Interventricular Delay Optimization: A Comparison among Three Different Echocardiographic Methods

Assessment of the correlation between Doppler derived dP/dt and aortic velocity-time integral during cardiac resynchronization therapy optimization

PURPOSE

Suboptimal response to cardiac resynchronization therapy (CRT) may be improved by optimization of device parameters using echocardiography. For this purpose, the aortic velocity-time integral (aVTI) has been used as a target metric to define optimal velocity timings for each ventricle. dP/dt is a parameter used for the assessment of myocardial contractility. In this study, we aimed to evaluate the effectiveness of Doppler-derived dP/dt in optimization by assessing the possible correlation between aVTI and dP/dt.

METHODS

Patients with CRT admitted for routine follow-up were included in the study. Aortic VTI and dP/dt measurements were recorded in four different standard pacing configurations during reprogramming.

RESULTS

A total of 45 patients were included in the final analysis. No correlation was found between the aVTI and the delta dP/dt value in the two configurations where the change in dP/dt was maximum (p = 0.894). In the two configurations where the change in aVTI was maximum, there was also no correlation between the delta dP/dt and the delta aVTI (p = 0.715). When patients were dichotomized according to the median value of dP/dt, there were no differences in aVTI, NYHA classes, LVEF, and mitral regurgitation (MR) severity (p = 0.4; p = 0.5; p = 0.7; p = 0.3; respectively). The change in both dP/dt and aVTI was statistically significant when switching from RV-only to QRS width-targeted configuration (p = 0.001; p = 0.041; respectively).

CONCLUSION

In conclusion, aVTI recorded at different pacing configurations did not correlate with dP/dt during interventricular optimization. However, both parameters consistently showed a positive effect of biventricular pacing on contractile synchronization and stroke volume.

Advances in atrioventricular and interventricular optimization of cardiac resynchronization therapy - what's the gold standard?

INTRODUCTION

Cardiac resynchronization therapy (CRT) is one of the most important advances in heart failure management in the last twenty years. Approximately one-third of patients appear not to respond to therapy. Although there are a number of possible mechanisms for non-response, an important factor is suboptimal atrioventricular (AV) and interventricular (VV) timing intervals. There remains controversy over whether routinely optimizing intervals is necessary and there is no agreed gold standard methodology. Optimization has classically been performed using echocardiography which has limits related to resource use, time-cost and variable reproducibility. Newer optimization methods using device-based sensors and algorithms show promise in reducing heart-failure hospitalization compared with echocardiography. Areas covered: This review outlines the rationale for optimization, the principles of AV and VV optimization, the standard echocardiographic approach and newer device-based algorithms and the evidence base for their use. Expert commentary: The incremental gains of optimization are likely to be real, but small, compared to the overall improvement gained from cardiac resynchronization itself. At this time routine optimization may not be mandatory but should be performed where there is no response to CRT. Device-based optimization algorithms appear to be practical and in some cases, deliver superior clinical outcomes compared to echocardiography.

Hemodynamic benefit of rest and exercise optimization of cardiac resynchronization therapy

The optimal method of cardiac resynchronization therapy (CRT) optimization is as yet unknown. We sought to investigate the responses of optimization at rest and on exercise. This 2 stage study involved 59 patients (age 65 ± 10, 75% male), who had all recently undergone successful CRT implantation. In the first stage, the 6-month response was compared between 30 individuals who underwent resting echocardiographic optimization of CRT [atrioventricular (AV delay) plus ventriculo-ventricular delays (VV delay)], compared with the 29 who did not. In the second stage, a subset of 37 patients from the original cohort were randomized (double-blind) to either resting echocardiographic optimization (n = 20) or exercise echocardiographic optimization (n = 17) and followed for a further 6 months. Clinical and echocardiographic data were collected at each stage. Patients undergoing rest optimization demonstrated improvement in almost all variables and significantly in B-type natriuretic peptide (BNP) in contrast to those without optimization. In a linear regression model, the only significant predictor of BNP change was whether an individual underwent resting optimization or not (β = 0.38, P = 0.04). In those undergoing resting optimization, the degree of change in AV delay was correlated with improvement in left ventricle (LV) end-diastolic volume (r(2)  = 0.33, P < 0.01). Optimization on exercise was associated with a significant decrease in 6-minute walk test compared to those randomized to rest optimization possibly due to inducing nonoptimization at rest. In conclusion, echocardiographic optimization of CRT at rest is superior to no optimization or optimization on exercise. Patients with the greatest change in AV delay to reach optimal may undergo greater LV remodeling.

Optimizing benefit from CRT: role of speckle tracking echocardiography, the importance of LV lead position and scar

Cardiac resynchronization therapy is demonstrated to be effective in patients with advanced heart failure. Correcting mechanical dyssynchrony is proposed as the predominant mechanism of response. Achieving optimum left ventricular lead position, at the site of maximal mechanical dyssynchrony but away from transmural scar, is identified as one of the main determinants of both symptomatic and prognostic benefit. Strategies employing multimodality cardiac imaging techniques have been used to identify this optimal pacing site, in addition to any potential anatomical limitations to successful implantation. Speckle tracking echocardiography offers prospective lead targeting, incorporating pathophysiological determinants of cardiac resynchronization therapy response. This review considers the key factors in defining optimum left ventricular lead location, emphasizing the role of myocardial scar. The use of speckle tracking echocardiography and the potential for this technique to be incorporated into routine practice to guide the implant strategy in an individual patient is discussed.

Comparison of dyssynchrony parameters for VV-optimization in CRT patients

BACKGROUND

Optimization of the interventricular delay (VV-optimization) in cardiac resynchronization therapy (CRT) patients can be performed by evaluation of mechanical dyssynchrony. However, there is no consensus on which method to use. In this study, three conceptually different methods were evaluated.

METHODS

Thirty consecutive CRT patients were included. At day 1, patients were atrioventricular and VV optimized by left ventricular outflow tract (LVOT) velocity time integral (VTI). At 6 months, 2D strain (2DS) echocardiography and tissue Doppler imaging (TDI) was performed at six different VV-programming delay in steps of 20 ms. LVOT and three indices of dyssynchrony were evaluated at each setting: standard deviation (SD) of time-to-peak strain in 12 segments (2DS-SD), SD of time-to-peak velocities in 12 segments (TDI-SD), and maximal activation delay (AD-max) by cross-correlation analysis (XCA) of TDI-derived myocardial acceleration curves.

RESULTS

Feasibility was 90% for 2DS-SD and TDI-SD and 97% for AD-max. Coefficients of variation for intraobserver variability were 13% for 2DS-SD, 11% for TDI-SD, and 6% for AD-max. A relative increase in LVOT VTI > 10% was observed in 5/12 (42%) nonresponders and 7/18 (39%) responders to CRT. Optimization by all three dyssynchrony indices significantly increased LVOT VTI compared to simultaneous pacing and optimal setting at day 1 (P < 0.05, all). LVOT VTI was highest when using AD-max, and AD-max showed the best agreement (k = 0.71).

CONCLUSION

VV optimization at 6 months acutely benefits both responders and nonresponders; however, dyssynchrony indices do not perform equally well. XCA has a high feasibility and reproducibility and appears to be superior to time-to-peak techniques.