bluuebunny/crossref_metadata_2025 huggingface dataset:
Acute Efficacy and Chronic Follow‐Up of Patients with Non‐Thoracotomy Third Generation Implantahle Defibrillators
Authors: BRACHMANN JOHANNES , STERNS LAURENCE D. , HILBEL THOMAS , SGHOELS WOLFGANG , BEYER THORSTEN , MEHMANESH HORMOZ , LANGE RUDIGER , RUF‐RIGHTER JUTTA , KRAET PATRIGIA , HAGL SIEGERIED , KUBLER WOLFGANG
Published: July 2006

Non‐thoracotomy implantation of implantable cardioverter defibrillators (ICDs) has simplified the process of device inserfion, promising to decrease associated procedural coniplications while providing sudden death protection at least equal to epicardial systems. This study presents the acute and chronic results of 110 patients who underwent attempted non‐thoracotomy ICD impiuntation wiih the Medtronic Transvene lead system and PCD model 7217 or 7219. Of the 110 patients attempted, 100 (91%) had the system successfully implanted without the need for an epicar‐dial patch. One patient died 1 week postoperatively of septic shock related to the implantation (0.9% perioperative mortality). During folloiv‐up of 16 ± 11 months, 45% of the patients had an event detected as ventricular tachycardia; 26% of these detections were felt clinically to be due to supraventricular rhythms. Of the remainder, 87% were successfully treated with the first VT therapy, and 98% were terminated by the final therapy; 66% of the patients had at least one episode of ventricular fibrillation, of which 5% were felt to be inappropriate detections; 65% of the appropriate episodes were successfully treated with the first VF therapy, and all were converted by the final therapy. Total mortality at 6, 12, and 24 months was 3%, 11%, and 19% respectively. Only one patient had sudden cardiac death, occurring at 13 months postimplant. Overall, the non‐thoracotomy lead system for this ICD displayed infrequent implant complications and proved to be reliable ai terminating arrhythmias and maintaining a low rate of sudden cardiac death in this high risk popuiation.
Strength‐Interval Curves in Canine Myocardium at Very Short Cycle Lengths
Authors: ALFERNESS CLIF , BAYLY PHILIP V. , KRASSOWSKA WANDA , DAUBERT JAMES P. , SMITH WILLIAM M. , IDEKER RAYMOND E.
Published: July 2006

While ventricular electrophysiological properties have been intensively studied at normal heart rates, little is known about these properties at the very short cycle lengths (approximately 100 msec), which are present in ventricular fibrillation. We examined refractoriness in the right ventricles of six dogs at stimulation intervals of 80 to 300 msec. Starting at 300 msec, the basic (S1) cycle length was decremented by 10 msec each beat to 200, 150, or 125 msec. A 1‐msec premature (S2) stimulus of 1, 5, 10, or 20 mA was then introduced. The S1‐S2 interval was decremented until capture was lost. The refractory period was considered to be the shortest interval that captured the heart for each S2 strength. Only pacing episodes that did not induce fibrillation were included. Strength‐interval curves maintained the same hyperbolic shape but shifted to very short refractory periods as the S1‐S1 interval was decreased. At the shortest S1‐S1 intervals, premature stimuli were capable of capturing the heart without inducing ventricular fibrillation for S1‐S2 intervals as short as 83 ±3 msec. Thus, decremental rapid pacing can produce refractory periods shorter than the cycle length during ventricular fibrillation. This finding suggests that there is no need to postulate a discontinuous jump to new electrophysiological properties or relationships at the onset of fibrillation, but that the capability for fibrillation is an integral part of normal electrophysiological parameters when they are pushed to values that do not occur normally. The results of this study should be useful in the further development of active membrane models and cellular automata models of cellular electrical behavior.
Short AV Interval VDD Pacing Does Not Prevent Tilt Induced Vasovagal Syncope in Patients with Cardioinhihitory Vasovagal Syndrome
Authors: PETERSEN MARK E.V. , PRICE DENISE , WILLIAMS TIM , JENSEN NICK , RIFT KENNETH , SUTTON RICHARD
Published: July 2006

Eleven subjects (mean age 50 years, range 33–71 years), who had previously received permanent dual chamber pacemakers for cardioinhibitory vasovagal syncope, underwent paired Westminster protocol tilt tests, one with short AV delay VDD pacing and one without pacing, to test the hypothesis that continuous ventricular pacing would prevent the cardiac initiation of vasovagal syncope. Nine (82%) of the paced tilts produced positive vasovagal outcomes compared with seven (64%) of the unpaced tilts. No important differences in the heart rate or blood pressure behavior during tilt or the time to positive vasovagal outcomes were observed between the paired tilts. There was more accelerated syncope/presyncope once symptoms had developed during the paced tilts of subjects in whom both study tilts were positive, although this did not reach statistical significance (P = 0.054). This study shows that atrial synchronous ventricular pacing does not prevent the initiation, or progression, of tilt induced vasovagal syncope in predisposed subjects.
The Effects of Pacing Site on Left Ventricular Epicardial Surface Velocity Patterns During Systole
Authors: HERR MICHAEL D. , LUCK JERRY C. , ORLEDGE JEFFREY D. , COPENHAVER GARY L. , McINERNEY JOSEPH J.
Published: July 2006

Changes in epicardial LV velocity patterns during isovolumic contraction and ejection as induced by ventricular pacing were studied in 15 canines. A noninvasive imaging technique that provided high temporal resolution was used to study the timing of an outward expansion of the LV during isovolumic contraction and the propagation pattern of an inward LV velocity wavefront during ejection. With this technique, surface displacements were measured (± 0.1 mm SD) at 50–70 locations on the LV free wall at 5‐msec intervals. Velocities were calculated by differentiating the surface displacement waveforms and an interpolation procedure was used to provide detailed color coded velocity maps of the LV surface. LV surface velocities were determined from data obtained during closed‐chest endocardial pacing from each of four sites: right atrium, right ventricular apex, left ventricular apex, and right ventricular outflow tract. These surface velocities showed a distinct spatial and temporal pattern for each pacing site. The results show that this noninvasive mapping procedure has potential for determining the location of an ectopic ventricular focus.
Inappropriate Sinus Tachycardia Following Radiofrequency Ablation of AV Nodal Tachycardia: Incidence and Clinical Significance
Authors: SKEBERIS VASSILIS , SIMONIS FRANK , TSAKONAS KALLINIKOS , CELIKER ALP AY , ANDRIES ERIK , BRUGADA PEDRO
Published: July 2006

The incidence and consequences of inappropriate sinus tachycardia following modification of the AV nodal area with radiofrequency energy were prospectively studied in a consecutive series of 118 patients. Twelve (10%) patients developed this complication, which persisted less than 1 week in all but three patients. Inappropriate sinus tachycardia was only observed after fast pathway ablation. Only four patients required temporary treatment with a beta blocker.
Plasma Levels of Natriuretic Peptides During Ventricular Pacing in Patients with a Dual Chamber Pacemaker
Authors: LA VILLA GIORGIO , PADELETTI LUIGI , LAZZERI CHIARA , SALVI SIMONE , MICHELUCGI ANTONIO , FRONZAROLI CATERINA , PORCIANI CRISTINA , MEZZANI ALESSANDRO , FRANCHI FRANCO
Published: July 2006

The mechanism(s) responsible for the release of brain natriuretic peptide (BNP), a cardiac hormone of ventricular origin, are still not completely understood. We measured plasma atrial natriuretic peptide (ANP) and BNP in 15 subjects (10 men, mean age 67 ± 3 years) with a dual chamber pacemaker and unimpaired heart function during ventricular pacing, which is known to induce an increase in atrial pressure and plasma ANP concentration. Under ECC monitoring, all subjects received sequential atrioventricular pacing for 30 minutes and ventricular pacing for 30 minutes, at the same rate of 80 beats/min. Arterial pressure and plasma BNP and ANP levels were measured every 10 minutes throughout the study. Ventricular pacing led to atrioventricular dissociation in eight subjects and to retrograde ventriculo‐atrial conduction in seven. Arterial pressure remained unchanged in all subjects. In the group with atrioventricular dissociation, plasma ANP increased from 10.14 ± 0.58 to 16.72 ± 0.92 fmol/mL at the 60th minute (P < 0.0001), whereas plasma BNP did not change at all (fiom 1.26 ± 0.07 to 1.16 ± 0.09 fmol/mL). In the group with retrograde conduction, plasma ANP concentration doubled (fiom 10.95 ± 1.66 to 21.40 ± 1.51 fmol/mL, P < 0.0001), BNP increased 1.5‐fold (from 1.16 ± 0.06 to 1.64 ± 0.14 fmol/mL, P < 0.001), and the ANP: BNP ratio augmented fiom 10:1 to 13.4:1. These results indicate that the release of ANP and BNP is regulated by different mechanisms, supporting the view that there is a dual natriuretic peptide system, comprising ANP fiom the atria and BNP fiom the ventricles.
Radiofrequency Catheter Ablation of an Accessory Pathway in a Young Man with Dextroversion
Authors: KLUG DIDIER , DUBUC MARC , FERRACCI ANGE , NADEAU RÉGINALD
Published: July 2006

We report an observation of a radiofrequency catheter ablation of an accessory pathway (AP) in a patient with Wolff‐Parkinson‐White syndrome (WPW) and dextroversion. Atrioventricular rings were mapped by the ablation catheter to locate the shortest local atrioventricular conduction time in sinus rhythm and ventriculoatrial conduction time during orthodromic tachycardia or ventricular pacing. Successful ablation confirmed a right posteroseptal AP localization. Thus, the electrocardiographic modifications due to an AP in this location in the presence of dextroversion were defined.
Sinus Dysrhythmia in Kearns‐Sayre Syndrome
Authors: ULICNY KARL S. , DETTERBECK FRANK C. , HALL COLIN D.
Published: July 2006

Kearns‐Sayre syndrome is the triad of progressive external ophthalmoplegia, pigmentary retinopathy, and complete AV block. The etiology is unknown, but is thought to be due to a mitochondrial DNA deletion. Reported electrocardiographic abnormalities include first‐degree AV block, fascicular blocks, and complete heart block, as well as nonspecific S‐T segment changes and T wave abnormalities, but has not included sinus node dysfunction. We report a case with episodes of sinus arrest in an asymptomatic patient with Kearns‐Sayre syndrome resulting in pauses lasting up to 6 seconds.
Ventricular Arrhythmia Factors in Mitral Valve Prolapse
Authors: BABUTY D. , COSNAY P. , BREUILLAC J.C. , CHARNIOT J.C. , DELHOMME C. , FAUCHIER L. , FAUCHIER J.P.
Published: July 2006

To assess tbe prevalence of ventricular arrhythmias and late potentials (LPs) in mitral valve prolapse (MVP) and to identify clinical, ECG, and echocardiographic markers of spontaneous ventricular arrhythmias, we studied 58 consecutive patients (mean age 46.6 ± 17.8 years; 29 males, 29 females) with MVP diagnosed by echocardiography. Patients underwent ambulatory ECG recording (n = 58), exercise stress test (n = 56), signal‐averaged ECG (n = 58), and programmed ventricular stimulation (n = 52). Ten patients (17.2%) had spontaneous nonsustained ventricular tachycardia (NSVT), 26 patients (44.8%) had premature ventricular contractions (PVGs), Lown grade ≥ 3 during 24‐hour EGG, and 19 had Lown grade ≥ 3 PVCs during exercise stress test; 13 patients had LPs (22.4%). We provoked sustained VT in one case and NSVT in ten cases. Patients with complex ventricular arrhythmias during 24‐hour EGG and exercise stress test were older and more often had mitral regurgitation. There was a statistical correlation between the presence of LPs and spontaneous VT (46.1 % vs 8.9%; P < 0.005) and induced ventricular arrhythmias (50% vs 12.8%; P < 0.005). No correlation was found between spontaneous ventricular arrhythmias and thickness or posterior displacement of the mitral valve. In conclusion, complex ventricular arrhythmia (especially VT) and LPs are frequent in MVP. Patient age and mitral regurgitation seem to be determinant factors of complex ventricular arrhythmias in MVP. On signal‐averaged EGG, absence of LPs seems to be a good additional marker to identify MVP patients without spontaneous VT. On the other hand, programmed ventricular stimulation does not appear valuable in determining a MVP subgroup with a high risk of ventricular arrhythmias.
Systolic Arterial Pressure Recovery After Ventricular Fibrillation/Flutter in Humans
Authors: PARK WOOSUP M. , AMIRHAMZEH MEHRDAD M.R. , JIA CHAO‐XIANG , BIELEFELD MARK R. , CABRERIZA SANTOS E. , DICKSTEIN MARC L. , SPOTNITZ HENRY M.
Published: July 2006

Although the elective induction of cardiac arrest for implantable defibrillator insertion under general anesthesia is widely used, the hemodynamics of recovery of arterial blood pressure after cardiac arrest is not well‐defined. Accordingly, the time course of recovery of systolic arterial pressure was studied in seven patients during the repetitive induction of ventricular fibrillation (n = 6) or ventricular flutter (n = 1). The mean number of episodes of cardiac arrest was 7 ± 2, and the mean drop in systolic pressure was 84 ± 16mmHg. The mean recovery time for systolic pressure was 10 ± 6 seconds, the average systolic pressure recovery rate was 13 ± 14 mmHg/sec, and the mean percent systolic pressure recovery was 94%± 9%. A negative logarithmic relation was found to exist between the rate of systolic arterial pressure recovery and the duration of ventricular fibrillation or flutter with a correlation coefficient of 0.68 to 0.97 (P < 0.05) in five of the seven patients. A linear relation between the time for systolic pressure recovery and duration of asystole was also defined. These results are consistent with the view that prolongation of ventricular fibrillation or flutter increases the duration of arterial pressure recovery through a negative effect on left ventricular contractility. Increased understanding of these relations may lead to increased safety of implantable defibrillator insertion.
A New Steroid‐Eluting Screw‐In Electrode
Authors: FRÖHLIG GERD , SCHWAAB BERNHARD , SCHWERDT HOLGER , LAWALL PETER , TRENDELENBURG MARTEN , SCHIEFFER HERMANN
Published: July 2006

A new lead design was tested that combined a small microporous steroid‐eluting electrode with an insulated, exposed helix for active fixation. This lead (model 5078, Medtronic, Inc., group I. n = 10) was compared to a conventional model (model Y 60 BP, Biotronik) with a larger surface of polished platinum‐iridium, equipped with a fixed, noninsulated screw but without steroid elution (group II, n = 10). The two lead models were studied in the atrial position of dual chamber pacing systems, which all had a tined ventricular lead (model 5024, Medtronic, Inc.), with essentially the same steroid‐aluting tip as the new active fixation lead design. Sensing and pacing data were recorded acutely and during 1 year of follow‐up, via the telemetry of a Relay pulse generator (Intermedics. Inc.). Intraoperatively, unfiltered atrial electrogram amplitudes did not differ between groups (group I; 7.12 ± 2.56 mV vs group II: 6.42 ± 1.87 mV; P > 0.05), nor did sensing thresholds 1 year after implantation (group I: 5.33 ± 1.70 mV vs group II: 4.26 ± 1.40 mV; P > 0.05). Atrial pacing thresholds as measured during surgery at a pulse width of 0.5 msec were lower in group I (0.49 ± 0.15 V) than in group II (0.68 ± 0.19 V; P < 0.05). From day 5 through day 360 of follow‐up, the difference in atrial pacing thresholds was highly significant (P < 0.01). with a smaller peaking of early thresholds and a much lower scattering of data for the steroid screw‐in leads than for controls. Chronic thresholds as measured 1 year postimplant in terms of minimum charge delivered for capture were 0.20 ± 0.03 μC in group I versus 0.54 ± 0.11 μC in group II (P < 0.01). There was no difference between groups on the ventricular level, both acutely and during follow‐up. If the active fixation atrial lead was compared to its tined ventricular counterpart in group I, pacing thresholds only differed within the early days postimplant, but they were virtually identical from week 3 through 1 year. It is concluded that the novel pacing lead design effectively combines low energy pacing with more versatility in electrode positioning by use of the active fixation mechanism.
Predictors of Successful Radiofrequency Ablation of Extranodal Slow Pathways
Authors: KELLY PATRICIA A. , MANN DAVID E. , ADLER STUART W. , EUENZALIDA CHARLES E. , BAILEY WILLIAM M. , REITER MICHAEL J.
Published: July 2006

Catheter positioning for radiofrequency ablation of extranodal slow pathways is often guided by local electrogram recordings. To determine the predictors of successful ablation sites, we reviewed data from 32 successful and 104 unsuccessful sites. Univariate predictors of a successful site included the occurrence of junctional rhythm during ablation (P < 0.001), shorter time to onset of junctional rhythm (P = 0.05), the presence of a discrete slow pathway potential (P < 0.001). a smaller ratio of the amplitude of the atrial‐ventricular electrogram (P = 0.04), later liming (P = 0.001) and longer duration (P < 0.001) of the atrial slow pathway electrogram, and the duration of (P < 0.001), and maximal voltage used during ablation (P < 0.001). By multivariate analysis junctional rhythm (P < 0.001), a discrete slow pathway potential (P = 0.003), a longer duration of the atrial slow pathway electrogram (P = 0.01) and the duration of ablation (P = 0.02) were predictors of success. Because ablations at unsuccessful sites were often aborted at 10–30 seconds, a separate analysis was performed using only the 41 unsuccessful sites where the duration of ablation was ≥ 30 seconds. The results were nearly identical. Thus, the occurrence of junctional rhythm during ablation and the morphology and duration of the atrial slow pathway electrogram may serve as guides for slow pathway ablation site selection.
Nonreentrant Supraventricular Tachycardia Due to Simultaneous Conduction Over Fast and Slow AV Node Pathways: Successful Treatment with Radiofrequency Ablation
Authors: LI HUAGUI G. , KLEIN GEORGE J. , NATALE ANDREA , THAKUR R.K. , YEE RAYMOND
Published: July 2006

A 55‐year‐old woman with frequent problematic supraventricular tachycardia is presented. The tachycardia was irregular with predominately normal QRS morphology and was refractory to multiple antiarrhythmic drugs. At electrophysiology study, the tachycardia was inducible with atrial or ventricular extrastimuli and dual pathways were observed. In contrast to the situation usually seen with dual atrioventricular node physiology, the slow pathway had a longer effective refractory period than the fast pathway and reentrant tachycardia was not induced. Simultaneous conduction over the fast and slow pathways during sinus rhythm was shown to be the mechanism for clinical tachycardia. The tachycardia was successfully treated using radiofrequency ablation of the slow pathway.
Observations From Intraatrial Recordings on the Termination of Electrically Induced Atrial Fibrillation in Humans
Authors: SIH HARIS J. , ROPELLA KRISTINA M. , SWIRYN STEVEN , GERSTENFELD EDWARD P. , SAHAKIAN ALAN V.
Published: July 2006

Background: The circulating wavelet hypothesis suggests that atrial fibrillation could terminate by either progressive fusion or simultaneous block of all wavelets. Methods: Intraatrial recordings from the right atrial free wall were made during procainamide induced (n = 8) or spontaneous (n = 7) termination of electrically induced atrial fibrillation in 14 patients. Atrial rate, mean magnitude squared coherence, and direction of activation during sequential electrograms were measured. Rate and coherence were calculated from the earliest point within 5 minutes prior to termination as well as from the 4‐second interval just prior to termination. Results: Termination was directly to sinus rhythm (13 episodes) or to atrial flutter (2 episodes). For the eight procainamide induced terminations, rate decreased between the first measurement and the measurement just prior to termination, from 443 ±127 beats/ min to 322 ± 119 beats/min. For the seven spontaneous terminations, rate also decreased from 373 ± 119 beats/min to 323 ± 88 beats/min; however, a slight increase in atrial rate prior to termination was observed in three episodes. No specific patterns of atrial cycle lengths were seen during the final few seconds of fibrillation. No increase in coherence was observed. In seven episodes, recordings were made using orthogonal bipoles in the x, y, and z directions, allowing direction of activation of wavefronts to be measured. Three episodes showed multiple instances where direction of activation remained similar over several electrograms as we have previously reported for chronic fibrillation. However, no such instances precipitated termination in any of the seven episodes. Conclusions: Atrial fibrillation usually terminates directly to sinus rhythm and does so abruptly and without forewarning. While we and others have previously reported that the rate of atrial fibrillation decreases with procainamide infusion, a decrease in the rate of atrial fibrillation is not required for the rhythm to terminate and consequently may not be a part of the termination process at all. Coherence does not demonstrate a progressive increase in the organization of atrial fibrillation prior to termination. Lack of stabilization in the direction of activation of wavefronts in the final few seconds also fails to support fusion of wavefronts as the mechanism of termination of atrial fibrillation. Simultaneous block of all wavelets is consistent with, but not proven by our observations.
Clinical Experience with a New Cardioverter Defibrillator Capable of Biphasic Waveform Pulse and Enhanced Data Storage: Results of a Prospective Multicenter Study
Authors: NEUZNER JOERG ,   for the EUROPEAN VENTAK P2 INVESTIGATOR GROUP
Published: July 2006

A recently introduced cardioverter defibrillator was implanted in 162 patients with refractory ventricular tachyarrhythmias and/or aborted sudden cardiac death. The new device is capable of delivering monophasic and biphasic defibrillation waveform pulses, arrhythmia detection, and therapy in two independently programmable zones, antibradycardia and postshock pacing. Additionally, the device provides enhanced data logs by storing intracardiac “far‐field” electrograms of spontaneous arrhythmic episodes. One hundred sixty‐two patients (mean age 55.5 years; mean left ventricular ejection fraction 36%) were enrolled in this multicenter investigation; coronary artery disease was the primary cardiac disease in 63.6% of the patients, idiopathic cardiomyopathy in 23.8%. Ventricular fibrillation was present in 49.7% of the patients; 29.3% of the patients experienced ventricular fibrillation and ventricular tachycardia; monomorphic ventricuiar tachycardia alone was present in 19.1% of the patients. In 26 patients the device was implanted with standard epicardial defibrillation leads (mean defibrillation threshold 11.5±3.7J). One hundred thirty‐nine patients underwent testing for implantation of a nonthoracotomy system and in 136 (98%), a nonthoracotomy system could be implanted. Defibrillation thresholds with a biphasic waveform (mean 10.2 ± 4.3 J) were lower than with a monophasic waveform (mean 17.4 ± 5.7 J). Two patients (1.2%) died perioperatively (< 30 days). During study time period follow‐up, there were 338 device discharges in 49 patients. Analysis of stored electrograms classified 25% of discharges as inappropriate and due to supraventricular tachyarrhythmias. At a mean follow‐up of 10.8 months, cumulative survival from sudden cardiac death was 98.8%, and survival from all‐cause mortality was 96.3%. This study demonstates the effectiveness of a new implantable cardioverter defibrillator in preventing arrhythmic death and the superior defibrillation efficacy of biphasic waveform pulses, which results in a higher implantation rate of nonthoracotomy systems, as well as the accurate arrhythmia classification made possible by the stored electrograms.
Fetal Heart Block: A New Experimental Model to Assess Fetal Pacing
Authors: ASSAD RENATO S. , JATENE MARCELO B. , MOREIRA LUIS F.P. , SALES PAULO C. , COSTA ROBERTO , HANLEY FRANK L. , JATENE ADIB D.
Published: July 2006

Epicardial fetal pacing via thoracotomy has the potential of being a safer and more reliable procedure to treat congenital complete heart block (CHB) associated with fetal hydrops refractory to medical therapy. To assess the acute electrophysiological characteristics of two ventricular epicardial leads, a new experimental model of fetal heart block induced by cryosurgical ablation of the AV node without the need for fetal cardiac bypass was performed in 12 pregnant ewes at 110–115 days gestation. A modified screw‐in lead (1½ turns) was used in six fetal lambs and a stitch‐on lead in the other six lambs. CHB was achieved in 100% of the fetal lambs, with no ventricular escape rate noticed in any of the lambs. The acute stimulation thresholds were consistently low for both leads, with lower values for the screw‐in lead at pulse duration below 0.9 msec (P < 0.03). Current measured at voltage threshold with pulse width below 0.5 msec was lower for the screw‐in lead (P < 0.048). Stimulation resistance, measured during constant‐voltage pacing, was not statistically different between the two leads (441.8 ± 13.7 Ω for the screw‐in lead vs 480.2 ± 59.2 Ω for the stitch‐on lead). No significant differences (P > 0.20) were found in R wave amplitude between the two electrodes. Slew rates were significantly higher in the screw‐in group than in the stitch‐on group (1.40 ± 0.2 vs 0.62 ± 0.2 V/sec, P = 0.04). This model of CHB is a simple and reproducible method to assess fetal pacing. We find the screw‐in electrode to be a better option when fetal pacing is indicated.
The Role of Parasympathetic Modulation of the Reentrant Arrhythmic Substrate in the Genesis of Sustained Ventricular Tachycardia
Authors: KJELLGREN OLLE , IP JOHN , SUH KYUNG , GOMES J. ANTHONY
Published: July 2006

The influence of parasympathetic activity on the reentrant arrhythmic substrate in the genesis of sustained ventricular tachycardia remains unclear. To assess this influence, we studied the heart rate variability in 59 patients referred for invasive electrophysiological testing. In addition, the presence of late potentials and high grade ventricular ectopy, and the left ventricular ejection fraction was determined. The 28 patients with inducible sustained ventricular tachycardia were found to have lower heart rate variability by time‐ and frequency‐domain measurements over 24 hours when compared to the 31 subjects who were noninducible. PNN50 was 4% in the inducible patients, whereas it was 9% in the subjects who were noninducible (P = 0.03). Similarly, HFP24H was 9 and 14 msec, respectively (P = 0.02). MAXHFP1H also differed (20 vs 27 msec [P = 0.04]) but not MINHFP1H (5 vs 6 msec). There was no association between heart rate variability and late potentials, degree of ventricular ectopy, or left ventricular ejection fraction. Thus, vagal tone does not appear to correlate with the presence of late potentials, ventricular ectopy, or left ventricular dysfunction. Low mean as well as maximal vagal tone, in contrast to minimal vagal tone, predicts inducibility of sustained ventricular tachycardia. Our data suggest that the inability to modulate parasympathetic tone appears to be an important determinant in the genesis of reentrant sustained ventricular tachycardia.
Spectral Analysis of Activation Time Sequences
Authors: LANGSTON MARK A. , PIEPER CARL F. , PACIFICO ANTONIO
Published: July 2006

Adequate spatial resolution of local activation is fundamental for the correct depiction of myocardial activation during ablative treatment of ventricular tachycardia. The widest allowable distances between recording sites that provide an accurate description of the field potential distribution is dictated by the Nyquist sampling theorem. Activation times are derived from the field potentials. However, because of noise intrinsic in activation detection algorithms, closer recording sites may be required than those theoretically computed. The purpose of this study is to examine the spatial frequency spectrum of epicardial activation time sequences computed by common activation detection algorithms, determine which algorithm is least noisy, and derive the recording site density necessary to avoid distortion of the epicardial activation map. Using 40 to 80 electrode linear arrays, monopolar and bipolar electrograms from the epicardium were recorded vertically (base to apex) and horizontally in 11 dogs. Activation times for bipolar electrograms were estimated using Peak, Fastest Zero Crossing, and Morphological algorithms. Activation times for monopolar electrograms were set equal to the time of the fastest negative deflection. Activation time sequences were analyzed using conventional Fourier techniques. Anomalous activation times from serially adjacent bipolar electrograms, which constitute algorithm noise, were studied. Horizontal and vertical interelectrode distances are 3.2 mm and 2.4 mm, respectively. Of the bipolar algorithms, the Morphological algorithm produced the fewest anomalous activation times. Mapping systems having more than 256 channels are required for accurate representation of epicardial activation in a typical 20‐kg dog. The endocardial electrode spacing is unknown, but is expected to be at least as dense. Large global mapping systems or regionally dense arrays may offer advantages during catheter ablations for ventricular tachycardia and for studies into the mechanisms of ventricular tachycardia by accurately defining the cardiac activation pattern.
Diagnosis of Ventricular Tachycardia Using a Pacemaker Holter Function
Authors: LASCAULT GILLES , FRANK ROBERT , HIMBERT CAROLINE , FONTAINE GUY , THOMAS DANIEL , GROSGOGEAT YVES
Published: July 2006

The diagnosis of ventricular tachycardia (VT) using the Holter function of an implanted pacemaker has not yet been reported. We present the case of a patient with episodes of slow VT. hemodynamically stable, but in whom long lasting attacks were not identified by the patient as VT recurrences, finally leading to progressive heart failure. Prospective analysis of the 24‐hour ECG and comparison with the pacemaker Holter data allowed us to determine diagnostic criteria to recognize VT using the pacemaker Holter function. Using these criteria it was possible to retrospectively diagnose VT occurrence during the weeks when the patient was out‐of‐hospital.
Two Unsung Heroes of Closed‐Chest Cardiac Pacing: Green and McWilliam
Authors: GEDDES LESLIE A.
Published: July 2006

In the latter half of the last century, cardiorespiratory arrest was not uncommon due to the anesthetic used (chloroform). Animal studies showed that the heart could be paced. One physician (Green) resuscitated 5 of 7 cardiac arrest patients with single stimuli applied to body surface electrodes. Another (McWilliam) issued a proposal for adoption of closed‐chest pacing and provided information on the procedure. The following historical footnote describes these pioneering events in the history of cardiac pacing.
Beat‐To‐Beat Behavior of QT Interval During Conducted Supraventricular Rhythm in the Normal Heart
Authors: VAINER JINDRICH , van der STELD BERT , SMEETS JOEP L.R.M. , GORGELS ANTON P.M. , SREERAM NARAYANSWAMI , WELLENS HEIN J.J.
Published: July 2006

To assess beat‐to‐beat behavior of QT interval under different conditions, high resolution recordings and computerized beat‐to‐beat analysis of the electrocardiogram were performed at rest, during recovery after short exercise, and during atrial pacing. Beat‐to‐beat variations of QT interval during sinus rhythm at rest and after short exercise were measured in ten healthy men. In an additional three patients with supraventricular tachycardia, beat‐to‐beat QT changes were studied after abrupt sustained acceleration and deceleration of heart rate by atrial pacing. Beat‐to‐beat changes in RH interval at rest are followed by minimal changes of the QT interval. The measured proportional change of the QT interval compared with the change in HR interval (Δ QT/A BR) was 0.02. This value represents 10% of the value expected for QT changes from Bazett's formula. Following short exercise QT interval did not change for 15 seconds and reached a maximal value 30 seconds later as compared to the RR interval (192 vs 115 sees, P < 0.001). The steady state of the QT interval during sustained atrial pacing was achieved after 132, 135, and 133 seconds for pacing intervals of 600, 500, and 600 msec, respectively. Our data indicate a relatively slow adaptation of the QT interval to changes in heart rate.
Correlation of the Endocardial Fragmented Electrogram with Body Surface Signal‐Averaged Electrocardiographic Mapping
Authors: SASAKI YASUYUKI , FURIHATA AKIKO , SUYAMA KAZUHIRO
Published: July 2006

We compared signal‐averaged electrocardiography (SAE), SAE mapping, and left ventricular catheter mapping in 60 patients with ischemic heart disease. Using the data obtained in patients with no fragmented electrograms (EE) in the left ventricle, the late potential was defined by SAE as a filtered QRS duration > 131 msec or a root mean square voltage < 16 μV for the last 40 msec of the QRS complex. SAE mapping was performed by recording the signal‐averaged electrocardiogram at 48 sites on the body surface. With SAE mapping, the filtered QRS duration and the area in the last 20 msec of the QRS complex were significantly different between the patients with and without EEs. The late potential was defined by SAE mapping as a filtered QRS duration > 136 msec or an area < 28 μV.msec for the last 20 msec of the QRS complex. The sensitivity and specificity of detecting FEs were 46% and 88%, respectively, by the SAE filtered QRS criterion, while they were 66% and 88% by the root mean square criterion. In contrast, SAE mapping gave values of 66% and 92% by the filtered QRS criterion, as well as values of 100% and 92% by the area criterion. Thus, SAE mapping provided better detection of the EE and was more closely correlated with the results of catheter mapping, suggesting its potential for clinical application.
Predictors of Device Activation for Ventricular Arrhythmias and Survival in Patients with Implantable Pacemakers/Defibrillators
Authors: REITER MICHAEL J. , FAIN ERIC S. , SENELLY KATHI M. , ROBERTSON ALASTAIR D. ,   THE CADENCE® INVESTICATORS
Published: July 2006

Predictors of survival and arrhythmia recurrence for patients with implanted defibrillators have been reported but patients with sustained, well‐tolerated ventricular tachycardia were often excluded from these trials. Arrhythmia recurrence and survival in populations including these patients have been less well studied. The purpose of the present study was to examine predictors of spontaneous ventricular arrhythmias and mortality in patients who received a tiered therapy antitachycardia pacemaker/defibrillator for ventricular tachycardia, fibrillation, or both. Three hundred thirty‐seven patients who received a Ventritex CADENCE® tiered therapy antitachycardia device at one of 19 participating centers between July 11, 1989 and March 4, 1991 are included in this retrospective analysis. Diagnostic summary data and stored electrograms telemetered from the implanted device were assessed to determine characteristics of recurrent arrhythmias. Mean follow‐up was 360 ± 10 (SEM) days. Thirty‐three patients died during follow‐up. At least one recurrent ventricular arrhythmia was observed in 205 patients (61 %). A total of 7,539 episodes were observed with a mean of 37 ± 5 per patient. Patients with recurrent ventricular arrhythmias were slightly but significantly older (64 ± 0.7 vs 59 ± 1.2 years; P < 0.001) but were not distinguished by gender or underlying structural disease. Patients whose presenting arrhythmia was monomorphic ventricular tachycardia were more likely to experience recurrent ventricular arrhythmias (69% recurrence rate) than patients presenting with ventricular fibrillation or polymorphic ventricular tachycardia (46% recurrence rate; P < 0.001). Cycle length of spontaneous tachycardia was also a predictor of arrhythmia recurrence. Patients having slower ventricular arrhythmias were less likely to remain recurrence free. Mean left ventricular ejection fraction was similar for patients with and without recurrences. Younger age and absence of arrhythmia recurrence but not presenting arrhythmia were predictors of survival. We conclude that age and presentation with monomorphic ventricular tachycardia are important predictors of arrhythmia recurrence for this patient population. Exclusion of patients with monomorphic ventricular tachycardia underestimates the rate of recurrent ventricular arrhythmias and utilization of device therapy.
Single Lead Atrial Synchronous Ventricular Pacing: A Dream Come True
Authors: ANTONIOLI GIOVANNI ENRICO
Published: July 2006

Single lead, atrial synchronous pacing systems were developed in the late 1970s. Clinical experience has demonstrated the need to position the “floating” atrial electrode in the mid‐to‐high right atrium and the need for a specially designed pulse generator (with very high atrial sensitivity) to provide a high quality and amplitude atrial electrogram for consistent sensing. A 12‐year experience with different electrode configurations, from the first unipolar designed in 1980 to the most recent atrial bipolar electrodes, has confirmed the validity of the original concept and the long‐term reliability of the single lead atrial synchronous pacing system, which can reliably produce long‐term atrial sensing and ventricular stimulation in the presence of normal sinoatrial function.
Transcatheter Radiofrequency Ablation of Ventricular Tachycardia Following Surgical Correction of Tetralogy of Fallot
Authors: BIBLO LEE A. , CARLSON MARK D.
Published: July 2006

Ventricular arrhythmias occur in up to 13.5% of patients after tetralogy of Fallot repair. We describe a patient with a 30‐year history of recurrent ventricular tachycardia, which followed the surgical repair of tetralogy of Fallot. Findings at electrophysiological study were consistent with reentry involving an area of slow conduction in the right ventricular outflow tract. Following the transcatheter application of radiofrequency energy in the right ventricular outflow tract, ventricular tachycardia could no longer be induced and has not occurred spontaneously during follow‐up (28 months). Thus, transcatheter radiofrequency ablation is an acceptable therapeutic option in some patients with ventricular tachycardia after the surgical repair of tetralogy of Fallot.
A Closed‐Chest Pig Model of Sustained Ventricular Tachycardia
Authors: ELDAR MICHAEL , OHAD DAN , BOR AMIR , VARDA‐BLOOM NIRA , SWANSON DAVID K. , BATTLER ALEXANDER
Published: July 2006

The goal of this study was to develop and explore a closed‐chest animal model of sustained VT. Seven of 11 domestic pigs had successful induction of myocardiai infarction by injection of agarose gel microbeads into the left anterior descending coronary artery tbrougb an inflated balloon angioplasty catheter. Four of the first five pigs died and seem to represent a “learning experience.” During a 3‐ to 50‐day follow‐up period, each pig underwent 1 ‐3 electropbysiological studies. Sustained, monomorpbic VT was induced 1–4 times in 5 of the 7 pigs (a total of 19 episodes), was reproducible during the same study in all pigs, and could be repetitively induced during successive studies in some. Ventricular fibrillation was induced less frequently (nine episodes) and was successfully terminated by DC shock in eight episodes. We conclude tbat a closed‐cbest pig model of VT is feasible and is associated witb a relatively bigb induction rate of sustained, monomorpbic, and reproducible VT and a relatively low mortality rate.
Myocardial Coagulation by Intraoperative Nd:YAG Laser Ablation and Its Dependence on Blood Perfusion
Authors: OHTAKE HIROSHI , MISAKI TAKURO , WATANABE GO , MUKAI KEIICHI , MATSUNAGA YASUHIRO , TSUBOTA MAKOTO , KAWASUJI MICHIO , WATANABE YOH
Published: July 2006

To investigate whether the efficacy of intraoperative laser ablation therapy is affected by myocardial blood perfusion, we irradiated 11 canine hearts through the epicardium with a Nd:YAG laser (10, 20. and 30 J/mm2) using air as the medium. Compared coagulated myocardial depth, width, and volume obtained in the red beating heart was compared with those in the white nonbeating heart infused with CC saline (cardioplegic model) via the coronary artery. Histologically, the macro‐ and microscopical findings were very similar. At each level of energy, the width and volume of red myocardium coagulated were significantly larger than those of white myocardium (P < 0.01). At 30 J/mn2, the depth of coagulation of red myocardium was significantly larger than that of white myocardium (P < 0.01). The coagulated volume of the white myocardium was about 60% of that of the red myocardium. NdiYAG laser energy was absorbed by blood (red color = hemoglobin), and more energy was transferred in the higher temperature myocardium. During intraoperative Nd:YAG laser ablation, the presence of blood perfusion in cardiac tissue is thought to be an important factor affecting safe irradiation.
Temperature May Be an Appropriate Sensor for Chronotropically Incompetent Patients with Postural Syncope
Authors: SINGER IGOR , RIPLEY KEN , JOHNSON BEN , STODDARD MARGUS
Published: July 2006

Chronotropically incompetent patients benefit most from sensor driven rate response during exercise. Postural syncope may occur despite the chronotropic response because of the failure of currently available sensors to respond physiologically to postural changes. Seven chronotropically incompetent patients with postural syncope who had a dual chamber rate adaptive pacemaker (CircadiaR) that modulates heart rate in response to temperature change were studied with respect to: (1) response to exercise: and (2) head‐up tilt (HUT). During exercise, continuous‐wave Doppler of aortic velocities and two‐dimensional echocardiographic derived measurements of left ventricular systolic function were used to assess cardiac function. Patients exercised longer (by an average of 168 sec) in the DDDF/compared to the DDl mode (P = 0.013). Increase in exercise duration was due mostly to the sensor driven increase during DDDH pacing. During DDDR pacing, heart rate increased from 71 ± 6 to 121 ± 17 ppm compared to 70 ± 1 to 103 ± 21 ppm for the DDl pacing (P = 0.038). Stroke volume as assessed by Doppler derived stroke distance (SD) contributed more significantly to the cardiac output increase during exercise in the DDl mode (SD increased from 13.4 ± 4 to 18 ± 7 cm in DDl compared to 13 ± 4 to 14 ± 2 cm in DDDR mode), although these mechanisms were insufficient to fully compensate for failure of appropriate chronotropic response. In response to the HUT, right ventricular temperature increased from 36.78°C ± 0.29°C to 36.89±± 0.28°C (P = 0.0002), and heart rate increased from 54 ± 3 to 71 ± 8 ppm (P = 0.0003) in the DDDR mode. No significant change in heart rate occurred in the DDl mode in response to the HUT. Strong positive correlation of temperature and heart rate was noted in all patients in response to HUT (P = 0.001, R2= 0.755–0.976). We conclude that temperature sensor responds physiologically to exercise and HUT. Therefore, temperature sensing rate adaptive dual chamber pacing may be appropriate for chronotropically incompetent patients with posture related syncope.
Catheter Entrapment in the Mitral Valve Apparatus During Radiofrequency Ablation
Authors: CONTI JAMIE B. , GEISER EDWARD , CURTIS ANNE B.
Published: July 2006

Catheter ablation of accessory atrioventricular pathways in patients with Wolff‐Parkinson‐White syndrome has become an increasingly popular therapeutic option. Catheter technology is rapidly evolving, allowing physicians to tailor the choice of catheter to the location of the pathway. We describe catheter entrapment in the mitral valve apparatus while using a valve mapping catheter with a peanut shaped tip to approach a left free‐wall pathway retrogradely across the aortic valve.
Left Heart Pacing and Cardioembolic Stroke
Authors: SHARIFI MOHSEN , SORKIN RICHARD , LAKIER JEFFREY B.
Published: July 2006

Three patients with inadvertently positioned left heart pacemaker leads were admitted for neurological symptoms consistent with embolic stroke. In one of them, the pacemaker lead crossed the interatrial septum, the mitral valve, and entered the left ventricle. In another it was erroneously placed through the subclavian artery, across the aortic valve, and into the left ventricular chamber In the third patient, the right ventricular lead of a DDD pacemaker was placed in the coronary sinus and the right atrial lead crossed the interatrial septum, and intermittently entered the left ventricular cavity. Once anticoagulation was initiated, symptoms resolved; they recurred when the level of anticoagulation dropped leading to a major stroke in one of the patients. Two of the patients were on aspirin at the onset of symptoms. We believe that every approach must be considered to remove the malpositioned lead. Otherwise, full dose anticoagulation must be initiated since antiplatelet therapy alone does not confer adequate protection against stroke.
Mexiletine Has No Effect on Defibrillation Energy Requirements in Dogs
Authors: SATO SHIGEHITO , TSUJI MARIKO H. , NAITO HIROSHI
Published: July 2006

Many of the antiarrhythmic drugs produce a rise in the ventricular defibrillation threshold (DFT). Although mexiletine has also been reported as the probable cause of a significant elevation of DFT, there has been no previous study; therefore, the effect of mexiletine on DFT was investigated in the present study. The experiments were performed on ten mongrel dogs in the open‐chest state using general anestbesia. Mexiletine 1,2,4, 6, or 8 mg/kg was administered as the loading dose, followed by the same dose/kg per hour. In these five groups, fibrillation/defibrillation (F/D) trials were performed repeatedly every 10 minutes, until 60 minutes after starting the maintenance dose. F/D trials were also performed at 30, 45, and 60 minutes after the completion of mexiletine infusion. The heart was allowed to fibrillate for a total of 30 seconds. Applying internal paddles to the beart, energies of 2, 3, 5, 7, 10, 20, and 30 J maximum were used. The minimal energy shock that caused defibrillation was defined as the DFT. The mexiletine concentration in each group cbanged from 0 to 6.11 μg/mL, DFT ranged from 2–10 J, and no statistical correlation was found between mexiletine concentration and DFT. We conclude that mexiletine does not induce an increase in DFT in dogs.
Ventriculoatrial Conduction in Patients with Implantable Cardioverter Defibrillators: Implications for Tachycardia Discrimination by Dual Chamber Sensing
Authors: LI HUAGUI G. , THAKUR RANJAN K. , YEE RAYMOND , KLEIN GEORGE J.
Published: July 2006

Incorporation of atrial electrograms in the tachycardia detection algorithm may improve tachyarrhythmia discrimination by ICDs but retrograde ventriculoatrial (VA) conduction over the AV node during ventricular tachyarrhythmia may be problematic. The present study analyzed VA conduction characteristics in 66 ICD patients who had evaluation of the VA conduction system by electrophysiological studies before implant. VA conduction was demonstrated in patients during ventricular decremental stimulation. Forty patients had inducible sustained monomorphic VT. The minimum cycle length maintaining 1:1 VA conduction during ventricular stimulation was longer than the cycle of VT in every patient (496 ±100 msec vs 320 ± 81 msec; P < 0.01). Occasional VA conduction during VT was observed in five patients and one patient had 2:1 VA conduction during induced VT. No patient had 1:1 VA conduction during VT. We conclude that brisk VA conduction is uncommon and 1:1 VA conduction during VT is rare in ICD recipients. VA conduction is unlikely to complicate the incorporation of atrial electrograms into tachyarrhythmia detection algorithms.