The Number of Recalled Leads is Highly Predictive of Lead Failure: Results From the Pacemaker and Implantable Defibrillator Leads Survival Study ("PAIDLESS")

OBJECTIVES

The purpose of this study was to determine if implantation of multiple recalled defibrillator leads is associated with an increased risk of lead failure.

BACKGROUND

The authors of the Pacemaker and Implantable Defibrillator Leads Survival Study ("PAIDLESS") have previously reported a relationship between recalled lead status, lead failure, and patient mortality. This substudy analyzes the relationship in a smaller subset of patients who received more than one recalled lead. The specific effects of having one or more recalled leads have not been previously examined.

METHODS

This study analyzed lead failure and mortality of 3802 patients in PAIDLESS and compared outcomes with respect to the number of recalled leads received. PAIDLESS includes all patients at Winthrop University Hospital who underwent defibrillator lead implantation between February 1, 1996 and December 31, 2011. Patients with no recalled ICD leads, one recalled ICD lead, and two recalled ICD leads were compared using the Kaplan-Meier method and log-rank test. Sidak adjustment method was used to correct for multiple comparisons. All calculations were performed using SAS 9.4. P-values <.05 were considered statistically significant.

RESULTS

This study included 4078 total ICD leads implanted during the trial period. There were 2400 leads (59%) in the no recalled leads category, 1620 leads (40%) in the one recalled lead category, and 58 leads (1%) in the two recalled leads category. No patient received more than two recalled leads. Of the leads categorized in the two recalled leads group, 12 experienced lead failures (21%), which was significantly higher (P<.001) than in the no recalled leads group (60 failures, 2.5%) and one recalled lead group (81 failures; 5%). Multivariable Cox's regression analysis found a total of six significant predictive variables for lead failure including the number of recalled leads (P<.001 for one and two recalled leads group).

CONCLUSIONS

The number of recalled leads is highly predictive of lead failure. Lead-based multivariable Cox's regression analysis produced a total of six predictive variable categories for lead failure, one of which was the number of recalled leads. Kaplan-Meier analysis showed that the leads in the two recalled leads category failed faster than both the no recalled lead and one recalled lead groups. The greater the number of recalled leads to which patients are exposed, the greater the risk of lead failure.

Failure rate and conductor externalization in the Biotronik Linox/Sorin Vigila implantable cardioverter-defibrillator lead

BACKGROUND

We observed a case of conductor externalization in a Biotronik Linox lead.

OBJECTIVE

The purpose of this study was to investigate lead performance of the Linox lead and the identical Sorin Vigila lead and prevalence of conductor externalization.

METHODS

We compared lead performance of all Linox and Vigila leads implanted at our center (BL group; n = 93) with that of all Boston Scientific Endotak Reliance leads (ER group; n = 190) and Medtronic Sprint Quattro leads (SQ group; n = 202) implanted during the same period. We screened all patients in the BL group for conductor externalization.

RESULTS

We identified 8 cases of lead failures in the BL group (index case of conductor externalization, 6 cases of nonphysiological high-rate sensing, and 1 case of high-voltage conductor fracture). Prospective fluoroscopic screening of 98% of all active BL group cases revealed 1 additional case of conductor externalization. The median follow-up was 41, 27, and 29 months for the BL group, ER group, and SQ group, respectively; lead survival was 94.9%, 99.2%, and 100% at 3 years and 88%, 97.5%, and 100% at 5 years (P = .038 for BL group vs ER group and P = .007 for BL group vs SQ group using the log-rank test). Younger age at implant was an independent predictor of lead failure in the BL group (adjusted hazard ratio 0.85; 95% confidence interval 0.77-0.94; P = .001).

CONCLUSION

At our center, survival of the Linox lead is 88% at 5 years and significantly worse than that of other leads. Conductor externalization is present in a minority of failed Linox leads. Younger age at implant is an independent predictor of Linox lead failure.

Do ultrasonic dental scalers interfere with implantable cardioverter defibrillators? An in vivo investigation

OBJECTIVES

To test the in vivo effects of an ultrasonic dental scaler on various implanted cardioverter defibrillator (ICD) models.

METHODS

12 consecutive patients with ICDs had continuous both electrocardiogram monitoring and device interrogation to detect interferences during the use of an ultrasonic dental scaler.

RESULTS

No interferences were detected by any ICD. Evaluation of the electrocardiograms for each patient failed to show any abnormalities in pacing during testing.

CONCLUSION

The results of this study suggest that the routinary clinic use of piezoelectric dental scalers do not interfere with the functioning of any of the tested ICDs.

CLINICAL SIGNIFICANCE

Ultrasonic dental scalers have been suspected of electromagnetic interference (EMI) with the normal functioning of ICDs and the use of this type of equipment for patients with these devices has been controversial. This is the first in vivo study to investigate EMI of ICD activity during the operation with ultrasonic dental scaler.

[Implantable pacemakers and defibrillators: implications for anesthesia and perioperative management]

The technological complexity of implantable devices for managing arrhythmias, specifically pacemakers and defibrillators, has increased spectacularly since their introduction a few decades ago. A growing number of patients with these devices are undergoing surgery and it is therefore essential to understand how they work and what the real associated risks are. Manuals and reference works on anesthesia may provide little information on these devices and their perioperative management. It is no longer satisfactory to place a magnet over these devices during surgery and assume that this action will protect the patient from the possible effects of electromagnetic interference. This review examines the basic principles and operation of implantable pacemakers and defibrillators, the relevant nomenclature, and the sources and effects of electromagnetic interference; the current recommendations for the perioperative management of patients fitted with these devices are also discussed.

[Sandwiched between the single- and triple-chamber ICD: do we still need the dual-chamber ICD?]

Since it has been shown that adverse events are more frequent with dual-compared to single-chamber ICDs in patients with heart failure, and since the importance of prevention of unnecessary right ventricular pacing and the success of biventricular pacing have been demonstrated in numerous studies, the need for dual-chamber ICD systems has to be reassessed. The development of these systems was accompanied by expectations of improved hemodynamics in patients with bradycardia, a reduced incidence of atrial fibrillation, inappropriate therapies, and bradycardia-associated ventricular tachyarrhythmias. Single-chamber ICDs should be used restrictively and with great caution in patients with (sinus-) bradycardia and heart failure, since a relevant proportion of these patients is at risk of hemodynamic deterioration. Even if the proportion of patients with proven pacemaker syndrome is so small that it does not reach the level of statistical significance in large studies, a small percentage of patients with hemodynamic deterioration due to VVI pacing is still clinically (and economically) intolerable. Since the development of bradycardia or symptomatic chronotropic incompetence (e.g., due to amiodarone) is difficult to predict, it seems reasonable to use the indication for dualchamber systems liberally. However, the systematic prevention of unnecessary right ventricular pacing is crucial if dual-chamber ICDs are used. If advanced tachycardia discrimination algorithms and careful, individual programming are used, dual-chamber ICDs are superior in the prevention of inappropriate therapies. Additionally, dualchannel electrograms allow a more reliable interpretation of stored tachycardia episodes. In summary, dual-chamber systems represent a valuable improvement of ICD therapy but require thorough programming to convey their advantage.

Causes and consequences of heart failure after prophylactic implantation of a defibrillator in the multicenter automatic defibrillator implantation trial II

BACKGROUND

Implantable cardioverter-defibrillator (ICD) therapy may be associated with an increased risk for heart failure (HF). The present study evaluated the frequency, causes, and consequences of HF after ICD implantation.

METHODS AND RESULTS

We performed a retrospective analysis of the clinical factors and outcomes associated with postenrollment HF events in 1218 patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial II. The adjusted hazard ratios (HRs) of ICD:conventional therapy for first and recurrent HF events were 1.39 (P=0.02) and 1.58 (P<0.001), respectively. The risk was increased among patients who received single-chamber or dual-chamber ICDs. Development of HF was associated with an increased mortality risk (HR, 3.80; P<0.001). Among patients who received a single-chamber ICD, there was a similar survival benefit before and after the development of HF (HR, 0.59 and 0.61, respectively; P=0.92 for difference), whereas among patients with dual-chamber devices, there was a significant reduction in survival benefit after HF (HR, 0.26 and 0.83, respectively; P=0.01 for difference). Within the defibrillator arm of the trial, patients who received life-prolonging therapy from the ICD had an increased risk for first and recurrent HF events (HR, 1.90; P=0.01 and 1.74; P<0.001, respectively).

CONCLUSIONS

Patients with chronic ischemic heart disease who are treated with either single-chamber or dual-chamber ICDs have improved survival but an increased risk of HF. The present data suggest that ICD therapy transforms sudden death risk to a subsequent HF risk. These findings should direct more attention to the prevention of HF in patients who receive an ICD.

Differences in outcomes between patients treated with single- versus dual-chamber implantable cardioverter defibrillators: a substudy of the Multicenter Automatic Defibrillator Implantation Trial II

OBJECTIVES

We sought to evaluate the influence of single- versus dual-chamber implantable cardioverter defibrillators (ICDs) on the occurrence of heart failure and mortality as well as appropriate and inappropriate ICD therapy in the Multicenter Automatic Defibrillator Implantation Trial II (MADIT-II).

BACKGROUND

In MADIT-II, ICD therapy in patients with a prior myocardial infarction and ejection fraction < or =0.30 was associated with a 31% reduction in risk of mortality when compared to conventionally treated patients. An unexpected finding was an increased occurrence of hospitalization for heart failure in the ICD group.

METHODS

Data from 717 patients randomized to ICD therapy with single- or dual-chamber pacing devices in MADIT-II were retrospectively analyzed. Endpoints selected for analysis included death from any cause, new or worsening heart failure requiring hospitalization, death or heart failure, appropriate therapy for ventricular tachycardia (VT) or ventricular fibrillation (VF), and inappropriate ICD therapy for atrial fibrillation or supraventricular tachycardia.

RESULTS

A total of 404 single-chamber ICDs (S-ICDs) and 313 dual-chamber ICDs (D-ICDs) were implanted. Patients receiving D-ICDs were at a higher risk at baseline than those receiving S-ICDs, with older age, higher NYHA class, more frequent prior CABG, wider QRS complex, more LBBB, higher BUN level, a history of more atrial arrhythmias requiring treatment, and a longer time interval from their index myocardial infarction to enrollment. While there was a trend toward an increase in adverse outcomes in the D-ICD group, no statistically significant differences in heart failure or mortality were observed between S-ICD versus D-ICD groups.

CONCLUSIONS

Patients with D-ICDs had a nonsignificant trend toward higher mortality and heart failure rates than patients with S-ICDs.

[The role of permanent pacing in atrial fibrillation]

Nowadays permanent pacing of the heart helps patients not only with pathological bradycardia or asystole in the tract of the AV blocks (AVB) and sick sinus syndrome (SSS), but is also valuable in the prevention of atrial fibrillation (AF) as well as the stabilization of the rhythm in chronic AF. For this reason patients with AF are often candidates for implantation of a cardiac pacemaker. The basic problem for doctor qualifying patients for pacemaker implantation with AF is the choice of a suitable type of pacing. However, this is not the only problem. New possibilities in the tract of solid and very quick progress in the field of pacing have appeared but there are also new doubts. The present publication presents the possibilities of utilization of types of pacing in this field including the newest solutions (antyarrhythmic algorithms) along with the role of placement of stimulation (dual site right ventricular pacing). Hybrid therapy is also described as the only alternative in special circumstances. All these methods were supported by the data from the latest trial.

Cost Advantage of Dual-Chamber Versus Single-Chamber Cardioverter-Defibrillator Implantation

OBJECTIVES

The purpose of this study was to determine the least expensive strategy for device selection in patients receiving implantable cardioverter-defibrillators (ICDs).

BACKGROUND

Device cost for a single-chamber ICD is less than an atrioventricular (dual-chamber) ICD (AV-ICD); however, some patients without clinical need for AV-ICD at implantation might require a later upgrade, potentially offsetting the initial cost advantage of the single-chamber device.

METHODS

Decision analysis was used to estimate expected resource utilization costs of three alternative implantation strategies: 1) single-chamber device in all, with later upgrade to AV-ICD if needed; 2) initial implantation of an AV-ICD in all; and 3) targeted device selection on the basis of results of electrophysiologic testing (presence or absence of induced bradyarrhythmias or atrial arrhythmias). Clinical base estimates were obtained from retrospective review of all patients receiving ICDs between June 1997 and July 2001 at a single university hospital. Economic inputs were collected from national and single-center sources.

RESULTS

In patients without other indications for electrophysiologic study (EPS), the expected per-person cost was least with the strategy of universal initial AV-ICD implantation (36,232 dollars) compared with initial single-chamber ICD/upgrade as needed (39,230 dollars) or EPS-guided selection (41,130 dollars). Sensitivity analyses demonstrated that universal AV-ICD implantation remained least expensive with upgrade rates as low as 10%. At a 5% upgrade rate, AV-ICD remained cheapest if the device cost-differential narrowed to 1,568 dollars. For patients undergoing EPS for risk assessment, EP-guided selection was least expensive.

CONCLUSIONS

The strategy of universal AV-ICD implantation, which provides the benefits of dual-chamber capability while obviating any potential need for future upgrade, is the least costly strategy for most patient populations receiving ICDs.

[Evaluating the first German diagnosis-related groups (G-DRG) in cardiological patients: problems in the correct medical and economic grouping]

About three years ago, the German Government initiated a complete change in the reimbursement system for costs of the in-hospital treatment of patients. A commission of representatives from every component of the German health system decided to adapt the Australian refined Diagnosis Related Groups (AR-DRG system). The AR-DRG system was selected as it would fit best to the German system and because of its high flexibility and preciseness reflecting severity of diseases and treatments. In October 2002, the first German Diagnosis Related Groups (G-DRGs) were calculated from the data of about 116 hospitals. These data now allow first analyses in how far a correct and precise grouping of patients in specific hospital settings is indeed performed and corresponds to the actual costs. Thus, we thoroughly calculated all costs for material and personnel during the in-hospital stay for each patient discharged during the first 4 months of 2002 from our cardiological department. After performing the grouping procedure for each patient, we analyzed in how far inhomogeneous patient distribution in the DRGs occurred and which impact this had on costs and potential reimbursements. Several different problems were identified which should be outlined in this work regarding three G-DRGs: costs of patients who received an implantable cardioverter defibrillator (F01Z) were markedly influenced by multimorbidity and additional expensive interventions which were not reflected by this G-DRG. Use of numerous catheters and expensive drugs represented a major factor for costs in patients with coronary angioplasty in acute myocardial infarction (F10Z) but seemed to be not sufficiently included in the cost weight. A specific area of patient management in our department is high frequency ablation of tachyarrhythmias which is included in other percutaneous interventions (F19Z). Complex procedures such as ablation of ventricular tachycardia or new innovative procedures as ablation of atrial fibrillation were associated with high costs leading to inadequate reimbursement. Furthermore, problems in the associated codes for diseases and procedures became apparent. Opportunities for future optimization such as specific new DRGs, splitting of DRGs, or the impact of changes in reimbursement for high-outliers were discussed.

[The progress of electrical treatment of arrhythmia]

Described here is the progress of the electrical treatment for arrhythmia during the past half a century. The mechanism, their expression and the principles of electrical treatment for bradycardia, tachycardia and fatal arrhythmia--ventricular fibrillation (VF) are introduced respectively. The current situation and future development of the pacemaker, RF ablation and implantable cardioversion defibrillator are also discussed in the paper.

Use of a transurethral microwave thermotherapeutic device with permanent pacemakers and implantable defibrillators

OBJECTIVE

To determine whether a device (Urologix Targis system) used for transurethral microwave treatment interferes with sensing, pacing, and arrhythmia detection by permanent pacemakers and implantable cardioverter-defibrillators (ICDs).

METHODS

We tested 13 pacemakers in both bipolar and unipolar sensing configurations and 8 ICDs in vitro. Pacemakers and ICDs were programmed to their most sensitive settings. Energy outputs of the microwave device were typical of those used clinically. The probe of the microwave device was anchored 1.2 cm from the pacemaker or ICD being tested.

RESULTS

No sensing, pacing, or arrhythmic interactions were noted with any ICD or any pacemaker programmed to the bipolar configuration. One pacemaker (Guidant Vigor 1230) showed intermittent tracking when programmed to the unipolar configuration.

CONCLUSIONS

Most patients with permanent pacemakers or ICDs can safely undergo transurethral microwave therapy using the device tested. Pacemakers and ICDs should be programmed to the bipolar configuration (if available) during therapy. The pacemaker or ICD should be interrogated before and after therapy to determine whether programming changes occurred as a result of treatment. However, our findings suggest that this is unlikely.

Effect of implantable cardioverter-defibrillator shocks on QT dispersion

Following transvenous implantable cardioverter defibrillator shocks, a significant increase in QT dispersion was observed. We suggest shock-induced increased dispersion of myocardial repolarization as one of the mechanisms of shock-induced proarrhythmia.

Variability of atrial sensing during exercise in a patient with a dual chamber ICD caused inappropriate ICD discharges

We present the case of a patient with a dual chamber implantable cardioverter defibrillator (ICD) who experienced inappropriate ICD discharges during exercise. Interrogation of the ICD revealed intermittent atrial undersensing during exercise that was responsible for the erroneous classification by the ICD of sinus tachycardia as ventricular tachycardia. Monitoring of the intracardiac electrograms and Marker Channels during an exercise test confirmed a marked decrease in P wave amplitude during exercise. By increasing the atrial sensitivity setting the problem was resolved.

Methods of ambulatory detection and treatment of cardiac arrhythmias using implantable cardioverter-defibrillators

The use of the implantable cardioverter-defibrillator (ICD) for the treatment of ventricular fibrillation, a condition that can lead to sudden cardiac death, is examined. Topics relevant to the development and implementation of ICD technology, such as defibrillation threshold optimization, battery design, lead configuration, arrhythmia-detection algorithms, and pacemakers-ICD interactions, are described. Clinical situations involving the surgical implantation procedures and the quality of life after implantation are also considered. Cost-benefit analysis of ICD treatment as well as an overview of cardiac arrhythmias and emerging technologies are also included. A survey of ICD recipients was conducted and its results are discussed.

[Dual-chamber implantable automatic defibrillators. Experiences apropos of 16 cases]

In view of the large number of inappropriate shocks observed in patients with implanted defibrillators, improved detection of ventricular arrhythmias has become a major objective. The addition of an atrial catheter has been proposed to improve discrimination between ventricular and non-ventricular arrhythmias. Besides this function, the additional catheter could be used for DDD pacing without risk of interaction between the pacemaker and defibrillator. The authors report their initial experience in 16 patients implanted with a DDD pacemaker. The indication was resuscitated sudden death (N = 5) or ventricular tachycardia (N = 11). The choice of a DDD defibrillator was justified by a bradycardia (N = 9), haemodynamic factors (N = 4) or supraventricular tachycardia (N = 3). The devices used were the Defender 9001 (ELA Medical SA, France, N = 3), the Ventak AV 1810 and the Ventak AV II DR 1821 (Guidant/CPI, Inc. USA, N = 11 and N = 2 respectively). There were three immediate complications. After 2 to 29 months' follow-up, 5 patients had received appropriate treatment by their devices. Five patients had inappropriate shocks : one patient received a shock triggered by electrical interference, two others had no active sensing algorithme when the shocks were delivered, and the other two had an activated algorithme with 1/1 conduction of a supraventricular arrhythmia. No recurrences were recorded after reprogramming the device. DDD or VDD pacing was permanent in 9 patients and intermittent in 3 others. Seven patients had dilated cardiomyopathy and severe cardiac failure and were clinically improved by dual chamber pacing. In many patients, candidates for a defibrillator, this new generation of devices has improved specificity of arrhythmia detection and cardiac pacing without risk of interaction. The authors propose a classification of the indications for a DDD defibrillator.

Initial clinical experience with an implantable human atrial defibrillator

Low energy biatrial shock is an effective means of restoring sinus rhythm in patients with atrial fibrillation (AF). Ventricular proarrhythmia is avoided provided that shocks are well synchronized to R waves that are not at closely coupled intervals or preceded by long-short cycles. Based on these principles, an implantable atrial defibrillator has been developed and was implanted in three patients with drug refractory paroxysmal AF. The device detects AF via an actively fixed right atrial and a self-retaining coronary sinus defibrillating leads, and delivers 3/3 ms biphasic shocks up to 300 V synchronized to the R wave. The mean implant threshold (ED50) was 195 V (1.8 J). and minimum voltage at conversion during follow-up assessments at 1, 3, and 6 months were 260 V, 2.5 J. 250 V, 2.3 J, and 300 V, 3.0 J respectively. Detection of AF was 100% specific and shocks were 100% synchronized, although only a proportion of synchronized R waves were considered suitable for shock delivery primarily because of closely coupled cycles. Three patients had 9 spontaneous AF episodes, 8/9 (89%) successfully defibrillated by shocks of 260-300 V. Sedation was not used in 4 out of 9 (45%) episodes. Backup ventricular pacing was initiated by the device in 6 out of (67%) episodes. One patient had more frequent AF after lead placement, which subsided after a change of medication. There was no ventricular proarrhythmia. It is concluded that an implantable atrial defibrillator is a viable therapy for selected patients with paroxysmal AF. The device is capable of accurate AF detection, R wave synchronization and ventricular support pacing after successful defibrillation of AF.

A multicenter, randomized trial comparing an active can implantable defibrillator with a passive can system. Jewel Active Can Investigators

Replacing one defibrillation electrode lead by the defibrillator can may simplify implantation of the ICD. In this multicenter study, 304 patients were randomized to receive either the biphasic active can (AC) (model 7219C system, Medtronic, Inc.) or the passive can (PC) (model 7219D system). The AC and PC systems were compared with respect to their ability to meet the implant defibrillation criterion and to defibrillate VF, and to DFTs, implant time, patient adverse events, and survival rates. A higher percentage fulfilled the implant defibrillation criterion on the first configuration with the AC (86.3% vs 75.9% for PC; P = 0.023), and the first shock success for terminating induced VF was 94% for AC compared to 89% for PC (P = 0.026). DFTs were significantly lower (10.9 vs 12.7 J; P = 0.031), and implant time was significantly shorter for the AC patients (99.2 vs 112.0 min; P = 0.002). The two groups showed no significant differences in 3-month adverse event rates, 3-month survival, and hospital stay.

The patient with a pacemaker or related device

Patients with implanted pacemakers and ICDs can be safely managed for surgery and anaesthesia. Anaesthetic management of such patients should be planned first according to the patient's underlying medical status with particular emphasis on ventricular function and electrolyte balance. The anaesthetist must understand the various modes of pacemakers and ICDs available in the patient population. These devices are safe and well shielded form most electromagnetic interference in the operating room. Some precautions are nevertheless necessary. A magnet should not be placed routinely over a programmable pacemaker or ICD in the operating room, especially in the presence of electrocautery. Rate-responsive pacemakers should have rate adaptive modes disabled before surgery whenever possible. The mechanism of rate response should be known, so that inappropriate changes in heart rate can be avoided in the perioperative period if the rate responsive mode cannot for some reason be disabled. Antitachycardia pacemakers, should have the antitachycardia function disabled preoperatively. Methods for the provision of alternate emergency pacing should be available when dealing with patients at risk of bradyarrhythmias or pacemaker failure in the operating room. The anaesthetist should have a safe, practical plan of action that suites his/her experience and capabilities. ICDs should have automatic cardioverter-defibrillator functions disabled for surgery and external modes of cardioversion/defibrillation should be available.

Implantable cardioverter defibrillators: a guide for clinicians

More than 30,000 patients in the United States have implanted devices that cardiovert, shock, or pace their hearts during a dangerous ventricular arrhythmia. This number grows daily as these devices are increasingly able to provide effective treatment for dangerous ventricular arrhythmias. In the past 5 years, the technology surrounding these devices has grown dramatically, going from a single "shock box" made by one vendor to a sophisticated group of devices with multiprogrammable functions. Clinicians who provide care to these patients must be able to understand the purpose of the device and validate its function. A guide to each of the implantable cardioverter defibrillator systems and to the various therapies available in each is presented.

North American Society of Pacing and Electrophysiology policy statement. The NASPE/BPEG defibrillator code

A new generic code, patterned after and compatible with the NASPE/BPEG Generic Pacemaker Code (NBG Code) was adopted by the NASPE Board of Trustees on January 23, 1993. It was developed by the NASPE Mode Code Committee, including members of the North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG). It is abbreviated as the NBD (for NASPE/BPEG Defibrillator) Code. It is intended for describing the capabilities and operation of implanted cardioverter defibrillators (ICDs) in conversation, record keeping, and device labeling, and incorporates four positions designating: (1) shock location; (2) antitachycardia pacing location; (3) means of tachycardia detection; and (4) antibradycardia pacing location. An additional Short Form, intended only for use in conversation, was defined as a concise means of distinguishing devices capable of shock alone, shock plus antibradycardia pacing, and shock plus antitachycardia and antibradycardia pacing.

Effective defibrillation in pigs using interleaved and common phase sequential biphasic shocks

Previous studies have shown that low internal defibrillation thresholds (DFTs) can be attained by using two pairs of electrodes and combining biphasic shocks with sequential timing. The purpose of this two-part study was to test the defibrillation efficacy of two new shock sequences, an interleaved biphasic, and a common phase sequential biphasic, that utilized two pairs of electrodes and were developed from the concept of sequential biphasic shocks. In the first part, defibrillation catheters were placed in the right ventricle and the superior vena cava of six anesthetized pigs. A small patch electrode was placed on the LV apex through a subxiphoid incision and a cutaneous patch was placed on the left thorax. The mean DFT energies for the interleaved biphasic (5.2 +/- 0.4 J) and the common phase sequential biphasic waveforms (5.4 +/- 0.4 J) were substantially less (P < 0.0001) than those for either the sequential monophasic (10.6 +/- 1.0 J) or single biphasic waveforms (9.0 +/- 1.0 J). In the second study, which used nine anesthetized pigs, the importance of phase reversal was demonstrated by the finding that the DFT energy of a common phase sequential biphasic shock (6.2 +/- 0.4 J) was much less than a common phase sequential monophasic shock (17.9 +/- 1.3 J, P < 0.0001); furthermore, the average DFT for four common phase sequential biphasic configurations (5.7 +/- 0.2 J) was much less than for a configuration that was similar except that current flow was not reversed in one phase so that no biphasic effect was present (19.7 +/- 1.2 J). The efficacy of common phase sequential biphasics was comparable to that of sequential biphasics. The effectiveness of sequential biphasics, interleaved biphasics, and common phase sequential biphasics is possibly due to two mechanisms: (A) an increase in the potential gradient during a later phase in regions that were low during the first phase, and (B) the exposure of most of the myocardium to a biphasic shock that reduces the minimum extracellular potential gradient needed to defibrillate.

Concomitant amiodarone and the implantable cardioverter-defibrillator: is there a place?

OBJECTIVE

To discuss the controversy surrounding concomitant therapy with amiodarone and the implantable cardioverter-defibrillator (ICD).

DATA SOURCES

A MEDLINE search identified English-language literature sources, including nonhuman studies.

STUDY SELECTION

Studies included those that specifically addressed the use of amiodarone plus the ICD as well as reviews of the ICD.

DATA EXTRACTION

Studies were evaluated for design, type of defibrillation electrode or defibrillator, method of defibrillation, amiodarone loading and maintenance dosages, duration of amiodarone therapy, and study endpoints.

DATA SYNTHESIS

Because the ICD functions by delivering energy to depolarize a mass of myocardium, concomitant use of antiarrhythmic agents that elevate the defibrillation threshold (DFT) beyond an ICD's energy capability may adversely effect patient outcome. Amiodarone has been shown to both increase and decrease the DFT. Trials examining the use of amiodarone plus the ICD have not provided strong evidence that amiodarone will decrease the number of ICD discharges or favorably affect the mortality rate. Amiodarone is also expensive and toxic. Although the cost of the ICD is relatively high, continuing improvements in battery life will decrease long-term costs.

CONCLUSIONS

Controlled trials are required to substantiate the improved survival rate with the ICD and to determine the role of antiarrhythmic agents in conjunction with the device. At present, there are no data to support the combination of amiodarone and an ICD in terms of improved quality or duration of life.