Newer Echocardiographic Techniques in Cardiac Resynchronization Therapy

Contractile asymmetry and survival in patients with left bundle branch abnormality treated with cardiac resynchronization therapy

Aims

Currently, electrical rather than mechanical parameters of delayed left ventricular (LV) activation are used for patient selection for cardiac resynchronization therapy (CRT). However, despite adhering to current guideline-based criteria, about one-third of heart failure (HF) patients fail to derive benefit from CRT. This study sought to investigate the prognostic survival significance of a recently introduced index of contractile asymmetry (ICA) based on the deformation of entire opposing LV walls in the context of selecting patients with HF and left bundle branch abnormality (LBBB) for CRT.

Methods and results

We analysed 367 patients with HF and LBBB undergoing CRT (31.6% females, 69 ± 9 years, ischaemic aetiology in 50.7%, LV ejection fraction 27 ± 6%). ICA was calculated using LV strain rate values from curved anatomical M-mode plots of apical 2D echocardiography images. The predictive value of ICA was assessed using Kaplan-Meier analysis and Cox proportional hazards models. During a median follow-up time of 5.54 years, death or cardiac transplantation occurred in 105 (28.6%) cases. Higher baseline ICA values in all apical views, particularly in the two-chamber view (ICA-2ch), were associated with increased event-free survival, and the unadjusted hazard ratio was 0.28 (95% confidence interval 0.18-0.46). Higher ICA-2ch (>0.319 s-1) consistently predicted survival across clinical subgroups and remained significant after covariate adjustment, while the event rate sharply increased in low ICA-2ch cases. Additionally, including ICA-2ch improved the predictive value of the multivariate risk model containing the typical LBBB pattern.

Conclusion

Pre-implant ICA suggests a quantitative prognostic threshold for both long-term survival and adverse outcomes following CRT implantation.

Evolving concept of dyssynchrony and its utility

The role of electromechanical dyssynchrony in heart failure gained prominence in literature with the results of trials of cardiac resynchronization therapy (CRT). CRT has shown to significantly decrease heart failure hospitalization and mortality in heart failure patients with dyssynchrony. Current guidelines recommend the use of electrical dyssynchrony based on a QRS > 150 ms and a left bundle branch block pattern on surface electrocardiogram to identify dyssynchrony in patients who will benefit from CRT implantation. However, predicting response to CRT remains a challenge with nearly one-third of patients gaining no benefit from the device. Multiple echocardiographic measures of mechanical dyssynchrony have been studied over the past two decade. However, trials where mechanical dyssynchrony used as an additional or lone criteria for CRT failed to show any benefit in the response to CRT. This shows that a deeper understanding of cardiac mechanics should be applied in the assessment of dyssynchrony. This review discusses the evolving role of imaging techniques in assessing cardiac dyssynchrony and their application in patients considered for device therapy.

Cardiac Imaging for Risk Assessment of Malignant Ventricular Arrhythmias in Patients With Mitral Valve Prolapse

Recent studies have described the occurrence of complex ventricular arrhythmias and sudden cardiac death among patients with mitral valve prolapse (MVP). The reported incidence rate of sudden cardiac death or ventricular tachycardia is about 1–1.5% among patients with MVP. Various imaging markers have been associated with this increased risk, including mitral annular disjunction, replacement fibrosis by late gadolinium enhancement, and mechanical dispersion. In this review, we briefly discuss how multimodality cardiac imaging can be applied to identify MVP patients with high risk of sudden cardiac death and complex ventricular arrhythmias.

Index of contractile asymmetry improves patient selection for CRT: a proof-of-concept study

BACKGROUND

Nearly one-third of heart failure (HF) patients do not respond to cardiac resynchronization therapy (CRT) despite having left bundle branch block (LBBB). The aim of the study was to investigate a novel method of quantifying left ventricular (LV) contractile asymmetry in HF.

METHODS

Patients with HF and LBBB undergoing CRT (n = 89, 37.1% females, 68 ± 9 years, ischemic etiology in 61%, LV ejection fraction 27.1 ± 7.1%) were analyzed. LV longitudinal systolic strain rate values were extracted from curved anatomical M-mode plots of standard long-axis 2D-echocardiography images and cubic spline interpolation was used to generate a 3D-phantom. Index of contractile asymmetry (ICA) was calculated based on standard deviation of differences in strain rate of opposing walls. Average ICA was individually assessed pairwise in 12 opposing 30-degree LV sectors. Reduction in LV end-systolic volume (ESV) ≥15% after 6 months was considered as positive response to CRT.

RESULTS

CRT response was found in 66 (74.2%) patients. Responders with both ischemic and non-ischemic cardiomyopathy had a higher and more extensive contractile asymmetry at baseline and achieved a greater ICA reduction after CRT than non-responders. Higher baseline ICA predicted higher degree and wider extent of ICA improvement. Also, both ICA at baseline and reduction of ICA correlated with the degree of ESV reduction after CRT.

CONCLUSIONS

Quantification of asymmetrical LV activation in 3D by ICA provides valuable insights into LV contraction in case of LBBB and is a promising tool for improved patient selection for CRT.

Current role of echocardiography in cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is an established treatment for patients with heart failure and left ventricular systolic dysfunction. Patients are usually assessed by echocardiography, which provides a number of anatomical and functional information used for cardiac dyssynchrony assessment, prognostic stratification, identification of the optimal site of pacing in the left ventricle, optimization of the CRT device, and patient follow-up. Compared to other cardiac imaging techniques, echocardiography has the advantage to be non-invasive, repeatable, and safe, without exposure to ionizing radiation or nefrotoxic contrast. In this article, we review current evidence about the role of echocardiography before, during, and after the implantation of a CRT device.

Non-responders to cardiac resynchronization therapy: Insights from multimodality imaging and electrocardiography. A brief review

BACKGROUND

Cardiac resynchronization therapy (CRT) is a successful strategy for heart failure (HF) patients. The pre-requisite for the response is the evidence of electrical dyssynchrony on the surface electrocardiogram usually as left bundle branch block (LBBB). Non-response to CRT is a significant problem in clinical practice. Patient selection, inadequate delivery and sub-optimal left ventricle lead position may be important causes.

OBJECTIVES

In an effort to improve CRT response multimodality imaging (especially echocardiography, computed tomography and cardiac magnetic resonance) could play a decisive role and extensive literature has been published on the matter. However, we are so far from routinary use in clinical practice. Electrocardiography (with respect to left ventricle capture and QRS narrowing) may represent a simple and low cost approach for early prediction of potential non-responder, with immediate practical implications.

CONCLUSION

This brief review covers the current recommendations for CRT in HF patients with particular attention to the potential benefits of multimodality imaging and electrocardiography in improving response rate.

Novel Imaging Techniques for Heart Failure

Imaging techniques play a main role in heart failure (HF) diagnosis, assessment of aetiology and treatment guidance. Echocardiography is the method of choice for its availability, cost and it provides most of the information required for the management and follow up of HF patients. Other non-invasive cardiac imaging modalities, such as cardiovascular magnetic resonance (CMR), nuclear imaging-positron emission tomography (PET) and single-photon emission computed tomography (SPECT) and computed tomography (CT) could provide additional aetiological, prognostic and therapeutic information, especially in selected populations. This article reviews current indications and possible future applications of imaging modalities to improve the management of HF patients.