Interaction of Left Ventricular Remodeling and Regional Dyssynchrony on Long-Term Prognosis after Cardiac Resynchronization Therapy

The saga of dyssynchrony imaging: Are we getting to the point

Cardiac resynchronisation therapy (CRT) has an established role in the management of patients with heart failure, reduced left ventricular ejection fraction (LVEF < 35%) and widened QRS (>130 msec). Despite the complex pathophysiology of left ventricular (LV) dyssynchrony and the increasing evidence supporting the identification of specific electromechanical substrates that are associated with a higher probability of CRT response, the assessment of LVEF is the only imaging-derived parameter used for the selection of CRT candidates.

This review aims to (1) provide an overview of the evolution of cardiac imaging for the assessment of LV dyssynchrony and its role in the selection of patients undergoing CRT; (2) highlight the main pitfalls and advantages of the application of cardiac imaging for the assessment of LV dyssynchrony; (3) provide some perspectives for clinical application and future research in this field.

Conclusion

the road for a more individualized approach to resynchronization therapy delivery is open and imaging might provide important input beyond the assessment of LVEF.

Trajectory of left ventricular ejection fraction in response to therapies in patients with muscular dystrophy

BACKGROUND

Patients with muscular dystrophy (MD) are at elevated risk of serious cardiac complications and clinical assessment is limited due to inherent physical limitations. We assessed the utility of left ventricular ejection fraction (LVEF) derived from transthoracic echocardiogram (TTE) as a prognostic marker for major adverse cardiac events (MACE) in a mixed adult MD cohort.

METHODS

One hundred and sixty-five MD patients (median age: 36 (interquartile range [IQR]: 23.0-49.0) years; 65 [39.4%] females) were enrolled in our prospective cohort study. Diagnoses included dystrophinopathies (n = 42), limb-girdle MD (n = 31), type 1 myotonic dystrophy (n = 71), and facioscapulohumeral MD (n = 21). Left ventricular ejection fraction, ventricular dimensions at end-diastole and end-systole, and serial measures (n = 124; follow-up period: 2.19 [IQR: 1.05-3.32] years) stratified patients for MACE risk.

RESULTS

Cardiomyopathy was diagnosed in 60 (36.4%) patients of the broader cohort (median LVEF: 45.0 [IQR: 35.0-50.0] %). Ninety-eight MACE occurred over the 7-year study period. At baseline, patients with a LVEF < 55.0% had a high risk of MACE (adjusted odds ratio: 8.30; 95% confidence interval [CI]: 3.18-21.7), concordant with the analysis of LV dimensions. Forty-one percent of these patients showed an improvement in LVEF with the optimization of medical and device therapies. Relative to patients with preserved LVEF, patients with reduced LVEF were at an elevated risk of MACE (adjusted hazard ratio [aHR]: 7.21; 95% CI: 1.99-26.1), and improved LVEF resulted in comparable outcomes (aHR: 1.84; 95% CI: .49-6.91) associated with optimization of medical and device therapies. Reduction in QRS duration by CRT therapy was associated with an improvement in LVEF (average improvement: 12.8 [± 2.30] %; p = .04).

CONCLUSIONS

Reduction in LVEF indicates an increased risk of cardiovascular events in patients with MD. Baseline and serial LVEF obtained by TTE can prognosticate patients for MACE and guide clinical management.

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 remodeling and arrhythmogenesis are ameliorated by administration of Cx43 mimetic peptide Gap27 in heart failure rats

Alterations in connexins and specifically in 43 isoform (Cx43) in the heart have been associated with a high incidence of arrhythmogenesis and sudden death in several cardiac diseases. We propose to determine salutary effect of Cx43 mimetic peptide Gap27 in the progression of heart failure. High-output heart failure was induced by volume overload using the arterio-venous fistula model (AV-Shunt) in adult male rats. Four weeks after AV-Shunt surgery, the Cx43 mimetic peptide Gap27 or scrambled peptide, were administered via osmotic minipumps (AV-Shunt_Gap27 or AV-Shunt_Scr) for 4 weeks. Cardiac volumes, arrhythmias, function and remodeling were determined at 8 weeks after AV-Shunt surgeries. At 8^th week, AV-Shunt_Gap27 showed a marked decrease in the progression of cardiac deterioration and showed a significant improvement in cardiac functions measured by intraventricular pressure-volume loops. Furthermore, AV-Shunt_Gap27 showed less cardiac arrhythmogenesis and cardiac hypertrophy index compared to AV-Shunt_Scr. Gap27 treatment results in no change Cx43 expression in the heart of AV-Shunt rats. Our results strongly suggest that Cx43 play a pivotal role in the progression of cardiac dysfunction and arrhythmogenesis in high-output heart failure; furthermore, support the use of Cx43 mimetic peptide Gap27 as an effective therapeutic tool to reduce the progression of cardiac dysfunction in high-output heart failure.

Lead one ratio in left bundle branch block predicts poor cardiac resynchronization therapy response

BACKGROUND

A low electrocardiogram (ECG) lead one ratio (LOR) of the maximum positive/negative QRS amplitudes is associated with lower left ventricular ejection fraction (LVEF) and worse outcomes in left bundle branch block (LBBB); however, the impact of LOR on cardiac resynchronization therapy (CRT) outcomes is unknown. We compared clinical outcomes and echocardiographic changes after CRT implantation by LOR.

METHODS

Consecutive CRT-defibrillator recipients with LBBB implanted between 2006 and 2015 at Duke University Medical Center were included (N = 496). Time to heart transplant, left ventricular assist device (LVAD) implantation, or death was compared among patients with LOR <12 vs ≥12 using Cox-proportional hazard models. Changes in LVEF and LV volumes after CRT were compared by LOR.

RESULTS

Baseline ECG LOR <12 was associated with an adjusted hazard ratio (HR) of 1.69 (95% CI: 1.12-2.40, P = .01) for heart transplant, LVAD, or death. Patients with LOR <12 had less reduction of LV end diastolic volume (ΔLVEDV -4 ± 21 vs -13 ± 23%, P = .04) and LV end systolic volume (ΔLVESV -9 ± 27 vs -22 ± 26%, P = .03) after CRT. In patients with QRS duration (QRSd) ≥150 ms, LOR <12 was associated with an adjusted HR of 2.01 (95% CI 1.21-3.35, P = .008) for heart transplant, LVAD, or death, compared with LOR ≥12.

CONCLUSIONS

Baseline ECG LOR <12 portends worse outcomes after CRT implantation in patients with LBBB, specifically among those with QRSd ≥150 ms. This ECG ratio may identify patients with a class I indication for CRT implantation at high risk for poor postimplantation outcomes.

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.

Left ventricular global longitudinal strain and mechanical dispersion predict response to multipoint pacing for cardiac resynchronization therapy

PURPOSE

To evaluate the acute effect of multipoint pacing (MPP) and search for the better baseline predictors of response to MPP for guiding patient selection.

METHODS

We enrolled 46 heart failure patients scheduled for implantation of MPP-enabled cardiac resynchronization therapy (CRT) devices. An acute pacing protocol including conventional CRT and MPP pacing configurations was performed after implantation. Echocardiography was used at baseline and during pacing test, and response was defined as left ventricular (LV) end-systolic volume (ESV) reduction ≥ 15% at 6-month follow-up.

RESULTS

MPP response was present in 32 (69%) patients. Responders showed significantly superior LV ejection fraction, global longitudinal peak strain (GLPS), and mechanical dispersion (MD) with MPP than with conventional CRT (all P < 0.05). Baseline GLPS (OR 1.524; 95% CI 1.031-2.251; P = 0.034) and MD (OR 1.048; 95% CI 1.016-1.081; P = 0.003) were independent predictors of MPP response in multivariate regression analysis. Both |GLPS| and MD were significantly correlated with percentage change in LVESV (▵LVESV%) at 6-month follow-up (r = 0.731 and r = 0.696, respectively; all P < 0.001). |GLPS| ≥ 5.0% combined with MD ≥ 120 ms predicted MPP response with the optimal sensitivity of 91% and specificity of 71% (AUC = 0.848, P < 0.001).

CONCLUSIONS

MPP tends to be superior to conventional CRT in improving acute response. |GLPS| and MD can successfully predict response to MPP, and their combination can further improve the prediction accuracy of response.

Why Dyssynchrony Matters in Heart Failure?

Cardiac resynchronization therapy (CRT) is an electrical therapy to resolve an electrical problem. Any method to predict CRT response must specifically reflect the electrical substrate. Time-to-peak dyssynchrony is too unspecific for prediction of response because dyssynchrony by this approach may reflect the presence of scar or fibrosis even in the absence of conduction delay. New methods are based on the actual physiology of activation delay-induced heart failure (HF) and are superior to time-to-peak methods in predicting CRT response. Time-to-peak dyssynchrony may be used for prognosis in HF patients without signs of delayed ventricular activation and for monitoring CRT response.

Speckle tracking echocardiography analyses of myocardial contraction efficiency predict response for cardiac resynchronization therapy

BACKGROUND

In patients with left ventricular (LV) dysssynchrony, contraction that doesn't fall into ejection period (LVEj) results in a waste of energy due to inappropriate contraction timing, which was now widely treated by cardiac resynchronization therapy(CRT). Myocardial Contraction Efficiency was defined as the ratio of Efficient Contraction Time (ECTR) and amplitude of efficient contraction (ECR) during LVEj against that in the entire cardiac cycle. This study prospectively investigated whether efficiency indexes could predict CRT outcome.

METHODS

Our prospective pilot study including 70 CRT candidates, parameters of myocardial contraction timing and contractility were measured by speckle tracking echocardiography (STE) and efficiency indexes were calculated accordingly at baseline and at 6-month follow-up. Primary outcome events were predefined as death or HF hospitalization, and secondary outcome events were defined as all-cause death during the follow-up. 16-segement Standard deviation of time to onset strain (TTO-16SD) and time to peak strain (TTP-16SD) were included as the dyssynchrony indexes.

RESULTS

According to LV end systolic volume (LVESV) and LV eject fraction(LVEF) values at 6-month follow-up, subjects were classified into responder and non-responder groups, ECR (OR 0.87, 95%CI 0.78-0.97, P < 0.05) and maximum longitudinal strain (MLS) (OR 2.22, 95%CI 1.36-3.61, P < 0.01) were the two independent predictors for CRT response, Both TTO-16SD and TTP-16SD failed to predict outcome. Patients with poorer myocardial contraction efficiency and better contractility are more likely to benefit from CRT.

CONCLUSIONS

STE can evaluate left ventricular contraction efficiency and contractility to predict CRT response. When analyzing myocardial strain by STE, contraction during LVEj should be highlighted.

Echocardiography for the management of patients with biventricular pacing: Possible roles in cardiac resynchronization therapy implementation

Cardiac resynchronization therapy (CRT) is an established therapeutic option for the subset of patients with heart failure (HF), reduced ejection fraction (EF), and dyssynchrony evidenced by electrocardiography. Benefit from CRT has been proven in many clinical trials, yet a sizeable proportion of these patients with wide QRS do not respond to this intervention, despite the updated practice guidelines. Several echocardiographic indices, targeting mechanical rather than electrical dyssynchrony, have been suggested to address this issue, but research so far has not succeeded in providing a single and simple measurement with adequate sensitivity and specificity for identification of responders. While there is still ongoing research in this field, echocardiography proves helpful in other aspects of CRT implementation, such as site selection for left ventricular (LV) lead pacing and optimization of pacing parameters during follow-up visits.