Cardiac magnetic resonance left atrial volumes and function to predict appropriate device therapy and death

Abstract

Sudden cardiac death (SCD) remains an important cause of mortality worldwide. Several landmark trials [1–3] have shaped current guidelines [4, 5] to recommend the implantation of implantable cardioverter defibrillator (ICD) in patients with reduced left ventricular ejection fraction (LVEF) < 35% for primary prevention. However, LVEF being the sole determinant of guiding ICD implantation has proven to be inadequate in multiple subsequent studies. Studies have shown the majority of patients experiencing SCD have LVEF > 35% [6, 7], and a high proportion of patients implanted with ICDs do not receive an ICD shock even before death [8]. In terms of patient outcomes, the 2016 DANISH trial [9] showed that prophylactic ICD implantation in patients with symptomatic non-ischaemic heart failure and LVEF < 35% was not associated with a significant reduction in mortality. Thus the search for additional parameters to LVEF to better guide ICD placement is ongoing. In recent years, cardiac magnetic resonance (CMR) has been established as the gold standard for left ventricular volume and systolic function due to its high reproducibility amongst observers and lack of geometric assumptions in volume and LVEF quantification [10]. Therefore, CMR quantification of left atrial size/volume and left atrial emptying fraction is regarded as an accurate tool for left atrial size and function assessment. Previous CMR studies have demonstrated associations between left atrial size/ function with atrial arrhythmias, impaired LV diastolic function, abnormal left ventricular filling pressures and adverse cardiovascular outcomes [11, 12]. In two CMR studies performed by Rijnierse et al. [13] and Lydell et al. [14], left atrial ejection fraction (LAEF) were both shown to be predictive of appropriate device therapy for ventricular arrhythmia with or without sudden cardiac death. However, both papers had relatively small numbers of primary end-points (ie. 62 and 35 end-points respectively). Furthermore, both papers did not have multivariable Cox regression models that incorporated LVEF. In Rijnierse et al.’s [13] paper, one of the multivariable models included LGE with both LAEF and LGE remaining statistically significant. Therefore, there is a lack of clarity whether LA volume and function replaces or is additive in value to LVEF and LGE as independent determinants of ventricular arrhythmias following ICD implantation. This issue has been partly addressed by Gong et al. [15]. The authors conducted a retrospective, multi-centre observational cohort study of 392 patients with ischaemic and non-ischaemic cardiomyopathy who underwent CMR prior to primary or secondary prevention ICD implantation. The primary outcome was a composite of independently adjudicated appropriate ICD shock or all-cause death. During a median follow-up time of 61 months, 140 (35.7%) experienced an appropriate ICD shock or death. Higher maximum LA volume index (maxLAVi), higher minimum LA volume index (minLAVi), and lower LAEF were associated with greater risk of appropriate ICD shock or death in univariate analysis. However, in multivariable analysis, LAEF and maxLAVi were not independent predictors of the primary outcome. The apparent differences in concluding the usefulness of LA volume and function to predict appropriate ICD shock or mortality of this study in contrast to the previously mentioned publications might stem from three intrinsic differences. Firstly, all three studies [13–15] agree that LAEF * Ming-Yen Ng [email protected]