Factors affecting the frequency of subcutaneous lead usage in implantable defibrillators

Incidence of ineffective safety margin testing (<10 J) and efficacy of routine subcutaneous array insertion during implantable cardioverter defibrillator implantation

The purpose of this study was to assess (1) the incidence of safety margin testing <10 J (SMT) and (2) the efficacy/safety of routinely adding a subcutaneous array (SQA) (Medtronic 6996SQ) for these patients.

Patients with SMT smaller than a 10-J safety margin from maximum output were considered to have very high readings and underwent SQA insertion. These patients were compared with the rest of the patients who had acceptable SMT (≥10 J).

A total of 616 patients underwent ICD implantation during the analysis period. Of those, 16 (2.6%) had SMT <10 J. By univariate analysis, younger age, and non-ischemic cardiomyopathy, were all significant predictors of SMT <10 J (p < 0.05). In all 16 cases, other methods to improve SMT prior to array insertion were attempted but failed for all patients: reversing shock polarity (n = 15), removing the superior vena cava coil (n = 14), reprogramming shock waveform (n = 9), and repositioning right ventricular lead (n = 9). Addition of the SQA successfully increased SMT to within safety margin for all patients (32 ± 2 versus 21 ± 3 J; p < 0.001). Follow-up (mean 48.1 ± 21 months) was available for all patients with SQA, only 2 cases with inappropriate shocks due to atrial fibrillation had to be noted. None of the patients experienced complications due to SQA implantation.

SMT <10 J occur in about 2.6% of patients undergoing ICD implantation. SQA insertion corrects this problem without procedural/mid-term complications.

Long-term experience with subcutaneous ICD leads: a comparison among three different types of subcutaneous leads

ICDs provide protection against sudden cardiac death in patients with life-threatening arrhythmias. Nevertheless, efficacy of defibrillation remains an important issue to guarantee the future safety of patients who receive an ICD. There is a significant number of patients who need an additional subcutaneous lead to obtain a defibrillation safety margin of at least 10 J between the maximum output of the ICD and the energy needed for ventricular defibrillation. However, few data exists about the long-term performance of different types of subcutaneous leads. Therefore, the aim of this study was to analyze the long-term experience with three different types of subcutaneous leads. The study included 132 patients (109 men, 23 women; mean age 59.8 years [SD +/- 10.7 years]). All of them received a subcutaneous lead in addition to a single chamber or dual chamber ICD between October 1990 and April 2002. Two patients received a second subcutaneous lead after the first lead had been removed so that a total of 134 subcutaneous leads were evaluated. Inclusion criteria for the implantation of an additional subcutaneous lead were (1) unsuccessful ventricular defibrillation at implant without a subcutaneous lead, (2) insufficient safety margin (< 10 J) between the maximum output of the ICD and the energy needed for ventricular defibrillation, or (3) clinical evaluation of a new subcutaneous lead (Medtronic 13014). There were no significant differences between the three study groups with regard to age, sex, underlying cardiac disease, left ventricular ejection fraction, NYHA class assessment and clinical arrhythmia. The results of the DFT testing during follow-up (prehospital discharge test and 1 and 3 years) were compared to the baseline value obtained during the implantation procedure. All lead related complications were analyzed. Eighty-two single element subcutaneous array electrodes (SQ-A1), 31 subcutaneous three-finger electrodes (SQ-A3), and 21 subcutaneous patch electrodes (SQ-P) were implanted during the study period. The median follow-up was 1,499 days (25th percentile: 798 days, 75th percentile: 1,976 days) in the SQ-A1 group, 2,209 days (25th percentile: 1,242 days, 75th percentile: 2,710 days) in the SQ-A3 group, and 1,419 days (25th percentile: 787 days, 75th percentile: 2,838 days) in the SQ-P group. None of the three groups had a significant change of the DFT during follow-up compared to baseline. Major complications occurred in six (7.3%) patients in group SQ-A1 and in two (9.5%) patients in group SQ-P. There were no major complications in group SQ-A3. Kaplan-Meier curves analyzing freedom from subcutaneous lead related complications did not show a significant difference between the three study groups (P = 0.16). SQ-A1, SQ-A3, and SQ-P leads provide stable DFTs during long-term follow-up. Major complications are rare. However, a careful follow-up including chest radiographs at regular intervals is needed to detect potentially fatal complications like lead fractures.

Subcutaneous array to transvenous proximal coil defibrillation as a solution to high defibrillation thresholds with implantable cardioverter defibrillator distal coil failure

Implantation of a subcutaneous array to improve the defibrillation threshold of an existing transvenous defibrillation lead system without the need for lead extraction is discussed.

The implantable cardioverter defibrillator

Implantable cardioverter defibrillators (ICDs) have evolved from the treatment of last resort to the gold standard therapy for patients at high risk for ventricular tachyarrhythmias. High-risk patients include those who have survived life-threatening arrhythmias, and individuals with cardiac diseases who are at risk for such arrhythmias, but are symptomless. Use of an ICD will affect the patient's quality of life. Some drugs can substantially affect defibrillator function and efficacy, and possible drug-device interactions should be considered. Patients with ICDs may encounter cell phones, antitheft detectors, and many other sources of potential electromagnetic Interference. In addition to treating ventricular tachyarrhythmias, new defibrillators provide full featured dual chamber pacing, and could treat atrial arrhythmias, and congestive heart failure by means of biventricular pacing.