Imaging in the field of cardiac resynchronization therapy: a real additive value?

Keywords:

• Heart failure
• cardiac resynchronization
• right ventricle
• echocardiography
• prognosis

Current guidelines on cardiac resynchronization therapy (CRT) justify the use of cardiac imaging only to estimate left ventricular ejection fraction (LV EF)1. Despite this, from the beginning of the successful story of CRT, several attempts have been made to demonstrate the value of cardiac imaging in the field of LV-dyssynchrony2. Unfortunately, the results have often been inconsistent.

The results of recent studies using simple qualitative approaches or semi-automatic quantitative techniques to assess LV dyssynchrony and CRT response are encouraging3–5. Nevertheless, their utility has not yet been validated in large multicentre studies. As a result, there is no reason to justify any change in the current guidelines. Larges studies, in the field of -echocardiography but also magnetic resonance imaging and their combination, are required.

In addition to the assessment of mechanical dyssynchrony (still complicated and without any consensus), imaging might play a pivotal role in the evaluation of cardiac anatomy and function. Even if this role for cardiac imaging modality in CRT is not recognized by the current guidelines, the predictive value of LV size6, or of the left atrial function and size7 in CRT populations have been demonstrated.

The estimation of right ventricular (RV) performance is of growing importance in the field of CRT. This is attributable to the close inter-relationship between the right (RV) and the left ventricle (LV) and to the impact of RV dysfunction on LV dyssynchrony and function8. This is especially obvious in patients undergoing LV-assisted device implantation, but it is much less evident in the field of CRT.

Recent studies have shown that RV function is an independent predictor of long-term outcome following CRT9,10. Interestingly, in patients with biventricular failure, the improvement in RV function after CRT is independent of the improvement in LV systolic performance but significantly associated with the improvement in LV-diastolic function. Also, in the CARE-HF trial, RV dysfunction assessed by the tricuspid annular plan systolic excursion (TAPSE) did not diminish the prognostic benefits of CRT.

As well summarized by Helsen et al.11, the main explanation for these somehow conflicting findings, is that in the past, the quantification of RV function was too simplistic and mainly based on a single parameter like TAPSE. The quantification of RV function should not be limited to the base-to-apex displacement of the tricuspid annulus, which is influenced by many parameters including the degree of tricuspid regurgitation and loading conditions. The RV is a complex chamber, heavily influenced by pre-load and after-load12. Less load-dependent parameters of function like isovolumic acceleration (IVA), RV strain13,14, and a specific attention at RV geometry, are probably data that will have to be looked at in the future to try to solve the issue15.

SHOULD THE IMPLANTATION OF A CRT DEVICE IN PATIENTS WITH A SICK RV BE DISCOURAGED?

Probably not, up to a certain point. Other factors should probably be considered like the class of indication according to the ECG, but also parameters like the gender, the aetiology of the cardiomyopathy, the renal function, the importance of signs and symptoms of right heart decompensation. Anyway, the presence of an excessive dilatation of the right atria and of the RV, often associated with significant tricuspid regurgitation probably will not impact favourably the outcome after CRT. So far, however, there is no objective reason to not implant these patients according to the guidelines.

The paper by Helsen et al.11 in this issue is in line with some previous studies9,10. The authors demonstrated that RV systolic function might improve during CRT. This seems mainly due to changed left-sided haemodynamics and LV remodelling. Unfortunately, the authors looked at the RV using the fractional area change and did not use a complex multi-parametric approach as suggested in the recommendations15. Also, do we have strong data for reporting an improvement in diastolic function in patients treated with CRT? This remains a partially unresolved issue in our understanding of the benefits of CRT. Nevertheless, a good RV systolic function is independently related to a better outcome. In a way, Helsen et al.11 encourage a multi-parametric approach to predict CRT response in patients with LV systolic heart failure. Noteworthy, besides septal flash and apical rocking, the degree of RV systolic dysfunction emerged as a good predictor of CRT response.

This is a valuable message: guidelines do not recognize the role of imaging techniques in the field of CRT, but increasing evidence is accumulating demonstrating that the LV assessment of mechanical dyssynchrony, quantification of cardiac cavities size and function should probably be considered for an optimal prediction of CRT response16. We are awaiting with great impatience large multicentre studies designed to convince the people writing the guidelines.

CONFLICT OF INTEREST

none.