A prospective, randomized evaluation of a nonthoracotomy implantable cardioverter defibrillator lead system. Endotak/PRX Investigator Group

Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study

The patch electrode and the array electrode are the two types of subcutaneous leads available as an adjunct to a transvenous lead system in patients with high defibrillation thresholds. A prospective randomized study was conducted in 30 consecutive patients comparing the efficacy and the long-term performance of a patch electrode with an array electrode. After determination of the defibrillation threshold for the transvenous lead alone, a subcutaneous patch or an array electrode was implanted in random order. Adding a patch electrode decreased the defibrillation threshold in seven out of 15 patients (47%) from 13.2+/-6.6 to 10.5+/-5.1 J (P<0.05). In 13 out of 15 patients (87%), the implantation of an array electrode caused a significant lowering of the defibrillation threshold from 15.4+/-6.6 to 8.2+/-5.0 J (P<0.0001). The array electrode was significantly more effective in lowering the defibrillation threshold than the patch electrode (P<0.01). Complications during follow-up associated with the subcutaneous patch electrode were observed in four patients whereas no complications were associated with the array electrode (P<0.01). The additional implantation of an array electrode is more effective and associated with fewer complications compared to a patch electrode.

Subpectoral cardioverter-defibrillator implantation using a lateral approach

INTRODUCTION

Third-generation cardioverter-defibrillators have revolutionized management of ventricular tachyarrhythmias. Implantation can be performed in the electro-physiology laboratory, with minimal morbidity. Generator size has shrunk to the point that subcutaneous implantation is feasible and safe, even under local anesthesia. The prepectoral technique, however, is associated with increased mechanical stress to the subcutaneous tissue and can predispose to device erosion or infection. These complications may be avoided by submuscular placement. Among subpectoral techniques, the lateral approach offers unrestricted ability to deploy patches or array electrodes, should the need arise, and may represent the optimal implant technique under some circumstances.

METHODS

We studied 29 male patients, aged 29-78 years, who presented with syncope or sustained ventricular tachycardia, and underwent subpectoral defibrillator implantation under general anesthesia or conscious sedation. All devices were third-generation active can systems with biphasic shock capability. Six dual-chamber defibrillators were used.

RESULTS

Subpectoral implantation was successful in all cases, with an estimated blood loss of 28+/-17 mL and no immediate complications. Except for one patient who developed twiddler's syndrome and ultimately required revision to a subcutaneous pocket, the implant site was tolerated well, and no limitation in the range of motion of the upper limb was observed during 20 months of follow-up.

CONCLUSIONS

Subpectoral implantation using a lateral approach is technically straightforward and can be applied globally, with modest additional resource and equipment requirements. Familiarity with this approach can maximize the likelihood of successful defibrillator implantation in the electrophysiology laboratory.

Factors affecting the frequency of subcutaneous lead usage in implantable defibrillators

Subcutaneous leads (SQ) add complexity to the defibrillation system and the implant procedure. New low output devices might increase the requirement for SQ arrays, although this might be offset by the effects of active can and biphasic technology. This study sought to assess the impact of these technologies on SQ lead usage, and to determine if clinical variables could predict the need for an SQ lead. Patients receiving nonthoracotomy systems (n = 554) at our institution underwent step-down-to-failure DFT testing with implant criteria of a 10-J safety margin. SQ leads were used only after several endovascular configurations failed. Use of biphasic waveforms significantly lowered the frequency of use of SQ leads from 48% to 3.7% (P < 0.000001). SQ leads were required in 4.4% of patients with cold can devices and 2.6% of patients with active can devices (P = NS). There was no increase in SQ lead usage with low energy (< 30-J delivered energy) devices. Clinical variables (including EF, heart disease, arrhythmia, and prior bypass) did not predict the need for an SQ lead. The implant DFT using SQ arrays (14.5 +/- 6.5 J) was not significantly lower than that for SQ patches (16.6 + 6.0 J). We conclude that biphasic waveforms significantly reduce the need for SQ leads. Despite this reduction, 3.7% of implants still use an SQ lead to achieve adequate safety margins. The introduction of lower output devices has not increased the need for SQ leads, and when an SQ lead is required, there is not a significant difference in the implant DFT of patches versus arrays. Clinical variables cannot predict which patients require SQ leads.

Effect of a single element subcutaneous array electrode added to a transvenous electrode configuration on the defibrillation field and the defibrillation threshold

Even with the use of biphasic shocks, up to 5% of patients need an additional subcutaneous lead to obtain a defibrillation safety margin of at least 10 J. The number of patients requiring additional subcutaneous leads may even increase, because recent generation devices have a < 34 J maximum output in order to decrease their size. In 20 consecutive patients, a single element subcutaneous array lead was implanted in addition to a transvenous lead system consisting of a right ventricular (RV) and a vena cava superior lead using a single infraclavicular incision. The RV lead acted as the cathode; the subcutaneous lead and the lead in the subclavian vein acted as the anode. The biphasic defibrillation threshold was determined using a binary search protocol. Patients were randomized as to whether to start them with the transvenous lead configuration or the combination of the transvenous lead and the subcutaneous lead. In addition, a simplified assessment of the defibrillation field was performed by determining the interelectrode area for the transvenous lead only and the transvenous lead in combination with the subcutaneous lead from a biplane chest X ray. The intraoperative defibrillation threshold was reconfirmed after 1 week, after 3 months, and after 12 months. The mean defibrillation threshold with the additional subcutaneous lead was significantly (P = 0.0001) lower (5.7 +/- 2.9 J) than for the transvenous lead system (9.5 +/- 4.6 J). With the subcutaneous lead, the impedance of the high voltage circuit decreased from 48.9 +/- 7.4 omega to 39.2 +/- 5.0 omega. In the frontal plane, the interelectrode area increased by 11.3% +/- 5.5% (P < 0.0001) and in the lateral plane by 29.5% +/- 12.4% (P < 0.0001). The defibrillation threshold did not increase during follow-up. Complications with the subcutaneous electrode were not observed during a follow-up of 15.8 +/- 2 months. The single finger array lead is useful in order to lower the defibrillation threshold and can be used in order to lower the defibrillation threshold.