Atrial Fibrillation Overview
The current estimate of the prevalence of atrial fibrillation (AF) in the developed world is approximately 1.5–2% of the general population, with the average age of patients with this condition steadily rising, such that it now averages between 75 and 85 years. The arrhythmia is associated with a five-fold risk of stroke and a three-fold incidence of congestive heart failure, and higher mortality. Hospitalization of patients with AF is also very common. This arrhythmia is a major cardiovascular challenge in modern society and its medical, social and economic aspects are all set to worsen over the coming decades. Fortunately, a number of valuable treatments have been devised in recent years that may offer some solution to this problem. (1)
Classification
The clinician should distinguish a first-detected episode of AF, whether or not symptomatic or self-limited, recognizing the uncertainty about the actual duration of the episode and about previous undetected episodes. After 2 or more episodes, AF is considered recurrent. If the arrhythmia terminates spontaneously, recurrent AF is designated paroxysmal; when sustained beyond 7 d, it is termed persistent. Termination with pharmacological therapy or direct-current cardioversion does not alter the designation. First-detected AF may be either paroxysmal or persistent. The category of persistent AF also includes cases of long-standing AF (e.g., longer than 1 y), usually leading to permanent AF, in which cardioversion has failed or has been foregone. (2)
From: AHA-ACC-HRS Guideline 2014 for AF page 2253
Prompt restoration of sinus rhythm once AF occurs should rapidly restore physiologic hemodynamics, avoid atrial remodeling that favor the maintenance of AF to reduce arrhythmia recurrence, and minimize the risk of stroke.(3)
Principles of management (4)
The management of AF still represents one of the major therapeutic challenges in medicine. Based on current evidence and guidelines, there are four main principles:
1. Restoration of sinus rhythm by pharmacological or electrical means.
2. Control of ventricular rate during paroxysmal or persistent AF, and chronically in those with permanent AF.
3. Prevention of recurrence of paroxysmal or persistent AF following successful restoration of sinus rhythm.
4. Prevention of thromboembolic phenomena.
When a patient is seen in the emergency setting, the main priority is to control the fast ventricular response and, depending on the haemodynamic status of patient, this can be achieved either by urgently restoring sinus rhythm or by controlling the ventricular rate. Immediate electrical cardioversion is indicated in patients with a rapid ventricular rate who are either haemodynamically unstable or have evidence of acute myocardial ischaemia or heart failure that do not respond promptly to pharmacological measures. In less acute situations, pharmacological cardioversion can be attempted, thereby avoiding the requirement for general anaesthesia.
ATRIAL REMODELING MAY LEAD TO PERSISTENCE OF AF (5)
Atrial remodeling: Any persistent change in atrial structure or function (6)
TIME COURSE OF ATRIAL REMODELING (5)
ATRIAL REMODELING MAY CONTRIBUTE TO: (5)
ELECTRICAL REMODELING
- Loss of physiologic rate dependence
- Shortening of atrial refractory period
CONTRACTILE REMODELING
- Loss of contractility, which may lead to thrombus formation
- Atrial dilation, which can help propagate AF
STRUCTURAL REMODELING
- Structural changes likely to perpetuate AF
- Atrial dilation, which can help propagate AF
Prompt return to sinus rhythm may be an important factor for avoiding atrial remodeling
Atrial Fibrillation Treatment (2)
A. Strategic Objectives
Management of patients with AF involves 3 objectives—rate control, prevention of thromboembolism, and correction of the rhythm disturbance—and these are not mutually exclusive. The initial management decision involves primarily a rate control or rhythm control strategy. Under the rate control strategy, the ventricular rate is controlled with no commitment to restore or maintain sinus rhythm. The rhythm control strategy attempts restoration and/or maintenance of sinus rhythm. The latter strategy also requires attention to rate control. Depending on the patient’s course, the strategy initially chosen may prove unsuccessful and the alternate strategy is then adopted. Regardless of whether the rate control or rhythm control strategy is pursued, attention must also be directed to antithrombotic therapy for prevention of thromboembolism.
B. Pharmacological and Nonpharmacological Treatment Options
Drugs and ablation are effective for both rate and rhythm control, and in special circumstances surgery may be the preferred option. Regardless of the approach, the need for anticoagulation is based on stroke risk and not on whether sinus rhythm is maintained. For rhythm control, drugs are typically the first choice and LA ablation is a second-line choice, especially in patients with symptomatic lone AF. In some patients, especially young persons with very symptomatic AF who need sinus rhythm, radiofrequency ablation may be preferred over years of drug therapy. Patients with preoperative AF undergoing cardiac surgery face a unique opportunity. While few are candidates for a stand-alone surgical procedure to cure AF using the maze or LA ablation techniques, these approaches can be an effective adjunct to coronary bypass or valve repair surgery to prevent recurrent postoperative AF. Because the LAA is the site of greater than 95% of detected thrombi, this structure is commonly removed from the circulation during cardiac surgery in patients at risk of developing postoperative AF, although this has not been proved to prevent stroke.