Electrophysiologic characteristics of the atrium in sinus node dysfunction: atrial refractoriness and conduction

Atrial arrhythmogenesis in a rabbit model of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) increases the risk of atrial fibrillation (AF), however, its arrhythmogenic mechanisms are unclear. This study investigated the effects of COPD on AF triggers (pulmonary veins, PVs) and substrates (atria), and their potential underlying mechanisms. Electrocardiographic, echocardiographic, and biochemical studies were conducted in control rabbits and rabbits with human leukocyte elastase (0.3 unit/kg)-induced COPD. Conventional microelectrode, Western blotting, and histological examinations were performed on PV, left atrium (LA), right atrium, and sinoatrial node (SAN) preparations from control rabbits and those with COPD. The rabbits with COPD had a higher incidence of atrial premature complexes, PV burst firing and delayed afterdepolarizations, higher sympathetic activity, larger LA, and faster PV spontaneous activity than did the control rabbits; but they exhibited a slower SAN beating rate. The LA of the rabbits with COPD had a shorter action potential duration and longer tachyarrhythmia induced by tachypacing (20 Hz) and isoproterenol (1 μM). Additionally, the rabbits with COPD had higher fibrosis in the PVs, LA, and SAN. H89 (10 μM), KN93 (1 μM), and KB-R7943 (10 μM) significantly suppressed burst firing and delayed afterdepolarizations in the PVs of the rabbits with COPD. Moreover, compared with the control rabbits, those with COPD had lower expression levels of the β1 adrenergic receptor, Cav 1.2, and Na⁺/Ca²⁺ exchanger in the PVs; Cav 1.2 in the LA; and hyperpolarization-activated cyclic nucleotide-gated K⁺ channel 4 in the SAN. COPD increases atrial arrhythmogenesis by modulating the distinctive electrophysiological characteristics of the PVs, LA, and SAN.

The incidence, indications and predictors of acute pacemaker implantation after ablation of persistent atrial fibrillation

INTRODUCTION

Patients with persistent atrial fibrillation (AF) may additionally suffer from a concealed sinus node disease. We sought to determine the incidence, indications and predictors of acute pacemaker [PM] implantation within 1 week after the ablation of persistent AF.

METHODS AND RESULTS

We performed a retrospective analysis of patients, who had had an ablation of persistent AF at our center. Between 01/2011 and 08/2016, 1234 patients (mean age 65 ± 10 years, 66.7% male) without prior PM implantation underwent an ablation of persistent AF. Pulmonary vein isolation (PVI) was performed in 1158 (93.8%), the additional ablation of complex fractionated atrial electrograms (CFAE) in 1109 (89.9%) and linear ablation in 524 (42.5%) patients. Temporary cardiac pacing was necessary in 27 (2.2%) patients. The temporary PM was removed in 15 patients (1.2%) because sinus node recovered after a median of 1.0 (minimum 0.1-maximum 2.0) day. The remaining 12 (1.0%) patients required the implantation of a permanent PM. Another 13 (1.1%) patients required permanent PM implantation without prior temporary pacing. In a multivariable regression model, age [OR 1.07 (1.02-1.12), p = 0.006], sinus pauses prior to ablation [OR 7.97 (2.36-26.88), p = 0.001] and atria with low voltage [OR 2.83 (1.31-6.11), p = 0.008] were identified as significant predictors for acute cardiac pacing.

CONCLUSION

Acute cardiac pacing within 1 week after the ablation of persistent AF was necessary in 40 (3.2%) patients. Age, sinus pauses in history prior to ablation and the existence of low-voltage areas in the atria were identified as relevant risk factors.

Hydrogen sulphide increases pulmonary veins and atrial arrhythmogenesis with activation of protein kinase C

Hydrogen sulphide (H₂ S), one of the most common toxic air pollutants, is an important aetiology of atrial fibrillation (AF). Pulmonary veins (PVs) and left atrium (LA) are the most important AF trigger and substrate. We investigated whether H₂ S may modulate the arrhythmogenesis of PVs and atria. Conventional microelectrodes and whole-cell patch clamp were performed in rabbit PV, sinoatrial node (SAN) or atrial cardiomyocytes before and after the perfusion of NaHS with or without chelerythrine (a selective PKC inhibitor), rottlerin (a specific PKC δ inhibitor) or KB-R7943 (a NCX inhibitor). NaHS reduced spontaneous beating rates, but increased the occurrences of delayed afterdepolarizations and burst firing in PVs and SANs. NaHS (100 μmol/L) increased I_KATP and I_NCX in PV and LA cardiomyocytes, which were attenuated by chelerythrine (3 μmol/L). Chelerythrine, rottlerin (10 μmol/L) or KB-R7943 (10 μmol/L) attenuated the arrhythmogenic effects of NaHS on PVs or SANs. NaHS shortened the action potential duration in LA, but not in right atrium or in the presence of chelerythrine. NaHS increased PKC activity, but did not translocate PKC isoforms α, ε to membrane in LA. In conclusion, through protein kinase C signalling, H₂ S increases PV and atrial arrhythmogenesis, which may contribute to air pollution-induced AF.

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.

Sinus Node Disease: An Idiopathic Right Atrial Myopathy

Sinus node disease was previously thought to be a disease limited to the sinus node and its atrial connections. However, recent reports have demonstrated sinus node disease as a disease of the entire right atrial myocardium. These patients have widespread electrophysiological abnormalities of their atria, including prolonged refractory periods and slowed conduction. In addition to these electrical changes, there are significant structural changes, such as fibrosis and fatty infiltration, which can be detected endocardially as regions of fractionated signals, low-voltage electrograms, and electrically silent areas. In most cases, the etiology of these changes is unknown. These changes may contribute to the high prevalence of atrial fibrillation seen in patients with sinus node disease.

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.

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.

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.

Pulmonary Vein Isolation for Atrial Fibrillation in Patients with Symptomatic Sinus Bradycardia or Pauses

INTRODUCTION

Sick sinus syndrome is commonly associated with tachyarrhythmias and bradyarrhythmias that often are symptomatic. The aim of this study was to assess the effect of pulmonary vein isolation in patients with sick sinus syndrome and atrial fibrillation (AF).

METHODS AND RESULTS

Three hundred fourteen consecutive patients who underwent pulmonary vein isolation between December 2000 and January 2002 were included in the study. Thirty-one patients had sick sinus syndrome, which was defined as a preprocedural history of symptomatic sinus bradycardia or pauses. Endpoints included AF recurrence, change in the frequency of sinus pauses, and symptoms of presyncope or syncope, as well as mean heart rate and percentage of atrial pacing in patients with pacemakers implanted prior to the pulmonary vein isolation. Patients had AF for an average of 6 +/- 3 years. Patients were 58 +/-8 years old and had ejection fractions of 55 +/- 4%. Sixty-one percent had implanted pacemakers. AF recurred within 6 months in 4 patients. Two had a successful second pulmonary vein isolation procedure. There were no recurrences of presyncopal events (P < 0.05) or documented sinus pauses (P < 0.05) after successful pulmonary vein isolation in the patients without permanent pacemakers. Patients with pacemakers had a 13-fold reduction in the percentage of atrial pacing (P < 0.05). Both groups showed a significant increase in average heart rates at 6-month follow-up.

CONCLUSION

Cure of AF by pulmonary vein isolation helped resolve the clinical manifestations of sick sinus syndrome, suggesting that the occurrence of AF and/or the associated treatment could be partially responsible for sick sinus syndrome.

Sinus and Paced P Wave Duration and Dispersion as Predictors of Atrial Fibrillation After Pacemaker Implantation in Patients with Isolated Sick Sinus Syndrome

The aim of this study was to prospectively evaluate the sinus and the paced P wave duration and dispersion as predictors of AF after pacemaker implantation in patients with isolated sick sinus syndrome (SSS). The study included 109 (69 women, mean age 72 +/- 11 years) patients with SSS, 59 with bradycardia-tachycardia syndrome (BTS). A 12-lead ECG was recorded before pacemaker implantation and during high right atrial and septal right atrial pacing at 70 and 100 beats/min. The ECGs were scanned into a computer and analyzed on screen. The patients were treated with AAIR (n = 52) or DDDR pacing. The P wave duration was measured in each lead and mean P wave duration and P wave dispersion were calculated for each ECG. AF during follow-up was defined as: AF in an ECG at or between follow-up visits; an atrial high rate episode with a rate of > or =220 beats/min for > or =5 minutes, atrial sensing with a rate of > or =170 beats/min in > or =5% of total counted beats, mode-switching in >/=5% of total time recorded, or a mode switching episode of > or =5 minutes recorded by the pacemaker telemetry. The ECG parameters were correlated to AF during follow-up. Mean follow-up was 1.5 +/- 0.9 years. None of the ECG parameters differed between patients with AF and patients without AF during follow-up, nor was there any difference between groups after correction for BTS and age. BTS was the strongest predictor of AF during follow-up (P < 0.001). P wave duration and dispersion measured before and during pacemaker implantation were not predictive of AF after pacemaker implantation in patients with isolated SSS.

Abnormal Right Atrial Electrograms Predict the Transition to Chronic Atrial Fibrillation in Paced Patients with Sick Sinus Syndrome

Although pacing therapy for sick sinus syndrome (SSS) is established, the risk of developing chronic atrial fibrillation (CAF) makes pacing therapy infeasible in some patients. We evaluated whether electrophysiological characteristics of atrial muscle can serve as predictors of the transition to CAF after pacemaker implantation in patients with SSS. Eighty-nine patients with SSS underwent electrophysiological study before pacing therapy. Catheter mapping of 12 right atrial sites was performed during sinus rhythm during electrophysiological. An abnormal atrial electrogram was defined as having a duration of 100 ms or longer, or eight or more fragmented deflections, or both. Right atrial extrastimulation was also performed for atrial vulnerability. After electrophysiological study, all patients underwent pacemaker implantation and were followed up. During the follow-up period of 85 +/- 50 months, development of CAF was observed in 12 patients (group A). The remaining 77 patients remained in sinus rhythm (group B). There were significantly more abnormal atrial electrograms in group A than group B (2.7 +/- 2.3 vs 0.8 +/- 1.2; P < 0.001). The distribution of abnormal atrial electrograms was also greater in group A; patients in group A had more abnormal atrial electrograms than patients in group B in both the high and middle right atrium (P < 0.005 and P < 0.01, respectively). Kaplan-Meier analysis showed that almost 50% of the paced patients with abnormal atrial electrograms (n = 42) developed CAF (P < 0.005). Our data suggest that the existence of abnormal atrial electrograms is predictive of the transition to CAF in paced patients with SSS.

Electrophysiological and electroanatomic characterization of the atria in sinus node disease: evidence of diffuse atrial remodeling

BACKGROUND

The normal sinus pacemaker complex is an extensive structure within the right atrium. We hypothesized that patients with sinus node disease (SND) would have evidence of diffuse atrial abnormalities.

METHODS AND RESULTS

Sixteen patients with symptomatic SND and 16 age-matched controls were studied. The following were evaluated: effective refractory periods (ERPs) from the high and low lateral right atrium (RA), high septal RA, and distal coronary sinus (CS); conduction time along the CS and lateral RA; P-wave duration; and conduction at the crista terminalis. Electroanatomic mapping was performed to define the sinus node complex and determine regional conduction velocity, double potentials, fractionated electrograms, regional voltage, and areas of electrical silence. Patients with SND demonstrated significant increase in atrial ERP at all right atrial sites, increased atrial conduction time along the lateral RA and CS, prolongation of the P-wave duration, and greater number and duration of double potentials along the crista terminalis. Electroanatomic mapping demonstrated the sinus node complex in SND to be more often unicentric, localized to the low crista terminalis at the site of the largest residual voltage amplitude. There was significant regional conduction slowing with double potentials and fractionation associated with areas of low voltage and electrical silence (or scar).

CONCLUSIONS

SND is associated with diffuse atrial remodeling characterized by structural change, conduction abnormalities, and increased right atrial refractoriness. There was a change in the nature of sinus pacemaker activity with loss of the normal multicentric pattern of activation, caudal shift of the pacemaker complex, and abnormal and circuitous conduction around lines of conduction block.

Effectiveness of ibutilide in cardioversion of persistent atrial fibrillation in patients with dual chamber stimulation

AIM OF THE STUDY

To evaluate the effectiveness of Ibutilide in cardioversion of persistent atrial fibrillation in patients with sinus node disease wearing a dual chamber pacemaker and to assess the potential role of overdrive ventricular pacing in prevention of drug related proarrhythmia.

METHODS AND RESULTS

Fifty-three sinus node disease patients (35 males; mean age 75 +/- 9.5 years), implanted with a dual chamber pacing system, with persistent atrial fibrillation, lasting for 328 +/- 416 days, received 1-2 mg of intravenous Ibutilide. Pacing mode was programmed in VVI at 90 ppm, in order to suppress spontaneous ventricular activity. All patients were monitored for 4 hours. Late occurrence of ventricular arrhythmias was evaluated using the pacemaker memory. Ventricular pacing threshold, spontaneous electrogram amplitude and pacing impedance were measured before and after Ibutilide infusion. Cardioversion to sinus rhythm occurred in twenty-two patients (41.5%). Treatment success was significantly related to shorter atrial fibrillation duration. Paced QT interval duration increased from 412 +/- 36 ms to 481 +/- 40 ms (p < 0.0001), without differences between responders and non responders; QRS width did not change significantly (from 152 +/- 25 ms to 161 +/- 25 ms; p = n.s.). No early or late episodes of sustained or non sustained polymorphic ventricular tachycardia were observed. Pacing and sensing threshold did not show any significant variation.

CONCLUSIONS

Ibutilide showed a good effectiveness in treating persistent atrial fibrillation in paced patients. Overdrive ventricular pacing may have played a role in preventing drug induced ventricular proarrhythmia. No adverse effect on pacing threshold was observed.

Age-related changes in the electrophysiologic properties of the atrium in patients with no history of atrial fibrillation

Although atrial fibrillation is a common arrhythmia, especially in the elderly, little is known about age-related changes in the electrophysiologic properties of the atrium. The aim of this study was to analyze the effect of aging on atrial vulnerability to atrial fibrillation. An electrophysiologic study was performed in 45 patients with no history of atrial fibrillation, Wolff-Parkinson-White syndrome, structural heart disease, or conditions with potential effects on cardiac hemodynamic or electrophysiologic function (15 females; mean age, 52 +/- 18 years; range, 14 to 84 years). The following atrial excitability parameters were assessed: spontaneous or paced (A1) and extrastimulated (A2) atrial electrogram widths, percent maximum atrial fragmentation (A2/A1 x 100), effective refractory period, wavelength index (ERP/A2), and inducibility of atrial fibrillation. Atrial fibrillation was induced in 9 patients. Percent maximum atrial fragmentation was greater (176 +/- 36 vs 137 +/- 26%, P < 0.001) and wavelength index was shorter (2.4 +/- 0.4 vs 3.2 +/- 0.9, P < 0.01) in the patients with than without inducible atrial fibrillation. However, age was similar in patients with and without inducible atrial fibrillation (47 +/- 11 vs 53 +/- 19 years, P = 0.36). Percent maximum atrial fragmentation and effective refractory period directly correlated with age (r = 0.32, P < 0.05 and r = 0.45, P < 0.001, respectively). On the other hand, wavelength index (3.1 +/- 0.9) did not correlate with age (r = -0.05, P = 0.77). This study suggests that the mechanism triggering atrial fibrillation may be very well different between older and younger patients with atrial fibrillation, because younger patients have no marked substrate for atrial fibrillation.

Relation of age and sex to atrial electrophysiological properties in patients with no history of atrial fibrillation

Although atrial fibrillation is a common arrhythmia, especially in elderly men, little is known about age related changes in atrial electrophysiological properties or gender differences. The aim of this study was to analyze the effects of aging on vulnerability to atrial fibrillation and assessed gender differences in those age related changes. An electrophysiological study was performed on 73 patients with no history of atrial fibrillation, structural heart disease, or conditions with potential effects on cardiac hemodynamic or electrophysiological function, including 25 women (mean age 49 +/- 18 years; range 12-84 years). The following atrial excitability parameters were assessed: spontaneous or paced (A1) and extrastimulated (A2) atrial electrogram widths, percent maximum atrial fragmentation (A2/A1 x 100), effective refractory period, wavelength index (effective refractory period/A2), and inducibility of atrial fibrillation. There were no significant differences in percent maximum atrial fragmentation (143 +/- 28 vs 142 +/- 35%), effective refractory period (241 +/- 39 vs 238 +/- 50 ms), wavelength index (2.9 +/- 0.8 vs 3.1 +/- 0.9), induction of atrial fibrillation (10 [21%] vs 7 [28%]), or age (50 +/- 17 vs 49 +/- 20 years) between men and women. Age was not statistically different between those patients with and without induction of atrial fibrillation in men (48 +/- 14 vs 50 +/- 18 years) and women (48 +/- 18 vs 49 +/- 21 years). Percent maximum atrial fragmentation and effective refractory period were directly correlated with age in men (r = 0.35, P = 0.01; r = 0.46, P < 0.001, respectively) and women (r = 0.42, P = 0.04; r = 0.45, P = 0.02, respectively), though wavelength index did not correlate with age in men (r = -0.04) or women (r = -0.04) with no history of atrial fibrillation. Considering these findings, the authors conclude that the mechanism triggering atrial fibrillation may be different between older and younger patients with atrial fibrillation, because younger patients who have no marked substrate for atrial fibrillation may need many trigger beats to induce atrial fibrillation.

Atrial fibrillation recurrence after internal cardioversion: prognostic importance of electrophysiological parameters

OBJECTIVE

To evaluate the clinical and electrophysiological determinants of arrhythmia recurrence in patients undergoing internal atrial cardioversion for chronic atrial fibrillation (AF).

SETTING

Tertiary cardiac referral centre.

METHODS

101 consecutive patients with failed external cardioversion or AF > or = 1 year underwent internal atrial cardioversion; once stable sinus rhythm (SR) was obtained, electrophysiological study was performed in 73 patients (72%) who gave informed consent. Patients were then followed on antiarrhythmic treatment.

RESULTS

101 consecutive patients underwent internal atrial cardioversion in the period 1996-1999 with 100% conversion to SR; prophylactic antiarrhythmic treatment was flecainide (52%), amiodarone (37%), and sotalol (11%). Average follow up at first AF recurrence was 18.4 (14.4) months (range 0.1-49.8 months); persistence of SR was observed in 72/101 (72%) patients. By logistic regression, AF duration (odds ratio (OR) 1.07, 95% confidence interval (CI) 1.01 to 1.13) and a lower sinus rate at discharge on antiarrhythmic drugs (OR 0.92, 95% CI 0.85 to 0.99) were independent predictors of AF recurrence, whereas age, New York Heart Association functional class, left atrial dimensions, and left ventricular ejection fraction were not predictive of arrhythmia recurrence. When electrophysiological parameters were added to the statistical model in 73 patients, a shorter atrial effective refractoriness (OR 1.04, 95% CI 1 to 1.08) and an abnormal relation of atrial effective refractoriness to cycle length (OR 31, 95% CI 3.7 to 266) were also independent predictors of AF recurrence at follow up, beyond AF duration and heart rate at discharge.

CONCLUSIONS

Patients with failed external cardioversion or long lasting AF may benefit from internal atrial cardioversion and antiarrhythmic treatment to keep SR at long term; electrophysiological study may identify patients at the highest risk of arrhythmia recurrence. Although preservation of SR seems unlikely for AF duration > 3 years, a consistent minority of this subgroup (38%) may benefit from this approach.

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.