Elsevier

Heart Rhythm

Volume 10, Issue 9, September 2013, Pages 1325-1331
Heart Rhythm

Cardiac magnetic resonance T1 mapping of left atrial myocardium

https://doi.org/10.1016/j.hrthm.2013.05.003Get rights and content

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.

Introduction

Atrial fibrillation (AF) is the most common arrhythmia, affects 1%–1.5% of the population and up to 10% of the elderly,1 and is associated with significant morbidity and mortality.2 Many studies highlight an association between atrial fibrosis and AF.3, 4, 5 Atrial fibrosis, an adaptive response to various insults, is mediated by excessive fibroblast proliferation resulting in the deposition of proteins within the cardiac interstitial space. Surgical biopsy and autopsy specimens from patients with AF have shown increased diffuse atrial fibrosis compared to those in sinus rhythm.6, 7, 8 Innovative studies of late gadolinium enhancement on cardiac magnetic resonance (LGE-CMR) have revealed the presence of focal/cohesive LA fibrosis before and after ablation procedures.5, 9 However, the presence of global/diffuse LA fibrosis has not been noninvasively examined.

Cardiac magnetic resonance (CMR) T1 mapping is a recently introduced technique to quantify contrast-enhanced T1 relaxation time in tissues of interest. It has been shown that an inverse linear relationship exists between contrast-enhanced left ventricular (LV) myocardial T1 time and the burden of global myocardial fibrosis.10, 11 LV T1 mapping has been used to identify reduced T1 times as a surrogate of increased fibrosis in patients with acute and chronic myocardial infarction,12 valvular disease,13 heart failure,10 nonischemic dilated cardiomyopathy,14 and hypertrophic cardiomyopathy.15 However, left atrial (LA) T1 mapping has not been investigated as a potential noninvasive measure of diffuse atrial fibrosis. The purpose of the present study was to (a) establish the feasibility of LA T1 measurements, (b) determine the range of LA T1 values in patients with AF vs healthy volunteers, and (c) validate T1 mapping vs global LA intracardiac electrogram amplitude measures as a surrogate of diffuse atrial fibrosis.

Section snippets

Patients with AF

The study protocol was reviewed and approved by the Johns Hopkins Institutional Review Board. We recruited patients referred for pulmonary vein antral isolation (PVAI) for the treatment of symptomatic AF from January 2011 to April 2012. During the course of the study, CMR was performed in 57 patients before AF ablation. We excluded 6 patients with AF from this study because of respiratory motion artifacts on CMR images. Therefore, data from 51 patients (74% man; median age 55 [interquartile

Results

Of 51 patients that underwent PVAI for the treatment of AF, 27 were undergoing their first ablation. Of all patients, AF type was paroxysmal in 20, persistent in 24, and long-standing persistent in 7 patients. Of these patients, 18 had lone AF. Table 1 summarizes baseline characteristics for the patients and healthy volunteers.

Discussion

CMR T1 mapping is a relatively new method, in which lower T1 times associate with higher degrees of myocardial fibrosis.10, 11, 12, 13, 14, 15, 19 The main finding of the present study is that CMR LA T1 mapping for noninvasive tissue characterization of the LA wall is feasible. LA T1 relaxation times were significantly lower in patients with AF vs healthy volunteers. LA T1 times were also lower in patients with AF with prior ablations vs patients with AF without prior intervention, suggesting

Conclusions

CMR T1 mapping of the LA myocardium is feasible and may be used to quantify fibrotic changes in the LA wall. Lower average LA T1 times, suggesting increased LA fibrosis, were observed in patients with AF and with increasing ablation attempts. Lower LA T1 relaxation times were also associated with lower bipolar LA voltage measurement as a method to validate our findings. LA T1 mapping may provide utility for AF management.

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      Tissue characterization using cMRF could be used to detect abnormalities in the left atrial wall associated with atrial fibrillation, HFpEF, and diastolic dysfunction. In patients with atrial fibrillation, myocardial T1 has been reported to be shorter than in healthy subjects, and lower T1 was associated with lower intracardiac bipolar left atrium voltage [93]. In HFpEF and patients exhibiting diastolic dysfunction, an enlarged left atrium and impaired function have been observed by CMR with larger volumes and worse function having poorer prognosis [94].

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    The study was funded by National Institutes of Health grant K23HL089333 (to Dr Nazarian) and by the Dr Francis P. Chiaramonte Foundation and the Norbert and Louise Grunwald Cardiac Arrhythmia Research Fund.

    Dr Nazarian is on the MRI Advisory Panel (unpaid) for Medtronic and is a scientific advisor to Biosense Webster; he is also the principal investigator for research funding awarded to Johns Hopkins from Biosense Webster and from the National Institutes of Health (K23HL089333). Dr van der Geest is a consultant to Medis Medical Imaging Systems.

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