Reverse of left ventricular volumetric and structural remodeling in heart failure patients treated with cardiac resynchronization therapy

Plasma Extracellular Vesicles as Liquid Biopsy to Unravel the Molecular Mechanisms of Cardiac Reverse Remodeling Following Resynchronization Therapy?

Cardiac resynchronization therapy (CRT) has become a valuable addition to the treatment options for heart failure, in particular for patients with disturbances in electrical conduction that lead to regionally different contraction patterns (dyssynchrony). Dyssynchronous hearts show extensive molecular and cellular remodeling, which has primarily been investigated in experimental animals. Evidence showing that at least several miRNAs play a role in this remodeling is increasing. A comparison of results from measurements in plasma and myocardial tissue suggests that plasma levels of miRNAs may reflect the expression of these miRNAs in the heart. Because many miRNAs released in the plasma are included in extracellular vesicles (EVs), which protect them from degradation, measurement of myocardium-derived miRNAs in peripheral blood EVs may open new avenues to investigate and monitor (reverse) remodeling in dyssynchronous and resynchronized hearts of patients.

Hemodynamic Doppler echocardiographic evaluation of permanent His bundle and biventricular pacing after AV nodal ablation

placing after atrioventricular (AV) nodal ablation for permanent atrial fibrillation (AF) may include cardiac resynchronization therapy (CRT) with either His bundle pacing (HBP) or biventricular pacing (BVP), or conventional single site right ventricular apical pacing (RVAP). To determine the relationship between pacing method and hemodynamic outcome, we used Doppler echocardiographic methods to evaluate left ventricular (LV) hemodynamics after AV nodal ablation and either HBP, BVP, or RVAP.

Method

20 patients were evaluated > 6 months after AV nodal ablation, 10 each with chronic HBP or BVP, and all with RVAP lead. Doppler echocardiography was used to measure 3 parameters indicative of CRT: 1) LV dP/dt, 2) the LV pre-ejection interval, and 3) myocardial performance index, relative to intra-patient RVAP.

Results

Primary endpoint of LV dP/dt on average improved by > 17% with both HBP and BVP, compared to RVAP. HBP but not BVP, had improvement across all three parameters.

Conclusion

HBP provides LV electromechanical synchrony across multiple echo Doppler parameters. Both HBP and BVP were hemodynamically superior to RVAP following AV nodal ablation.

Three-dimensional echocardiography to assess left ventricular geometry and function

Introduction: Quantification of left ventricular (LV) size and function represents the most frequent indication for an echocardiographic study. New echocardiographic techniques have been developed over the last decades in an attempt to provide a more comprehensive, accurate, and reproducible assessment of LV function.Areas covered: Although two-dimensional echocardiography (2DE) is the recommended imaging modality to evaluate the LV, three-dimensional echocardiography (3DE) has proven to be more accurate, by avoiding geometric assumptions about LV geometry, and to have incremental value for outcome prediction in comparison to conventional 2DE. LV shape (sphericity) and mass are actually measured with 3DE. Myocardial deformation analysis using 3DE can early detect subclinical LV dysfunction, before any detectable change in LV ejection fraction.Expert opinion: 3DE eliminates the errors associated with foreshortening and geometric assumptions inherent to 2DE and 3DE measurements approach very closely those obtained by CMR (the current reference modality), while maintaining the unique clinical advantage of a safe, highly cost/effective, portable imaging technique, available to the cardiologist at bedside to translate immediately the echocardiography findings into the clinical decision-making process.

Left axis deviation in patients with left bundle branch block is a marker of myocardial disease associated with poor response to cardiac resynchronization therapy

AIMS

Patients with left axis deviation (LAD) and left bundle branch block (LBBB) show less benefit from cardiac resynchronization therapy (CRT) compared to other LBBB-patients. This study investigates the reasons for this.

METHODS

Sixty-eight patients eligible for CRT were included. Patients were divided into groups according to QRS-axis; normal axis (NA), left axis deviation (LAD) and right axis deviation (RAD). Before CRT implantation CMR imaging was performed to evaluate scar tissue. Echocardiography was performed before and after implantation. The electrical substrate was assessed by measuring interlead electrical delays. Response was evaluated after 8 months by left ventricular (LV) remodelling and clinical response.

RESULTS

Forty-four (65%) patients were responders in terms of LV remodelling. The presence of LAD was found to be independently associated with a poor LV remodelling non-response OR 0.21 [95% CI 0.06-0.77] (p = 0.02). Patients with axis deviation had more myocardial scar tissue (1.3 ± 0.6 vs. 0.9 ± 0.6, P = 0.04), more severe LV hypertrophy (14 (64%) and 6 (60%) vs. 7 (29%), P = 0.05) and tended to have a shorter interlead electrical delay than patients with NA (79 ± 40 ms vs. 92 ± 48 ms, P = 0.07). A high scar tissue burden was more pronounced in non-responders (1.4 ± 0.6 vs. 1.0 ± 0.5, P = 0.01).

CONCLUSIONS

LAD in the presence of LBBB is a predictor of poor outcome after CRT. Patients with LBBB and LAD have more scar tissue, hypertrophy and less activation delay.

Sheep can be used as animal model of regional myocardial remodeling and controllable work

BACKGROUND

Pacing the right heart has been shown to induce reversible conduction delay and subse-quent asymmetric remodeling of the left ventricle (LV) in dogs and pigs. Both species have disadvantages in animal experiments. Therefore the aim of this study was to develop a more feasible and easy-to-use animal model in sheep.

METHODS

Dual-chamber (DDD) pacemakers with epicardial leads on the right atrium and right ven-tricular free wall were implanted in 13 sheep. All animals underwent 8 weeks of chronic rapid pacing at 180 bpm. Reported observations were made at 110 bpm.

RESULTS

DDD pacing acutely induced a left bundle branch block (LBBB) - like pattern with almost doubling in QRS width and the appearance of a septal flash, indicating mechanical dyssynchrony. Atrial pacing (AAI) resulted in normal ventricular conduction and function. During 8 weeks of rapid DDD pacing, animals developed LV remodeling (confirmed with histology) with septal wall thinning (-30%, p < 0.05), lateral wall thickening (+22%, p < 0.05), LV volume increase (+32%, p < 0.05), decrease of LV ejection fraction (-31%, p < 0.05), and functional mitral regurgitation. After 8 weeks, segmental pressure-strain-loops, representing regional myocardial work, were recorded. Switching from AAI to DDD pacing decreased immediately work in the septum and increased it in the lateral wall (-69 and +41%, respectively, p < 0.05). Global LV stroke work and dP/dtmax decreased (-27% and -25%, respectively, p < 0.05).

CONCLUSIONS

This study presents the development a new sheep model with an asymmetrically remod-eled LV. Simple pacemaker programing allows direct modulation of regional myocardial function and work. This animal model provides a new and valuable alternative for canine or porcine models and has the potential to become instrumental for investigating regional function and loading conditions on regional LV remodeling.

Left ventricular mechanical dyssynchrony in patients with impaired left ventricular function undergoing gated SPECT myocardial perfusion imaging

INTRODUCTION

Gated SPECT myocardial perfusion imaging (MPI) has been used to quantify mechanical dyssynchrony. Mechanical dyssynchrony appears to be related to response to cardiac resynchronization therapy.

OBJECTIVE

To evaluate the presence and predictors of mechanical dyssynchrony in patients with impaired left ventricular function (LVEF) ≤50%.

METHODS

The study included 143 consecutive patients referred for gated SPECT MPI with LVEF ≤50%. Gated SPECT MPI was performed according to a stress/rest protocol acquiring images with Tc 99m-tetrofosmin. Emory Cardiac Toolbox software was used for phase analysis and a standard deviation (SD) ≥43° was considered to indicate mechanical dyssynchrony.

RESULTS

Mechanical dyssynchrony was present in 53.1% of the patients. Its predictors were diabetes (OR 2.0, p≤0.05), summed stress score (OR 1.1, p≤0.0005), summed rest score (OR 1.1, p≤0.0001), end-diastolic volume (OR 1.0, p≤0.0001), LVEF (OR 0.9, p≤0.0001), LVEF ≤35% (OR 3.1, p≤0.005) and LVEF ≤35% and QRS ≥120 ms (OR 3.5, p≤0.05). In this study QRS width and QRS ≥120 ms were not predictors of mechanical dyssynchrony.

CONCLUSIONS

Myocardial perfusion imaging can be used to assess mechanical dyssynchrony. In patients with impaired ventricular function mechanical dyssynchrony was highly prevalent and was related to parameters of left ventricular function and perfusion.

Predictors of sustained ventricular arrhythmias in cardiac resynchronization therapy

BACKGROUND

Patients undergoing cardiac resynchronization therapy (CRT) are at high risk for ventricular arrhythmias (VAs), and risk stratification in this population remains poor.

METHODS AND RESULTS

This study followed 269 patients (left ventricular ejection fraction <35%; QRS >120 ms; New York Heart Association class III/IV) undergoing CRT with a defibrillator for 553±464 days after CRT with defibrillator implantation to assess for independent predictors of appropriate device therapy for VAs. Baseline medication use, medical comorbidities, and echocardiographic parameters were considered. The 4-year incidence of appropriate device therapy was 36%. A Cox proportional hazard model identified left ventricular end-systolic diameter >61 mm as an independent predictor in the entire population (hazard ratio [HR], 2.66; P=0.001). Those with left ventricular end-systolic diameter >61 mm had a 51% 3-year incidence of VA compared with a 26% incidence among those with a less dilated ventricle (P=0.001). Among patients with left ventricular end-systolic diameter ≤61 mm, multivariate predictors of appropriate therapy were absence of β-blocker therapy (HR, 6.34; P<0.001), left ventricular ejection fraction <20% (HR, 4.22; P<0.001), and history of sustained VA (HR, 2.97; P=0.013). Early (<180 days after implant) shock therapy was found to be a robust predictor of hospitalization for heart failure (HR, 3.41; P<0.004) and mortality (HR, 5.16; P<0.001.)

CONCLUSIONS

Among patients with CRT and a defibrillator, left ventricular end-systolic diameter >61 mm is a powerful predictor of VAs, and further risk stratification of those with less dilated ventricles can be achieved based on assessment of ejection fraction, history of sustained VA, and absence of β-blocker therapy.

Mechanistic Evaluation of Echocardiographic Dyssynchrony Indices

Background—

The power of echocardiographic dyssynchrony indices to predict response to cardiac resynchronization therapy (CRT) appears to vary between indices and between studies. We investigated whether the variability of predictive power between the dyssynchrony indices can be explained by differences in their operational definitions.

Methods and Results—

In 132 CRT-candidates (left ventricular [LV] ejection fraction, 19 ± 6%; QRS width, 170 ± 22 ms), 4 mechanical dyssynchrony indices (septal systolic rebound stretch [SRSsept], interventricular mechanical dyssynchrony [IVMD], septal-to-lateral peak shortening delay [Strain-SL], and septal-to-posterior wall motion delay [SPWMD]) were quantified at baseline. CRT response was quantified as 6-month percent change of LV end-systolic volume. Multiscale computer simulations of cardiac mechanics and hemodynamics were used to assess the relationships between dyssynchrony indices and CRT response within wide ranges of dyssynchrony of LV activation and reduced contractility. In patients, SRSsept showed best correlation with CRT response followed by IVMD, Strain-SL, and SPWMD ( R =−0.56, −0.50, −0.48, and −0.39, respectively; all P <0.01). In patients and simulations, SRSsept and IVMD showed a continuous linear relationship with CRT response, whereas Strain-SL and SPWMD showed discontinuous relationships characterized by data clusters. Model simulations revealed that this data clustering originated from the complex multipeak pattern of septal strain and motion. In patients and simulations with (simulated) LV scar, SRSsept and IVMD retained their linear relationship with CRT response, whereas Strain-SL and SPWMD did not.

Conclusions—

The power to predict CRT response differs between indices of mechanical dyssynchrony. SRSsept and IVMD better represent LV dyssynchrony amenable to CRT and better predict CRT response than the indices assessing time-to-peak deformation or motion.

Conduction block in micropatterned cardiomyocyte cultures replicating the structure of ventricular cross-sections

AIMS

Structural and functional heterogeneities in cardiac tissue have been implicated in conduction block and arrhythmogenesis. However, the propensity of specific sites within the heart to initiate conduction block has not been systematically explored. We utilized cardiomyocyte cultures replicating the realistic, magnetic resonance imaging-measured tissue boundaries and fibre directions of ventricular cross-sections to investigate their roles in the development of conduction block.

METHODS AND RESULTS

The Sprague-Dawley neonatal rat cardiomyocytes were micropatterned to obtain cultures with realistic ventricular tissue boundaries and either random or realistic fibre directions. Rapid pacing was applied at multiple sites, with action potential propagation optically mapped. Excitation either failed at the stimulus site or conduction block developed remotely, often initiating reentry. The incidence of conduction block in isotropic monolayers (0% of cultures) increased with the inclusion of realistic tissue boundaries (17%) and further with realistic fibre directions (34%). Conduction block incidence was stimulus site-dependent and highest (77%) with rapid pacing from the right ventricular (RV) free wall. Furthermore, conduction block occurred exclusively at the insertion of the RV free wall into the septum, where structure-mediated current source-load mismatches acutely reduced wavefront and waveback velocity. Tissue boundaries and sharp gradients in fibre direction uniquely determined the evolution, shape, and position of conduction block lines.

CONCLUSION

Our study suggests that specific micro- and macrostructural features of the ventricle determine the incidence and spatiotemporal characteristics of conduction block, independent of spatial heterogeneities in ion channel expression.

The use of exercise echocardiography in the evaluation of mitral regurgitation

Mitral regurgitation (MR) is the second most common valvular disease in western countries after aortic stenosis. Optimal management of patients with MR depends on the etiology of the regurgitation and is based predominantly on left ventricular function and functional status. Recent outcome studies report high risk subsets of asymptomatic patients with MR, and practice guidelines underscore the importance of a well-established estimation of exercise tolerance and recommend exercise testing to objectively assess functional status and hemodynamic factors.

Event-free survival following CRT with surgically implanted LV leads versus standard transvenous approach

BACKGROUND

While surgical epicardial lead placement is performed in a subset of cardiac resynchronization therapy patients, data comparing survival following surgical versus transvenous lead placement are limited. We hypothesized that surgical procedures would be associated with increased mortality risk.

METHODS

Long-term event-free survival was assessed for 480 consecutive patients undergoing surgical (48) or percutaneous (432) left ventricle (LV) lead placement at our institution from January 2000 to September 2008.

RESULTS

Baseline clinical and demographic characteristics were similar between groups. While there was no statistically significant difference in overall event-free survival (P = 0.13), when analysis was restricted to surgical patients with isolated surgical lead placement (n = 28), event-free survival was significantly lower in surgical patients (P = 0.015). There appeared to be an early risk (first approximately 3 months postimplantation) with surgical lead placement, primarily in LV lead-only patients. Event rates were significantly higher in LV lead-only surgical patients than in transvenous patients in the first 3 months (P = 0.006). In proportional hazards analysis comparing isolated surgical LV lead placement to transvenous lead placement, adjusted hazard ratios were 1.8 ([1.1,2.7] P = 0.02) and 1.3 ([1.0,1.7] P = 0.07) for the first 3 months and for the full duration of follow-up, respectively.

CONCLUSIONS

Isolated surgical LV lead placement appears to carry a small but significant upfront mortality cost, with risk extending beyond the immediate postoperative period. Long-term survival is similar, suggesting those surviving beyond this period of early risk derive the same benefit as coronary sinus lead recipients. Further work is needed to identify risk factors associated with early mortality following surgical lead placement.

Prevalence and predictors of mechanical dyssynchrony as defined by phase analysis in patients with left ventricular dysfunction undergoing gated SPECT myocardial perfusion imaging

BACKGROUND

A novel method to quantify dyssynchrony using phase analysis of single-photon emission computed tomography (SPECT) myocardial perfusion imaging has been developed. We sought to determine the prevalence of SPECT-derived mechanical dyssynchrony, and we report clinical variables which predict mechanical dyssynchrony in patients with left ventricular dysfunction.

METHODS

We used a count-based Fourier analysis method to convert the regional myocardial counts from discrete frames per cardiac cycle into a continuous thickening function which allows resolution of the phase of the onset of myocardial contraction. The standard deviation of left ventricular phases (Phase SD) describes the regional phase dispersion as a measure of dyssynchrony. Significant dyssynchrony was defined as Phase SD ≥ 43°. 260 patients with left ventricular ejection fraction ≤ 35% were examined.

RESULTS

The prevalence of mechanical dyssynchrony in the entire cohort of patients studied was 52%. Univariate predictors of Phase SD were age (P = .03), black race (P = .0005), QRS duration, EF, EDV, summed stress score (SSS), and summed rest score (SRS) (all P = <.0001). Black race, male gender, QRS EF, and SRS were independent predictors of SPECT-based mechanical dyssynchrony.

CONCLUSIONS

Significant SPECT-based mechanical dyssynchrony is relatively common among patients with left ventricular dysfunction. In a population of patients with predominantly ischemic heart disease referred for SPECT, a reduced EF, increasing QRS duration, severity and extent of myocardial scar on SPECT imaging are independent predictors of mechanical dyssynchrony and may serve to identify patients for dyssynchrony screening.

Prediction of appropriate defibrillator therapy in heart failure patients treated with cardiac resynchronization therapy

The necessity of implantable cardioverter-defibrillator (ICD) implantation in patients with systolic heart failure (HF) who undergo cardiac resynchronization therapy (CRT) may be questioned. The aim of this study was to identify patients at low risk for sustained ventricular arrhythmia. One hundred sixty-nine consecutive patients with HF (mean age 60 +/- 12 years, 125 men, 73% in New York Heart Association class III) referred for CRT and prophylactic, primary prevention ICD implantation underwent baseline clinical and echocardiographic assessment and regular device follow-up. The primary study end point was appropriate ICD therapy. During a mean follow-up period of 654 +/- 394 days, 35 patients (21%) had sustained ventricular arrhythmias requiring appropriate ICD therapy. Of the 3 patients who experienced sudden cardiac death, 2 had been treated with appropriate ICD therapy before sudden cardiac death. In a multivariate model, only history of nonsustained ventricular tachycardia (p = 0.001), a severely (<20%) decreased left ventricular ejection fraction (p = 0.001), and digitalis therapy (p = 0.08) independently predicted appropriate ICD therapy. Patients with 0 (n = 46), 1 (n = 36), 2 (n = 73), and 3 (n = 14) risk factors for appropriate ICD therapy had a 7%, 14%, 27%, and 64% and 0%, 6%, 10%, and 43% incidence of appropriate ICD therapy for ventricular arrhythmias and for rapid ventricular tachycardia or ventricular fibrillation, respectively. In conclusion, apart from commonsense considerations (age and significant co-morbidities), ICD addition seems ineffective in CRT patients without nonsustained ventricular tachycardia, digoxin therapy, and severely reduced left ventricular systolic function.

A mechanistic investigation into how long-term resynchronization therapy confers ongoing cardiac functional benefits and improved exercise capacity

The exact mechanisms underpinning the longer term benefits of cardiac resynchronization therapy (CRT) were not fully understood. It was still unclear whether there was any ongoing functional benefit conferred by the partial resynchronization of ventricular contraction. To resolve this, a randomized controlled double-blind crossover trial was conducted to investigate the impact of temporary cessation of CRT on cardiac function both at rest and during peak exercise. Fifteen patients with severe heart failure and a CRT device implanted at least 3 months previously were randomly assigned to have the CRT mode switched to either off or on during exercise tests with central hemodynamic measurements (including noninvasive cardiac output measured using rebreathing methods), then crossed over on separate days to the opposite CRT mode. There were no significant changes in hemodynamic variables at rest with either mode of CRT. When CRT was acutely turned off, there was 19% lower peak exercise cardiac power (2.10 +/- 0.46 vs 2.59 +/- 0.75 W; p <0.005), 6% lower mean arterial pressure (92 +/- 12 vs 98 +/- 13 mm Hg; p <0.05), and 11.5% lower peak cardiac output (10.4 +/- 1.9 vs 11.8 +/- 2.5 L/min; p <0.05). Exercise capacity was also diminished with lower peak oxygen uptake (15.7 +/- 4.3 vs 17.2 +/- 4.9 ml/kg/min; p <0.01) and shorter exercise duration (542 +/- 204 vs 587 +/- 212 seconds; p <0.05). These changes were seen without differences in peak respiratory exchange ratio and peak systemic vascular resistance. In conclusion, these observations provided evidence that after CRT, left ventricular resynchronization continued to confer cardiac functional benefits manifest during peak exercise, but imperceptible at rest.

Reverse changes in cardiac substrate oxidation in dogs recovering from heart failure

When recovering from heart failure (HF), the myocardium displays a marked plasticity and can regain normal gene expression and function; however, recovery of substrate oxidation capacity has not been explored. We tested whether cardiac functional recovery is matched by normalization of energy substrate utilization during post-HF recovery. HF was induced in dogs by pacing the left ventricle (LV) at 210-240 beats/min for 4 wk. Tachycardia was discontinued, and the heart was allowed to recover. An additional group was studied in HF, and healthy dogs served as controls (n = 8/group). Cardiac free fatty acids (FFAs) and glucose oxidation were measured with [3H]oleate and [14C]glucose. At 10 days of recovery, hemodynamic parameters returned to control values; however, the contractile response to dobutamine remained depressed, LV end-diastolic volume was 28% higher than control, and the heart mass-to-body mass ratio was increased (9.8 +/- 0.4 vs. 7.5 +/- 0.2 g/kg, P < 0.05). HF increased glucose oxidation (76.8 +/- 19.7 nmol.min(-1).g(-1)) and decreased FFA oxidation (20.7 +/- 6.4 nmol.min(-1).g(-1)), compared with normal dogs (24.5 +/- 6.3 and 51.7 +/- 9.6 nmol.min(-1).g(-1), respectively), and reversed to normal values at 10 days of recovery (25.4 +/- 6.0 and 46.6 +/- 6.7 nmol.min(-1).g(-1), respectively). However, similar to HF, the recovered dogs failed to increase glucose and fatty acid uptake in response to pacing stress. The activity of myocardial citrate synthase and aconitase was significantly decreased during recovery compared with that in control dogs (58 and 27% lower, respectively, P < 0.05), indicating a persistent reduction in mitochondrial oxidative capacity. In conclusion, cardiac energy substrate utilization is normalized in the early stage of post-HF recovery at baseline, but not under stress conditions.