Current clinical perspectives on implantable devices for atrial defibrillation

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.

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.

Predictors of atrial antitachycardia pacing efficacy in patients affected by brady-tachy form of sick sinus syndrome and implanted with a DDDRP device

Predictors of ATP efficacy in brady/tachy patients.

BACKGROUND

Recent options to treat atrial tachyarrhythmias (ATA) include implantable devices delivering antitachycardia pacing therapies (ATP). No prospective study selected patients with higher chances of episode termination by ATP or indicated the most effective ATP use. Our aim was to study ATP efficacy in patients with brady-tachy form of sinus node disease (SND), identifying clinical factors, ATA characteristics, and device features predicting ATP efficacy.

METHODS AND RESULTS

Three hundred and sixteen patients (105 M, aged 71.1+/-8.8 years) received a DDDRP pacemaker and were prospectively followed. Median follow-up was 18 months: 37,125 ATA episodes occurred in 217 patients; ATP treated 5,536 of them. Overall, ATP efficacy was 50.0%. A multivariate analysis identified longer arrhythmia cycle lengths (OR=1.25; CI=1.07-1.47) and shorter delays to ATP delivery (OR=0.15; CI=0.10-0.22) as independent predictors of ATP efficacy for episodes preceded by >or=5 minutes of sinus rhythm. Additionally, ATP efficacy for all treated episodes was predicted by lower New York Heart Association (NYHA) class (OR=0.64; CI=0.42-0.98), episode classification as nonimmediate recurrence of ATA (non-IRAT) (OR=0.07; CI=0.02-0.33), absence of overlap in the device detection windows (OR=0.54; CI=0.32-0.91), and flecainide treatment (OR=2.22; CI=1.04-4.71).

CONCLUSIONS

In patients paced for SND, multivariate analysis shows that ATP efficacy is associated to longer arrhythmia cycle lengths, shorter ATP delivery delays, NYHA class I, episode classification as non-IRAT, absence of overlap in the atrial arrhythmia device detection windows, and flecainide treatment.

A controlled study on the effect of verapamil on atrial tachycaarrhythmias in patients with brady-tachy syndrome implanted with a DDDR pacemaker

While verapamil has been proposed as a treatment for reducing electrophysiological remodeling due to atrial fibrillation and atrial tachyarrhythmias, no previous study has tested its effects in brady-tachy patients implanted with a dual-chamber pacemaker. Fourteen patients with frequent episodes of atrial fibrillation (> or =2 episodes/month) in the setting of brady-tachy syndrome, implanted with a DDDR pacing system with extensive monitor function (Selection 900, Vitatron) were enrolled. Four months after implantation, they were randomly allocated to a 2-month period of treatment with verapamil (240 mg/day) or to no treatment, followed by a crossover. The burden of atrial tachyarrhythmias, the total number of hours spent in atrial tachyarrhythmia and the mean number of hours per day spent in atrial tachyarrhythmia were retrieved from diagnostic devices. The accuracy of atrial tachyarrhythmias detection was confirmed independently by two observers. The main results showed that treatment with verapamil was associated with a trend towards an higher percentage of atrial pacing in comparison with control (mean value+/-S.D.=63.2+/-29.9% vs. 57.3+/-30.6%, median value 53% vs. 49%, P value at Wilcoxon signed rank test=0.069), but without any significant reduction in atrial tachyarrhythmia burden (4.5+/-11.8 vs. 3.3+/-9.1%) or total hours spent in atrial tachyarrhythmia (65+/-161 vs. 48+/-131 h). Palpitation episodes were not significantly reduced by verapamil treatment in comparison with control (10.3+/-7.8 vs. 6.1+/-6.5). In conclusion, verapamil does not exert any beneficial effect on documented episodes of atrial tachyarrhythmia in patients with brady-tachy syndrome implanted with a DDDR device. Moreover, this drug was ineffective in reducing the number of palpitation episodes reported by the patient.

Atrial Fibrillation in Patients with a Dual Defibrillator: Characteristics of Spontaneous and Induced Episodes and Effect of Ventricular Tachyarrhythmia Induction

BACKGROUND

The pattern of FF intervals during atrial fibrillation (AF) has been analyzed in induced and spontaneous AF episodes, after the induction of ventricular fibrillation (VF) and after atrial shock, in order to suggest practical considerations for AF management in patients implanted with antitachycardia devices.

METHODS

In 13 patients implanted with a dual-chamber defibrillator, FF intervals were analyzed during two separate induced AF episodes, before and after VF induction over AF, as well as during spontaneous AF episodes and after unsuccessful atrial shocks. The following parameters were considered: mean atrial cycle length (CL), atrial CL stability, and standard deviation of the atrial cycle.

RESULTS

The AF pattern had comparable characteristics considering two separate inductions of AF, as well as spontaneous AF episodes. Ventricular tachyarrhythmia induction resulted in a shortening of atrial CL (P < 0.02) and in a less organized AF pattern (P < 0.005). Changes in the FF interval after ineffective shock therapy showed a shortening of AF cycles after shocks with energies far below the defibrillation threshold.

CONCLUSIONS

(a) The AF pattern is reproducible in separate inductions of sustained AF and in spontaneous episodes, (b) dynamic changes involving a shortening of the AF cycle and an evolution to a less homogeneous pattern occur after VF induction, revealing a complex interplay between AF and VF, and (c) FF interval analysis after ineffective shock delivery may allow the relationship between delivered shock energy and effective defibrillation energy to be estimated, thereby providing practical suggestions for step-up protocols in atrial cardioversion.

Implantable Dual-Chamber Defibrillator for the Selective Treatment of Spontaneous Atrial and Ventricular Arrhythmias: Arrhythmia Incidence and Device Performance

INTRODUCTION

Atrial tachyarrhythmias are a common co-morbidity in patients with an ICD indication. Recently introduced ICD's are equipped to independently detect and treat atrial and ventricular tachyarrhythmias. The purpose of this prospective study was to evaluate the incidence and termination of spontaneous atrial and ventricular tachyarrythmias in patients with a history of atrial tachyarrhythmias.

METHODS AND RESULTS

Ninety patients, 70% male with an ICD indication and history of atrial tachyarrhythmia (LVEF 45 +/- 6%, [AT/AF indication 55 +/- 10, AT/VT 45 +/- 16], 46% CAD) were enrolled and 89 were implanted with a VENTAK PRIZM AVT (Guidant). Spontaneous atrial and ventricular tachyarrhythmias were printed and evaluated during an average follow-up period of 272 +/- 72 days utilizing the stored intracardial electrogram function of the device. Nineteen patients (21%) presented had only atrial tachyarrhythmias, 32 patients (36%) had both atrial and ventricular tachyarrhythmias and 18 patients (20%) had only ventricular tachyarrhythmias. Patients with only atrial tachyarrhythmias had a total of 3274 atrial episodes; 2002 terminated spontaneously, 1264 were treated with ATP and 8 with shock therapy. ATP was successful in 735 (58%) of 1264 episodes. Patients with both atrial and ventricular tachyarrhythmias had 7277 documented atrial tachyarrhythmias, 5231 terminated spontaneously, 1153 of 2009 were terminated by ATP (57.4%) and 37 by shock therapy (20 patient controlled). Atrial tachyarrhythmias identified as atrial flutter (AT) by the atrial rhythm classification (ARC) algorithm had a higher ATP conversion success rate than episodes identified as atrial fibrillation (AF); 66.7% for AT and 26.4% for AF. Patients with only ventricular tachyarrhythmias had 690 documented episodes, 401 terminated spontaneously, 248 (85.8%) were terminated by ATP and 41 by shock.

CONCLUSION

Seventy-seven percent of patients with an ICD indication had spontaneous atrial and/or ventricular tachyharrhythmias within the first 6 months after ICD implantation. ATP therapy terminated 58% of all atrial tachyarrhytmias and 66.7% of the atrial flutters. The dual chamber ICD detected, classified and terminated all ventricular tacharrhythmias appropriately.

Rapid atrial pacing does not decrease the atrial defibrillation threshold

The aim of the study was to evaluate the effect of preshock atrial pacing on the atrial defibrillation threshold (DFT) during internal cardioversion of AF. The implantable atrial defibrillator has been added to the therapeutic options for patients with recurrent episodes of persistent AF. Although the device is efficient in restoring sinus rhythm, patient discomfort is a limitation. Methods that lower the ADFT are needed. Eleven patients with AF underwent internal cardioversion. In a randomized, crossover design, ADFT testing was performed, applying a step-up protocol starting at 100 V. Rapid atrial pacing was performed with a right atrial catheter for 20 seconds at 90% of the average cycle length of the fibrillatory waves and was immediately followed by a biphasic defibrillation shock. At each energy level, pacing + shock was compared to shock only, until the level at which sinus rhythm was restored by both modes. The step-up protocol was thereafter repeated using the inverse sequence of the two modes. A total of 19 ADFTs were obtained. For 10 the ADFT was lower with pacing + shock, in 4 equal and in 5 higher, than with shock only. The ADFT (mean +/- SD) with pacing + shock was 260 +/- 84 V(3.4 +/- 2.9 J) and did not differ from shock only: 268 +/- 85 V(3.8 +/- 3.0 J) (P > 0.05). The coefficient of variation and the coefficient of reproducibility for pacing + shock was 16% and 60 V, respectively, and for shock only 17% and 61 V. Rapid atrial pacing did not influence the internal ADFT in AF. The randomized, crossover protocol used was reproducible between different modes, and seems useful when testing the impact of different interventions on the ADFT.

Evaluation of a dual chamber implantable cardioverter defibrillator for the treatment of atrial and ventricular arrhythmias

Eighty-nine patients with a documented history of atrial tachyarrhythmias or fibrillation (AF) received a cardioverter defibrillator designed to selectively differentiate and treat atrial and ventricular arrhythmias. Twenty-two patients received a coronary sinus lead and, therefore, could use a separate shock vector for selective treatment of atrial tachyarrhythmias/AF. The device is designed to treat tachyarrhythmias with antitachycardia pacing (ATP) and/or shock therapy using an atrial and/or a ventricular shock vector. Patients underwent induction and shock termination of atrial or dual tachyarrhythmias (AF/VF) to verify proper device function and to measure the arrhythmia detection time with enhancements and preventive algorithms programmed On and Off, respectively. Detection time for 329 VF inductions was 2.41 +/- 0.64 seconds with enhancements On and 2.29 +/- 0.47 with enhancements Off (NS). At implant or predischarge, 283 AF and/or AF/VF (121 atrial and 162 atrial/ventricular fibrillation) were induced. Shock conversion efficacy was 89.8% with AF conversion energies ranging from 0.9 to 27 J. Thirteen of the 23 patients had atrial shock conversions using the separate shock vector with an average conversion energy of 1.9 +/- 1.4 J. (range 0.5-5 J). During follow-up the efficacy of ATP on atrial tachyarrhythmias was 59% and the efficacy of delivered shocks on AF was 85%. This new dual chamber cardioverter defibrillator appropriately detected and classified atrial arrhythmias, and shock therapy for AF was highly effective. The detection algorithm differentiated atrial tachyarrhythmia/AF and did not delay VF detection. The separate shock vector converted induced AF with energies ranging from 0.6 to 5 J.

Transvenous internal cardioversion for atrial fibrillation: a randomized comparison between catheters with different coil length

OBJECTIVES

The aim of this study was to evaluate the effects of 2 different right atrial electrode coil lengths on energy and voltage requirements for transvenous atrial cardioversion.

METHODS

Twenty-six patients (mean age 61 +/- 11 years) with chronic persistent atrial fibrillation (AF) (mean duration 11 +/- 10 months) underwent transvenous cardioversion. A 6F catheter with a 5.5-cm coil was positioned in the coronary sinus. Another catheter with either a 5.5-cm or an 8-cm coil was positioned along the lateral wall of the right atrium, according to a randomized allocation. R wave-synchronized biphasic shocks were delivered according to a step-up protocol. After cardioversion of baseline AF, AF was reinduced, the right atrial catheter was substituted, and cardioversion was repeated with the alternative right atrial coil.

RESULTS

Successful cardioversion was obtained in all of the patients. Leading edge voltage of effective shocks was significantly lower when catheters with an 8-cm coil in right atrium were used compared with the alternative 5-cm coil catheters (301 +/- 80 volts vs 340 +/- 78 volts, P <.001), and delivered energy (6.75 +/- 4.25 joules vs 7.86 +/- 4.29 joules, P =.043) and shock impedance (60 +/- 9 ohm vs 66 +/- 10 ohm, P <.001) were lower. Moreover, shock-induced discomfort, evaluated by assessment of pain score, was reduced (3.69 +/- 1.09 vs 4.12 +/- 0.99, P =.035).

CONCLUSIONS

The use of a longer right atrial coil results in lower shock impedance, lower energy and voltage requirements, and lower discomfort during transvenous atrial cardioversion. The results of the current study are of value either for transvenous internal cardioversion of chronic persistent AF or for implantable atrial defibrillators.