Showing papers in "Journal of Interventional Cardiac Electrophysiology in 2000"

Clinical relevance of silent atrial fibrillation: prevalence, prognosis, quality of life, and management.

Abstract: Although first described about 100yr ago, atrial fibrillation (AF) is now recognized as the most common of all arrhythmias. It has a substantial morbidity and presents a considerable health care burden. Improved diagnosis and an ageing population with an increased likelihood of underlying cardiac disease results in AF in more than 1% of population. AF is associated with an approximately two-fold increase in mortality, largely due to stroke which occurs at an annual rate of 5-7%. Another risk to survival is heart failure, which is aggravated by poor control of the ventricular rate during AF. Usually AF is associated with a variety of symptoms: palpitations, dyspnea, chest discomfort, fatigue, dizziness, and syncope. Paroxysmal AF is likely to be symptomatic and frequently presents with specific symptoms, while permanent AF is usually associated with less specific symptoms. However, in at least one third of patients, no obvious symptoms or noticeable degradation of quality of life are observed. This asymptomatic, or silent, AF is diagnosed incidentally during routine physical examinations, pre-operative assessments or population surveys. Recently, a very large incidence of generally short paroxysms of AF has been seen in patients with implantable pacemakers or defibrillators and these arrhythmias are often silent. Pharmacological suppression of arrhythmia may be associated with a conversion from a symptomatic to an asymptomatic form of AF. Holter monitoring and transtelephonic monitoring studies have demonstrated that asymptomatic episodes of AF exceed symptomatic paroxysms by twelve-fold or more. Although symptoms may not stem directly from AF, the risk of complications is probably the same for symptomatic and asymptomatic patients. AF is found incidentally in about 25% of admissions for a stroke. Studies in patients with little or no awareness of their arrhythmia condition indicate that unrecognized and untreated AF may cause congestive heart failure. In patients with coronary bypass, AF may not only represent risk for immediate postoperative morbidity and increase hospital resource utilization, but being unrecognized, may produce a significant impact on long-term survival and quality of life. Although silent AF merits consideration for anticoagulation and rate control therapy according to standard criteria, whether antiarrhythmic therapy is relevant in this condition remains unclear.

The effect of ablation sequence and duration on lesion shape using rapidly pulsed radiofrequency energy through multiple electrodes

Abstract: Sequences of energy application to multiple electrodes and a study of ablation duration with distal tip and multi-electrode ablations were explored with a radiofrequency controller that distributes energy from a generator to up to 4 electrodes with various duty cycles. In vitro ablations were performed on bovine left ventricle in circulating blood and lesions in goats were performed to verify the in vitro results.

Biventricular pacing in end-stage heart failure improves functional capacity and left ventricular function.

Abstract: Background Asynchronous patterns of contraction and relaxation may contribute to hemodynamic and functional impairment in heart failure. In 1993, we introduced biventricular pacing as a novel method to treat heart failure by synchronous stimulation of the right and left ventricles after an appropriate atrioventricular delay. The objectives of this study were to assess the early and long-term effects of this therapy on functional capacity and left ventricular function in patients with severe heart failure and left bundle branch block. Methods and Results Twelve patients with end-stage congestive heart failure, sinus rhythm and complete left bundle branch block were treated with biventricular stimulation at optimized atrioventricular delay. The NYHA functional class and maximal bicycle exercise capacity were assessed. Systolic and diastolic left ventricular function were studied with echocardiography and radionuclide angiography. Data was collected at various intervals during 1-year follow-up. Cumulative survival [95% CI] was 66.7% [40.0,93.4] at 1 year and 50 % [21.8, 78.2] at 2 and 3 years. Median NYHA class improved from class IV to class II at 1 year (p=0.008). After 6weeks an increase in exercise capacity occurred, which was sustained. A less restrictive left ventricular filling pattern, an increase in dP/dt and left ventricular ejection fraction, and a decrease in mitral regurgitation were observed early and long-term. Conclusions Biventricular pacing at optimized atrioventricular delay results in improvement in functional capacity, which is associated with improved systolic and diastolic left ventricular function, and a decrease in mitral regurgitation during short- and long-term follow-up.

Is there an adverse outcome from abandoned pacing leads

Abstract: Background. Indications for extraction of an abandoned pacemaker lead (APL) are controversial. The purpose of this study was to determine whether or not APLs should be extracted in the absence of pacemaker-related problems. Methods and Results. We retrospectively reviewed, from 1977 through 1998, all patients with retained, non-functional leads and identified 433—266 males and 167 females. Mean age at initial pacemaker implantation was 68[emsp4 ]years. These patients received a total of 259 atrial and 948 ventricular leads. Of the total of 1,207 leads, 611 became non-functional. A total of 531 non-functional leads were abandoned, of which 18 were later extracted: one APL in 345 patients, two in 78, and three in 10. Indications for new lead placement when non-functional leads were abandoned included capture and/or sensing failure (243), lead recall (177), lead fracture (86), pacing system replacement to the contralateral side (11), accommodating patient growth (5), pacemaker function upgrade (5), replacement with implantable cardioverter defibrillator (ICD, 2), interference with ICD (1), and unknown (1). Complications that were associated with pacemakers were found in 24 patients (5.5%)—pacemaker system infection (8 patients) and venous occlusion at the time of a subsequent procedure of new lead placement when APLs had already been in place (16) which resulted in APL extraction (7) or transfer of the pacemaker system to the contralateral side (9). Neither venous thrombosis nor other complications were found in the remaining 409 patients (94.5%). The incidence of complications was higher in patients with three APLs than in patients with two or fewer APLs (40% vs. 4.7%, P=1×10−6), in patients with four or more total lead implantations than in patients with three or fewer total lead implantations (26.2% vs. 0.6%, P<1×10−10), and in patients with three or more procedures of new lead placements than in patients with two or fewer procedures of new lead placements (36.4% vs. 3.9%, P=1×10−10). Patients with complications were younger than those without complications both at the time of initial pacemaker implantation (59±16 vs. 68±17[emsp4 ]y, P=0.01) and when non-functional leads were abandoned (63±15 vs. 71±16[emsp4 ]y, P=0.04). Mean numbers of APLs, total leads implanted, and procedures of new lead placement were significantly larger in patients with complications than in those without complications (1.58±0.78 vs. 1.2±0.44, 4.96±1.23 vs. 2.66±0.8, and 2.13±0.85 vs. 1.25±0.53, P=0.03, 4×10−9 and 4×10−5, respectively). Conclusions. 1. With only 5.5% of patients having had pacemaker-related complications, the adverse outcome of APL is small. 2. Clinical clues to the possible occasion for pacemaker-related complications include three or more APLs, four or more total leads, three or more procedures of new lead placement, and a younger age at initial pacemaker implantation. 3. Patients with a large number of APLs, total lead implantations, and procedures of new lead placement should be carefully observed to detect possible pacemaker-associated complications.

Electrode impedance: an indicator of electrode-tissue contact and lesion dimensions during linear ablation.

Abstract: Pre-ablation impedance was evaluated for its ability to detect electrode-tissue contact and allow creation of long uniform linear lesions with a multi-electrode ablation catheter. The study consisted of 2 parts, both of which used the in vivo pig thigh muscle model. In part 1, a 7 Fr. multi-electrode catheter was held in 3 electrode-tissue contact conditions: (1) non-contact; (2) light contact with a 30[emsp4 ]g downward force; and (3) tight contact with a 90[emsp4 ]g downward force. Impedances were measured in unipolar, modified unipolar and bipolar configurations using a source with frequencies from 100[emsp4 ]Hz to 500[emsp4 ]kHz. Compared with non-contact, the impedance increased 35±22±% with 30[emsp4 ]g contact pressure and 68±40±% when the contact pressure was increased to 90[emsp4 ]g across the range of frequencies studied. In part 2, the same catheter was held against the tissue with different forces. Pre-ablation impedance was measured using a 10[emsp4 ]kHz current. Phased radiofrequency energy was applied to the 5 electrodes simultaneously using 10[emsp4 ]W power at each electrode for 120[emsp4 ]s. A total of 32 linear lesions were created. The lesion dimensions correlated with pre-ablation impedance. A unipolar impedance ≥190[emsp4 ]Ω indicates 95±% possibility to create a uniform linear lesion of at least 3[emsp4 ]mm depth with our ablation system. We conclude that pre-ablation impedance may be a useful indicator for predicting electrode-tissue contact and the ability to create a continuous and transmural linear lesion with a multi-electrode catheter.

A Targeted Disruption in Connexin40 Leads to Distinct Atrioventricular Conduction Defects

Abstract: Introduction: Gap junctions consist of connexin (Cx) proteins that enable electrical coupling of adjacent cells and propagation of action potentials. Cx40 is solely expressed in the atrium and His-Purkinje system. The purpose of this study was to evaluate atrioventricular (AV) conduction in mice with a homozygous deletion of Connexin40 (Cx40−/−). Methods: Surface ECGs, intracardiac electrophysi-ology (EP) studies, and ambulatory telemetry were performed in Cx40−/− mutant mice and wild-type (WT) controls. Atrioventricular (AV) conduction parameters and arrhythmia inducibility were evaluated using programmed stimulation. Analysis of heart rate variability was based on results of ambulatory monitoring. Results: Significant findings included prolonged measures of AV refractoriness and conduction in connexin40-deficient mice, including longer PR, AH, and HV intervals, increased AV refractory periods, and increased AV Wenckebach and 2:1 block cycle lengths. Connexin40-deficient mice also had an increased incidence of inducible ventricular tachycardia, decreased basal heart rates, and increased heart rate variability. Conclusion: A homozygous disruption of Cx40 results in prolonged AV conduction parameters due to abnormal electrical coupling in the specialized conduction system, which may also predispose to arrhythmia vulnerability.

Early ECG abnormalities associated with transcatheter closure of atrial septal defects using the Amplatzer septal occluder.

Abstract: Conduction abnormalities and arrhythmias may occur in patients following secundum atrial septal defect (ASD) closure using the Amplatzer® septal occluder (ASO). Therefore, the aim of this study was to prospectively perform ambulatory ECG monitoring to assess the electrocardiographic effects of transcatheter closure (TCC) of ASD using the ASO device. From 5/97 to 3/99, 41 patients with secundum ASD, underwent TCC using the ASO device at a median age of 9.2[emsp4 ]y. (0.5–87[emsp4 ]y.) and median weight of 34[emsp4 ]kg (5.6–88[emsp4 ]kg.). Ambulatory Holter monitoring was performed pre- and immediately post TCC. Holter analysis included heart rate (HR), ECG intervals, supraventricular ectopy (SVE), ventricular ectopy (VE), and AV block. No change in baseline rhythm was noted in 37 patients (90%). Changes in AV conduction occurred in 3 patients (7%), including intermittent second degree AV block type II, and complete AV dissociation post closure. SVE was noted in 26 patients (63%) post closure, ranging from 5–2207 supraventricular premature beats (SVPB), including 9 patients (23%) with non-sustained supraventricular tachycardia (SVT), 3 of whom had short runs of SVT prior to closure. A significant increase in post-closure number of SVPB per hour (p=0.047) was noted. No significant difference was noted in PR interval, ventricular premature beats per hour, or QRS duration. Conclusions: Based on ambulatory ECG analysis, TCC of ASD with the ASO device is associated with an acute increase in SVE and a small risk of AV conduction abnormalities, including complete heart block. Long term follow-up studies will be necessary to determine late arrhythmia prevalence and relative frequency compared with standard surgical ASD repair.

Progressive atrioventricular conduction block in a mouse myotonic dystrophy model.

Abstract: Introduction: Myotonic dystrophy is caused by expansion of a CTG trinucleotide repeat on human chromosome 19, and leads to progressive skeletal myopathy and atrioventricular conduction disturbances. A murine model of myotonic dystrophy has been designed by targeted disruption of the myotonic dystrophy protein kinase (DMPK) gene. The DMPK-deficient mice display abnormalities in A-V conduction characteristics, similar to the human cardiac phenotype. The purpose of this study was to determine whether age-related progression of A-V block occurs in a mouse model of DMPK-deficiency.

Case report: pulmonary vein stenosis following RF ablation of paroxysmal atrial fibrillation: successful treatment with balloon dilation.

Abstract: Paroxysmal atrial fibrillation and atrial tachycardia may originate from a focal source in one or multiple pulmonary veins. A focal origin facilitates a potential cure amendable to radiofrequency ablation. Herein we report the case of a 16 year old adolescent male with a tachycardia induced cardiomyopathy who presented with very frequent paroxysmal episodes of atrial fibrillation, atrial flutter and atrial tachycardia. The origin of the arrhythmia was mapped to the secondary branches of the left lower pulmonary vein using an octapolar micro-mapping catheter. Immediately following application of three radiofrequency lesions, angiography of the left lower pulmonary vein revealed a region of focal stenosis at the site of energy application, with delayed pulmonary venous emptying. Attempts to relieve any element of spasm using direct administration of nitroglycerin were unsuccessful. Three months later repeat catheterization revealed an unchanged region of tight anatomical stenosis. Balloon dilation of two stenotic areas resulted in dramatic relief of the obstruction and improved venous drainage. Recatheterization 6 months later revealed mild restenosis that was successfully redilated. Intracardiac ultrasound demonstrated focal constriction. Care should be exercised in attempting RF ablation in distal arborization sites of the pulmonary veins in children, because of the small caliber compared to adult subjects. Radiofrequency induced focal areas of stenosis may be amenable to balloon catheter dilation.

Endovascular neural stimulation via a novel basket electrode catheter: comparison of electrode configurations.

Abstract: We previously showed that parasympathetic stimulation by a basket electrode catheter (BEC) positioned in the superior vena cava (SVC) can slow sinus rate (SR) or ventricular response (VR) during atrial fibrillation (AF). In 11 dogs, anesthetized with Na-pentobarbital, standard ECG leads II and aVR, blood pressure and right atrial electrograms were continuously monitored. Two different BEC configurations (B1, B2) were tested in the SVC. B1 consisted of five metal splines, each 3cm in length. Stimulation was applied between adjacent splines. B2 consisted of 2 electrodes at opposite ends of each of 5 splines and a larger electrode at the middle of each spline. Stimulation was delivered between the two end electrodes and the middle electrode on the same arm. Stimulation consisted of square wave stimuli, each 0.1msec duration, frequency 20Hz at voltages from 1–40V. Six dogs were studied with B1 and five were studied with the B2 configuration. The average voltage required to produce a 50% decrease in heart rate was 22± 12V when stimulating between adjacent splines (B1) compared to 10± 5V when stimulating along a single spline (B2), a 55% decrease (p≤0.05). During AF, the voltage required to reduce the average ventricular rate to 100beats/min was 19± 13V for B1 and 8± 5V for B2, a 58% reduction (p≤0.05). Thus, the significant difference between B1 and B2 and in slowing SR or VR during AF was probably due to a greater current density delivered with B2 to the endovascular wall and adjacent neural elements.

Microwave radiometric thermometry and its potential applicability to ablative therapy.

Abstract: Introduction: Current techniques for estimating catheter tip temperature in ablative therapy for cardiac arrhythmias rely on thermocouples or thermistors attached to or embedded in the tip electrode These methods may reflect the electrode temperature rather than the tissue temperature during electrode cooling so that the highest temperature away from the ablation site may go undetected A microwave radiometer is capable of detecting microwave radiation as a result of molecular motion In this study, we evaluated microwave radiometric thermometry as a new technique to monitor temperature away from the electrode tip during ablative therapy utilizing a saline model Methods and Results: A microwave radiometer antenna and fluoroptic thermometer were inserted in a test tube with circulating room temperature saline kept constant at 235°C while the surrounding saline bath was heated from 37°C to 70°C For every degree rise in the warm saline bath placed either 5mm or 8mm from the radiometer antenna, the radiometer temperature changed 026°C and 014°C respectively while the fluoroptic temperature probe remained constant at 235°C The radiometer temperature was highly correlated with the warm saline bath temperature (R2=0997 for warm saline 5mm from the antenna, R2=0991 for warm saline 8mm from the antenna) Conclusions: Microwave radiometry can estimate distant temperatures by detecting microwave electromagnetic radiation The sensitivity of the microwave radiometer is also distance-dependent The microwave radiometer thus serves as a promising instrument for monitoring temperatures at depth away from the catheter-electrode tip in ablative therapy for cardiac arrhythmias

The MUSTT study: evaluating testing and treatment.

Abstract: The multicenter unsustained tachycardia trial (MUSTT) tested the value of electrophysiologically guided antiarrhythmic drug therapy against no therapy in high risk coronary artery disease with poor left ventricular function (LV-EF ≤ 40%) and nonsustained ventricular tachycardia. Risk assessment was performed by testing inducibility of a sustained ventricular tachycardia. The primary endpoint of the study was sudden arrhythmic death or cardiac arrest. Significant information on risk stratification was gathered by the follow-up of patients that were noninducible. Although MUSTT was not a specific ICD trial for primary prevention of SCD the results of the trial revealed that only with ICD back-up—a significant reduction of arrhythmic death or cardiac arrest can be achieved. EP-guided antiarrhythmic drug treatment had a lower incidence of SCD/CA compared to no treatment (12% versus 25%, p = 0.043, hazard ratio 0.73 after 24 months and 18% versus 32% after 60 months). A subgroup analysis showed that the benefit of antiarrhythmic treatment was only due to ICD implantation. No difference was found between those inducible pts treated exclusively with antiarrhythmic drugs and those who were randomized to no drug treatment. Patients who were not inducible did significantly better than pts who were inducible wether or not treated with antiarrhythmic drugs. MUSTT results strengthen the data of the MADIT study. They confirm the inducibility testing as the most accurate risk stratifier. MUSST demonstrated the poor value of serial EP drug testing as well as the risk of “stand alone” antiarrhythmic drug treatment.

Atrial fibrillation: role of arrhythmogenic foci.

Abstract: Atrial fibrillation, the most common of all sustained cardiac arrhythmias can be cured by Surgical atriotomies or linear RF catheter ablation. We have investigated the role of focal RF ablation in paroxysmal atrial fibrillation

The effect of a residual isthmus of surviving tissue on conduction after linear ablation in atrial myocardium.

Abstract: The aim of this study was to determine the relationship between the size of discontinuities in lines of ablation and wavefront propagation. Discontinuities in linear radiofrequency lesions used for the treatment of atrial fibrillation may be proarrhythmic and a major clinical problem. A better understanding of the electrophysiological properties of these discontinuities (isthmuses) may assist in their detection and treatment. Linear lesions were made in the right atrial free wall using a Nd:YAG laser in 12 dogs. Conduction properties across the discontinuities were studied by pacing from either side of the lesion. Two of the three isthmuses less than 0.8mm2 in cross section (smallest 0.2mm2) conducted at extrastimulus intervals of 300ms. All three failed to conduct at cycle lengths close to the atrial effective refractory period. Isthmuses above 0.8mm2 (n}=8) conducted at all cycle lengths. Conduction slowing (mean slowest conduction 0.5\plusmn; 0.3m/s) occurred in the region of the isthmus but the overall delay was only 6plusmn; 6ms where propagation through the isthmus occurred. The effect on conduction of small discontinuities in linear lesions is dependent on the size of the residual isthmus. All but the very smallest of discontinuities in linear lesions conduct and therefore have the potential to participate in reentrant arrhythmias. Efforts should be directed toward the development of ablation techniques that reliably produce continuous transmural linear lesions for cure of atrial fibrillation and flutter.

Quality of life in atrial fibrillation.

Abstract: In patients with atrial fibrillation (AF), the restoration and maintenance of sinus rhythm is the primary therapeutic goal. Once sinus rhythm is maintained, physiological rate control is restored, and left ventricular ejection fraction, cardiac output, and exercise capacity are increased. This improved cardiovascular performance thereby enhances the patient's ability to perform the functions of normal daily life. The primary intervention for maintaining sinus rhythm after restoration is the use of anti-arrhythmic agents. Although physicians mostly use class 1A anti-arrhythmic drugs, these oral agents only maintain sinus rhythm in a limited number of cases and are accompanied by considerable side effects. Therefore, more effective tools are needed. Effective treatment for AF is based on the above objective criteria, but subjective criteria such as the quality of life are growing in importance. To address these quality-of-life issues, we have initiated a prospective study in which patients are assigned to one of two groups: those with paroxysmal AF who are candidates for permanent implantable atrial defibrillators and those with chronic or paroxysmal AF who are not candidates for atrial defibrillators. Specifically designed questionnaires and various standardized and validated instruments are used to measure quality of life. The questionnaires cover social demographic data, including age, education, occupation level, driving behavior, return to work, and sexual activity. Quality of life is a multidimensional construct, and thus its definition must consider the many factors mentioned above. In the final analysis, therefore, both objective and subjective criteria are necessary to define appropriate treatment of AF.

The AFFIRM trial: main trial and substudies-what can We expect?

Abstract: The clinical categorization of patients who present with atrial fibrillation is a major determinant of the most appropriate strategy for rhythm management. For those patients with recurrent atrial fibrillation that has not become permanent the two available strategies are rhythm control and anticoagulation or rate control and anticoagulation. There is no clear evidence that one of these strategies is superior to the other. In the AFFIRM trial these two strategies are being compared to one another in a randomized trial. Patients are randomly assigned to one of the two strategies and the treating physician then uses therapies from an approved menu as clinically indicated. Both pharmacologic and nonpharmacologic therapies are used. An overview of the main study protocol is presented. The primary endpoint is total mortality but there are a number of clinically important secondary endpoints. Several substudies will explore important ancillary questions and some of these are also described. At this time over 3000 patients have been enrolled and the planned enrollment is 4300. Enrollment will end late in 1999 and the last patient enrolled will be followed for two years. The AFFIRM Trial will provide important information concerning the management of atrial fibrillation in a large portion of the patients who have this arrhythmia.

Transcatheter cryoablation of ventricular myocardium in dogs.

Abstract: Introduction: Surgical cryoablation, a highly effective technique used during antiarrhythmic surgery, produces voluminous, histologically uniform and discreet myocardial lesions. In contrast, radiofrequency (RF) catheter ablation, which as a result of its less invasive nature has largely supplanted antiarrhythmic surgery, produces smaller, histologically heterogeneous myocardial lesions. Since small lesion size and heterogeneity may reduce antiarrhythmic efficacy, we sought to reproduce the large, histologically homogeneous lesions created by surgical cryoablation, using a catheter cryoablation system (Cryogen, Inc., San Diego, CA) in the canine ventricle. Methods and Results: In seven dogs, nineteen ventricular lesions (two right and seventeen left) were created with a 10F cryoablation catheter with either a 2 or 6[emsp4 ]mm tip. In one dog AV node ablation was also performed. For each 'freeze', catheter tip nadir temperature, lesion width, depth, and transmurality were recorded, and lesion volume calculated. Average tip nadir temperature was −79.6±4.9°C. Cooler nadir tip temperature was associated with deeper (p=.007) and more voluminous lesions (p=.042), and a greater likelihood of lesion transmurality (p=.034). Average lesion volume was 500±356[emsp4 ]mm3. No other variables predicted lesion volume or transmurality. Histologically, the catheter cryoablation lesions were sharply demarcated and homogeneous. The single freeze performed at the AV junction produced complete AV block. One complication, catheter rupture following its repetitive use, resulted in a coronary air embolus and death. Conclusion: Catheter cryoablation of canine ventricular myocardium produced voluminous, discrete, transmural lesions, which might be effective for ablation of ventricular tachycardia. Lesion volume and transmurality were dependent on catheter tip nadir temperature.

Clinical experience with implantable atrial and combined atrioventricular defibrillators.

Abstract: The high prevalence of atrial fibrillation (AF) and its clinical complications, the poor efficacy of medical therapy for preventing recurrences, and dissatisfaction with alternative modes of therapy stimulated interest in implantable atrial and combined atrioventricular defibrillators. In a multicenter study, the safety and efficacy of a stand alone implantable atrial defibrillator, the Metrix system, were evaluated. The device was implanted in 51 patients with highly symptomatic episodes of AF refractory to pharmacological treatment. During a follow-up of 9 months, 96% of 227 spontaneous AF episodes were successfully converted to sinus rhythm in 41 patients. In 62 episodes (27%), several shocks and/or additional drug treatment were required to maintain stable sinus rhythm because of early recurrences of AF. A total of 3719 shocks were delivered and no induction of ventricular proarrhythmia or inaccurately synchronized shocks occurred. The AF detection algorithm exhibited a 100% specificity for the recognition of sinus rhythm and a 92.3% sensitivity for the detection of AF. The combined atrioventricular defibrillator, Jewel AF 7250, was evaluated in a multicenter, randomized, cross-over trial. The primary study objectives included: overall safety as determined by complications-free survival at 6 months, efficacy of tiered atrial pacing and defibrillation therapies for termination of spontaneous atrial tachycardias (AT) and AF, and relative sensitivity of a new dual-chamber detection algorithm. The device was implanted in 211 patients with either a history of ventricular tachyarrhythmias (VT/VF) alone or with a history of both AT/AF and VT/VF. During a mean follow-up of 4.5 months, it has been shown that the Jewel AF is safe and effective in treating atrial and ventricular tachyarrhythmias. Pace termination of 85% of AT episodes were achieved with painless delivery of antitachycardia pacing; additional 35% of AT episodes were terminated by high frequency burst pacing. Conclusions: The stand alone implantable atrial defibrillator may be safe and clinically useful in selected patients for the treatment of highly symptomatic, drug resistant recurrences of AF. The combined atrioventricular defibrillator may be particularly indicated in patients presenting with both a history of atrial and ventricular tachyarrhythmias.

Cardiac lead extraction with a novel locking stylet.

Abstract: Extraction of chronically implanted pacing and defibrillator leads is facilitated by using specialized locking stylets placed in the lead to allow application of traction and to stabilize the lead during sheath dissection of fibrotic tissue. We report the initial multicenter series of cases using a novel lead locking device (LLD). In 57 consecutive patients presenting at 6 institutions for lead extraction, 99 leads were treated using the LLD. After removing the pulse generator, leads were severed, the inner coil dilated and an LLD was successfully inserted and locked in the inner lumen of 95/99 (96 %) leads. With traction applied to the LLD, a variety of sheaths were advanced over the lead body to separate it from adhesions. In 97/99 (98 %) leads, all or most of the lead was removed via the implant vein; 2 leads were removed via the femoral vein. No major complications were observed. The LLD deploys safely and reliably, and provides stable support for advancement of dissecting sheaths.

Increased defibrillation threshold with right-sided active pectoral can.

Abstract: The aim of this study was to identify the optimal position on the chest wall to place an implant able cardioverter defibrillator in a two-electrode system, consisting of a right ventricular electrode and active can. Methods and Results: Defibrillation thresholds (DFT) were measured in 10 anaesthetised pigs (weight 33–45kg). An Angeflex™ lead was introduced transvenously to the right ventricular apex. The test-can (43cc) was implanted submuscularly in each of four locations: left pectoral (LP), right pectoral (RP), left lateral (LL) and apex (A). The sequence in which the four locations were tested was randomized. Ventricular fibrillation (VF) was induced using 60Hz alternating current. Rectangular biphasic shocks were delivered 10 seconds after VF induction. The DFT was measured using a modified four-reversal binary search. The results of the four configurations were: LP, 14.6± 4.0J; RP, 18.8± 4.2J; LL, 14.7± 4.1J; A, 14.9± 3.1J. Repeated measures analysis of variance showed that the DFT of RP was significantly higher than LP, LL and A (p < 0.05). Conclusions: Implanting an active can in the RP position increases the DFT by 29% compared to LP, LL and A sites. The can position on the left thorax does not appear to have a significant influence on DFT.

Threshold tracking pacing based on beat by beat evoked response detection: clinical benefits and potential problems.

Abstract: Continuous monitoring of pacemaker stimulation thresholds and automatic adjustment of pacemaker outputs were among the longstanding goals of the pacing community. The first clinically successful implementation of threshold tracking pacing was the Autocapture feature which has accomplished automatic ventricular capture verification for every single stimulus by monitoring the Evoked Response (ER) signal resulting from myocardial depolarization. The Autocapture feature not only decreases energy consumption by keeping the stimulation output slightly above the actual threshold, but also increases patient safety by access to high-output back-up pulses if there is loss of capture. Furthermore, it provides valuable documentation of stimulation thresholds over time and serves as a valuable research tool. Current limitations for its widespread use include the requirements for implantation of bipolar low polarization leads and unipolar pacing in the ventricle. Fusion/pseudofusion beats with resultant insufficient or even non-existent ER signal amplitudes followed by unnecessary delivery of back-up pulses and a possible increase in pacemaker output is not an uncommon observation unique to the Autocapture feature. The recent incorporation of the Autocapture algorithm in dual chamber pacemakers has been challenging because of more frequent occurrence of fusion/pseudofusion beats in the presence of normal AV conduction. Along with a review of the previously published studies and our clinical experience, this article discusses the clinical advantages and potential problems of Autocapture.

Prevention of short term reversible chronic atrial fibrillation by permanent pacing at the triangle of Koch

Abstract: Objectives: The purpose of this study was to investigate if single lead interatrial septum pacing could be effective in maintaining sinus rhythm in patients in whom restoration of sinus rhythm was only possible for a period of 2–24 hours after one or more previous electrical cardioversions, and in whom a sinus bradycardia was documented before arrhythmia restarted. The two hours limit was chosen because it was considered a sufficient time to implant a dual chamber pacemaker.

Novel catheter technology for ablative cure of atrial fibrillation.

Abstract: Atrial ~brillation (AF) is the most common sustained arrhythmia in clinical practice. It affects approximately 2,000,000 Americans with 160,000 new cases per year. Drug therapy can be associated with a number of untoward effects such as proarrhythmia, long term inef~cacy and even an increase in mortality, especially in those with impaired ventricular function [1,2]. Catheter ablation of the atrioventricular node with pacemaker implantation [3,4], or modi~cation of the AV node without pacer implantation [5,6] can be useful to facilitate ventricular rate control, but thromboembolic risk is unchanged and atrial systole is not restored. Given the limitations of medical therapy, repeated cardioversions and atrioventricular conduction ablation, an approach that cures atrial ~brillation would be highly desirable. At the present time, catheter-based cure of atrial ~brillation must be considered highly investigational. Nevertheless, because the clinical need for better therapy of atrial ~brillation is so vast, there are a number of on-going efforts to develop devices and techniques for atrial ablation in order to effectively restore sinus rhythm and atrial mechanical contraction. Do we need a cure for atrial ~brillation? Certainly, given the problems with drug treatment and the impact on quality of life, a cure would be highly desirable, and efforts to create such a cure well rewarded. In the history of electrophysiologic intervention, there are many examples in which a cycle of clinical science and new interventional techniques has been demonstrated. That is, we start with a given hypothesis of arrhythmia mechanism or substrate, we intervene to alter what we believe to be the substrate (with surgery, or with catheter-based techniques), in the process of intervention we have an opportunity to garner further, more accurate insights into mechanism and substrate and to develop subsets of what we has thought was a single disorder, and this in turn allows us to develop better interventional tools and techniques. For example, all regular narrow complex tachycardias used to go by the moniker of “PAT.” First with surgery, and then with catheter-based techniques, we came to be able to discern that “PAT” may actually be one of several speci~c arrhythmia substrates such as WPW, AV nodal reentry, etc. In the era of catheter ablation, we can now even describe three or more types of AV nodal reentry. So, too, our ability to intervene on patients with atrial ~brillation has just begun to allow us to develop more detailed descriptions of mechanism. “Atrial ~brillation” as such may come to be recognized as the common surface manifestation of multiple potential mechanisms. This will allow us to develop tools and techniques that are more directly targeted to a given mechanism. In the case of atrial ~brillation this will be particularly important, since if one considers the current “gold standard” for curative intervention to be the extensive lesions produced during the Cox surgical maze operation, then recognition of AF mechanisms that require a less extensive lesion set would be highly desirable. Recently, it has come to be understood that the initiating event in many cases of AF is a “focal trigger” arising in the vast majority of cases from within one of the pulmonary veins [7]. The purpose of the present paper is to brie_y describe early progress towards the development of a novel technology addressing this particular class of AF mechanism.

Early detection of lead fracture by painless high voltage lead impedance measurement in a transvenous ICD lead system.

Abstract: We report the case of a 69 year old patient, who underwent transvenous implantable cardioverter defibrillator (ICD) device change (Medtronic GEM VR 7227 Cx Active Can) because the ICD reached its replacement indicators. Preoperative chest X-ray and intraoperative defibrillation threshold tests and high voltage impedance did not show lead fracture of the five year old lead (Transvene 6936-65). At the second postoperative day the alarm of the newly implanted ICD device was activated because of high impedance in the painless lead impedance measurement (PLI) and the lead was replaced. The explanted lead showed a fracture detectable only by PLI.

Electrophysiological heterogeneity of atrial fibrillation and local effect of propafenone in the human right atrium: analysis based on symbolic dynamics.

Abstract: A recently developed algorithm that is based on symbolic dynamics and computation of the normalized algorithmic complexity (Cα) was applied to basket-catheter mapping of the atrial fibrillation (AF). The aim of our study was to analyze the spatial distribution of the Cα during AF and effects of propafenone on this distribution. During right atrial mapping in 25 patients with AF 31 intra-atrial and 1 surface bipolar channels were acquired. The anatomical location of the intra-atrial electrodes was defined fluoroscopically. Cα was calculated for a moving window (size: 2000 points; step 500 points). Generated Cα was analyzed within 10 minutes before and after administration of propafenone. The inter-regional Cα distribution was analyzed using the Friedman-test (intra-individually) and Kruskall-Wallis-H-test (inter- individually). A value of p=0.05 was set for an error probability. Inter-regional Cα differences were found in all patients (p<0.001). The right atrium could be divided in high- and low complexity areas according to individual patterns. A significant Cα increase in cranio-caudal direction (with the exception of septum) was confirmed inter-individually (p<0.01). The administration of propafenone enlarged the areas of low complexity.

Combining antiarrhythmic drugs and implantable devices therapy: benefits and outcome.

Abstract: At least 50% of patients who received an ICD have been treated with antiarrhythmic drugs (AAD). The potential indications for combining antiarrhythmic drugs and ICD are generally the following: reduction of the number of episodes of ventricular tachycardia or ventricular fibrillation and therefore of the number of shocks, improving patient's quality of life and extending the battery life of the ICD, prevention of supraventricular arrhythmias and/or control of their rate, lengthening of the tachycardia cycle length to allow ventricular tachycardia conversion by antitachycardia pacing and reduction of the number of episodes of syncope. Although previous papers reported conflicting results about pharmacologic therapy in reducing the frequency of iCD shocks, some recent randomized prospective studies showed the efficacy of pharmacologic therapy in reducing the frequency of ICD shocks. The use of antiarrhythmic drugs can have also adverse effect: an increase in the defibrillation threshold, an increase in the pacing threshold and an increase in the VT cycle length leading to detection failure. We have also to consider that some advantages derived from antiarrhythmic drugs can be reached by the new devices with atrial sensing and pacing and/or the possibility of atrial defibrillation or by using catheter ablation as adjunctive therapy to ICD. For these reasons, the concomitant use of antiarrhythmic drugs and ICD should be evaluated in each patient in relation to specific clinical and electrophysiologic features including: the frequency, the rate and the clinical presentation of the ventricular arrhythmia, the effect of the selected drug on the defibrillation threshold, the defibrillation threshold at the implant, the effect of the selected drug on the ventricular function and the likelihood of proarrhythmic events.

New devices and hybrid therapies and new devices for treatment of atrial fibrillation.

Abstract: Atrial ~brillation [AF] is the most common arrhythmia, whose prevalence is expected to increase with aging of our population. It is a potentially disabling illness with an independent contribution to morbidity and mortality [1,2]. Due to recurrent nature of arrhythmia and lack of uniformally effective therapy, treatment of AF has been a frustrating task for the clinician. Pharmacologic approaches when used alone have poor long-term ef~cacy with 50% to 70% of patients eventually progressing to chronic AF [3,4]. It also carries the risk of proarrhythmia and may increase mortality especially in patients with left ventricular dysfunction [5,6]. Several new nonpharmacologic technologies, pacing, ablation and implantable atrial de~brillators, are being developed and seem to improve outcome of therapy for AF in different patient subgroups. All these therapies, however, when applied alone have limited ef~cacy, patient acceptance, questionable practicality or relatively high incidence of serious complications. Therefore, there is an increased interest in combination/hybrid therapy where few different therapeutic modalities are used in a given patient in an attempt to achieve synergistic effect, increase their ef~cacy over any single approach while decreasing side effects and improve tolerance.

A Novel Indication for Transvenous Lead Extraction: Upgrading Implantable Cardioverter Defibrillator Systems

Abstract: Technological advances have resulted in the development of dual chamber pacemaker/defibrillator systems with smaller pectoral 'active cans'. Patients now have the option of upgrading from abdominal to pectoral or from single to dual chamber devices. In addition, due to the potential complications which may arise with abandoned ICD leads, extraction of preexisting leads may be preferable. Methods and Results: Twenty consecutive patients (11 males), underwent lead extraction and upgrade, either from an abdominal to a pectoral, or from a single to a dual chamber device. The mean age was 62±18[emsp4 ]years and mean implant duration was 50±14 months. Indications for extraction included lead fracture/malfunction (13), ERI/EOL (2), new SVT/VT (2), long charge times (2), and impending erosion (1). An initial attempt was made to remove the lead with gentle traction. If excessive scar tissue prohibited extraction, then a laser sheath was employed. Reimplantation proceeded following standard protocol. Clinical success was achieved in all patients. Eleven of thirty leads were removed with traction. The remaining 19 leads required removal with the laser sheath. All ICD reimplants were placed in the left pectoral position, of which 10 were dual chamber. The mean defibrillation threshold was 9.5±5.8 Joules. There were no procedure related perforations or deaths. At follow up (13±10 mos.) there were no infections, lead malfunctions or venous thromboses. There were two deaths, both from intractable heart failure. Conclusions: This study demonstrates that, when indicated, ICD leads can be safely extracted and systems successfully upgraded to take advantage of new technology.

Electrophysiologic assessment in selecting patients for multisite atrial pacing.

Abstract: Electrophysiologic mechanisms of atrial fibrillation (AF) initiation are being actively studied. Multisite atrial pacing has shown, in acute studies, significant potential for prevention of AF. Dual site pacing reduces of intra and inter-atrial conduction time, atrial refractoriness dispersion, and to a limited extent atrial premature beats which modify the atrial remodelling induced by AF. Recently, two clinical trials have shown long term efficacy of multisite atrial pacing. At 3 years of follow-up, 56% of patients are free of AF recurrence with dual site right atrial pacing. Rhythm control was achieved in 86 of patients. Similar results are observed with biatrial resynchronization. In both studies, primary indication for multisite atrial pacing was AF prevention in more than 50% of patients. Selection of patients based solely on long P wave duration and prolonged interatrial conduction is not necessary as clinical outcome and comparable. These patients are comparable to patients who did not have these characteristics. Ongoing multicenter trials will likely definitively answer this question. However, preexcitation of diseased atrial regions or site of ectopic activity previously selected by high density atrial mapping or suppression of inducible AF may offer an interesting future development of multisite atrial pacing.