bluuebunny/crossref_metadata_2025 huggingface dataset:
The Probability of Defibrillation Success and the Incidence of Postshock Arrhythmia as a Function of Shock Strength
Authors: CATES ADAM W. , WOLF PATRICK D. , HILLSLEY RUSSELL E. , SOUZA JOSEPH J. , SMITH WILLIAM M. , IDEKER RAYMOND E.
Published: July 2006

The effects of high voltage defibrillation shocks given to six swine were studied to determine if there is a limit to the advantage gained from increasing the shock strength. An endocardial electrode was placed in the right ventricle, and a 114‐cm2 cutaneous patch was placed on the left lateral thorax. Monophasic (10 msec) and single capacitor biphasic (5/5 msec) shocks with leading edge voltages of 200, 400, 600, 800. and 990 volts (approximately 2.3–59 J) were tested. For monophasic shocks, the probability of successful defibrillation ranged from 0% at 200 V to 90% at 990 V. The incidence of postshock arrhythmia increased from 0% for successful shocks at 600 V to 67% for successful shocks at 990 V. For biphasic shocks, the probability of success peaked at 97% for the 600‐, 800‐, and 990‐V shocks. The incidence of postshock arrhythmia increased from 8% at 400 V to 55% at 990 V. Although more postshock arrhythmias occurred at lower strengths for bipbasic than for monophasic shocks, an efficacy criterion, quantifying the probability of defibrillation success and the probability that a postshock arrhythmia will not occur, was always higher for biphasic shocks. The probability of success never reached 100% for either waveform while the incidence of postshock arrhythmia increased as the shock strength increased. In conclusion, for the catheter‐patch electrode configuration, increasing the shock strength does not always improve the probability of success and may increase the incidence of postshock arrhythmia.
Scatter Diagram Analysis: A New Technique for Discriminating Ventricular Tachyarrhythmias
Authors: THRONE ROBERT D. , WINDLE JOHN R. , EASLEY ARTHUR R. , OLSHANSKY BRIAN , WILBER DAVID
Published: July 2006

With the increasing flexibility allowed by implantable cardioverter defibrillators that use tiered therapy, it is important to match the therapy with the arrhythmia. In this article we present scatter diagram analysis, a new computationally efficient two‐channel algorithm for distinguishing monomorphic ventricular tachycardia (VT) from polymorphic ventricular tachycardia and ventricular fibrillation (VF). Scatter diagram analysis plots the amplitude from one channel versus the amplitude from another channel on a graph with a 15 × 15 grid. The fraction (percentage) of the 225 grid blocks occupied by at least one sample point is then determined. We found that monomorphic VT traces nearly the same path in space and occupies a smaller percentage of the graph than a nonregular rhythm such as polymorphic VT or VF. Scatter diagram analysis was tested on 27 patients undergoing intraoperative implantable cardioverter defibrillator testing. Passages of 4.096 seconds were obtained from rate (bipolar epicardial) and morphology (patch) leads, and digitized at 125 Hz. Scatter diagram analysis distinguished 13 episodes of monomorphic VT (28.6%± 4.0%) from 27 episodes of polymorphic VT or VE (48.0%± 8.2%) with P < 0.0005. There was overlap in only one monomorphic VT episode and one polymorphic VT or VF episode.
Invasive and Noninvasive Methods to Predict the Long‐Term Efficacy of Amiodarone: A Compilation of Clinical Observations Using Meta‐Analysis
Authors: ROBERTS SHEILA A. , VIANA MARLOS A. , NAZARI JOSE , BAUMAN JERRY L.
Published: July 2006

Background: The method of choice to predial the long‐term efficacy of amiodarone in the treatment of complex ventricular arrhythmias is unknown. Whether electrophysiological testing or Holter monitoring better predicts long‐term outcome is controversial. Methods and Results: We performed a meta‐analysis of trials using electrophysiological testing or electrocardiographic monitoring to predict the efficacy of amiodarone in patients with sustained ventricular tachycardia. Arrhythmia recurrence data were combined after homogeneity testing across trials. Bayesian estimates and 95% credibility intervals were constructed to compare the arrhythmia‐free probability among groups. Nine studies using electrophysiological testing (351 patients) and three using Holter monitoring (167 patients) met criteria for inclusion determined a priori. The combined arrhythmia‐free probability estimate and credibility intervals were 0.86 (0.78–0.92) for patients rendered noninducible and 0.81 (0.73–0.87) for patients with abolition of ventricular tachycardia during Holter monitoring on amiodarone. With this primary analysis, there was no significant difference between the predictive value of noninducibility during electrophysiological testing and abolition of ventricular tachycardia with Holter. However, if only those electrophysiological studies using at least triple extrastimuli were included, arrhythmia‐free probability for patients rendered noninducible increased to 0.96 (0.88–0.99), significantly better than noninvasive testing. Conclusions: Noninducible ventricular tachycardia during electrophysiological testing and abolition of ventricular tachycardia during electrocardiographic monitoring on amiodarone appear equally predictive of long‐term amiodarone success, but this conclusion seems dependent on the stimulation protocol used. Although the vield is lower (compared to Holter monitoring), ventricular tachycardia rendered noninducible with a stimulation protocol using triple extrastimuli is the most highly predictive test of long‐term amiodarone efficacy.
Radiofrequency Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia in Children
Authors: TEIXEIRA OTTO H.P. , BALAJI SESHADRI , CASE CHRISTOPHER L. , GILLETTE PAUL C.
Published: July 2006

Radiofrequency (RF) catheter ablation has been widely used in the treatment of cardiac arrhythmias. In atrioventricular nodal reentrant tachycardia (AVNRT), the experience has been predominantly in adults. The cardiac electrophysiological records of 18 consecutive children undergoing RF catheter AV node modification for AVNRT were reviewed. The patients (10 females, 8 males) were 8.2–17.9 years of age (mean 13.6 ± 3.0), weight 15.2–88.1 kg (mean 52.2 ± 20.8), and height 103–190 cm (mean 157.1 ± 21.7). Thirteen were on antiarrhythmic medications (1–3, average 1.5 drugs/day). All drugs were discontinued 48 hours prior to the ablations. The procedures were performed under sedation and local anesthesia. Pre‐ and post‐AV node modification electrophysiological studies were performed in all procedures. The 18 patients underwent a total of 25 procedures (1.39 ± 0.61 per patient): the anterior approach aimed at the antegrade fast pathway in the first four patients and the posterior approach aimed at the slow pathway in the remainder. Thenumber of energy applications was 8–54 (19.8 ± 10.7) per procedure. The maximum energy used in each procedure was 30–50 watts (33.8 ± 8.4). The average energy was 24–50 watts (33.0 ± 6.8). The fluoroscopy time was 7.1–73.4 minutes (29.9 ± 20.0) per procedure, for a total catheterization time of 228–480 minutes (300.3 ± 59.1). Preablation spontaneous or induced AVNRT (cycle length 310.4 ± 55.0 msec) was seen in all except one who had the arrhythmia (cycle length 270 msec) on surface ECG. In 22 of 25 studies, the AH interval measured 67.4 ± 13.2 msec pre‐ and 98.7 ± 58.4 msec post‐AV node modification (P < 0.02). Procedures were initially successful in 16 (89%) of 18 patients. One patient developed complete AV block requiring DDD pacemaker and has since recovered normal AV conduction. Transient third‐ or second‐degree block was seen in four. Other complications included airway obstruction in one and excessive emesis in another. In follow‐up of 2–26 months (13.0 ± 7.3), one patient underwent surgical ablation for failed initial RF catheter ablation, and two underwent successful RF procedures for recurrences. RF catheter AV node modification for AVNRT in children is a useful technique. Under ideal circumstances, it is safe and efficacious. Follow‐up to determine the potential long‐term complications is necessary.
Effect of Pacing Site on the Atrial Electrogram at Target Sites for Slow Pathway Ablation in Patients with Atrioventricular Nodal Reentrant Tachycardia
Authors: HUMMEL JOHN , STRICKBERGER S. ADAM , KALBELEISCH STEVEN , WILLIAMSON BRIAN , MAN K. CHING , VORPERIAN VICKEN , MORADY ERED , LANGBERG JONATHAN
Published: July 2006

Atrial electrograms recorded from target sites during radiofrequency catheter ablation of the slow atrioventricular (AV) nodal pathway are often fractionated and may be associated with a late, high frequency component (the slow pathway potential). The purpose of the current study was to assess the effects of slow pathway ablation on the morphology of the atrial electrogram and to determine whether target site electrograms display direction dependent changes in morphology during atrial pacing maneuvers. Twenty‐six patients with typical AV nodal reentry had electrograms recorded from target sites before and after successful ablation of the slow A V nodal path way and during pacing from the high right atrium and distal coronary sin us at cycle lengths of 500 and 300 msec. There was no significant change in the duration or degree of fractionation of the atrial electrogram as the result of slow pathway ablation. In contrast, the duration and degree of fractionation were less when pacing from the coronary sinus compared with sinus rhythms or right atrial pacing. Pacing rate did not affect electrogram morphology. These data suggest that the morphology of the slow pathway target site electrogram is dependent on the direction of atrial activation and that the “slow pathway potential” does not represent activation of an anatomically discrete pathway.
Radiofrequency Catheter Ablation of Accessory Pathways During Entrainment of AV Reentrant Tachycardia
Authors: LI HUAGUI G. , KLEIN GEORGE J. , ZARDINI MARGO , THAKUR RANJAN K. , MORILLO GARLOS A. , YEE RAYMOND
Published: July 2006

Radiofrequency ablation of accessory pathways must sometimes be done during orthodromic atrioventricular reentrant tachycardia when manifest anterograde accessory pathway conduction is absent or retrograde fusion obscures accessory pathway location during ventricular pacing. Unfortunately, abrupt heart rate slowing upon radiofrequency induced termination of atrioventricular reentrant tachycardia often causes catheter dislodgment. We report our experience in circumventing this problem during radiofrequency ablation by using entrainment of atrioventricular reentrant tachycardia. The latter maintains retrograde activation pattern over the accessory pathway while preventing abrupt ventricular rate change. Eight patients (4 men and 4 women, mean age 37.3 ± 17.9) with eleven left‐sided accessory pathways were included. Ablation during entrainment was used as the first approach in three patients with concealed accessory pathways and one patient with a bidirectional accessory pathway. In another four patients, ablation during entrainment was used after technical difficulties in ablating during tachycardia. Only 1–3 radiofrequency applications were required to eliminate the accessory pathway using the entrainment technique. The catheter remained stable when accessory pathway conduction was interrupted by radiofrequency current. In conclusion, entrainment of atrioventricular reentrant tachycardia during radiofrequency application is useful for maintaining catheter position for accessory pathway ablation during atrioventricular reentrant tachycardia.
Clinical Surveillance of an Active Fixation, Bipolar, Polyurethane Insulated Pacing Lead, Part I: The Atrial Lead
Authors: GLIKSON MICHAEL , VON FELDT LINDA K. , SUMAN VERA J. , HAYES DAVID L.
Published: July 2006

Since 1989, 168 Telectronics model 330–801 active fixation, polyurethane insulated atrial leads (Accufix) have been implanted at the Mayo Clinic. There were four (2.4%) acute lead related complications, (i.e., perforation, microdislodgment, and pericarditis). Over a median follow‐up time of 7.6 months (up to 2.7 years), there were 14 (8.3%) chronic complications, including 1 instance (0.6%) of definite lead failure. Most of these complications were early (within the first month) and transient. Four patients (2.4%) required reoperation for chronic complications. During follow‐up, 23% of the examined patients had high pacing thresholds, most at about 3 months after implantation, necessitating high‐output programming. The exact mechanism and natural history of this phenomenon should be further investigated.
The Use of Serotonin Reuptake Inhibitors for the Treatment of Recurrent Syncope Due to Carotid Sinus Hypersensitivity Unresponsive to Dual Chamber Cardiac Pacing
Authors: GRUBB BLAIR P. , SAMOIL DANIELA , KOSINSKl DANIEL , TEMESY‐ARMOS PETER , AKPUNONU BASIL
Published: July 2006

Carotid sinus hypersensitivity can be a cause of recurrent unexplained syncope in the older patient. Dual chamber cardiac pacing may relieve the bradycardia, but may not affect the vasodilatory component of this disorder. We report on two patients with carotid sinus hypersensitivity with a predominant vasodilatory component who experienced recurrent syncope following permanent pacemaker implantation. Both patients were treated with serotonin reuptake inhibitors and after 4–6 weeks of therapy had complete resolution of symptoms. We conclude that serotonin reuptake inhibitors may be useful in the treatment of recurrent syncope due to carotid sinus hypersensitivity resistant to dual chamber cardiac pacing.
Long‐Term Follow‐Up of Patients with Single Lead VDD Stimulation
Authors: FOLINO ANTONIO F. , BUJA GIANFRANCO , RUZZA LUISA , NAVA ANDREA
Published: July 2006

The purpose of this study was to assess the long‐term results of a single lead VDD pacing system (Phymos MPS) in 85 patients (48 males, 37 females, mean age 74 ± 9 years). The system, which incorporates two atrial floating electrodes (Phymos 830‐S). was implanted for second‐ or third‐degree Mobitz II AV block. The percentage of AV synchronized pacing, the presence of fusion beats due to short AV delay, and the occurrence of supraventricuiar arrhythmias was evaluated by Holter monitoring at 6‐month intervals. Over a mean period of follow‐up of 44 months (range 2–56), over 90% of AV synchronized pacing events were noted in 74 patients (87%). The presence of persistent fusion beats was detected in 12 patients (14%). In ten patients the pacemaker was reprogrammed to VVI mode for supraventricuiar arrhythmias (7 patients, 8.2%) or unsatisfactory atrial sensing (3 patients, 3.5%). One pacemaker was removed for pocket infection and two for battery depletion. These observations support the use of VDD single lead pacing to combine a physiological mode of stimulation with simple implantation techniques.
Four Chamber Pacing in Dilated Cardiomyopathy
Authors: CAZEAU S. , RITTER P. , BAKDACH S. , LAZARUS A. , LIMOUSIN M. , HENAO L. , MUNDLER O. , DAUBERT J.C. , MUGICA J.
Published: July 2006

A 54‐year‐old man received a four chamber pacing system for severe congestive heart failure (NYHA functional Class IV). His ECG showed a left bundle branch block (200‐msec QHS duration) with 200‐msec PR interval, normal QRS axis, and 90‐msec interatrial interval. An acute hemodynamic study with insertion of four temporary leads was performed prior to the implant, which demonstrated a significant increase in cardiac output and decrease of pulmonary capillary wedge pressure. A permanent pacemaker was implanted based on the encouraging results of the acute study. The right chamber leads were introduced by cephalic and suhcla vian approaches. The left atrium was paced with a coronary sinus lead, Medtronic SP 2188–58 model. An epicardial Medtronic 5071 lead was placed on the LV free wall. The four leads were connected to a standard bipolar DDD pacemaker. Chorus 6234. The two atrial leads were connected via a Y‐connector to the atrial channel of the pacemaker with a bipolar pacing configuration. The two ventricular leads were connected in a similar fashion to the ventricular channel of the device. The right chamber leads were connected to the distal poles. The left chamber leads were connected to the proximal poles of the pacemaker. Six weeks later, the patient's clinical status improved markedly with a weight loss of 17 kg and disappearance of peripheral edema. His functional class was reduced to NYHA II. Four chamber pacing is technically feasible. In patients with evidence of interventricular dyssynchrony, this original pacing mode probably provides a mechanical activation sequence closer to the natural one. We doubt that this technique will have an impact on long‐term survival, but it could be of major importance to improve the patient's well‐being and control heart failure.
Early Complications After Dual Chamber Versus Single Chamber Pacemaker Implantation
Authors: CHAUHAN A. , GRACE A.A. , NEWELL S.A. , STONE D.L. , SHAPIRO L.M. , SCHOFIELD P.M. , PETCH M.C.
Published: July 2006

This study was performed to compare the frequency of early complications after single chamber versus dual chamber permanent pacemaker implantation. Early complication was defined as one occurring in the 6‐week period following implantation. We prospectively analyzed consecutive pacemaker implantation from January 1987 to June 1993 at our regional center. All complications were also analyzed for the relationship to operator experience, the venous access route, and the presence of temporary pacing wire at the time of implantation of the permanent pacing system. A total of 2019 new pacemaker units were implanted during this period. 1733 patients (85.8%) received a VVI pacemaker and 286 (14.2%) a DDD unit. Wound infection occurredin 11 (0.6%) VVI patients and 6 (2.1%) DDD patients. Lead displacement occurred in 18(1 %) VVI patients and 15 (5.2%) DDD patients (11 [3.8%] atrial and 4 [1.4 %] ventricular). There were 10 (0.6%)pneumothoraces, 9 (0.5%) hematomas requiring drainage, 1 (0.06%) chylocele, and 2 (0.1%) deaths in the VVI group. There were 2 (0.7%) pneumothoraces, 2 (0.7%) hematomas, and no deaths in the DDD group. There was no significant increase in complications for experienced infrequent implanters (< 12 systems per year). In both groups the subclavian approach was associated with a risk of pneumothorax when compared to the cephalic approach. The rate of wound infection was higher in patients who had a temporary pacing wire in place. The use of prophylactic antibiotics does not appear to affect the incidence of wound infection. The early complications in the DDD group were higher than in the VVI group (8.7% vs 2.9%, P < 0.05), being mainly due to an increased incidence of wound infection and atrial lead displacement.
Outcomes of an Ambulatory Cardiac Pacing Program: Indications, Risks, Benefits, and Outcomes
Authors: IRWIN MARLEEN E. , GULAMHUSEIN S.S. , SENARATNE M.P. , St. CLAIR W.R.
Published: July 2006

The purpose of this review was to evaluate the economical benefits and outcomes of an ambulatory pacing system implantation program that began in 1991 for new and replacement pacing system implantations. Patient access, incidetice of complications, hospital bed day utilization, economic impact, safety, and practicality of the Ambulatory Pacing System Implantation Program was retrospectively reviewed from August 1991 to March 1994. The Ambulatory Pacing System Implantation Program includes pre‐operative outpatient assessment in the pacemaker clinic, admission to the Day Medical Unit followed by same day pacing system implantation, discharge home after a short period of observation, and, in selected cases, cardiac monitoring, followed by pacemaker clinic visit 24‐hours postimplantation. Results: Two hundred four cardiac pacing systems, 154 new and 50 replacements (pulse generator/leads), were implanted under the guidelines of the Ambulatory Pacing System Implantation Program between August 1991 and March 1994. Eighty‐seven percent of the patients were implanted with passive fixation leads, the remaining with active fixation leads: all but four of which were leads implanted in the atria. Preprocedure wait time was decreased from 16 to 2 days for elective pacing system implantation. The incidence of lead dislodgment in the first, second, and third year of the Ambulatory Pacing System Implantation Program was 20%, 12%, 5%, respectively: compared to 11% for a similar number of cases in previous years done as inpatients. The incidence of new infection was 2.4% compared to < 1% in previous years. Six of the 204 (2%) cases required admission overnight. A total savings of 1,456 bed days ($1,275,450.00: Canadian) has been realized for an equivalent number of cases when compared with previous years. The operational cost was reduced by $3,976.00 per case. Conclusion: It has been shown that the Ambulatory Pacing System Implantation Program has improved client access, and is a safe and economical approach to implantation of cardiac pacing systems.
High Atrial Pacing Impedance: Efficient or Wasteful? A Comparison of an Active and a Passive Fixation Lead
Authors: SNOECK JOS , BERKHOF MARC , GOETHALS MARNIX , VRINTS CHRIS
Published: July 2006

We compared the stimulation characteristics of two atrial fixation leads: the CPI model 4269 (n = 45) and Cordis‐Telectronics model 327–752 (n = 42). The CPI lead uses an active fixation method, whereas the Cordis‐Telectronics lead is fixated passively. Impedance and threshold were measured at implant and during 12 months of follow‐up. P wave sensing was good with both types of leads. Follow‐up of these 87 leads showed that both the impedance and threshold increased with the active leads, but not with the passive fixation leads. In the active fixation group, regardless of the high atrial pacing impedance, 93% could still be programmed to 2.5 V‐0.6 msec (with a 2:1 threshold safety margin). It is concluded that the high chronic pacing impedance of the active fixation leads will be beneficial on current drain if no major increase in pacing threshold occurs simultaneously.
Modulation of the Electrical Restitution of Canine Purkinje Fibers by Local Anesthetic Drugs: A Study with Flecainide and Propafenone
Authors: MALFATTO GABRIELLA , ZAZA ANTONIO , SCHWARTZ PETER J.
Published: July 2006

Some antiarrhythmic drugs that depress conduction also influence action potential duration (APD). This could modify the time course of changes in the APD of premature stimuli (electrical restitution) and affect dispersion of repolarization and homogeneity of refractoriness. The effects of two potent local anesthetic drugs, i.e., flecainide and propafenone, on electrical restitution were studied in canine Purkinje fibers, superfused with Tyrode's solution and impaled with glass microelectrodes. APD was measured at 90% repolarization (APD90): fibers were stimulated for 3 minutes at cycle lengths (CLs) between 350 msec and 1.5 seconds, and kept quiescent for 5 minutes in between. For each run we calculated the percent ratio of the second APD (APD test = APDt) to the first APD after quiescence (APDo) (APDt/APD0× 100). The ratio was correlated with the CL of the run (i.e., the coupling interval between APD0 and APDt= CI) by the monoexponential function APDt/APDo× 100 = 100 ‐ exp(‐τ/CI), whose time constant τ indicates the speed of electrical restitution. At 1 μM, flecainide decreased τ by 26%± 4% (to 310 ± 41 msec from 245 ± 30 msec, n = 6, P < 0.05), while propafenone did not change it. Thus, unlike propafenone, flecainide slows the process of electrical restitution in Purkinje fibers. This may derive from the drug's action on currents other than Na current (i.e., Ik), relevant to the duration of action potential. In a reentrant circuit, despite similar effects on conduction, APD and refractoriness of the first beat would be differently modulated by flecainide and propafenone.
Inter‐ and Intraindividual Variations in Shortening of Ventricular Effective Refractory Period After an Abrupt Decrease in Pacing Cycle Length
Authors: LEERSSEN HENDRIK M. , VOS MARC A. , DULK KAREL Den , van der ZANDE JOLANDA , BEGEMANN MALCOLM J. , WELLENS HEIN J.
Published: July 2006

After an abrupt decrease in pacing cycle length (PCL), the ventricular effective refractory period (VERP) shortens. The pacing protocol needed to determine accurate and reproducible values for the VERP during this process is elaborate and time consuming. In this study, steady‐state values of VERP at 800 and 350 msec PCL and dynamic values of VERP due to an abrupt change in PCL from 800 to 350 msec were determined. This was done for 11 different dogs to test the interindividual variation and repetitively in the same dog to test the intraindividual variation. The results for steady‐state and dynamic values of the VERP show a wide range for both groups. This means that accurate prediction of steady‐state and dynamic values of VERP based on previous measurements is not possible.
Diagnosis of Atrial Arrhythmias Using the Holter Function of a New DDD Pacemaker
Authors: CAZEAU S. , RITTER P. , NITZSCHÉ R. , LIMOUSIN M. , MUGICA J.
Published: July 2006

The extension of random access memory now makes it possible to store electrocardiographic (ECG) information, referred to here as Holter function (HE), in the memories of new pacemakers, which can be used as diagnostic tools during long‐term follow‐up. This report describes our experience in 26 consecutive patients for whom the device was used to detect episodes of atrial arrhythmias (AA). An illustrative case is also presented to describe in detail the device's analytical method. Results: Fourteen AA profiles were successfully recorded in 10 patients by the pacemaker HF and correlated with confirmatory simultaneous surface ECG tracings. Three additional profiles were recorded in three other patients without simultaneous ECG recordings. A diagnosis of AA is established when the following findings are combined: (1) in all cases a large number of short interatrial inteivals (A INT); (2) in presence of AV block, interventricular intervals (VINT) stored between the lower programmed pacing rate and the upper rate limit or the fallback rate; (3) in absence of AV block, V INT stored between the basic rate and the AV node refractory period; (4) in case of fallback, (VVI function) no stored AV INT; and (5) in absence of fallback, great variability of AV INT (Wenckebach function). Conclusions: (1) Diagnoses of AA can be made with the pacemaker HE; (2) The homogeneity of the HF profiles makes them useful for long‐term follow‐up and will probably contribute and clarify the natural history of AA in DDD patients; (3) HF may also serve to monitor the safety and efficacy of antiarrhythmic drug therapy during long‐term follow‐up.
Ambulatory Assessment of the QT Interval in Patients with Hypertrophic Cardiomyopathy: Risk Stratification and Effect of Low Dose Amiodarone
Authors: FEI LÜ , SLADE ALISTAIR K. , GRACE ANDREW A. , MALIK MAREK , CAMM A. JOHN , McKENNA WILLIAM J.
Published: July 2006

This study aims to assess the dynamics of the QT interval in patients with hypertrophic cardiomyopathy (HCM). Three consecutive QT intervals and the preceding RR intervals were measured on 24‐hour ambulatory electrocardiograms at 30‐minute intervals in ten high risk patients with HCM (sudden cardiac death [SCD] and/or documented ventricular fibrillation), aged 29 ± 17 years, compared with ten age and sex matched low risk patients with HCM (no syncope, no adverse family history, and no ventricular tachycardia on Holter monitoring), and ten normal subjects. Another ten patients who were on amiodarone therapy (200‐mg daily) were also studied. Patients witb intraventricular conduction defects were excluded. There were 4,424 pairs of QT intervals and their preceding RR intervals were measured in this study. A nonsignificant prolongation in the QT interval and a significant prolongation in QTc values (Bazett's and Fridericia's formulas) were demonstrated in patients with HCM compared with normals. There were no significant differences in the QT and QTc between high and low risk patients. The slope of regression line for the QT against RR interval was significantly different between normals and HCM (0.1583 ± 0.040 vs 0.2017 ± 0.043. P < 0.05), but not between high and low risk patients. Amiodarone significantly prolonged the QT and QTc without significantly altering the slope of the regression line (0.2017 ± 0.043 vs 0.2099 ± 0.037, NS). Our findings support the observations that there is a prolonged QT interval in patients with HCM and that there is no significant use dependent effect of amiodarone on ventricular repolarization. In conclusion, ambulatory assessment of the QT interval provides an alternative method for the assessment of ventricular repolarization and for the assessment of use dependent effects of anti arrhythmic drugs on ventricular repolarization during normal daily activities. However, this method does not help in the identification of patients at high risk of SCD in HCM.
Sudden Death and Staged Therapy for Hemodynamic Stabilization in Patients Enrolled in a Heart Transplantation Program
Authors: FREY BERNHARD , WUTTE MICHAEL , BERGER RUDOLF , IOANNIDES CLEANTHIS , HÜLSMANN MARTIN , STANEK BRIGITTE , PACKER RICHARD
Published: July 2006

To investigate the impact of staged therapy for advanced heart failure on therapeutic endpoints, 236 consecutive patients (coronary artery disease/dilated cardiomyopathy in 61/175 patients, left ventricular ejection fraction 14%± 5%, New York Heart Association Class IIl/IIIIV in 102/79/55 patients, respectively) with advanced heart failure were prospectively followed. One hundred thirtyseven patients enrolled from January 1989 to December 1991 were treated conventionally with digoxin, furosemide, and low dose angiotension converting enzyme (ACE) inhibition. Patients refractory to this therapy underwent urgent heart transplantation. Ninetynine patients enrolled from January 1992 to August 1993 underwent staged therapy: stage 1: maximal tolerated ACE inhibition; stage 2: therapy with PGE1 for preand afterload reduction to achieve hemodynamic stabilization; or stage 3: refractory patients bridged to heart transplantation with continuous outpatient dobutamine. Sudden death was defined as death within 1 hour of symptoms if heart failure symptoms remained stable over the previous 7 days. Conventionally treated patients were followed for 10 ± 9 months; patients who underwent staged therapy for 9 ±5 months. In the group of patients that underwent standard therapy, 39 of 137 (28%) patients died: 5 (13%) deaths occurred suddenly, and death due to progressive pump failure occurred in the remaining 34 (87%) patients. In the group of patients that underwent staged therapy, 25 of 99 (25%) patients died: 13 (52%) deaths occurred suddenly, and 12 (48%) deaths occurred due to progressive pump failure. Thus, patients who underwent staged therapy were at increased risk for sudden death (P = 0.01, relative risk 3.4, 95% confidence interval 1.2–9.7) but were at lower risk for death from pump failure (P = 0.009, relative risk 0.44, 95% confidence interval 0.22–0.84). In patients who underwent therapy with continuous outpatient PGE1 (n = 7) or dobutamine (n= 21), risk for sudden death (P = NS by log rank test) did not increase. In conclusion, staged therapy significantly reduced death from pump failure; however, patients who could be stabilized and considered too well for heart transplantation were at increased risk for sudden death. Thus, overall survival did not improve. Of note, outpatient dobutamine did not increase the risk for sudden death.
Initial Clinical Experience with a Dual Lead Endocardial Defibrillation System with Atrial Pace/Sense Capability
Authors: LUCERI RICHARD M , ZILO PHILIP ,   THE UNITED STATES,   CANADIAN ENGUARD INVESTIGATORS
Published: July 2006

Ninety‐three patients underwent implants of the Telectronics Model 4211 ICD attached to the Enguard PFX endocardial defibrillation lead system. Eighty‐one males and 12 females ranging in age from 25–85 years (mean= 64). Coronary disease was the substrate in the majority (88%); mean left ventricular ejection fraction was 30%. VT was present in 66%, VF in 22%, and both in7%, Three lead configurations were used in the study: ventriculo‐atrial (Ul, 86%); bidirectional (B2,12%); and ventricular to patch (U2, 2%). Mean RVpacing thresholds were 0.46 V preand 0.54 Vposttesting, with no significant differences between the two. Mean R wave voltage was 11.05 mVpreand 11.72 mV posttesting, also not significantly different. A subgroup of 13 patients had mean atrial pacing thresholds of 0.59 V at 0.5 msec pulse width, with mean P waves of 4.01 mV. Mean defibrillation threshold for the entire group was 10.6 J using biphasic waveforms. Defibrillation thresholds by configuration were: 399 V (U1);475 V(U2);and350 V(B2). All patients but one had thresholds ±550 V in at least one configuration. The 4211/Enguard system was implanted without (86%) or with (14%) a subcutaneous patch electrode. Early postoperative findings related to the ICD system include: one device circuit failure, one early lead dislodgement, and one pacing exit block. There were five patient deaths during the follow‐up period of 8.5 months: three cardiac nonsudden and two noncardiac. These data suggest that the 4211/Enguard defibrillation system can be successfully implanted in the majority of patients in need of such therapy.
Transthoracic DC Shock May Represent a Serious Hazard in Pacemaker Dependent Patients
Authors: ALTAMURA GIULIANO , BIANCONI LEOPOLDO , LO BIANCO FRANCESCO , TOSCANO SALVATORE , AMMIRATI FABRIZIO , PANDOZI CLAUDIO , CASTRO ANTONIO , CARDINALE MARIO , MENNUNI MAURO , SANTINI MASSIMO
Published: July 2006

External defibrillation is widely used for the termination of various atrial and ventricular tachyarrhythmias, including pacemaker patients. Our study was intended to evaluate the effects of DC shocks in 36 patients with unipolar pacemakers implanted in the right pectoral region (25 DDD, 10 VVI, 3 AAI). The shocks were delivered with paddles on the anterior surface of the thorax, as far as possible away from the pacemaker. The pacing output was programmed at 0.5 msec and 5 V (25 patients), 4 V (1 patient), and 2.5 V (10 patients). Transient loss of capture occurred in 18 patients (50%). These patients, compared with those without capture failure, received higher peak and cumulative shock energies, respectively, 216 ± 99 versus 123 ± 50 joules (P < 0.002) and 352 ± 62 versus 147 ± 98 joules (P < 0.004) and had a lower pacemaker pulse amplitude (4.0 ± 1.2 vs 4.6 ± 1.0 V, P = 0.11). Failure to capture lasted from 5 seconds to 30 minutes (mean 157 sec). In 15 patients the ventricular stimulation threshold was measured before and serially after cardioversion. A six‐fold threshold increase was observed 3 minutes after the shock (P < 0.004) with gradual recovery to nearly baseline values at 24 hours. Transient sensing failure occurred in 7 of the 17 patients in whom it could be evaluated (41%). Furthermore, three cases of shock induced pacemaker malfunctions were observed requiring replacement of the stimulator in two patients. In conclusion, the incidence of loss of capture in pacemaker patients subjected to electrical cardioversion/defibrillation is high. The phenomenon is due to an abrupt rise in stimulation threshold, caused by the electrical shock, and may represent a serious hazard in pacemaker dependent patients. The risk of pacing failure could be reduced by utilizing low shock energies when possible, and by programming the pacemaker at its maximal output before cardioversion.
Analog‐Digital Recording of Current and Voltage During High Voltage DC Shocks
Authors: PETERS WERNER , SCHARF RAINER , MEESMANN MALTE
Published: July 2006

Efficient on‐line digitization is the prerequisite for computerized analysis of the electrical phenomena occurring during defibrillation. Conventional hardware presently provides only limited time resolution. The performance of various digitization rates for recording of voltage, current, and calculation of derived quantities like impedance, energy, and defibrillator capacitance was investigated. It was assessed both experimentally and by computer simulation of a trapezoidal discharge (of 9 msec duration into a constant resistive load of 50 Ω with a defibrillator capacitance of 132 μF). The accuracy achieved with different digitization rates is given. For example, an accuracy of 1% for analog‐digital conversion for impedance calculation during this kind of DC shock requires a sampling rate of 8 kHz without, and a rate of 1 kHz with linear interpolation to correct for the hardware dependent error due to sequential sampling.

Conclusion: Highly efficient analog‐digital conversion of delivered voltage and current during DC shocks is available within the limits of conventional inexpensive hardware.
Woven Wire Patches Are Superior to Solid Disks for Subcutaneous Electrodes: Implications for Active Can Defibrillation
Authors: LEONELLI FABIO M. , WRIGHT HART , BREWER JAMES E. , ADAMS TED P. , KROLL MARK W.
Published: July 2006

The housing of the implantable cardioverter defibrillator (ICD) is being considered for a remote electrode to replace the conventional subcutaneous woven wire patch. It is not clear that the solid smooth and rigid metal surface of the ICD housing will provide the same performance as does the woven wire patch. We compared a solid titanium disk to a titanium woven wire patch for defibrillation performance in a canine model. The patch had a smaller outline area, a slightly smaller conductive perimeter, and slightly less of a small feature surface area than did the disk. The remote electrode (disk or patch) was inserted at the point of maximal apical cardiac impulse. A commercially available endocardial electrode was placed in the right ventricle (RV). Conventional biphasic shocks (140‐μFrench capacitor and 65% tilt) were delivered between the RV and subcutaneous electrode. The patch had significantly lower resistances than did the disk (81.6 ± 8.0 Ω vs 90.0 ± 11.6 Ω P < 0.006). The patch also had significantly lower stored energy defibrillation thresholds than did the disk (8.0 ± 2.6 J vs 9.3 ± 3.3 J, P < 0.007). In spite of smaller values for every geometrical dimension, the woven wire patch out performed the solid disk for defibrillation with conventional biphasic waveforms. Since the ICD housingis typically smooth titanium, the use of waveforms better suited for the active can configuration may deserve a systematic evaluation.
Long‐Term Follow‐Up of Pacemaker Lead Systems: Establishment of Standards of Quality
Authors: FURMAN SEYMOUR , BENEDEK Z. MICHAEL , ANDREWS CAROLYN A. , GROSS JAY N. , RITACCO ROSEANNE
Published: July 2006

The functional details of all 5,405 pacemaker leads implanted on Montefiore Medical Center were contemporaneously recorded between 1960 and May 31, 1993. Some models have been observed for as long as 24 years. Ventricular leads with more than 50 and atrial leads with more than 30 implanted units have been continually and repeatedly subjected to actuarial cumulative survival rate (CSR) analysis during which clinical decisions, such as continued lead implantation, cessation of use, or early withdrawal from service, were made. CSR evaluation for many lead models by the Mantel‐Haenszel method allowed comparison of the performance of contemporaneous lead models with older and new technologies. No effect on lead longevity, durability, on mode of end of lead service, lead removal independent of function (e.g., for infection), materials, or physiological failure was found due to an operator or anatomical route of venous access. Multifilar silicone rubber insulated leads have longevity (CSR) superior to monofilar silicone rubber leads. The cumulative survival of silicone rubber insulated monofilar models 6901, 6907, continuous lead (CL), 4 mm, and 2 mm was 79%–91%, 20 years after implantation. Multifilar silicone rubber insulated models 6961 and4116hada cumulative survival of 99%–100%, 15 years after implantation. Among m ultifilar polyurethane insulated leads, distinct longevity differences exist between form ulations and contemporaneous models that are normally similar, yielding a bimodal longevity distinction; model 6971 (ventricular) has 95% CSR and 6991U (atrial) has 94% CSR, 10 years after implantation. Both performed less well than other contemporaneous models, which approximate 100% CSR. The 10 year CSR for leads implanted between 1960–1975 (Era 1) is 98.7%, and the 10‐year CSR of leads implanted between 1981–1985 (Era 3) is 99.4%. Comparison of individual lead models, and all leads of specific eras, allows development of survival expectations and standards of quality for comparison between contemporaneous lead models and different eras of manufacture. As the highest available lead CSR sets the standard, statistical deviation of a model from the best performance of a specific era should be considered as an indication of reduced quality.
The Left Subclavian Vein as an Alternative Site for Implantation of the Second Defibrillation Lead
Authors: MARKEWITZ ANDREAS , KAULBACH HANS , MATTKE SÖREN , DORWARTH UWE , HOFFMANN ELLEN , WEINHOLD CHRISTIAN , STEINBECK GERHARD , REICHART BRUNO
Published: July 2006

The optimal placement for the second defibrillation lead in a twolead system has never been addressed. We retrospectively reviewed the data of 33 patients with an average age of 59.2 years (range 41–78 years), predominantly mala (n = 29), who underwent implantation of a cardioverter defibrillator (ICD) for treatment of ventricular tachycardia (n = 19) or ventricular fibrillation (n = 14). In all patients an attempt was made to implant an endovenous ICD device (leads only, no subcutaneous patch). In group I (n = 18) the defibrillation anode, a separate unipolar lead, was placed in the common position, the superior vena cava. In group II (n =15) the lead was placed in the left subclavian vein. At least two consecutive shocks reverting ventricular fibrillation at energies ±24J were required for implantation of the ICD device. All shocks were monophasic. The success rate of endovenous defibrillation was significantly higher in group II than in group I (67% vs 28%, P < 0.05). Thus, it could be demonstrated that the position of the defibrillation anode can influence the defibrillation efficacy in transvenous ICD systems. Prospective randomized trials are needed to investigate the optimal position for the second defibrillation electrode, which may gain increasing importance as soon as dual chamber ICDs become available.
How Do Physicians Determine When to Perform an “On‐Drug” Electrophysiology Study for Efficacy Determination in Patients with Sustained Ventricular Tachyarrhythmias: A Previously Unaddressed Variable That May Affect Efficacy Rates
Authors: REIFFEL JAMES A. , BANKER JEFFREY
Published: July 2006

In patients with ventricular tachyarrhythmias, efficacy rates of antiarrhythmic agents, as judged by serial electrophysiological (EP) tests, have been variable. Factors underlying this variability have been reported to include: specific drug, type of arrhythmia, type of heart disease, left ventricular function, and number of prior drug failures. We hypothesized that variability in physician practice behavior as to when a drug assessment is performed might be another important factor affecting drug efficacy. Using a survey sent to 103 electrophysiology centers we determined from the 46 respondents that this is indeed the case. Twenty‐six of the 46 respondents always, 9 of 46 sometimes, and 11 of 46 did not require ectopy reduction on continuous electrocardiographic monitoring before proceeding to an EP study. The ectopy reduction required, however, varies among physicians in percentage and type. Twenty‐seven of the 35 respondents who utilize rhythm monitoring also require attainment of an acceptable blood level, a prespecified minimal target dose, and/or one or more ECG interval changes prior to proceeding to EP testing. Fifteen out of 46 do not require “therapeutic” drug levels. Of 11 who don't use rhythm monitoring, 5 also don't use blood levels. The lower value for “therapeutic ranges” varied by up to 3‐fold and the upper value by up to 2 1/2‐fold for individual drugs. The minimum time for testing varied from 1 half‐life to over 10 half‐lives. Similarly, the response to failure of a submaximal dose also varied: 9% always retested at a high dose, 2% never tested at a higher dose, and 91 % were inconsistent. Moreover, what was considered the maximal dose for an individual drug varied by 3‐ to 6‐ fold for most agents queried. We believe these variations in dose, time, and coassessment factors must have an influence on efficacy rates of antiarrhythmic agents.
Clinical Comparison of Acute Single to Dual Chamber Pacing in Chronotropically Incompetent Patients with Left Ventricular Dysfunction
Authors: BARRINGTON WILLIAM W. , WINDLE JOHN R. , EASLEY ARTHUR R. , RUNDLETT REBECCA , EISENGER GEORGE
Published: July 2006

Dual chamber, rate responsive (DDDR) pacing is felt to be superior to ventricular, rate responsive (VVIR) pacing since it more closely mimics the normal electrical and hemodynamic activity of the heart. This reasoning has been used to justify the higher initial costs and increased complexity of dual chamber systems. This study was designed to determine if objective criteria could be identified during acute testing to justify implanting a dual chamber instead of a single chamber system in patients with left ventricular dysfunction. Eight patients with DDDR pacemakers (implanted for chronotropic incompetence) and left ventricular dysfunction underwent exercise radionuclide angiography and graded exercise treadmill testing. Each patient performed the tests in the single (VVIR) and dual (DDDR) chamber modes in a randomized, blinded fashion. We found that objective parameters such as ejection fraction (31%± 13% vs 31%± 10%), exercise tolerance (6.1 ± 2.7 min vs 6.3 ± 2.9 min), oxygen consumption (VO2) (941 ± 286 mL/min vs 994 ± 314 mL/min), carbon dioxide production (VCO2) (995 ± 332 mL/min vs 1054 ± 356 mL/min), and maximum attainable workload (43 ± 24 W vs 46 ± 22 W) did not differ between the single and dual chamber pacing modes. These findings suggest that in the acute setting, the additional cost and complexity of dual chamber, rate responsive pacing cannot be justified by objective improvements in exercise tolerance in patients with underlying left ventricular dysfunction.