Evaluating the Atrial Myopathy Underlying Atrial Fibrillation: Identifying the Arrhythmogenic and Thrombogenic Substrate

Abstract

Atrial disease or myopathy forms the substrate for atrial fibrillation (AF) and underlies the potential for atrial thrombus formation and subsequent stroke. Current diagnostic approaches in patients with AF focus on identifying clinical predictors with the evaluation of left atrial size by echocardiography serving as the sole measure specifically evaluating the atrium. Although the atrial substrate underlying AF is likely developing for years before the onset of AF, there is no current evaluation to identify the preclinical atrial myopathy. Atrial fibrosis is 1 component of the atrial substrate that has garnered recent attention based on newer MRI techniques that have been applied to visualize atrial fibrosis in humans with prognostic implications regarding the success of treatment. Advanced ECG signal processing, echocardiographic techniques, and MRI imaging of fibrosis and flow provide up-to-date approaches to evaluate the atrial myopathy underlying AF. Although thromboembolic risk is currently defined by clinical scores, their predictive value is mediocre. Evaluation of stasis via imaging and biomarkers associated with thrombogenesis may provide enhanced approaches to assess risk for stroke in patients with AF. Better delineation of the atrial myopathy that serves as the substrate for AF and thromboembolic complications might improve treatment outcomes. Furthermore, better delineation of the pathophysiologic mechanisms underlying the development of the atrial substrate for AF, particularly in its earlier stages, could help identify blood and imaging biomarkers that could be useful to assess risk for developing new-onset AF and suggest specific pathways that could be targeted for prevention.

Keywords: arrhythmias, cardiac; biological markers; cardiovascular imaging agents/techniques; clinical medicine; diagnostic imaging; electrophysiology; stroke.

Figure 1

Schematic of the progression of disease in patients who are developing the substrate for AF.

Figure 2

Multiple noninvasive techniques to evaluate the left atrium in patients with atrial fibrillation.

Figure 3

ECG V1 lead recordings from 4 different patients with AF showing f waves. Although f waves in AF are variable throughout a recording, they are sometimes well-visualized, allowing the variation in their rate and amplitude to be characterized. Differences in f wave rate can be appreciated in some parts of these recordings. In the 1^st and 4^th tracings, the same size box encompasses 3 and 5 F waves, respectively; in the 2^nd and 3^rd tracings, the same size box encompasses 2 and 3 F waves, respectively. Other characteristics differ, as well – F wave amplitude and consistency of activation.