Effect of high intensity drive train stimulation on dispersion of atrial refractoriness: role of autonomic nervous system

Incident atrial fibrillation and heart failure in treated hypertensive patients with left ventricular hypertrophy. The LIFE Study

Aim: The present study investigated the appearance and severity of atrial fibrillation (AF) and heart failure (HF) in 8,702 hypertensive patients with left ventricular hypertrophy (LVH) receiving antihypertensive treatment in a prospective trial. Methods: Patients who had a history of AF or HF were not included, and the participants had sinus rhythm when they were randomly allocated to blinded study medication. Endpoints were adjudicated. Results: Incident AF occurred in 679 patients (7.8%) and HF in 246 patients (2.8%) during 4.7 ± 1.1 years mean follow-up. Incident AF was associated with a > 4-fold increased risk of developing subsequent HF [hazards ratios (HRs) = 4.7; 95% confidence intervals (CIs), 3.1–7.0; P < 0.001] in multivariable Cox analyses adjusting for age, sex, race, randomized treatment, standard cardiovascular risk factors and incident myocardial infarction. The development of HF as a time-dependent variable was associated with a multivariable-adjusted 3-fold increase of the primary study endpoint (HRs = 3.11; 95% CIs, 1.52–6.39; P < 0.001) which was a composite of myocardial infarction, stroke or cardiovascular death. Incident HF was associated with a > 3-fold increased risk of developing subsequent AF (HRs = 3.3; 95% CIs, 2.3–4.9; P < 0.001). This development of AF was associated with a > 2-fold increase of the composite primary study endpoint in multivariable Cox analysis (HRs = 2.26; 95% CIs, 1.09–4.67; P = 0.028). Conclusions: Incident atrial fibrillation and heart failure are associated with increased risk of the other in treated hypertensive patients with left ventricular hypertrophy. Such high-risk hypertensive patients who subsequently develop both atrial fibrillation and heart failure have particular high risk of composite myocardial infarction, stroke or cardiovascular death (ClinicalTrials.gov identifier: NCT00338260).

Arrhythmogenic Remodeling in the Failing Heart

Chronic heart failure is a clinical syndrome with multiple etiologies, associated with significant morbidity and mortality. Cardiac arrhythmias, including ventricular tachyarrhythmias and atrial fibrillation, are common in heart failure. A number of cardiac diseases including heart failure alter the expression and regulation of ion channels and transporters leading to arrhythmogenic electrical remodeling. Myocardial hypertrophy, fibrosis and scar formation are key elements of arrhythmogenic structural remodeling in heart failure. In this article, the mechanisms responsible for increased arrhythmia susceptibility as well as the underlying changes in ion channel, transporter expression and function as well as alterations in calcium handling in heart failure are discussed. Understanding the mechanisms of arrhythmogenic remodeling is key to improving arrhythmia management and the prevention of sudden cardiac death in patients with heart failure.

Resveratrol and derivatives for the treatment of atrial fibrillation

Resveratrol is a bioactive polyphenol, found in grapes, red wine, and peanuts, and has recently garnered much media and scientific attention for its diverse beneficial health effects as a nutritional supplement or nutraceutical. Of particular interest are the well-documented cardioprotective effects of resveratrol that are mediated by diverse mechanisms, including its antioxidant and vascular effects. However, it is now becoming clear that resveratrol may also exhibit direct effects on cardiac function and rhythm through modulation of signaling pathways that regulate cardiac remodeling and ion channel activity that controls cardiac excitability. Resveratrol may therefore possess antiarrhythmic properties that contribute to the cardiovascular benefits of resveratrol. Atrial fibrillation (AF) is the most common cardiac arrhythmia, although current therapies are suboptimal. Our laboratory has been studying resveratrol's effects on cardiac ion channels and remodeling pathways, and we initiated a drug development program aimed at generating novel resveratrol derivatives with improved efficacy against AF when compared to currently available therapeutics. This review therefore focuses on the effects of resveratrol and new derivatives on a variety of cardiac ion channels and molecular pathways that contribute to the development and maintenance of atrial fibrillation.

[Effectiveness of D,L-sotalol in post-ablative atrial arrhythmias in patients with atrial fibrillation treated with radiofrequency ablation]

Left atrial tachycardia is the most common arrhythmia developing after pulmonary vein (PV) isolation in patients with atrial fibrillation.

AIM

To compare the clinical effectiveness of class Ic propafenone and class III D,L sotalol in antiarrhythmic treatment of post-ablation left atrial tachycardias.

METHODS AND RESULTS

A total of 75 consecutive patients with an age of 55.4 +/- 7.14 (mean +/- SD) years underwent real electrical isolation of the pulmonary veins. Beside electroanatomical guidance, a circular mapping catheter was used to achieve total electrical disconnection of the pulmonary veins from left atrium at the antrum level. After procedure, the antiarrhythmic drug therapy was continued with the tendency to taper down during follow up visits. These were scheduled 1 and later 3 monthly after PV isolation. After the first 3 months follow-up period, left atrial tachycardia occurred in 21 patients (31.3 %). 11 of them were on propafenone therapy, 6 were on sotalol therapy and 4 patients with left atrial tachycardia received amiodarone. In the first and third group, after developing left atrial tachycardia, the 1C class drug or amiodarone was changed to III D,L sotalol. In the second group, after developing left atrial tachycardia, the III D,L sotalol was changed to 1C class drug. 9 months later, in III D,L sotalol treated group of left atrial tachycardia patients (15), the drug was considered effective in 12 patients.

CONCLUSION

In prevention of left atrial tachycardia occurred after PV isolation, sotalol is not more effective than 1C class propafenone. Otherwise, III D,L sotalol seems to be effective in anti-arrhythmic treatment of developed post-ablation in late left atrial tachycardias.

Structural and functional evidence for discrete exit pathways that connect the canine sinoatrial node and atria

Surface electrode recordings cannot delineate the activation within the human or canine sinoatrial node (SAN) because they are intramural structures. Thus, the site of origin of excitation and conduction pathway(s) within the SAN of these mammals remains unknown. Canine right atrial preparations (n=7) were optically mapped. The SAN 3D structure and protein expression were mapped using immunohistochemistry. SAN optical action potentials had diastolic depolarization and multiple upstroke components that corresponded to the separate excitations of the node and surface atrial layers. Pacing-induced SAN exit block eliminated atrial optical action potential components but retained SAN optical action potential components. Excitation originated in the SAN (cycle length, 557+/-72 ms) and slowly spread (1.2 to 14 cm/sec) within the SAN, failing to directly excite the crista terminalis and intraatrial septum. After a 49+/-22 ms conduction delay within the SAN, excitation reached the atrial myocardium via superior and/or inferior sinoatrial exit pathways 8.8+/-3.2 mm from the leading pacemaker site. The ellipsoidal 13.7+/-2.8/4.9+/-0.6 mm SAN structure was functionally insulated from the atrium. This insulation coincided with connexin43-negative regions at the borders of the node, connective tissue, and coronary arteries. During normal sinus rhythm, the canine SAN is functionally insulated from the surrounding atrial myocardium except for 2 (or more) narrow superior and inferior sinoatrial exit pathways separated by 12.8+/-4.1 mm. Conduction failure in these sinoatrial exit pathways leads to SAN exit block and is a modulator of heart rate.

Paroxysmal Atrial Fibrillation Coincident With Cardiac Decompensation is a Predictor of Poor Prognosis in Chronic Heart Failure

BACKGROUND

The prognostic significance of atrial fibrillation (AF) in chronic heart failure (CHF) remains poorly understood.

METHODS AND RESULTS

Death and rehospitalizaion for CHF exacerbation for 427 consecutive patients hospitalized from 1996 to 2002 were retrospectively analyzed in relation to cardiac rhythm: sinus rhythm (SR; n=239) or AF (n=188). The AF group was classified according to an Intervention (n=57) or Non-Intervention (n=131) group for defibrillating AF. During the follow-up of 34+/-23 months, there was no significant difference of mortality or morbidity between the SR and AF groups, or between the Intervention and Non-Intervention groups, respectively. However, the Non-Intervention group consisted of 28 patients with paroxysmal AF (PAF), which spontaneously converted to SR during hospitalization, and 103 with chronic AF (CAF). The rehospitalization for CHF exacerbation was significantly higher in PAF than that in CAF and SR (p=0.00005 and 0.002, respectively). Multivariate Cox analysis demonstrated that, PAF, but not CAF, was a predictor of readmission (relative risk 2.30, p=0.004, 95% confidence interval 1.30 to 4.05).

CONCLUSIONS

The present data implied that PAF coincident with cardiac decompensation could be a new predictor of prognosis for CHF. The management strategies of AF in CHF should be discussed according to the phenotype of AF.

Temporal relations of atrial fibrillation and congestive heart failure and their joint influence on mortality: the Framingham Heart Study

BACKGROUND

Atrial fibrillation (AF) and congestive heart failure (CHF) frequently occur together, but there is limited information regarding their temporal relations and the combined influence of these conditions on mortality.

METHODS AND RESULTS

We studied participants in the Framingham Study with new-onset AF or CHF. Multivariable Cox proportional hazards models with time-dependent variables were used to evaluate whether mortality after AF or CHF was affected by the occurrence and timing of the other condition. Hazard ratios (HRs) were adjusted for time period and cardiovascular risk factors. During the study period, 1470 participants developed AF, CHF, or both. Among 382 individuals with both conditions, 38% had AF first, 41% had CHF first, and 21% had both diagnosed on the same day. The incidence of CHF among AF subjects was 33 per 1000 person-years, and the incidence of AF among CHF subjects was 54 per 1000 person-years. In AF subjects, the subsequent development of CHF was associated with increased mortality (men: HR 2.7; 95% CI, 1.9 to 3.7; women: HR 3.1; 95% CI, 2.2 to 4.2). Similarly, in CHF subjects, later development of AF was associated with increased mortality (men: HR 1.6; 95% CI, 1.2 to 2.1; women: HR 2.7, 95% CI, 2.0 to 3.6). Preexisting CHF adversely affected survival in individuals with AF, but preexisting AF was not associated with adverse survival in those with CHF.

CONCLUSIONS

Individuals with AF or CHF who subsequently develop the other condition have a poor prognosis. Additional studies addressing the pathogenesis, prevention, and optimal management of the joint occurrence of AF and CHF appear warranted.

The comparative effects of drive and test stimulus intensity on myocardial excitability and vulnerability

The number and intensity of stimuli that set basic cycle length in cardiac electrophysiological studies can influence the electrical properties assessed by extrastimuli. The relative contribution of drive (S1) and test (S2) stimulus intensity in defining myocardial excitability and vulnerability has not been reported. The purpose of this investigation was to assess this interaction and to determine whether atrial and ventricular findings differed. The effects of S1 and S2 intensity on atrial and ventricular stimulus-intensity-refractory-period curves were determined in open-chest dogs: comparisons were made between curves with S1 intensity varied between diastolic threshold (DT) and 10 mA and S2 intensity maintained at DT and those with S1 intensity maintained at DT and S2 intensity varied between DT and 10 mA. S1-S1 was held constant and S1-S2 varied. The effects of different stimulation sites, cycle length, number of stimulations, and neural blockade were assessed. S1 intensity amplification shifted atrial stimulus-intensity-refractory period curves in the direction of increased excitability and vulnerability; the changes were more pronounced than those obtained by modulating S2 intensity. The changes produced by increasing S1 intensity were evident at different cycle lengths and were enhanced by an increased number of stimulations, but were not evident when S1 and S2 were delivered at different atrial sites. Although beta-blockade attenuated the effects of increasing S1 intensity somewhat, the addition of cholinergic blockade virtually abolished it. Ventricular refractoriness was also changed by modulation of S1 intensity, but the changes were less striking. In the atrium, modulation of S1 intensity has greater effects of stimulus-intensity-refractory-period relations than modulation of S2 intensity; in the ventricule, the converse is true.

Effects of procainamide and dl-sotalol on the changes of atrial electrophysiology induced by high current stimulation

The relation between high current atrial stimulation and antiarrhythmic drugs was not clear. We evaluated the effects of procainamide and dl-sotalol on the electrophysiological changes induced by high current stimulation. Effects of high current atrial stimulation on effective refractory period, dispersion of refractoriness, conduction velocity, and wavelength of the earliest atrial premature beat were evaluated at baseline and after infusion of procainamide (10 patients) and dl-sotalol (10 patients). High current atrial stimulation shortened effective refractory period locally (-12% +/- 4.0%, -7.0% +/- 3.0%, -5.1 +/- 3.3%, and -3.0 +/- 2.0%, at 0, 7, 14, and 21 mm from the S1 stimulation site, respectively; P < 0.001); increased the dispersion of refractoriness (from 17.8 +/- 8.5 to 27.4 +/- 12.5 ms, P < 0.001); decreased conduction velocity of the earliest premature beat (from 0.58 +/- 0.10 to 0.52 +/- 0.09 ms, P = 0.01); and decreased wavelength of the earliest atrial premature beat (from 10.9 +/- 2.4 to 8.8 +/- 2.1 cm, P < 0.001). These effects of high current stimulation persisted after procainamide infusion. However, after dl-sotalol infusion, high current atrial stimuli did not change the dispersion of refractoriness (23.1 +/- 10 ms vs 26.4 +/- 10.4 ms; P > 0.05, twice diastolic threshold vs 10 mA); conduction velocity of the earliest premature beat (0.54 +/- 0.06 ms vs 0.50 +/- 0.06 ms, P > 0.05); or wavelength of the earliest premature atrial beat (11.5 +/- 1.6 m/s vs 10.1 +/- 1.7 cm; P > 0.05). Although high current atrial stimulation shortened effective refractory period locally, increased dispersion of refractoriness, and decreased the wavelength of the earliest premature atrial impulse, these effects were abolished by dl-sotalol but not procainamide.

Effects of different atrial pacing modes on atrial electrophysiology: implicating the mechanism of biatrial pacing in prevention of atrial fibrillation

BACKGROUND

Multiple-site atrial pacing has been shown to prevent recurrence of atrial fibrillation. However, information about the mechanisms of different atrial pacing modes in prevention of atrial fibrillation was not clear.

METHODS AND RESULTS

Forty-two patients without structural heart disease were classified into group 1 and group 2 according to absence or presence of clinical atrial fibrillation, respectively. Atrial conduction time and electrogram width of the right posterior interatrial septum (RPS) were measured during drive-train stimulation (S1) and early extrastimulation (S2). The locations of S1 were the high right atrium (HRA), distal coronary sinus (DCS), or both sites simultaneously. Effective refractory periods (ERPs) of the HRA and DCS were also determined during S1 stimulation at each site and during biatrial pacing. The ERPs were not different between single-site atrial pacing and biatrial pacing. In contrast, early S2 stimulation at the HRA caused greater atrial conduction delay and greater increment of electrogram width of the RPS in patients with a history of atrial fibrillation. Biatrial pacing significantly reduced the conduction delay and electrogram width of the RPS caused by HRA extrastimulation. In addition, in 17 group 2 patients, atrial fibrillation was induced by an early HRA S2 coupled to HRA pacing. However, with the same coupling interval of S2 at HRA, only 6 of them had the arrhythmia induced during biatrial pacing. Furthermore, conduction delay and increase of electrogram width caused by early S2 at the HRA were reduced by biatrial pacing only in patients whose arrhythmia induction was successfully prevented by biatrial pacing.

CONCLUSIONS

Biatrial pacing reduced both the atrial conduction delay and increase of electrogram width at the RPS caused by early S2 at HRA, and these effects could prevent induction of atrial fibrillation.