Endocardial Left Ventricular Pacing Improves Cardiac Resynchronization Therapy in Chronic Asynchronous Infarction and Heart Failure Models

Dyssynchronous heart failure models in canines: New insights into electrocardiographic, echocardiographic and histological features

BACKGROUND

We investigated the similarities and differences between two experimental approaches using tachy-pacing technology to induce desynchronized heart failure in canines.

METHODS

A total of eight dogs were included in the experiment, four were tachy-paced in right ventricle apex (RVAP) and 4 were paced in right atrium after the ablation of left bundle branch to achieve left bundle branch block (RAP+LBBB). Three weeks of follow-up were conducted to observe the changes in cardiac function and myocardial staining was performed at the end of the experiment.

RESULTS

Both experimental approaches successfully established heart failure with reduced ejection fraction models, with similar trends in declining cardiac function. The RAP+LBBB group exhibited a prolonged overall ventricular activation time, delayed left ventricular activation, and lesser impact on the right ventricle. The RVAP approach led to a reduction in overall right ventricular compliance and right ventricular enlargement. The RAP+LBBB group exhibited significant reductions in left heart compliance (LVGLS, %: RAP+LBBB -12.60 ± 0.12 to -5.93 ± 1.25; RVAP -13.28 ± 0.62 to -8.05 ± 0.63, p = 0.023; LASct, %: RAP+LBBB -15.75 ± 6.85 to -1.50 ± 1.00; RVAP -15.75 ± 2.87 to -10.05 ± 6.16, p = 0.035). Histological examination revealed more pronounced fibrosis in the left ventricular wall and left atrium in the RAP+LBBB group while the RVAP group showed more prominent fibrosis in the right ventricular myocardium.

CONCLUSION

Both approaches establish HFrEF models with comparable trends. The RVAP group shows impaired right ventricular function, while the RAP+LBBB group exhibits more severe decreased compliance and fibrosis in left ventricle.

A case report of left ventricular lead implantation via total three-dimensional transseptal puncture after tricuspid valve replacement

Background

Ventricular lead implantation is relatively difficult for patients with bradyarrhythmia after tricuspid valve replacement. Right atrial (RA) abnormalities often occurred in patients with tricuspid valve disease; conventional coronary sinus (CS) lead implantation is not easy to operate. Therefore, it is necessary to develop a safe method for implanting LV endocardial leads in patients after tricuspid valve replacement.

Case presentation

A 76-year-old Asian woman who had been implanted with a metal tricuspid valve replacement 4 years ago was admitted to the Department of Cardiology for pacemaker implantation due to transient blackout related to persistent atrial fibrillation with long pauses. The patient's family rejected the surgical placement of an epicardial LV lead. Therefore, we first intended to operate LV lead implantation through the CS; however, the orifice of the CS was virtually difficult to seek. Ultimately, we utilized total 3-dimensional (T3D) transseptal puncture (TSP) under the guidance of the CARTO 3 system; thus, we implanted the LV endocardial lead, which contributed to the accurate puncture of the central fossa ovalis and ensured the safety of TSP in the case of RA enlargement. Meanwhile, the CARTO 3 system contributed to the localization of the LV lead to the LV free wall during implantation. All the intraoperative and postoperative pacemaker parameters were favorable; no intraoperative or postoperative complications occurred.

Conclusions

This case report may provide a novel surgical approach for LV lead implantation in patients who underwent tricuspid valve replacement or patients who may benefit from cardiac resynchronization therapy but failed to implant CS lead.

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.

Left Ventricular Endocardial Pacing: Update and State of the Art

Initially, left ventricular (LV) endocardial pacing was performed as a bailout procedure after unsuccessful transvenous cardiac resynchronization therapy implantation in the presence of surgical contraindications. Additional possible advantages of endocardial LV pacing are a more physiologic activation, being less arrhythmogenic, more effective on the hemodynamic level, with better thresholds, and without the risk of phrenic stimulation. Different techniques have been proposed to stimulate the LV endocardium in humans, with feasibility and safety studies involving limited numbers of patients. In this review, we will describe the different techniques proposed to allow LV endocardial pacing, the results observed, and then we will discuss the reasons why LV endocardial pacing seems to be out of fashion today and what are the possible perspectives for development.

Electrical management of heart failure: from pathophysiology to treatment

Electrical disturbances, such as atrial fibrillation (AF), dyssynchrony, tachycardia, and premature ventricular contractions (PVCs), are present in most patients with heart failure (HF). While these disturbances may be the consequence of HF, increasing evidence suggests that they may also cause or aggravate HF. Animal studies show that longer-lasting left bundle branch block, tachycardia, AF, and PVCs lead to functional derangements at the organ, cellular, and molecular level. Conversely, electrical treatment may reverse or mitigate HF. Clinical studies have shown the superiority of atrial and pulmonary vein ablation for rhythm control and AV nodal ablation for rate control in AF patients when compared with medical treatment. Ablation of PVCs can also improve left ventricular function. Cardiac resynchronization therapy (CRT) is an established adjunct therapy currently undergoing several interesting innovations. The current guideline recommendations reflect the safety and efficacy of these ablation therapies and CRT, but currently, these therapies are heavily underutilized. This review focuses on the electrical treatment of HF with reduced ejection fraction (HFrEF). We believe that the team of specialists treating an HF patient should incorporate an electrophysiologist in order to achieve a more widespread use of electrical therapies in the management of HFrEF and should also include individual conditions of the patient, such as body size and gender in therapy fine-tuning.

Endocardial left ventricular pacing

Cardiac resynchronization therapy (CRT) is an effective treatment for dyssynchronous heart failure; however, 30–50% of patients fail to improve after implant. Endocardial left ventricular (LV) pacing is an alternative therapy for patients who do not respond to conventional CRT or in whom placement of a lead via the coronary sinus is not possible. It enables pacing at a wide variety of sites, without restrictions due to coronary sinus anatomy, and there is evidence of superior electrical resynchronization and hemodynamic response compared with conventional epicardial CRT. In this article, we discuss the potential advantages and disadvantages of endocardial LV pacing compared with conventional CRT, review the evidence for the delivery of endocardial LV pacing using both lead-based and leadless systems, and explore possible future directions of this novel technology.

European experience with a first totally leadless cardiac resynchronization therapy pacemaker system

Aims

Totally leadless cardiac resynchronization therapy (CRT) can be delivered with a combination of Micra and WiSE-CRT systems. We describe the technical feasibility and first insights into the safety and efficacy of this combination in European experience.

Methods and results

Patients enrolled had indication for both Micra and WiSE-CRT systems because of heart failure related to high burden of pacing by a Micra necessitating system upgrade or inability to implant a conventional CRT system because of infectious or anatomical conditions. The endpoints of the study were technical success of WiSE-CRT implantation with right ventricle-synchonized CRT delivery, acute QRS duration reduction, and freedom from procedure-related major adverse events. All eight WiSE-CRT devices were able to detect the Micra pacing output and to be trained to deliver synchronous LV endocardial pacing. Acute QRS reduction following WiSE-CRT implantation was observed in all eight patients (mean QRS 204.38 ± 30.26 vs. 137.5 ± 24.75 mS, P = 0.012). Seven patients reached 6 months of follow-up. At 6 months after WiSE-CRT implantation, there was a significant increase in LV ejection fraction (28.43 ± 8.01% vs. 39.71 ± 11.89%; P = 0.018) but no evidence of LV reverse remodelling or improvement in New York Heart Association class.

Conclusion

The Micra and the WiSE-CRT systems can successfully operate together to deliver total leadless CRT to a patient. Moreover, the WiSE-CRT system provides the only means to upgrade the large population of Micra patients to CRT capability without replacing the Micra. The range of application of this combination could broaden in the future with the upcoming developments of leadless cardiac pacing.

Leadless Left Ventricular Endocardial Pacing and Left Bundle Branch Area Pacing for Cardiac Resynchronisation Therapy

Cardiac resynchronisation therapy is an important intervention to reduce mortality and morbidity, but even in carefully selected patients approximately 30% fail to improve. This has led to alternative pacing approaches to improve patient outcomes. Left ventricular (LV) endocardial pacing allows pacing at site-specific locations that enable the operator to avoid myocardial scar and target areas of latest activation. Left bundle branch area pacing (LBBAP) provides a more physiological activation pattern and may allow effective cardiac resynchronisation. This article discusses LV endocardial pacing in detail, including the indications, techniques and outcomes. It discusses LBBAP, its potential benefits over His bundle pacing and procedural outcomes. Finally, it concludes with the future role of endocardial pacing and LBBAP in heart failure patients.

Left ventricular endocardial pacing is less arrhythmogenic than conventional epicardial pacing when pacing in proximity to scar

Background

Epicardial pacing increases risk of ventricular tachycardia (VT) in patients with ischemic cardiomyopathy (ICM) when pacing in proximity to scar. Endocardial pacing may be less arrhythmogenic as it preserves the physiological sequences of activation and repolarization.

Objective

The purpose of this study was to determine the relative arrhythmogenic risk of endocardial compared to epicardial pacing, and the role of the transmural gradient of action potential duration (APD) and pacing location relative to scar on arrhythmogenic risk during endocardial pacing.

Methods

Computational models of ICM patients (n = 24) were used to simulate left ventricular (LV) epicardial and endocardial pacing 0.2–3.5 cm from a scar. Mechanisms were investigated in idealized models of the ventricular wall and scar. Simulations were run with/without a 20-ms transmural APD gradient in the physiological direction and with the gradient inverted. Dispersion of repolarization was computed as a surrogate of VT risk.

Results

Patient-specific models with a physiological APD gradient predict that endocardial pacing decreases VT risk (34%; P <.05) compared to epicardial pacing when pacing in proximity to scar (0.2 cm). Endocardial pacing location does not significantly affect VT risk, but epicardial pacing at 0.2 cm compared to 3.5 cm from scar increases it (P <.05). Inverting the transmural APD gradient reverses this trend. Idealized models predict that propagation in the direction opposite to APD gradient decreases VT risk.

Conclusion

Endocardial pacing is less arrhythmogenic than epicardial pacing when pacing proximal to scar and is less susceptible to pacing location relative to scar. The physiological repolarization sequence during endocardial pacing mechanistically explains reduced VT risk compared to epicardial pacing.

Transfemoral transcatheter puncture of interventricular septum in a swine model: A novel transfemoral-venous access to left ventricle with the assistance of arterio-venous circuit

OBJECTIVE

Via subclavian/jugular vein, successful puncture of interventricular septum (IVS) has been achieved transvenously. However, the approach was limited by acute entry-angle. The study was conducted to investigate a novel transcatheter puncture of IVS via femoral access and transfemoral-venous access to left ventricle (LV) through IVS.

METHODS

Via femoral artery, transcatheter puncture of mid-IVS was performed with a custom-made nickel-titanium needle and 6F-sheath in 16 healthy mini-swine. Then femoral arterio-venous circuit was established through IVS. After pre-dilation of IVS, a 20F-sheath was introduced into LV transvenously over-the-guidewire in 15 swine. Furthermore, transfemoral-venous TAVR was attempted with the approach in another swine. IVS was evaluated postoperatively and was further confirmed pathologically 2 months later.

RESULTS

All transcatheter puncture of IVS was performed successfully in LV and the mid-IVS thickness was 7.67 ± 0.98 mm. In all swine, femoral arterio-venous circuit was established via IVS, and a 20F-sheath was introduced into LV and aorta transfemoral-venously (entry-angle: 145.3 ± 12.2° in front view). After the procedure, there was one swine with moderate tricuspid-regurgitation and five swine with mild residual-shunt (2.6 ± 0.7 mm). Two months later, residual-shunt was still detected in three swine and the communication was confirmed pathologically. In other swine, no defect occurred and replacement-scar was identified along puncture-tract. In the swine underwent transfemoral-venous TAVR, prosthetic valve was deployed successfully with good function.

CONCLUSIONS

Transfemoral transcatheter puncture of IVS is feasible and safe in a swine model, and large sheath can be introduced into LV transfemoral-venously using the novel access with the aid of vessel circuit.

The influence of scar on the spatio-temporal relationship between electrical and mechanical activation in heart failure patients

Aims

The aim of this study was to determine the relationship between electrical and mechanical activation in heart failure (HF) patients and whether electromechanical coupling is affected by scar.

Methods and results

Seventy HF patients referred for cardiac resynchronization therapy or biological therapy underwent endocardial anatomo-electromechanical mapping (AEMM) and delayed-enhancement magnetic resonance (CMR) scans. Area strain and activation times were derived from AEMM data, allowing to correlate mechanical and electrical activation in time and space with unprecedented accuracy. Special attention was paid to the effect of presence of CMR-evidenced scar. Patients were divided into a scar (n = 43) and a non-scar group (n–27). Correlation between time of electrical and mechanical activation was stronger in the non-scar compared to the scar group [R = 0.84 (0.72–0.89) vs. 0.74 (0.52–0.88), respectively; P = 0.01]. The overlap between latest electrical and mechanical activation areas was larger in the absence than in presence of scar [72% (54–81) vs. 56% (36–73), respectively; P = 0.02], with smaller distance between the centroids of the two regions [10.7 (4.9–17.4) vs. 20.3 (6.9–29.4) % of left ventricular radius, P = 0.02].

Conclusion

Scar decreases the association between electrical and mechanical activation, even when scar is remote from late activated regions.

A rule-based method for predicting the electrical activation of the heart with cardiac resynchronization therapy from non-invasive clinical data

Background

Cardiac Resynchronization Therapy (CRT) is one of the few effective treatments for heart failure patients with ventricular dyssynchrony. The pacing location of the left ventricle is indicated as a determinant of CRT outcome.

Objective

Patient specific computational models allow the activation pattern following CRT implant to be predicted and this may be used to optimize CRT lead placement.

Methods

In this study, the effects of heterogeneous cardiac substrate (scar, fast endocardial conduction, slow septal conduction, functional block) on accurately predicting the electrical activation of the LV epicardium were tested to determine the minimal detail required to create a rule based model of cardiac electrophysiology. Non-invasive clinical data (CT or CMR images and 12 lead ECG) from eighteen patients from two centers were used to investigate the models.

Results

Validation with invasive electro-anatomical mapping data identified that computer models with fast endocardial conduction were able to predict the electrical activation with a mean distance errors of 9.2 ± 0.5 mm (CMR data) or (CT data) 7.5 ± 0.7 mm.

Conclusion

This study identified a simple rule-based fast endocardial conduction model, built using non-invasive clinical data that can be used to rapidly and robustly predict the electrical activation of the heart. Pre-procedural prediction of the latest electrically activating region to identify the optimal LV pacing site could potentially be a useful clinical planning tool for CRT procedures.

Comparison between endocardial and epicardial cardiac resynchronization in an experimental model of non-ischaemic cardiomyopathy

Aims

Pacing from the left ventricular (LV) endocardium might increase the likelihood of response to cardiac resynchronization therapy. However, experimental and clinical data supporting this assumption are limited and controversial. The aim of this study was to compare the acute response of biventricular pacing from the LV epicardium and endocardium in a swine non-ischaemic cardiomyopathy (NICM) model of dyssynchrony.

Methods and results

A NICM was induced in six swine by 3 weeks of rapid ventricular pacing. Biventricular stimulation was performed from 16 paired locations in the LV (8 epicardial and 8 endocardial) with two different atrioventricular (80 and 110 ms) intervals and three interventricular (0, +30, -30 ms) delays. The acute response of the aortic blood flow, LV and right ventricular (RV) pressures, LVdP/dtmax and LVdP/dtmin and QRS complex width and QT duration induced by biventricular stimulation were analysed. The haemodynamic and electrical beneficial responses to either LV endocardial or epicardial biventricular pacing were similar (ΔLVdP/dtmax: +7.8 ± 2.2% ENDO vs. +7.3 ± 1.5% EPI, and ΔQRS width: -16.8 ± 1.3% ENDO vs. -17.1 ± 1.9% EPI; P = ns). Pacing from LV basal regions either from the epicardium or endocardium produced better haemodynamic responses as compared with mid or apical LV regions (P < 0.05). The LV regions producing the maximum QRS complex shortening did not correspond to those inducing the best haemodynamic responses (EPI: r2 = 0.013, P = ns; ENDO: r2 = 0.002, P = ns).

Conclusion

Endocardial LV pacing induced similar haemodynamic changes than pacing from the epicardium. The response to endocardial LV pacing is region dependent as observed in epicardial pacing.

Left Ventricular Endocardial Pacing/Leadless Pacing

Several clinical trials have established the role of cardiac resynchronization therapy in patients with heart failure, impaired left ventricular function and dyssynchrony. Challenges to traditional therapy include coronary sinus anatomy and failure to respond. Left ventricular endocardial pacing could overcome anatomic constraints, provide more flexibility, and allow for more physiologic activation. Cases and case series have demonstrated the promise of the approach. Preclinical studies support the superior hemodynamic effects of left ventricular endocardial pacing. Leadless left ventricular endocardial pacing is a recent innovation that is undergoing prospective testing. Successful delivery may be associated with clinical response and positive cardiac structural remodeling.

Electrical remodelling post cardiac resynchronization therapy in patients with ischemic and non-ischemic heart failure

BACKGROUND

The beneficial effects of cardiac resynchronization therapy (CRT) in heart failure are largely considered to be due to improved mechanical contractility. The contributory role of electrical remodelling is less clear. We sought to evaluate the impact of electrical remodelling in these patients.

METHODS

33 patients with conventional indications for CRT and with ischemic (ICM) (n = 17) and non-ischemic (NICM) (n = 16) aetiologies for heart failure were prospectively recruited. Functional parameters of peak exercise oxygen consumption (VO₂max) and Minnesota quality of life (QOL) score, echocardiographic measures of LV functions and parameters of electrical remodelling, e.g. intrinsic QRS duration (iQRSD), intracardiac conduction times of LV pacing to RV electrocardiogram (LVp-RVegm), were measured at CRT implant and after 6 months.

RESULTS

Only two electrical parameters predicted functional or symptomatic improvement. LVp-RVegm reduction significantly correlated with improvement in VO₂max (r = -0.42, p = 0.03 while reduction in iQRSD significantly correlated with improvement in QOL score (r = 0.39, p = 0.04). The extent of changes in LVp-RVegm and iQRSD was significantly greater in NICM than in ICM patients (p = 0.017 and p = 0.042 for heterogeneity). There was also significant differential impact on QOL score in the NICM relative to the ICM group (p = 0.003) but none with VO₂max. On multivariate analysis, only non-ischemic aetiology was a significant determinant of reduction in iQRSD.

CONCLUSION

CRT induces potentially beneficial reduction in LVp-RVegm and iQRSD, which are seen selectively in NICM rather than ICM patients. The extent of improvement in these markers is associated with some functional and symptomatic measures of CRT efficacy.

[Leadless endocardial ultrasound based left ventricular stimulation : WISE CRT System: alternative to conventional methods]

There are still several limitations in delivering cardiac resynchronisation therapy (CRT). After 6 months, 20-40% of patients fail to have clinical benefit due to various reasons. Endocardial stimulation rather than conventional epicardial pacing has been shown to be more physiological, improves electrical stimulation of the left ventricle (LV), has less dispersion of electrical activity and results in better resynchronisation. The WiSE™ CRT System ("Wireless stimulation endocardial system"; EBR Systems, Sunnyvale, CA, USA) provides an option for wireless, LV endocardial pacing triggered by a conventional right ventricular pacing spike from a co-implant. The feasibility of the WiSE™ CRT System has been successfully demonstrated in a population of failed cardiac resynchronisation patients with either failed implantation of a conventional system, nonresponse to conventional therapy or upgrade from pacemaker or defibrillator, where a conventional system was not an option. The WiSE™ CRT System is an innovative technology with promising safety, performance and preliminary efficacy.

Visualisation of coronary venous anatomy by computed tomography angiography prior to cardiac resynchronisation therapy implantation

BACKGROUND

The purpose of this study was to illustrate the additive value of computed tomography angiography (CTA) for visualisation of the coronary venous anatomy prior to cardiac resynchronisation therapy (CRT) implantation.

METHODS

Eighteen patients planned for CRT implantation were prospectively included. A specific CTA protocol designed for visualisation of the coronary veins was carried out on a third-generation dual-source CT platform. Coronary veins were semi-automatically segmented to construct a 3D model. CTA-derived coronary venous anatomy was compared with intra-procedural fluoroscopic angiography (FA) in right and left anterior oblique views.

RESULTS

Coronary venous CTA was successfully performed in all 18 patients. CRT implantation and FA were performed in 15 patients. A total of 62 veins were visualised; the number of veins per patient was 3.8 (range: 2-5). Eighty-five per cent (53/62) of the veins were visualised on both CTA and FA, while 10% (6/62) were visualised on CTA only, and 5% (3/62) on FA only. Twenty-two veins were present on the lateral or inferolateral wall; of these, 95% (21/22) were visualised by CTA. A left-sided implantation was performed in 13 patients, while a right-sided implantation was performed in the remaining 2 patients because of a persistent left-sided superior vena cava with no left innominate vein on CTA.

CONCLUSION

Imaging of the coronary veins by CTA using a designated protocol is technically feasible and facilitates the CRT implantation approach, potentially improving the outcome.

Acute electrical and hemodynamic effects of endocardial biventricular pacing using the WiSE CRT system and conventional epicardial biventricular pacing

Wireless left ventricular endocardial pacing with the WiSE CRT system has recently become available as alternative to conventional epicardial CRT pacing. We report the first comparison of the acute electrical and hemodynamic response produced by the two CRT pacing modalities in a patient undergoing WiSE CRT implant after a failed conventional CRT procedure. WiSE CRT pacing showed an additive acute benefit compared with conventional CRT. These findings could potentially translate into long-term clinical benefit and introduce the potential for tri-ventricular pacing using both systems simultaneously.

The effect of left ventricular pacing on transmural activation delay in myopathic human hearts

Aims

Left ventricular (LV) epicardial pacing (LVEpiP) in human myopathic hearts does not decrease global epicardial activation delay compared with right ventricular (RV) endocardial pacing (RVEndoP); however, the effect on transmural activation delay has not been evaluated. To characterize the transmural electrical activation delay in human myopathic hearts during RVEndoP and LVEpiP compared with global epicardial activation delay.

Methods and results

Explanted hearts from seven patients (5 male, 46 ± 10 years) undergoing cardiac transplantation were Langendorff-perfused and mapped using an epicardial sock electrode array (112 electrodes) and 25 transmural plunge needles (four electrodes, 2 mm spacing), for a total of 100 unipolar transmural electrodes. Electrograms were recorded during LVEpiP and RVEndoP, and epicardial (sock) and transmural (needle) activation times, along with patterns of activation, were compared. There was no difference between the global epicardial activation times (LVEpiP 147 ± 8 ms vs. RVEndoP 156 ± 17 ms, P = 0.46). The mean LV transmural activation time during LVEpiP was significantly shorter than that during RVEndoP (125 ± 44 vs. 172 ± 43 ms, P < 0.001). During LVEpiP, of the transmural layers endo-, mid-myocardium and epicardium, LV endocardial layer was often the earliest compared with other transmural layers.

Conclusion

In myopathic human hearts, LVEpiP did not decrease global epicardial activation delays compared with RVEndoP. LV epicardial pacing led to early activation of the LV endocardium, revealing the importance of the LV endocardium even when pacing from the LV epicardium.

Technology Advances to Improve Response to Cardiac Resynchronization Therapy: What Clinicians Should Know

Cardiac resynchronization therapy (CRT) is a well-established treatment for symptomatic heart failure patients with reduced left ventricular ejection fraction, prolonged QRS duration, and abnormal QRS morphology. The ultimate goals of modern CRT are to improve the proportion of patients responding to CRT and to maximize the response to CRT in patients who do respond. While the rate of CRT nonresponders has moderately but progressively decreased over the last 20 years, mostly in patients with left bundle branch block, in patients without left bundle branch block the response rate is almost unchanged. A number of technological advances have already contributed to achieve some of the objectives of modern CRT. They include novel lead design (the left ventricular quadripolar lead, and multipoint pacing), or the possibility to go beyond conventional delivery of CRT (left ventricular endocardial pacing, His bundle pacing). Furthermore, to improve CRT response, a triad of actions is paramount: reducing the burden of atrial fibrillation, reducing the number of appropriate and inappropriate interventions, and adequately predicting heart failure episodes. As in other fields of cardiology, technology and innovations for CRT delivery have been at the forefront in transforming-improving-patient care; therefore, these innovations are discussed in this review.

New insights from a computational model on the relation between pacing site and CRT response

AIMS

Cardiac resynchronization therapy (CRT) produces clinical benefits in chronic heart failure patients with left bundle-branch block (LBBB). The position of the pacing site on the left ventricle (LV) is considered an important determinant of CRT response, but the mechanism how the LV pacing site determines CRT response is not completely understood. The objective of this study is to investigate the relation between LV pacing site during biventricular (BiV) pacing and cardiac function.

METHODS AND RESULTS

We used a finite element model of BiV electromechanics. Cardiac function, assessed as LV dp/dt_max and stroke work, was evaluated during normal electrical activation, typical LBBB, fascicular blocks and BiV pacing with different LV pacing sites. The model replicated clinical observations such as increase of LV dp/dt_max and stroke work, and the disappearance of a septal flash during BiV pacing. The largest hemodynamic response was achieved when BiV pacing led to best resynchronization of LV electrical activation but this did not coincide with reduction in total BiV activation time (∼ QRS duration). Maximum response was achieved when pacing the mid-basal lateral wall and this was close to the latest activated region during intrinsic activation in the typical LBBB, but not in the fascicular block simulations.

CONCLUSIONS

In these model simulations, the best cardiac function was obtained when pacing the mid-basal LV lateral wall, because of fastest recruitment of LV activation. This study illustrates how computer modeling can shed new light on optimizing pacing therapies for CRT. The results from this study may help to design new clinical studies to further investigate the importance of the pacing site for CRT response.

Defibrillators: Selecting the Right Device for the Right Patient

Advances in the field of defibrillation have brought to practice different types of devices that include the transvenous implantable cardioverter-defibrillator (ICD) with or without cardiac resynchronization therapy, the subcutaneous ICD (S-ICD), and the wearable cardioverter-defibrillator. To ensure optimal use of these devices and to achieve best patient outcomes, clinicians need to understand how these devices work, learn the characteristics of patients who qualify them for one type of device versus another, and recognize the remaining gaps in knowledge surrounding these devices. The transvenous ICD has been shown in several randomized clinical trials to improve the survival of patients resuscitated from near-fatal ventricular fibrillation and those with sustained ventricular tachycardia with syncope or systolic heart failure as a result of ischemic or nonischemic cardiomyopathy despite receiving guideline-directed medical therapy. Important gaps in knowledge regarding the transvenous ICD involve the role of the ICD in patient subgroups not included, or not well represented, in clinical trials and the need to refine the selection criteria for the ICD in patients who are indicated for it. S-ICDs were recently introduced into the clinical arena as another option for many patients who have an approved indication for a transvenous ICD. The main advantage of the S-ICD is a lower risk of infection and lead-related complications; however, the S-ICD does not offer bradycardia or antitachycardia pacing. The S-ICD may be ideal for patients with limited vascular access, high infection risk, or some congenital heart diseases. However, more data are needed regarding the efficacy and effectiveness of the S-ICD in comparison to transvenous ICDs, the extent of defibrillation testing required, and the use of the S-ICD with other novel technologies, including leadless pacemakers. Cardiac resynchronization therapy-defibrillators are indicated in patients with a left ventricular ejection fraction ≤35%, QRS width ≥130 ms, and New York Heart Association class II, III, or ambulatory IV symptoms despite treatment with guideline-directed medical therapy. Multiple randomized controlled trials have shown that the cardiac resynchronization therapy-defibrillator improves survival, quality of life, and several echocardiographic measures. One main challenge related to cardiac resynchronization therapy-defibrillators is the 30% nonresponse rate. Many initiatives are underway to address this challenge including improved cardiac resynchronization therapy and imaging technologies and enhanced selection of patients and device programming.

Exploring the Electrophysiologic and Hemodynamic Effects of Cardiac Resynchronization Therapy: From Bench to Bedside and Vice Versa

Cardiac resynchronization therapy (CRT) is an important therapy for heart failure patients with prolonged QRS duration. In patients with left bundle branch block the altered left ventricular electrical activation results in dyssynchronous, inefficient contraction of the left ventricle. CRT aims to reverse these changes and to improve cardiac function. This article explores the electrophysiologic and hemodynamic changes that occur during CRT in patient and animal studies. It also addresses how novel techniques, such as multipoint and endocardial pacing, can further improve the electromechanical response.

Improvement of Right Ventricular Hemodynamics with Left Ventricular Endocardial Pacing during Cardiac Resynchronization Therapy

Background

Cardiac resynchronization therapy (CRT) with biventricular epicardial (BV‐CS) or endocardial left ventricular (LV) stimulation (BV‐EN) improves LV hemodynamics. The effect of CRT on right ventricular function is less clear, particularly for BV‐EN. Our objective was to compare the simultaneous acute hemodynamic response (AHR) of the right and left ventricles (RV and LV) with BV‐CS and BV‐EN in order to determine the optimal mode of CRT delivery.

Methods

Nine patients with previously implanted CRT devices successfully underwent a temporary pacing study. Pressure wires measured the simultaneous AHR in both ventricles during different pacing protocols. Conventional epicardial CRT was delivered in LV‐only (LV‐CS) and BV‐CS configurations and compared with BV‐EN pacing in multiple locations using a roving decapolar catheter.

Results

Best BV‐EN (optimal AHR of all LV endocardial pacing sites) produced a significantly greater RV AHR compared with LV‐CS and BV‐CS pacing (P < 0.05). RV AHR had a significantly increased standard deviation compared to LV AHR (P < 0.05) with a weak correlation between RV and LV AHR (Spearman r_s = −0.06). Compromised biventricular optimization, whereby RV AHR was increased at the expense of a smaller decrease in LV AHR, was achieved in 56% of cases, all with BV‐EN pacing.

Conclusions

BV‐EN pacing produces significant increases in both LV and RV AHR, above that achievable with conventional epicardial pacing. RV AHR cannot be used as a surrogate for optimizing LV AHR; however, compromised biventricular optimization is possible. The beneficial effect of endocardial LV pacing on RV function may have important clinical benefits beyond conventional CRT.

Assessment of left ventricular mechanical dyssynchrony in left bundle branch block canine model: Comparison between cine and tagged MRI

PURPOSE

To compare cine and tagged magnetic resonance imaging (MRI) for left ventricular dyssynchrony assessment in left bundle branch block (LBBB), using the time-to-peak contraction timing, and a novel approach based on cross-correlation.

MATERIALS AND METHODS

We evaluated a canine model dataset (n = 10) before (pre-LBBB) and after induction of isolated LBBB (post-LBBB). Multislice short-axis tagged and cine MRI images were acquired using a 1.5 T scanner. We computed contraction time maps by cross-correlation, based on the timing of radial wall motion and of circumferential strain. Finally, we estimated dyssynchrony as the standard deviation of the contraction time over the different regions of the myocardium.

RESULTS

Induction of LBBB resulted in a significant increase in dyssynchrony (cine: 13.0 ± 3.9 msec for pre-LBBB, and 26.4 ± 5.0 msec for post-LBBB, P = 0.005; tagged: 17.1 ± 5.0 msec at for pre-LBBB, and 27.9 ± 9.8 msec for post-LBBB, P = 0.007). Dyssynchrony assessed by cine and tagged MRI were in agreement (r = 0.73, P = 0.0003); differences were in the order of time difference between successive frames of 20 msec (bias: -2.9 msec; limit of agreement: 10.1 msec). Contraction time maps were derived; agreement was found in the contraction patterns derived from cine and tagged MRI (mean difference in contraction time per segment: 3.6 ± 13.7 msec).

CONCLUSION

This study shows that the proposed method is able to quantify dyssynchrony after induced LBBB in an animal model. Cine-assessed dyssynchrony agreed with tagged-derived dyssynchrony, in terms of magnitude and spatial direction. J. MAGN. RESON. IMAGING 2016;44:956-963.

Tailor-made heart simulation predicts the effect of cardiac resynchronization therapy in a canine model of heart failure

Despite extensive studies on clinical indices for the selection of patient candidates for cardiac resynchronization therapy (CRT), approximately 30% of selected patients do not respond to this therapy. Herein, we examined whether CRT simulations based on individualized realistic three-dimensional heart models can predict the therapeutic effect of CRT in a canine model of heart failure with left bundle branch block. In four canine models of failing heart with dyssynchrony, individualized three-dimensional heart models reproducing the electromechanical activity of each animal were created based on the computer tomographic images. CRT simulations were performed for 25 patterns of three ventricular pacing lead positions. Lead positions producing the best and the worst therapeutic effects were selected in each model. The validity of predictions was tested in acute experiments in which hearts were paced from the sites identified by simulations. We found significant correlations between the experimentally observed improvement in ejection fraction (EF) and the predicted improvements in ejection fraction (P<0.01) or the maximum value of the derivative of left ventricular pressure (P<0.01). The optimal lead positions produced better outcomes compared with the worst positioning in all dogs studied, although there were significant variations in responses. Variations in ventricular wall thickness among the dogs may have contributed to these responses. Thus CRT simulations using the individualized three-dimensional heart models can predict acute hemodynamic improvement, and help determine the optimal positions of the pacing lead.

Exploring the Electrophysiologic and Hemodynamic Effects of Cardiac Resynchronization Therapy: From Bench to Bedside and Vice Versa

Cardiac resynchronization therapy (CRT) is an important therapy for heart failure patients with prolonged QRS duration. In patients with left bundle branch block the altered left ventricular electrical activation results in dyssynchronous, inefficient contraction of the left ventricle. CRT aims to reverse these changes and to improve cardiac function. This article explores the electrophysiologic and hemodynamic changes that occur during CRT in patient and animal studies. It also addresses how novel techniques, such as multipoint and endocardial pacing, can further improve the electromechanical response.

Beneficial Effect on Cardiac Resynchronization From Left Ventricular Endocardial Pacing Is Mediated by Early Access to High Conduction Velocity Tissue: Electrophysiological Simulation Study

BACKGROUND

Cardiac resynchronization therapy (CRT) delivered via left ventricular (LV) endocardial pacing (ENDO-CRT) is associated with improved acute hemodynamic response compared with LV epicardial pacing (EPI-CRT). The role of cardiac anatomy and physiology in this improved response remains controversial. We used computational electrophysiological models to quantify the role of cardiac geometry, tissue anisotropy, and the presence of fast endocardial conduction on myocardial activation during ENDO-CRT and EPI-CRT.

METHODS AND RESULTS

Cardiac activation was simulated using the monodomain tissue excitation model in 2-dimensional (2D) canine and human and 3D canine biventricular models. The latest activation times (LATs) for LV endocardial and biventricular epicardial tissue were calculated (LVLAT and TLAT), as well the percentage decrease in LATs for endocardial (en) versus epicardial (ep) LV pacing (defined as %dLV=100×(LVLATep-LVLATen)/LVLATep and %dT=100×(TLATep-TLATen)/TLATep, respectively). Normal canine cardiac anatomy is responsible for %dLV and %dT values of 7.4% and 5.5%, respectively. Concentric and eccentric remodeled anatomies resulted in %dT values of 15.6% and 1.3%, respectively. The 3D biventricular-paced canine model resulted in %dLV and %dT values of -7.1% and 1.5%, in contrast to the experimental observations of 16% and 11%, respectively. Adding fast endocardial conduction to this model altered %dLV and %dT to 13.1% and 10.1%, respectively.

CONCLUSIONS

Our results provide a physiological explanation for improved response to ENDO-CRT. We predict that patients with viable fast-conducting endocardial tissue or distal Purkinje network or both, as well as concentric remodeling, are more likely to benefit from reduced ATs and increased synchrony arising from endocardial pacing.

Patient-specific modelling of cardiac electrophysiology in heart-failure patients

Aims

Left-ventricular (LV) conduction disturbances are common in heart-failure patients and a left bundle-branch block (LBBB) electrocardiogram (ECG) type is often seen. The precise cause of this pattern is uncertain and is probably variable between patients, ranging from proximal interruption of the left bundle branch to diffuse distal conduction disease in the working myocardium. Using realistic numerical simulation methods and patient-tailored model anatomies, we investigated different hypotheses to explain the observed activation order on the LV endocardium, electrogram morphologies, and ECG features in two patients with heart failure and LBBB ECG.

Methods and results

Ventricular electrical activity was simulated using reaction–diffusion models with patient-specific anatomies. From the simulated action potentials, ECGs and cardiac electrograms were computed by solving the bidomain equation. Model parameters such as earliest activation sites, tissue conductivity, and densities of ionic currents were tuned to reproduce the measured signals. Electrocardiogram morphology and activation order could be matched simultaneously. Local electrograms matched well at some sites, but overall the measured waveforms had deeper S-waves than the simulated waveforms.

Conclusion

Tuning a reaction–diffusion model of the human heart to reproduce measured ECGs and electrograms is feasible and may provide insights in individual disease characteristics that cannot be obtained by other means.

Narrow QRS systolic heart failure: is there a target for cardiac resynchronization?

Cardiac resynchronization therapy has revolutionized the management of systolic heart failure in patients with prolonged QRS during the past 20 years. Initially, the use of this treatment in patients with shorter QRS durations showed promising results, which have since been opposed by larger randomized controlled trials. Despite this, some questions remain, such as, whether correction of mechanical dyssynchrony is the therapeutic target by which biventricular pacing may confer benefit in this group, or are there other mechanisms that need consideration? In addition, novel techniques of cardiac resynchronization therapy delivery such as endocardial and multisite pacing may reduce potential detrimental effects of biventricular pacing, thereby improving the benefit/harm balance of this therapy in some patients.

Noninvasive mapping of electrical dyssynchrony in heart failure and cardiac resynchronization therapy

Causes for diverse effects of cardiac resynchronization therapy (CRT) are poorly understood. Because CRT is an electrical therapy, it may be best understood by detailed characterization of electrical substrate and its interaction with pacing. Electrocardiogram (ECG) features affect CRT outcomes. However, the surface ECG reports rudimentary electrical data. In contrast, noninvasive electrocardiographic imaging provides high-resolution single-beat ventricular mapping. Several complex characteristics of electrical substrate, not decipherable from the 12-lead ECG, are linked to CRT effect. CRT response may be improved by candidate selection and left ventricular lead placement directed by more precise electrical evaluation, on an individual patient basis.

Strategies to improve cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) emerged 2 decades ago as a useful form of device therapy for heart failure associated with abnormal ventricular conduction, indicated by a wide QRS complex. In this Review, we present insights into how to achieve the greatest benefits with this pacemaker therapy. Outcomes from CRT can be improved by appropriate patient selection, careful positioning of right and left ventricular pacing electrodes, and optimal timing of electrode stimulation. Left bundle branch block (LBBB), which can be detected on an electrocardiogram, is the predominant substrate for CRT, and patients with this conduction abnormality yield the most benefit. However, other features, such as QRS morphology, mechanical dyssynchrony, myocardial scarring, and the aetiology of heart failure, might also determine the benefit of CRT. No single left ventricular pacing site suits all patients, but a late-activated site, during either the intrinsic LBBB rhythm or right ventricular pacing, should be selected. Positioning the lead inside a scarred region substantially impairs outcomes. Optimization of stimulation intervals improves cardiac pump function in the short term, but CRT procedures must become easier and more reliable, perhaps with the use of electrocardiographic measures, to improve long-term outcomes.

Delayed trans-septal activation results in comparable hemodynamic effect of left ventricular and biventricular endocardial pacing: insights from electroanatomical mapping

BACKGROUND

We sought to compare left ventricular (LVepi) and biventricular epicardial pacing (BIVepi) with LV (LVendo) and BIV endocardial pacing (BIVendo) in patients with chronic heart failure with an emphasis on the underlying electrophysiological mechanisms and hemodynamic effects.

METHODS AND RESULTS

Ten patients with chronically implanted cardiac resynchronization devices underwent temporary LVendo and BIVendo pacing with an LV endocardial roving catheter. A pressure wire and noncontact mapping array were placed to the LV cavity to measure LVdP/dtmax and perform electroanatomical mapping. At the optimal endocardial position, the acute hemodynamic response (AHR) was superior to epicardial stimulation, the AHR to BIVendo pacing and LVendo pacing being comparable (21±15% versus 22±17%; P=NS). During intrinsic conduction, QRS duration was 185±30 ms, endocardial LV total activation time 92±27 ms, and trans-septal activation time 60±21 ms. With LVendo pacing, QRS duration (187±29 ms; P=NS) and endocardial LV total activation time (91±23 ms; P=NS) were comparable with intrinsic conduction. There was no significant difference in endocardial LV total activation time between LVendo and BIVendo pacing (91±23 versus 85±15 ms; P=NS). Assessment of isochronal maps identified slow trans-septal conduction with both LVendo and BIVendo pacing resulting in activation of almost the entire LV endocardium prior to septal breakout, thereby limiting any possible fusion with either pacing mode.

CONCLUSIONS

The equivalent AHR to LVendo and BIVendo pacing may be explained by prolonged trans-septal conduction limiting fusion of electrical wavefronts. The optimal AHR was associated with predominantly LV pre-excitation and depolarization. Our results suggest that LV pacing alone may offer a viable endocardial stimulation strategy to achieve cardiac resynchronization.