Implantable atrial defibrillator with a single-pass dual-electrode lead

OBJECTIVES

We examined the feasibility and efficacy of using a single-pass, dual-electrode (Solo) lead for atrial fibrillation (AF) detection and defibrillation.

BACKGROUND

The efficacy and safety of an implantable atrial defibrillator (IAD) has been extensively studied; however, separate right atrial (RA) and coronary sinus (CS) defibrillation leads are used for the present system.

METHODS

We studied the use of the Solo lead for AF detection and defibrillation in 17 patients who underwent cardioversion of chronic AF. The Solo lead with a proximal 6-cm RA electrode and a distal 6-cm spiral-shaped CS electrode were positioned into the CS with the RA electrode against the anterolateral RA wall. The RA-CS electrogram signal amplitudes were measured and the efficacy of the Solo lead for AF detection and defibrillation was assessed by using an external version of the IAD.

RESULTS

The leads were inserted in all patients without complication (mean fluoroscopy time: 13.3 ± 6.8 min). The mean RA-CS signal amplitude was 484 ± 229 μV during sinus rhythm and 274 ± 88 μV during AF (p < 0.05). All patients had satisfactory atrial signal amplitude to allow accurate detection of sinus rhythm. Successful cardioversion was achieved in 16/17 (94%) patients with an atrial defibrillation threshold of 320 ± 70 V (5.5 ± 2.7 J). Insufficient interelectrode spacing resulted in suboptimal electrode locations, associated with a lower atrial signal amplitude, a higher atrial defibrillation threshold and diaphragmatic stimulation.

CONCLUSIONS

These results suggest a simplified lead configuration with optimal interelectrode spacing can be used with an IAD for AF detection and defibrillation.     

Pacemaker Repetitive Nonreentrant Ventriculoatrial Synchronous Rhythm. A Review

The normal functioning of dual chamber pacemaker-cardioverter defibrillator (AV pacer/ICD) may be affected by oversensing of the farfield R wave (FFRW) by the atrial channel. This study aimed to investigate whether placement of the AV pacer/ICD's atrial lead at a lateral (LAT) wall location compared to a medial (MED) location i.e. the appendage of the right atrium, would reduce the amplitude of FFRWs but not the nearfield atrial electrograms (AEGMs) during sinus rhythm (SR) and ventricular fibrillation (VF). In 17 patients, real time electrograms were recorded during SR and induced VF through the atrial lead initially at the MED and subsequently at the LAT location. In 10 patients the electrograms in SR were also recorded on a computerized data acquisition and recording system at different band-pass filter settings. Although FFRWs were recorded both at MED and LAT locations, they were much smaller, 3.5±4.1[emsp4 ]mm during SR and 1.7±2.2[emsp4 ]mm during VF at the LAT location. At 30–500[emsp4 ]Hz band-pass filter, lower amplitudes of FFRWs 0.14±0.09[emsp4 ]mV were recorded at the LAT location. The V/A ratios of the amplitudes of FFRWs and AEGMs were smaller at the LAT location during SR and VF. The nearfield AEGMs were of similar amplitudes at the MED and LAT locations. These data indicate that lower amplitudes of FFRWs are recorded by placement of the atrial lead at the lateral wall of the right atrium. Oversensing of FFRWs may be prevented to improve functioning of the AV pacer-ICD.     

Low-Energy Transvenous Cardioversion of Atrial Fibrillation Using a Single Atrial Lead System

Atrial Cardioversion Using a Single Atrial Lead System. Introduction: Clinical studies have shown that electrical conversion of atrial fibrillation (AF) is feasible with transvenous catheter electrodes at low energies. We developed a single atrial lead system that allows atrial pacing, sensing, and defibrillation to improve and facilitate this new therapeutic option. Methods and Results: The lead consists of a tripolar sensing, pacing, and defibrillation system. Two defibrillation coil electrodes are positioned on a stylet-guided lead. A ring electrode located between the two coils serves as the cathode for atrial sensing and pacing. We used this lead to cardiovert patients with acute or chronic AE. The distal coil was positioned in the coronary sinus, and the proximal coil and the ring electrode in the right atrium. R wave synchronized biphasic shocks were delivered between the two coils. Atrial signal detection and pacing were performed using the proximal coil and the ring electrode. Eight patients with acute AF (38 ± 9 min) and eight patients with chronic AF (6.6 ± 5 months) were included. The fluoroscopy time for lead placement was 3.5 ± 4.3 minutes. The atrial defibrillation threshold was 2.0 ± 1.4 J for patients with acute AE and 9.2 ± 5.9 J for patients with chronic AF (P < 0.01). The signal amplitude detected was 1.7 ± 1.1 mV during AF and 4.0 ± 2.9 mV after restoration of sinus rhythm (P < 0.001). Atrial pacing was feasible at a threshold of 4.4 ± 3.3 V (0.5-msec pulse width). Conclusions: Atrial signal detection, atrial pacing, and low-energy atrial defibrillation using this single atrial lead system is feasible in various clinical settings. Tbis system might lead to a simpler, less invasive approach for internal atrial cardioversion.     

Incidence of Atrial Fibrillation Following Ventricular Defibrillation with Transvenous Lead Systems in Man

Atrial Fibrillation After Ventricular Defibrillation. Introduction: The induction of atrial fibrillation (AF) following implantable defibrillator therapy of ventricular fibrillation carries multiple risks. The frequency of shock-induced AF may be more problematic in patients with transvenous defibrillators because current is often delivered through atrial tissue. Thus, the purpose of this study was to determine the incidence of AF following transvenous ventricular defibrillation. Methods and Results: Atrial electrograms were recorded before and after energy delivery in patients undergoing intraoperative testing of transvenous defibrillation lead systems. A total of 114 tracings were examined from 21 patients following ventricular defibrillation. Transvenous deflbrillation shock strength ranged between 200–800 volts (2–40 joules). Bipolar atrial electrograms were obtained from atrial electrodes with 1-cm interelectrode spacing located on one of the defibrillation catheters. The timing of the ventricular defibrillation shock was expressed as a percentage of the preceding sinus PP interval. Three of the 114 transvenous shocks (2.6%) generated AF. Each episode of AF occurred in a different patient. The shocks responsible for AF occurred at 21%, 43%, and 84% of the preceding sinus PP interval. No relation was found between AF induction and the timing of pulse delivery, pulse strength, or pulse number. Conclusion: We conclude that transvenous ventricular defibrillation infrequently causes AF and that timing shock delivery to the atrial cycle is likely to be of marginal or no benefit in the prevention of shock-induced AF. (J Cardiovasc Electrophysiol, Vol. 3, pp. 411–417, October 1992)     

Optimum lead positioning for recording bipolar atrial electrocardiograms during sinus rhythm and atrial fibrillation

Background: To date, Holter monitoring has been predominantly utilized in the investigation and monitoring of ventricular arrhythmias and myocardial ischemia. Whether currently employed lead configurations are optimal for recording atrial electrocardiograms (ECGs) is unknown. Hypothesis: This study was undertaken to determine which conventional and novel lead configurations are optimal for recording atrial electrical activity during sinus rhythm and atrial fibrillation. Methods: Recordings were performed on eight healthy volunteers in sinus rhythm and four patients in atrial fibrillation. Each subject had 10 ECGs of three bipolar and three augmented unipolar leads recorded during supine rest, while rising to upright, and during standing rest, yielding a total of 60 leads (30 bipolar leads). Each tracing was inspected by two observers, and parameters such as P-wave amplitude and duration, whether the P-wave onset was clearly seen, atrial fibrillatory-wave amplitude, and amplitude of noise during standing were scored. Results: Leads recording interiorly and leftward orientated bipoles provided the best registration of sinus P waves. The Pwave amplitude in the standard bipolar C5 lead (0.12 d? 0.02 mV) was, however, inferior to others such as recordings between Cl and C6 positions (P-wave amplitude 0.16 d? 0.02 mV) or from below the right clavicle to the left upper quadrant of the abdomen (0.16 d? 0.01 mV). Optimal recording of fibrillatory waves was from different leads, such as a bipole from below the left clavicle to a low C1 position (fibrillatory wave amplitude 0.27 d? 0.03 mV). Conclusion: When Holter recordings are performed for the investigation of atrial arrhythmias, nonstandard lead configurations provide superior recording of atrial electrical activity. We advocate the use of electrodes positioned from C1 to C6, from below the left clavicle to a low C1 position, and a vertically orientated lead from the manubium to the twelfth vertebra or the xiphisternum.     

Nutzen einer VDD-Defibrillationselektrode zur Aufzeichnung von atrialen Elektrogrammen bei Vorhofflimmern/-flattern

BACKGROUND: Monitoring of atrial signals improves the accuracy in identifying supraventricular tachyarrhythmias to prevent inappropriate therapies in patients with implantable cardioverter-defibrillators (ICD). Since complications due to the additional atrial lead were found in dual chamber ICD systems with 2 leads, we designed a single-pass VDD-lead for use with dual chamber ICDs. PATIENTS AND METHODS: After promising animal experiments in a German multicenter study a prototype VDD lead (single-coil defibrillation electrode with 2 additional fractally coated rings for bipolar sensing in the atrium) was temporarily used in 20 patients. Atrial and ventricular signals were recorded during sinus rhythm, atrial flutter, atrial fibrillation and ventricular tachycardia or ventricular fibrillation. Terminations of ventricular arrhythmias were performed by internal DC shock. RESULTS: The implantation of the electrode was successful in 18 of 20 patients. Mean atrial pacing threshold was 2.45 +/- 0.9 V/0.5 ms, mean atrial impedance was 215 +/- 31 Ohm. Atrial amplitudes were greater during sinus rhythm (2.7 +/- 1.6 mV) than during atrial flutter (1.36 +/- 0.28 mV, p < 0.05) or atrial fibrillation (0.92 +/- 0.29 mV, p < 0.01). During ventricular fibrillation atrial "sinus"-signals had significantly (p < 0.01) lower amplitudes than during sinus rhythm. Mean ventricular sensing was 13.3 +/- 7.9 mV, mean ventricular impedance was 577 +/- 64 Ohm. Defibrillation was successful with 20 J shock. 99.6% of P waves could be detected in sinus rhythm and 85 +/- 9.9% of flutter waves during atrial flutter. During atrial fibrillation 55% of atrial signals could be detected without modification of the signal amplifier. CONCLUSIONS: A new designed VDD dual chamber electrode provides stable detection of atrial and ventricular signals during sinus rhythm and atrial flutter. For reliable detection of atrial fibrillation modifications of the signal amplifier are necessary.     

The new selective IKs–blocking agent HMR 1556 restores sinus rhythm and prevents heart failure in pigs with persistent atrial fibrillation

Background Antiarrhythmic drugs for treatment of atrial fibrillation in patients with heart failure are limited by proarrhythmia and low efficacy. Experimental studies indicate that the pure I_Ks blocking agents chromanol 293b and HMR 1556 prolong repolarization more markedly at fast than at slow heart rates and during –adrenergic stimulation. These properties may overcome some of the above quoted limitations. Methods and results Ten domestic swine underwent pacemaker implantation (PM) and atrial burst pacing to induce persistent AF. Four days after onset of persistent AF, pigs were randomized to HMR 1556 (30 mg/kg, p.o., 10 days) or placebo. All animals receiving HMR 1556 converted to SR (5.2 ± 1.9 days), whereas placebo pigs remained in AF. Pigs treated with placebo developed high ventricular rates (297 ± 5 bpm) and severe heart failure, whereas pigs treated with HMR 1556 remained hemodynamically stable. Left ventricular ejection fraction on the day of euthanization was significantly lower in the placebo compared to the HMR 1556 group (30 ± 4% vs. 69 ± 5%, p < 0.005). Similar results were seen with epinephrine levels (placebo 1563 ± 193 pmol/l vs. HMR 613 ± 196 pmol/l, p < 0.05). Right atrial monophasic action potentials were significantly longer in the HMR 1556 compared to the placebo group (230 ± 7 ms vs. 174 ± 13 ms, p < 0.05). Conclusions The new I_Ks blocker HMR 1556 efficiently and safely restores SR and prevents CHF in a model of persistent AF. Restoration of SR is most likely linked to a marked prolongation of atrial repolarization even at high heart rates.     

Atrial defibrillation with a transvenous lead: a randomized comparison of active can shocking pathways.

OBJECTIVES: The purpose of this study was to compare transvenous atrial defibrillation thresholds with lead configurations consisting of an active left pectoral electrode and either single or dual transvenous coils. BACKGROUND: Low atrial defibrillation thresholds are achieved using complex lead systems including coils in the coronary sinus. However, the efficacy of more simple ventricular defibrillation leads with active pectoral pulse generators to defibrillate atrial fibrillation (AF) is unknown. METHODS: This study was a prospective, randomized assessment of shock configuration on atrial defibrillation thresholds in 32 patients. The lead system was a dual coil Endotak DSP lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and an active can in common with the proximal atrial coil (triad) or between the atrial coil and active can (transatrial). RESULTS: Delivered energy at defibrillation threshold was 7.1 +/- 6.0 J in the transatrial configuration and 4.0 +/- 4.2 J in the triad configuration (p < 0.005). Moreover, a low threshold (< or = 3 J) was observed in 69% of subjects in the triad configuration but only 47% in the transatrial configuration. Peak voltage and shock impedance were also lowered significantly in the triad configuration. Left atrial size was the only clinical predictor of the defibrillation threshold (r = 0.57, p < 0.002). CONCLUSIONS: These results indicate that low atrial defibrillation thresholds can be achieved using a single-pass transvenous ventricular defibrillation lead with a conventional ventricular defibrillation pathway. These data support the development of the combined atrial and ventricular defibrillator system.     

Role of oral amiodarone in patients with atrial fibrillation and congestive heart failure

Background

Amiodarone is recognized as the most effective therapy for maintaining sinus rhythm (SR) post cardioversion in patients with atrial fibrillation (AF). It is also recommended for controlling AF in patients with congestive heart failure (CHF). We retrospectively examined the efficacy and safety of oral amiodarone in patients with AF and CHF.

Methods

Forty-eight consecutive AF patients whose left ventricular ejection fraction (LVEF) was less than 50% and B-type natriuretic peptide (BNP) was higher than 100 pg/ml were investigated retrospectively, and divided into 3 groups: paroxysmal AF, 16 patients; persistent AF, 9 patients; and permanent AF, 23 patients.

Results

The permanent AF group had a longer history of AF, larger left ventricular end-diastolic diameter (LVDd) and left atrial diameter (LAD) than paroxysmal and persistent AF groups (p < 0.05). After median follow-up of 265 days, amiodarone suppressed paroxysms in 88% of paroxysmal AF patients, while SR was maintained in all persistent AF patients, and 35% of permanent AF patients. Of the 32 persistent and permanent AF patients, 12 (71%) out of 17 maintained SR after successful electrical cardioversion, and conversion to SR occurred spontaneously in 5 (33%) out of 15. The effective group had significantly smaller LVDd and LAD than the ineffective group. In the effective group, BNP decreased significantly from 723 ± 566 pg/ml to 248 ± 252 pg/ml, (p < 0.0005) and LVEF increased significantly from 33 ± 7% to 50 ± 13% (p < 0.0005) during follow up, while no changes were observed in the ineffective group. The patients with low LVEF (≤30%) benefited comparably from amiodarone to the patients with LVEF >30%. Complications occurred in 24 (50%) patients leading to discontinuation of amiodarone in 11 (23%).

Conclusions

Oral amiodarone helped restore SR in paroxysmal and persistent AF patients with CHF. The successful rhythm control by amiodarone resulted in the improvement of LV function and the decrease of BNP levels.     

Interatrial septum pacing: A new approach to prevent recurrent atrial fibrillation.

Background. There are a variety of approaches to the prevention of atrial fibrillation (AF) with pacing. Aim of this study was to test the safety and feasibility of interatrial septum pacing at the posterior triangle of Koch for AF prevention and to exclude potential arrhythmic effects.Matherial and Methods.Interatrial septum pacing was performed in 34 patients (21 males, 13 females, mean age 69±12 years): 9 without a history and clinical evidence of atrial fibrillation (AF) (6 with sinus bradycardia, 2 with second-degree AV block, and 1 with carotid sinus hypersensitivity) and 25 with sinus bradycardia and paroxysmal atrial fibrillation (PAF) (mean symptomatic episodes/month 6.2±10). In all patients a screw-in bipolar lead was positioned in the interatrial septum superiorly to the coronary sinus.Results.At implant the mean P wave amplitude was 2.5±1.5 mV, the pacing threshold was 1±0.6 V and the impedance was 907±477 Ohm. Mean P wave duration was 118±17 ms in sinus rhythm and 82±15 during interatrial septum pacing (p < 0.001). During a mean follow-up period of 10±7 months, no patients without atrial tachyarrhythmias before implantation experienced AF. During a 9±6 months follow-up we observed only 2 symptomatic arrhythmia recurrences between AF patients (mean symptomatic episodes/month 0.006±0.0022) (p < 0.01 vs before implant period).Conclusions. Our data indicate that interatrial septal pacing is safe and feasible. A significant less incidence of arrhythmic episodes has been observed during follow-up. Further controlled randomized prospective studies are necessary to establish the exact role of this technique respect to conventional or multisite stimulation when patients with paroxysmal AF need to be permanently paced.     

Spatial correlation of left atrial low voltage substrate in sinus rhythm versus atrial fibrillation: The rhythm specificity of atrial low voltage substrate

Introduction

Improved sinus rhythm (SR) maintenance rates have been achieved in patients with persistent atrial fibrillation (AF) undergoing pulmonary vein isolation plus additional ablation of low voltage substrate (LVS) during SR. However, voltage mapping during SR may be hindered in persistent and long-persistent AF patients by immediate AF recurrence after electrical cardioversion. We assess correlations between LVS extent and location during SR and AF, aiming to identify regional voltage thresholds for rhythm-independent delineation/detection of LVS areas. (1) Identification of voltage dissimilarities between mapping in SR and AF. (2) Identification of regional voltage thresholds that improve cross-rhythm substrate detection. (3) Comparison of LVS between SR and native versus induced AF.

Methods

Forty-one ablation-naive persistent AF patients underwent high-definition (1 mm electrodes; >1200 left atrial (LA) mapping sites per rhythm) voltage mapping in SR and AF. Global and regional voltage thresholds in AF were identified which best match LVS < 0.5 mV and <1.0 mV in SR. Additionally, the correlation between SR-LVS with induced versus native AF-LVS was assessed.

Results

Substantial voltage differences (median: 0.52, interquartile range: 0.33–0.69, maximum: 1.19 mV) with a predominance of the posterior/inferior LA wall exist between the rhythms. An AF threshold of 0.34 mV for the entire left atrium provides an accuracy, sensitivity and specificity of 69%, 67%, and 69% to identify SR-LVS < 0.5 mV, respectively. Lower thresholds for the posterior wall (0.27 mV) and inferior wall (0.3 mV) result in higher spatial concordance to SR-LVS (4% and 7% increase). Concordance with SR-LVS was higher for induced AF compared to native AF (area under the curve[AUC]: 0.80 vs. 0.73). AF-LVS < 0.5 mV corresponds to SR-LVS < 0.97 mV (AUC: 0.73).

Conclusion

Although the proposed region-specific voltage thresholds during AF improve the consistency of LVS identification as determined during SR, the concordance in LVS between SR and AF remains moderate, with larger LVS detection during AF. Voltage-based substrate ablation should preferentially be performed during SR to limit the amount of ablated atrial myocardium.     

Recording of Pacing Stimulus Artifacts by Endovascular Defibrillation Lead Systems: Comparison of True and Integrated Bipolar Circuits

Background: The occurrence ICD undersensing of ventricular fibrillation due to the presence of a pacing stimulus artifact (PSA) is in part related to the amplitude of the artifact recorded on the ICD rate sensing circuit. There is little comparative data regarding PSA amplitude recorded by commercial ICD rate-sensing circuits.Purpose: To compare PSA amplitude recorded by commercial endovascular defibrillation leads utilizing integrated or true bipolar sensing circuits.Methods: Nineteen large (60–120 kg) pigs were utilized. Two different commercial endovascular defibrillation leads were evaluated, each with its distal tip located at the right ventricular apex: (1) Medtronic Transvene; and (2) CPI Endotak. Three different rate-sensing circuits were evaluated: (1) Transvene true bipolar (tip-ring); (2) Transvene integrated bipolar (tip-coil); and (3) Endotak integrated bipolar (tip-coil). Using a separate pacing lead located at the left ventricular apex (n = 19 animals) or right ventricular outflow tract (n = 10 animals), pacing was performed at a pulse width of 0.5 milliseconds at outputs of 1.5, 5 and 10 volts. PSA amplitude was recorded at each output by each circuit.Results: During pacing from the left ventricular apex, at each pacing output voltage the PSA amplitude recorded by the true bipolar circuit (0.6 ± 0.1 mV at 1.5 volts, 2.0 ± 0.5 mV at 5 volts, 3.7 ± 0.8 mV at 10 volts) was significantly smaller than recorded by the Transvene integrated circuit (1.4 ± 0.3 mV at 1.5 volts, 3.8 ± 0.7 mV at 5 volts, 4.1 ± 0.8 mV at 10 volts) or the Endotak integrated circuit (1.8 ± 0.4 mV at 1.5 volts, 4.2 ± 1.0 mV at 5 volts, 6.3 ± 1.8 mV at 10 volts). During pacing from the right ventricular outflow tract, at each pacing output voltage the PSA amplitude recorded by the true bipolar circuit (0.7 ± 0.1 mV at 1.5 volts, 1.7 ± 0.4 mV at 5 volts, 4.0 ± 0.7 mV at 10 volts) was significantly smaller than recorded by the Transvene integrated circuit (1.1 ± 0.4 mV at 1.5 volts, 3.9 ± 1.2 mV at 5 volts, 7.5 ± 1.8 mV at 10 volts) or the Endotak integrated circuit (1.6 ± 0.7 mV at 1.5 volts, 4.3 ± 1.7 mV at 5 volts, 7.5 ± 2.6 mV at 10 volts). For both pacing sites, the PSA amplitude recorded by the two integrated circuits was not significantly different.Conclusions: For a given pacing output voltage, PSA amplitude recorded by commercial endovascular rate sensing/defibrillation leads is greater when the sensing circuit is integrated than when it is true bipolar. These data may be helpful in planning ICD implantation in patients with previously implanted permanent pacemakers.     

The effect of calcium concentration on spontaneous ventricular defibrillation and VF threshold

Summary In order to investigate the influence of the effective refractory period on spontaneous ventricular defibrillation, isolated rat hearts were perfused with Krebs-Henseleit solution containing 0.5, 2.7 and 5.1 mM calcium. After measuring the fibrillation threshold at spontaneous rate (SR), ventricular fibrillation (VF) was induced during basic ventricular pacing of 110% SR, or the highest rate permitting 11 electromechanical coupling. The VF threshold was significantly reduced from 13.6±3.5 to 7.9±5.3 and 5.1±3.4 mA at 0.5, 2.7 and 5.1 mM Ca⁺⁺ concentrations, respectively. The incidence of spontaneous recovery from VF, induced during basic pacing, was 100%, 83% and 50% at calcium concentrations of 0.5, 2.7 and 5.1 mM, respectively, (p<0.01 for the incidences at 0.5 mM versus 5.1 mM Ca⁺⁺). The incidence of spontancous defibrillation decreased when the hearts were driven rapidly, with spontaneous recovery rates of 92%, 58% and 0% (p<0.0001)) for corresponding increases in Ca⁺⁺ concentration. Induced ventricular fibrillation of fine morphology was frequently observed at 5.1 mM Ca⁺⁺. It appears that progressive impairment of spontaneous defibrillation is caused by an increase in calcium concentration, this effect being more pronounced at high ventricular rates. Variations in the effective refractory period, caused by alterations in extracellular calcium concentration and differences in intracellular Ca⁺⁺ accumulation, may account for the above results.     

Identification of Transmural Necrosis Along a Linear Catheter Ablation Lesion During Atrial Fibrillation and Sinus Rhythm

Background: Determining whether a linear catheter radio frequency (RF) ablation lesion is transmural may be difficult, especially during atrial fibrillation. We hypothesized that changes in pacing thresholds and electrogram amplitude during atrial fibrillation and sinus rhythm could be used to assess whether a radiofrequency ablation resulted in transmural necrosis. Methods: A hexapolar, linear, RF ablation catheter was positioned between the caval veins in the right atrium of seven sheep. Pacing thresholds and electrogram amplitudes during atrial fibrillation and sinus rhythm were measured before and after the application of RF energy. Sites along the linear lesion were assessed histologically. Results: The electrogram amplitude in atrial fibrillation decreased significantly more at transmural sites (unipolar recording: 33 ± 11% transmural vs. 22 ± 13% non-transmural, p 0.01; bipolar recording: 62 ± 9% transmural vs. 43 ± 15% non-transmural, p 0.01). The electrogram amplitude in sinus rhythm decreased significantly more at transmural sites (unipolar recording: 49 ± 18% transmural vs. 15 ± 20% non-transmural, p < 0.001; bipolar recording: 63 ± 17% transmural vs. 42 ± 19% non-transmural, p = 0.002). The pacing threshold increased significantly more at sites with transmural necrosis (unipolar: increased by 378 ± 103% transmural vs. 207 ± 93% non-transmural, p < 0.001; bipolar: 370 ± 80% transmural vs. 259 ± 60% non-transmural, p < 0.001). Conclusions: The amplitude of the atrial electrogram from an ablation catheter can be used to discriminate areas with transmural necrosis from those without transmural necrosis during either atrial fibrillation or sinus rhythm. Termination of atrial fibrillation may not be necessary to estimate the histologic characteristics of an ablation lesion.     

Dual Site Right Atrial Pacing can Improve the Impact of Standard Dual Chamber Pacing on Atrial and Ventricular Mechanical Function in Patients with Symptomatic Atrial Fibrillation: Further Observations from the Dual Site Atrial Pacing for Prevention of Atrial Fibrillation Trial

Background: The effects of atrial pacing mode on atrial and ventricular function in patients with atrial fibrillation (AF) and bradycardia have not been evaluated. We evaluated atrial and ventricular function during randomization to support pacing (SP), high right atrial pacing (HRA), and dual site right atrial pacing (DAP).Methods: Seventy-nine patients (66 ± 12 yr, 46 male) with standard pacing indications and symptomatic AF were randomized to each of three pacing modes (DAP, HRA, SP) for 6 months in a crossover design. Echocardiographic studies were performed at enrollment and the end of each mode. Paired comparisons of atrial and ventricular function parameters were performed between each pacing mode and baseline.Results: HRA pacing in DDDR mode resulted in increased left ventricular (LV) end systolic volume (78 ± 42 vs. 60 ± 31 ml, p = 0.001) and reduced LV ejection fraction (44 ± 14 vs. 50 ± 11%, p = 0.007) compared to baseline. These parameters did not change during DAP. DAP resulted in increased peak A wave velocity (75 ± 19 vs. 63 ± 23 cm/s, p = 0.003) and atrial filling fraction compared to baseline (0.47 ± 0.15 vs. 0.38 ± 0.13, p = 0.005). Atrial and ventricular function were similar between control and SP.Conclusion: DAP, but not HRA or SP, improved left atrial (LA) function in patients with AF and bradycardia. HRA pacing in DDDR mode resulted in LA dilatation and deterioration of LV function which was not observed with DAP.This study was supported by a grant from the Electrophysiology Research Foundation, Warren, NJ and Medtronic Inc., Minneapolis, MN. Drs. Delfaut and Prakash were supported by grants from the Electrophysiology Research Foundation during the term of this study. Drs. Saksena and Nanda were consultants to Medtronic during this study. Dr. Hettrick and Mr. Ziegler are employees of Medtronic.     

Single Shock Endocavitary Low Energy Intracardiac Cardioversion of Chronic Atrial Fibrillation

Background.Discomfort related to low-energy internal cardioversion (LEIC) represents a real problem in patients (pts) with atrial fibrillation (AF). The aim of our study was to verify if a single shock could restore sinus rhythm (SR) with a lower discomfort for the pt.Methods. Thirty pts with chronic AF were randomized to receive a single 350 V shock (15 pts) or multiple shocks of increasing energy (15 pts). Three leads were positioned, respectively, in the coronary sinus and in the lateral right wall for shock delivery, and in the right ventricular apex for R wave synchronization. Truncated, biphasic shocks were used. In the first group a single 350 V shock was directly delivered and a second 400 V shock was given only if SR has not been restored. In the second group, beginning at 50 volts the voltage was increased in steps of 50 volts until SR restoration. No patient was sedated. After each shock the pts were asked to rate their discomfort on a scale of 1 to 5 (1 = not perceived, 5 = severe discomfort)Results. SR was restored in all the subjects. In group 1 SR was obtained in 12/15 (80%) pts with the first 350 V (8.1±0.8 joules) shock, while the remaining 3 patients required the second 400 V (10.2±10.3 joules) shock. In group 2 the mean atrial defibrillation threshold was 346.7±29.7 volts (8.0±1.5 joules). Then discomfort score was 2.5±0.6 in group 1 and 3.3±0.6 in group 2 (p < 0.01).Conclusions. A single shock of 350 V restores SR in the majority of pts with chronic AF; by use this new approach, LEIC is tolerated better than the multiple shocks step-up protocol.     

Pharmacologic Enhancement of Atrial Electrical Defibrillation Efficacy: Role of Ibutilide

The study was designed to identify the influence of ibutilide on activation during atrial fibrillation (AF) and determine its role in enhancing the efficacy of electrical conversion of AF. Vagally-mediated acute AF was induced in 12 anesthetized dogs. In 5 dogs, a cross-shaped epicardial patch containing 16 recording electrodes was placed on the right atrium. In 7 dogs, defibrillation patch electrodes overlying both atria were used to deliver biphasic shocks (50% tilt; 90 °F). Measurements were made at baseline and following ibutilide (0.075 mg/kg bolus followed by 0.075 mg/kg infusion over 10 minutes). Right atrial multisite electrogram recordings revealed significant prolongation in AF cycle length at all sites following ibutilide. In all dogs, AF cycle length increased with ibutilide from 90±23 to 130±49 ms (p < 0.005). Whereas, atrial defibrillation threshold decreased from 0.83±0.5 to 0.53±0.29 J (p =0.020). In conclusion, ibutilide prolongs cycle length of canine vagally-mediated acute AF. Furthermore, ibutilide facilitates electrical conversion of AF by lowering energy requirement. Thus, controlled drug infusion in conjunction with electrical defibrillation may be useful for managing AF.     

Electrophysiological effects of flecainide and sotalol in the human atrium during persistent atrial fibrillation

Aims Atrial fibrillation (AF) shortens the atrial action potential and the atrial refractory period. These changes promote persistence of AF. Pharmacological prolongation of atrial action potential duration (APD) may therefore help to prevent recurrent AF. In addition to prolonging APD, sodium channel blockers may prevent AF by inducing post–repolarization refractoriness (PRR). We studied whether two antiarrhythmic drugs (sotalol, flecainide) prolong APD or induce PRR in the fibrillating human atrium. Methods In 12 patients with persistent AF (11 male, 58 ± 5 yrs, 27 ± 7 months duration of AF), we recorded monophasic action potentials from the right atrial appendage and inferior right atrium at baseline and 15 minutes after intravenous administration of sotalol (1.5 mg/kg) or flecainide (2 mg/kg). APD and effective refractory periods (ERP) were determined. Results Both drugs prolonged APD90 during AF (flecainide from 109 ± 7 ms to 137 ± 10 ms, sotalol from 108 ± 6 ms to 131 ± 8 ms, both p < 0.05 vs. baseline). Sotalol prolonged ERP in parallel to APD (from 119 ± 8 ms to 139 ± 8 ms, p < 0.05). Flecainide induced PRR by prolonging ERP more than APD90 (from 134 ± 9 ms to 197 ± 28 ms, p < 0.05 vs. baseline and vs. sotalol). Conclusions Flecainide and sotalol prolong the atrial action potential during atrial fibrillation in humans. In addition, flecainide induces atrial PRR. These electrophysiological effects may reduce AF recurrences and prevent their persistence.Drs. Kirchhof, Engelen and Breithardt are Members of the Kompetenznetz Vorhofflimmern     

Placement of atrial pacing leads during atrial fibrillation. Feasibility and subsequent lead performance.

AIMS: To assess the feasibility of placing permanent atrial pacing leads during atrial fibrillation (AF) and whether such leads function satisfactorily. METHODS AND RESULTS: Prospective study of 17 consecutive patients in whom permanent atrial leads were positioned during an episode of paroxysmal AF. Fluoroscopic position ('figure of 8' or side-to-side movement and anterior position in RAO projection), lead impedance (> 300 but < 1000 ohms) and intracardiac electrogram (average peak to peak amplitude > 1 mV) were used to define an acceptable lead position. At 8 weeks post implant we measured: pulse duration pacing threshold at 5 V; lead impedance at 5 V and 0.5 ms; intracardiac electrogram (EGM) signal amplitude. At the end of the study we reviewed patients to establish whether AF had become permanent. In all patients, follow-up demonstrated satisfactory lead function. All leads had impedances between 300 and 1000 ohms. Pacing thresholds were all < 0.1 ms at 5 V. Mean atrial EGM amplitude seen in sinus rhythm was 3.3 mV (range 1.2-8.4); in patients where all follow-up was in AF in was 2.1 mV (range 1.5-2.5). Nine patients (53%) developed permanent AF. CONCLUSION: Placing atrial leads during AF is feasible using the technique described. However, some patients progress to chronic AF, eliminating the benefits of atrial pacing.     

Merits and Limitations of the Mode Switching Rate Stabilization Pacing Algorithms in the Implantable Cardioverter Defibrillator

Background: The 7250 Jewel AF Medtronic model of ICD is the first implantable device in which both therapies for atrial arrhythmias and pacing algorithms for atrial arrhythmia prevention are available. Feasibility of that extensive atrial arrhythmia management requires correct and synergic functioning of different algorithms to control arrhythmias. Methods and results: The ability of the new pacing algorithms to stabilize the atrial rate following termination of treated atrial arrhythmias was evaluated in the marker channel registration of 600 spontaneously occurring episodes in 15 patients with the Jewel AF. All patients (55±15 years) had structural heart disease and documented atrial and ventricular arrhythmias. Dual chamber rate stabilization pacing was present in 245 (41%) of episodes following arrhythmia termination and was a part of the mode switching operation during which pacing was provided in the dynamic DDI mode. This algorithm could function as the atrial rate stabilization pacing only when there was a slow spontaneous atrial rhythm or in presence of atrial premature beats conducted to the ventricles with a normal AV time. In case of atrial premature beats with delayed or absent conduction to the ventricles and in case of ventricular premature beats, the algorithm stabilized the ventricular rate. The rate stabilization pacing in DDI mode during sinus rhythm following atrial arrhythmia termination was often extended in time due to the device-based definition of arrhythmia termination. This was also the case in patients, in whom the DDD mode with true atrial rate stabilization algorithm was programmed. Conclusions: The rate stabilization algorithms in the Jewel AF applied after atrial arrhythmia termination provide pacing that is not based on the timing of atrial events. Only under certain circumstances the algorithm can function as atrial rate stabilization pacing. Adjustments in availability and functioning of the rate stabilization algorithms might be of benefit for the clinical performance of pacing as part of device therapy for atrial arrhythmias.