Image Intensity Ratio, a Novel Magnetic Resonance-Based Measure for Quantification of Left Atrial Fibrosis, Correlates with the Distribution of Atrial Bipolar Voltage

Abstract

Background Recurrence of atrial fibrillation (AF) after catheter ablation has been associated with left atrial (LA) fibrosis. However, arbitrary units of measure limit the interpatient comparison of delayed enhancement intensity. We sought to quantify LA fibrosis using a novel normalized measure: the image intensity ratio (IIR) of late-gadolinium enhanced magnetic resonance imaging (LGE-MRI). Methods LGE-MRI images (1.5 Tesla) were obtained in 30 patients (37% female, mean age 62 ± 8) prior to first (60%), second (23%), or third (17%) ablation procedure for AF. Multiplanar reformatted images were reconstructed from the stack of 3-D axial image data. Epicardial and endocardial contours were manually drawn around LA myocardium. The IIR, defined as local LA myocardial signal intensity divided by the mean LA blood pool image intensity, was measured for each of 20 sectors created on contiguous axial planes through the LA. Electroanatomic map (EAM) points were registered to the corresponding LGE-MRI images using custom software. Results A total of 2569 EAM points were analyzed. The average bipolar voltage was 0.9 ± 1.0 mV (0.5 between and 0.9 within patient standard deviation). Local IIR was strongly associated with bipolar voltage (Figure, P <.001). Using a generalized estimating equations model clustered by patient and adjusting for age, LA volume, rhythm, gender, CHADS score, and type of AF, each unit increase in local IIR was associated with –1.4 mV decrease in bipolar LA voltage (P <.001). Conclusions Higher IIR values were observed in areas with lower bipolar voltage on EAM. The IIR obtained from LGE-MRI may improve the quantification of LA fibrosis Recurrence of atrial fibrillation (AF) after catheter ablation has been associated with left atrial (LA) fibrosis. However, arbitrary units of measure limit the interpatient comparison of delayed enhancement intensity. We sought to quantify LA fibrosis using a novel normalized measure: the image intensity ratio (IIR) of late-gadolinium enhanced magnetic resonance imaging (LGE-MRI). LGE-MRI images (1.5 Tesla) were obtained in 30 patients (37% female, mean age 62 ± 8) prior to first (60%), second (23%), or third (17%) ablation procedure for AF. Multiplanar reformatted images were reconstructed from the stack of 3-D axial image data. Epicardial and endocardial contours were manually drawn around LA myocardium. The IIR, defined as local LA myocardial signal intensity divided by the mean LA blood pool image intensity, was measured for each of 20 sectors created on contiguous axial planes through the LA. Electroanatomic map (EAM) points were registered to the corresponding LGE-MRI images using custom software. A total of 2569 EAM points were analyzed. The average bipolar voltage was 0.9 ± 1.0 mV (0.5 between and 0.9 within patient standard deviation). Local IIR was strongly associated with bipolar voltage (Figure, P <.001). Using a generalized estimating equations model clustered by patient and adjusting for age, LA volume, rhythm, gender, CHADS score, and type of AF, each unit increase in local IIR was associated with –1.4 mV decrease in bipolar LA voltage (P <.001). Higher IIR values were observed in areas with lower bipolar voltage on EAM. The IIR obtained from LGE-MRI may improve the quantification of LA fibrosis