Subcutaneous Patch Research Articles

Feasibility and acceptability of continuous at-home glucose monitoring during pregnancy: a mixed-methods pilot study

Background: Continuous monitoring of glucose (CGM) via subcutaneous patch is an accurate self-monitoring tool of blood glucose, but also introduces a range of additional benefits such as real-time feedback. While its value among pregnant women with gestational diabetes mellitus (GDM) is established in high-income countries, little is known about the feasibility and acceptability among pregnant women without GDM in low-resource settings in low- and middle-income countries. Objectives: This study aims to assess the feasibility and acceptability of CGM with pregnant mothers in South Africa and to explore the value of a collected data set for GDM prevention. Methods: Ten women between 12 and 18 weeks pregnant were recruited from the antenatal clinic at Chris Hani Baragwanath Academic Hospital into a prospective mixed-methods pilot study. Demographic and anthropometric data, HbA1c and a lipid panel were collected. Women then wore two consecutive Freestyle Libre 2 patches for a total of 28 days. In-depth interviews were undertaken with all 10 women on study exit to explore themes of acceptability and the use of technology during pregnancy. Thematic analysis was performed on the qualitative data while exploratory data-analysis techniques were applied to the CGM data. Results: Pregnant women (n = 10) had a mean (SD) age of 29.81 years (4.39), with most being unemployed (8), unmarried (8) and without a tertiary degree (7). Analysis suggests that fear of use was greater than the actual discomfort experienced during use of the CGM patch. The main barrier to use was the patch falling off and women being uncomfortable to reapply it. This was borne out by all 10 women wearing the first patch for at least 12 of the 14 days, but only 4 managing the same with patch two – primarily applied by themselves at home. Women expressed support for the use of technology during pregnancy, especially as it related to feeling that their pregnancy was being monitored and that they were being supported. Conclusion: In this pilot study, women overwhelmingly found the wearing of a CGM patch during pregnancy to be acceptable. Feasibility was reasonable with most data being successfully retrieved from the devices over a two-week period. Longer use was found to have additional challenges. The use of CGM patches appear to be a possible candidate for inclusion in GDM prevention or behavioural interventions during pregnancy in South Africa.

Rabbits (Oryctolagus cuniculus) as a Model System for Longitudinal Experimental Opioid Treatments: Implications for Orthopedic and Biomedical Research

Due to the high prevalence of opioid prescription following orthopedic procedures, there is a growing need to establish an animal model system to evaluate the effects of opioids on bone remodeling. Rabbits have been employed as model organisms in orthopedic research as they exhibit well-defined cortical bone remodeling similar to humans. Existing research in rabbits has been limited to modes of opioid administration that are short-acting and require repeated application. Here, we present data from a proof-of-principle longitudinal study employing two opioid analgesic administration routes (subcutaneous injection and transdermal patch) to evaluate the efficacy of studying chronic opioid exposure in a rabbit model. Skeletally mature male New Zealand White rabbits (Oryctolagus cuniculus) were divided into three groups of seven animals: morphine, fentanyl, and control. Experimental treatments were conducted for eight weeks. Preparation of the skin at the fentanyl patch site and subsequent patch removal presented experimental difficulties including consistent skin erythema. Though noninvasive, the patches further caused acute stress in fentanyl animals. We conclude that though transdermal fentanyl patches may be preferred in an acute clinical setting, this method is not feasible as a means of long-term pain relief or opioid delivery in a laboratory context.

Future Treatments for Parkinson's Disease: Surfing the PD Pipeline

ABSTRACTOur current wish list for the treatment of Parkinson's disease (PD) includes therapies that will provide robust and sustained antiparkinsonian benefit through the day, ameliorate or prevent dyskinesia, and slow or prevent the progression of the disease. In this article, I review selected new therapies in clinical development for motor features or treatment complications of PD, and some that may slow disease progression. These include adenosine 2a (A2a) antagonists (istradefylline, preladenant, and SYN115), levodopa/carbidopa intestinal gel (LCIG), IPX066—an extended-release formulation of carbidopa/levodopa, XP21279—a sustained-release levodopa prodrug, ND0611—a carbidopa subcutaneous patch, safinamide—a mixed mechanism of action medication that may provide both MAO-B and glutamate inhibition, PMY50028—an oral neurotrophic factor inducer, antidyskinesia medications (AFQ056 and fipamezole), and gene therapies (AAV2-neurturin and glutamic acid decarboxylase gene transfer). Some of these therapies will never be proven efficacious and will not come to market while others may play a key role in the future treatment of PD.

Designer Natriuretic Peptides for Heart Failure

The endogenous natriuretic peptides ANP, BNP and CNP, via particulate guanylyl cyclase (GC) receptors and the second messenger cyclic guanosine monophosphate (cGMP), are potent activators of key signaling pathways. Emerging research suggests that in human disease such as heart failure (HF) these natriuretic peptides (NP), which possess broad pleiotropic protective properties, may be deficient or may be released by the heart as abnormal molecular forms with reduced pGC activating properties. Therefore, novel NP/GC/cGMP therapies and innovative NP peptide delivery systems are being developed. CD-NP (cenderitide) represents a new class of NP, which we call designer NPs which was designed at Mayo Clinic. CD-NP represents the most clinically advanced of the designer NPs that is now in clinical trials for HF. CD-NP was uniquely designed to co-activate both the GC-A receptor to which ANP and BNP bind as well as GC-B to which CNP binds. Thus it has the unique ability to optimally activate the entire NP/GC receptor family. Clinical trials are now underway to chronically deliver CD-NP by a subcutaneous patch pump simulating the strategy for chronic insulin administration to reduce rehospitalization for HF. Other innovative delivery systems also include oral delivery and gene delivery. As increasing evidence supports the key role of hypertension especially resistant hypertension as a cause of HF, we also will discuss our second designer NP which is named MANP which functions as a super ANP and a pure GC-A agonist. Motivated by genetic studies that human hypertension may be linked in part to an ANP deficiency; MANP serves as a potent natriuretic, aldosterone suppressing and blood pressure lowering peptide, which goes beyond native ANP. Importantly, it may be delivered chronically both by subcutaneous, oral and novel nanotechnologies permitting enhanced hypertension control, which goes beyond conventional anti-hypertensive agents. Thus, designer NPs hold the promise as novel treatments as well as preventive strategies for HF resulting in a reduction in the burden of cardiovascular disease.

Efficacy of an implantable cardioverter-defibrillator in a neonate with LQT3 associated arrhythmias

We present a case in which LQTS induced severe prenatal and neonatal arrhythmias. LQT3 was diagnosed (mutation R1623Q). Short-acting beta-blockers were ineffective as well as sotalol and mexiletine in preventing recurrent ventricular arrhythmias. An ICD was implanted at the age of 7 months (weight and length of the infant at implantation 6 kg and 60 cm respectively). Flecainide was prescribed in addition to the ICD implantation. After an appropriate shock the flecainide plasma levels were shown to be subtherapeutic. Readjustment of the flecainide dose resulted in adequate plasma levels. No further shocks occurred during a further 17 months follow-up period. The combination of an active can with a subcutaneous patch proved feasible, and lifesaving shocks occurred at 7 months after implantation.

Fracture of the Subcutaneous Patch Electrode in a Patient With an Implanted Cardioverter-Defibrillator

There are more than 20 years of experience with implantation of defibrillator devices in humans and the procedure is an important therapeutic option for patients at high risk of life-threatening ventricular arrhythmias. The incidence of new defibrillator implantation has gradually increased, being used even in children, (1) although pediatric use is associated with several complications, especially with epicardial systems,(2) including fracture of the subcutaneous patch,(3-5) mainly because of growth.(3) We present a case of subcutaneous patch electrode fracture in the left axillary pectoral region of a patient who needed the patch for effective defibrillation, and we discuss the methods of treatment.

Long‐Term Experience with Subcutaneous ICD 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.

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.

Electrophysiologist‐Implanted Transvenous Cardioverter Defibrillators Using Local Versus General Anesthesia

With the advent of smaller biphasic transvenous implantable cardioverter defibrillators (ICDs) and the experience gained over the years, it is now feasible for electrophysiologists to implant them safely in the abdominal or pectoral area without surgical assistance. Throughout the years, general anesthesia has been used as the standard technique of anesthesia for these procedures. However, use of local anesthesia combined with deep sedation only for defibrillation threshold (DFT) testing might further facilitate and simplify these procedures. The purpose of this study was to test the feasibility of using local anesthesia and compare it with the standard technique of general anesthesia, during implantation of transvenous ICDs performed by an electrophysiologist in the electrophysiology laboratory. For over 4 years in the electrophysiology laboratory, we have implanted transvenous ICDs in 90 consecutive patients (84 men and 6 women, aged 58 +/- 15 years). Early on, general anesthesia was used (n = 40, group I), but in recent series (n = 50, group II) local anesthesia was combined with deep sedation for DFT testing. Patients had coronary (n = 58) or valvular (n = 4) disease, cardiomyopathy (n = 25) or no organic disease (n = 3), a mean left ventricular ejection fraction of 35%, and presented with ventricular tachycardia (n = 72) or fibrillation (n = 16), or syncope (n = 2). One-lead ICD systems were used in 74 patients, two-lead systems in 10 patients, and an AVICD in 6 patients. ICDs were implanted in abdominal (n = 17, all in group I) or more recently in pectoral (n = 73) pockets. The DFT averaged 9.7 +/- 3.6 J and 10.2 +/- 3.6 J in the two groups, respectively (P = NS) and there were no differences in pace-sense thresholds. The total procedural duration was shorter (2.1 +/- 0.5 hours) in group II (all pectoral implants) compared with 23 pectoral implants of group I (2.9 +/- 0.5 hours) (P < 0.0001). Biphasic devices were used in all patients and active shell devices in 67 patients; no patient needed a subcutaneous patch. There were six complications (7%), four in group I and two in group II: one pulmonary edema and one respiratory insufficiency that delayed extubation for 3 hours in a patient with prior lung resection, both probably related to general anesthesia, one lead insulation break that required reoperation on day 3, two pocket hematomas, and one pneumothorax. There was one postoperative arrhythmic death at 48 hours in group I. No infections occurred. Patients were discharged at a mean time of 3 days. All devices functioned well at predischarge testing. Thus, it is feasible to use local anesthesia for current ICD implants to expedite the procedure and avoid general anesthesia related cost and possible complications.

Lead-related complications in 340 patients with an implantable cardiverter/defibrillator

From February 1991 to May 1998, 340 patients had a cardioverter/defibrillator (ICD) implanted. Mean age was 64 +/- 9 years, 278 male and 62 female. 60% of patients had coronary artery disease and 31% dilatative cardiomyopathy. Ejection fraction was 38 +/- 14%. The indication for an implantable cardioverter/defibrillator was in 57% of patients ventricular tachycardia, in 43% ventricular fibrillation. 298 patients had a single-chamber cardioverter/defibrillator implanted, 42 patients a dual-chamber cardioverter/defibrillator. In 25 patients additional subcutaneous patch or array electrodes and in 2 patients additional epicardial patch electrodes were implanted. Implantation site was in 92 patients abdominal and in 248 pectoral. Over a period of 7 years 34 lead-related complications occurred in 33 patients (9.7%), after a median of 2 months after implantation. Diagnosis was made by routine chest x-ray in about 55% of lead-related complications, by clinical presentation (inadequate therapy, pain) in 24%, and by electrical parameters in 21%. In patients with an abdominal implantation site, lead-related complications occurred in 20%, in contrast to 6% in patients with a pectoral implantation site. Regarding patients with pectoral implantation site, lead-related complications were observed in 12% of patients with a dual-chamber ICD vs 4% with a single-chamber ICD (p = 0.05), due to dislocation of atrial electrodes with dual-chamber ICD. There were no differences in clinical parameters between patients with pectoral vs abdominal and between single vs dual-chamber ICD. There were no deaths due to lead-related complications.

Bispectral energies within electrocardiograms during ventricular fibrillation are correlated with defibrillation shock outcome.

We investigated whether the degree of phase coupling among orthogonal electrocardiograms during ventricular fibrillation (VF) was correlated with defibrillation shock outcome. We used cross bispectrum to estimate the degree of phase coupling. In dogs, VF was electrically induced and terminated with a defibrillation shock with a 50% probability of success. The defibrillation shock was delivered between the right ventricular apex and a subcutaneous patch electrode. Bispectra were integrated within 8.7-11.7, 8.7-11.7 Hz bandwidths and compared between those trials for which the defibrillation shocks were successful (206 trials, 49%) and unsuccessful (221 trials, 51%) in terminating VF. Results showed that between 200 and 1000 ms before defibrillation shock, unsuccessful trials had greater bispectral energy than successful trials (p<0.05). Although correlations between degree of phase coupling and shock outcome do not indicate causal relationship or predictability, they provide further evidence of the organization during fibrillation. We discuss the nonstationary wavelet hypothesis, previously proposed in the literature by other investigators, as one of the possible mechanisms to explain the correlation between bispectral energy and shock outcome.

Relation between ventricular fibrillation voltage and probability of defibrillation shocks: Analysis using Hilbert transforms

We used Hilbert transforms to re-evaluate the previously reported correlation between defibrillation shock outcome and absolute ventricular fibrillation voltage (AVFV). Previously in the literature, single values of AVFV acquired just prior to shock delivery were used to show a correlation between AVFV and shock outcome. In subsequent studies, a modified analysis procedure was used to show a correlation between shock outcome and moving average of AVFV. The use of single values of AVFV makes the AVFV sensitive to the local phase of the electrocardiographic (ECG) waveform, whereas moving averages are weighted by previous values of the ECG. The envelope is independent of the phase of the ECG and is not weighted by previous values of ECG as is the moving average. We explored, therefore, whether the AVFV computed from the envelopes of the ECG showed a stronger correlation with shock outcome than single values and moving averages of the AVFV. We estimated envelopes using the Hilbert transform. Orthogonal ECGs (sagittal, X; transverse, Y; and longitudinal, Z) were recorded from 11 dogs during 10 seconds of electrically induced ventricular fibrillation followed by a defibrillation shock with 50% probability of success. We used transvenous (right ventricular apex to subcutaneous patch) leads to deliver defibrillation shocks. Results from 236 successful and 249 unsuccessful trials showed, in contrast with the previously reported correlation, that moving average of AVFV was not higher for successful trials. In the Z direction, unsuccessful trials had higher voltage than successful trials ( P < .05). Comparison of envelope voltages between successful and unsuccessful trials did not show any consistent and statistically significant differences. Although there were some methodological differences between ours and the previously reported studies, they are unlikely to have caused the discrepant observations. Our results suggest, therefore, that the absolute voltage of ECG during ventricular fibrillation is not robustly correlated with shock outcome.

Infections with Nonthoracotomy Implantable Cardioverter Defibrillators: Can These Be Prevented?

Nonthoracotomy ICDs are believed to be the best therapeutic modality for treatment of life-threatening ventricular arrhythmias. Little is known about the risk of infection with initial implantation of these devices. We studied the incidence, clinical characteristics, and risk factors associated with infections in 1,831 patients with nonthoracotomy ICD from the Endotak-C nonthoracotomy lead registry of Cardiac Pacemakers, Inc. A transvenous lead was implanted in 950 patients (51.9%) and a combination transvenous plus subcutaneous patch was used in 881 patients (48.1%). Nine preselected data variables were studied, and all investigators identified as having patients with infections were personally contacted. Infections occurred in 22 (1.2%) of 1,831 patients receiving this nonthoracotomy ICD system. The mean time to infection was 5.7 +/- 6.5 months (range 1-25 months). Staphylococci were isolated in 58% of patients with reported infection. The presence of a subcutaneous defibrillator patch system was associated with the development of infection. Six of 950 patients (0.63%) with a totally transvenous lead system developed infection versus 16 of 838 (1.9%) patients with a transvenous lead plus subcutaneous patch system configuration (P = 0.015, Chi-square test), with an unadjusted estimated odds ratio of 3.06 (CI 1.19-7.86). The risk of infection encountered with the nonthoracotomy ICD is low, estimated from our data to be 1.2%. Placement of a subcutaneous defibrillator patch appears to be an independent risk factor for development of infection.

A patch in the pectoral position lowers defibrillation threshold.

Implantable pacemaker cardioverter defibrillators are now available with biphasic waveforms, which have been shown to markedly improve defibrillation thresholds (DFTs). However, in a number of patients the DFT remains high. Also, DFT may increase after implantation, especially if antiarrhythmic drugs are added. We report on the use of a subcutaneous patch in the pectoral position in 15 patients receiving a transvenous defibrillator as a method of easily reducing the DFT. A 660-mm2 patch electrode was placed beneath the generator in a pocket created on the pectoral fascia. The energy required for defibrillation was lowered by 56% on average, and the system impedance was lowered by a mean of 25%. This maneuver allowed all patients to undergo a successful implant with adequate safety margin.

Einfluß von Amiodaron auf Defibrillationsschwelle und perioperative Komplikationen bei Patienten mit implantierbarem Kardioverter-Defibrillator mit transvenösen Elektroden und biphasischen Schocks

In order to evaluate the safety of implantation of a third generation automatic cardioverter-defibrillator (ICD) in patients with amiodarone therapy, we retrospectively analyzed implantation results and perioperative complications in 17 consecutive patients with continued amiodarone therapy and 38 patients without antiarrhythmics at first ICD implantation.ICD implantation could be performed successfully in all 55 patients using a transvenous electrode system. In one of 17 patients with amiodarone (6%) versus three of 38 patients without antiarrhythmics (8%), additional implantation of a subcutaneous patch electrode was necessary to achieve a defibrillation threshold </=24 Joules (p=n.s.). Intraoperatively tested defibrillation threshold was 13+/-5 Joules in the amiodarone group versus 12+/-5 Joules in patients without antiarrhythmics (p=n.s.). The incidence of perioperative complications was not different between patients with amiodarone and patients without antiarrhythmics.In summary, patients with amiodarone did not have higher defibrillation thresholds or a higher incidence of perioperative complications than patients without antiarrhythmics. The occasionally postulated discontinuation of amiodarone with subsequent waiting for the elimination of this antiarrhythmic drug is unnecessary. For final clarification of the influence of amiodarone-therapy on the defibrillation threshold in patients with third generation ICDs, a prospective randomized study in a large patiente cohort with standardized study conditions would be required.

Long‐Term Survival and Complications in Patients With Malignant Ventricular Tachyarrhythmias: Treatment With a Nonthoracotomy Implantable Cardioverter Defibrillator With or Without a Subcutaneous Patch

The Endotak lead system and ICD has been used to treat patients with malignant ventricular arrhythmias. We analyzed the clinical characteristics of 1,053 patients who underwent implantation of the Endotak lead system with or without a subcutaneous patch. Group A consisted of 567 patients receiving the Endotak lead with a subcutaneous patch; group B consisted of 486 patients receiving the Endotak lead alone. The 2-year survivals from sudden death, cardiac death, and total death in groups A and B were 97.6%/98.2% (P = 0.38), 88.6%/92.7% (P = 0.09), and 84.7%/86.8% (P = 0.06), respectively. Minimum tested effective defibrillation energy at implantation was 17.2 +/- 5.2 J for group A and 15.8 +/- 5.1 J for group B (P < 0.01). The operative mortality was 1.8% in group A and 0.6% in group B (P = 0.09). The incidence of lead dislodgment, malfunction, and infection was 6.7% for group A and 3.5% for group B (P < 0.01). Sudden death survival was excellent in both groups with less lead complications in group B. The Endotak lead alone may be the preferred choice of lead configuration in those patients who have adequate defibrillation thresholds at implant.

Relation Between Amiodarone and Desethylamiodarone Plasma Concentrations and Ventricular Defibrillation Energy Requirements

The main finding of this prospective, controlled study is that amiodarone and desethylamiodarone plasma concentrations < 1 mg/L are associated with a 23% increase in the acute defibrillation energy requirement and with a 31% increase in the requirement for a subcutaneous patch or array. The defibrillation energy requirement does not correlate with the plasma concentrations of amiodarone, desethylamiodarone, amiodarone plus desethylamiodarone, or with the duration or daily dosage of amiodarone therapy.

Factors Associated With Elevated Impedance With a Nonthoracotomy Defibrillation Lead System

Peak current flow across the heart determines the success of defibrillation and is inversely dependent on impedance between defibrillation electrodes. Factors associated with elevated impedance in patients with implantable defibrillators using nonthoracotomy lead systems have not been well described. Clinical and echocardiographically derived variables were analyzed in 41 patients in whom implantation of a nonthoracotomy lead system was attempted. Lead impedance was measured at end-expiration with 5-J monophasic shocks. Successful defibrillation with or without addition of a subcutaneous patch with ≤20 J with a monophasic waveform was required for nonthoracotomy lead placement. Patients were divided into 2 groups based on impedance: low (≤47 ohms, n = 30) and high (>47 ohms, n = 11). Twenty-four patients had successful defibrillator implantation using a transvenous lead alone, 13 required placement of a subcutaneous patch, and 4 required epicardial patch placement. The mean left ventricular end-diastolic and end-systolic volumes were significantly smaller (p = 0.01 for both) in patients in the low- versus high-impedance groups and were significantly correlated with impedance (r = 0.44, p < 0.005 for both). Impedance was not significantly different between patients with successful defibrillation using a transvenous lead alone compared with those who required either subcutaneous or epicardial patches. Thus, impedance using a nonthoracotomy lead system with monophasic shocks is significantly correlated with both end-systolic and end-diastolic volumes, but elevated impedance does not predict increased defibrillation energy requirements.This study examined the influence of clinical, radiographic, and echocardiographic variables on impedance measured with 5-J monophasic shocks at end-expiration with a nonthoracotomy lead system in 41 patients. Significant correlations (r = 0.44, p < 0.005 for both) were found between impedance and both end-systolic and end-diastolic volumes, but elevated impedance did not predict increased defibrillation energy requirements with a nonthoracotomy lead or the need for either subcutaneous or epicardial patches.

First experience with a new nonthoracotomy defibrillation lead system

The clinical efficacy and safety of a new nonthoracotomy defibrillation lead system (TVL lead system, Ventritex, Inc., Sunnyvale, Calif.) was studied in patients with ventricular tachycardia or fibrillation. Implantation of the TVL lead system and a Cadence pulse generator (Ventritex, Inc.) was attempted in 27 patients. A subcutaneous patch lead was added if required to achieve adequate defibrillation energy. Patients were monitored for an average of 6 ± 4 months (range 1 week to 14 months). Implantation was successful in 26 patients (96%). Twenty-three of those patients (88%) were implanted in a lead-alone configuration; the remaining three (12%) required a subcutaneous patch lead. The mean defibrillation threshold was 401 ± 120 V (12 ± 7 J) at implantation, 467 ± 134 V (15 ± 8 J) at predischarge testing, and 452 ± 151 V (14 ± 9 J) at 4-month follow-up. The mean defibrillation threshold at 4 months was not significantly different from that at implant. No deaths, sensing anomalies, infections, lead fractures, or lead dislodgments occurred. One patient required addition of a subcutaneous patch 4 months after device implantation because of an elevated defibrillation threshold. Eight patients (31%) experienced 545 spontaneous arrhythmic episodes, and all episodes were successfully terminated by the device. In conclusion, the TVL lead system combined with Cadence tiered-therapy defibrillator has a high success rate and low complication rate, and it can be recommended for treatment of patients with life-threatening ventricular tachyarrhythmias.

Serial defibrillation lead impedance in patients with epicardial and nonthoracotomy lead systems.

The stability of implantable cardiac defibrillation lead impedance subsequent to implantation has not been reported and may have important clinical implications. The objective was to characterize the incidence and degree of impedance changes occurring after implantation of defibrillation lead systems. The study cohort consisted of patients who received epicardial or nonthoracotomy lead systems. Defibrillation impedance was recorded at implantation, prior to hospital discharge (predischarge), and during follow-up. For each individual the magnitude of the impedance change relative to implantation was characterized. Among patients with an epicardial system, a significant decrease in impedance was observed at predischarge (mean 9.3 omega). The magnitude of the decrease was large in 39% and moderate in 31% of individuals. Subsequently, a gradual rise in mean impedance was apparent. At 18-21 months postimplantation, impedance was significantly increased relative to implantation (mean 6.8 omega). At this time, the magnitude of the increase was large in 46% and moderate in 23% of patients. Among patients with a nonthoracotomy lead system including a subcutaneous patch, a significant decrease in mean impedance was observed at predischarge (mean 3.5 omega). The magnitude of the decrease was large in 8% and moderate in 50% of individuals. Subsequently, a gradual rise in impedance was apparent. At 5-6 months, it was significantly increased relative to implantation (mean 2.3 omega). The magnitude of the increase was large in 10% and moderate in 33% of patients. Among the group of patients whose nonthoracotomy lead system did not include a subcutaneous patch, there was no significant change in mean impedance at predischarge relative to implantation. In subsequent intervals, a gradual rise was apparent. At 5-6 months, impedance was significantly increased relative to implantation (mean 4.3 omega). The magnitude of the increase was large in 16% and moderate in 47% of individuals. Significant changes in defibrillation lead impedance occur after implantation of epicardial and nonthoracotomy defibrillation lead systems. These data may serve as a standard for identifying the anticipated maximum change in lead impedance and thus may be useful as a tool for recognizing problems with defibrillation lead integrity.