Subcutaneous array

Occasionally ICD systems require the placement of additional leads and/or patches to achieve adequate DFTs. An additional patch electrode may be added through a small, left anterior chest incision (Fig. 4.57). This incision is generally placed along the left inframammary skin fold. A subcutaneous pocket is developed and a supplemental patch placed. The patch is sutured to the chest wall. The proximal lead is then tunneled to the ICD. A variation on this system is the subcutaneous array developed by CPI (Fig. 4.58). The array consists of three flexible defibrillator leads that are joined at a common connector. The leads are designed to be placed subcutaneously along the contour of the chest wall. The leads fuse as a common electrode that connects to the ICD. Creating a small incision in the left lateral inframammary skin fold places the array. Three separate subcutaneous tracts are created using a blunt-tipped malleable stylet. The stylet is loaded with a sheath that is advanced down each traa. The stylet is removed and the limbs of the array are passed down each sheath. 

Fig. 4.58 Subcutaneous array system. Left-sheaths middle tunneling tool loaded with sheath and right snbcutaneous array. (Courtesy of Guidant, Inc., St. Paul, MN.)...

Fig. 4.59 Endocardial pacing and shocking electrode tunnel to the pocket in the left upper quadrant. Subcutaneous array similarly positioned and fixed to the left anterior chest wall and tunneled to the ICD. (From Belott PH, Reynolds DW. Permanent pacemaker and cardioverter defibrillation implantation. In EUenbogen KA, Kay N, Wilkoff BL, eds. Clinical cardiac pacing and defibrillation, 2nd ed. Philadelphia WB Saunders, 2000, with permission.)...

Gradaus R, Block M, Seidl K, Brunn J, Isgro F, Hammel D, Hauer B, Bieithardt G, Bocker D. Defibrillation efficacy comparing a subcutaneous array electrode versus an active can implantable cardioverter defibrillator and a subcutaneous array electrode in addition to an active can implantable cardioverter defibrillator results from active can versus array trials I and B. J Cardiovasc Electrophysiol 2001 12 921-7. 

Kuhlkamp V, Domberger V, Mewis C, Seipel L. Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study. Int J Cardiol 2001 78 247-56. 

Fig. 18.23 Posteroanterior (A) and lateral (B) chest radiographs from a patient with an implantable cardioverter-defibrillator. Unacceptable defibrillation thresholds necessitated placement of a subcutaneous array.

When an ICD system is inspected radiographically, it is possible to determine whether the ICD lead has a single coil (Fig. 18.9) or a dual coil (Fig. 18.22) and whether any additional leads are associated with the ICD. Although additional leads are not commonly used, they may include a superior vena cava lead, subcutaneous array (Fig. 18.23), or subcutaneous patch. 

Rarely, the ICD is unable to convert VF with an adequate safety margin despite an optimally positioned transvenous system. One way to improve this situation is to implant a "subcutaneous array or patch." Either provides... 

Even with an appropriately positioned dual coil system and attempts using both shock polarities the DPT may rarely remain unacceptably high. In this instance the implanting physician has the option of taking the proximal coil out of the defibrillation circuit and adding a subcutaneous array or patch as a means of improving the DPT. 

Ward WK, Wood MD, Casey HM, Quinn MJ, Federiuk IF. An implantable subcutaneous glucose sensor array in ketosis-prone rats closed loop glycemic control. Artificial Organs 2005, 29, 131-143. 

First, some AAD medications may cause an increase in the DFT (see below). As such the ICD may need to be tested after the medication has been loaded or a dosage increased to ensure an adequate defibrillation safety margin. An inadequate safety margin can potentially require surgical revision of the ICD system to resolve this situation (i.e. implantation of a "high energy" ICD or addition of an SVC coil or subcutaneous patch/array). 

An adequate assessment of the subcutaneous tissue can be efficiently performed be means of less specialized high-resolution transducers chararter-izedby the same frequency range (5-15 MHz) appropriate for other musculoskeletal examinations. The type and frequency of the selected transducer vary depending on the region of the body to be examined. For the thin subcutaneous tissue of the dorsum of the hand and wrist, linear-array transducers working at a center frequency >7.5-10 MHz are the most appropriate. Superficial focusing capabilities and a thin... 

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