Pharmacologic control of heart rate in atrial fibrillation

Longitudinal analysis of echocardiographic and cardiac biomarker variables in dogs with atrial fibrillation: The optimal rate control in dogs with atrial fibrillation II study

BACKGROUND

Rate control (RC; meanHRHolter ≤ 125 bpm) increases survival in dogs with atrial fibrillation (AF). The mechanisms remain unclear.

HYPOTHESIS/OBJECTIVES

Investigate echocardiographic and biomarker differences between RC and non-RC (NRC) dogs. Determine if changes post-anti-arrhythmic drugs (AAD) predict successful RC in subsequent Holter monitoring. Evaluate if early vs late RC affects survival.

ANIMALS

Fifty-two dogs with AF.

METHODS

Holter-derived mean heart rate, echocardiographic and biomarker variables from dogs receiving AAD were analyzed prospectively at each re-evaluation and grouped into RC or NRC. The primary endpoint was successful RC. Between group comparisons of absolute values, magnitude of change from admission to re-evaluations and end of study were performed using Mann-Whitney tests or unpaired t-tests. Logistic regression explored variables associated with inability to achieve RC at subsequent visits. Kaplan-Meier survival analysis was used to compare survival time of early vs late RC.

RESULTS

At visit 2, 11/52 dogs were RC; at visit 3, 14/52 were RC; and at visit 4, 4/52 were RC. At the end of study, 25/52 remained NRC. At visit 2, both groups had increased cardiac dimensions, but NRC dogs had larger dimensions; biomarkers did not differ. At the end of study, RC showed decreased cardiac dimensions and end-terminal pro-brain natriuretic peptide (NT-proBNP) compared with NRC. No variables were useful at predicting RC success in subsequent visits. Survival analysis found no differences between early vs late RC.

CONCLUSIONS AND CLINICAL IMPORTANCE

The RC dogs had decreased cardiac dimensions and NT-proBNP, suggesting HR-mediated reverse-remodeling might benefit survival, even with delayed RC achievement. Pursuit of RC is crucial despite initial failures.

A Comparison of Rate Control Agents for the Treatment of Atrial Fibrillation: Follow-Up Investigation of the AFFIRM Study

There are limited data from randomized controlled trials comparing rate control agents in atrial fibrillation. Patient-level data from the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) trial was used to compare outcomes in patients randomized to the rate control arm who were treated with a single rate control agent at baseline. The rate control agents used were beta-blockers, non-dihydropyridine calcium channel blockers, and digoxin. The independent variable for this analysis was the initial study drug used and the dependent variables were time to first hospitalization and time to death from any cause. We analyzed 1,144 out of 2,027 participants assigned to the rate control group who were on a single rate control agent at the start of the trial. There were 485 (42.5%) participants in the beta-blocker group, 344 (30%) in the calcium channel blocker group, and 315 (27.5%) in the digoxin group. All hospitalization and all-cause mortality occurred in 55.9% and 12.5% of those in the beta-blocker group, 58.4% and 16.7% in the calcium channel blocker group, and 55.2% and 21.1% in the digoxin group, respectively. After adjustment for differences in baseline characteristics, there were no significant differences in time to hospitalization or death for any group. In the AFFIRM trial, the initial rate control drug used was not associated with statistically significant differences in time to hospitalization or death after controlling for differences in baseline characteristics. There is limited data at present to guide the selection of rate control agents in patients with atrial fibrillation.

Pharmacotherapy of Atrial Fibrillation

Atrial fibrillation is the most common sustained arrhythmia of clinical significance. Its prevalence rises with age. It is a significant cause of thromboembolic phenomena. We describe briefly the etiology and classification of atrial fibrillation, the risk factors for thromboembolism and stroke associated with it, the indications for hospitalization, and the therapeutic goal. We discuss in depth the management strategies for such patients and compare the impact of rate versus rhythm control in reducing morbidity and mortality attributed to arrhythmia, in light of past and present trials. A brief overview of the drugs used in the management of atrial fibrillation, their pharmacology and dosage, their effects and use in rhythm versus rate control with important side effects are also included. Finally, the prevention and treatment of thromboembolism in patients with atrial fibrillation, an important aspect of therapy, is revisited in light of recent advances.

A perspective on rate control in the treatment of atrial fibrillation

Until recently, the standard approach to therapy of atrial fibrillation (AF) in most cases was restoration and maintenance of sinus rhythm (rhythm control). Although difficult to accomplish, and associated with potential serious adverse effects of antiarrhythmic agents, this therapeutic approach was influenced by the belief that rhythm control was associated with better survival, fewer symptoms, better exercise tolerance, lower risk of stroke, better quality of life, and absence of need for long-term anticoagulation. However, four clinical trials comparing rate control with rhythm control have failed to demonstrate these advantages, indicating that rate control should be considered a legitimate primary therapeutic option, particularly in patients at risk for stroke. Pursuit of rate or rhythm control should be decided on a case-by-case basis.

The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study

OBJECTIVES

We sought to evaluate approaches used to control rate, the effectiveness of rate control, and switches from one drug class to another in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study.

BACKGROUND

The AFFIRM study showed that atrial fibrillation (AF) can be treated effectively with rate control and anticoagulation, but drug efficacy to control rate remains uncertain.

METHODS

Patients (n = 2,027) randomized to rate control in the AFFIRM study were given rate-controlling drugs by their treating physicians. Standardized rate-control efficacy criteria developed a priori included resting heart rate and 6-min walk tests and/or ambulatory electrocardiographic results.

RESULTS

Average follow-up was 3.5 +/- 1.3 years. Initial treatment included a beta-adrenergic blocker (beta-blocker) alone in 24%, a calcium channel blocker alone in 17%, digoxin alone in 16%, a beta-blocker and digoxin in 14%, or a calcium channel blocker and digoxin in 14% of patients. Overall rate control was achieved in 70% of patients given beta-blockers as the first drug (with or without digoxin), 54% with calcium channel blockers (with or without digoxin), and 58% with digoxin alone. Adequate overall rate control was achieved in 58% of patients with the first drug or combination. Multivariate analysis revealed an association between first drug class and several clinical variables. There were more changes to beta-blockers than to the other two-drug classes (p < 0.0001).

CONCLUSIONS

Rate control in AF is possible in the majority of patients with AF. Beta-blockers were the most effective drugs. To achieve the goal of adequate rate control in all patients, frequent medication changes and drug combinations were needed.

Antiarrhythmic drugs and cardiac ion channels: mechanisms of action

In this review a description and an analysis are given of the interaction of antiarrhythmic drugs with their molecular target, i.e. ion channels and receptors. Our approach is based on the concept of vulnerable parameter, i.e. the electrophysiological property which plays a crucial role in the genesis of arrhythmias. To prevent or stop the arrhythmia a drug should modify the vulnerable parameter by its action on channel or receptor targets. In the first part, general aspects of the interaction between drugs channel molecules are considered. Drug binding depends on the state of the channel: rested, activated pre-open, activated open, or inactivated state. The change in channel behaviour with state is presented in the framework of the modulated-receptor hypothesis. Not only inhibition but also stimulation can be the result of drug binding. In the second part a detailed and systematic description and an analysis are given of the interaction of drugs with specific channels (Na+, Ca2+, K+, "pacemaker") and non-channel receptors. Emphasis is given to the type of state-dependent block involved (rested, activated and inactivated state block) and the change in channel kinetics. These properties vary and determine the voltage- and frequency-dependence of the change in ionic current. Finally, the question is asked as to whether the available drugs by their action on channels and receptors modify the vulnerable parameter in the desired way to stop or prevent arrhythmias.