Atrioverter: an implantable device for the treatment of atrial fibrillation

Historical Perspective of the Cardiac Autonomic Nervous System

The contemporary history of the cardiac autonomic nervous system includes early descriptions of neuroanatomy in the 19th century, followed by an understanding of the physiologic determinants of neurocardiology in the 20th century. Neurology and cardiology preceded the arrival of clinical cardiac electrophysiology, a specialized field in medicine devoted to the diagnosis and treatment of cardiac arrhythmias. The rapid growth in pharmacology, ablation, pacing and defibrillation, associated with significant technological breakthroughs, have resulted in new opportunities for neuromodulation in the 21st century. Small changes in autonomic tone can potentially provide important therapeutic benefits for patients with cardiac and arrhythmia disorders.

[History of the implantable cardioverter-defibrillator in Germany]

The implantable cardioverter-defibrillator (ICD) was a breakthrough in the prevention of sudden cardiac death. After years of technical development in the USA, Michel Mirowski succeeded in proving reliable automatic defibrillation of ventricular tachyarrhythmias through initial human implantations in 1980, despite many obstacles. Nearly 4 years later, the first patients received ICDs at multiple centers in Germany. Subsequently, outside the USA, Germany became the country with highest implantation rates. The absolute number of implantations remained small as long as implantations required epicardial defibrillation electrodes and therefore thoracotomy by cardiac surgeons. Pacemaker-like implantation using a transvenous defibrillation electrode with a pectoral ICD became feasible in the early 1990s pushing implantation rates to the next level. Technical advancements were accompanied by clinical research in Germany, and often, the first-in-human studies were conducted in Germany. In 1991, the first guidelines for indications were established in the USA and Germany. Several randomized studies on indications were published between 1996 and 2009, mostly led by American teams with German participation, but also under German leadership (CASH, CAT, DINAMIT, IRIS). The DANISH study in 2016 questioned the results of these long-standing studies. Instead of providing ICDs to patients using a broad indication, future efforts aim to identify patients who, despite optimal medical therapy, cardiac resynchronization therapy (CRT), and/or catheter ablation, need protection against sudden cardiac death. Risk scores incorporating myocardial scars in magnetic resonance imaging (MRI) and genetic information are expected to contribute to more individualized and effective indications.

Optoelectronic control of cardiac rhythm: Toward shock-free ambulatory cardioversion of atrial fibrillation

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, progressive in nature, and known to have a negative impact on mortality, morbidity, and quality of life. Patients requiring acute termination of AF to restore sinus rhythm are subjected to electrical cardioversion, which requires sedation and therefore hospitalization due to pain resulting from the electrical shocks. However, considering the progressive nature of AF and its detrimental effects, there is a clear need for acute out-of-hospital (i.e., ambulatory) cardioversion of AF. In the search for shock-free cardioversion methods to realize such ambulatory therapy, a method referred to as optogenetics has been put forward. Optogenetics enables optical control over the electrical activity of cardiomyocytes by targeted expression of light-activated ion channels or pumps and may therefore serve as a means for cardioversion. First proof-of-principle for such light-induced cardioversion came from in vitro studies, proving optogenetic AF termination to be very effective. Later, these results were confirmed in various rodent models of AF using different transgenes, illumination methods, and protocols, whereas computational studies in the human heart provided additional translational insight. Based on these results and fueled by recent advances in molecular biology, gene therapy, and optoelectronic engineering, a basis is now being formed to explore clinical translations of optoelectronic control of cardiac rhythm. In this review, we discuss the current literature regarding optogenetic cardioversion of AF to restore normal rhythm in a shock-free manner. Moreover, key translational steps will be discussed, both from a biological and technological point of view, to outline a path toward realizing acute shock-free ambulatory termination of AF.

Light transmittance in human atrial tissue and transthoracic illumination in rats support translatability of optogenetic cardioversion of atrial fibrillation

BACKGROUND

Optogenetics could offer a solution to the current lack of an ambulatory method for the rapid automated cardioversion of atrial fibrillation (AF), but key translational aspects remain to be studied.

OBJECTIVE

To investigate whether optogenetic cardioversion of AF is effective in the aged heart and whether sufficient light penetrates the human atrial wall.

METHODS

Atria of adult and aged rats were optogenetically modified to express light-gated ion channels (i.e., red-activatable channelrhodopsin), followed by AF induction and atrial illumination to determine the effectivity of optogenetic cardioversion. The irradiance level was determined by light transmittance measurements on human atrial tissue.

RESULTS

AF could be effectively terminated in the remodeled atria of aged rats (97%, n = 6). Subsequently, ex vivo experiments using human atrial auricles demonstrated that 565-nm light pulses at an intensity of 25 mW/mm2 achieved the complete penetration of the atrial wall. Applying such irradiation onto the chest of adult rats resulted in transthoracic atrial illumination as evidenced by the optogenetic cardioversion of AF (90%, n = 4).

CONCLUSION

Transthoracic optogenetic cardioversion of AF is effective in the aged rat heart using irradiation levels compatible with human atrial transmural light penetration.

Does conduction heterogeneity determine the supervulnerable period after atrial fibrillation?

Atrial fibrillation (AF) resumes within 90 s in 27% of patients after sinus rhythm (SR) restoration. The aim of this study is to compare conduction heterogeneity during the supervulnerable period immediately after electrical cardioversion (ECV) with long-term SR in patients with AF. Epicardial mapping of both atria was performed during SR and premature atrial extrasystoles in patients in the ECV (N = 17, age: 73 ± 7 years) and control group (N = 17, age: 71 ± 6 years). Inter-electrode conduction times were used to identify areas of conduction delay (CD) (conduction times 7-11 ms) and conduction block (CB) (conduction times ≥ 12 ms). For all atrial regions, prevalences and length of longest CB and continuous CDCB lines, magnitude of conduction disorders, conduction velocity, biatrial activation time, and voltages did not differ between the ECV and control group during both SR and premature atrial extrasystoles (p ≥ 0.05). Hence, our data suggest that there may be no difference in biatrial conduction characteristics between the supervulnerable period after ECV and long-term SR in AF patients. The supervulnerable period after AF termination is not determined by conduction heterogeneity during SR and PACs. It is unknown to what extent intra-atrial conduction is impaired during the supervulnerable period immediately after ECV and whether different right and left atrial regions are equally affected. This high-resolution epicardial mapping study (upper left panel) of both atria shows that during SR the prevalences and length of longest CB and cCDCB lines (upper middle panel), magnitude of conduction disorders, CV and TAT (lower left panel), and voltages did not differ between the ECV and control group. Likewise, these parameters were comparable during PACs between the ECV and control group (lower left panel). †Non-normally distributed. cm/s = centimeters per second; mm = millimeter; ms = millisecond; AF = atrial fibrillation; AT = activation time; BB = Bachmann's bundle; cCDCB = continuous lines of conduction delay and block; CB = conduction block; CD = conduction delay; CT = conduction time; CV = conduction velocity; ECV = electrical cardioversion; LA = left atrium; LAT = local activation times; PAC = premature atrial complexes; PVA = pulmonary vein area; RA = right atrium; SR = sinus rhythm; TAT = total activation time.

Novel Low-Voltage MultiPulse Therapy to Terminate Atrial Fibrillation

OBJECTIVES

This first-in-human feasibility study was undertaken to translate the novel low-voltage MultiPulse Therapy (MPT) (Cardialen, Inc., Minneapolis, Minnesota), which was previously been shown to be effective in preclinical studies in terminating atrial fibrillation (AF), into clinical use.

BACKGROUND

Current treatment options for AF, the most common arrhythmia in clinical practice, have limited success. Previous attempts at treating AF by using implantable devices have been limited by the painful nature of high-voltage shocks.

METHODS

Forty-two patients undergoing AF ablation were recruited at 6 investigational centers worldwide. Before ablation, electrode catheters were placed in the coronary sinus, right and/or left atrium, for recording and stimulation. After the induction of AF, MPT, which consists of up to a 3-stage sequence of far- and near-field stimulation pulses of varied amplitude, duration, and interpulse timing, was delivered via temporary intracardiac leads. MPT parameters and delivery methods were iteratively optimized.

RESULTS

In the 14 patients from the efficacy phase, MPT terminated 37 of 52 (71%) of AF episodes, with the lowest median energy of 0.36 J (interquartile range [IQR]: 0.14 to 1.21 J) and voltage of 42.5 V (IQR: 25 to 75 V). Overall, 38% of AF terminations occurred within 2 seconds of MPT delivery (p < 0.0001). Shorter time between AF induction and MPT predicted success of MPT in terminating AF (p < 0.001).

CONCLUSIONS

MPT effectively terminated AF at voltages and energies known to be well tolerated or painless in some patients. Our results support further studies of the concept of implanted devices for early AF conversion to reduce AF burden, symptoms, and progression.

A shock-free approach for ambulatory cardioversion in atrial fibrillation

Atrial fibrillation (AF), the most common persistent arrhythmia, is terminated most effectively by electrical cardioversion. This therapy requires in-hospital sedation to relieve the pain caused by electric shocks. Recently, our research group showed how the heart itself could be enabled to detect and terminate arrhythmias, including AF, thereby revealing the discovery of fully biological, shock-free cardioversion. Because of its biological nature, neither electric shocks nor hardware/software is required for sinus rhythm (SR) restoration, which creates a new perspective for ambulatory AF termination. Increasing evidence suggests that patients may indeed benefit from such continuous real-time rhythm control.

Cardiac Optogenetics in Atrial Fibrillation: Current Challenges and Future Opportunities

Although rarely life-threatening on short term, atrial fibrillation leads to increased mortality and decreased quality of life through its complications, including heart failure and stroke. Recent studies highlight the benefits of maintaining sinus rhythm. However, pharmacological long-term rhythm control strategies may be shadowed by associated proarrhythmic effects. At the same time, electrical cardioversion is limited to hospitals, while catheter ablation therapy, although effective, is invasive and is dedicated to specific patients, usually with low amounts of atrial fibrosis (preferably Utah I-II). Cardiac optogenetics allows influencing the heart's electrical activity by applying specific wavelength light pulses to previously engineered cardiomyocytes into expressing microbial derived light-sensitive proteins called opsins. The resulting ion influx may give rise to either hyperpolarizing or depolarizing currents, thus offering a therapeutic potential in cardiac electrophysiology, including pacing, resynchronization, and arrhythmia termination. Optogenetic atrial fibrillation cardioversion might be achieved by inducing a conduction block or filling of the excitable gap. The authors agree that transmural opsin expression and appropriate illumination with an exposure time longer than the arrhythmia cycle length are necessary to achieve successful arrhythmia termination. However, the efficiency and safety of biological cardioversion in humans remain to be seen, as well as side effects such as immune reactions and loss of opsin expression. The possibility of delivering pain-free shocks with out-of-hospital biological cardioversion is tempting; however, there are several issues that need to be addressed first: applicability and safety in humans, long-term behaviour, anticoagulation requirements, and fibrosis interactions.

Self-restoration of cardiac excitation rhythm by anti-arrhythmic ion channel gating

Homeostatic regulation protects organisms against hazardous physiological changes. However, such regulation is limited in certain organs and associated biological processes. For example, the heart fails to self-restore its normal electrical activity once disturbed, as with sustained arrhythmias. Here we present proof-of-concept of a biological self-restoring system that allows automatic detection and correction of such abnormal excitation rhythms. For the heart, its realization involves the integration of ion channels with newly designed gating properties into cardiomyocytes. This allows cardiac tissue to i) discriminate between normal rhythm and arrhythmia based on frequency-dependent gating and ii) generate an ionic current for termination of the detected arrhythmia. We show in silico, that for both human atrial and ventricular arrhythmias, activation of these channels leads to rapid and repeated restoration of normal excitation rhythm. Experimental validation is provided by injecting the designed channel current for arrhythmia termination in human atrial myocytes using dynamic clamp.

An automated hybrid bioelectronic system for autogenous restoration of sinus rhythm in atrial fibrillation

Because of suboptimal therapeutic strategies, restoration of sinus rhythm in symptomatic atrial fibrillation (AF) often requires in-hospital delivery of high-voltage shocks, thereby precluding ambulatory AF termination. Continuous, rapid restoration of sinus rhythm is desired given the recurring and progressive nature of AF. Here, we present an automated hybrid bioelectronic system for shock-free termination of AF that enables the heart to act as an electric current generator for autogenous restoration of sinus rhythm. We show that local, right atrial delivery of adenoassociated virus vectors encoding a light-gated depolarizing ion channel results in efficient and spatially confined transgene expression. Activation of an implanted intrathoracic light-emitting diode device allows for termination of AF by illuminating part of the atria. Combining this newly obtained antiarrhythmic effector function of the heart with the arrhythmia detector function of a machine-based cardiac rhythm monitor in the closed chest of adult rats allowed automated and rapid arrhythmia detection and termination in a safe, effective, repetitive, yet shock-free manner. These findings hold translational potential for the development of shock-free antiarrhythmic device therapy for ambulatory treatment of AF.

Electrical treatment of atrial arrhythmias in heart failure patients implanted with a dual defibrillator CRT device. Results from the TRADE-HF study

BACKGROUND

Ventricular and atrial arrhythmias commonly occur in heart failure patients and are a significant source of symptoms, morbidity and mortality. Some specific generators referred to as dual defibrillators, Dual CRT-Ds, have the ability to treat atrial and ventricular arrhythmias. TRADE-HF is a prospective two-arm randomized study aimed at assessing the benefits of complete automatic management of atrial arrhythmias in patients implanted with a dual CRT-D.

METHODS

Primary objective of the TRADE-HF study was to document reduction of unplanned hospital admission for cardiac reasons or death for cardiovascular causes or progression to permanent AF, by comparing fully-automatic device driven therapy for atrial tachycardia or fibrillation (AT/AF) to an in-hospital approach for treatment of symptomatic AT/AF. Randomized Patients were followed every 6months for 3years to assess the primary objective.

RESULTS

Four-hundred-twenty patients have been enrolled in the study. At the end of the study 30 subjects died for cardiovascular causes, 60 had at least one hospitalization for cardiovascular causes and 14 developed permanent AF. Eighty-seven patients experienced a composite event. Hazard Ratio for device-managed automatic therapy arm compared to traditional was 0.987 (95% CI: 0.684-1.503; p=0.951). The primary endpoint analysis resulted in no difference between the device managed and in-hospital treatment arm.

CONCLUSION

The TRADE-HF study failed to demonstrate a reduction in the composite of unplanned hospitalizations for cardiovascular causes or death for cardiovascular causes or progression to permanent AF using automatic atrial therapy compared to a traditional approach including hospitalization for symptomatic episodes and/or in-hospital treatment of AT/AF.

Towards Low Energy Atrial Defibrillation

A wireless powered implantable atrial defibrillator consisting of a battery driven hand-held radio frequency (RF) power transmitter (ex vivo) and a passive (battery free) implantable power receiver (in vivo) that enables measurement of the intracardiacimpedance (ICI) during internal atrial defibrillation is reported. The architecture is designed to operate in two modes: Cardiac sense mode (power-up, measure the impedance of the cardiac substrate and communicate data to the ex vivo power transmitter) and cardiac shock mode (delivery of a synchronised very low tilt rectilinear electrical shock waveform). An initial prototype was implemented and tested. In low-power (sense) mode, >5 W was delivered across a 2.5 cm air-skin gap to facilitate measurement of the impedance of the cardiac substrate. In high-power (shock) mode, >180 W (delivered as a 12 ms monophasic very-low-tilt-rectilinear (M-VLTR) or as a 12 ms biphasic very-low-tilt-rectilinear (B-VLTR) chronosymmetric (6ms/6ms) amplitude asymmetric (negative phase at 50% magnitude) shock was reliably and repeatedly delivered across the same interface; with >47% DC-to-DC (direct current to direct current) power transfer efficiency at a switching frequency of 185 kHz achieved. In an initial trial of the RF architecture developed, 30 patients with AF were randomised to therapy with an RF generated M-VLTR or B-VLTR shock using a step-up voltage protocol (50–300 V). Mean energy for successful cardioversion was 8.51 J ± 3.16 J. Subsequent analysis revealed that all patients who cardioverted exhibited a significant decrease in ICI between the first and third shocks (5.00 Ω (SD(σ) = 1.62 Ω), p < 0.01) while spectral analysis across frequency also revealed a significant variation in the impedance-amplitude-spectrum-area (IAMSA) within the same patient group (|∆(IAMSA_S1-IAMSA_S3)[1 Hz − 20 kHz] = 20.82 Ω-Hz (SD(σ) = 10.77 Ω-Hz), p < 0.01); both trends being absent in all patients that failed to cardiovert. Efficient transcutaneous power transfer and sensing of ICI during cardioversion are evidenced as key to the advancement of low-energy atrial defibrillation.

Hybrid therapy in the management of atrial fibrillation

Atrial fibrillation is the most common sustained arrhythmia. Because of the sub-optimal outcomes and associated risks of medical therapy as well as the recent advances in non-pharmacologic strategies, a multitude of combined (hybrid) algorithms have been introduced that improve efficacy of standalone therapies while maintaining a high safety profile. Antiarrhythmic administration enhances success rate of electrical cardioversion. Catheter ablation of antiarrhythmic drug-induced typical atrial flutter may prevent recurrent atrial fibrillation. Through simple ablation in the right atrium, suppression of atrial fibrillation may be achieved in patients with previously ineffective antiarrhythmic therapy. Efficacy of complex catheter ablation in the left atrium is improved with antiarrhythmic drugs. Catheter ablation followed by permanent pacemaker implantation is an effective and safe treatment option for selected patients. Additional strategies include pacing therapies such as atrial pacing with permanent pacemakers, preventive pacing algorithms, and/or implantable dual-chamber defibrillators are available. Modern hybrid strategies combining both epicardial and endocardial approaches in order to create a complex set of radiofrequency lesions in the left atrium have demonstrated a high rate of success and warrant further research. Hybrid therapy for atrial fibrillation reviews history of development of non-pharmacological treatment strategies and outlines avenues of ongoing research in this field.

Rate Control Strategy Elevated To Primary Treatment For Atrial Fibrillation: Has The Last Word Already Been Spoken?

In the last decade, we were able to see the light shed by several trials and observational studies that dealt with the appropriate manner of treating patients with atrial fibrillation (AF). Recently the AF management by cardiologists has become more aggressive, in part because of an improved comprehension of this rhythm disturbance, as well as, the availability of new treatment strategies. Increasing awareness of AF as a disease rather than as an acceptable alternative to sinus rhythm has led to search for clear arguments to support a certain strategy as a gold standard. In this respect, the decision of whether to restore sinus rhythm, or to control the ventricular rate and allow AF to persist is of critical importance. The results of randomized, controlled trials addressing this matter shed some light on the proper way of treatment for these AF patients. The AFFIRM and RACE trials and their respective sub-studies showed surprising results. The vast majority of physicians were surprised to learn that the rate control strategy was elevated to the position of primary treatment for the AF management instead of the all-time recognized rhythm control approach to restoration and maintenance of sinus rhythm. The use of anticoagulants in the trials was different in the treatment strategies. There was a greater anticoagulant use in the rate control arm because of the belief that anticoagulation can be discontinued in the rhythm control arm when sinus rhythm was restored and maintained for one month. On the other hand, only pharmacological agents were used to maintain sinus rhythm in those trials, however, there is increasing evidence that AF ablation can restore and maintain sinus rhythm in a great proportion of patients. Indeed, there are some limitations and several interesting aspects of these trials and other studies that will be discussed. The last word has not been spoken yet.

Light-induced termination of spiral wave arrhythmias by optogenetic engineering of atrial cardiomyocytes

AIMS

Atrial fibrillation (AF) is the most common cardiac arrhythmia and often involves reentrant electrical activation (e.g. spiral waves). Drug therapy for AF can have serious side effects including proarrhythmia, while electrical shock therapy is associated with discomfort and tissue damage. Hypothetically, forced expression and subsequent activation of light-gated cation channels in cardiomyocytes might deliver a depolarizing force sufficient for defibrillation, thereby circumventing the aforementioned drawbacks. We therefore investigated the feasibility of light-induced spiral wave termination through cardiac optogenetics.

METHODS AND RESULTS

Neonatal rat atrial cardiomyocyte monolayers were transduced with lentiviral vectors encoding light-activated Ca(2+)-translocating channelrhodopsin (CatCh; LV.CatCh∼eYFP↑) or eYFP (LV.eYFP↑) as control, and burst-paced to induce spiral waves rotating around functional cores. Effects of CatCh activation on reentry were investigated by optical and multi-electrode array (MEA) mapping. Western blot analyses and immunocytology confirmed transgene expression. Brief blue light pulses (10 ms/470 nm) triggered action potentials only in LV.CatCh∼eYFP↑-transduced cultures, confirming functional CatCh-mediated current. Prolonged light pulses (500 ms) resulted in reentry termination in 100% of LV.CatCh∼eYFP↑-transduced cultures (n = 31) vs. 0% of LV.eYFP↑-transduced cultures (n = 11). Here, CatCh activation caused uniform depolarization, thereby decreasing overall excitability (MEA peak-to-peak amplitude decreased 251.3 ± 217.1 vs. 9.2 ± 9.5 μV in controls). Consequently, functional coresize increased and phase singularities (PSs) drifted, leading to reentry termination by PS-PS or PS-boundary collisions.

CONCLUSION

This study shows that spiral waves in atrial cardiomyocyte monolayers can be terminated effectively by a light-induced depolarizing current, produced by the arrhythmogenic substrate itself, upon optogenetic engineering. These results provide proof-of-concept for shockless defibrillation.

Multistage electrotherapy delivered through chronically-implanted leads terminates atrial fibrillation with lower energy than a single biphasic shock

OBJECTIVES

The goal of this study was to develop a low-energy, implantable device-based multistage electrotherapy (MSE) to terminate atrial fibrillation (AF).

BACKGROUND

Previous attempts to perform cardioversion of AF by using an implantable device were limited by the pain caused by use of a high-energy single biphasic shock (BPS).

METHODS

Transvenous leads were implanted into the right atrium (RA), coronary sinus, and left pulmonary artery of 14 dogs. Self-sustaining AF was induced by 6 ± 2 weeks of high-rate RA pacing. Atrial defibrillation thresholds of standard versus experimental electrotherapies were measured in vivo and studied by using optical imaging in vitro.

RESULTS

The mean AF cycle length (CL) in vivo was 112 ± 21 ms (534 beats/min). The impedances of the RA-left pulmonary artery and RA-coronary sinus shock vectors were similar (121 ± 11 Ω vs. 126 ± 9 Ω; p = 0.27). BPS required 1.48 ± 0.91 J (165 ± 34 V) to terminate AF. In contrast, MSE terminated AF with significantly less energy (0.16 ± 0.16 J; p < 0.001) and significantly lower peak voltage (31.1 ± 19.3 V; p < 0.001). In vitro optical imaging studies found that AF was maintained by localized foci originating from pulmonary vein-left atrium interfaces. MSE Stage 1 shocks temporarily disrupted localized foci; MSE Stage 2 entrainment shocks continued to silence the localized foci driving AF; and MSE Stage 3 pacing stimuli enabled consistent RA-left atrium activation until sinus rhythm was restored.

CONCLUSIONS

Low-energy MSE significantly reduced the atrial defibrillation thresholds compared with BPS in a canine model of AF. MSE may enable painless, device-based AF therapy.

A new look at atrial fibrillation: lessons learned from drugs, pacing, and ablation therapies

Atrial fibrillation (AF) is the most common arrhythmia and among the leading causes of stroke and heart failure in Western populations. Despite the increasing size of clinical trials assessing the efficacy and safety of AF therapies, achieved outcomes have not always matched expectations. Considering that AF is a symptom of many possible underlying diseases, clinical research for this arrhythmia should take into account their respective pathophysiology. Accordingly, the definition of the study populations to be included should rely on the established as well as on the new classifications of AF and take advantage from a differentiated look at the AF-electrocardiogram and from increasingly large spectrum of biomarkers. Such an integrated approach could bring researchers and treating physicians one step closer to the ultimate vision of personalized therapy, which, in this case, means an AF therapy based on refined diagnostic elements in accordance with scientific evidence gathered from clinical trials. By applying clear-cut patient inclusion criteria, future studies will be of smaller size and thus of lower cost. In addition, the findings from such studies will be of greater predictive value at the individual patient level, allowing for pinpointed therapeutic decisions in daily practice.

Is An Atrial Defibrillator Still An Option In Treating Patients With Atrial Fibrillation?

Atrial fibrillation (AF) is a common disorder associated with significant morbidities and presents several challenges for the control of symptoms and prevention of long-term implications. Atrial defibrillators (ADs), used for rhythm control in patients with symptoms refractory to medical therapy, can detect recurrences of the arrhythmia, allow prompt patient-directed treatment, and have the potential to reduce hospitalizations and improve quality of life. The efficacy of this form of therapy is highest in patients with paroxysmal AF, and with the use of a coronary sinus shocking lead. While R-wave synchronized shocks are a prerequisite for a safe use, the procedure is well tolerated and usually not associated with long-term psychological side effects. Limitations of ADs include acute and chronic complications related to cardiac rhythm device implantation, the requirement in some cases for more than one shock to terminate AF, the discomfort from shocks, as well as the need for sedation to alleviate pain from the shocks. With the ever-expanding role of catheter-based therapies for AF, it seems that the role of ADs in this regard is rather limited.

Low-energy multistage atrial defibrillation therapy terminates atrial fibrillation with less energy than a single shock

BACKGROUND

Implantable device therapy of atrial fibrillation (AF) is limited by pain from high-energy shocks. We developed a low-energy multistage defibrillation therapy and tested it in a canine model of AF.

METHODS AND RESULTS

AF was induced by burst pacing during vagus nerve stimulation. Our novel defibrillation therapy consisted of 3 stages: stage (ST) 1 (1-4 low-energy biphasic [BP] shocks), ST2 (6-10 ultralow-energy monophasic [MP] shocks), and ST3 (antitachycardia pacing). First, ST1 testing compared single or multiple MP and BP shocks. Second, several multistage therapies were tested: ST1 versus ST1+ST3 versus ST1+ST2+ST3. Third, 3 shock vectors were compared: superior vena cava to distal coronary sinus, proximal coronary sinus to left atrial appendage, and right atrial appendage to left atrial appendage. The atrial defibrillation threshold (DFT) of 1 BP shock was <1 MP shock (0.55 ± 0.1 versus 1.38 ± 0.31 J, P=0.003). Two to 3 BP shocks terminated AF with lower peak voltage than 1 BP or 1 MP shock and with lower atrial DFT than 4 BP shocks. Compared with ST1 therapy alone, ST1+ST3 lowered the atrial DFT moderately (0.51 ± 0.46 versus 0.95 ± 0.32 J, P=0.036), whereas 3-stage therapy (ST1+ST2+ST3) dramatically lowered the atrial DFT (0.19 ± 0.12 versus 0.95 ± 0.32 J for ST1 alone, P=0.0012). Finally, the 3-stage therapy was equally effective for all studied vectors.

CONCLUSIONS

Three-stage electrotherapy significantly reduces the AF DFT and opens the door to low-energy atrial defibrillation at or below the pain threshold.

Atrial Fibrillation: The New Epidemic of the Ageing World

The prevalence of atrial fibrillation (AF) increases with age. As the population ages, the burden of AF increases. AF is associated with an increased incidence of mortality, stroke, and coronary events compared to sinus rhythm. AF with a rapid ventricular rate may cause a tachycardia-related cardiomyopathy. Immediate direct-current (DC) cardioversion should be performed in patients with AF and acute myocardial infarction, chest pain due to myocardial ischemia, hypotension, severe heart failure, or syncope. Intravenous beta blockers, diltiazem, or verapamil may be administered to reduce immediately a very rapid ventricular rate in AF. An oral beta blocker, verapamil, or diltiazem should be used in persons with AF if a fast ventricular rate occurs at rest or during exercise despite digoxin. Amiodarone may be used in selected patients with symptomatic life-threatening AF refractory to other drugs. Digoxin should not be used to treat patients with paroxysmal AF. Nondrug therapies should be performed in patients with symptomatic AF in whom a rapid ventricular rate cannot be slowed by drugs. Paroxysmal AF associated with the tachycardia-bradycardia syndrome should be treated with a permanent pacemaker in combination with drugs. A permanent pacemaker should be implanted in patients with AF and symptoms such as dizziness or syncope associated with ventricular pauses greater than 3 seconds which are not drug-induced. Elective DC cardioversion has a higher success rate and a lower incidence of cardiac adverse effects than does medical cardioversion in converting AF to sinus rhythm. Unless transesophageal echocardiography has shown no thrombus in the left atrial appendage before cardioversion, oral warfarin should be given for 3 weeks before elective DC or drug cardioversion of AF and continued for at least 4 weeks after maintenance of sinus rhythm. Many cardiologists prefer, especially in elderly patients , ventricular rate control plus warfarin rather than maintaining sinus rhythm with antiarrhythmic drugs. Patients with chronic or paroxysmal AF at high risk for stroke should be treated with long-term warfarin to achieve an International Normalized Ratio of 2.0 to 3.0. Patients with AF at low risk for stroke or with contraindications to warfarin should be treated with aspirin 325 mg daily.

Effect of verapamil on prevention of atrial fibrillation in patients implanted with an implantable atrial defibrillator

BACKGROUND

The role of verapamil in the prevention of atrial fibrillation (AF) in patients with recurrent AF is unknown.

HYPOTHESIS

The aim of this study was to evaluate the effect of verapamil on the prevention of AF in patients implanted with an implantable atrial defibrillator (IAD).

METHODS

The effects of verapamil (240 mg/day) on the total duration of AF, number of AF recurrences, and number of cardioversions were prospectively evaluated in a randomized, crossover fashion over an 8-week period in 11 patients (9 men, 2 women; mean age: 60 +/- 6 years) implanted with an IAD.

RESULTS

Implantable atrial defibrillators successfully converted 13 of 14 (93%) spontaneous episodes of AF. There was no significant difference in the efficacy of cardioversion (86 vs. 100%, p = 0.8), the total duration of AF (173 +/- 198 vs. 270 +/- 241 h, p = 0.5), the number of AF episodes (8.5 +/- 9.0 vs. 9.3 +/- 10.2, p = 0.3), and the number of cardioversions (1.7 +/- 2.4 vs. 1.8 +/- 2.1 p = 0.7) with or without treatment with verapamil.

CONCLUSIONS

The results of the present study suggest that treatment with verapamil has no significant effect on the prevention of AF in patients treated with an LAD.

Etiology, pathophysiology, and treatment of atrial fibrillation: part 1

Atrial fibrillation (AF) is associated with a higher incidence of mortality, stroke, and coronary events than is sinus rhythm. AF with a rapid ventricular rate may cause a tachycardia-related cardiomyopathy. Immediate direct-current cardioversion should be performed in patients with AF and acute myocardial infarction, chest pain due to myocardial ischemia, hypotension, severe heart failure, or syncope. Intravenous beta blockers, verapamil, or diltiazem may be given to immediately slow a very rapid ventricular rate in AF. An oral beta blocker, verapamil, or diltiazem should be used in persons with AF if a fast ventricular rate occurs at rest or during exercise despite digoxin. Amiodarone may be used in selected patients with symptomatic life-threatening AF refractory to other drugs. Digoxin should not be used to treat patients with paroxysmal AF. Nonpharmacologic therapies should be used in patients with symptomatic AF in whom a rapid ventricular rate cannot be slowed by drugs. This is part 1 of a 2-part review of the etiology, pathophysiology, and treatment of atrial fibrillation. The second part will be published in the subsequent issue of Cardiology in Review.

Diagnostic tools for atrial tachyarrhythmias in implantable pacemakers: a review of technical options and pitfalls

BACKGROUND

Correct pacemaker (PM) diagnosis of paroxysmal atrial tachyarrhythmias is crucial for their prevention and intervention with specific atrial pacing programmes. The PM mode switch to only ventricular pacing after detection of atrial tachyarrhythmias is often used as the parameter to quantify the 'burden' of atrial tachyarrhythmias.

OBJECTIVES

This review addresses potential errors in the detection and diagnosis of atrial tachyarrhythmias, sometimes resulting in incorrect mode switches. The interpretation of PM-stored data of patients with atrial tachyarrhythmias and the results of trials of pace prevention and intervention can be better appreciated with more insight into the technical options and pitfalls.

RESULTS

Literature and clinical experience demonstrate that the correctness of PM-derived diagnosis of atrial tachyarrhythmias depends on 1) the sensitivity setting to detect the onset and perpetuation of atrial tachyarrhythmias frequently characterised by variable and low-voltage signals, 2) the rejection of far-field R wave sensing by the atrial sense amplifier, 3) the facility for verification of mode switches by a high-quality intracardiac registration of the nonmodified atrial electrogram. The configuration of the atrial lead also contributes to the diagnostic performance of the PM.

CONCLUSION

Not only pacing algorithms and diverse technical PM features but also the atrial lead configuration are currently the limiting factors to the fully reliable, automated detection and diagnosis of atrial tachyarrhythmias. If these technical shortcomings can be improved, better signal processing will result. Then atrial pacing to prevent or suppress atrial tachyarrhythmias will be more justified. (Neth Heart J 2008;16:201-10.).

Atrial fibrillation: a historical perspective

Atrial fibrillation (AF) undoubtedly has become one of the most well studied arrhythmias today in terms of pathophysiology and diagnostic and therapeutic (interventional) electrophysiology. Although it lends itself to an apparently easy diagnosis on a surface ECG, myriad electromechanical mechanisms underlie its origin. An era of technology has been reached that makes AF not only "treatable" but also potentially "curable." This article aims at walking through the historical corridors and maze that have led to the present-day understanding of this most common yet complex arrhythmia.

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.

Intracardiac atrial defibrillation

Intravascular ventricular defibrillation and intravascular atrial defibrillation have many similarities. An important factor influencing the outcome of the shock is the potential gradient field created throughout the ventricles or the atria by the shock. A minimum potential gradient is required throughout the ventricles and probably the atria in order to defibrillate. The value of this minimum potential gradient is affected by several factors, including the duration, tilt, and number of phases of the waveform. For shock strengths near the defibrillation threshold, earliest activation following failed shocks arises in a region in which the potential gradient is low. The defibrillation threshold energy can be decreased by adding a third and even a fourth defibrillation electrode in regions where the shock potential gradient is low for the shock field created by the first two defibrillation electrodes and giving two sequential shocks, each through a different set of electrodes. However, the addition of more electrodes and sequential shocks complicates both the device and its implantation. Because patients are conscious when the atrial defibrillation shock is given, they experience pain during the shock, which is one of the main drawbacks of intravascular atrial defibrillation. Unfortunately, the pain threshold for defibrillation shocks is so low that a shock less than 1 J is uncomfortable and is not much less painful than shocks several times stronger. Therefore, even though electrode configurations exist that have lower atrial defibrillation threshold energy requirements than the atrial defibrillation threshold with standard defibrillation electrode configurations used in implantable cardioverter-defibrillators (ICDs) for ventricular defibrillation, they are not clinically practical because their shocks are almost as painful as with the standard ICD electrode configurations. Such electrode configurations would make the ICD more complicated, leading to greater difficulty and longer time required for implantation.

Physiologic Pacing for Atrial Fibrillation Prevention in Sinus Node Disease: Long-Term Results

BACKGROUND

Physiologic pacing has been demonstrated to be effective in preventing atrial fibrillation recurrences in patients with sinus bradycardia. Aim of the study was to evaluate long-term incidence of atrial fibrillation in a large population of patients affected by sinus node disease receiving physiologic pacing. Furthermore, predictors of arrhythmia recurrence and effect of pacing mode were investigated.

POPULATION

Four hundred twenty-five patients (220 Male, 77 +/- 9 years) were retrospectively analyzed: implanted system was AAI in 20.5% and DDD in 79.5%. Thirty-four percent had atrial fibrillation before implant.

RESULTS

Follow-up lasted on average 51 +/- 36 months (median 42, range 1 month-18 years). Sixty-six percent were on antiarrhythmic drug therapy. After 5 years, 89% survived, 74.5% had at least one episode of atrial fibrillation, 39.9% were submitted to electrical cardioversion, 67.2% were hospitalized because of cardiac causes, 33.3% developed permanent atrial fibrillation. Primary conduction system disease and valvular heart disease were independent predictors for atrial fibrillation recurrence. Preimplant atrial fibrillation predicted arrhythmia recurrence during the follow-up, but it did not predict development of permanent atrial fibrillation. AAI pacing, when compared with DDD, was associated to a lower rate of atrial fibrillation recurrences (AAI 28.7%, DDD 53.3%, P < 0.001).

CONCLUSION

In spite of expected benefits of physiologic pacing, the development of atrial fibrillation and permanent atrial fibrillation were quite common. The additional benefits of multifunction pacemakers designed to prevent and treat atrial fibrillation should be evaluated in controlled studies.

Late-phase 3 EAD. A unique mechanism contributing to initiation of atrial fibrillation

Early (EAD) and delayed (DAD) afterdepolarizations-induced triggered activity is capable of initiating and maintaining cardiac arrhythmias. EAD-induced triggered responses are traditionally thought to be involved in the generation of ventricular arrhythmias under long QT conditions and are precipitated by bradycardia or long pauses. In contrast, DAD-induced triggered activity commonly underlies arrhythmias precipitated by tachycardia. Spontaneous release of calcium from the sarcoplasmic reticulum (SR) secondary to cellular calcium overload induces DADs and some forms of EADs. Recent studies from our laboratory have uncovered a novel mechanism giving rise to triggered activity, termed "late-phase 3 EAD," which combines properties of both EAD and DAD, but has its own unique character. Late-phase 3 EAD-induced triggered extrasystoles represent a new concept of arrhythmogenesis in which abbreviated repolarization permits "normal SR calcium release" to induce an EAD-mediated closely coupled triggered response, particularly under conditions permitting intracellular calcium loading. This review briefly describes the mechanisms and properties of late-phase 3 EADs, how they differ from conventional EADs and DADs, as well as their role in the initiation of cardiac arrhythmias, such as atrial fibrillation.

Acute anticoagulation adjustment in patients with atrial fibrillation at risk for stroke: approaches, strategies, risks and benefits

The acute management of anticoagulation in patients with atrial fibrillation to prevent stroke and other thromboembolic complications includes the use of individualized strategies tailored to the patient and based on the situation (cardioversion, surgeries, dental procedures, cardiac interventions, other invasive procedures and initiation of, or adjustment to, warfarin dosing). The vast range of choices can cause confusion and few randomized controlled clinical trials in this area provide adequate guidance. Chronic anticoagulation management is more straightforward since clinical evidence is ample, randomized clinical trial data provides cogent informaiton and guidelines have been established. Acute management of anticoagulation in patients with atrial fibrillation to prevent thromboembolic complications is often unrecognized but is emerging as a crucial, but challenging, and increasingly complex aspect of the care of patients with atrial fibrillation. This review addresses issues regarding such patients who may be at risk for stroke and require acute adjustments of anticoagulation (in light of, or in lieu of, chronic anticoagulation). Several promising new strategies are considered in light of established medical care. This analysis provides practical recommendations based on available data and presents results from recent investigations that may provide insight into future strategies.

Clinical Experience with Tiered Atrial Therapies and Atrial Arrhythmia Prevention Algorithms in a Dual Chamber Cardioverter Defibrillator

INTRODUCTION

The acceptance of atrial arrhythmia features in implantable cardioverter defibrillators (ICDs) will depend on their ability to appropriately discriminate atrial tachyarrhythmias/atrial fibrillation (AT/AF). This study tested the effectiveness of an atrial/ventricular ICD with advanced atrial detection and new algorithms designed to prevent atrial arrhythmias.

METHODS AND RESULTS

Ninety-five patients were implanted with a dual chamber ICD (Model 1900, Guidant Corporation, MN, USA) at 25 US centers. Ten patients received a coronary sinus (CS) lead allowing a defibrillation vector for AT/AF cardioversion. Follow-up was 12.2 months. The addition of new atrial features designed for detection, discrimination, and prevention of AT/AF had no adverse effect upon detection of induced ventricular fibrillation (VF) (mean detection time with new features ON was 2.22 seconds vs 2.19 seconds with features OFF). A total of 100% of the induced and spontaneous ventricular and atrial arrhythmias receiving shock therapy were reviewed as appropriate detection. Atrial shock conversion efficacy for spontaneous and induced AT/AF episodes was 83% and 96%, respectively (144 spontaneous, 162 induced episodes). A 3-month randomized crossover trial of atrial preventative pacing features did not result in adverse effects, but there was no clinical efficacy for prevention of AT/AF.

CONCLUSION

Enhanced atrial detection and discrimination features combined with tiered atrial therapies did not adversely impact the ability of the ICD (Model 1900) to appropriately detect and treat ventricular tachyarrhythmias.

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.

A perspective on antiarrhythmic drug therapy to treat atrial fibrillation: there remains an unmet need

Because presently available antiarrhythmic drugs are neither as highly efficacious nor as safe as desirable for the prevention of atrial fibrillation (AF), rate control-versus-rhythm control trials for the treatment of AF were evaluated. They demonstrated that rate control is not simply a therapeutic fallback option if rhythm control should fail, but rather, it is a legitimate primary therapeutic option. Nevertheless, there remain many reasons to consider maintenance of sinus rhythm (rhythm control) over AF (rate control) if only there were antiarrhythmic agents that could provide this treatment more effectively and safely. In fact, an important analysis of the AFFIRM trial data indicated that rhythm control offers a significant survival advantage over rate control if it could be safely achieved. Therein lie an important clinical dilemma and an unmet need. Sinus rhythm is good, but we need better ways to maintain it effectively and safely.

Impact of atrial fibrillation duration on postcardioversion recurrence

BACKGROUND

"Begetting," a mechanistic tenet of atrial fibrillation (AF), stipulates that the rate of recurrence of AF after cardioversion is proportional to the preceding arrhythmia duration. However, recent reports suggest that, for brief durations, the incidence of early recurrence of AF (ERAF) is inversely proportional to duration. These reports were based on potentially biased data.

OBJECTIVES

We performed a prospective study to examine the impact of AF duration on postcardioversion recurrence.

METHODS

Forty-four patients underwent placement of an implantable cardioverter-defibrillator (ICD) capable of delivering patient-elicited AF cardioversion shocks. Subsequently, in the ambulatory setting, the timing of shocks in relationship to perceived AF onset was randomly assigned within individuals to early (as soon as possible) or delayed (1 day later).

RESULTS

During a follow-up averaging 199 days per patient, a total of 61 AF episodes among 17 patients occurred for which a patient-elicited cardioversion shock was delivered. Twenty-three shocks were delivered using early protocol (mean 6.8 hours after AF onset), and 38 shocks were delivered using delayed protocol (mean 34.7 hours after AF onset). The incidence of ERAF was significantly lower using the delayed protocol.

CONCLUSION

A strategy of approximately 24-hour delay in cardioversion shock timing decreased the incidence of ERAF, relative to a shock delivered within a few hours of AF onset. This observation has important mechanistic and therapeutic implications.

Internal defibrillation: where we have been and where we should be going?

Internal cardioversion has been developed as an alternative technique for patients who are resistant to external DC cardioversion of atrial fibrillation (AF) and was found to be associated with higher success rates. It used initially high energies (200-300 J) delivered between an intracardiac catheter and a backplate. Subsequent studies have shown that it is possible to terminate with energies of 1 to 6 Joules, paroxysmal or induced AF in 90 percent of patients and persistent AF in 75 percent of patients, using biphasic shocks delivered between a right atrium-coronary sinus vectors. Consequently, internal atrial defibrillation can be performed under sedation only without the need for general anesthesia. Recently developed external defibrillators, capable of delivering biphasic shocks, have increased the success rates of external cardioversion and reduced the need for internal cardioversion. However, internal defibrillation is still useful in overweight or obese patients, in patients with chronic obstructive pulmonary disease or asthma who are more difficult to defibrillate, and in patients with implanted devices which may be injured by high energy shocks. Low energy internal defibrillation has also proven to be safe and this has prompted the development of implantable devices for terminating AF. The first device used was the Metrix system, a stand-alone atrial defibrillator (without ventricular defibrillation) which was found to be safe and effective in selected groups of patients. Unfortunately, this device is no longer being marketed. Only double chamber defibrillators with pacing capabilities are presently available: the Medtronic GEM III AT, an updated version of the Jewel AF and the Guidant PRIZM AVT. These devices can be patient-activated or programmed to deliver automatically ounce atrial tachyarrhythmias are detected, therapies including pacing or/and shocks. Attempts to define the group of patients who might benefit from these devices are described but the respective role of atrial defibrillators versus other non-pharmacologic therapies for AF, such as surgery and radiofrequency catheter ablation, remains to be determined. Advantages and limitations or atrial defibrillators and approaches to reduce shock related discomfort which may be a concern in some patients, are reviewed. Studies have shown that despite shock discomfort, quality of life was improved in patients with atrial defibrillators and the need for repeated hospitalizations was reduced. The cost of these devices remains a concern for the treatment of a non-lethal arrhythmia. Attention that atrial defibrillators will receive from cardiologists and from the industry in the future, will depend of the long-term results of other non-pharmacological options and of the identification of the group of AF patients which will require restoration and maintenance of sinus rhythm. But there is no doubt that selected subsets of patients with AF could benefit from atrial defibrillation.

Is Dual Defibrillator Better than Conventional DDD Pacing in Brady-Tachy Syndrome? Results of the ICARUS Trial (Internal Cardioversion Antitachypacing and Prevention: Resource Utilization Study)

AIM OF THE STUDY

To compare the impact of dual defibrillator versus conventional DDD pacing on quality of life and hospitalizations in patients with sinus node disease and recurrent symptomatic atrial fibrillation.

STUDY DESIGN

Prospective, parallel, controlled trial.

METHODS

Sixty-three patients (41 M, mean age 71 +/- 8 years) with sinus node disease and at least three symptomatic episodes of atrial fibrillation during the last year were enrolled. Thirty-one consecutive patients received a dual defibrillator (group A) and 32 standard DDD pacing (group B). In group A, 12 patients received an external remote-control device in order to shock themselves in case of atrial fibrillation, while 19 were scheduled for early in-hospital manual shock. Seventy-five percent had been hospitalized during the last year and 57% had required electrical cardioversion. Atrial fibrillation was persistent in 63.5% and paroxysmal in 37.5%. The follow-up lasted 1 year.

RESULTS

Atrial fibrillation recurred in 83.3% in group A and 79.3% in group B (p = ns). Electrical cardioversion was applied in 54.8% in group A and in 21.9% in group B (p < 0.05). On the whole, 89.5% of electrical cardioversions were delivered in the defibrillator group (p < 0.0001). In the whole population 27.0% patients had cardiac-related hospitalization (31.2% in the pacemaker group and 22.6% in the defibrillator group, p = n.s.). In patients with persistent atrial fibrillation, cardiac-related hospitalization rate was significantly lower in the group A (0% vs. 30%, p < 0.05). Considering Symptom Check List, symptoms significantly improved in the whole population, but symptom number and frequency improved significantly only in the group A. Similarly, SF-36 questionnaire scores showed a little higher quality of life improvement in the group A.

CONCLUSIONS

Dual defibrillator showed consistent trends toward a higher effectiveness when compared with standard DDD pacing. Dual defibrillator was associated to reduced in-patient cardioversions and to better quality of life. All-cause hospitalizations were reduced only in patients with persistent atrial fibrillation.

Internal defibrillation with minimal skeletal muscle activation: A new paradigm toward painless defibrillation

BACKGROUND

Shock-induced pain produces substantial morbidity in recipients of implantable cardioverter-defibrillators (ICDs). This pain likely derives from activation of skeletal muscle and associated nerves in the chest and abdomen. In an effort to develop a painless defibrillation system, we designed an electrode arrangement that incorporates a conductive sock placed around the heart to confine the electric shock field to cardiac tissue.

OBJECTIVES

The purpose of this study was to test whether cardiac defibrillation could be achieved without skeletal muscle activation using a novel electrode system.

METHODS

Eight adult mongrel dogs were studied. Force of skeletal muscle contraction was measured by strain gauges attached to the forelimbs during delivery of internal shocks ranging in energy from 0.1 to 31 J. Biphasic shocks were delivered (1) between a right ventricular coil and a subcutaneous dummy can (standard configuration), and (2) between a left ventricular coil and an epicardial electrode sock. Internal and external defibrillation thresholds (DFTs) were determined for each electrode configuration.

RESULTS

Shock-induced muscle contraction force was significantly lower using the sock electrode than with standard ICD electrodes at every shock energy level tested (P < .0001). Internal DFT was similar between electrode configurations (sock electrode: 8.6 +/- 4.2 J; standard: 11.0 +/- 6.3 J, P = .4), but muscle contraction force at DFT was greatly reduced with the new electrode system (1.8 +/- 2.0 kg vs 10.6 +/- 2.1 kg, P < .0001). The sock electrode rendered external defibrillation impossible, however, even at 360 J.

CONCLUSION

Skeletal muscle activation induced by ICD shocks can be greatly reduced using an electrode system that confines the electric shock field to the heart. Refinement of this strategy may allow for delivery of painless shocks by ICDs. Further development is needed to overcome implant complexity and the higher external DFT with this type of electrode system.

Device-based therapies for atrial fibrillation

Ablation of the atrioventricular conduction system and pacemaker implantation is the preferred procedure for patients with atrial fibrillation (AF) in whom a rate control strategy has been selected but in whom rate-controlling medications are intolerable or ineffective. Selection of standard right ventricular (RV) pacing versus biventricular pacing is individualized, based on the degree and etiology of left ventricular dysfunction. Atrial-based pacing is clearly preferable to ventricular-based pacing in patients with sick sinus syndrome, because it leads to a reduction in the development of AF. Emerging evidence indicates that excess RV pacing is deleterious, increasing AF, heart failure, and possibly mortality. Therefore, physiologic pacing with minimization of RV pacing is desirable. Atrial pacing algorithms that increase the frequency of atrial pacing have shown modest efficacy in the prevention of AF. Use of atrial pacing algorithms is reasonable for patients with a history of AF and standard bradycardia indications for permanent pacing in whom maintenance of sinus rhythm is desirable. Studies assessing novel and multiple site atrial pacing therapies have mixed results, without compelling evidence of clinically important benefit. The exceptions are biatrial and right atrial overdrive pacing immediately after cardiac surgery. Several studies have shown effective suppression of postoperative AF with their use. Device therapy (eg, atrial antitachycardia pacing and defibrillation) for the termination of AF is effective in reducing arrhythmia burden. However, improvement in clinically relevant end points is not established and indications are not clearly defined. If a patient lacks an indication for an implantable cardioverter-defibrillator, we do not offer atrial defibrillation as a treatment option. Atrial arrhythmias may be better prevented by programming to avoid ventricular pacing than by specific atrial interventions.

Noninvasive Assessment of Acute Changes in Atrial Electrophysiology After Cardioversion by Signal-Averaged P-Wave Electrocardiography

BACKGROUND

Atrial remodeling secondary to atrial fibrillation (AF) may be important in the arrhythmogenic process. Unfortunately, the study of electrophysiologic remodeling in humans has been limited by the invasive nature of most tests of electrophysiologic characteristics. We sought to determine whether changes in atrial electrophysiology occur acutely (within the first hour) after cardioversion and whether these changes could be detected noninvasively by measuring the signal-averaged P-wave.

METHODS

The filtered P-wave duration (FPD) was measured by signal-averaged electrocardiography (ECG) at 20 and 60 minutes after cardioversion in 46 patients with AF, and the difference between the two values was calculated. The root-mean-square voltage of the terminal 40 ms of the signal-averaged P-wave at 20 and 60 minutes and the difference between them were also determined.

RESULTS

The FPD at 20 minutes was significantly different from that at 60 minutes (153.0 +/- 19.1 vs 159.7 +/- 24.8 ms; P = 0.02). In a univariate linear regression model, none of the clinical variables studied was significantly associated with the change in FPD. The root-mean-square voltage at 20 minutes was not significantly different from that at 60 minutes (5.8 +/- 3.0 vs 5.5 +/- 2.7; P = 0.14).

CONCLUSIONS

We conclude that significant changes in atrial electrophysiology occur within the first hour after cardioversion of AF. These changes can be detected by measuring the FPD.