptomatic individuals (mean age 53 ± 13 years) with no history of syncope and negative tilt testing were used as a control group. The SD and %SD (39 ± 38 and 5 ± 4 msec) in the WS group were statistically higher at the tenth minute of tilt testing than in the control group (20 ± 14 and 2.5 ±1.8 msec, P = 0.03 and P < 0.05, respectively). The mean RR interval (mean heart rate) was shorter after the 15th minute of tilt testing in the WS group than in the control group (RR‐WS 687 ± 136 msec, RR‐control 801 ± 131 msec, P < 0.05). It is concluded that heart rate variability, as expressed by the SD of the mean RR interval, and the SD as a percentage of the mean RR interval (%SD) are significantly higher in VVS patients than in control asymptomatic individuals.
Atrial Fixation Leads—A Visual Aid Confirming Actual Fixation
Authors: CONTI JAMIE B. , CURTIS ANNE B.
Published: July 2006

Various active fixation mechanisms are available for atrial lead implantation. Confirmation of actual fixation of the lead tip in the myocardium is sometimes difficult with standard techniques such as fluoroscopy. Our observation of organized clockwise/counterclockwise motions of the fixation stylet in synchrony with atrial systole confirms adequate positioning of the AccufixR model #330‐801 atrial lead in the right atrial appendage, which is helpful when the screw is difficult to visualize underfjuoroscopy. This observation was confirmed in nine patients.
An Unusual Cause of Carotid Sinus Syndrome: Multiple Symmetric Lipomatosis
Authors: ROMANÓ MASSIMO , SPINELLI ACHILLE , FELLER SANDRO , TIBY VITO , SBRASCINI SERGIO , MUZIO LUCIANO
Published: July 2006

A 45‐year‐old man with multiple symmetric lipomatosis suffered recurrent syncope attributed to carotid sinus syndrome caused by extrinsic compression of the carotid body by the lipomatous masses. Surgical removal reduced but did not stop syncope, which was then controlled by implantation of a DDD pacemaker.
Atrial Paralysis in a Patient with Emery‐Dreifuss Muscular Dystrophy
Authors: MARSHALL TIMOTHY M. , HUCKELL VICTOR F.
Published: July 2006

Emery‐Dreifuss disease is a benign X‐linked muscular dystrophy characterized by a distinct pattern of muscle weakness, which is of insidious onset and slow progression. It is associated with atrial paralysis that results in sudden death in early adulthood if left untreated. The authors report the documentation of electrical and mechanical silence confined to the atria in a patient with this disease. Electrocardiography and electrophysiological study document the absence of electrical atrial activity, and inability to pace the atria, Hemodynamic studies demonstrate the absence of A waves, and angiography revealed immobility of the atria. This patient has done well following the institution of permanent ventricular pacing. His brother, who also had muscular dystrophy, died a sudden cardiac death at the age of 29 after refusing medical intervention. Emery‐Dreifuss muscular dystrophy is particularly worthy of recognition because of the preventable occurrence of sudden death in young patients with an otherwise excellent prognosis. Permanent ventricular pacing is indicated.
Is Epicardial Dual Chamber Pacing a Realistic Alternative to Endocardial DDD Pacing? Initial Results of a Prospective Study
Authors: ESPERER HANS‐DIETER , MAHMOUD FAHIDI O. , von der EMDE JÜRGEN
Published: July 2006

Seventeen patients, in whom an epicardial (n = 7) or a transvenous DDDM pacemaker system had been implanted between June 1988 and October 1990, were followed up for pacemaker and lead related complications, pacemaker longevity, and electrophysiological lead parameters. The mean follow‐up interval was 18 ± 12 months, maximum 34 months. There were no differences in chronic arrial and ventricular sensing thresholds between epicardial and endocardial stimulation, nor were there any differences concerning lead related complications between the two pacing modalities. However, atrial as well as ventricular chronic stimulation thresholds were significantly higher with epicardial stimulation resulting in a twofold increase in atrial energy consumption and a threefold increase in the ventricular energy consumption. Thus, in one patient with an epicardial DDD system, the pacemaker had to be replaced prematurely because of battery depletion. It is concluded that epicardial DDD stimulation can be reliably performed as far as atrial and ventricular sensing is concerned, but that the energy requirements of available myocardial leads are not satisfactory for making optimal use of modern pacemaker capability.
Effects of Verapamil on Ventricular Tachycardia Induced by Ouabain in Guinea Pigs
Authors: GOLDBERGER JEFFREY J. , ARONSON RONALD S.
Published: July 2006

Calcium ions appear to play a central role in the development of ventricular arrhythmias associated with digitalis intoxication. Therefore, the effects of the calcium channel antagonist, verapamil, on ouabain‐induced ventricular tachycardia were investigated. Ventricular tachycardia (three or more consecutive wide QRS complexes) was induced in guinea pigs by intravenous infusion of ouabain (1 μg/ min) and bursts of rapid ventricular stimulation. Of seven guinea pigs given the infusion of ouabain, all developed ventricular tachycardia at a dose of 82 ± 17 μg/kg (mean ± SD) and none developed heart block or asystole. Eight guinea pigs were treated with verapamil (2 μg/min for 30 minutes) prior to exposure to ouabain. Of those eight animals, only two developed ventricular tachycardia but six developed heart block or asystole at a significanlly higher dose of ouabain (154 ± 47 μg/kg), None of three control guinea pigs given an infusion of normal saline for 90 minutes developed ventricular tachycardia. These results show that pretreatmenf with verapamil inhibits ouabain‐induced ventricular tachycardia in guinea pigs. Combined treatment with verapamil and ouabain is associated with a high incidence of heart block and asystole, which may limit the usefulness of verapamil.
A New Pacemaker Algorithm for Continuous Capture Verification and Automatic Threshold Determination: Elimination of Pacemaker Afterpotential Utilizing a Triphasic Charge Balancing System
Authors: FELD GREGORY K. , LOVE CHARLES J. , CAMERLO JOHN , MARSELLA† ROBERT
Published: July 2006

A new pacemaker algorithm designed to automatically verify pacemaker capture and determine pacing threshold by detection of a stimulus evoked potential was studied in 20 patients undergoing permanent pacemaker implantation. To eliminate pacing stimulus afterpotential and detect an evoked response, a hardware feedback circuit and a software template matching algorithm were used to produce a triphasic charge‐balanced pacing pulse. After charge balancing the pacing lead, a residual artifact is measured. A capture window is defined as the area integral of the first 24 msec of the evoked depolarization, and a capture threshold as one third the amplitude of the capture window. The maximum allowable residual artifact is one eighth the amplitude of the capture window. Once the stimulus afterpotential is eliminated and the evoked response detected, capture threshold is automatically and continuously determined and the algorithm adds a 0.8‐V safety margin to the pacemaker output. This algorithm was run automatically and after simulated loss of capture, produced by manually decreasing pacer output below threshold, in the bipolar (13 patients) and unipolar (20 patients) pacing modes. In each patient loss of capture was immediately detected. The data were consistent (P = NS) between algorithm runs. During unipolar pacing the area integral of the first 24 msec of the evoked response was 412 ± 137 versus 413 ± 144 and the residual artifact 5.8 ± 4.8 versus 8.1 ± 7.5. The resulting ratio (signal/noise) of the two parameters was 150 ± 141 versus 145 ± 181. Automatically determined threshold was 0.69 ± 0.43 V versus 0.69 ± 0.42. During bipolar pacing the area integral of the first 24 msec of the evoked response was 266 ± 102 versus 275 ± 102 and the residual artifact 4.0 ± 3.3 versus 3.9 ± 3.0, The resulting ratio was 193 ± 210 versus 157 ± 170. The automatically determined threshold was 0.84 ± 0.61 versus 0.87 ± 0.72 V. This study has demonstrated that accurate detection of a stimulus evoked response is possible after charge balancing a permanent pacing lead, thus allowing for consistent and reliable verification of capture and automatic threshold determination. By continuously verifying capture and maintaining pacemaker output only 0.8 V above threshold, this automated system may increase patient safety and reduce pulse generator battery depletion.
Long‐Term Therapy of Antitachycardia Pacing for Supraventricular Tachycardia
Authors: JUNG WERNER , MLETZKO RALPH , MANZ MATTHIAS , ÜLUUDERITZ BERNDT
Published: July 2006

Long‐term antitachycardia pacing therapy with the InterTach 262–12 and 262–16 was evaluated in 32 consecutive patients (mean age 50 ± 13 years) with recurrent, drug refractory Supraventricular tachycardia. AV nodal reentrant tachycardia was present in 20 patients, Wolff‐Parkinson‐Whife syndrome in ten patients, and a reentrant tachycardia due to Mahaim fibers in one patient. During follow‐up of 39 ± 17 months, 250 persistent tachycardia episodes occurred in 22 patients. By adjusting detection and termination mode, recurrent Supraventricular tachycardia could be controlled in 19 of 32 patients (60%) by antitachycardia pacing alone. Concomitant antiarrhythmic drug therapy was required in ten of 32 patients (30%). During follow‐up antitachycardia pacing became ineffective in three patients (10%). Thus, chronic antitachycardia pacing proved to be safe and effective in selected patients with drug refractory Supraventricular tachycardia and could significantly improve quality of life by rapid termination of recurrent supraventricular tachycardia episodes.
Propagation Versus Delayed Activation During Field Stimulation of Cardiac Muscle
Authors: KRASSOWSKA WANDA , CABO CANDIDO , KNISLEY STEPHEN B. , IDEKER RAYMOND E.
Published: July 2006

This modeling study seeks to explain the experimentally detected delay between the application of an electric field and the recorded response of the transmembrane potential. In this experiment, conditions were deliberately set so that the field should excite all cells at once and so that no delay should be caused by a propagating wave front. The explanation of the observed delay may lie in the intrinsic properties of the membrane. To test this hypothesis, the strength latency curves were determined for three cases: (1) for a membrane patch model, in which the membrane is uniformly polarized and its intrinsic properties can be studied; (2) for the cardiac strand directly excited by the electric field; and (3) for the cardiac strand excited by a propagating wave front. The models of the membrane patch and the directly excited strand yield excitation delays that are comparable to those observed experimentally in magnitude and in the overall shape of the strength latency curves. The delays resulting from propagation are, in general, dependent on the position along the strand, although for some positions the strength latency curves for propagation are similar to those obtained from the directly activated strand and from the patch model. Therefore, the delay in excitation does not necessarily imply the presence of propagating wave fronts and can be attributed to intrinsic membrane kinetics.
Development of a Rate Adaptive Pacemaker Based on the Maximum Rate‐of‐Rise of Right Ventricular Pressure (RV dP/dtmax)
Authors: BENNETT TOM , SHARMA ARJUN , SUTTON RICHARD , CAMM A. JOHN , ERICKSON MARK , BECK ROBERT
Published: July 2006

The maximum rate of rise of right ventricular pressure (RV dP/dtmax) may change in response to physiological stress and thereby provide an appropriate parameter upon which to base rate adaptive pacing. Initial feasibility testing was carried out in six patients using externally closed loop rate adaptive pacing with a pressure sensing lead (Model 6220) and an investigational VVI pulse generator (Medtronic, Model 2451). During exercise, maximum positive RV dP/dtmax increased from 223 ± 55 to 405 ±181 mmHg‐sec1 (P < 0.05). Based on these results, rote adaptive pulse generators using maximum positive RV dP/dt were implanted in 12 patients (Medtronic, Model 2503), Exercise treadmill testing in the VVI mode resulted in heart rates ranging from 69 ± 6 beats/min at rest to 79 ± 14 beats/min (n = 12; P > 0.05). In contrast, VVIR mode pacing rates ranged from 71 ± 11 beats/ min to 115 ± 24 beats/min (n = 17; P < 0.05). Holter recording showed heart rates ranging from 51 ± 6 to 110 ± 22 beats/min during activities of normal daily living (n = 9; P < 0.05). Passive postural tilt resulted in rates of 69 ± 8 beats/min in the supine position increasing to 74 ± 14 beats/min with 60° upright tilt (n= 16; P > 0,05). With up to 5‐year follow‐up data, there have been no late failures of pacing but one lead showed insulation failure with over‐ and under sensing after 4.5 years, A number of deficiencies were identified in the prototypes leading to modifications of a subsequent generation of rate responsive pacemaker based on RV dP/dtmax. These initial data demonstrate that rate adaptive pacing based on RV dP/dtmax responds in a physiological manner. This rate responsive system is of particular interest as it is based on a beat‐to‐beat parameter of cardiac mechanical function.
Tachycardia Sensing Failure of an Implantable Cardioverter Defibrillator in a Patient with Hypertrophic Cardiomyopathy
Authors: GRUBB BLAIR P. , DURZINSKY DENNIS , TEMESY‐ARMOS PETER , HAHN HARRY , ELLIOTT LAURA
Published: July 2006

A 17‐year‐old white male was found to have nonobstructive hypertrophic Cardiomyopathy after suffering three severe syncopal episodes. He experienced an episode of sustained polymorphic ventricular tachycardia during exercise tolerance testing that required cardio‐version. Electrophysiological studies were able to reproduce sustained polymorphic ventricular tachycardia that was unresponsive to standard pharmacotherapy. An automatic implantable defibrillafor was placed, However, during implantation with the rate sensing electrodes on the left ventricle, it was found that the extremely polymorphic nature of the tachycardia caused such rapid fluctuations in the sensed R wave signal that the device could not properly detect the tachycardia. This was felt to be due to the automatic gain control circuit of the Ventak 1550. The problem was solved by moving the rate sensing electrodes to the lateral right ventricle. This case suggests that the unique arrhythmic substrate of hypertrophic Cardiomyopathy may present sensing difficulties during automatic implantable defibrillator insertion.
Intraoperative Identification of a Radiofrequency Lesion Allowing Validation of Catheter Mapping of Ventricular Tachycardia with a Computerized Balloon Mapping System
Authors: POLLAK SCOTT J. , STOWE GARY L. , WYNDHAM CHRISTOPHER R.C. , COLE MALCOLM
Published: July 2006

Radiofrequency current was utilized to mark the anatomic location of earliest endocardial activation during catheter mapping of ventricular tachycardia. Intraoperative identification of the radiofrequency lesion allowed validation that the site of earliest endocardial activation determined by a catheter mapping study was the same as assessed by a computerized balloon mapping system, fladiofrequency current may be a useful method of marking areas of endocardium thought to be potential sites for ablative surgery as well as allowing correlation between different mapping techniques.
Ventricular Fibrillation Produced by Stimulation of External Transthoracic Electrodes—An Experimental Study
Authors: VOORHEES CHRISTINE R. , VOORHEES WILLIAM D. , GEDDES LESLIE A. , BOURLAND JOE D. , HINDS MARVIN
Published: July 2006

The threshold for ventricular fibrillation was determined in 12 pentobarbital anesthetized dogs using transthoracic electrodes located at the optimal axillary electroventilation sites. Electroventilation is the name used to designate inspiration produced by stimuli applied to body surface electrodes. The optimal stimulation site for electroventilation was first determined using hand‐held electrodes. Then electrodes, 4.1 cm in diameter, were sutured bilaterally to the optimal anterior axillary stimulation site. The threshold current for producing ventricular fibrillation was determined using single pulses ranging from 0.1–10 msec in duration delivered during the vulnerable period of the cardiac cycle. Fibrillation was produced in all dogs with the 10‐ and 5‐msec pulse durations, in 11 dogs with 0.3‐msec, in 6 dogs with 0.2‐msee, and in 1 dog with 0.1‐msec pulse duration. In all dogs, the current required to produce ventricular fibrillation increased greatly as the pulse duration was decreased. The current required for fibrillation was much in excess of that required to produce one tidal volume. With the longer duration pulses, the ratio was about 80. With the 8 μsec duration pulses used for electroventilation the estimated ratio is about 800.
Slowing of Ventricular Tachycardia as a Possible Endpoint for Serial Drug Testing at Electrophysiological Study
Authors: HANDLIN LARRY R. , BRODINE WILLIAM N. , GIBBS HARRY , VACEK JAMES L.
Published: July 2006

Certain patients who cannot be rendered noninducible by serial drug testing during electrophysiology study demonstrate significant slowing of their ventricular tachycardia rate with selected agents. We evaluated the characteristics and outcome of 19 such patients to assess whether this slowing could be considered an acceptable endpoint for treatment. This group consisted of 14 males and 5 females (mean age 63 ± 9) with a mean ejection fraction of 28 ± 13% and inducible sustained ventricular tachycardia. Sixteen patients had known coronary artery disease and 13 had prior myocardial infarction. The other three patients had idiopathic cardiomyopathy. Serial drug testing during an electrophysiology protocol that used up to three extrastimuli at two or three cycle lengths at two right ventricular sites was used to select a medication regimen that provided optimal ventricular tachycardia slowing without limiting side effects. Five patients were treated with amiodarone, three with Ic agents fall with ejection fraction > 30%), and the remainder with la and Ib agents alone or in combination. Mean initial ventricular tachycardia rate was 219 ± 26 beats/mm with posttreafment ventricular tachycardia rate 137 ±17 fmean initial cycle length 278 ± 35 msec, posttreatment 443 ± 53 msec). Two groups were identified, those who had recurrent (although well‐tolerated) ventricular tachycardia (group 1, n = 6, mean time to recurrence = 15 months), and those who did not (group II, n = 11, mean follow‐up 22 months). Overall sudden death rate was 5%, while total mortality was 11% (all mortality in group I). No factor such as sex, age, drug type, ejection fraction, presence of coronary artery disease or aneurysm, or ventricular tachycardia morphology was significantly different between the groups. Conclusions: Significant ventricular tachycardia slowing by selected drug therapy at electrophysiology study is an acceptable therapeutic endpoint for certain patients, with a low rate of subsequent sudden death. However, recurrence, even if well tolerated, may be a marker for need for nonmedical therapy such as a device or surgery.
Clinical Evaluation of the Safety of Repetitive Intraoperative Defibrillation Threshold Testing
Authors: FRAME ROSEMARY , BRODMAN RICHARD , FURMAN SEYMOUR , KIM SOO G. , ROTH JAMES , FERRICK KEVIN , HOLLINGER INGRID , GROSS JAY , FISHER JOHN D.
Published: July 2006

One goal of the initial implantation procedure for a cardioverter defibrillator is determination of the configuration and patch location with the lowest defibrillation threshold (DFT). To determine the safety of multiple defibrillation tests, an analysis of the intraoperative defibrillation threshold tests (DFTT) in our patients was performed. In 84 patients, the mean number of DFT trials was 5.27; the mean number of joules received was 275.0. The maximum number of shocks in one implant procedure was 50 for a total of 4,895 joules without complications. Four patients received 30 or more DFT shocks without complication. There were two complications related directly to the DFTT: one patient with severe noninflammatory cardiomyopathy developed electromechanical dissociation and was subsequently resuscitated and survived; the second patient with severe triple vessel coronary artery disease suffered an intraoperative myocardial infarction during testing and eventually died 22 days postoperatively. All patients received an ICD unit; six patients had DFTs of > 20 joules. Based on our experience, we followed the clinical status (heart rate, blood pressure, EGG changes, fluid status, total anesthesia time) during the DFTT to determine the extent and duration of our testing protocol. Multiple shocks due to repositioning of the leads in a stable patient should not prohibit extensive testing as adverse consequences do not appear to be cumulative.
Relationship Between Beat‐to‐Beat Changes in Hemodynamic State and Action Potential Duration of the Left Ventricle During Rapid Ventricular Pacing in Man
Authors: HUIKURI HEIKKI V. , PEUHKURINEN KEIJO J. , TAKKUNEN JUHA T.
Published: July 2006

A relationship between beat‐to‐beat changes in hemodynamic state and action potential duration (APD) of the left ventricle was studied by pacing the right ventricle with a constant cycle length (400 msec) for 3 minutes and recording simultaneously the intraarterial pressure and left ventricular monophasic action potential in 16 patients (mean age 51 ± 8 years) undergoing routine cardiac catheterization. The APD measured at the point of 90% repolarization (APD‐90) shortened gradually from a baseline value of 305 ± 25 msec to a minimum of 246 ± 25 msec (P < 0.001) by 160 ± 10 seconds after the onset of pacing. After reaching the minimum duration, the APD and blood pressure were measured from 30 consecutive beats. The magnitude of beat‐to‐beat variation in the APD was directly correlated to variation in the mean arterial blood pressure (r = 0.65, P < 0.01). Beat‐to‐beat changes in hemodynamic and electrical state were related in that an increase of at least 10 mmHg in the blood pressure of one beat was associated with an increase in the APD of the concomitant beat by at least 5 msec, fn six patients with ventriculoatrial dissociation during the rapid ventricular pacing, the sequential ventriculoatrial pacing decreased the beat‐to‐beat variation of APD from 2.8%± 1.4% to 0.8%± 0.7% (P < 0.01) and variation of blood pressure from 6.4%± 3.2% to 1.4%± 0.9% (P < 0.01). The observed association between beat‐to‐beat changes in hemodynamic state and APD of the left ventricle demonstrates that an immediate force‐interval relationship exists in the human left ventricle.
Adaptive Rate Pacing Controlled by the Right Ventricular Preelection Interval: Clinical Experience With a Physiological Pacing System
Authors: RUITER J.H. , HEEMELS J.P. , KEE D. , VAN MECHELEN R.
Published: July 2006

In the PreceptTM pacing system, the right ventricular intracardiac impedance waveform is used to evaluate either of two indicators of metabolic demand relative right ventricular stroke volume and preelection interval (PEI). PEI is known to reliably parallel contractility changes, which is reflective of physical and emotional stress. The stability and dynamic behavior of PEI were tested in ten patients with a Precept(tm) pacing system under various forms of exercise and during postural changes, Although significant patient‐to‐patient variability of the sensor values was observed, reflecting individual physiological differences, the chronic stability of PEI was excellent in the total device experience of 147 months. In all patients, PEI shortened significantly during bicycle ergometry from a mean value of 137.7 ± 17.8 (range 96‐162) to a mean value of 103,0 ± 21.6 (range 92‐109) (P < 0.05). Low level bicycle exercise of short duration resulted in a prompt decrease in PEI and increase in pacing rate in all patients. There were no uniform postural responses overall, although some posture related rate changes were observed in two patients. We conclude that the first generation of a PEI based pacing system holds promise for adaptive rate pacing.
The Value of Transesophageal Atrial Pacing in Predicting the Efficacy of Antiarrhythmic Drugs in Patients with Paroxysmal Narrow QRS Complex Tachycardia
Authors: KULAKOWSKI PIOTR , DLUZNIEWSKI MIROSLAW , O'NUNAIN SEAN , CAMM A. JOHN , WARDZYNSKA MALGORZATA , CEREMUZYNSKI LESZEK
Published: July 2006

Transesopha‐geal atrial pacing (TAP) is used in the diagnosis and treatment of paroxysmal narrow QRS complex tachycardia (NQT). The aim of this study was to assess the value of this technique in predicting the efficacy of antiarrhythmic therapy. The study group consisted of 30 consecutive patients with spontaneous NQT whose clinical tachycardia was inducible by TAP. Baseline TAP was performed off all antiar‐rhythmic medication and repeated during oral antiarrhyfhmic drug therapy. The pacing protocol consisted of three stages: a single extrastimulus introduced at progressively shorter coupling intervals during sinus rhythm, pacing at incremental rates to the point of second‐degree AV block, and bursts of rapid pacing. On repeat stimulation while on oral antiarrhythmic therapy (37 pacing studies) NQT was still inducible in 12 cases. During the follow‐up period ten patients developed a recurrence of NQT: nine cases out of 12 (75%), in whom NQT was inducible while on antiarrhythmic therapy, and one case out of 25 (4%), in whom NQT was not inducible (P < 0.001). The sensitivity of TAP in predicting the outcome of the patients with NQT was 90%, and the specificity 89%. The negative predictive value of TAP (prediction of no recurrence of NQT) was 96%, and the positive predictive value (prediction of recurrence of NQT) was 75%. We conclude that TAP is a simple and accurate method for predicting the efficacy of antiarrhythmic treatment in patients with NQT.
A Double‐Blind Study of Submaximal Exercise Tolerance and Variation in Paced Rate in Atrial Synchronous Compared to Activity Sensor Modulated Ventricular Pacing
Authors: LINDE‐EDELSTAM CECILIA , NORDLANDER ROLF , PEHRSSON S. KENNETH , RYDEN LARS
Published: July 2006

To assess the variation in paced rate during everyday activity and the importance of atrioventricular synchronization (AV synchrony) for submaximal exercise tolerance, atrial synchronous (DDD) and activity rate modulated ventricular (VVI,R) pacing were compared in 17 patients with high degree AV block. The patients were randomly assigned to either mode and evaluated by treadmill exercise to moderate exertion and by 24‐hour Holter monitoring after 2 months in the DDD and VVI,R modes, respectively. At the end of the study, the patients were programmed to the pacing mode corresponding to the preferred study period. During the treadmill test, the mean exercise time to submaximal exertion (Borg 5/10), exertion ratings and respiratory rate did not differ between pacing modes despite a significantly lower ventricular rate in the VVI,R mode. The atrial rate during VVI,R pacing was significantly higher than the ventricular rate, but did not differ from the ventricular rate during DDD pacing. There was a diurnal variation in paced rate in both pacing modes. Paced ventricular rate was, however, higher and variation in paced rate greater in DDD compared to VVI,R pacing. Nine patients preferred the DDD mode, three patients preferred the VVI,R mode, while five subjects did not express any preference. The results from this study indicate that the variation in paced rate during activity sensor‐driven VVI,R pacing does not match that during DDD pacing neither during everyday activities nor during submaximal treadmill exercise, Nevertheless, no differences in exercise time, Borg ratings, and respiratory rate during submaximal exercise were found. Thus, for most patients with high degree AV block, DDD and VVI,R pacing seem equally satisfactory for submaximal exercise.
Effect of Successful Coronary Angioplasty on the Signal‐Averaged Electrocardiogram
Authors: MANOLIS ANTONIS S. , KATSAROS COSTAS , FOUSSAS STEPHANOS , OLYMPICS CHRISTOPHER , FAKIOLAS COSTAS , COKKINOS DENNIS V. , MORA VASSO
Published: July 2006

The effect of successful coronary artery angioplasty on the signal‐averaged electrocardiogram (SAECG) was examined in 50 patients (41 men, 9 women, aged 55 ± 8 years) with stable (26 patients) or unstable angina (24 patients) and good overall left ventricular function (ejection fraction ‐ 55%± 8%). The SAECG was recorded before and within 24‐48 hours after the angioplasty and was filtered at 40‐250 Hz, with 250 beats averaged. The noise level averaged 0.57 ± 0.15 p.V before and 0.56 ± 0.17 p,V after the procedure. There was no overall significant difference between pre‐ and postangioplasty SAECGs. Subgroup analysis showed that 14 patients had a significant increase of the root mean square voltage of the last 40 msec of the filtered QflS that was independent of noise level changes, previous myocardial infarction, stable or unstable angina status, positive or negative baseline SAECG, or vessel being dilated. Eleven patients (22%) had late potentials at baseline, of whom four (36%) lost them after angioplasty, while one patient developed them after the procedure, all due to root mean square voltage changes. Thus, successful angioplasfy exerted no significant overall effect on the SAECG, suggesting that the substrate of late potentials was not grossly altered by the procedure in our patients. However, there appear to be some patients, constituting approximately one third of this study population, who derive a favorable influence on the SAECG from angioplasty, a subgroup that needs to be further defined in future studies.
The Next Step in Cardiac Pacing: The View From 1958
Authors: JEFFREY KIRK
Published: July 2006

At a 1‐day conference sponsored by the Rockefeller Institute in September 1958, physicians and engineers held a confused debate over future directions for the young field of cardiac pacing. Many of the existing impediments to long‐term pacing for chronic illness received little attention; the participants focused instead on whether atrial synchrony would be a requirement for long‐term pacing. The Rockefeller conference illustrates the observation that cardiac pacing has undergone several major redefinitions. This process is rarely a smooth one but involves uncertainty, intense debate, and explicit choice.
Short‐Term Reproducibility Over Time of Right Ventricular Pulse Pressure as a Potential Hemodynamic Sensor for Ventricular Tachyarrhythmias
Authors: ELLENBOGEN KENNETH A. , WOOD MARK A. , KAPADIA KETAN , LU BIN , VALENTA HARRY
Published: July 2006

The implantable cardioverter defibrillator (ICD) has been shown to effectively terminate episodes of ventricular tachyarrhythmias. Multiple investigators have suggested that the incorporation of hemodynamic sensors may allow ICDs to differentiate between hemodynamically unstable and stable ventricular tachyarrhythmias (VT), as well as differentiate ventricularfrom supraventricular tachycardias. Right ventricular (RV) pulse pressure has been shown to possess acceptable characteristics as a sensor for incorporation in ICDs. We sought to determine the short‐term reproducibility of RV pulse pressure measurements by comparing RV pulse pressure measured during two separate episodes of VT in each of ten study patients. The mean VT cycle length for VT episode 1 was 293 ± 15 msec, and was 298 ± 15 msec for VT episode 2 (P = NS). The decrease in mean arterial pressure was 40 ± 7 mmHg in episode 1 and 37 ± 7 mmHg in episode 2 (P = NS). The decrease in RV pulse pressure during episode 1 was ‐13 ± 2 mmHg, and ‐ 12 ± 2 during episode 2 (P ‐ NS). The decrease in RV pulse pressure during episodes of VT at two different times during a single electrophysiology study is highly reproducible, suggesting that RV pulse pressure may be a reliable sensor aver time.
High and Low Strength Nonsynchronized Shocks Given During Canine Ventricular Tachycardia
Authors: MCCLELLAND JAMES H. , DAUBERT JAMES P. , KAVANAGH KATHERINE M. , Jr. HARRELL FRANK E. , IDEKER RAYMOND E.
Published: July 2006

Cardioversion shocks given during ventricular tachycardia may cause ventricular fibrillation or acceleration of ventricular tachycardia, or arrest the tachycardia. A recently proposed theory may explain why the former two phenomena may occur. Briefly, this theory states that potential gradient shock fields of a critical strength delivered to tissue with a critical degree of refractoriness will cause circulating wave fronts of ventricular activation (“rotors”) manifest as ventricular arrhythmia. We tested this theory by delivering nonsynchronized shocks 50% higher than defibrillation threshold or 50% lower than defibrillation threshold during 275 episodes of ventricular tachycardia in eight dogs with 5‐to 7‐day‐old myocardial infarcts. Shocks stronger than the defibrillation threshold are likely to create shock fields in the ventricles everywhere stronger than this critical value, and therefore would not generate rotors. Shocks less strong than the defibrillation threshold may create shock fields within the ventricles that include the critical value, and therefore cause rotors if given when critically refractory tissue is present. Nonsynchronized shocks were used to increase the likelihood of encountering tissue with a critical degree of refractoriness. Ventricular fibrillation or acceleration of ventricular tachycardia occurred following 83 of 138 (60%) low strength shocks and following 20 of 137 (14.6%) high strength shocks. The pooled odds ratio for induction of ventricular fibrillation or accelerated ventricular tachycardia after low strength shocks as compared to high strength shocks was 8.9. Conclusion: when given during ventricular tachycardia, low strength shocks are much more likely to cause ventricular fibrillation or accelerated ventricular tachycardia than are high strength shocks (P < 0.01). These findings suggest that shock synchronization may be critical to the success of low shock strength cardioversion techniques.
Comparative Evaluation of Rate Modulation in New Generation Evoked QT and Activity Sensing Pacemakers
Authors: BELLAMY CHRISTOPHER M. , ROBERTS DAVID H. , HUGHES SUSAN , CHARLES RICHARD G.
Published: July 2006

Two new generation rate adaptive pacemakers, the Rhythmyx (Vitatron) using the evoked QT interval and the Legend (Medtronic) using vibration as indicators of metabolic demand, were compared for rate adaptive characteristics during different forms of exercise. While both showed improvements over previous generation pacemakers, they still show deficiencies in some aspects of rate modulation. Rhythmyx was slow to respond to changes in metabolic need and showed an “overshoot” with increasing pacing rate on cessation of exercise. Legend was quick to adapt rate at beginning and end of exercise but showed a plateaus of rate modulation during the period of slowly increasing workload. Legend also showed only modest rate adaptation to changes in treadmill gradient and to bicycle ergometer exercise. Further developments in pacemaker technology are required if physiological rate adaptation to exercise is required.
Analysis of Local Electrogram Characteristics Correlated with Successful Radiofrequency Catheter Ablation of Accessory Atrioventricular Pathways
Authors: SILKA MICHAEL J. , KRON JACK , HALPERIN BLAIR D. , GRIFFITH KAREN , CRANDALL BRIAN , OLIVER RONALD P. , WALANCE CHARLES G. , MCANULTY JOHN H.
Published: July 2006

Due to the limited myocardial lesions produced by radiofrequency current, the ablation of accessory pathways (AP) requires precise localization of such connections. The purpose of this study was to ascertain ivhich characteristicfs) of the local bipolar electrogram, recorded from the ablation and adjacent electrode immediately prior to the application of radio/requency current, correlated with precision in localization adequate to permit AP ablation. Signal analysis was performed for 326 sets of electrograms preceding the attempted ablation of 107 APs in 100 consecutive patients. For 80 antegrade APs, the following variables were evaluated: (1) the presence or absence of an AP potential; (2) the local atrial‐AP interval; (3) the local atrioventricular (AV) interval; and (4) the relationship between the onset of local ventricular depolarization and onset of delta wave of the surface electrocardiogram. For the 27 concealed APs, the following characteristics were evaluated; (1) the presence or absence of an AP potential; and (2) the local VA interval during reciprocating tachycardia or ventricular pacing. Results: Antegrade APs: By statistical analysis, the best correlate of successful ablation of an antegrade AP was a local AV interval < 40 msec (positive predictive value = 94%; 95% confidence intervals (CI) = 81%–100%), Local AV intervals ≤ 50 msec preceded 88% of successful AP ablations, compared to only 8% of failed radiofrequency current applications. The positive predictive value of the other variables were: presence of an AP potential: 35% (95% CI = 27%–40%); local atrial‐AP intervals < 40 msec: 54% (95% CI = 43%‐66%); and local ventricular depolarization preceding onset of the delta wave 43% (95% CI = 34%‐52%). For concealed APs, the positive predictive value of a VA interval < 60 msec was 71% (95% CI = 48%–88%); the positive predictive value for the presence of an AP potential was 58% (95% CI = 32%–81%). Conclusions: No single electrogram characteristic had a positive predictive value and a sensitivity > 90% for AP localization adequate for radiofrequency current ablation. For antegrade APs, the best correlate of adequate localization was a local AV interval < 40 msec; as a corollary, radiofrequency current applications at sites where the local AV was > 60 msec, were unlikely to be effective. Objective criteria for the localization of concealed APs were less certain. Electrogram analysis, as a guide to AP localization and ablation, requires careful analysis of multiple variables, with analysis of the local AV interval a salient objective factor.
Holter Documented Sudden Death in a Patient with an Implanted Defibrillator
Authors: BIRGERSDOTTER‐GREEN ULRIKA , ROSENQVIST MÅRTEN , LINDEMANS FRED W. , RYDÉN LARS , RADEGRAN KJELL
Published: July 2006

A 68‐year‐old man with recurrent attacks of monomorphic ventricular tachycardia (VT) received a pacer cardioverter defifarillalor featuring antitachycardia pacing and cardioversion/defibrillation. Over 300 episodes of VT were successfully terminated by antitachycardia pacing. During Holter monitoring the patient experienced supra ventricular tachycardia with delivery of multiple antitachycardia pacing, cardioversion, and defibrillation therapies ending with the death of the patient. The following factors played a role in the unfortunate outcome of this patient: 1. triggering of VT therapy by an unexpected high sinus rate; 2. atrial fibrillation induced by cardioversion therapy; 3, a gradual and continuous increase in rate during atrial fibrillation possibly caused by repeated VT and ventricular fibrillation therapies and/or by a thrombus, found at autopsy, in a bypass graft; and 4. the limited ability of presently available defibrillators to distinguish between ventricular and supraventricular arrhythmias.