Pharmacotherapy of Atrial Fibrillation: A Pathophysiological Perspective and Review

Influence of Continuous Training on Atrial Myocytes IK1 and IKAch and on Induction of Atrial Fibrillation in a Rabbit Model

BACKGROUND

Elucidation of mechanisms underlying continuous training-related atrial fibrillation (AF) may inform formulation of novel therapeutic approaches and training method selection. This study was aimed at assessing mechanisms underlying continuous training-induced AF in an animal model.

METHODS

Healthy New Zealand rabbits were divided into three groups (n=8 each), namely, control (C), and moderate intensity (M), and high intensity (H) continuous training according to treadmill speed. Atrial size andintrinsic and resting heart rates were measured by transthoracic echocardiography before, and 8 and 12 weeks after training. Using a Langendorff perfusion system, AF was induced by S1S2 stimulation and the induction rate was recorded. Atrial IK1 and IKAch ion current densities were recorded using whole-cell patch-clamp technique in isolated atrial myocytes. Changes in atrial Kir2.1, Kir2.2, Kir3.1, and Kir3.4 mRNA expression were assessed by reverse transcriptase-coupled polymerase chain reaction.

RESULTS

After 8 and 12 weeks, Groups M and H vs. Group C had greater (all P < 0.05) atrial anteroposterior diameter; greater incidence of AF (60% and 90% vs. 45%, respectively; P < 0.05, also between Groups H and M); and greater atrial IKAch current density. In Group H, Kir2.1 and Kir2.2 mRNA expression in the left and right atria was increased (P < 0.05, vs. Groups C and M) as was left atrial Kir3.1 and Kir3.4 mRNA expression (P < 0.05, vs. Group C).

CONCLUSION

In a rabbit model, continuous training enlarges atrial diameter leading to atrial structural and electrical remodeling and increased AF incidence.

Advances in the management of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide, increasing in incidence with the aging population. Substantial morbidity and mortality accompany its diagnosis. Management should focus on rate and rhythm management, on reducing thromboembolic risk, and also potentially on targeting the mechanisms responsible for its perpetuation. Current antiarrhythmic therapy has only modest efficacy and substantial side effects, and anticoagulation regimes are cumbersome and require regular monitoring. Novel anticoagulants and antiarrhythmics hold the promise of improved efficacy and safety. This review covers current therapy for AF, major advances in pharmacological management and future directions for therapy.

Comparison of mortality and morbidity in patients with atrial fibrillation and heart failure with preserved versus decreased left ventricular ejection fraction

Almost 50% of patients with congestive heart failure (HF) have preserved ejection fraction (PEF). Data on the effect of HF-PEF on atrial fibrillation outcomes are lacking. We assessed the prognostic significance of HF-PEF in an atrial fibrillation population compared to a systolic heart failure (SHF) population. A post hoc analysis of the National Heart, Lung, and Blood Institute-limited access data set of the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) trial was carried out. The patients with a history of congestive HF and a preserved ejection fraction (EF >50%) were classified as having HF-PEF (n = 320). The patients with congestive HF and a qualitatively depressed EF (EF <50%) were classified as having SHF (n = 402). Cox proportional hazards analysis was performed. The mean follow-up duration was 1,181 ± 534 days/patient. The patients with HF-PEF had lower all-cause mortality (hazard ratio [HR] 0.62, 95% confidence interval [CI] 0.46 to 0.85, p = 0.003) and cardiovascular mortality (HR 0.56, 95% CI 0.38 to 0.84, p = 0.006), with a possible decreased arrhythmic end point (HR 0.39, 95% CI 0.16 to 1.006, p = 0.052) than did the patients with SHF. No differences were observed for ischemic stroke (HR 1.08, 95% CI 0.48 to 2.39, p = 0.86), rehospitalization (HR 0.89, 95% CI 0.75 to 1.07, p = 0.24), or progression to New York Heart Association class III-IV (odds ratio 0.80, 95% CI 0.42 to 1.54, p = 0.522). In conclusion, although patients with HF-PEF have better mortality outcomes than those with SHF, the morbidity appears to be similar.