Electrophysiological characteristics of the atrium in sinus node dysfunction with and without postpacing atrial fibrillation

Efficacy of an Adjunctive Electrophysiological Test-Guided Left Atrial Posterior Wall Isolation in Persistent Atrial Fibrillation Without a Left Atrial Low-Voltage Area

BACKGROUND

Electrical remodeling precedes structural remodeling. In adjunctive left atrial (LA) low-voltage area (LVA) ablation to pulmonary vein isolation of atrial fibrillation (AF), LA areas without LVA have not been targeted for ablation. We studied the effect of adjunctive LA posterior wall isolation (PWI) on persistent AF without LA-LVA according to electrophysiological testing (EP test).

METHODS

We examined consecutive patients with persistent AF with (n=33) and without (n=111) LA-LVA. Patients without LA-LVA were randomly assigned to EP test-guided (n=57) and control (n=54) groups. In the EP test-guided group, an adjunctive PWI was performed in those with positive results (PWI subgroup; n=24), but not in those with negative results (n=33). The criteria for positive EP tests were an effective refractory period ≤180 ms, effective refractory period>20 ms shorter than the other sites, and/or induction of AF/atrial tachycardia (AT) during measurements. LVA ablation was performed in the patients with LA-LVA.

RESULTS

During the follow-up period (62±33 weeks), the EP test-guided group had significantly lower recurrence rates (19%,11/57 versus 41%, 22/54, P=0.012) and higher Kaplan-Meier AF/AT-free survival curve rates than the control group (P=0.01). No significant differences in the recurrence and AF/AT-free survival curve rates between the PWI (positive EP test) and non-PWI (negative EP test) subgroups were observed. Therefore, PWI for positive EP tests reduced the AF/AT recurrence in the EP test-guided group. A stepwise Cox proportional hazard analyses identified EP test-guided ablation as a factor reducing the recurrence rate. The recurrence rates in the LA-LVA ablation group and EP test-guided group were similar.

CONCLUSIONS

This pilot study proposed that an EP test-guided adjunctive PWI of persistent AF without LA-LVA potentially reduced AF/AT recurrences. The results suggest that there is an AF substrate in the LA with altered electrophysiological function even when there is no LA-LVA. Graphic Abstract: A graphic abstract is available for this article.

Sinus node revisited

PURPOSE OF REVIEW

Sinus node disease (SND) is a common clinical condition and is the most common indication for permanent pacemaker implantation. This review aims to revisit the complex sinus node anatomy, the evolving understanding of its pacemaking mechanisms, the atrial myopathy in SND and sinus node remodeling.

RECENT FINDINGS

Recent high-density noncontact mapping of the human sinus node showed multiple origins of sinus activation and exit sites with preferential pathways of conduction. Perhaps, a newly described discrete paranodal area containing a molecular mixture of nodal and atrial cells may account for this long recognized discrepancy between the anatomical and functional sinus node. The funny current (I(f)) driven 'membrane clock' is not solely responsible for sinus node automaticity, following recent recognition of the importance of the 'calcium clock'. Several molecular links to sinus node remodeling have recently been identified: loss of connexin-43 expression and down-regulation of I(ca,L) in aging; reduced I(f) and down-regulation of I(f) encoding HCN4 and HCN2 subunits in heart failure; and calcium clock malfunction with down-regulated HCN4, HCN2 and minK in atrial fibrillation.

SUMMARY

Ongoing research with improved technology and techniques continues to unravel new understandings and challenges to the century old discovery of the anatomical sinus node.

Efficacy of low interatrial septum and right atrial appendage pacing for prevention of permanent atrial fibrillation in patients with sinus node disease: results from the electrophysiology-guided pacing site selection (EPASS) study

BACKGROUND

The role of pacing sites and atrial electrophysiology on the progression of atrial fibrillation (AF) to the permanent form in patients with sinus node dysfunction (SND) has never been investigated. The aim of the study was to investigate the relationship between atrial electrophysiology and the efficacy of atrial pacing at the low interatrial septum (IAS) or at the right atrial appendage (RAA) to prevent persistent/permanent AF in patients with SND.

METHODS AND RESULTS

The Electrophysiology-Guided Pacing Site Selection (EPASS) Study was a prospective, controlled, randomized study. Atrial refractoriness, basal and incremental conduction times from the RAA to the coronary sinus ostium were measured before implantation, and the difference (ΔCTos) was calculated. Patients with ΔCTos ≥ 50 ms (study group) and those with ΔCTos <50 ms (control group) were randomly assigned to RAA or IAS with algorithms for continuous atrial stimulation "on." The primary end point was time to development of permanent or persistent AF within a 2-year follow-up in the study group, IAS versus RAA. Data were analyzed by intention to treat. One hundred two patients (77 ± 7 years, 44 mol/L) were enrolled, 69 (68%) in the study group and 33 (32%) in the control group. Of these, 97 ended the study, respectively, randomly assigned: 29 IAS versus 36 RAA and 18 IAS versus 14 RAA. After a mean follow-up of 15 ± 7 (median, 17) months, 11 (16.6%) patients in the study group met the primary end point: 2 IAS versus 9 RAA (log rank=3.93, P=0.047).

CONCLUSIONS

In patients with SND and intra-atrial conduction delay, low IAS pacing was superior to RAA pacing in preventing progression to persistent or permanent AF.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00239226.

Prevalence of conduction delay of the right atrium in patients with SSS: implications for pacing site selection

OBJECTIVES

To evaluate the prevalence of severe right atrial conduction delay in patients with sinus node dysfunction (SND) and atrial fibrillation (AF) and the effects of pacing in the right atrial appendage (RAA) and in the inter-atrial septum (IAS).

METHODS

Forty-two patients (15 male, 72 +/- 7 years) underwent electrophysiologic study to measure the difference between the conduction time from RAA to coronary sinus ostium during stimulation at 600 ms and after extrastimulus (DeltaCTos). Patients were classified as group A if DeltaCTos > 60 ms and group B if < 60 ms. Each Group was randomized to RAA/IAS pacing and algorithms ON/OFF.

RESULTS

Fifteen patients (36%, group A) had DeltaCTos = 76 +/- 11 ms and 27 patients (64%, group B) had DeltaCTos = 36 +/- 20 ms. Twenty-two patients were paced at the RAA and 20 at the IAS. During the study, no AF recurrences were reported in 11 of 42 (26%) patients, independently of RAA or IAS pacing. Patients from group A and RAA pacing had 0.79 +/- 0.81 episodes of AF/day during DDD, which increased to 1.52 +/- 1.41 episodes of AF/day during DDDR + Alg (P = 0.046). Those with IAS pacing had 0.5 +/- 0.24 episodes of AF/day during DDD, which decreased to 0.06 +/- 0.08 episodes of AF/day during DDDR + Alg (P = 0.06). In group B, no differences were reported between pacing sites and pacing modes.

CONCLUSIONS

Severe right atrial conduction delay is present in one-third of patients with SND and AF: continuous pacing at the IAS is superior to RAA for AF recurrences. In patients without severe conduction delay, no differences between pacing site or mode were observed.

Duration of P-Wave Is Associated with Atrial Fibrillation Hospitalizations in Patients with Atrial Fibrillation and Paced for Bradycardia

BACKGROUND

Atrial fibrillation (AF) is a common problem in pacemaker patients. We conducted a prospective observational study in patients paced for bradycardia with associated paroxysmal or persistent AF, to determine whether P-wave duration may stratify patients at higher risk for AF recurrences and AF-related hospitalizations. The patients were evaluated for the prevalence, cause, and predictors of hospitalization.

METHODS

We studied 660 consecutive patients (50% male, 72 +/- 9 years) who received a dual-chamber pacemaker. Median value of baseline P-wave duration was equal to 100 ms (25%-75% quartile range equal to 80-120 ms). We used this cut-off to divide the patients into group A (P < or = 100 ms), composed of 385 (58.3%) patients, and group B (P>100 ms), composed of 275 (41.7%) patients.

RESULTS

In a median follow-up of 19 months, 173 patients were hospitalized for all causes, 130 for cardiovascular causes, and 85 for AF-related hospitalizations. Multivariate logistic analysis showed that P-wave duration >100 ms identified patients at higher risk (OR = 1.6, 95% confidence interval (1.1-2.8), P = 0.044) for AF-related hospitalizations. Patients in group B (P > 100 ms) more frequently suffered AF-related hospitalizations (16.4% vs 10.4%, P = 0.02) and underwent more frequent cardioversions (14.5% vs 9.1%, P = 0.029) compared with group A (P < or = 100 ms).

CONCLUSIONS

P-wave duration may define the risk of persistent AF requiring cardioversion or AF-related hospitalization in patients with a pacemaker for bradycardia with associated paroxysmal or persistent AF.

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.

Intra- and interatrial conduction delay: implications for cardiac pacing

Atrial conduction disorders are frequent in elderly subjects and/or those with structural heart diseases, mainly mitral valve disease, hyperthrophic cardiomyopathies, and hypertension. The resultant electrophysiological and electromechanical abnormalities are associated with a higher risk of paroxysmal or persistent atrial tachyarrhythmias, either atrial fibrillation, typical or atypical flutter or other forms of atrial tachycardias. Such an association is not fortuitous because intra- and interatrial conduction abnormalities delays disrupt (spatial and temporal dispersion) electrical activation, thus promoting the initiation and perpetuation of reentrant circuits. Preventive therapeutic interventions induce variable, sometimes paradoxical effects as with the proarrhythmic effect of class I antiarrhythmic drugs. Similarly, atrial pacing may promote proarrhythmias or an antiarrhythmic effect according to the pacing site(s) and mode. Multisite atrial pacing was conceived to correct, as much as possible, abnormal activation induced by spontaneous intra- or interatrial conduction disorders or by single site atrial pacing, which are situations responsible for commonly refractory arrhythmias. Atrial electrical resynchronization can also be used to correct mechanical abnormalities like left heart AV dyssynchrony resulting from intraatrial conduction delays.

Clinical significance of prolonged P wave width after right atrial appendage pacing in sick sinus syndrome

The present study investigated both the clinical significance of atrial fibrillation (AF) before right atrial appendage (RAA) pacing and the influence of prolonged P wave on AF occurrence in RAA-paced patients with sick sinus syndrome (SSS). Fifty-seven patients (age 68+/-10 years; 19 men, 38 women) with SSS who underwent RAA pacing were divided into 2 groups: 23 patients without AF before pacing (I + II; Rubenstein I or II) and 34 patients with AF before pacing (III; Rubenstein III). The P wave duration in intrinsic rhythm and with RAA pacing were measured on the standard electrocardiography in leads II and V(1) with the use of a digitizing tablet. Group III was further subdivided into 2 groups: 20 patients (IIIb) with a paced P wave >130 ms in both leads II and V(1) and the other 14 patients (IIIa). The duration of the intrinsic P wave in leads II and V(1) was significantly greater in group III than in group I + II (119+/-20 vs 108+/-21 ms, p=0.0417, 106+/-16 vs 95+/-21 ms, p=0.0258, respectively). During the follow-up of 40+/-21 months, AF recurrence was significantly higher in group IIIb than in groups IIIa and I + II (17/20 vs 5/14 vs 2/23 p<0.0001). A few occurrences of AF were observed by conventional RAA pacing in patients without AF before pacing. However, SSS with AF before pacing caused a significant intra-atrial conduction disturbance and a high incidence of AF recurrence after implantation of RAA pacing, especially in patients with a prolonged paced P wave, in whom new pacing modalities may be needed to shorten paced P wave duration and prevent AF.

Determinants of persistent atrial fibrillation in patients with DDD pacemaker implantation

Occurrence of AF in a pacemaker implanted patient is a significant cause of morbidity and mortality. The aim of this study was to prospectively investigate the clinical, echocardiographic, and electrocardiographic determinants of persistent AF in patients with DDD pacemakers. A 101 consecutive patients were followed for an average of 19.8 +/- 11.8 months. Persistent AF was documented in 21 (20.8%) patients and 80 (79.2%) patients were in sinus or physiologically paced rhythm. In patients with persistent AF, previous AF attacks were observed more frequently (P < 0.03) and left atrial dimension was higher (3.5 +/- 0.6 vs 3.0 +/- 0.5 cm, P < 0.001). Average P maximum and P wave dispersion (PWD) values calculated in a 12-lead surface electrocardiogram were also found to be significantly higher in patients with persistent AF (P < 0.001). Cox regression analysis demonstrated that the presence of previous AF attacks (RR 8.95, P < 0.001), increased left atrial dimension (RR 2.1, P < 0.02), P maximum duration 120 ms (RR 6.1, P < 0.001), and PWD 40 ms (RR 12.2, P < 0.001) were associated with an increased risk of persistent AF. Cut-off points were 120 ms for P maximum and 40 ms for PWD. Sensitivity, specificity, and positive and negative predictive values were calculated as 76.2, 82.5, 53.3, and 92.9 for P maximum and as 85.7, 87.5, 64.3, and 95.9 for PWD, respectively. In patients with DDD pacemakers, previous AF attacks, increased left atrial dimension, P maximum value of 120 ms, and a PWD value of 40 ms were associated with a significantly increased risk of persistent AF. These patients must further be managed with other treatment modalities to prevent the development of persistent AF.

Is dual site better than single site atrial pacing in the prevention of atrial fibrillation?

Long-term prevention of atrial fibrillation is not constantly realized by single-site right atrial pacing, and the beneficial role of multisite atrial pacing is still being studied. Accordingly, we compared the effectiveness of dual site and single site atrial pacing in 83 patients (50 men, 33 women, aged 69 +/- 10 years), who received a DDD device for primary sinus node dysfunction or bradycardia with documented atrial fibrillation. Inclusion criteria for dual site pacing were a sinus P wave > or = 120 ms and at least two episodes of documented paroxysmal AF in the 6 months preceding implantation. Dual site atrial pacing (high right atrium-coronary sinus ostium) was performed in 30 cases, and was compared to 53 single site paced patients, 21 with a P wave > or = 120 ms and 32 with a P wave < 120 ms. The basic pacing rate was programmed at 68 +/- 4 beats/min (range 60-75 beats/min). Sinus P wave (133 +/- 20 vs 95 +/- 9 ms; P < 0.001), paced P wave (107 +/- 14 vs 99 +/- 15; P < 0.05), number of antiarrhythmic drugs used (2.4 +/- 1.2 vs 1.6 +/- 1.5, P < 0.05), and the duration of symptoms (8.1 +/- 4.5 vs 3.8 +/- 2.4 years; P < 0.001) were significantly higher in dual site patients. The other characteristics were similar. During the follow-up of 18 +/- 15 months (range 3-30 months), paroxysmal AF was documented in 33 patients. Among these patients, 13 developed permanent AF following at least one episode of paroxysmal AF. When comparing dual site patients and single site patients with a P wave duration > or = 120 ms, paroxysmal AF incidence was lower in the dual site group (9/30 patients vs 15/21 patients, P < 0.01), as well as permanent AF (1/30 patients vs 8/21 patients, P < 0.01). By contrast, comparison between dual site patients and the group of single site patients with a P wave duration < 120 ms did not evidence any significant differences in paroxysmal (9/30 patients vs 9/32 patients) and permanent (1/30 patients vs 4/32 patients) AF incidences. Dual site seems better able than single site atrial pacing to improve the natural history of patients with a prolonged P wave, reducing the incidence of paroxysmal and permanent AF. No benefit could be expected in patients with a normal P wave duration.