Ann Thorac Surg 1997;64:1177-1179
© 1997 The Society of Thoracic Surgeons
Case Report
Single-Incision and Single-Element Array Electrode to Lower the Defibrillation Threshold
Volker Kühlkamp, MD,
Kourosh Khalighi, MD,
Volker Dörnberger, MD,
Gerhard Ziemer, MD
Medical Department III and Department of Cardiothoracic Surgery, Eberhard-Karls-University, Tübigen, Germany
Accepted for publication May 28, 1997.
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Abstract
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Occasional patients have excessive defibrillation energy requirements despite appropriate transvenous defibrillation lead position and the use of biphasic shocks. A single-element subcutaneous array electrode was implanted in 2 patients with a high defibrillation threshold. The array electrode was implanted through the same infraclavicular incision that was used for implantation of the transvenous lead. The defibrillation threshold decreased from 30 J to 15 J and from 24 J to 9 J with the subcutaneous array electrode.
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Introduction
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The implantable defibrillator is an accepted mode of treatment in patients with aborted sudden death [1]. With a unipolar device capable of biphasic shocks a sufficient defibrillation threshold is usually achieved. However in some cases an additional subcutaneous patch or array electrode is necessary to achieve an acceptable defibrillation threshold [2–5]. We report on 2 patients with a high defibrillation threshold in whom an easy-to-implant subcutaneous single-element array electrode was used to lower the defibrillation threshold.
A 58-year-old man and a 60-year-old man, both with dilated cardiomyopathy and aborted sudden death, were referred for implantation of an automatic defibrillator. Left ventricular ejection fraction was determined from left ventricular angiography and was 0.25 and 0.41, respectively, and the patients were classified as having New York Heart Association class II heart failure.
An implantable defibrillator (Phylax 06 AH; Biotronik, Berlin, Germany) with an active shell and a complete transvenous lead system (SPS 65-UP/BP; Biotronik) was implanted. After the lead was positioned in the right ventricular apex and the quality of the signals and the pacing threshold was verified, the defibrillation threshold with this system was determined using a binary search protocol. Ventricular fibrillation was induced using a T-wave shock. If a shock failed, ventricular fibrillation was terminated by a 40-J shock. The defibrillation threshold was defined as the lowest shock strength (stored energy) to terminate ventricular fibrillation with at least one lower energy shock failure. With the unipolar system the defibrillation threshold was 30 J in 1 patient and 24 J in the other patient.
In both patients an additional subcutaneous single element array electrode to lower the defibrillation threshold was implanted. The subcutaneous single element electrode is a unipolar lead with a surface area of 5 cm2 and consists of a platinum alloy (Medtronic Transvene SQ 13014; Medtronic Inc, Minneapolis, MN). The overall length is 58 cm, and the length of the coil is 25 cm. The lead was inserted through the same infraclavicular incision used to implant the transvenous lead and was positioned using a tunneling rod introducer and an introducer sheath (peel-away sheath; both from Medtronic Inc). The stylus is introduced with a slightly curved rod introducer, starting from the infraclavicular incision. The tip of the stylus should be placed as posterior as possible. To move the introducing rod with the stylus accurately through the subcutaneous tissue, the tip of the introducing rod was guided from the unsterile field by a second person. It took less than 5 minutes using this approach to place the subcutaneous electrode. The subcutaneous single-element array electrode and the shell of the defibrillator acted as the anode, and the coil in the right ventricular apex acted as the cathode. The binary search protocol was used to determine the defibrillation threshold. In the patient with the 30-J defibrillation threshold, the defibrillation threshold with the subcutaneous electrode was 15 J, and in the patient with the 24-J defibrillation threshold, the defibrillation threshold was 9 J with the additional lead. The impedance decreased from 55 
to 40 and from 66 to 45 , respectively.
In postoperative chest radiographs of the patients in the upright standing position, the subcutaneous finger electrode travels along the lateral aspect of the thorax to the inferior angulus of the scapula (Fig 1
).
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Fig 1. . These chest radiographs illustrate a typical location of the subcutaneous single-finger lead. The subcutaneous lead is positioned along the lateral aspect of the thorax to the posterior area. The device is implanted in a left-sided submuscular pocket. The right ventricular lead is placed in the right ventricular apex.
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Before discharge from the hospital and after 3 months the intraoperative defibrillation thresholds of 15 J and 9 J were successfully reconfirmed after intravenous sedation of the patients with midazolam. At the 3-month follow-up test a slight increase of the impedance of the high-voltage circuit of 3 and 5 , respectively, was seen. During follow-up (12 and 9 months, respectively) both patients had spontaneous arrhythmic events, successfully terminated by the device. Complications associated with the subcutaneous lead or dislocation of the subcutaneous lead were not observed.
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Comment
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It has been shown that a patch or an array electrode is effective in lowering the defibrillation threshold in combination with a transvenous lead system [2–6]. Important points regarding the implantation of a subcutaneous electrode are ease of implantation, efficacy, acute and chronic complications with the lead, and the tolerance of the lead during long-term follow-up. With the patch electrode severe bleeding at the site of implantation, wrinkling of the patch, and the development of a seroma have been reported [2, 3, 7]. In our experience patch electrodes are poorly tolerated and removal of the electrode is sometimes required. These problems have not been seen in our patients with a three-element array electrode [8]. Furthermore, with biphasic shocks an array electrode proved to be more effective at lowering the defibrillation threshold than a patch electrode [8]. The subcutaneous position of the single-element array electrode used in this study is very stable [9].
The array electrode used in multiple studies consists of three subcutaneous lead elements yoked into a common lead [2, 3]. We used a subcutaneous electrode with a single element, which turned out to be very effective at lowering the defibrillation threshold. However, this lead is easier to implant than a three-element array electrode and can with some experience easily be inserted from an infraclavicular incision, as has been described for the array electrode [6]. Two factors might be responsible for the significant decrease in the defibrillation threshold: First, with this type of electrode the defibrillation field is significantly enlarged, especially to the posterior area. Second, the impedance of the high-voltage circuit is decreased. A small increase in the impedance was seen at the 3-month follow-up test. However, this did not lead to an increase of the defibrillation threshold.
The procedure of implanting the single-element array electrode described in this article is of importance, because malpositioning of subcutaneous array leads is a significant problem. If the tip of the rod introducer is guided from the unsterile field it is almost impossible to perforate the cutis or to push the tip into the pleural cavity or the spleen as has been reported for an array electrode [3]. Furthermore, the tip can easily be guided to a posterior position. We therefore recommend this technique for implantation of subcutaneous single-element array electrode.
We conclude that the single-element array electrode used in this study is easy to implant, very efficacious, and well tolerated during follow-up. For these reasons the single-element subcutaneous array electrode is an promising adjunct to a transvenous lead system if the defibrillation threshold with the lead only is inacceptable.
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Footnotes
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Address reprint requests to Dr Kühlkamp, Medical Department III, Otfried Müller Str 10, D-72076 Tübingen, Germany (e-mail: volker.kuehlkamp.{at}uni-tuebingen.de).
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References
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- Kühlkamp V, Dörnberger V, Mewis C, Seipel L. Prospektiver Vergleich einer subcutanen Flächenelektrode und einer subcutanen Fingerelektrode zur Senkung der Defibrillationsschwelle [Abstract]. Z Kardiol 1996;85(Suppl):14.
- Kühlkamp V, Dörnberger V, Khalighi K, Seipel L. Prospective randomized evaluation of a new subcutaneous unipolar lead in comparison to a transvenous electrode system with enhanced surface area [Abstract]. Circulation 1996;94(Suppl 1):439.
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Abstract
Introduction
