Cardiac magnetic resonance T1 mapping of left atrial myocardium

Abstract

Background: Cardiac magnetic resonance (CMR) T1 mapping is an emerging tool for objective quantification of myocardial fibrosis.

Objectives: To (a) establish the feasibility of left atrial (LA) T1 measurements, (b) determine the range of LA T1 values in patients with atrial fibrillation (AF) vs healthy volunteers, and (c) validate T1 mapping vs LA intracardiac electrogram voltage amplitude measures.

Methods: CMR imaging at 1.5 T was performed in 51 consecutive patients before AF ablation and in 16 healthy volunteers. T1 measurements were obtained from the posterior LA myocardium by using the modified Look-Locker inversion-recovery sequence. Given the established association of reduced electrogram amplitude with fibrosis, intracardiac point-by-point bipolar LA voltage measures were recorded for the validation of T1 measurements.

Results: The median LA T1 relaxation time was shorter in patients with AF (387 [interquartile range 364-428] ms) compared to healthy volunteers (459 [interquartile range 418-532] ms; P < .001) and was shorter in patients with AF with prior ablation compared to patients without prior ablation (P = .035). In a generalized estimating equations model, adjusting for data clusters per participant, age, rhythm during CMR, prior ablation, AF type, hypertension, and diabetes, each 100-ms increase in T1 relaxation time was associated with 0.1 mV increase in intracardiac bipolar LA voltage (P = .025).

Conclusions: Measurement of the LA myocardium T1 relaxation time is feasible and strongly associated with invasive voltage measures. This methodology may improve the quantification of fibrotic changes in thin-walled myocardial tissues.

Keywords: AF; Atrial fibrillation; CI; CMR; Cardiac magnetic resonance; GEE; IQR; LA; LGE-CMR; LV; Late gadolinium enhancement; Left atrial fibrosis; PVAI; ROI; T1 mapping; atrial fibrillation; cardiac magnetic resonance; confidence interval; generalized estimating equation; interquartile range; late gadolinium enhancement on cardiac magnetic resonance; left atrial; left ventricular; pulmonary vein antral isolation; region of interest.

Figure 1

Methodology for the measurement of left atrial T1 relaxation time. The cardiac magnetic resonance image was acquired by using a vertical long-axis modified Look-Locker inversion-recovery sequence. The region of interest (yellow circle) has been placed on the posterior LA wall. LA = left atrial; LV = left ventricular.

Figure 2

Distribution of T1 relaxation time among patients with AF and healthy volunteers. The scatter and box plot overlay diagram displays the postcontrast myocardial T1 times in healthy volunteers and patients with AF. The box plots display the median and the 25th–75th percentile range (center white line and solid black box), the lower and upper adjacent values (thin lines), and data points (dots). AF = atrial fibrillation; LA = left atrial.

Figure 3

Association between left atrial and left ventricular T1 relaxation times. The scatter diagram and line of best fit display the association between LA and LV postcontrast T1 relaxations times. LA = left atrial; LV = left ventricular.

Figure 4

LA T1 relaxation curve examples and the corresponding left atrial bipolar electrogram voltage amplitude maps. Examples of LA T1 relaxation curves (left panels) and the corresponding electroanatomic bipolar electrogram voltage amplitude map as a surrogate of atrial fibrosis (posteroanterior views): (A) 52-year-old man with history of hypertension, diabetes, and persistent AF without prior ablation; (B) 73-year-old woman with history of coronary artery disease, persistent AF, and prior ablation. In the electroanatomic map, the color code represents voltage amplitude, with red corresponding to amplitude <0.1 mV indicative of atrial fibrosis and purple to healthy regions with amplitude >0.5 mV. AF = atrial fibrillation; LA = left atrial.