Background

The broad selection of cardiac magnetic resonance imaging (MRI) techniques as well as its high reproducibility has positioned MRI as the standard of reference (SOR) in assessment of ventricular size and as a prime choice for myocardial tissue characterization.Effects of predominately systemic but also local cancer therapy regimens on the cardiovascular system are known since early studies and continue to affect overall patient outcome by either the need for cancer regimen changes with potential limitation of treatment efficiency or the development of heart failure with substantially increased morbidity and mortality.Therefore, assessment of patient’s individual risks, serial surveillance during therapy as well as early identification of cardiovascular adverse effects such as cardiotoxicity has become of high importance.In recent years, cardiac MRI has been considered a possible approach in patient populations undergoing cancer therapy with high risks of related cardiovascular effects.

Global and Regional Cardiac Function

The principal application of cardiac MRI relates to the general definition of cardiotoxicity. While various echocardiography-based definitions with minor differences in cut-off values exist (most definitions with >10% threshold), cardiotoxicity is primarily assessed by identification of cancer therapy related cardiac dysfunction (CTRCD). With the need of identifying changes in left ventricular (LV) ejection fraction (EF) of 5-10% temporal variability and consistency of measurements are of outmost importance. Recently published data has shown that cine balanced steady state free precession (bSSFP) techniques demonstrate an absolute temporal variability of ~2.2% (SEM=Standard Error of the Measurement) resulting in a minimum detectable difference (MDD=2xSEM) of 4.4% (2D-Echo 6.5%, 3D Echo 3.7%) (1). The same study has also demonstrated that patients with CTRCD (CREC criteria) demonstrate a substantially higher variability that patients without CTRCD (1).
Myocardial strain assessment, a technique providing a more detailed insight into myocardial mechanics, is not only being considered a clinical add on to volumetric LV assessment in echocardiography but has also pushed the envelope in cardiac MRI. It has been demonstrated that cardiac MRI derived strain measurements also demonstrate a reduction in asymptomatic cancer patients undergoing therapy (2 ). Surprisingly, MRI tagging based longitudinal and circumferential strain values partially demonstrate higher temporal variability then Echo-based strain and no improvement over cardiac MRI based LVEF with respect to interobserver test-retest variability (1). More recent investigations focus on the use of bSSFP based strain derivation and may provide further benefit in assessment of CTRCD.

Tissue Characterization

Assessment of myocardial tissue details has long been a domain of cardiac MRI. Beside qualitative assessment of the myocardium with/without gadolinium-based contrast agents (GBCA), recent quantitative techniques aiming at the assessment of myocardial T1 and T2 as a surrogate for underlying changes in tissue composition have further advanced knowledge in a variety of cardiomyopathies and cardiac diseases. In the assessment of cardiotoxicity, the presence of late gadolinium enhancement (LGE) has been reported in various studies (2). However, the predictive value with respect to early identification and prognosis of improvement in case of CTRDC remains somewhat unknown. In patients with remote cancer therapy the incidence of LGE appears rather low (<10%). The assessment of myocardial T1 and T2 have demonstrated the ability to identify changes related to myocardial edema in controlled animal experiences. In general, T1 and T2 values increased early n animals undergoing chemotherapy and correlated to water content. At later stages, assessment of ECV demonstrated elevation in treated animals corresponding to fibrotic changes (3). In patients undergoing cancer therapy, especially the use of T1 mapping partially demonstrated controversial results. While patients undergoing cancer therapy generally demonstrated increased T1 values while singular studies early (<48h) after completion of a therapy cycle demonstrated lowered T1 values in patients that later developed CTRCD) (4).
Similar to LVEF assessment also temporal variability of T1/T2/ECV measurements is of high importance. Recent data demonstrated that in single patient scenarios the application of such quantitative values may remain problematic (5).
However, cardiac T1 and T2 assessment appear of increased value in the assessment of autoimmune myocarditis, a rare but severe side effect of now more commonly applied ICI cancer therapies.

Conclusion

Cardiac MRI provides a magnitude of techniques that are well suited for assessment of cardiotoxicity and cancer therapy related cardiac dysfunction. However, with respect to daily clinical application it is of high importance to consider test-retest variabilities of various techniques. At present, the assessment of LVEF remains the main approach in MRI. Further studies are required to assess the added value of strain and quantitative tissue parameters in early detection of cardiotoxicity and long-term prediction of patient outcome.

Acknowledgements

No acknowledgement found.