An epicardial subxiphoid implantable defibrillator lead: superior effectiveness after failure of standard implants

A single epicardial implantable lead using the subxiphoid approach is described in this article. It consists of a single halo-shaped coil that is implanted under the inferior surface of the heart, including the right and left inferior ventricular surfaces. It has been implanted in four patients who could not be defibrillated with a transvenous system, even with the adjunct use of subcutaneous leads or left chest wall patch. Three of the patients had progressive heart failure due to ischemic myocardiopathy; the fourth patient had a dilated idiopathic myocardiopathy. The approach is simple and appears to be effective due to its ability to encompass the left and right ventricles. This vector seems to significantly lower the threshold for defibrillation, and may offer substantial benefit in the setting of high defibrillation thresholds with conventional leads, or when conventional systems are inadequate to achieve consistent defibrillation.     

Influence of Anodal Electrode Position on Transvenous Defibrillation Efficacy in Humans: A Prospective Randomized Comparison

Nonthoracotomy lead systems for implantable cardioverter defibrillators (ICDs) have reduced operative mortality and morbidity as compared to epicardial lead systems but are usually associated with higher defibrillation thresholds (DFTs). The purpose of this prospective randomized trial was to investigate if the second defibrillation electrode in the left subclavian vein can increase defibrillation efficacy and decrease DFT as compared to the superior vena cava (SVC) position in nonthoracotomy lead systems for ICDs. Seventeen patients (mean age; 49.9 ± 11.3 years, mean ejection fraction; 46.1%± 15.8%) were implanted with an investigational unipolar electrode (Medtronic 13001) used as the defibrillation anode. DFT testing was started in the SVC (n = 10, group A) or the left subclavian vein (n = 7, group B), and repeated in the alternative position starting at the DFT of the initial position. Fifteen patients were eligible for analysis (group A: n = 9, group B: n = 6). With the electrode in the SVC, ventricular fibrillation could be successfully terminated in 9 out of 15 patients (60%). In the left subclavian vein the success rate was 100% (P < 0.01). Mean DFT in the SVC was 13.0 ± 5.2 J and in the left subclavian vein 10.2 ± 4.9 J. DFTs in the left subclavian vein were either lower (group A: n = 5/9, group B: n = 5/6) or equal to the results in the SVC position (P < 0.001). Thus, the left subclavian vein appears to be a superior alternative for positioning of the defibrillation anode as compared to the SVC for nonthoracotomy lead systems using two separate leads.     

Bipolar Transvenous Defibrillation: Efficacy of Two Different Positions of the Anode

For most nonthoracotomy defibrillotion lead systems, the transvenous anode can be positioned independently of the right ventricular (RV) cathode. Usually a vertical position in the superior vena cava (SVC) is chosen. However, it is unknown if this position yields the optimal defibrillation threshold (DFT). There-fort, in 15 patients undergoing defibrillator implantation the SVC position was compared in a crossover study design with a horizontal position in the left brachiocephalic vein (BCV). Mean DFT was not different for SVC and BCV (19.2 ± 9.6) vs 18.5 ± 9.1 J) but DFT of individual patients differed by up to 12 joules. A positive correlation between impedance and DFT in the BCV position (r = 0.6; P ≤ 0.05) indicated that the improved geometry of the defibrillation field with the BCV position is opposed by a higher impedance found for this position (63 ± 15 Ω vs 52 ± 7 Ω). Thus, defibrillation is not improved in general although individual patients might benefit.     

Defibrillator Implantation in a Patient with a Persistent Left Superior Vena Cava

The implantation of a transvenous cardioverter defibrillator (PCD 7217B) was performed in a patient with a persistent left superior vena cava. The defibrillation electrodes were positioned in the right ventricle and the superior vena cava via the right subclavian vein. A subcutaneous patch had to be implanted at the left lateral chest wall to achieve sufficient defibrillation thresholds. Three weeks later the system had to be removed because of a generator pocket infection. During the second implantation we placed one electrode in the persistent left superior vena cava perpendicular to the electrode in the right ventricle. Using this configuration transvenous defibrillation was possible without an additional subcutaneous patch.     

Cardiac resynchronization therapy

About 30% of patients with left ventricular systolic dysfunction also have ventricular conduction delays (prolonged QRS duration greater than 0.12 second) most frequently seen as left bundle branch block. This intraventricular conduction delay causes nonsynchronous ventricular activation between the right ventricle and the left ventricle (or dyssychrony), compromising cardiac function. Cardiac resynchronization therapy, or biventricular pacing, is a recent intervention for ventricular dyssychrony that incorporates 3 leads for pacing the right atrium and simultaneous pacing of the right ventricle and left ventricle. Left ventricular lead placement can be difficult to implant because of coronary venous anatomy and can require longer procedure time for the patient. Restoring ventricular synchrony has been shown to decrease septal wall dyskinesis, decrease mitral regurgitation, increase left ventricular filling time, decrease pulmonary capillary wedge pressure, and reverse ventricular modeling.     

Paradoxic Embolism Due to Altered Hemodynamic Sequencing Following Transvenous Pacing

A young patient, who experienced a cerebral embolic event 30 days after transvenous pacemaker iead placement, is reported. This patient had previously been paced with an epicardial lead without evidence of right to left intracardiac shunt. However, hemodynamic evaluation post-embolism demonstrated a marked temporal disparity of the pulmonary and systemic ventricles. This phasic divergence resulted in a brief reversal of right and left ventricular pressure ratios, and a paradoxic intracardiac shunt at a small ventricular septal defect. The potential for similar events in the presence of any defect of the atrial or ventricular septum mandates caution in the use of transvenous pacemaker leads in such patients.     

Internal Cardiac Defibrillation: Single and Sequential Pulses and a Variety of Lead Orientations

A sequential pulse system for internal cardiac defibrillation incorporating catheter and patch electrodes with two current pathways has been shown to reduce defibrillation threshold in comparison to the single pulse technique. The relative advantage of the sequential pulse over the single pulse technique with other lead systems is not known. We compared defibrillation thresholds using sequential and single pulses delivered to a variety of lead orientations with the same electrode surface areas, when possible. Defibrillation threshold totals determined in halothane-anesthetized open-chest pigs averaged: For the single pulse shock passed between (1) superior vena cava (SVC) and left ventricular apical patch (LVA), 27.2 +/- 9.1 joules (J) and (2) LV epicardial patch (LVE) to right ventricular epicardial (RVE) patch leads, 16.5 +/- 2.1 J; and for the sequential pulse shock with two pulses passed between: (1) the SVC to RV intracavitary apex (RVA) and a quadripolar catheter in the coronary sinus to the RVA, 11.6 +/- 1.0 J; (2) the SVC to LVA and the LVE to RVE, 9.6 +/- 1.3 J and (3) the SVC to RVA and the LVE to RVA, 8.9 +/- 0.4 J. Defibrillation thresholds for sequential pulse shocks were all significantly lower than either of the defibrillation thresholds for single pulse shocks (p less than 0.001). We conclude that the sequential pulse system provides a substantial reduction in defibrillation threshold over the single pulse regardless of the lead system when the surface area and pulse characteristics are controlled. Sequential pulse technique may be valuable in the design of an implantable automatic defibrillator.(ABSTRACT TRUNCATED AT 250 WORDS)     

Internal Cardiac Defibrillation Threshold: Effects of Acute Ischemia

The influence of myocardial ischemia on defibrillation success was studied using two different lead orientations in halothane-anesthetized pigs. Ischemia was induced by ligating the left anterior descending artery in its distal third. Controls had loosely tied ligatures placed around the artery at the same site. Ventricular fibrillation was induced by electrical stimulation 30 minutes after coronary artery ligation. Defibrillation used a single truncated pulse of approximately 6 ms duration passed to either: a transvenous electrode catheter (Medtronic, 6880) with the cathode in the apex of the right ventricle and the anode in the superior vena cava-atrial junction region, or the cathode in the apex of the right ventricle and a mesh plaque on the epicardium of the basal lateral left ventricle as anode. Ten seconds after the onset of ventricular fibrillation, defibrillation was attempted with increasing incremental energies until defibrillation was achieved. Fibrillation episodes were repeated at 15-minute intervals until the minimum first shock was successful in defibrillating the animal (i.e., defibrillation threshold). The number of animals successfully defibrillated with a minimum energy above or below 30 J was not different between normal and ischemic animals for either electrode configuration (i.e., 3 out of 20 vs 1 out of 13 for the catheter and 5 out of 6 vs 6 out of 7 for the epicardial plaque, respectively). Also, the cumulative percent success as a function of defibrillation energy was similar in both the normal and ischemic groups. There was a significant reduction in the minimum energy necessary for defibrillation when passing current between the right ventricular apex and the left ventricular epicardial plaque. The present results indicate that, despite differences in lead orientations, acute ischemia in the anesthetized pig does not appear to influence defibrillation success.     

Pacing from the Right Ventricular Septum: Is There a Danger to the Coronary Arteries?

Background: Pacing from right ventricular (RV) septal sites has been suggested as an alternative to RV apical pacing in an attempt to avoid long-term adverse consequences on left ventricular function. Concern has been raised as to the relationship of the left anterior descending coronary artery (LAD) to pacing leads in these positions.
Methods and Results: We retrospectively analyzed three cases in which patients with RV active-fixation leads in situ also had coronary angiography. Multiple fluoroscopic views were used to determine the relationship of the lead tip at various pacing sites to the coronary arteries. A lead placed on the anterior wall was in close proximity to the LAD, whereas septal and free wall positioning was not.
Conclusion: Placement of RV active-fixation leads on the septum avoids potential coronary artery compromise.     

Inadvertent Left Ventricle Endocardial or Uncomplicated Right Ventricular Pacing: How to Differentiate in the Emergency Department

Background

Temporary transvenous pacemaker implantation is an important and critical procedure for emergency physicians. Traditionally, temporary pacemakers are inserted by electrocardiography (ECG) guidance in the emergency department because fluoroscopy at the bedside in an unstable patient can be limited by time and equipment availability. However, in the presence of atrial septal defect, ventricular septal defect, and patent foramen ovale, the pacemaker lead can be implanted inadvertently into the left ventricle or directly into the coronary sinus instead of right ventricle. Regular pacemaker rhythm can be achieved despite inadvertent implantation of the pacemaker lead into the left ventricle, leading to ignorance of the possibility of lead malposition.

微创手术治疗慢性心功能衰竭

目的；探讨微创手术植入左心室心外膜起搏电极进行慢性心功能衰竭的再同步治疗的可行性、安全性和临床疗效。方法 按美国心脏病学会和美国心脏病学院（ACC／AHA）标准选择1例扩张性心肌病患者行再同步治疗，应用Medtrorile 5076心内膜起搏电极，通过心导管将右心房电极植入右心耳，右心室电极植入右宣流出道。通过微创手术经胸路径将Metronic 6945心外膜起搏电极植入左室侧后壁，电极经皮下隧道连至脉冲发生器。结果：三腔起搏电极均放置顺利。术后左心室同步性较前改善，患者恢复良好。结论：对于心导管径路左心室起搏电极放置失败的患者，微创手术植入左心室心外膜起搏电极是此类患者进行心脏再同步治疗的一种有效、可行和安全的方法。     

Transseptal Defibrillation Is Superior for Transvenous Defibrillation

The conventional electrode configuration of current internal defibrillation systems most commonly use superior vena caval (SVC) or combined SVC and subcutaneous (SC) electrodes as anode, and right ventricular apex (HVA) electrode as cathode. We have demonstrated earlier that the septal mass is important for defibrillation. The purpose of the present study was to compare a transseptal to a conventional electrode arrangement in the canine model. Three endocardial electrodes, 5 French EnGuard™ were positioned in RVA, SVC, and the right ventricular outflow (RVO) in eight dogs. A 5 French SC electrode was positioned in the fifth left intercostal space. RVA-RVO^-/SC⁺ (configuration 2) was compared to SVC-SC⁺/RVA^-(configuration 1). Defibrillation threshold testing was performed using asymmetrical biphasic shock, 6 msec⁺/2 msec^-. Probit fit was used to compare the results at 40%, 50%, 60%, and 90% probabilities, and the logistic regression analysis to estimate the impact of variables. Electrode configuration had the strongest predictive value. Configuration 2 was superior to configuration 1 (P = 0.0016). At any voltage settings the probability of success for configuration 2 was greater, and current less (P < 0.00005). The energy requirements were reduced by approximately 33% for configuration 2. There were no significant differences in impedance between the two configurations. We conclude that transseptal defibrillation is more effective because of the improved lead geometry and voltage gradient.     

Delayed presentation of totally avulsed right superior vena cava after extraction of permanent pacemaker lead

Pacemaker lead extraction has been shown to be an effective and safe treatment for infected permanent pacemaker leads, however, they may lead to potentially serious complications, usually occurring during the extraction procedure. This report describes a case of a 48-year-old woman with a patent persistent left SVC and an infected permanent pacemaker lead of a DDD pacing system who underwent transvenous laser-assisted lead extraction using a combined SVC and femoral approach. Two days after the procedure the patient developed symptoms of SVC obstruction requiring surgical intervention. The right SVC was found to be almost completely destroyed with only a thin strip of the lateral wall intact and active bleeding. The probable causative mechanisms and surgical management are discussed.     

Transvenous Defibrillation Leads: Is There an Ideal Position of the Defibrillation Anode?

A potential benefit of two-lead transvenous defibrillation systems is the ability to independently position the defibrillation electrodes, changing the vector field and possibly decreasing the DFT, Using the new two-lead transvenous TVL lead system, we studied whether DFT is influenced by SVC lead position and whether there is an optimal position. TVL leads and Cadence pulse generators were implanted in 24 patients. No intraoperative or perioperative complications were observed. In each patient, the DFTs were determined for three SVC electrode positions, which were tested in random order: the brachiocephalic vein, the mid-RA, and the RA-SVC junction. The mean DFTs in the three positions were not statistically different, nor was any single lead position consistently associated with lower DFTs. However, an optimal electrode position was identified in 83% of patients, and the DFT from the best lead position for each patient was significantly lower than for any one of the electrode positions (P < 0.01). The mean safety margin for the best SVC lead position was approximately 27 J. These results demonstrate the advantage of a two-lead system, as well as the importance of testing multiple SVC lead positions when the patient's condition permits. Both of these factors can decrease the DFT and maximize the defibrillation safety margin. This will become increasingly important as pulse generator capacitors become smaller (as part of the effort to decrease generator size) and the energy output of the generators consequently decreases.     

Right ventricular outflow tract pacing: radiographic and electrocardiographic correlates of lead position

OBJECTIVE: To characterize the pacing site in an unselected series of patients undergoing right ventricular outflow tract (RVOT) lead placement and investigate the role of the electrocardiogram (ECG) in predicting implantation. BACKGROUND: Right ventricular apical pacing is associated with long-term adverse effects on left ventricular function, fuelling interest in alternative pacing sites, especially the RVOT. Previous studies have been conflicting, possibly due to poor definition of pacing site within the RVOT. METHODS: In 150 patients undergoing pacemaker implantation, implanters were asked to place the lead in the RVOT. Radiographs were performed in the antero-posterior (AP) and 40 degrees right and left anterior-oblique projections post procedure. Fifty-six had left lateral radiographs. Lead position was categorized using AP/RAO (right anterior oblique) to confirm RVOT placement and left anterior oblique to distinguish free wall from septum. A 12-lead ECG was performed during ventricular pacing. RESULTS: Leads were below the RVOT in 18. Of the remaining 132, the majority (94%) were in the inferior/low RVOT. Eighty-one out of 132 were septal and 51 free wall. Septal sites were associated with shorter QRS duration (134 ms vs 143 ms, P < 0.02). Free wall sites displayed more frequent notching of the inferior leads (P < 0.01). A negative deflection in lead I provided a positive predictive value of 90% for septal sites. In those with lateral radiographs, a posteriorly projected lead was 100% specific for septal placement. CONCLUSIONS: This study demonstrates the heterogeneity of lead placement within the RVOT. Septal and free wall sites display characteristic ECG patterns which may be used to aid placement. The left lateral radiograph is useful in confirming a true septal location.     

Transvenous Atrial Cardioversion Threshold in Patients with Implantable Cardioverter Defibrillator: Influence of Active Pectoral Can

Recent studies have shown that transvenous atrial cardioversion is feasible with lead configurations primarily designed for implantable cardioverter defibrillators (ICD). The purpose of this study was to examine the influence of an active pectoral ICD can on the atrial cardioversion threshold (ADFT). Forty consecutive patients received a transvenous single lead system (Endotak DSP 0125, CPI, St. Paul, MN, USA) in combination with a left subpectoral ICD (Ventak Mini, CPI) for treatment of malignant ventricular tachyarrhythmias. Patients were randomized into two groups: 21 received a Hot Can 1743 and 19 patients a Cold Can 1741. Step-down testing of the ventricular defibrillation threshold (VDFT) was performed intraoperatively and evaluation of the ADFT for induced atrial fibrillation (AF) at predischarge. After testing, each patient received a 2-J shock and was asked to quantify discomfort on a numerical scale ranging from 0 to 10. Both groups were comparable with regard to all clinical parameters studied. The mean VDFT in patients with a Hot Can device was significantly lower than in patients with a Cold Can (7.5 ± 2.3 J vs 9.8 ± 3.8 J; P < 0.03). The mean ADFT in the Hot Can group tended to be lower than in the group with Cold Cans (3.4 ± 1.4 J vs 4.5 ± 2.4 J; P = 0.07), and the proportion of patients in whom atrial cardioversion was accomplished at low energies (≤ 3 J) was higher in patients with active compared with patients with inactive pulse generators (57% vs 26%; P < 0.04). The mean discomfort reported after delivery of a 2-J shock was comparable in both groups (Hot Can 5.2 ± 1.9; Cold Can: 5.3 ± 2.1; P = NS). We conclude that the inclusion of an active left subpectoral can in the defibrillation vector of a ventricular ICD seems to reduce the energy requirements for atrial cardioversion without increasing the discomfort caused by low energy shocks.     

Lead Fracture in Cephalic Versus Subclavian Approach with Transvenous Implantable Cardioverter Defibrillator Systems

Lead fracture, occurring in approximately 1%–4% of patients, is an infrequent, but potentially catastrophic complication of permanent pacing systems. Its incidence in transvenous defibrillator systems has not been established. We analyzed data from 757 patients undergoing implantation of transvenous Cardioverter defibrillator systems using the Medtronic Transvene Lead® system between October 20, 1989 and June 25, 1992 to determine if site of venous approach influenced incidence of lead fracture. All patients received a 3-lead system in 1 of 3 configurations: (1) right ventricle/superior vena cava/subcutaneous patch; (2) right ventricle/coronary sinus/subcutaneous patch; or (3) right ventricle/superior vena cava/coronary sinus. Of 767 right ventricular leads placed, 523 were placed via the subclavian vein, 221 via cephalic vein, and 18 via the internal jugular (5 leads were implanted using another vein). The total number of leads is greater than the total number of patients, as five patients received a second defibrillator system if the initial system was explanted and reimplanted for any reason. Seven patients (0.9%) had right ventricular lead fracture, presenting with inappropriate defibrillator shocks (1), loss of pacing ability (3), both loss of pacing ability and inappropriate shocks (1), or increased pacing threshold (2). All patients required reoperation. AH had leads placed by the subclavian venous approach, with chest X ray confirming fracture at the clavicle-first rib junction in 6 of 7 cases. Using Fisher's Exact test, the difference in lead fracture between subclavian and cephalic vein implant approached statistical significance (P = 0.08). The trend toward increased lead fracture incidence with leads placed via subclavian vein suggests that cephalic vein approach may be preferable to avoid this complication.     

Differences in the Pathological Changes in Dogs' Hearts After Defibrillation with Extrapericardial Paddles and Implanted Defibrillator Electrodes

A comparison was made between the pathological changes in the myocardium of eight dogs, each receiving about 90 joules of energy in a series of defibrillation discharges, delivered either between paddles placed against the pericardium (3 dogs) or between implanted Telectronics 040–105 defibrillation patch electrodes (5 dogs). The changes in the myocardium were most pronounced where the paddles had been applied to the pericardium. There was transmural damage beneath the left and right paddle positions and in the surrounding tissues. Extensive subepicardial and subendocardial myocyte damage was obvious histologically in the right ventricle of one of the patch dogs and in all of the paddle dogs. The percentage of damaged myocardial mass, both right ventricular and total involvement, was higher in the three paddle dogs compared with the five patch dogs. There was septal damage in the heart of one paddle dog. Necrosis of the right ventricular wall was observed in three of the patch dogs and in all the three paddle dogs. Scattered necrotic myocytes and some patches of mild necrosis up to 1-mm deep were observed in the left ventricle of the patch dogs (severity score 1–3). The necrosis was more extensive in the paddle dogs, ranging from mild necrosis < 1-mm deep to marked necrosis incorporating half-to-whole ventricular wall thickness (severity score 3–5).     

Transvenous Single Lead Atrial Defibrillation: Efficacy and Risk of Ventricular Fibrillation in an Ischemic Canine Model

Transvenous atrial defibrillation with multiple atrial lead systems has been shown to be effective in models without the potential for ventricular arrhythmias. The specific aim of this study was to evaluate the efficacy and safety of transvenous single lead atrial defibrillation in a canine model of ischemia cardiomyopathy. Ten dogs had ischemia cardiomyopathy induced by repeated intracoronary micmsphere injections. The mean LV ejection fraction decreased from 71%± 9% to 38%± 14% (P = 0.003). Spontaneous atrial fibrillation (AF) developed in four dogs, and in six AF was induced electrically. Atrial defibrillation thresholds (ADFTs) were determined with synchronous low energy shocks using a transvenous tripolar lead with two defibrillation coils (right ventricle, superior vena cava) and an integrated sensing lead (RV coil vs electrode tip). The ADFTs derived by logistic regression were compared at 50% and 90% probability of success (ED₅₀, ED₉₀): ED₅₀ was 2.4 ±1.7 J and 2.9 ±2.1 J, respectively, for 5- and 10-ms monophasic shocks, and 1.8 ± 0.9 J and 2.1 ± 1.3 J, respectively, for 5- and 10-ms biphasic shocks. Immediately after 3 of 2,179 (0.1%) synchronized shocks, ventricular fibrillation (VF) developed. VF was induced in 3 of 1,062 (0.3%) shocks with integrated sensing (RV coil vs electrode tip) compared to 0 of 1,117 shocks when a separate bipolar RV sensing electrode was used for synchronization. In our canine model of ischemic cardiomyopathy, low energy atrial defibrillation via a transvenous single lead system was highly effective. However, there was a small but definite risk of VF induction, which seemed to be greater when an integrated as opposed to a true bipolar RV sensing was used.     

Comparison of a Unipolar Defibrillation System with a Dual Lead System Using an Enlarged Defibrillation Anode

The unipolar system for transvenous defibrillation, consisting of a single right ventricular lead as the cathode and the device shell as anode, has been shown to combine low de- fibrillation thresholds (DFTs) and simple implantation techniques. We compared the defibrillation efficacy of this system with the defibrillation efficacy of a dual lead system with a 12-cm long defibrillation anode placed in the left subclavian vein. The data of 38 consecutive patients were retrospectively analyzed. The implantation of an active can system was attempted in 20 patients (group 1), and of the dual lead system in 18 patients (group 2). Both groups had comparable demographic data, cardiac disease, ventricular function, or clinical arrhythmia. The criterion for successful implantation was a DFT of > 24 J. This criterion was met in all 18 patients of group 2, The active can system could not be inserted in 3 of the 20 group 1 patients because of a DFT > 24 J. In these patients, the implantation of one (n = 2) or two (n = 1) additional transvenous leads was necessary to achieve a DFT ≤ 24). The DFTs of the 17 successfully implanted group 1 patients were not significantly different from the 18 patients in group 2 (12.3 ± 5.7 f vs 10.8 ± 4.8 J). The defibrillation impedance was similar in both groups (50.1 ± 6.1 ± 48.9 ± 5.2 Ω). In group 1, both operation duration (66.8 ± 17 min vs 80.8 ± 11 min; P < 0.05) and fluoroscopy time (3.3 ± 2.1 min vs 5.7 ± 2.9 min; P < 0,05) were significantly shorter. Thus, the active can system allows reliable transvenous defibrillation and a marked reduction of operation duration and fluoroscopy time. The dual lead system, with an increased surface area defibrillation anode, seems to he a promising alternative for active can failures.