Cardiac resynchronization therapy non-responder to responder conversion rate in the MORE-CRT MPP trial

Evolving Indications, Challenges, and Advances in Cardiac Resynchronization Therapy for Heart Failure

Cardiac resynchronization therapy (CRT) via biventricular pacing has markedly improved heart failure outcomes over the past two decades. However, some patients show no clinical improvement or evidence of reverse remodeling following device implantation. Challenges include suboptimal patient selection, limitations in the characterization of conduction disease (especially nonspecific interventricular conduction delays), procedural constraints, inappropriate device programming, and delayed referral. Moreover, there remains no formal consensus on evaluating and characterizing CRT efficacy. Underutilization persists among women and minoritized racial and ethnic groups. Targeted research addressing unmet needs has led to evolving guideline indications. Novel electrocardiographic and imaging techniques are continually being developed to improve patient selection and alternate pacing strategies have emerged. Conduction system pacing may allow for a more physiologic approach to CRT. Observational studies and small clinical trials have shown comparable or superior efficacy of conduction system pacing over traditional biventricular pacing; however, more studies are needed. LAY SUMMARY: Cardiac resynchronization therapy via biventricular pacing has transformed heart failure management over the past two decades. This review examines persistent challenges in clinical practice and evolving guideline recommendations. Key issues, including refining patient selection, better characterizing conduction abnormalities, and optimizing device programming, were highlighted. Emerging evidence suggests conduction system pacing as a physiologic alternative to biventricular pacing, with early studies showing promising outcomes. However, rigorous clinical trials are needed to confirm these findings and guide future practice. Advancing CRT necessitates continued innovation and strategies to improve equity and access across diverse populations.

European Society of Cardiology (ESC) clinical consensus statement on indications for conduction system pacing, with special contribution of the European Heart Rhythm Association of the ESC and endorsed by the Asia Pacific Heart Rhythm Society, the Canadian Heart Rhythm Society, the Heart Rhythm Society, and the Latin American Heart Rhythm Society

Conduction system pacing (CSP) is being increasingly adopted as a more physiological alternative to right ventricular and biventricular pacing. Since the 2021 European Society of Cardiology pacing guidelines, there has been growing evidence that this therapy is safe and effective. Furthermore, left bundle branch area pacing was not covered in these guidelines due to limited evidence at that time. This Clinical Consensus Statement provides advice on indications for CSP, taking into account the significant evolution in this domain.

The Functional and Imaging Implications of Left Bundle Branch Pacing in Ischemic Cardiomyopathy

Heart failure with reduced ejection fraction due to ischemic cardiomyopathy remains a significant clinical challenge. Electrical conduction delays exacerbate symptoms by causing uncoordinated contractions, reducing pumping efficiency, and increasing mortality. Right ventricular pacing further worsens dyssynchrony, while resynchronization therapy improves outcomes but has a high non-responder rate. Given these limitations, bundle branch pacing engages the heart's conduction system, restoring synchronized contraction and enhancing cardiac function. This review examines the impact of left-bundle-branch-block-induced dyssynchrony, the role of advanced imaging in assessing ventricular function, and the clinical outcomes of bundle branch pacing in heart failure patients. Specifically, we explore the mechanical and hemodynamic effects of left bundle branch block, imaging techniques for dyssynchrony evaluation, and the comparative benefits of bundle branch pacing versus resynchronization therapy. Conduction delays impair function, increase myocardial stress, and worsen clinical outcomes. Advanced imaging plays a critical role in patient selection, identifying those most likely to benefit from conduction system pacing. By restoring electrical coordination, bundle branch pacing enhances ventricular function, reduces hospitalizations, and promotes reverse remodeling. It offers similar or superior benefits to conventional resynchronization therapy, regulates stress hormones, reduces oxidative damage, and improves calcium handling. Bundle branch pacing represents a significant advancement in heart failure management, but careful patient selection remains crucial. Future research should focus on optimizing implantation techniques and validating long-term benefits through large-scale clinical trials.

Optimizing CRT Lead Placement Accuracy With CMR-Guided On-Screen Targeting: A Randomized Controlled Trial (ADVISE-CRT III)

BACKGROUND

To improve cardiac resynchronization therapy (CRT) an on-screen image-guidance platform, CARTBox-Suite (CART-Tech B.V.), was developed to identify left ventricular pacing electrode (LVPE) implantation sites and facilitate precise LVPE placement. This multicenter randomized trial evaluated the efficacy of image guidance on LVPE implantation accuracy and its impact on left ventricular end-systolic volume (LVESV) reduction 6 months after CRT.

OBJECTIVES

The aim of this trial is to improve the accuracy and efficacy of LVPE placement in CRT.

METHODS

A total of 131 heart failure patients (80% with Class I CRT indication) were enrolled across 7 hospitals in the Netherlands. CARTBox-Suite, which utilizes a cloud-based AI algorithm, was used to identify a target area with late mechanical activation based on cardiac magnetic resonance imaging. Scarred areas marked by late gadolinium enhancement were excluded. Patients were randomized to image-guided implantation, with on-screen guidance during the procedure or conventional implantation.

RESULTS

The primary endpoint, LVPE implantation in the target area, was achieved significantly more often in the image-guided group (66.7% vs 29.2%; P < 0.001). The secondary endpoint was fewer LVPE placed in scarred areas in the image-guided group (7.1% vs 36.4%; P = 0.006). Mean LVESV reduction was greater in the image-guided group (43.2% vs. 37.6%), although not significantly (P = 0.166). Patients with myocardial scar showed greater LVESV reduction with image guidance (40.7% vs 27.7%; P = 0.028).

CONCLUSIONS

Image-guided implantation resulted in significantly more LVPE placed in the target area and greater LVESV reduction in patients with myocardial scar.

Recent Advances in Cardiac Resynchronization Therapy: Current Treatment and Future Direction

Cardiac Resynchronization Therapy (CRT) has been established as a major component of heart failure management, resulting in a significant reduction in patient morbidity and death for patients with increased QRS duration, low left ventricular ejection fraction (LVEF), and high risk of arrhythmias. The ability to synchronize both ventricles, lower heart failure hospitalizations, and optimize clinical outcomes are some of the attractive characteristics of biventricular pacing, or CRT. However, the high rate of CRT non-responders has led to the development of new modalities including leadless CRT pacemakers (CRT-P) and devices focused on conduction system pacing (CSP). This comprehensive review aims to present recent findings from CRT clinical trials and systematic reviews that have been published that will likely guide future directions in patient care.

Cardiac resynchronization therapy (CRT) nonresponders in the contemporary era: A state-of-the-art review

In the 2000s, cardiac resynchronization therapy (CRT) became a revolutionary treatment for heart failure with reduced left ventricular ejection fraction (HFrEF) and wide QRS. However, about one-third of CRT recipients do not show a favorable response. This review of the current literature aims to better define the concept of CRT response/nonresponse. The diagnosis of CRT nonresponder should be viewed as a continuum, and it cannot rely solely on a single parameter. Moreover, baseline features of some patients might predict an unfavorable response. A strong collaboration between heart failure specialists and electrophysiologists is key to overcoming this challenge with multiple strategies. In the contemporary era, new pacing modalities, such as His-bundle pacing and left bundle branch area pacing, represent a promising alternative to CRT. Observational studies have demonstrated their potential; however, several limitations should be addressed. Large randomized controlled trials are needed to prove their efficacy in HFrEF with electromechanical dyssynchrony.

Left bundle branch area pacing versus endocardial resynchronization in patients with heart failure

BACKGROUND

Left bundle branch area pacing (LBBAP) and endocardial resynchronization (Endo-CRT) are alternatives to biventricular pacing for cardiac resynchronization therapy (CRT).

OBJECTIVE

To compare the outcomes of LBBAP versus Endo-CRT using conventional pacing leads.

METHODS

Patients with heart failure (HF) undergoing CRT with LBBAP or Endo-CRT were included. The primary efficacy outcome was a composite of HF-related hospitalization and all-cause mortality. The primary safety outcome was any procedure-related complication. Secondary outcomes included procedural characteristics, electrocardiographic, and echocardiographic parameters.

RESULTS

A total of 223 patients (LBBAP n = 197, Endo-CRT n = 26; mean age 69 ± 10.3 years, 32.3% female) were included. Patients in the LBBAP group had lower NYHA class, shorter preprocedural QRS durations (161 [142-183] vs. 180 [170-203] msec, p < .001), and a lower preprocedural spironolactone use (57.4% vs. 84.6%, p = .009) than patients in the Endo-CRT group. Fluoroscopy time was significantly shorter in patients undergoing LBBAP (11.4 [7.2-20] vs. 23 [14.2-34.5] min; p < .001). There was no significant difference in the primary efficacy outcome between both groups (Cox proportional HR 1.21, 95% CI 0.635-2.31; p = .56). During follow-up, patients undergoing LBBAP had a lower incidence of stroke than patients in the Endo-CRT group (0% vs. 11.5%, p = .001). Postprocedural LVEF (35% [25-45] vs. 40% [20-55]; p = .307) and change in LVEF (7% [0-20] vs. 11% [2-18]; p = .384) were similar between the LBBAP and the Endo-CRT groups, respectively.

CONCLUSION

LBBAP and Endo-CRT using conventional leads are associated with similar mortality and HF-related hospitalization, as well as improvements in LVEF. Endo-CRT is associated with longer fluoroscopy times and a higher risk of stroke.

Multipoint pacing is associated with improved prognosis and cardiac resynchronization therapy response: MORE-CRT MPP randomized study secondary analyses

AIMS

Cardiac resynchronization therapy (CRT) via biventricular (BIV) pacing is indicated in patients with heart failure (HF), reduced ejection fraction, and prolonged QRS duration. Quadripolar leads and multipoint pacing (MPP) allow multiple left ventricle (LV) sites pacing. We aimed to assess the clinical benefit of MPP in patients who do not respond to standard BIV pacing.

METHODS AND RESULTS

Overall, 3724 patients were treated with standard BIV pacing. After 6 months, 1639 patients were considered as CRT non-responders (echo-measured relative reduction in LV end-systolic volume (LVESV) < 15%) and randomized to MPP or BIV. We analysed 593 randomized patients (291 MPP, 302 BIV), who had BIV pacing >97% of the time before randomization and complete 12 months of clinical and echocardiographic data. The endpoint composed of freedom from cardiac death and HF hospitalizations and by LVESV relative reduction ≥15% between randomization and 12 months occurred more frequently in MPP [96/291 (33.0%)] vs. BIV [71/302 (23.5%), P = 0.0103], which was also confirmed at multivariate analysis (hazard ratio = 1.55, 95% confidence interval = 1.02-2.34, P = 0.0402 vs. BIV). HF hospitalizations occurred less frequently in MPP [14/291 (4.81%)] vs. BIV [29/302 (9.60%), incidence rate ratio = 50%, P = 0.0245]. Selecting patients with a large (>30 ms) dispersion of interventricular electrical delay among the four LV lead dipoles, reverse remodelling was more frequent in MPP [18/51 (35.3%)] vs. BIV [11/62 (17.7%), P = 0.0335].

CONCLUSION

In patients who do not respond to standard CRT despite the high BIV pacing percentage, MPP is associated with lower occurrence of HF hospitalizations and higher probability of reverse LV remodelling compared with BIV pacing.

Contemporary clinical role of echocardiography in patients with advanced heart failure

Echocardiography represents an essential tool for imagers and clinical cardiologists in the management of patients with heart failure. Advanced heart failure (AdHF) is a more severe and, typically, later stage of HF that exposes patients to a high risk of adverse outcomes, with a 1-year mortality rate of around 50%. Currently, several therapies are available to improve the outcomes of these patients, reduce their mortality rate, and, possibly, delay the need for advanced therapies such as heart transplant and long-term mechanical circulatory support. When accurately performed and interpreted, echocardiography provides crucial information to properly tailor medical and device therapy of patients with AdHF and to identify those at even higher risk. In this review, we present the state of the art of echocardiography applications in the clinical management of patients with AdHF. We will discuss the role of echocardiography chronologically, beginning with the prediction of AdHF, proceeding through diagnosis, and detailing how echocardiography informs clinical decision-making, before concluding with indications for advanced therapies.

Improved all-cause mortality with left bundle branch area pacing compared to biventricular pacing in cardiac resynchronization therapy: a meta-analysis

BACKGROUND

Left bundle branch area pacing (LBBAP) has emerged as a physiological alternative pacing strategy to biventricular pacing (BIVP) in cardiac resynchronization therapy (CRT). We aimed to assess the impact of LBBAP vs. BIVP on all-cause mortality and heart failure (HF)-related hospitalization in patients undergoing CRT.

METHODS

Studies comparing LBBAP and BIVP for CRT in patients with HF with reduced left ventricular ejection fraction (LVEF) were included. The coprimary outcomes were all-cause mortality and HF-related hospitalization. Secondary outcomes included procedural and fluoroscopy time, change in QRS duration, and change in LVEF.

RESULTS

Thirteen studies (12 observational and 1 RCT, n = 3239; LBBAP = 1338 and BIVP = 1901) with a mean follow-up duration of 25.8 months were included. Compared to BIVP, LBBAP was associated with a significant absolute risk reduction of 3.2% in all-cause mortality (9.3% vs 12.5%, RR 0.7, 95% CI 0.57-0.86, p < 0.001) and an 8.2% reduction in HF-related hospitalization (11.3% vs 19.5%, RR 0.6, 95% CI 0.5-0.71, p < 0.00001). LBBAP also resulted in reductions in procedural time (mean weighted difference- 23.2 min, 95% CI - 42.9 to - 3.6, p = 0.02) and fluoroscopy time (- 8.6 min, 95% CI - 12.5 to - 4.7, p < 0.001) as well as a significant reduction in QRS duration (mean weighted difference:- 25.3 ms, 95% CI - 30.9 to - 19.8, p < 0.00001) and a greater improvement in LVEF of 5.1% (95% CI 4.4-5.8, p < 0.001) compared to BIVP in the studies that reported these outcomes.

CONCLUSION

In this meta-analysis, LBBAP was associated with a significant reduction in all-cause mortality as well as HF-related hospitalization when compared to BIVP. Additional data from large RCTs is warranted to corroborate these promising findings.

Conduction System Pacing: Hope, Challenges, and the Journey Forward

PURPOSE OF THE REVIEW

Cardiac pacing has evolved in recent years currently culminating in the specific stimulation of the cardiac conduction system (conduction system pacing, CSP). This review aims to provide a comprehensive overview of the available literature on CSP, focusing on a critical classification of studies comparing CSP with standard treatment in the two fields of pacing for bradycardia and cardiac resynchronization therapy in patients with heart failure. The article will also elaborate specific benefits and limitations associated with CSP modalities of His bundle pacing (HBP) and left bundle branch area pacing (LBBAP).

RECENT FINDINGS

Based on a growing number of observational studies for different indications of pacing therapy, both CSP modalities investigated are advantageous over standard treatment in terms of narrowing the paced QRS complex and preserving or improving left ventricular systolic function. Less consistent evidence exists with regard to the improvement of heart failure-related rehospitalization rates or mortality, and effect sizes vary between HBP and LBBAP. LBBAP is superior over HBP in terms of lead measurements and procedural duration. With regard to all reported outcomes, evidence from large scale randomized controlled clinical trials (RCT) is still scarce. CSP has the potential to sustainably improve patient care in cardiac pacing therapy if patients are appropriately selected and limitations are considered. With this review, we offer not only a summary of existing data, but also an outlook on probable future developments in the field, as well as a detailed summary of upcoming RCTs that provide insights into how the journey of CSP continues.

[New pacing strategies for heart failure]

In patients with a reduced left ventricular (LV) systolic function (ejection fraction < 35%) and a left bundle branch block with a QRS duration > 130 ms, cardiac resynchronization therapy (CRT) can contribute to an improvement in the quality of life and a reduction in mortality. The resynchronization is mostly achieved by pacing via an epicardial LV lead in the coronary sinus; however, this approach is often limited by the patient's venous anatomy and an increase in the stimulation threshold over time. In addition, up to 30% of patients do not respond to the intervention. New treatment approaches involve direct stimulation of the conduction system by pacing of the bundle of His or left bundle branch. This enables a more physiological propagation of the stimulus. Pacing of the left bundle branch is achieved by advancing the lead into the right ventricle and screwing it deep into the interventricular septum. Due to the relatively large target area of the left bundle branch the success rate is very high (currently > 90%). Observational studies have shown a greater reduction in the QRS duration, a more pronounced improvement in systolic function and a lower hospitalization rate for heart failure associated with conduction system pacing compared to CRT using a coronary sinus lead. These findings have been confirmed in small randomized trials. Therefore, the use of left bundle branch pacing should be considered not only as a bail out in the case of failed resynchronization using coronary sinus lead placement but increasingly also as an initial pacing strategy. The results of the first large randomized trials are expected to be released in late 2024.

Heart Size Difference Drives Sex-Specific Response to Cardiac Resynchronization Therapy: A Post Hoc Analysis of the MORE-MPP CRT Trial

BACKGROUND

Studies have reported that female sex predicts superior cardiac resynchronization therapy (CRT) response. One theory is that this association is related to smaller female heart size, thus increased relative dyssynchrony at a given QRS duration (QRSd). Our objective was to investigate the mechanisms of sex-specific CRT response relating to heart size, relative dyssynchrony, cardiomyopathy type, QRS morphology, and other patient characteristics.

METHODS AND RESULTS

This is a post hoc analysis of the MORE-CRT MPP (More Response on Cardiac Resynchronization Therapy with Multipoint Pacing)  trial (n=3739, 28% women), with a subgroup analysis of patients with nonischemic cardiomyopathy and left bundle-branch block (n=1308, 41% women) to control for confounding characteristics. A multivariable analysis examined predictors of response to 6 months of conventional CRT, including sex and relative dyssynchrony, measured by QRSd/left ventricular end-diastolic volume (LVEDV). Women had a higher CRT response rate than men (70.1% versus 56.8%, P<0.0001). In subgroup analysis, regression analysis of the nonischemic cardiomyopathy left bundle-branch block subgroup identified QRSd/LVEDV, but not sex, as a modifier of CRT response (P<0.0039). QRSd/LVEDV was significantly higher in women (0.919) versus men (0.708, P<0.001). CRT response was 78% for female patients with QRSd/LVEDV greater than the median value, compared with 68% with QRSd/LVEDV less than the median value (P=0.012). The association between CRT response and QRSd/LVEDV was strongest at QRSd <150 ms.

CONCLUSIONS

In the nonischemic cardiomyopathy left bundle-branch block population, increased relative dyssynchrony in women, who have smaller heart sizes than their male counterparts, is a driver of sex-specific CRT response, particularly at QRSd <150 ms. Women may benefit from CRT at a QRSd <130 ms, opening the debate on whether sex-specific QRSd cutoffs or QRS/LVEDV measurement should be incorporated into clinical guidelines.

Non-Pharmacological Treatment of Heart Failure-From Physical Activity to Electrical Therapies: A Literature Review

Heart failure (HF) represents a significant global health challenge that is still responsible for increasing morbidity and mortality despite advancements in pharmacological treatments. This review investigates the effectiveness of non-pharmacological interventions in the management of HF, examining lifestyle measures, physical activity, and the role of some electrical therapies such as catheter ablation, cardiac resynchronization therapy (CRT), and cardiac contractility modulation (CCM). Structured exercise training is a cornerstone in this field, demonstrating terrific improvements in functional status, quality of life, and mortality risk reduction, particularly in patients with HF with reduced ejection fraction (HFrEF). Catheter ablation for atrial fibrillation, premature ventricular beats, and ventricular tachycardia aids in improving left ventricular function by reducing arrhythmic burden. CRT remains a key intervention for selected HF patients, helping achieve left ventricular reverse remodeling and improving symptoms. Additionally, the emerging therapy of CCM provides a novel opportunity for patients who do not meet CRT criteria or are non-responders. Integrating non-pharmacological interventions such as digital health alongside specific medications is key for optimizing outcomes in HF management. It is imperative to tailor approaches to individual patients in this diverse patient population to maximize benefits. Further research is warranted to improve treatment strategies and enhance patient outcomes in HF management.

Efficacy and safety of novel left ventricular pacing leads: 1-year analysis of the NAVIGATOR trial

OBJECTIVES

Assess safety and performance of novel quadripolar preshaped left ventricular (LV) leads: NAVIGO 4LV 2D ('S shaped') and NAVIGO 4LV ARC ('U shaped').

METHODS

Patients indicated for cardiac resynchronisation therapy were enrolled in a multicentre, prospective, controlled study (NAVIGATOR, NCT03279484). Patients were implanted with either a NAVIGO 4LV 2D or ARC lead, and assessed at 10 weeks, 6, 12 and 24 months post-implant. Co-primary safety and performance endpoints were assessed at 10 weeks. Safety endpoint was the patients' rate free from lead-related complications. Performance endpoint was the rate of patients with successful lead performance, defined as LV pacing threshold ≤2.5 V at 0.5 ms on at least one pacing vector, and the absence of phrenic nerve stimulation at the final programmed configuration. Lead-related complications and electrical parameters were monitored throughout study.

RESULTS

A NAVIGO 4LV lead was successfully implanted in 211 out of 217 patients (97.2%). The safety endpoint was met, with 100% and 96.1% of patients free from complications for NAVIGO 4LV 2D and ARC, respectively. The performance endpoint was met with 98.1% and 98.9% of patients with a successful lead performance for NAVIGO 4LV 2D and ARC, respectively. Over 12 months, the global complication-free rate for both leads was 97.1% (95% CI: 93.71% to 98.70%), with a mean pacing capture threshold of 1.23 V±0.73 V and a mean impedance of 951 Ω±300.1 Ω.

CONCLUSION

A high implantation success rate and low complication rate was reported for the novel NAVIGO 4LV 2D and ARC leads, along with successful performance up to 12 months.

Current Role of Electrocardiographic Imaging in Patient Selection for Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) is a recognized therapy for heart failure with altered ejection fraction and abnormal left ventricular activation time. Since the introduction of the therapy, a 30% rate of non-responders is observed and unchanged. The 12-lead ECG remains the only recommended tool for patient selection to CRT. The 12-lead ECG is, however, limited in its inability to provide a precise pattern of regional electrical activity. Electrocardiographic imaging (ECGi) provides a non-invasive detailed mapping of cardiac activation and therefore appears as a promising tool for CRT candidates. The non-invasive ventricular activation maps acquired by ECGi have been primarily explored for the diagnosis and guidance of therapy in patients with atrial or ventricular tachyarrhythmia. However, the accuracy of the system in this field is lacking and needs further improvement before considering a clinical application. On the other hand, its use for patient selection for CRT is encouraging. In this review, we introduce the technical considerations and we describe how ECGi can precisely characterize ventricular activation, especially in patients with left bundle branch block, thus identifying the electrical substrate responsive to CRT.

Feasibility of Conduction System Pacing in Patients with Baseline Bundle Branch Block-A Single-Center Mid-Term Follow-Up Study

BACKGROUND

The primary prerequisite for a successful conduction system pacing (CSP) procedure is the integrity of the conduction system, which may be impaired if a baseline bundle branch block (BBB) is present. This study aimed to evaluate the feasibility and mid-term performance of permanent CSP in patients with baseline BBB and to compare the results between left bundle branch block (LBBB) and right bundle branch block (RBBB) patterns.

MATERIAL AND METHODS

A total of 101 patients with typical BBB and an attempt at CSP were retrospectively reviewed. Procedural characteristics, pacing, sensing parameters, and complications at baseline and after a mid-term follow-up were analyzed.

RESULTS

The global procedural success for CSP was 93%. His bundle pacing (HBP) had a significantly lower success rate than left bundle branch area pacing (LBBAP) (50.5% vs. 86%). The paced QRS duration was significantly narrower with HBP. The pacing and sensing thresholds were significantly better with LBBAP. Procedural complications occurred only in the LBBAP group (two acute perforations in the LV cavity and one acute chest pain during lead fixation) without long-term sequelae. The HBP and the LBBAP procedural success rates were higher in the RBBB versus the LBBB group (62.5% vs. 44.9% and 100% vs. 81.5%, respectively). Baseline QRS duration, atrial volumes, and right ventricular diameters were significantly associated with HBP procedural failure. The follow-up pacing and sensing thresholds were similar to the baseline values for all pacing methods and BBB morphology. Only one device-related complication leading to pacing interruption was recorded.

CONCLUSION

In patients with bundle branch blocks, CSP is a feasible procedure associated with a high success rate, stable pacing and sensing parameters, and low complication rates over a mid-term follow-up.

Association of vectorcardiographic T-wave area with clinical and echocardiographic outcomes in cardiac resynchronization therapy

AIMS

Data on repolarization parameters in cardiac resynchronization therapy (CRT) are scarce. We investigated the association of baseline T-wave area, with both clinical and echocardiographic outcomes of CRT in a large, multi-centre cohort of CRT recipients. Also, we evaluated the association between the baseline T-wave area and QRS area.

METHODS AND RESULTS

In this retrospective study, 1355 consecutive CRT recipients were evaluated. Pre-implantation T-wave and QRS area were calculated from vectorcardiograms. Echocardiographic response was defined as a reduction of ≥15% in left ventricular end-systolic volume between 3 and 12 months after implantation. The clinical outcome was a combination of all-cause mortality, heart transplantation, and left ventricular assist device implantation. Left ventricular end-systolic volume reduction was largest in patients with QRS area ≥ 109 μVs and T-wave area ≥ 66 μVs compared with QRS area ≥ 109 μVs and T-wave area < 66 μVs (P = 0.004), QRS area < 109 μVs and T-wave area ≥ 66 μVs (P < 0.001) and QRS area < 109 μVs and T-wave area < 66 μVs (P < 0.001). Event-free survival rate was higher in the subgroup of patients with QRS area ≥ 109 μVs and T-wave area ≥ 66 μVs (n = 616, P < 0.001) and QRS area ≥ 109 μVs and T-wave area < 66 μVs (n = 100, P < 0.001) than the other subgroups. In the multivariate analysis, T-wave area remained associated with echocardiographic response (P = 0.008), but not with the clinical outcome (P = 0.143), when QRS area was included in the model.

CONCLUSION

Baseline T-wave area has a significant association with both clinical and echocardiographic outcomes after CRT. The association of T-wave area with echocardiographic response is independent from QRS area; the association with clinical outcome, however, is not.

Heart size disparity drives sex-specific response to cardiac resynchronization therapy: a post-hoc analysis of the MORE-MPP CRT trial

Background

Studies have reported that female sex predicts superior cardiac resynchronization therapy (CRT) response. One theory is that this association is related to smaller female heart size, thus increased "relative dyssynchrony" at given QRS durations (QRSd).

Objective

To investigate the mechanisms of sex-specific CRT response relating to heart size, relative dyssynchrony, cardiomyopathy type, QRS morphology, and other patient characteristics.

Methods

A post-hoc analysis of the MORE-CRT MPP trial (n=3739, 28% female), with a sub-group analysis of patients with non-ischaemic cardiomyopathy (NICM) and left bundle branch block (LBBB) (n=1308, 41% female) to control for confounding characteristics. A multivariable analysis examined predictors of response to 6 months of conventional CRT, including sex and relative dyssynchrony, measured by QRSd/LVEDV (left ventricular end-diastolic volume).

Results

Females had a higher CRT response rate than males (70.1% vs. 56.8%, p<0.0001). Subgroup analysis: Regression analysis of the NICM LBBB subgroup identified QRSd/LVEDV, but not sex, as a modifier of CRT response (p<0.0039). QRSd/LVEDV was significantly higher in females (0.919) versus males (0.708, p<0.001). CRT response was 78% for female patients with QRSd/LVEDV>median value, compared to 68% < median value (p=0.012). Association between CRT response and QRSd/LVEDV was strongest at QRSd<150ms.

Conclusions

In the NICM LBBB population, increased relative dyssynchrony in females, who have smaller heart sizes than their male counterparts, is a driver of sex-specific CRT response, particularly at QRSd <150ms. Females may benefit from CRT at a QRSd <130ms, opening the debate on whether sex-specific QRSd cut-offs or QRS/LVEDV measurement should be incorporated into clinical guidelines.