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A modified subcutaneous implantable cardioverter–defibrillator implant in a patient with a previous left ventricular epicardial defibrillation patch

Paresh A. Mehta, Julian Bostock, Christopher A. Rinaldi
DOI: http://dx.doi.org/10.1093/europace/eur262 149-150 First published online: 27 August 2011

Abstract

We describe a case of subcutaneous implantable cardioverter–defibrillator (ICD) implant in a patient with an existing epicardial defibrillation patch. Potential issues with shock vector shielding were overcome by a modification of the generator implant site and poor sensing were successfully managed by programming a sensing vector which excluded the generator.

Case

A 46-year-old woman with arrhythmogenic right ventricular (RV) cardiomyopathy and prior ventricular fibrillation (VF) arrest underwent implantation of a left pectoral endocardial implantable cardioverter–defibrillator (ICD) in 1998. This was complicated by device-related infection requiring system extraction. Surgical implantation of an abdominal ICD with epicardial atrial and right ventricular pace/sense leads and a single left ventricular (LV) epicardial defibrillation patch to the lateral wall of the LV was performed [Guidant CPI (UK) A76]. Subsequently, a fracture of the RV lead occurred, which was capped, and an endocardial RV pace/sense lead was placed via the right subclavian vein and tunnelled to the abdominal generator. Further ICD generator changes occurred in 2004 and 2010. A routine ICD check in 2011 demonstrated a significant increase in defibrillation patch impedance from 68 to >200 Ω and electrical noise on the ‘far-field’ patch-can electrogram during provocation testing. Impedance trends demonstrated the rise had occurred 1 month after the last generator change. These indicated a conductor break in the ICD shock circuit. Surgical exploration found no visible fault with the lead connections and the leads were capped and generator was removed.

As a consequence of previous endocardial device infection and absence of a pacing indication, we elected to implant a subcutaneous ICD (S-ICD) (Cameron Health SQ RX 1010)1 with a tunnelled S-ICD lead (Cameron Health QTRAK 3010) (Figure 1). This device has three available sensing vectors: ‘Primary’ vector from the proximal parasternal sensing electrode to device, ‘Secondary’ vector from the distal parasternal sensing electrode to device, and ‘Alternate’ vector from distal to proximal parasternal electrode (‘cold-can’). A pre-procedure sensing check using a patient screening tool (Cameron Health) was satisfactory in all vectors. There was a concern regarding electrical shielding of the S-ICD shock vector by the existing epicardial defibrillation patch. We therefore opted to position the generator in a lower-than-customary left lateral position (eighth intercostal space mid-axillary line) for the shock vector to avoid the existing defibrillation patch. VF induction (using 50 Hz burst pacing) was successful at the first attempt with a 65 J ICD shock in the ‘primary’ sense vector position.

Figure 1

Subcutaneous ICD implant in a low left lateral position in a patient with a left ventricular epicardial defibrillation patch.

Within a day of implant she suffered two inappropriate shocks and interrogation showed poor R wave sensing, followed by sensing of baseline noise as tachycardia. On re-testing using the patient screening tool, a low-amplitude R wave was found in the ‘Primary’ vector position. The ‘Secondary’ vector had a larger R wave but unacceptably large amplitude T waves. The ‘Alternate’ vector had acceptable R wave amplitude with smaller T waves. The device was reprogrammed to this ‘Alternate’ (cold-can) vector removing the device from the sensing circuit with no further inappropriate therapy.

The optimal S-ICD device configuration has been demonstrated to be a parasternal-positioned electrode and left lateral thoracic pulse generator1 although numerous configurations have been modelled.2 There is an interplay between a successful shock vector across the left chest between the can and parasternal coil and the most appropriate sensing vector as two of the three possible sensing vectors include the device can. To our knowledge this is the first-reported case of S-ICD implant in a patient with an existing LV epicardial defibrillation patch. In this case the shock vector was unconventional due to the low left lateral position of S-ICD to avoid potential shielding from the epicardial patch. This case highlights two important issues. First, the ability to overcome the potential risk of electrical shielding by placing the generator in a lower position and, secondly, the resulting sensing problems in such a case, which were overcome by programming a sensing vector which excluded the generator.

Conflict of interest: none declared.

References

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