The potential usage of dual chamber pacing in patients with implantable cardioverter defibrillators

Inappropriate Implantable Cardioverter-Defibrillator Therapy

Although improvements in implantable cardioverter-defibrillator (ICD) therapy have taken place, many challenges do remain. Inappropriate delivery of therapy is a big problem that impacts the quality of life of ICD recipients. Although there is now a clear understanding that atrial arrhythmias are the main cause of inappropriate ICD therapies, physicians have not been very successful in preventing them. Additionally, although many tachycardia detection discriminators have been shown to be helpful, it is not clear that there is a particular combination that is ideal for all patients. Until such an algorithm is developed (which may not be possible), a detailed knowledge and use of all available programming options, guided by special characteristics of each unique patient, are the only foreseeable solutions. Finally, one must face the prospect that this problem cannot be vanquished, but only ameliorated.

[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.

Programmed inappropriate ICD ventricular defibrillation for cardioversion of persistent atrial fibrillation

In this report we briefly describe a patient with a dual chamber implantable cardioverter defibrillator in the context of severe ischemic cardiomyopathy who developed persistent atrial fibrillation. After appropriate anticoagulation and under mild sedation the patient was successfully cardioverted to sinus rhythm after a programmed ventricular synchronized defibrillation using his defibrillator. Programmed internal cardioversion of persistent atrial fibrillation in patients who have an implantable cardioverter defibillator without atrial defibrillation capabilities could be an effective and safe therapeutic option. Unlike external electrical cardioversion, this strategy does not interfere with the implantable cardioverter defibrillator, is more effective, and obviates the need of general anesthesia. This strategy should be further evaluated in clinical trials.

Device therapies in the post-myocardial infarction patient with left ventricular dysfunction

The post-myocardial infarction (MI) patient with left ventricular dysfunction (LVD) is at risk for ventricular arrhythmias resulting in sudden cardiac death. In high-risk post-MI patients with a depressed left ventricular ejection fraction, prophylactic implantable cardioverter defibrillators (ICDs) may significantly improve survival. These benefits are in addition to those of optimal pharmacologic therapy, and ICD therapy should be considered the standard of care in these patients. Recent device trials have demonstrated the benefits of prophylactic ICD placement in patients who have been selected based on post-MI left ventricular systolic dysfunction alone. In addition, cardiac resynchronization therapy can improve the quality of life beyond that achievable with drug therapy alone and should be considered in patients with symptomatic heart failure with QRS prolongation. Further risk stratification studies of post-MI LVD patients will allow ICD therapy to be applied in a more cost-effective manner.

How, why, and when may atrial defibrillation find a specific role in implantable devices? A clinical viewpoint

This viewpoint article discusses the potential for incorporation of atrial defibrillation capabilities in modern multi-chamber devices. In the late 1990s, the possibility of using shock-only therapy to treat selected patients with recurrent atrial fibrillation (AF) was explored in the context of the stand-alone atrial defibrillator. The failure of this strategy can be attributed to the technical limitations of the stand-alone device, low tolerance of atrial shocks, difficulties in patient selection, a lack of predictive knowledge about the evolution of AF, and, last but not least, commercial considerations. An open question is how atrial defibrillation capability may now assume a specific new role in devices implanted for sudden death prevention or cardiac resynchronization. For patients who already have indications for implantable devices, device-based atrial defibrillation appears attractive as a "backup" option for managing AF when preventive pharmacological/electrical measures fail. This and several other personalized hybrid therapeutic approaches await exploration, though assessment of their efficacy is methodologically challenging. Achievement of acceptance by patients is an essential premise for any updated atrial defibrillation strategy. Strategies that are being investigated to improve patient tolerance include waveform shaping, pharmacologic modulation of pain, and patient-activated defibrillation (patients might also perceive the problem of discomfort somewhat differently in the context of a backup therapy). The economic impact of implementing atrial defibrillation features in available devices is progressively decreasing, and financial feasibility need not be a major issue. Future studies should examine clinically relevant outcomes and not be limited (as occurred with stand-alone defibrillators) to technical or other soft endpoints.

Coronary sinus electrode does not reduce atrial defibrillation thresholds

BACKGROUND

Atrial defibrillation can be achieved with a conventional dual-coil, active pectoral implantable cardioverter-defibrillator (ICD) lead system. Shocking vectors that incorporate an additional electrode in the CS have been used, but it is unclear if they improve atrial DFTs.

OBJECTIVE

The objective of this prospective, randomized study was to determine if a coronary sinus (CS) electrode reduces atrial defibrillation thresholds (DFTs).

METHODS

This was a prospective study of 36 patients undergoing initial ICD implant for standard indications. A defibrillation lead with superior vena cava (SVC) and right ventricular (RV) shocking coils was implanted in the RV. An active can emulator (Can) was placed in a pre-pectoral pocket. A lead with a 4 cm long shocking coil was placed in the CS. Atrial DFTs were determined in the following 3 shocking configurations in each patient, with the order of testing randomized: RV --> SVC + Can (Ventricular Triad), distal CS --> SVC + Can (Distal Atrial Triad), and proximal CS --> SVC + Can (Proximal Atrial Triad).

RESULTS

The Proximal and Distal Atrial Triad configurations were both associated with significant reductions in peak current (p < 0.01), but this effect was offset by significant increases in shock impedance (p < 0.01), resulting in no net change in the peak voltage or DFT energy in comparison to the Ventricular Triad configuration (Ventricular Triad: 4.9 +/- 6.6 J, Proximal Atrial Triad: 3.3 +/- 4.1J, Distal Atrial Triad: 4.4 +/- 6.7 J, p > 0.2).

CONCLUSION

Shocking vectors that incorporate a CS coil do not significantly improve atrial defibrillation efficacy. Since the Ventricular Triad shocking pathway provides reliable atrial and ventricular defibrillation, this configuration should be preferred for combined atrial and ventricular ICDs.

Recurrence of Atrial Tachyarrhythmias in Implantable Cardioverter-Defibrillator Recipients

BACKGROUND

Because the natural history of atrial tachyarrhythmia (AT) is not known in patients with implantable cardioverter-defibrillators (ICDs) but without device-based atrial therapies, we aimed to describe the characteristics and recurrence of AT in such patients.

METHODS

In this multicenter trial, 269 patients with standard indications for ICD placement and 2 episodes of AT in the preceding year received a dual-chamber ICD capable of logging AT. Patients were randomly assigned to 3-month periods of atrial therapies "on" or "off." This analysis considered only the 118 patients with atrial therapies programmed off at ICD placement.

RESULTS

Fifty-eight patients (49%) had at least 1 AT episode longer than 1 minute, and 21 (18%) had at least 1 prolonged episode (>24 hours). The median episode frequency for each patient (episodes per month) was 1.8 episodes longer than 1 minute, 0.8 longer than 1 hour, and 0 longer than 24 hours. The median AT burden was 12.2 hours per month.

CONCLUSIONS

Patients with standard ICD indications and history of AT have infrequent episodes, frequent short episodes, or prolonged episodes of AT-atrial fibrillation. However, the clinical characteristics examined did not distinguish among the groups. Improved diagnostic tools may help identify patients at risk for development of AT, thereby allowing specific therapies to be targeted to each group of patients.

Clinical predictors of atrial defibrillation thresholds with a dual-coil, active pectoral lead system

OBJECTIVES

The purpose of this study was to identify clinical predictors of atrial defibrillation thresholds (DFTs) with standard implantable cardioverter-defibrillator (ICD) leads.

BACKGROUND

Atrial defibrillation can be achieved with active pectoral, dual-coil transvenous ICD lead systems. If clinical predictors of atrial defibrillation efficacy with these lead systems were identified, they could be used to predict which patients may require more complex lead systems for atrial defibrillation, such as a coronary sinus electrode.

METHODS

This was a prospective study of 135 consecutive patients undergoing initial ICD implant for standard indications. The lead system evaluated was a transvenous defibrillation lead with coils in the superior vena cava (SVC) and right ventricular apex (RV), and a left pectoral pulse generator emulator (CAN). The shocking pathway was RV-->SVC+CAN. Atrial DFT was measured using a step-up protocol. Clinical and echocardiographic parameters were evaluated as predictors of atrial DFT and multiple linear regression was performed.

RESULTS

Mean atrial DFT was 4.6 +/- 3.8 J. Atrial DFT was < or =3 J in 70 patients (52%) and < or = 10 J in 97% of patients. The highest atrial DFT was 20 J (one patient). Left atrial size (r = 0.21, P = .01) and left ventricular end-diastolic diameter (r = 0.19, P = .02) were independent predictors of atrial DFT. However, these two predictors accounted for only 6% of the variability in atrial DFT.

CONCLUSIONS

Clinical parameters are of limited use in predicting atrial DFT with a dual-coil, active pectoral ICD lead system. Because the RV--> SVC + CAN shocking pathway provides reliable atrial and ventricular defibrillation, this configuration should be preferred for combined atrial and ventricular ICDs.

Cardiac pacing: the state of the art

Permanent cardiac pacing remains the only effective treatment for chronic, symptomatic bradycardia. In recent years, the role of implantable pacing devices has expanded substantially. At the beginning of the 21st century, exciting developments in technology seem to happen at an exponential rate. Major advances have extended the use of pacing beyond the arrhythmia horizon. Such developments include dual-chamber pacers, rate-response algorithms, improved functionality of implantable cardioverter defibrillators, combinations of sensors for optimum physiological response, and advances in lead placement and extraction. Cardiac pacing is poised to help millions of patients worldwide to live better electrically. We review pacing studies of sick-sinus syndrome, neurocardiogenic syncope, hypertrophic obstructive cardiomyopathy, and cardiac resynchronisation therapy, which are common or controversial indications for cardiac pacing. We also look at the benefits and complications of implantation in specific arrhythmias, suitability of different pacing modes, and the role of permanent pacing in the management of patients with heart failure.

The impact of atrial prevention and termination therapies on atrial tachyarrhythmia burden in patients receiving a dual-chamber defibrillator for ventricular arrhythmias

INTRODUCTION

This prospective, multicenter, randomized trial evaluated the effects of atrial prevention and termination therapies on atrial tachyarrhythmia (ATA) burden in patients with a standard indication for an implantable cardioverter defibrillator (ICD).

METHODS

A Jewel AF or GEM III AT ICD was implanted in 451 patients. At 1-month post-implant, patients were randomized to atrial prevention and termination therapies ON ( n = 199) or OFF ( n = 206) and followed for 6 additional months. Automatic atrial shocks were enabled in only 14% of the ON group. The follow-up time after randomization was 6.9 +/- 2.4 months ON versus 6.8 +/- 2.3 months OFF.

RESULTS

There were 126/405 (31.1%) patients who had AT/AF episodes during follow-up. Only four patients received a shock to treat ATA's during follow-up. The median ATA burden was 0 hours/month in both the ON and OFF groups ( P = 0.40). The mean ATA burden was 4.3 +/- 20.0 hours/month ON versus 9.0 +/- 50.0 hours/month OFF ( P = 0.11). In a subgroup of 192 patients with a history of ATA's, the median burden was 0 hours/month in the both groups ( P = 0.23). However, the mean burden in this subgroup was 7.6 +/- 27.1 hours/month ON versus 19.2 +/- 73.7 hours/month OFF ( P = 0.056).

CONCLUSIONS

In patients receiving an ICD for ventricular arrhythmias, no significant change in ATA burden was observed when atrial prevention and termination therapies were enabled. This may have been due to the low ATA burden in this population. In a subgroup of patients with history of ATA's, there was a trend towards a reduction in mean burden.

Incidence and rate characteristics of atrial tachyarrhythmias in patients with a dual chamber defibrillator

Atrial tachyarrhythmias play an important role in the treatment of patients with malignant ventricular tachyarrhythmias not only with respect to inappropriate discharges but also to left ventricular function and stroke risk. A combined dual chamber defibrillator provides separate therapies for atrial and ventricular tachyarrhythmias. To assess the incidence of atrial tachyarrhythmias in patients with this dual chamber implantable defibrillator, 40 patients with ventricular tachyarrhythmias and concomitant atrial tachyarrhythmias and/or AV conduction disturbances were included in a prospective study. During a mean follow-up of 25 +/- 11 months, 26 of 40 patients had a total of 1,430 recurrences of atrial tachyarrhythmias. The vast majority of the atrial tachyarrhythmias with regular atrial cycles had a mean median atrial cycle length of 235 +/- 37 ms and a mean duration of 34 +/- 144 minutes. Atrial tachyarrhythmias with irregular atrial cycles exhibited a median atrial cycle length of 198 +/- 31 ms and had a mean duration of 246 +/- 1,264 minutes. In addition, 67% of 375 tachyarrhythmias, in which the median ventricular cycle length during the ongoing episode could be documented, had a ventricular rate <100 beats/min. Continuous atrial arrhythmia detection with a dual chamber ICD reveals a high incidence of atrial tachyarrhythmias with a predominantly short duration of paroxysmal recurrences <1 hour in the vast majority of episodes.

The results of pacing trials for the prevention and termination of atrial tachyarrhythmias: is there any evidence of therapeutic breakthrough?

Atrial fibrillation (AF) is now recognized as the most prevalent sustained cardiac arrhythmia and it is associated with considerable mortality and morbidity. The demand for effective therapeutic strategies for AF has always been high and is anticipated to further increase. Anticoagulation and pharmacologic antiarrhythmic therapy or radiofrequency catheter ablation remain the mainstay of treatment for AF. Among the wide range of nonpharmacologic options which are presently being investigated, only ablation in or around the pulmonary veins and the surgical maze procedure have been shown to accomplish the aim of the curative treatment of the arrhythmia. Preventative atrial pacing and antitachycardia pacing may offer an attractive alternative option for the management of AF by either eliminating the triggers and/or by modifying the substrate of the arrhythmia. The results of several recent trials have shown a significant increase in the time to first AF recurrence, a decrease in atrial conduction time, and a trend towards reduction in AF burden, suggesting that atrial pacing may prevent AF due to improved synchronization of atrial depolarization. The recognition of potential triggers of AF, such as atrial premature complexes, short-long sequence, and bradycardia, has encouraged the development of novel atrial pacing algorithms designed to prevent the initiation of the arrhythmia on an individual basis. Observations of AF often starting with regular atrial activity consistent with atrial tachycardia have supported the hypothesis that early antitachycardia pacing may prevent progression to AF. The concept of "hybrid therapy" based on the combination of several different therapeutic strategies suggests that antitachycardia pacing therapy, integrated with an atrial defibrillator and preventative atrial pacing modes, may act synergistically to prevent AF. Dual chamber cardioverter-defibrillators with capacity to prevent and interrupt AF may offer more comprehensive and successful treatment for patients with advanced heart disease, frequent paroxysms of AF, and the risk of proarrhythmia.

[The impact of the Multicenter Automatic Defibrillator Implantation Trial II in a university hospital--do all patients with myocardial infarction and reduced left ventricular function need an implantable cardioverter-defibrillator?]

BACKGROUND AND OBJECTIVES

Patients with coronary artery disease (CAD) and severely compromised left ventricular ejection fraction are at high risk to die from sudden cardiac death. The Multicenter Automatic Defibrillator implantation Trial II (MADIT II) shows a significant benefit of a cardioverter-defibrillator (ICD) therapy compared to standard treatment alone in this selected group of patients. The objective of the present study was to investigate the number of patients who will fulfil the MADIT II criteria and are candidates for prophylactic ICD implantation.

METHODS AND MATERIAL

From January to December 2001 a total of 2653 patients underwent coronary angiography at our institution due to angina pectoris, positive exercise stress testing, pathological SPECT myocardial perfusion images, suspected dilated cardiomyopathy or ventricular arrhythmias. According to the MADIT II inclusion criteria patients with significant coronary artery disease (diameter stenosis > 50%), ejection fraction < 0.31% and previous myocardial infarction were included. Exclusion criteria were acute coronary syndromes, patients with ventricular tachyarrhythmias or an existing indication for ICD therapy, and patients with coronary artery bypass graft surgery or percutaneous transluminal coronary angioplasty within the past or following three months.

RESULTS

Out of 2653 patients 185 (7%) had an ejection fraction less than 0.31, 149 (5.6%) showed significant coronary artery stenosis and 70 (2.6%) patients fulfilled the MADIT II criteria. The mean age of these patients was 68 +/- 9 years, the left ventricular ejection fraction 24 +/- 6. In 37 patients an ICD system was implanted according to the existing guidelines. 70 patients met the MADIT II inclusion criteria, resulting in an increase of 189% of ICD implantations per year.

CONCLUSION

2.6% out of 2653 patients who were referred to coronary angiography fulfilled the criteria of MADIT II. The expanding indication for ICD therapy will result in an annual increase of 70 (189%) prophylactic ICD implantations in our study population.

Do atrial tachyarrhythmias beget ventricular tachyarrhythmias in defibrillator recipients?

OBJECTIVES

This study was designed to analyze the incidence of "dual tachycardia"-ventricular tachycardia (VT) or ventricular fibrillation (VF) preceded by paroxysmal atrial tachycardia (AT) or atrial fibrillation (AF)-in patients receiving dual-chamber implantable cardioverter defibrillators (ICDs).

BACKGROUND

Paroxysmal AT/AF occurs commonly in patients who receive ICDs for the treatment of life-threatening VT/VF. Although AF is associated with an adverse prognosis in the setting of structural heart disease, the relationship between AT/AF and VT/VF is unclear.

METHODS

We followed 537 patients undergoing implantation of the Jewel AF ICD (Model 7250, Medtronic, Minneapolis, Minnesota) for 11.4 +/- 8.2 months. These included 398 patients with a history of at least two episodes of AT or AF during the preceding year as well as 139 patients enrolled because of VT/VF alone.

RESULTS

There were 233 dual tachycardia episodes in 45 patients during follow-up. Overall, 8.9% of episodes detected as VT/VF were dual tachycardias, and 20.3% of patients with VT/VF had at least one dual tachycardia episode. The median duration of AT/AF preceding the first VT/VF detection was 1.09 h (25% to 75% quartile 0.24 to 33.4 h). When AT/AF continued between two consecutive VT/VF detections, the median interdetection interval was 11 min. When AT/AF terminated either because of a ventricular therapy or spontaneously, the median interdetection interval was prolonged to 71 h (p < 0.001).

CONCLUSIONS

Dual tachycardia is common in ICD recipients with a history of AT/AF. The duration of AT/AF preceding the first VT/VF detection is < or =1 h about 50% of the time. Termination of the AT/AF significantly delays the time to the next VT/VF detection.

Implantable cardioverter defibrillators in heart failure

Implantable cardioverter defibrillators provide effective and reliable treatment of spontaneous VT and VF. These devices can be expected to decrease the risk for arrhythmic death in patients with heart failure but do not improve overall survival when death from severe pump dysfunction is imminent. Appropriate patient selection is a major aspect of arrhythmia management. Future devices will incorporate features that have the potential to reduce atrial arrhythmias, improve ventricular function, monitor hemodynamics, and prevent sudden arrhythmic death.

Should all implantable cardioverter defibrillators for ventricular arrhythmias be dual-chamber devices?

The advantages of a dual-chamber implantable cardioverter defibrillator (ICD) over a single-chamber ICD include physiologic pacing capability, atrial electrogram storage, enhanced arrhythmia discrimination algorithms, and a potential to treat atrial arrhythmia by pacing or defibrillation. Current evidence supports the supposition that dual-chamber ICDs are definitely indicated in patients who have a concomitant indication for physiologic pacing, such as bradycardia or bradycardia-dependent ventricular tachyarrhythmias. Refined dual-chamber arrhythmia discrimination algorithms and enhanced atrial therapies are probably required for patients with frequent supraventricular arrhythmias. Furthermore, in patients with systolic heart failure, low ejection fraction, and intraventricular conduction delay, triple-chamber ICDs with biventricular pacing may improve their functional status and prevent sudden arrhythmic death. Careful patient selection is required to optimize the cost-effectiveness of these sophisticated technologies.

Atrial therapies reduce atrial arrhythmia burden in defibrillator patients

BACKGROUND

Approximately 25% of patients who receive an implantable cardioverter-defibrillator (ICD) to treat ventricular tachyarrhythmias have documented atrial tachyarrhythmias before implantation. This study assessed the ability of device-based prevention and termination therapies to reduce the burden of spontaneous atrial tachyarrhythmias.

METHODS AND RESULTS

Patients with a standard indication for the implantation of an ICD and 2 episodes of atrial tachyarrhythmias in the preceding year received a dual-chamber ICD (Medtronic 7250 Jewel AF) that uses pacing and shock therapies for prevention and/or termination of atrial tachyarrhythmias. In a multicenter trial, patients were randomized to 3-month periods with atrial therapies "on" or "off" and subsequently crossed over. Analysis was performed on the 52 of 269 patients who had episodes of atrial tachyarrhythmia and had >/=30 days of follow-up with atrial therapies on and off. The atrial therapies resulted in a reduction of atrial tachyarrhythmia burden from a mean of 58.5 to 7.8 h/mo. A paired analysis (Wilcoxon signed-rank test) showed that the median difference in burden (1.1 h/mo) was highly significant (P=0.007). When the subgroup of 41 patients treated only with atrial pacing therapies was analyzed, the reduction in burden persisted (P=0.01).

CONCLUSIONS

In this study, patients with a standard ICD indication and atrial tachyarrhythmias had a significant reduction in atrial tachyarrhythmia burden with use of atrial pacing and shock therapies.

Prevalence of central venous occlusion in patients with chronic defibrillator leads

BACKGROUND

Many patients with previously implanted ventricular defibrillators are candidates for an upgrade to a device capable of atrial-ventricular sequential or multisite pacing. The prevalence of venous occlusion after placement of transvenous defibrillator leads is unknown. The purpose of this study was to determine the prevalence of central venous occlusion in asymptomatic patients with chronic transvenous defibrillator leads.

METHODS

Thirty consecutive patients with a transvenous defibrillator lead underwent bilateral contrast venography of the cephalic, axillary, subclavian, and brachiocephalic veins as well as the superior vena cava before an elective defibrillator battery replacement. The mean time between transvenous defibrillator lead implantation and venography was 45 +/- 21 months. Sixteen patients had more than 1 lead in the same subclavian vein. No patient had clinical signs of venous occlusion.

RESULTS

One (3%) patient had a complete occlusion of the subclavian vein, 1 (3%) patient had a 90% subclavian vein stenosis, 2 (7%) patients had a 75% to 89% subclavian stenosis, 11 (37%) patients had a 50% to 74% subclavian stenosis, and 15 (50%) patients had no subclavian stenosis.

CONCLUSIONS

The low prevalence of subclavian vein occlusion or severe stenosis among defibrillator recipients found in this study suggests that the placement of additional transvenous leads in a patient who already has a ventricular defibrillator is feasible in a high percentage of patients (93%).

The implantable cardioverter defibrillator

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

A prospective randomized-controlled trial of ventricular fibrillation detection time in a DDDR ventricular defibrillator. Ventak AV II DR Study Investigators

Implantable cardioverter defibrillators (ICDs) with dual chamber and dual chamber rate responsive pacing may offer hemodynamic advantages for some ICD patients. Separate ICDs and DDDR pacemakers can result in device to device interactions, inappropriate shocks, and underdetection of ventricular fibrillation (VF). The objectives of this study were to compare the VF detection times between the Ventak AV II DR and the Ventak AV during high rate DDDR and DDD pacing and to test the safety of dynamic ventricular refractory period shortening. Patients receiving an ICD were randomized in a paired comparison to pacing at 150 beats/min (DDD pacing) or 175 beats/min (DDDR pacing) during ICD threshold testing to create a "worst case scenario" for VF detection. The VF detection rate was set to 180 beats/min, and VF was induced during high rate pacing with alternating current. The device was then allowed to detect and treat VF. The induction was repeated for each patient at each programmed setting so that all patients were tested at both programmed settings. Paired analysis was performed. Patient characteristics were a mean age of 69 +/- 11 years, 78% were men, coronary artery disease was present in 85%, and a mean left ventricular ejection fraction of 0.34 +/- 0.11. Fifty-two episodes of VF were induced in 26 patients. Despite the high pacing rate, all VF episodes were appropriately detected. The mean VF detection time was 2.4 +/- 1.0 seconds during DDD pacing and 2.9 +/- 1.9 seconds during DDDR pacing (P = NS). DDD and DDDR programming resulted in appropriate detection of all episodes of VF with similar detection times despite the "worst case scenario" tested. Delays in detection may be seen with long programmed ventricular refractory periods which shorten the VF sensing window and may be avoided with dynamic ventricular refractory period shortening.

Methods of minimizing inappropriate implantable cardioverter-defibrillator shocks

As more and more patients receive complex implantable cardioverter-defibrillators (ICDs), profound knowledge about the incidence of inappropriate device therapy, the reasons it happens, and the possibilities for prevention is crucial. In this article, the most important prevention algorithms incorporated in current ICD models and their advantages and handicaps are discussed in detail, which should help to guide the device selection for a particular patient. Also, emphasis is put on adjunctive drug therapy and interventional treatment strategies, which are crucial in managing patients with inappropriate ICD shocks.

Implantable dual-chamber cardioverter-defibrillator-pacemaker

The fifth generation of implantable cardioverter-defibrillators offer enhanced modes of detection of atrial and ventricular arrhythmias, antitachycardia pacing and shocks, multiprogrammability, intracardiac electrogram storage, and all functions of antibradycardia dual-chamber pacing including rate responsiveness and mode switching. There is no consensus on the indications for dual-chamber pacemaker defibrillator systems. This review focuses on the four major options of newer devices that might benefit patients: 1) permanent dual-chamber pacing in ischemic coronary disease patients, 2) detection and management of atrial fibrillation or other atrial tachyarrhythmias, 3) some newer indications for pacing, and 4) the suppression of inappropriate interventions. On the basis of published data, newer indications for the dual-chamber systems, advantages and limitations, and future perspectives are discussed.

Pitfalls of the concept of incremental specificity used in comparisons of dual chamber VT/VF detection algorithms

The concepts of incremental specificity and incremental positive predictive accuracy (PPA) have been proposed to measure the success of dual chamber cardioverter defibrillator (ICD) algorithms for tachyarrhythmia detection in improving specificity while maintaining very high sensitivity to detection of episodes of ventricular tachycardia/fibrillation (VT/VF). While dual chamber VT/VF detection algorithms differ substantially among different ICD manufacturers, they all operate as "add-on" features to the single chamber elementary detection algorithms that are based on simple criteria of increased ventricular rate. The incremental specificity and PPA characterize the performance of the dual chamber detection operation in this "add-on" mode, that is within a database of rhythm episodes all meet the simple rate-based criteria. A statistical model of hypothetical devices has been used to demonstrate that the concepts of incremental specificity and PPA are very dependent on the composition of the database used to evaluate a particular dual chamber ICD. Because some sinus tachycardia and supraventricular tachyarrhythmias with regular atrioventricular conduction are more easily discriminated from true VT/VF than other supraventricular tachyarrhythmias, the model shows that rather than the performance of the dual chamber detection functions, the major contributor to the incremental specificity may be the proportion between the "easy" and "difficult" supraventricular episodes. The algorithms used by different ICD manufacturers to detect tachyarrhythmias based on ventricular rate are known to differ substantially in the ability to differentiate true VT/VF from other tachyarrhythmias. Consequently, the databases of rhythms against which the different dual camber ICDs are tested are also different in composition of different types of supraventricular tachyarrhythmias. Therefore, the values of incremental specificity and PPA reported by different manufacturers do not have an equivalent meaning and do not offer a valid comparison of the true performance of different dual chamber ICDs.

Defibrillator challenges for the new millennium: the marriage of device and patient-making and maintaining a good match

Although it has become clear that implantable cardioverter defibrillators (ICDs) are effective, important challenges remain for the physician. Due to the limitations of available risk stratification tools, patient selection for primary sudden death prevention remains controversial in many populations. Additionally, the proliferation of device choices has led to challenges in matching the appropriate device to the individual patient: device size is balanced against longevity; the advantages of dual chamber systems is weighed against their increased complexity; physician and patient preferences in device implant site are constrained by site-dependent effects on defibrillation effectiveness and lead failure rates; and special consideration must be given to the patient with a preexisting pacemaker. After ICD placement, determination of appropriate follow-up frequency and methodology to assess device function must be considered. This article will review patient selection, device implant site selection, device-device interactions, single versus dual chamber ICD selection, and follow-up.

Comparison of therapy detection times between implantable cardioverter defibrillators with standard dual- and single-chamber pacing

Previous implantable cardioverter defibrillators (ICDs) required patients in need of dual-chamber (DDD) pacing for improved hemodynamic status to undergo implantation of separate devices to treat bradycardia and/or ventricular arrhythmias. An investigation was conducted to verify the performance of a new ICD that combines both therapies.Sixty-nine patients at 17 European and Canadian centers were implanted with VENTAK AV models 1810/1815, ICD's that includes DDD pacing and algorithms designed to differentiate between atrial and ventricular arrhythmias. 36 of the cohort were compared to 32 patients tested at six centers with an external test device (VENTAK MINI). In both cohorts detection times were calculated for ventricular fibrillation (VF) induced at implant. The mean detection times (DT) from the VENTAK AV device were compared to the DT from the VENTAK MINI device. Patient characteristics of the VENTAK AV and the VENTAK MINI control groups were similar. Mean VF detection time (+/-SD) with the VENTAK AV device was 2.21 +/- 0.54 seconds, as compared with 1.87 +/- 0.62 seconds with the VENTAK MINI (p < 0.01), indicating that the difference in means did not exceed one second. The VENTAK AV system function did not demonstrate interaction with the pacemaker function, as indicated by the clinical significance with the detection times of the study device. The difference in detection times between cohorts did not statistically exceed one second. Appropriate detection of the new ICD was not compromised by the addition of the dual-chamber pacing therapy.

Dual chamber implantable cardioverter defibrillator benefits and limitations

Dual chamber ICD capable of providing dual chamber pacing (DDD) and ventricular arrhythmia therapy is now available. We report our experience of clinical performance of dual chamber ICDs amongst Chinese population.

METHODS

9 patients (6 men and 3 women) received dual chamber ICDs, mean age 50 +/- 18.8 years. The indications were ventricular fibrillation (VF) [5], hemodynamic intolerant ventricular tachycardia (VT) [3] and unexplained syncope plus positive induction of VF [1]. The underlying cardiac pathology were congenital LQT syndrome(1), hypertrophic cardiomyopathy [2], coronary artery disease [2], rheumatic valvular disease [1], Brugada syndrome [1], arrhythmogenic right ventricular dysplasia [1] and idiopathic VF [1]. Four patients have documented paroxysmal atrial fibrillation (AF). All patients have defibrillation thresholds (DFT) determined with a binary search protocol starting at 12 joules (J) at implantation.

RESULTS

A total of 34 episodes of VF were induced at implantation with mean DFT 13.8 +/- 7 J. The average shocking impedance was 40 +/- 3.6 Omega. The mean acute P wave measured 3.3 +/- 1.3 mV and R wave measured 13.2 +/- 3.2 mV. Atrial and ventricular thresholds, at pulse width 0.5 ms, averaged 0.8 +/- 0.4 V and 0.4 +/- 0.2 V. During follow-up period, 16 episodes of VF were documented and were successfully treated with the first programmed shock. In the patient with LQT syndrome, DDD was initiated to prevent pause-dependant VF. Three episodes of inappropriate therapy (15.8%) were delivered. One patient experienced 2 shocks after exercise. Stored electrograms showed sinus tachycardia with first degree heart block which was misdiagnosed as VT with retrograde 1:1 conduction. Another inappropriate therapy occurred with AF with fast ventricular response within the VF zone and VT therapy inhibitor was disabled.

CONCLUSION

Dual chamber ICD allows combined benefits of DDD and VT/VF therapy. Storage of both atrial and ventricular electrograms provide more information in elucidation of nature of dysarrhythmias. Inappropriate shocks, though reduced, are still possible and the rigid algorithms of SVT discrimination from VT will need further published.