Editorial for “Cardiac MRI Reveals Late Diastolic Changes in Left Ventricular Relaxation Patterns During Healthy Aging”

Most cardiac studies focus on evaluating systolic left ventricular (LV) function. However, the assessment of diastolic cardiac function is becoming more appreciated, especially with an increasing prevalence of pathologies associated with diastolic dysfunction like heart failure with preserved ejection fraction (HFpEF). In HFpEF, the myocardium loses its relaxing capacity, making it incapable of achieving adequate intracavitary filling time, which leads to changes in diastolic cardiac function despite normal systolic function. In this context, cardiac magnetic resonance imaging (MRI) has the capability for differentiating between normal and abnormal myocardial relaxation patterns, and therefore offers the prospect of early detection of diastolic dysfunction. Although diastolic cardiac function can be assessed from the ratio between early and atrial filling peaks (E/A ratio), measuring different parameters of heart contractility during diastole would allow for evaluating spatial and temporal patterns of cardiac function with potential for illustrating subtle changes related to age, gender, or other differences among healthy subjects. For example, cardiac MRI revealed that early diastole is characterized by a release of torsion and shear strain in addition to radial thinning before the aortic valve closure, which results in rapid reduction of the LV pressure. Isovolumetric relaxation then follows, which is associated with changes in principal strains and untwisting that result in expansion of the LV myocardium. However, little information is available about heart mechanics at late diastole. MRI tagging is the gold standard for measuring regional cardiac function and myocardial contractility. Although the value of standard MRI tagging has been established for systolic function analysis, little has been reported about the value of MRI tagging for evaluating diastolic cardiac function, especially at late diastole. This could be partially attributed to fading of the taglines toward the end of the cardiac cycle due to longitudinal magnetization relaxation. While this limitation can be avoided, for example, by implementing a ramped flip angle data acquisition scheme, using complementary spatial modulation of magnetization (CSPAMM) tagging, using techniques that encode tissue deformation information in the received signal phase, as in myocardial tissue phase mapping, or imaging at a higher magnetic field. However, these approaches are mainly used for research purposes, with limited availability for clinical use. The recent development of MRI feature-tracking techniques enabled access to information about heart contractility from standard cine images, which are acquired in almost every cardiac MRI exam. Not only do these cine-based techniques allow access to regional cardiac function information without the need for using specialized imaging sequences, they also allow for evaluating cardiac function during late diastole, as these techniques do not suffer from the taglines fading problem. Although the lack of intramyocardial markers in the cine images imposes a limitation on the capabilities of these techniques compared to standard MRI tagging, several studies showed promising results from feature-tracking analysis with good agreement with tagging results. In the article “Cardiac MRI reveals late diastolic changes in left ventricular relaxation patterns during healthy aging,” Lin et al show an important application of cine-based myocardial motion analysis for evaluating changes in diastolic cardiac function with age in subjects free from cardiovascular diseases. As cine images can be analyzed throughout the whole cardiac cycle, the authors were able to generate measures of heart mechanics at both early and late diastolic phases. Specifically, myocardial tissue displacement, velocity, strain, and strain rate parameters were measured in both the circumferential and radial directions during early and late diastole. A key finding from this study was that all measurements, except for strain, showed a double-peak (bimodal) diastolic pattern, similar to the early and atrial filling peaks. The results showed that older participants (75–84 years old) had significantly lower early radial displacement, radial velocity, and circumferential strain rate, but higher late circumferential strain rate compared to the younger participants (65–74 years old), despite insignificant differences in LV ejection fraction between the two groups. These results suggest a reduced LV compliance with aging, where opposite effects on early and late diastolic relaxation patterns were observed in the two studied groups. The observed stronger active LV relaxation at late diastole (atrial kick) in the older participants could be