American Heart Journal
Volume 140, Issue 3 , Pages 436-440, September 2000

Decreasing the number of leads required for an implantable atrial defibrillator: Use of a new 2-lead system☆

Maastricht, The Netherlands, and Redmond, Wash

From the aDepartment of Cardiology, Academic Hospital Maastricht, Maastricht, The Netherlands; and bInControl Inc, Redmond, Wash

Received 21 June 1999; accepted 29 March 2000.

Article Outline

Abstract 

Background The purpose of this study was to evaluate the use of a new 2-lead system for detection of atrial fibrillation (AF) and atrial defibrillation. Methods In 16 patients undergoing elective cardioversion of AF, a 2-lead system was compared with the conventional 3-lead system in a randomized trial. The new 2-lead system consisted of a catheter with a distal bipolar right ventricular electrode pair and a proximal right atrial shock electrode coil and a separate decapolar defibrillation catheter in the coronary sinus. For the 3-lead system, an additional decapolar catheter was placed in the right atrium. AF and sinus rhythm signal amplitude detection and atrial defibrillation threshold (ADFT) were compared in each patient with both systems. Results Successful defibrillation was obtained in all patients. ADFT for the 2-lead system was significantly higher compared with the 3-lead system (370 ± 112 vs 316 ± 100 V, P < .05; 9.3 ± 5.2 vs 6.8 ± 4.2 J, P < .05). In contrast, there was an increase in impedance for the 3-lead system (77 ± 16 Ω vs 68 ± 13 ω; P < .05). AF had a lower signal amplitude compared with sinus rhythm for both systems (P < .05), and the 2-lead system had a lower signal amplitude compared with the 3-lead system for both rhythms (P < .05). Conclusion The use of a 2-lead system with this configuration is not superior to the 3-lead system regarding AF signal amplitude detection and ADFT. Further study is needed with implantable-quality leads in place of the temporary catheters used in this study. (Am Heart J 2000;140:e11.)

 

Catheter-based internal cardioversion of atrial fibrillation (AF) has been successfully performed in human beings.1, 2, 3, 4, 5, 6 The safety and efficacy of this new method of cardioversion has resulted in the development of the Atrioverter (In Control/Guidant, Inc, Redmond, Wash). The Atrioverter has been used in an initial clinical trial of safety and efficacy.7 The system uses 3 leads: 1 in the coronary sinus, 1 in the right atrium, and 1 in the right ventricle. The leads in the coronary sinus and right atrium are used for detection of AF and defibrillation shock delivery. The right ventricular lead has a bipolar pair of electrodes used for synchronization and postshock pacing. Successful efforts were made to reduce the number of leads required by the Atrioverter by combining the right atrial and coronary sinus defibrillation electrodes on the same lead.8, 9 Another 2-lead system concept would be to combine the right ventricular bipolar electrodes and the right atrial defibrillation electrode on the same lead. If such an approach would function adequately for the Atrioverter, it would provide another option to decrease the required number of leads. We therefore evaluated this 2-lead system compared with the conventional 3-lead system in terms of AF signal amplitude detection and atrial defibrillation threshold (ADFT).

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Methods 

Study population 

Sixteen consecutive patients with AF were prospectively studied. Fifteen of the patients underwent elective internal atrial defibrillation of AF; in 1 patient AF was induced at time of study. Evaluation of the patients included a clinical history, physical examination, routine laboratory and thyroid function tests, a 12-lead electrocardiogram, and transthoracic echocardiography.

Patients were excluded from the study if they met any one of the following criteria: (1) a left ventricular ejection fraction of <20% or uncompensated heart failure; (2) a history of a sustained ventricular arrhythmia, cardiac arrest, congenital long QT syndrome, or anterograde conduction over an accessory pathway; (3) AF from reversible causes (eg, hyperthyroidism); (4) unstable angina in the previous week, a history of myocardial infarction or a revascularization procedure within the past 4 months; (5) digitalis toxicity or significant electrolyte imbalance; or (6) an implanted pacing device.

The administration of antiarrhythmic drugs was not interrupted for the procedure. Anticoagulation was interrupted 2 days before the procedure and restarted after the procedure. To perform a safe venous puncture, an international normalized ratio value of ≤2.5 was required. The study protocol was approved by the Medical Ethics Committee of the Academic Hospital Maastricht, and informed consent was obtained from all patients.

Internal atrial defibrillation protocol 

A specially designed 6F catheter (VascoMed, Institut für Kathetertechnologie GmbH, Weil am Rhein, Germany) with a distal bipolar electrode pair and a proximal 6-cm electrode coil (surface area 5 cm2) was inserted through the left brachial vein (n = 13 patients) (Figure 1) or the right femoral vein (n = 3 patients) (Figure 2).

  • View full-size image.
  • Fig. 1. 

    A, Anteroposterior fluoroscopic projection of position of defibrillation catheters for 3-lead system. Sheath marker (SM) is positioned distal to right atrial (RA) coil electrode so that sheath is covering coil electrode. Distal bipolar electrode pair of catheter is located in right ventricular apex (RV) . Decapolar defibrillation catheter is added in high right atrium. Coronary sinus (CS) decapolar defibrillation catheter is located distal in CS. B, Anteroposterior fluoroscopic projection, and C, left oblique fluoroscopic projection of position of defibrillation catheters for 2-lead system with brachial approach shown in same patient. Note that sheath is withdrawn from RA coil electrode.

The femoral approach was only used when adequate brachial venous access could not be obtained. As can be seen in Fig. 1, Fig. 2, the right atrial coil electrode location was kept constant independent of venous access.

The catheter was positioned with a long vascular sheath (Daig Corp, Minnetonka, Minn), with the tip in the apex of the right ventricle. The catheter had 3 possible spacings (11, 15, and 20 cm) from the proximal electrode of the bipole to the distal part of the coil electrode. The size of the spacing was optimized on a per-patient basis with an attempt made to select the spacing that would result in positioning the coil electrode in the high right atrium for both the femoral and the antecubital approach. A temporary 6F catheter (Elecath, Electro-Catheter Corp, Rahway, NJ) consisting of 10 parallel stainless steel rings (surface area 3.12 cm2) was inserted into the right femoral vein and positioned in the distal coronary sinus. For the 2-lead system, the right atrium-coronary sinus detection signals were obtained and shocks were delivered between the decapolar catheter in the coronary sinus and the shock coil in the right atrium. For the 3-lead system, a second decapolar catheter was positioned in the high right atrium. The right atrial electrodes for both systems were positioned to attempt to achieve the best shock vector. The right atrial coil electrode was covered with the sheath and was disconnected, isolating it from the shock. The right atrium-coronary sinus detection signals were obtained, and shocks were delivered between the 2 decapolar catheters (Figure 1, A ). For both systems, shocks were synchronized and postshock pacing was performed with the bipolar pair of electrodes in the right ventricle.

Defibrillation shocks were delivered by the Metrix defibrillation system analyzer (Model 2102, InControl Inc, Redmond, Wash) unless >400 V (approximately 10 J) was needed for defibrillation. For higher shock strengths, an external defibrillator (Ventritex HVS-02, Sunnyvale, Calif) was used. Biphasic defibrillation shocks (6/6 ms), synchronized to the R wave, were given. To prevent inadvertent induction of ventricular fibrillation, shocks were delivered only after R-R intervals >500 ms.10 In 1 patient, in whom a femoral venous access was used for insertion of the lead containing the right atrial shock electrode and the right ventricular pace/sense electrodes, AF was induced by right atrial burst pacing.

ADFTs were determined in a randomized order in each patient, twice for each lead system, with a 180-V start/40-V step-up protocol until cardioversion of AF occurred. After successful shocks, AF was reinduced with rapid atrial pacing and allowed to sustain for 5 minutes before the next shock being delivered. Conscious sedation was provided with intravenous midazolam (0.1 mg/kg). Oxygen saturation was monitored with a pulse oximeter, and blood pressure was measured every 15 minutes. During the study, the 12-lead electrocardiogram and endocardial electrograms were recorded and stored by PC-EMS 3.0 (Cardiovascular Research Institute, Maastricht, The Netherlands).

AF detection signals (right atrium-coronary sinus) were obtained with the automatic gain control algorithm of the Metrix defibrillation system analyzer. The signals across the shock vector were analyzed at 2 different sense margin ratios for each lead system and for both sinus rhythm and AF. The automatic gain control algorithm uses the 4 largest atrial deflections seen in 8 seconds of the detection electrogram to set the sensitivity. The amplitude of the signals was calculated from the sense margin ratio set and the resultant sensitivity provided by the system.11

Statistical analysis 

Continuous variables are expressed as mean ± SD. ADFT (voltage, delivered energy) and impedance for the 2 lead systems were compared with the Student paired t test. Order effects were evaluated by using the testing order as a covariate. Comparison of signal amplitude detections was made with a 2-way mixed model analysis of variance. To ensure that the mode of venous access for insertion of the lead containing the right atrial shock electrode and the right ventricular pace/sense electrodes did not significantly affect the ADFT or sensing results, statistical analysis was performed including and excluding the patients in whom the femoral approach was used. A value of P < .05 was considered statistically significant.

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Results 

Clinical characteristics 

Table I gives the clinical and echocardiographic characteristics of the patients studied.

Table I. Clinical and echocardiographic characteristics of the patients studied
M/F14/2
Age (y)
Mean ± SD54 ± 9
Range39-76
Duration AF as disease (mo)
Mean ± SD50.8 ± 45.8
Range6-144
Duration treated AF episode (d)
Mean ± SD475 ± 290*
Range0.13-1953
Current antiarrhythmic drug class
I2
II5
III5
IV0
Combination of antiarrhythmic drugs2
No antiarrhythmic drug2
LA diameter (mm)
Mean ± SD54 ± 5
Range42-60
LVEF (%)
Mean ± SD53 ± 11
Range34-72

LA, Left atrial; LVEF, left ventricular ejection fraction.

*Calculated for 15 patients.

Twelve of the 16 patients had previously not responded to 1 or more attempts at external cardioversion. In general, the patients had a long history of AF with associated changes in left atrial diameter.

Outcome of internal atrial defibrillation and comparison of lead systems 

All patients were successfully cardioverted with both lead systems, and all patients completed the entire protocol. The mean ADFT and impedance for the 2-lead system was 370 ± 112 V, 9.3 ± 5.2 J, and 68 ± 13 Ω. For the 3-lead system, these values were 316 ± 100 V, 6.8 ± 4.2 J, and 77 ± 16 Ω, respectively. Comparing threshold voltage and delivered energy for the 2 lead systems showed a significantly lower threshold for the 3-lead system (P < .05, Figure 3).

Conversely, the impedance for the 3-lead system was significantly higher (P < .05). We tested whether the order of testing had any effect on the threshold comparison and found that there was no ordering effect (P > .05). On a per-patient basis, the 3-lead system had lower energy requirements for 9 patients (average decrease of 5.3 J) and was within 1 J of the 2-lead system for 5 patients. In only 2 patients were the energy requirements lower for the 2-lead system (average decrease of 4.2 J).

The results of the comparison of the signal amplitude detection (right atrium-coronary sinus) for both lead systems during AF and sinus rhythm are shown in Figure 4.

For both lead systems, AF had a lower signal amplitude compared with sinus rhythm (P < .05). For both rhythms, the signal amplitudes were greater for the 3-lead system compared with the 2-lead system (P < .05). Excluding the patient with induced AF and the 2 patients in whom the femoral venous access was used, the results of the statistical analyses did not change.

All patients were in stable sinus rhythm at the end of the procedure despite the fact that 6 of the patients had immediate reinitiation of AF at some time during the procedure.12 Despite the multiple shocks and reinductions, there were no acute or long-term complications observed.

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Discussion 

Internal atrial defibrillation was effective in restoring stable sinus rhythm in all patients, despite the long mean duration of AF and previously failed external attempts. The high efficacy rate of the technique and the ADFTs found in this study are similar to the results of other studies.1, 2, 3, 4, 5, 6 It seems that in patients who have not responded to external cardioversion attempts, it is worthwhile to attempt internal defibrillation for the restoration of sinus rhythm. We did not find a significant order effect, indicating that the first threshold terminating an episode of long standing AF was not significantly different from later thresholds, determined after induced AF episodes. This finding is similar to the results of previous studies of defibrillation of induced and spontaneous AF.4, 6

The main finding in our study was that the new 2-lead system for atrial defibrillation was inferior to the conventional 3-lead system in terms of the defibrillation threshold and AF detection. It is important to consider that, despite the fact the 2-lead system offers greater simplicity, potentially lower morbidity rates and fewer lead dislodgments, its use will be limited because of the higher thresholds and less optimal atrial signals. The findings of this study are in deference to the results of a study by Tse et al,8 in which a different 2-lead system (Solo lead) for atrial defibrillation had similar thresholds and atrial signals when compared with the conventional 3-lead system. The reasons for the different findings of our versus the earlier study are likely related to the position of the right atrial electrode. For the 2-lead system tested in the earlier study, the right atrial and coronary sinus electrodes were both on the same lead. The configuration of the Solo lead caused the right atrial electrode to be aligned against the lateral wall when the lead exited the coronary sinus os. The lead tested in our study tended to cause the right atrial electrode to float in the right atrium, and this electrode was positioned more medially than was the case with either the Solo lead or with the 3-lead system. The forces applied to the lead as it exited the right ventricle through the tricuspid valve primarily affected the location of the right atrial electrode. The lack of contact of the right atrial electrode with the lateral right atrial wall likely accounted for the higher thresholds and lower signal amplitudes seen in this study.

As with the Solo lead system, variable interelectrode spacing was necessary to ensure that the right atrial electrode was located in the right atrium. A potential advantage that the right atrial/right ventricular lead might have versus the Solo is that the right atrial electrode positioning is independent of the coronary sinus electrode position, whereas it is not independent with the Solo lead. However, in this study, even with the use of leads with 3 different interelectrode spacings (distance from the right ventricular bipolar pair to the right atrial coil electrode), it was not possible to optimize the right atrial electrode along the lateral wall. It remains clear that the 3-lead system allows greater flexibility because all 3 leads are independently positioned. For example, when the coronary sinus is not cannulated as deeply, the right atrial electrode can be independently optimized when using the 3-lead system. This is not true of the Solo lead or the right ventricular/right atrial lead used in this study.

In conclusion, we have shown that a 2-lead system for atrial defibrillation, with 1 lead combining the right ventricular bipolar and right atrial coil electrode, is able to convert AF in all patients, but with higher thresholds compared with the conventional 3-lead system. Additionally, the detection signals from the 2-lead system were of lower amplitude, potentially making AF detection more difficult and/or more sensitive to noise.

Limitations 

One potential limitation of this study is that we attempted to mimic a long-term implantable lead with a temporary catheter. We were trying to evaluate the practical limitations of the 2 systems tested and attempted to optimize each lead system for the anatomical and vascular approach. There is a potential difference because of the different electrodes (coil vs decapolar) of the 2 systems. However, a study by Elabbady et al13 comparing a coil and a temporary decapolar electrode in sheep showed no difference in defibrillation threshold or impedance. Additionally, the flexibility of this catheter and the long vascular course of the catheter from the arm required that we used a long vascular sheath to position this catheter. To avoid the need to replace the catheter, we had to cover the right atrial electrode when testing the 3-lead system. This sheath may have resulted in a somewhat unnatural curvature and a less optimal position of the catheter.

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References 

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☆ Reprint requests: Carl Timmermans, MD, Department of Cardiology, Academic Hospital Maastricht, CARIM (Cardiovascular Research Institute Maastricht), PO Box 5800, 6202 AZ Maastricht, The Netherlands.E-mail: C.Timmermans@cardio.azm.nl

PII: S0002-8703(00)67020-5

doi:10.1067/mhj.2000.107552

American Heart Journal
Volume 140, Issue 3 , Pages 436-440, September 2000

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