Acute testing of the rate-smoothed pacing algorithm for ventricular rate stabilization

Ventricular rate smoothing for atrial fibrillation: a quantitative comparison study

AIMS

To quantitatively compare the ventricular rate-smoothing (VRS) effects of different ventricular pacing (VP) protocols for atrial fibrillation (AF).

METHODS AND RESULTS

Using a recently developed open-source model that can simulate the ventricular response in AF and VP, the performance of fixed-rate pacing and four previously published VRS algorithms were assessed by the mean RR (mRR), the root mean square of successive RR differences (RMSSD), the percentage of ventricular senses (VS%), and the percentage of short RR intervals (sRR%). All pacing protocols cause rate-dependent reduction of RMSSD, VS%, and sRR% with or without shortening of mRR compared to spontaneous AF. Fixed-rate pacing was more sensitive to the intrinsic rate than the VRS algorithms. The performance was generally comparable between different VRS algorithms, although higher mRR and VS% can be achieved at the expense of larger RMSSD and sRR%.

CONCLUSION

The effect of VP on ventricular rhythm in AF depends on both intrinsic rate and the aggressiveness of the pacing protocol. Adequate rate control is necessary for effective operation of the VRS algorithm. Choosing VRS algorithm should balance between the beneficial effects of rate regularization and the negative effects of increasing heart rate and percentage of VP.

On the role of ventricular conduction time in rate stabilization for atrial fibrillation

AIM

Ventricular pacing (VP) could stabilize the ventricular rhythm in atrial fibrillation (AF). This study investigates the role of ventricular conduction time (VCT) in rate stabilization for AF.

METHODS AND RESULTS

A novel computer model was used to generate various patterns of RR intervals in AF. For each model configuration, the rate stabilization effect of VP was compared with respect to different VCTs. In all tested cases, the ventricular rate in AF could be stabilized at pacing intervals longer than the shortest spontaneous RR intervals. For each model configuration, slightly longer pacing interval (difference <100 ms) was needed to achieve 95% VP when the antegrade/retrograde VCT was increased from 10/10 to 110/110 ms, whereas the VCT had less effect at lower pacing rate. Although longer VCT was associated with increased percentage of ventricular fusion, its role was diminished at higher pacing rate when more retrograde waves could conduct to the atrium.

CONCLUSION

Ventricular conduction time has limited effects on rate stabilization, which could be explained by multi-level interactions between antegrade waves induced by AF and retrograde waves induced by VP.

Role of rate control and regularization through pacing in patients with chronic atrial fibrillation and preserved ventricular function: the VRR study

AIM

High heart rates in chronic atrial fibrillation (CAF) is one of the factors responsible for hemodynamic alterations and may lead to tachycardiomyopathies. The ventricular rate regulation (VRR) study evaluates the effect of ventricular rate regularization in CAF patients with preserved ventricular function, marked ventricular rate variability, and indications for pacemaker (PM) implantation owing to symptomatic pauses. Rate regularization was achieved using VRR algorithm (INSIGNIA pacemakers, Guidant Corp., St. Paul, MN, USA).

METHODS

One month after PM implantation, 58 patients followed two 3-month crossover periods (VRR-OFF; VRR-ON) in which the VRR algorithm was randomized and compared to fixed rate stimulation at 60 ppm. During follow-up visits a 6-minute walk test was performed under partially inhibited conditions (PM at 40 ppm) and ventricular response was recorded. The following parameters were measured: mean ventricular rate (MR), rate variability (RR30), rate recovery after exercise (SLOPE = (R-END - R-REC)/(R-END - 40)), R-END being the rate at end of walk and R-REC the rate 1 minute after exercise.

RESULTS

The VRR algorithm decreased rate variability (RR30: -7.36 +/- 8.8; P < 0.01) without increasing ventricular rate (MR: -1.11 +/- 8.3 P = NS), while SLOPE improved significantly (SLOPE: +15.41 +/- 16.8 P < 0.01).

CONCLUSIONS

VRR effectively stabilizes rate, without increasing pacing rate above spontaneous rhythm and helps achieve a more favorable autonomic balance, improving rate recovery after exercise.

Pacing delivered rate and rhythm control for atrial fibrillation

PURPOSE OF REVIEW

Device therapy for atrial fibrillation remains contentious despite the recognized benefit of atrial pacing in sinus node dysfunction. There are various new specialized pacing algorithms that aim to provide rhythm or rate control in atrial fibrillation. We review the various options for device therapy and the evidence available concerning their effectiveness.

RECENT FINDINGS

Randomized trials on preventative algorithms for atrial fibrillation have not shown consistent benefit. Anti-tachycardia pacing for atrial fibrillation has inherent problems illustrated in this review and has failed to demonstrate objective improvement except in the case of atrial flutter. Several large randomized trials have demonstrated an adverse outcome with right ventricular apical pacing. These studies have shown an increase in atrial fibrillation with ventricular pacing. Recent studies have emphasised the importance of right ventricular apical pacing in burden of atrial fibrillation and therefore we discuss the likely confounding effect on previous trials and speculate on future directions.

SUMMARY

The use of a device with atrial fibrillation prevention algorithms in a patient with a bradycardia indication for pacing is not unreasonable but there is no hard evidence of benefit. Patients with sinus node dysfunction should be paced in the atrium alone. There is no indication for use of a device for atrial fibrillation without a conventional indication for pacing.

Computer modeling of ventricular rhythm during atrial fibrillation and ventricular pacing

We propose a unified atrial fibrillation (AF)-ventricular pacing (VP) (AF-VP) model to demonstrate the effects of VP on the ventricular rhythm during atrial fibrillation AF. In this model, the AV junction (AVJ) is treated as a lumped structure characterized by refractoriness and automaticity. Bombarded by random AF impulses, the AVJ can also be invaded by the VP-induced retrograde wave. The model includes bidirectional conduction delays in the AVJ and ventricle. Both refractory period and conduction delay of the AVJ are dependent upon its recovery time. The electrotonic modulation by blocked impulses is also considered in the model. Our simulations show that, with proper parameter settings, the present model can account for most principal statistical properties of the RR intervals during AF. We further demonstrate that the AV conduction property and the ventricular rate in AF depend on both AF rate and the degree of electrotonic modulation in the AVJ. Finally, we show that multilevel interactions between AF and VP can generate various patterns of ventricular rhythm that are consistent with previous experimental observations.

Prospective Randomized Study of Mode Switching in a Clinical Trial of Pacemaker Therapy for Sinus Node Dysfunction

INTRODUCTION

Atrial fibrillation (AF) is common in pacemaker patients with sinus node dysfunction (SND) and may result in rapid ventricular pacing (RVP) in the DDDR mode. Mode switching (MS) reduces RVP, but its clinical benefit in patients with SND is unknown.

METHODS AND RESULTS

Two hundred two patients in the Mode Selection Trial (MOST; 2,010-patient, 6-year trial of DDDR vs VVIR pacing in SND) randomized to DDDR pacemakers with atrial high-rate episode (AHRE) storage capabilities were subrandomized to MS ON (N = 96) or MS OFF (N = 106). Cardiovascular symptoms, quality of life (QOL), reprogramming due to RVP, death, stroke, and heart failure hospitalization (HFH) were compared between groups. The treatment groups were similar with regard to AF history (59% MS ON vs 57% MS OFF). AHREs occurred in 49% patients during median follow-up of 2.2 years. Median AHRE duration (in min; MS ON 116 vs MS OFF 58, P = 0.29), frequency AHREs/week (MS ON 3.5 vs MS OFF 6.4, P = 0.23), and time spent in AHRE (min/week) (MS ON 450, MS OFF 268) were similar. Reprogramming due to any RVP during AHREs occurred more in MS OFF vs MS ON (13.2% vs 3.1%, P = 0.011) and marginally more for symptomatic RVP (8.5% vs 2.1%, P = 0.062). Cardiovascular symptoms occurred in 93.6% MS ON vs 90.2% MS OFF (P = 0.38). Median number of symptoms reported per visit was similar (MS ON 1.3 vs MS OFF 1.5, P = 0.62). Median symptom frequency/severity, summed and averaged over visits, was similar (MS ON 4.3 vs MS OFF 4.5, P = 0.74). QOL was not different between groups. Death, stroke, and HFH were not different between groups.

CONCLUSION

MS reduces pacemaker reprogramming due to RVP during AHREs in a small number of patients but does not improve QOL or cardiovascular symptoms overall among patients with SND.

Safety and feasibility of a novel rate-smoothed ventricular pacing algorithm for atrial fibrillation

OBJECTIVES

This study was conducted to establish the safety and performance of a new rate-smoothing pacing algorithm for patients with atrial fibrillation (AF).

BACKGROUND

Irregularity of the ventricular response is a hallmark of AF. This irregularity may contribute to symptoms and hemodynamic compromise in patients with AF. Interventions designed to reduce irregularity have not previously been evaluated in a long-term, clinical setting.

METHODS

We designed a prospective, double-blind study with randomized crossover. Patients with either paroxysmal or chronic AF whose conditions were medically refractory and who were referred for an atrioventricular node ablation procedure all underwent pacemaker implantation. Subjects were then randomly assigned to either DDD mode with the rate-smoothing algorithm (RSA) on, or to OOO mode. After 2 months they were crossed over to the other arm.

RESULTS

Fourteen patients (9 with paroxysmal AF and 5 with chronic AF) were enrolled. There were no significant differences between the group randomly assigned to RSA first versus the group assigned to OOO first. The mean left ventricular ejection fraction with the RSA was not significantly different than it was in OOO mode (45.1 +/- 18.6 vs 51.9 +/- 12.3; P =.11), although some individuals with uncontrolled ventricular rates did have a large decrease in ejection fraction with rate smoothing. One developed overt heart failure. One quality-of-life instrument detected a significant improvement in the "physical limitations" domain with the rate-smoothing mode. Eleven of 14 patients preferred the RSA ON arm, and 6 of those 11 elected to defer the ablation procedure.

CONCLUSIONS

Long-term rate-smoothed pacing is feasible. Because of concerns about pacing-induced heart failure in some patients with rapid ventricular rates, rate-smoothed pacing should be reserved for those who remain symptomatic despite adequate control of the ventricular rate. The RSA may help to reduce symptoms in patients with medically refractory AF; more study is required to define its efficacy in reducing symptoms and morbidity in this population.

Cardiac pacing in the long QT syndrome: review of available data and practical recommendations

A review of published data on cardiac pacing in the long QT syndrome (LQTS) is presented, in the hope that optimization of patient selection and pacemaker programming will prevent arrhythmic death. LQT3 patients may derive particular benefit from pacing because the dispersion of repolarization worsens steeply during bradycardia in this genotype. However, concluding that other genotypes will not benefit from pacing is premature. Pacing may be especially beneficial for patients with "pause-dependent" arrhythmias. Programming should include a sufficiently fast lower rate limit. Features that allow heart rate slowing beyond the lower rate limit or that may trigger pauses must be programmed "off" because pauses are proarrhythmic in this population. Pause-prevention pacing algorithms may be beneficial.