Atrial fibrillation: mechanistic insights and treatment options.

Atrial fibrillation (AF) remains the most common clinically encountered arrhythmia. Unlike supraventricular arrhythmias that use a defined mechanism, AF involves a wide spectrum of arrhythmias from lone AF to paroxysmal to chronic AF. AF is an arrhythmia that may develop in several ways. Mechanical remodeling manifests as decreased atrial contractility and increased atrial compliance which leads to a stretch of the atrial myocardium. Atrial remodeling may also increase in atrial fibrosis which can slow conduction velocity and can shorten the refractory period in atria with long-standing AF. It is still unclear whether initiation of AF activates direct inflammatory effects or whether the presence of a pre-existing systemic inflammatory state promotes further persistence of AF. Currently, the patient population undergoing AF ablation has greatly expanded. Patients are older and have larger left atrial size and are more likely to have persistent/permanent AF. It is likely that AF comprises a spectrum of disease with no single mechanism adequate enough to comprehensively explain AF and its variability. The management of patients with AF involves elements of anticoagulation, rate control and rhythm control and such treatment strategies are not necessarily mutually exclusive of each other.

Mitral annular remodeling with varying degrees and mechanisms of chronic mitral regurgitation.

HYPOTHESES: Degree of mitral annular remodeling is directly associated with severity of chronic mitral regurgitation (MR). Mitral annular remodeling occurs in a symmetric fashion, regardless of MR severity. In addition to MR severity, MR mechanism plays a significant role in mitral annular remodeling. BACKGROUND: Limited data exists on mitral annular remodeling in patients with MR. Identification of annular changes may be important in aiding surgical repair. METHODS: Mitral annular dimensions (anteroposterior, intercommissural, surface area, and circumference) were measured in end systole and diastole using 3-dimensional reconstructive software in 83 patients: trace to no MR (23), mild MR (15), moderate MR (26), and severe MR (19). Annular sphericity indices were determined by dividing intercommissural by anteroposterior dimensions. Patients were further subgrouped by mechanism of MR. RESULTS: With increasing MR severity, there was a corresponding increase in all annular measurements, most pronounced in the anteroposterior dimension, circumference, and area. Larger increases were seen in patients with prolapse/flail and dilated mechanisms. Furthermore, the mitral annulus became more circular (sphericity index approached 1.0) with increasing MR severity. Patients with prolapse/flail mechanisms exhibited normal left ventricular volumes despite significant annular enlargement. CONCLUSIONS: Mitral annular remodeling is directly associated with MR severity and occurs in an asymmetric fashion, yet is not limited to one region of the annulus. Mechanism of MR plays a significant role in annular remodeling. Annular remodeling can occur independently of left ventricular remodeling.

Relationship of mitral annular remodeling to severity of chronic mitral regurgitation.

HYPOTHESES: (1) Mitral regurgitation (MR) severity is directly associated with mitral annular remodeling as evidenced by mitral annular enlargement. (2) Increasing severity of chronic MR will result in symmetric enlargement of the mitral annulus as measured by annular shape indices. BACKGROUND: Limited data exist on mitral annular remodeling for patients with MR. Identification of annular changes may be important in aiding surgical repair. METHODS: The mitral annulus was measured in several planes using transthoracic echocardiography in 173 patients: trace to no MR (34), mild MR (48), moderate MR (45), and severe MR (46). Patients were subgrouped by mechanism of MR and annular shape indices were determined. RESULTS: With increasing MR severity, there was a corresponding symmetric increase in all systolic and diastolic measurements, but no significant differences in annular shape indices between subgroups by MR severity or by MR mechanism. CONCLUSIONS: Mitral annular remodeling is symmetric, regardless of degree or mechanism of MR.