Pacemaker Failure Following External Defibrillation

An 81-year-old female with the sick sinus syndrome had a permanent pacemaker implanted. She subsequently developed ventricular fibrillation and was successfully defibrillated. However, the defibrillation paddle was placed on the pulse generator which led to a complete loss of function of the pulse generator. External defibrillation can produce varying degrees of damage to the implanted pulse generator. The resultant abnormalities are discussed and recommended defibrillation procedures are also outlined in this report.     

Effects of Antiarrhythmic Drugs on Epicardial Defibrillation Energy Requirements and the Rate of Defibrillator Discharges

Antiarrhythmic drugs are commonly used with the implantable cardioverter/defibrillator to treat recurrent ventricular tachyarrhythmias. Since various antiarrhythmic drugs have been reported to alter defibrillation threshold, an important question is whether the device will provide adequate energy for defibrillation during long-term follow-up and to what extent antiarrhythmic drug treatment will affect defibrillation energy requirements. To answer these questions, the defibrillation thresholds were determined in 20 patients using an epicardial patch-patch lead configuration at the time of implantation and at the time of pulse generator replacement. During a mean follow-up period of 24 ± 6 months, the defibrillation threshold increased significantly from 14.2 ± 3.7 joules to 18.3 ± 5.5 joules in the entire group (P < 0.05). This increase in defibrillation threshold was due to a marked elevation of defibrillation energy requirements in the subgroup of patients taking amiodarone compared with patients receiving mexiletine. Based on these results it is mandatory to retest defibrillation threshold at any time of pulse generator replacement to guarantee continued effectiveness. In particular, if amiodarone treatment is initiated after implantation of a defibrillator, it is recommended to reevaluate defibrillation threshold to ensure an adequate margin of safety.     

Myopotential Interference Inducing Pacemaker Tachycardia in a DVI Programmed Pacemaker

A 67-year-old male, suffering from ventricular tachycardia unresponsive to drug therapy, received a universal AV sequential pacemaker (DDD,M). Tim pacemaker was programmed in the DVI mode, pacing role 100 bpm, AV interval 250 ms. After implantation, the patient experiences two episodes of tachycardia that proved to be pacemaker tachycardia with a rate of 150 bpm. The first period was self-terminating, and the second had to be stopped by reprogramming the pulse generator. Pacemaker tachycardia could easily be provoked by instructing the patient to contract the pectoral muscle adjacent to the pulse generator. To our knowledge, this is the first report to pacemaker tachycardia provoked by myopotentials in a pulse generator programmed in the DVI mode.     

Prospective Randomized Comparison of Biphasic Waveform Tilt Using a Unipolar Defibrillation System

Background: A unipolar defihrillation system using a single right ventricular (RV) electrode and the active shell or container of an implantable cardioverter defibrillator situated in a left infraclavicular pocket has been shown to be as efficient in defibrillation as an epicardial lead system. Additional improvements in this system would have favorable practice implications and could derive from alterations in pulse waveform shape. The specific purpose of this study is to determine whether defibrillation efficacy can be improved further in humans by lowering biphasic waveform tilt. Methods: We prospectively and randomly compared the defibrillation efficacy of a 50% and a 65% tilt asymmetric biphasic waveform using the unipolar defibrillation system in 15 consecutive cardiac arrest survivors prior to implantation of a presently available standard transvenous defibrillation system. The RV defibrillation electrode has a 5-cm coil located on a 10.5 French lead and was used as the anode. The system cathode was the active 108 cm² surface area shell (or “CAN”) of a prototype titanium alloy pulse generator placed in the left infraclavicular pocket. The defibrillation pulse derived from a 120-μF capacitor and was delivered from RV ± CAN, with RV positive with respect to the CAN during the initial portion of the cycle. Defibrillation threshold (DFT) stored energy, delivered energy, leading edge voltage and current, pulse resistance, and pulse width were measured for both tilts examined. Results: The unipolar single lead system, RV ± CAN, using a 65% tilt biphasic pulse resulted in a stored energy DFT of 8.7 ± 5.7 J and a delivered energy DFT of 7.6 ± 5.0 J. In ail 15 patients, stored and delivered energy DFTs were < 20 J. The 50% tilt biphasic pulse resulted in a stored energy DFT of 8.2 ± 5.4 J and a delivered energy DFT of 6.1 ± 4.0 J;P = 0.69 and 0.17, respectively. As with the 65% tilt pulse, all 15 patients had stored and delivered energy DFTs < 20 J. Conclusion: The unipolar single lead transvenous defibrillation system provides defibrillation at energy levels comparable to that reported with epicardial lead systems. This system is not improved by use of a 50% tilt biphasic waveform instead of a standard 65% tilt biphasic pulse. (PACE 1995; 18:1369–1373)     

The Noise Sampling Period: A New Cause of Apparent Sensing Malfunction of Demand Pacemakers

Two patients with Omni-Stanicor pulse generators presented an apparent sensing problem characterized by intermittent reversion to fixed-rate pacing only during atrial fibrillation with a very rapid ventricular rate. Every fixed-rate cycle contained two unsensed beats. The first unsensed beat fell in the noise sampling period (the last 1/6 of the pacemaker refractory period) and, therefore, disabled the demand function of the pulse generator for a single timing cycle. The presence of two consecutively unsensed beats within one timing cycle (automatic or escape interval) during tachycardia suggests normal function of the noise sampling period of this particular pulse generator, rather than a true sensing problem. The diagnosis becomes evident if the sensing problem disappears when abbreviation of the refractory period occurs by reprogramming the pulse generator at a higher rate.     

Inappropriate Slowing of the Pacemaker Rate with Programmahle Demand Pacemaker

A 60-year-old male with a programmable pacemaker developed inappropriate slowing of the pacemaker rate. This was due to oversensing of the T waves combined with after-potential sensing. This does not represent generator malfunction and can usually be corrected by reprogramming the pulse duration, or the milliamperage.     

The Superfast Atrial Recharge Pulse: A Cause of Pectoral Muscle Stimulation in Patients Equipped with a Unipolar DDD Pacemaker

Pectoral muscle stimulation may cause serious discomfort to patients equipped with a pulse generator. Insulation defects of the lead, connector problems and defective coating of the pacemaker can are common causes of local muscle contractions. This report describes pectoral muscle stimulation caused by the atrial superfast recharge pulse incorporated into the atrial channel of a commercially available unipolar DDD pacemaker. As pectoral muscle stimulation could not be eliminated by reprogramming the pacemaker to a lower atrial output in some patients a redesign of the pacemaker is highly required.     

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.     

Biphasic Defibrillation Using a Single Capacitor with Large Capacitance: Reduction of Peak Voltages and ICD Device Size

The volume of current implantable cardioverter defibrillators (ICD) is not convenient for pectoral implantation. One way to reduce the size of the pulse generator is to find a more effective defibrillation pulse waveform generated from smaller volume capacitors. In a prospective randomized crossover study we compared the step-down defibrillation threshold (DFT) of a standard biphasic waveform (STD), delivered by two 250-μF capacitors connected in series with an 80% tilt, to an experimental biphasic waveform delivered by a single 450μF capacitor with a 60% tilt. The experimental waveform delivered the same energy with a lower peak voltage and a longer duration (LVLDj. Intraopera-tively, in 25 patients receiving endocardial (n = 12) or endocardial-subcutaneous array (n = 13) defibrillation leads, the DFT was determined for both waveforms. Energy requirements did not differ at DFT for the STD and LVLD waveforms with the low impedance (32 ± 4Ω) endocardial-subcutaneous array defibrillation lead system (6.4 ± 4.4 J and 5.9 ± 4.2 J, respectively) or increased slightly (P - 0.06) with the higher impedance (42 ± 4 Ω) endocardial lead system (10.4 ± 4.6 J and 12.7 ± 5.7 /. respectively), However, the voltage needed at DFT was one-third lower with the LVLD waveform than with the STD waveform for both lead systems (256 ± 85 V vs 154 ± 53 V and 348 ± 76 V vs 232 ± 54 V, respectively). Thus, a single capacitor with a large capacitance can generate a defibrillation pulse with a substantial lower peak voltage requirement without significantly increasing the energy requirements. The volume reduction in using a single capacitor can decrease ICD device size.     

Effect of Biphasic Waveform Pulse on Endocardial Defibrillation Efficacy in Humans

Several clinical studies have proved increased defibrillation efficacy for implantable cardioverter defibrillators with biphasic pulse waveforms compared to monophasic pulse waveforms. This difference in defibrillation efficacy depends on the type of defibrillation lead system used. The influence of biphasic defibrillation pulse waveforms on the defibrillation efficacy of purely endocardial defibrillation lead systems has not yet been sufficiently examined, we, therefore studied 30 consecutive patients with drug refractory ventricular tachyarrhythmias during the implantation of a cardioverter defibrillator. After implanting an endocardial "integrated" sensing/defibrillation lead we performed a prospective randomized comparison of the defibrillation efficacy of monophasic and biphasic defibrillation waveform pulses. For endocardial defibrillation with the biphasic waveform the mean defibrillation threshold was 12.5 ± 4.9 joules and for the monophasic waveform 22.2 ± 5.6 joules (P < 0.0001). There was a decrease in the required defibrillation energy of biphasic defibrillation in 29/30 patients. Thus considering purely endocardial defibrillation a statistically significant and clinically relevant increase in defibrillation efficacy can be demonstrated for biphasic defibrillation waveform pulses.     

A Prospective, Randomized, Comparison in Patients Between a Pectoral Unipolar Defibrillation System and That Using an Additional Inferior Vena Cava Electrode

The decrease of defibrillation energy requirement would render the currently available transvenous defibrillator more effective and favor the device miniaturization process and the increase of longevity. The unipolar defibrillation systems using a single RV electrode and the pectoral pulse generator titanium shell (CAN) proved to be very efficient. The addition of a third defibrillating electrode in the coronary sinus did not prove to offer advantages and in the superior vena cava showed only a slight reduction of the defibrillation threshold (DFT). The purpose of this study was to determine whether the defibrillation efficacy of the single lead unipolar transvenous system could be improved by adding an electrode in the inferior vena cava (IVC). In 17 patients, we prospectively and randomly compared the DFT obtained with a single lead unipolar system with the DFT obtained using an additional of an IVC lead. The RV electrode, Medtronic 6936, was used as anode (first phase of biphasic) in both configurations. A 108 cm2 surface CAN, Medtronic 7219/7220 C, was inserted in a left submuscular infraclavicular pocket and used as cathode, alone or in combination with IVC, Medtronic 6933. The superior edge of the IVC coil was positioned 2-3 cm below the right atrium-IVC junction. Thus, using biphasic 65% tilt pulses generated by a 120 microF external defibrillator, Medtronic D.I.S.D. 5358 CL, the RV-CAN DFT was compared with that obtained with the RV-CAN plus IVC configuration. Mean energy DFTs were 7.8 +/- 3.6 and 4.8 +/- 1.7 J (P < 0.0001) and mean impedance 65.8 +/- 13 O and 43.1 +/- 5.5 O (P < 0.0001) with the RV-CAN and the IVC configuration, respectively. The addition of IVC significantly reduces the DFT of a single lead active CAN pectoral pulse generator. The clinical use of this biphasic and dual pathway configuration may be considered in patients not meeting implant criteria with the single lead or the dual lead RV-superior vena cava systems. This configuration may also prove helpful in the use of very small, low output ICDs, where the clinical impact of ICD generator size, longevity, and related cost may offset the problems of dual lead systems.     

Failure of One Conductor in a Nonthoracotomy Implantable Defibrillator Lead Causing Inappropriate Sensing and Potentially Ineffective Shock Delivery

We describe how a single defect in a new model transvenous lead for an implantable curdiuverter defibrillator can result in malfunction of the sensing and defibrillation circuits. The patient had received shocks during atrial fibrillation without premonitory symptoms. At least one shock was delivered and not fell by the patient. In addition, late in the course, a shock was delivered during atrial fibrillation documented to be with a slow ventricular response. In the transvenous lead, a distal spring functions as the anode for rate sensing and the cathode for defibrillation. The wire from this spring bifurcates near the proximal end of the catheter. One wire from the bifurcation leads to the positive (anode) rate-sensing socket of the pulse generator, and the other wire leads to the negative (cathode) high voltage output socket of the defibrillator for defibrillation and cardioversion. After the inappropriate and unperceived shocks were documented, intraoperative and postoperative electrical testing indicated that intermittent discontinuity of the distal spring system within the proximal yoke of the catheter caused faulty sensing and potentially unreliable defibrillation. This dual malfunction was possible because the distal spring of the lead functions in the high-voitage output and the rate-sensing iow-vollage input circuits of the implantable defibrillator.     

Incidence of Lead System Malfunction Detected During Implantable Defibrillator Generator Replacement

Implantable cardioverter-defibrillator (ICD) generator replacement due to a depleted battery is a frequently performed procedure. The frequency with which sensing and defibrillation system failures are identified during device replacement procedures has not been previously described. Therefore, the purpose of this study was to prospectively determine the frequency of lead system malfunction detected at the time of device replacement in 55 consecutive patients undergoing ICD generator replacement. The mean age of the patients was 63 ± 10 years and 40 of them were men. Forty-nine patients had an epicardial lead system, and six patients had a nonthoracotomy lead system. Four (7%) of these 55 patients were noted to have previously undetected lead system failure, either sensing (n = 3) or defibrillation (n = 1), necessitating system revision. The lead systems that failed were 40 ± 6 months old (33–49 months). In summary, during ICD generator replacement, previously undetected problems with sensing or defibrillation may be identified in approximately 10% of patients. Therefore, a comprehensive evaluation of the sensing and the defibrillation functions should be an essential component of the ICD generator replacement procedure.     

Management of high defibrillation threshold

The implantable cardioverter defibrillator (ICD) has become the primary therapy for the treatment of potentially lethal ventricular arrhythmias. Ventricular arrhythmias encompass a spectrum of rhythm disturbances ranging from the occasional monomorphic ventricular premature complex to the almost universally fatal ventricular fibrillation. Our understanding of the mechanisms of ventricular fibrillation and defibrillation is still in evolution. At present, the most common ICD configuration consists of a pectoral pulse generator (active-can) with a bipolar transvenous dual coil lead. A transvenous system with an active-can has improved defibrillation thresholds and the ease of implantation. However, there are various clinical scenarios in which patients with high defibrillation threshold (DFT) are encountered. Although the incidence of high DFT patients is low, it is of significant concern since it may account for sudden cardiac death in patients with ICDs. At present, there are few clinical trials that are rigorous and well designed, and which can define a perfect methodology for the treatment of high DFT patients. In this review, in the context of commonly encountered clinical scenarios, we discuss therapeutic strategies to help manage patients with high DFT.     

Long-Term Internal Cardiac Defibrillation Threshold Stability

The automatic implantable cardioverter-defibrillator is tested intraoperatively with defibrillation trials to ensure effectiveness. It is unknown if the energy requirement for internal defibrillation remains stable and that once demonstrated effective, if the device will continue to be effective in terminating lethal ventricular arrhythmias. In this study, the defibrillation energy requirement was compared in 56 patients at the time of lead implantation to that obtained at the time of generator replacement. Mean time to generator replacement was 17. +/- 6.6 months. The defibrillation threshold was stable over that time (11.9 +/- 6.7 joules compared to 12.7 +/- 8.4 joules, NS). There was no relation between transmyocardial impedance and defibrillation threshold. In addition, no effect on defibrillation threshold was demonstrated by the use of various cardiac medications, concomitant surgery or the occurrence of clinical shocks during follow-up.     

Management of high defibrillation threshold

The implantable cardioverter defibrillator (ICD) has become the primary therapy for the treatment of potentially lethal ventricular arrhythmias. Ventricular arrhythmias encompass a spectrum of rhythm disturbances ranging from the occasional monomorphic ventricular premature complex to the almost universally fatal ventricular fibrillation. Our understanding of the mechanisms of ventricular fibrillation and defibrillation is still in evolution. At present, the most common ICD configuration consists of a pectoral pulse generator (active-can) with a bipolar transvenous dual coil lead. A transvenous system with an active-can has improved defibrillation thresholds and the ease of implantation. However, there are various clinical scenarios in which patients with high defibrillation threshold (DFT) are encountered. Although the incidence of high DFT patients is low, it is of significant concern since it may account for sudden cardiac death in patients with ICDs. At present, there are few clinical trials that are rigorous and well designed, and which can define a perfect methodology for the treatment of high DFT patients. In this review, in the context of commonly encountered clinical scenarios, we discuss therapeutic strategies to help manage patients with high DFT.     

Internal Ventricular Defibrillation with Sequential Pulse Countershock in Pigs: Comparison with Single Pulses and Effects of Pulse Separation

We compared single to sequential pulse shocks with different pulse separations on internal cardiac defibrillation by using a catheter and plaque electrodes in open-chest halothane-anesthetized pigs. Ten seconds after fibrillation onset, defibrillation was attempted using trapezoidal pulses of 65% tilt, approximately 5 ms duration and fixed outputs from 1.0 to 50 joules (J). With single pulses, minimum defibrillation energy for the catheter alone was 2.4 ± 0.3 J/kg (mean ± standard error) and 2.1 ± 0.2 J/kg for the catheter tip to plaque configuration. With sequential pulse shocks, the first pulse delivered via the catheter and the second pulse from the catheter tip to the plaque electrode, the energy necessary for defibrillation was dependent on the separation time between the two pulses (2.0 ± 0.2, 1.5 ± 0.2, 0.9 ± 0.1, 1.3 ± 0.3, 0.6 ± 0.2, and 1.2 ± 0.2 J/kg at 100, 10, 1, 0.5, 0.2, and 0.1 ms, respectively). Further, at the 0.2 ms separation, 100% of the animals could be defibrillated with less than 2.0 J/kg (35 J total). We conclude that sequential pulse defibrillation provides a significant improvement over single pulse defibrillation. The optimum separation between the sequential pulses in this study was 0.2 ms.     

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)     

"Cold Can for a Hot Case": Use of a Coronary Sinus Shocking Lead in Association with Cold Can to Achieve Successful Defibrillation

Attaining an adequate defibrillation threshold is critical in the functioning of an implantable cardioverter-defibrillator. This is achieved in a majority of implants but in those where this does not occur, reprogramming, lead repositioning, and ultimately placement of a subcutaneous array lead may be necessary.     

Value of Pre-Hospital Discharge Defibrillation Testing in Recipients of Implanted Cardioverter Defibrillators

Opinions vary regarding the need to perform defibrillation testing prior to hospital discharge in recipients of state-of-the-art cardioverter defibrillators (ICDs). Our protocol is to perform predischarge ICD testing 1 day after implant. This report includes 682 consecutive implants. Adverse observations at testing were grouped into (1) risk of defibrillation failure, (2) surgical complications, (3) sensing/pacing issues or narrow defibrillation margin warranting closer follow-up, or (4) findings correctable by device reprogramming. Among the 682 patients, 63% had single-chamber and 37% dual-chamber or biventricular ICDs. In 48 patients (7%) there were 69 concerns and/or interventions, with overlaps among the four categories, including one failure to defibrillate (0.15%), and six other patients at risk. Surgical complications included 11 hematomas (1.6%), and six lead dysfunctions. Closer follow-up was indicated in 19 patients (2.7%), for high pacing thresholds in seven, sensing issues in seven, and <10 J defibrillation margin in five. Device reprogramming was needed in 31 patients (4.5%), for tachycardia detection and therapy settings in 12, and for pacing/sensing functions in 22 patients. In eight patients ventricular fibrillation could not be induced. There was no morbidity or mortality due to testing. The state-of-the-art ICDs delivering biphasic shocks are remarkably reliable. The routine pre-hospital discharge defibrillation testing of such ICDs may be optional and left to the physicians' discretion.