Proximity to the descending aorta predicts regional fibrosis in the adjacent left atrial wall: aetiopathogenic and prognostic implications.

AIMS: Left atrial (LA) fibrosis is present in patients with atrial fibrillation (AF) and can be visualized by magnetic resonance imaging with late gadolinium enhancement (LGE-MRI). Previous studies have shown that LA fibrosis is not randomly distributed, being more frequent in the area adjacent to the descending aorta (DAo). The objective of this study is to analyse the relationship between fibrosis in the atrial area adjacent to the DAo and the distance to it, as well as the prognostic implications of this fibrosis. METHODS AND RESULTS: Magnetic resonance imaging with late gadolinium enhancement was obtained in 108 patients before AF ablation to analyse the extent of LA fibrosis and the distance DAo-to-LA. A high-density electroanatomic map was performed in a subgroup of 16 patients to exclude the possibility of an MRI artifact. Recurrences after ablation were analysed at 1 year of follow-up. The extent of atrial fibrosis in the area adjacent to the DAo was inversely correlated with the distance DAo-to-LA (r = -0.34, P < 0.001). This area had the greatest intensity of LGE [image intensity ratio (IIR) 1.14 ± 0.15 vs. 0.99 ± 0.16; P < 0.001] and also the lowest voltage (1.07 ± 0.86 vs. 1.54 ± 1.07 mV; P < 0.001) and conduction velocity (0.65 ± 0.06 vs. 0.96 ± 0.57 mm/ms; P < 0.001). The extent of this regional fibrosis predicted recurrence after AF ablation [hazard ratio (HR) 1.02, 95% CI 1.01-1.03; P = 0.01], however total fibrosis did not (HR = 1.01, 95% CI 0.97-1.06, P = 0.54). CONCLUSIONS: Atrial fibrosis was predominantly located in the area adjacent to the DAo, and increased with the proximity between the two structures. Furthermore, this regional fibrosis better predicted recurrence after AF ablation than total atrial fibrosis.

Left atrial fibrosis quantification by late gadolinium-enhanced magnetic resonance: a new method to standardize the thresholds for reproducibility.

AIMS: Identification of left atrial (LA) fibrosis through late gadolinium-enhanced cardiac magnetic resonance (LGE-CMR) remains controversial due to the heterogeneity and lack of reproducibility of proposed methods. Our aim is to describe a normalized, reproducible, standardized method to evaluate LA fibrosis through LGE-CMR. METHODS AND RESULTS: Electrocardiogram- and respiratory-gated 3-Tesla LGE-CMR was performed in 10 healthy young volunteers and 30 patients with atrial fibrillation (AF): 10 with paroxysmal AF, 10 with persistent AF, and 10 with a previous AF ablation procedure. Local image intensity ratio (IIR) of the LA was calculated as the absolute pixel intensity to mean blood pool intensity ratio. The healthy atrial tissue threshold was defined in young healthy volunteers (upper limit of normality set at IIR tissue mean plus 2 SDs). Dense atrial scarring was characterized in patients with previous radiofrequency-induced scarring (post-AF ablation patients). Validation groups consisted of patients with paroxysmal and persistent AFs. The upper limit of normal IIR was 1.20; IIR values higher than 1.32 (60% of mean maximum pixel intensity in post-ablation patients) were considered dense scar. Image intensity ratio values between 1.2 and 1.32 identified interstitial fibrosis. Patients with paroxysmal and persistent AFs had less atrial fibrotic tissue compared with post-ablation patients. Endocardial bipolar voltage was correlated to IIR values. CONCLUSIONS: An IIR of 1.2 identifies the upper limit of normality in healthy young individuals. An IIR of >1.32 defines dense atrial fibrosis in post-ablation patients. Our results provide a consistent, comparable, and normalized tool to assess atrial arrhythmogenic substrate.

Analysis of temporal delay in myocardial deformation throughout the cardiac cycle: utility for selecting candidates for cardiac resynchronization therapy.

BACKGROUND: Analysis of myocardial strain using two-dimensional (2D) echocardiography to assess left ventricular (LV) mechanical dyssynchrony by measuring time differences in peak systolic strains from opposing LV walls has been proposed. However, peak systolic strain may be difficult to identify. OBJECTIVE: The purpose of this study was to evaluate (1) LV dyssynchrony by assessing the overlap among strain traces of the LV walls throughout the cardiac cycle and (2) its usefulness in identifying responders to cardiac resynchronization therapy (CRT). METHODS: Fifty patients with heart failure and LV systolic dysfunction undergoing CRT were studied with 2D echocardiography at baseline and 6-month follow-up. Myocardial radial strain and circumferential strain were analyzed using commercially available software. The resulting strain traces were postprocessed with a mathematical script. RESULTS: Quantification of LV dyssynchrony was expressed as an index of temporal overlap from the analyzed traces. Responders to CRT were defined by ≥15% reduction of LV end-systolic volume at 6-month follow-up. Responders to CRT had higher LV dyssynchrony in both radial strain and circumferential strain analysis. A cutoff time overlap ≥7% for radial strain (area under the curve 0.79) and ≥8.5% for circumferential strain (area under the curve 0.66) identified responders to CRT. CONCLUSION: Quantifying the temporal superposition of LV wall deformations with a computed algorithm allows measurement of LV intraventricular dyssynchrony throughout the cardiac cycle. The derived index is useful in stratifying the probability of response to CRT.