The Benefit of Cardiac Resynchronization Therapy and QRS Duration: A Meta-Analysis

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.

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.

2023 HRS/APHRS/LAHRS guideline on cardiac physiologic pacing for the avoidance and mitigation of heart failure

Cardiac physiologic pacing (CPP), encompassing cardiac resynchronization therapy (CRT) and conduction system pacing (CSP), has emerged as a pacing therapy strategy that may mitigate or prevent the development of heart failure (HF) in patients with ventricular dyssynchrony or pacing-induced cardiomyopathy. This clinical practice guideline is intended to provide guidance on indications for CRT for HF therapy and CPP in patients with pacemaker indications or HF, patient selection, pre-procedure evaluation and preparation, implant procedure management, follow-up evaluation and optimization of CPP response, and use in pediatric populations. Gaps in knowledge, pointing to new directions for future research, are also identified.

Cardio-oncology for Pediatric and Adolescent/Young Adult Patients

OPINION STATEMENT

As chemotherapy continues to improve the lives of patients with cancer, understanding the effects of these drugs on other organ systems, and the cardiovascular system in particular, has become increasingly important. The effects of chemotherapy on the cardiovascular system are a major determinant of morbidity and mortality in these survivors. Although echocardiography continues to be the most widely used modality for assessing cardiotoxicity, newer imaging modalities and biomarker concentrations may detect subclinical cardiotoxicity earlier. Dexrazoxane continues to be the most effective therapy for preventing anthracycline-induced cardiomyopathy. Neurohormonal modulating drugs have not prevented cardiotoxicity, so their widespread, long-term use for all patients is currently not recommended. Advanced cardiac therapies, including heart transplant, have been successful in cancer survivors with end-stage HF and should be considered for these patients. Research on new targets, especially genetic associations, may produce treatments that help reduce cardiovascular morbidity and mortality.

Atrio-Ventricular Dyssynchrony After Cardiac Resynchronization Therapy: An Unusual Contributor to Heart Failure Symptoms

Cardiac resynchronization therapy (CRT) is the mainstay for the management of systolic heart failure with LVEF <35% and evidence of dyssynchrony despite optimal medical therapy. After CRT placement, persistent dyssynchronization is possible and can contribute to heart failure symptoms despite a well-functioning CRT device. Echo-guided imaging can be beneficial for the optimization of CRT in selected patients who have evidence of continued dyssynchrony despite a well-functioning CRT device.

Dyssynchronous Heart Failure: A Clinical Review

PURPOSE OF THE REVIEW

Dyssynchrony occurs when portions of the cardiac chambers contract in an uncoordinated fashion. Ventricular dyssynchrony primarily impacts the left ventricle and may result in heart failure. This entity is recognized as a major contributor to the development and progression of heart failure. A hallmark of dyssynchronous heart failure (HF_d) is left ventricular recovery after dyssynchrony is corrected. This review discusses the current understanding of pathophysiology of HF_d and provides clinical examples and current techniques for treatment.

RECENT FINDINGS

Data show that HF_d responds poorly to medical therapy. Cardiac resynchronization therapy (CRT) in the form of conventional biventricular pacing (BVP) is of proven benefit in HF_d, but is limited by a significant non-responder rate. Recently, conduction system pacing (His bundle or left bundle branch area pacing) has also shown promise in correcting HF_d. HF_d should be recognized as a distinct etiology of heart failure; HF_d responds best to CRT.

Clinical impacts of scar reduction on gated myocardial perfusion SPECT after cardiac resynchronization therapy

BACKGROUND

It had not been reported that myocardial scar shown on gated myocardial perfusion SPECT (GMPS) might reduce after cardiac resynchronization therapy (CRT). In this study, we aim to investigate the clinical impact and characteristic of scar reduction (SR) after CRT.

METHODS AND RESULTS

Sixty-one heart failure patients following standard indication for CRT received twice GMPS as pre- and post-CRT evaluations. The patients with an absolute reduction of scar ≥ 10% after CRT were classified as the SR group while the rest were classified as the non-SR group. The SR group (N = 22, 36%) showed more improvement on LV function (∆LVEF: 18.1 ± 12.4 vs 9.4 ± 9.9 %, P = 0.007, ∆ESV: - 91.6 ± 52.6 vs - 38.1 ± 46.5 mL, P < 0.001) and dyssynchrony (ΔPSD: - 26.19 ± 18.42 vs - 5.8 ± 23.0°, P < 0.001, Δ BW: - 128.7 ± 82.8 vs - 25.2 ± 109.0°, P < 0.001) than non-SR group (N = 39, 64%). Multivariate logistic regression analysis showed baseline QRSd (95% CI 1.019-1.100, P = 0.006) and pre-CRT Reduced Wall Thickening (RWT) (95% CI 1.016-1.173, P = 0.028) were independent predictors for the development of SR.

CONCLUSION

More than one third of patients showed SR after CRT who had more post-CRT improvement on LV function and dyssynchrony than those without SR. Wider QRSd and higher RWT before CRT were related to the development of SR after CRT.

CRT Efficacy in "Mid-Range" QRS Duration Among Asians Contrasted to Non-Asians, and Influence of Height

OBJECTIVES

The purpose of this study was to test the hypotheses that cardiac resynchronization therapy (CRT) efficacy differed among Asians compared with non-Asian populations, differed between QRS duration (QRSd) ranges 120-149 and ≥150 ms, and was influenced by height in the multinational ADVANCE CRT trial.

BACKGROUND

CRT guidelines, derived from trials among U.S./European patients, assign weaker recommendations to those with midrange QRSd (QRSd <150 ms). Patient height may modulate CRT efficacy. Together, these may affect CRT prescription and efficacy in Asia.

METHODS

CRT response was assessed using the Clinical Composite Score 6 months postimplant (n = 934). Heart failure events and cardiac deaths were reported until 12 months. Asian and non-Asian patients were compared overall, by QRSd <150 ms (Asian n = 71 vs non-Asian n = 248), and QRSd ≥150 ms (Asian n = 180 vs non-Asian n = 435) and by height.

RESULTS

Asians comprised 27% (251 of 934) of the primary study population. More Asians had QRSd ≥150 ms (72% [180 of 251] vs 64% [435 of 683] in non-Asian patients; P = 0.022). Overall CRT response was better in Asians vs non-Asians (Clinical Composite Score 85% vs 65%; P <0.001), and following QRSd dichotomization (QRSd <150 ms: 80% vs 59%; P <0.001; QRS ≥150 ms: 86% vs 69%; P < 0.001). HF events and cardiac deaths were fewer in Asians irrespective of QRSd (P < 0.001). Stepwise multivariable analysis indicated that in group QRSd <150 ms, nonischemic cardiomyopathy, number of other comorbidities (0-1 vs ≥4), and atrial fibrillation influenced CRT response. The trend favoring Asian race (OR: 1.46; 95% CI: 0.72-2.95) was eliminated (OR: 1.00; 95% CI: 0.47-2.11) when height or QRSd/height were included (QRSd/height P = 0.006; OR: 1.64; 95% CI: 1.15-2.35). In QRSd <150 ms, probability of CRT response diminished as height increased, but increased with QRSd/height, in both Asians and non-Asians. In QRSd ≥150 ms, height or QRSd/height had minimal effect in Asians or non-Asians.

CONCLUSIONS

Height modulates CRT efficacy among patients with QRSd <150 ms and contributes to high probability of benefit from CRT among Asians. CRT should be encouraged among Asian patients with midrange QRSd. (Advance Cardiac Resynchronization Therapy [CRT] Registry; NCT01805154).

A Simple Predictive Marker in Cardiac Resynchronization Therapy Recipients: Prominent S-Wave in Right Precordial Leads

Background and objectives: Current guidelines criteria do not satisfactorily discriminate responders to cardiac resynchronization therapy (CRT). QRS amplitude is an established index to recognize the severity of myocardial disturbance and might be a key to optimal patient selection for CRT. Materials and Methods: (1) Initial R-wave amplitude, (2) S-wave amplitude, and (3) a summation of maximal R- or R′-wave amplitude and S-wave amplitude were measured at baseline. These parameters were averaged according to right (V1 to V3) or left (V4 to V6) precordial leads. The impact of these parameters on response to CRT, which was defined as a decrease in left ventricular end-systolic volume ≥15% at six-month follow-up, was investigated. Results: Among 47 patients (71 years old, 28 men) who received guideline-indicated CRT implantation, 25 (53%) achieved the definition of CRT responder. Among baseline electrocardiogram parameters, only the higher S-wave amplitude in right precordial leads was an independent predictor of CRT responders (odds ratio: 2.181, 95% confidence interval: 1.078–4.414, p = 0.030) at a cutoff of 1.44 mV. The cutoff was independently associated with cumulative incidence of heart failure readmission and appropriate electrical defibrillation following CRT implantation (p < 0.05, respectively). Conclusions: Prominent S-wave in right precordial leads might be a promising index to predict left ventricular reverse remodeling and greater clinical outcomes following CRT implantation.

Association of QRS narrowing with response to cardiac resynchronization therapy-a systematic review and meta-analysis of observational studies

Prolonged QRS duration, which reflects a higher degree of mechanical dysynchrony, is a predictor of response to CRT. However, the association of QRS narrowing after biventricular pacing with CRT response rates is not clear. Our aim was to conduct a systematic review and meta-analysis on the association between QRS narrowing after cardiac resynchronization therapy (CRT) and clinical and echocardiographic response to CRT in patients with heart failure. Two independent investigators searched MedLine and EMBASE databases through July 2018 without any limitations. Studies providing estimates (continuous data) on the association of QRS shortening with either clinical (defined as New York Heart Association (NYHA) reduction ≥ 1) or echocardiographic (defined as left ventricular end-systolic volume (LVESV) reduction ≥ 15%) response to CRT were finally included in the quantitative synthesis. We included 32 studies (14 studies (1274 patients mean age 64 years old, males 79.3%) using clinical CRT response and 18 studies (1270 patients, mean age 64 years old, males 69.1%) using echocardiographic CRT response). A significant association between QRS narrowing and shorter attained QRS duration with clinical and echocardiographic CRT response was observed. The observed association was independent of the timing of QRS width measurement after CRT implantation. Acute and late improvement of electrical dysynchrony as depicted by QRS narrowing following biventricular pacing is associated with clinical and echocardiographic response to CRT. However, large prospective studies are needed to further examine our findings.

Bradyarrhythmias and Physiologic Pacing in the ICU

Bradyarrhythmias represent a common pathology in the intensive care unit (ICU) with etiologies of varying severity. Treatment has often been focused on correcting underlying causes and may require pacing for urgent hemodynamic support. In recent years, there has been interest in physiologic pacing modalities which avoid the dyssynchrony from right ventricular (RV) only pacing. Cardiac resynchronization therapy (CRT) through biventricular pacing is a well-established device-based electrical therapy in patients with wide QRS and heart failure. Recently, it has been shown that biventricular pacing may also be pursued for hemodynamic rescue in the ICU setting. Efforts to re-engage the conduction system with His bundle pacing or further downstream have also emerged as alternative means to deliver resynchronization, with early applications in the ICU now being reported. The goal of the review is to examine bradyarrhythmia causes and management in the ICU as well as investigate new approaches in physiologic pacing and their potential roles in critically ill patients.

Multipoint Pacing with Fusion-optimized Cardiac Resynchronization Therapy: Using It All to Narrow QRS Duration

Adaptive atrioventricular (AV)-shortening algorithms have achieved QRS duration (QRSd) narrowing in traditional cardiac resynchronization therapy (CRT) patients. Multipoint pacing (MPP) has also demonstrated benefit in this population. An additional site of activation via intrinsic conduction of the septum may further contribute to CRT; however, the incorporation of all strategies together has yet to be explored. We therefore developed and tested a method combining MPP-CRT and controlled septal contribution to create a multifuse pacing (MFP) technique, establishing four ventricular activation sites for CRT patients using measurements from intracardiac electrograms (EGMs) and incorporating an AV-delay shortening algorithm (SyncAV™; Abbott Laboratories, Chicago, IL, USA) to narrow the QRSd. Patients in sinus rhythm with an AV conduction time of less than 350 ms were included in this analysis and were further stratified by strictly defined left bundle branch block (sLBBB) or nonspecific intraventricular conduction delay (IVCD). EGM-based measurements to determine the QRS septal onset to right ventricular (RV) time (SRAT) and the left ventricular (LV) to RV pacing conduction time were collected and applied to a formula to facilitate MFP. QRSd was compared between before and after programming. A total of 22 patients (19 men and three women) with similar baseline characteristics were compared (all values in mean ± standard deviation). The overall baseline QRSd of 153.31 ± 24.60 ms was decreased to 115.31 ± 16.31 ms after MFP programming (p < 0.0001). The measured SRAT was 59.40 ± 28.49 ms, resulting in a negative AV offset of −20.0 ± 24.97 ms. Patients in the sLBBB group (n = 7) were aged 67.8 ± 13.3 years and had a QRSd of 168.85 ± 27.29 ms that decreased to 113 ± 16.69 ms for a reduction of 55.42 ± 19.3 ms or 32.1% (p = 0.0003). In the IVCD group (n = 15), the baseline QRSd of 146.06 ± 20.29 ms was decreased to 116 ± 16.66 ms for a reduction of 30.07 ± 16.41 ms or 20.62% (p = 0.0001). When comparing the sLBBB and IVCD groups, the sLBBB group was favored by a reduction of 25.35 ms (p = 0.00046). Ultimately, MFP achieved statistically significant reductions in QRSd in all patients tested in this analysis. The benefit was also significantly better in the sLBBB group as compared with in the IVCD group.

Predictors of response to cardiac resynchronization therapy in patients with chronic right ventricular pacing

Background

The benefits of de novo cardiac resynchronization therapy (CRT) in patients with QRS-prolongation and impaired left-ventricular function (LVEF) are well established. Current guidelines also recommend CRT-upgrade in patients requiring permanent or frequent right ventricular pacing (RVP) with symptomatic heart failure and reduced LVEF. Whereas several predictors of response to de novo CRT-implantation such as female gender, QRS-duration, non-ischemic cardiomyopathy (NICM) are known due to large prospective trials, similar factors regarding CRT-upgrade are currently lacking.

Methods and results

We examine 114 patients 3–6 months after CRT-upgrade due to frequent RVP (> 50%) and symptomatic heart failure. Response to CRT was evaluated by improvement in NYHA class referring to the Minnesota Living With Heart Failure Questionnaire. Only cardiomyopathy type and use of Angiotensin-converting-enzyme (ACE) inhibitor had an impact on response to CRT-upgrade in a linear regression model. Patients with NICM presented a greater responder rate than patients with ischemic cardiomyopathy (ICM) (80.4 vs. 60.3%, p < 0.05). Other traditional response predictors in de novo CRT recipients (e.g. QRS-width, female gender) showed no effect on CRT-response in this cohort.

Conclusion

Only underlying heart disease (NICM vs. ICM) and the use of ACE inhibitor were significant predictors of response to CRT-upgrade. In contrast to de novo CRT-recipients, where pre-implant QRS-duration is a key predictor, QRS-duration during RV-pacing has no significant impact on CRT-response in this cohort.

Graphic abstract

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Cardiac Implantable Electronic Device Therapy in Heart Failure

The population of patients with heart failure continues to grow, which introduced significant challenges in clinical practice related to the management of cardiac arrhythmia and advanced heart failure syndromes. Device therapy has increasingly become essential in the management of life-threatening arrhythmia and clinical heart failure in this population. This review will discuss the use of cardiac implantable electronic devices in heart failure with primary focus on sudden cardiac death prevention and cardiac resynchronization, including published evidence and evolving technologies.

Association between changes in QRS width and echocardiographic responses to cardiac resynchronization therapy: A systematic review and meta-analysis

BACKGROUND

Numerous studies have illustrated the association of QRS width with the incidence of echocardiographic response to cardiac resynchronization therapy (CRT). This study aimed to summarize the observational studies regarding the magnitude of change in QRS width between responders and nonresponders to CRT.

METHODS

The PubMed, Embase, and the Cochrane Library were systematically searched for relevant studies investigating the changes of QRS width with the incidence of echocardiographic response to CRT from inception till May 2019. The pooled weighted mean difference (WMD) with 95% confidence interval (CI) was calculated through random-effects model.

RESULTS

Five prospective and 6 retrospective studies with a total of 1524 patients were selected for final analysis. The reduction of QRS width in responders was significantly greater than nonresponders (WMD: -20.54 ms; 95% CI: -26.78 to -14.29; P < .001). Moreover, responders were associated with greater percentage reduction in QRS width when compared with nonresponders (WMD: -8.80%; 95% CI: -13.08 to -4.52; P < .001). Finally, the mean change in QRS width between responders and nonresponders differed when stratified by country, study design, mean age, percentage male, ejection fraction, measuring time of postimplanted QRS, ischemic cardiomyopathy, atrial fibrillation, and study quality.

CONCLUSIONS

These findings indicated that shortening QRS width after CRT device implantation showed association with greater incidence of echocardiographic responses to CRT. Further prospective studies should be conducted to evaluate the prognostic values of QRS width on the incidence of echocardiographic response to CRT.

Efficacy of a Device-Based Continuous Optimization Algorithm for Patients With Cardiac Resynchronization Therapy

BACKGROUND

Cardiac resynchronization therapy (CRT) is less effective in patients with mildly wide QRS or non-left bundle branch block (non-LBBB). A new algorithm of every minute's optimization (adaptive CRT: aCRT algorithm) is effective in patients with CRT devices. This study investigated the clinical effect of the aCRT algorithm, especially in mildly wide QRS (120≤QRS<150 ms) or non-LBBB patients receiving CRT.Methods and Results:This study included 104 CRT patients (48 patients using the aCRT algorithm [adaptive group] and 56 patients not using the aCRT algorithm [non-adaptive group]). The primary endpoint was a composite clinical outcome of cardiac death and/or heart failure (HF) hospitalization. During a median follow-up of 700 days (interquartile range 362-1,173 days), aCRT reduced the risk of the clinical outcome, even in patients with mildly wide QRS or non-LBBB (log-rank P=0.0030 and P=0.0077, respectively) by Kaplan-Meier analysis. Use of the aCRT algorithm was an independent predictor of clinical outcomes in the multivariate analysis (hazard ratio (HR) 0.28, 95% confidence interval (CI): 0.096-0.78, P=0.015), the same as in patients with mildly wide QRS (HR 0.12, 95% CI: 0.006-0.69, P=0.015).

CONCLUSIONS

The new aCRT algorithm was useful and significantly reduced the risk of the clinical outcome, even in patients with mildly wide QRS.

The Past, Present and Future of Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) has revolutionized the care of the patients with heart failure with reduced ejection fraction and electrical dyssynchrony. The current guidelines for patient selection include measurement of left ventricular systolic function, QRS duration and morphology, and functional classification. Despite consistent and increasing evidence supporting CRT use in appropriate patients, CRT has been underutilized. Notwithstanding the heterogeneous definitions of non-response, more than one-third of patients demonstrate a lack of echocardiographic reverse remodeling or poor clinical outcome following CRT. Since the causes of this non-response are multifactorial, it will require multidisciplinary efforts to overcome including optimal patient selection, procedural strategies, as well as optimizing post-implant care in patients undergoing CRT. The innovations of novel pacing approaches combined with advanced imaging technologies may eventually offer a personalized CRT system uniquely tailored to each patient's dyssynchrony signature.

Cardiac resynchronization therapy: a comprehensive review

Despite improved understanding of heart failure (HF) and advances in medical treatments, its prevalence continues to rise, and the role of implantable devices continues to evolve. While cardiac resynchronization therapy (CRT) is an accepted form of treatment for many suffering from HF, there is an ever-evolving body of evidence examining novel indications, optimization of lead placement and device programming, with several competing technologies now also on the horizon. This review aims to take a clinical perspective on the major trials, current indications, controversies and emerging aspects of CRT in the treatment of HF.

Cardiac Resynchronization Therapy in Pediatrics

Cardiac resynchronization therapy (CRT) has proven to be a powerful and effective tool in the treatment of adults with severe dilated or ischemic cardiomyopathy. A substantial portion of the adult heart failure population has severely depressed systolic function, heart failure symptoms, QRS prolongation, and left bundle branch block. Indications for CRT in adults are commonly focused on these characteristics. However, pediatric patients represent a heterogeneous group with many etiologies of heart failure and anatomic variants, with most of them not fitting the typical adult CRT criteria. The heterogeneity of the pediatric population has hindered the identification of ideal candidates for CRT, but initial experience with CRT in various groups of pediatric patients has been encouraging. This article reviews indications for and outcomes of CRT in pediatric and congenital heart disease patients.

Contemporary Review of Left Bundle Branch Block in the Failing Heart - Pathogenesis, Prognosis, and Therapy

Cardiac resynchronisation therapy (CRT) is a cornerstone in the contemporary management of heart failure. The most effective way of predicting response to this therapy remains electrocardiographic (ECG) criteria of electromechanical dyssynchrony. The left bundle branch block (LBBB) pattern is currently the most robust ECG criterion in predicting improvement in symptoms and reduction in mortality. However, recent studies using three-dimensional (3D) mapping and cardiac magnetic resonance imaging (CMR) have demonstrated heterogeneous left ventricular activation patterns in patients with LBBB. This has led to intense debate on the activation pattern of "true LBBB" and resulted in the proposal of stricter criteria for defining LBBB. This review will focus on the definitions and implications of LBBB in the CRT era. At a minimum, the use of stricter ECG criteria appears warranted, and adjunctive pre-implant imaging or mapping may further identify patient-specific electrophysiological patterns that determine response to CRT.

Ventricular dyssynchrony assessment using ultra-high frequency ECG technique

Purpose

The aim of this proof-of-concept study is to introduce new high-dynamic ECG technique with potential to detect temporal-spatial distribution of ventricular electrical depolarization and to assess the level of ventricular dyssynchrony.

Methods

5-kHz 12-lead ECG data was collected. The amplitude envelopes of the QRS were computed in an ultra-high frequency band of 500–1000 Hz and were averaged (UHFQRS). UHFQRS V lead maps were compiled, and numerical descriptor identifying ventricular dyssynchrony (UHFDYS) was detected.

Results

An electrical UHFQRS maps describe the ventricular dyssynchrony distribution in resolution of milliseconds and correlate with strain rate results obtained by speckle tracking echocardiography. The effect of biventricular stimulation is demonstrated by the UHFQRS morphology and by the UHFDYS descriptor in selected examples.

Conclusions

UHFQRS offers a new and simple technique for assessing electrical activation patterns in ventricular dyssynchrony with a temporal-spatial resolution that cannot be obtained by processing standard surface ECG. The main clinical potential of UHFQRS lies in the identification of differences in electrical activation among CRT candidates and detection of improvements in electrical synchrony in patients with biventricular pacing.

Electronic supplementary material

The online version of this article (doi:10.1007/s10840-017-0268-0) contains supplementary material, which is available to authorized users.

Utilization of cardiac resynchronization therapy in eligible patients hospitalized for heart failure and its association with patient outcomes

OBJECTIVES

We examined trends in CRT utilization overall and by sex and race and to assess whether CRT use is associated with a reduction in HF hospitalization and mortality.

BACKGROUND

It is unknown whether underutilization and race/sex-based differences in cardiac resynchronization therapy (CRT) use have persisted. The association between CRT and heart failure (HF) hospitalization and mortality in real-world practice remains unclear.

METHODS

We linked 72,008 HF patients from 388 hospitals participating in Get With The Guidelines HF eligible for CRT with Centers for Medicare & Medicaid Services data to assess CRT utilization trends, HF hospitalization rates, and all-cause mortality.

RESULTS

From 2005-2014, 18,935 (26.3%) eligible patients had CRT in place, implanted, or prescribed. The majority were male (60.0%) and white (61.9%). CRT utilization increased during the study period (P = .0002) especially in the early period. Women were less likely to receive CRT, and this difference increased over time (interaction P = .0037) despite greater mortality risk reduction (interaction P = .0043). Black patients were less likely than white patients to have CRT throughout the study period (adjusted hazard ratio (HR) 0.79; 95% CI 0.74-0.85). Patients with CRT implanted during the index hospitalization had lower mortality (adjusted HR 0.65; 95% CI 0.59-0.71) and were less likely to be readmitted for HF than patients without CRT (adjusted HR 0.64; 95% CI 0.58-0.71).

CONCLUSIONS/RELEVANCE

CRT use has increased in all populations, but it remains underutilized. CRT remains more common among white than black HF patients, and women were less likely than men to receive CRT despite deriving greater benefit.

Left Ventricular Size does not Modify the Effect of QRS Duration in Predicting Response to Cardiac Resynchronization Therapy

BACKGROUND

QRS duration (QRSd) may be impacted by both left ventricular (LV) dilatation and conduction delay. It is possible therefore that the same QRSd may portend significantly different amounts of LV activation delay in patients with small versus large left ventricles. We hypothesized that LV size modifies the effect of QRSd on predicting outcomes in patients undergoing CRT implant.

METHODS

We extracted data on consecutive patients presenting for initial CRT implant. In patients with a follow-up echocardiogram, response was defined as an absolute improvement in LV ejection fraction ≥5%. Multivariate models were created to determine if left ventricular end-diastolic diameter (LVEDD) modified the effect of QRSd on its association with both long-term survival free of left ventricular assist device (LVAD) and heart transplant and echocardiographic response.

RESULTS

464 patients met inclusion criteria. At a mean follow-up of 4.9 ± 2.6 years, there were 210 deaths, 13 heart transplants, and 12 LVAD placements. There was a weak but significant correlation between baseline QRSd and LVEDD (Spearman's Rho 0.106, P < 0.001). In a multivariate analysis, there was no evidence of effect modification of LVEDD on QRSd (LVEDDi*QRS interaction term HR 1.0 [0.995-1.006], P = 0.94). Note that 305 patients had a follow-up echocardiogram, of whom 193 met the criteria for response. In a multivariate analysis, there was no evidence of effect modification of LVEDD on QRSd (LVEDDi*QRS interaction term odds ratio 0.998 (0.988-1.008), P = 0.65).

CONCLUSION

LV size does not modify the effect of QRSd and its association with outcomes following CRT. The correlation between LV size and QRSd in patients with a QRSd ≥ 120 ms is weak.

Left ventricular partitioning in systolic heart failure subjects: addressing a mechanistic void with current therapies

ICD patients with narrow QRS, CRT non-responders, and functional MR patients all have one mechanistic failure mode that is left untreated - the scar left behind following an MI. ICDs, CRTs, and MitraClip implantation are all well-proven therapies, but the Parachute device may address the mechanistic void that remains after each of these therapies has been used and may further improve patients' outcomes. A pooled analysis of 134 subjects was conducted using the first three clinical trials which included subjects with symptomatic ischaemic HF with LV wall motion abnormalities secondary to MI, and an LV ejection fraction less than 40%. The two-year cumulative mortality rate was 12.9%, with 8.7% in the first year and an increment of 4.2% in the second, which is a 53% reduction as compared to the first year. There is a significant proportion of patients with ischaemic heart failure being excluded from cardiac rhythm management (CRT, etc.), leaving a large treatment gap until mechanical support devices (LVAD) or heart transplantation in progressive heart failure are indicated. Along with other heart failure devices, Parachute may be a useful treatment modality, addressing a mechanistic void in the treatment of this disease. Current data support improvements in haemodynamics, functional capacity, six-minute walk distance, quality of life and a promising decline in mortality two years after Parachute implantation.

Adjusting the QRS Duration by Body Mass Index for Prediction of Response to Cardiac Resynchronization Therapy: Does One QRS Size Fit All?

BACKGROUND

QRS duration (QRSd) is known to be affected by body weight and length. We tested the hypothesis that adjusting the QRSd by body mass index (BMI) may provide individualization for patient selection and improve prediction of cardiac resynchronization therapy (CRT) response.

METHODS

A total of 125 CRT recipients was analyzed to assess functional (≥1 grade reduction in NYHA class) and echocardiographic (≥15% reduction in LVESV) response to CRT at 6 months of implantation. Baseline QRSd was adjusted by BMI to create a QRS index (QRSd/BMI) and tested for prediction of CRT response in comparison to QRSd.

RESULTS

Overall, 81 patients (65%) responded to CRT volumetrically. The mean QRS index was higher in CRT responders compared to nonresponders (6.2 ± 1.1 vs 5.2 ± 0.8 ms.m(2) /kg, P < 0.001). There was a positive linear correlation between the QRS index and the change in LVESV (r = 0.487, P < 0.001). Patients with a high QRS index (≥5.5 ms.m(2) /kg, derived from the ROC analysis, AUC = 0.787) compared to those with a prolonged QRSd (≥150 ms, AUC = 0.729) had a greater functional (72% vs 28%, P < 0.001) and echocardiographic (80% vs 44%, P < 0.001) improvement at 6 months. QRS index predicted CRT response at regression analysis.

CONCLUSIONS

Indexing the QRSd by BMI improves patient selection for CRT by eliminating the influence of body weight and length on QRSd. QRS index is a novel indicator that provides promising results for prediction of CRT response.

Cardiac Resynchronization Therapy in Women

The benefits of cardiac resynchronization therapy (CRT) on the outcomes of patients with heart failure are unquestionable. Women are under-represented in all CRT studies. Most of the available data show that CRT produces a greater clinical benefit in women than men. In several studies, women have left bundle branch block more frequently than men. Women have a remarkably high (90%) CRT response over a wide range of QRS lengths (130-175 milliseconds). Use of a QRS duration of 150 milliseconds as the threshold for CRT prescription may deny a life-saving therapy to many women likely to benefit from CRT.

Cardiac resynchronization therapy update: evolving indications, expanding benefit?

Cardiac resynchronisation therapy (CRT) is an effective intervention for appropriately selected patients with heart failure, but exactly how it works is uncertain. Recent data suggest that much, or perhaps most, of the benefits of CRT are not delivered by re-coordinating left ventricular dyssynchrony. Atrio-ventricular resynchronization, reduction in mitral regurgitation and prevention of bradycardia are other potential mechanisms of benefit that will vary from one patient to the next and over time. Because there is no single therapeutic target, it is unlikely that any single measure will accurately predict benefit. The only clinical characteristic that appears to be a useful predictor of the benefits of CRT is a QRS duration of >140 ms. Many new approaches are being developed to try to improve the effectiveness of and extend the indications for CRT. These include smart pacing algorithms, better pacing-site targeting, new sensors, multipoint pacing, remote device monitoring and leadless endocardial pacing. Whether CRT is effective in patients with atrial fibrillation or whether adding a defibrillator function to CRT improves prognosis awaits further evidence.

Incidence, definition, diagnosis, and management of the cardiac resynchronization therapy nonresponder

PURPOSE OF REVIEW

Cardiac resynchronization therapy (CRT) reduces morbidity and mortality in patients with mild-to-severe heart failure. However, up to 40% of CRT recipients are nonresponders. This review addresses important aspects with regard to the identification and management of CRT nonresponders.

RECENT FINDINGS

Mid-term clinical or echocardiographic nonresponse is associated with worse clinical outcomes during the extended follow-up. A number of predictors are indicative of CRT response, which include patient characteristics, electrical determinants, and imaging techniques from preimplant to postimplant period, and can be grouped as modifiable and nonmodifiable contributors to treatment response. Advanced age, male sex, ischemic cause, end-stage heart failure, inadequate electrical delay, and absence of mechanical dyssynchrony are regarded as unfavorable but nonmodifiable factors, for which considering underutilization of CRT by refining patient selection is reasonable. On the contrary, more efforts should be made to optimize patient management by correcting those modifiable factors, such as suboptimal medical therapy, uncontrolled atrial fibrillation, left ventricular lead dislodgement or inappropriate location, loss of biventricular capture, and lack of device optimization.

SUMMARY

Proper management and careful selection of CRT recipients will transform a proportion of treatment nonresponders into responders, which is vital to improve patients' outcome.

Individual patient data network meta-analysis of mortality effects of implantable cardiac devices

OBJECTIVE

Implantable cardioverter defibrillators (ICD), cardiac resynchronisation therapy pacemakers (CRT-P) and the combination therapy (CRT-D) have been shown to reduce all-cause mortality compared with medical therapy alone in patients with heart failure and reduced EF. Our aim was to synthesise data from major randomised controlled trials to estimate the comparative mortality effects of these devices and how these vary according to patients' characteristics.

METHODS

Data from 13 randomised trials (12 638 patients) were provided by medical technology companies. Individual patient data were synthesised using network meta-analysis.

RESULTS

Unadjusted analyses found CRT-D to be the most effective treatment (reduction in rate of death vs medical therapy: 42% (95% credible interval: 32-50%), followed by ICD (29% (20-37%)) and CRT-P (28% (15-40%)). CRT-D reduced mortality compared with CRT-P (19% (1-33%)) and ICD (18% (7-28%)). QRS duration, left bundle branch block (LBBB) morphology, age and gender were included as predictors of benefit in the final adjusted model. In this model, CRT-D reduced mortality in all subgroups (range: 53% (34-66%) to 28% (-1% to 49%)). Patients with QRS duration ≥150 ms, LBBB morphology and female gender benefited more from CRT-P and CRT-D. Men and those <60 years benefited more from ICD.

CONCLUSIONS

These data provide estimates for the mortality benefits of device therapy conditional upon multiple patient characteristics. They can be used to estimate an individual patient's expected relative benefit and thus inform shared decision making. Clinical guidelines should discuss age and gender as predictors of device benefits.

Prediction of response to cardiac resynchronization therapy using left ventricular pacing lead position and cardiovascular magnetic resonance derived wall motion patterns: a prospective cohort study

BACKGROUND

Despite marked benefits in many heart failure patients, a considerable proportion of patients treated with cardiac resynchronization therapy (CRT) fail to respond appropriately. Recently, a "U-shaped" (type II) wall motion pattern identified by cardiovascular magnetic resonance (CMR) has been associated with improved CRT response compared to a homogenous (type I) wall motion pattern. There is also evidence that a left ventricular (LV) lead localized to the latest contracting LV site predicts superior response, compared to an LV lead localized remotely from the latest contracting LV site.

METHODS

We prospectively evaluated patients undergoing CRT with pre-procedural CMR to determine the presence of type I and type II wall motion patterns and pre-procedural echocardiography to determine end systolic volume (ESV). We assessed the final LV lead position on post-procedural fluoroscopic images to determine whether the lead was positioned concordant to or remote from the latest contracting LV site. CRT response was defined as a ≥ 15% reduction in ESV on a 6 month follow-up echocardiogram.

RESULTS

The study included 33 patients meeting conventional indications for CRT with a mean New York Heart Association class of 2.8 ± 0.4 and mean LV ejection fraction of 28 ± 9%. Overall, 55% of patients were echocardiographic responders by ESV criteria. Patients with both a type II pattern and an LV lead concordant to the latest contracting site (T2CL) had a response rate of 92%, compared to a response rate of 33% for those without T2CL (p = 0.003). T2CL was the only independent predictor of response on multivariate analysis (odds ratio 18, 95% confidence interval 1.6-206; p = 0.018). T2CL resulted in significant incremental improvement in prediction of echocardiographic response (increase in the area under the receiver operator curve from 0.69 to 0.84; p = 0.038).

CONCLUSIONS

The presence of a type II wall motion pattern on CMR and a concordant LV lead predicts superior CRT response. Improving patient selection by evaluating wall motion pattern and targeting LV lead placement may ultimately improve the response rate to CRT.

Regenerative Therapy Prevents Heart Failure Progression in Dyssynchronous Nonischemic Narrow QRS Cardiomyopathy

Background

Cardiac resynchronization therapy using bi-ventricular pacing is proven effective in the management of heart failure (HF) with a wide QRS-complex. In the absence of QRS prolongation, however, device-based resynchronization is reported unsuitable. As an alternative, the present study tests a regenerative cell-based approach in the setting of narrow QRS-complex HF.

Methods and Results

Progressive cardiac dyssynchrony was provoked in a chronic transgenic model of stress-triggered dilated cardiomyopathy. In contrast to rampant end-stage disease afflicting untreated cohorts, stem cell intervention early in disease, characterized by mechanical dyssynchrony and a narrow QRS-complex, aborted progressive dyssynchronous HF and prevented QRS widening. Stem cell-treated hearts acquired coordinated ventricular contraction and relaxation supporting systolic and diastolic performance. Rescue of contractile dynamics was underpinned by a halted left ventricular dilatation, limited hypertrophy, and reduced fibrosis. Reverse remodeling reflected a restored cardiomyopathic proteome, enforced at systems level through correction of the pathological molecular landscape and nullified adverse cardiac outcomes. Cell therapy of a dyssynchrony-prone cardiomyopathic cohort translated prospectively into improved exercise capacity and prolonged survivorship.

Conclusions

In narrow QRS HF, a regenerative approach demonstrated functional and structural benefit, introducing the prospect of device-autonomous resynchronization therapy for refractory disease.

Relation of QRS duration to response to cardiac resynchronization therapy

Left bundle branch block (LBBB) is the most reliable electrocardiographic predictor of responsiveness to cardiac resynchronization therapy (CRT). However, not all patients with LBBB will respond to CRT. Our aim was to investigate the interaction between QRS duration, LBBB-type morphology, and the responsiveness to CRT. We retrospectively analyzed electrocardiograms of 243 patients who underwent CRT implantation according to current clinical indications. A 6-month reduction of left ventricular end-systolic volume >15% was used to identify CRT responders. The clinical end point consisted of death, hospitalization for heart failure and sustained rapid ventricular tachyarrhythmias. An LBBB morphology was present in 169 patients (70%) and 101 of these (60%) were responders to CRT. Analyzing the interaction between QRS duration and CRT responsiveness in patients with LBBB, a "U shaped" distribution resulted, with nonresponders clustered between 120 and 130 ms and above 180 ms. The receiver operating characteristic curve analysis identified 178 ms as the optimal cut-off value of QRS to predict a nonresponsiveness to CRT (area under the curve = 0.67 [95% confidence interval 0.57 to 0.76]). At multivariate analysis, only an ischemic cause and a QRS ≥178 ms were independent predictors of nonresponsiveness to CRT (area under the curve = 0.75). Patients with LBBB with QRS ≥178 ms had greater likelihood of adverse clinical events during a mean follow-up of 32 months (p = 0.049). In conclusion, in patients with LBBB undergoing CRT, a marked QRS widening (i.e., ≥178 ms) is related to worse echocardiographic responsiveness and lower event free survival rate compared with patients with an intermediate QRS widening.

Identification of Genetic Markers for Treatment Success in Heart Failure Patients

Background—

Cardiac resynchronization therapy (CRT) can improve ventricular size, shape, and mass and reduce mitral regurgitation by reverse remodeling of the failing ventricle. About 30% of patients do not respond to this therapy for unknown reasons. In this study, we aimed at the identification and classification of CRT responder by the use of genetic variants and clinical parameters.

Methods and Results—

Of 1421 CRT patients, 207 subjects were consecutively selected, and CRT responder and nonresponder were matched for their baseline parameters before CRT. Treatment success of CRT was defined as a decrease in left ventricular end-systolic volume >15% at follow-up echocardiography compared with left ventricular end-systolic volume at baseline. All other changes classified the patient as CRT nonresponder. A genetic association study was performed, which identified 4 genetic variants to be associated with the CRT responder phenotype at the allelic ( P <0.035) and genotypic ( P <0.031) level: rs3766031 ( ATPIB1 ), rs5443 ( GNB3 ), rs5522 ( NR3C2 ), and rs7325635 ( TNFSF11 ). Machine learning algorithms were used for the classification of CRT patients into responder and nonresponder status, including combinations of the identified genetic variants and clinical parameters.

Conclusions—

We demonstrated that rule induction algorithms can successfully be applied for the classification of heart failure patients in CRT responder and nonresponder status using clinical and genetic parameters. Our analysis included information on alleles and genotypes of 4 genetic loci, rs3766031 ( ATPIB1 ), rs5443 ( GNB3 ), rs5522 ( NR3C2 ), and rs7325635 ( TNFSF11 ), pathophysiologically associated with remodeling of the failing ventricle.

Impact of pacing site on QRS duration and its relationship to hemodynamic response in cardiac resynchronization therapy for congestive heart failure

INTRODUCTION

Recent studies have demonstrated that left ventricular (LV) pacing site is a critical parameter in optimizing cardiac resynchronization therapy (CRT). The present study evaluates the effect of pacing from different LV locations on QRS duration (QRSd) and their relationship to acute hemodynamic response in congestive heart failure patients.

METHODS AND RESULTS

Thirty-five patients with nonischemic dilated cardiomyopathy and left bundle branch block referred for CRT device implantation were studied. Eleven predetermined LV pacing sites were systematically assessed in random order: epicardial: coronary sinus (CS); endocardial: basal and mid-cavity (septal, anterior, lateral, and inferior), apex, and the endocardial site facing the CS pacing site. For each patient QRSd and +dP/dtmax during baseline (AAI) and DDD LV pacing at 2 atrioventricular delays were compared. Response to CRT was significantly better in patients with wider baseline QRSd (≥150 milliseconds). Hemodynamic response was inversely correlated to increase of QRSd during LV pacing (short atrioventricular [AV] delay: r = 0.44, P < 0.001; long AV delay: r = 0.59, P < 0.001). Compared to baseline, LV pacing at the site of shortest QRSd significantly improved +dP/dtmax (+18 ± 25%, P < 0.001) but was not superior to other conventional strategy (lateral wall, CS pacing, and echo-guided) and was inferior to a hemodynamically guided strategy.

CONCLUSIONS

In our study, we have demonstrated that changes of QRSd during LV pacing correlated with acute hemodynamic response and that LV pacing location was a primary determinant of paced QRSd. Although QRSd did not predict the maximum hemodynamic response, our results confirm the link between electrical activation and hemodynamic response of the LV during CRT.

Regression of fragmented QRS complex: a marker of electrical reverse remodeling in cardiac resynchronization therapy

BACKGROUND

Fragmented QRS (fQRS) marks inhomogeneous activation and asynchronous cardiac contraction. It has been proved that cardiac resynchronization therapy (CRT) could reverse geometrical remodeling as well as correct electrical dyssynchrony. We aimed to investigate whether fQRS changed corresponding to the therapeutic response to CRT.

METHODS

Patients who underwent de novo CRT implantation previously and had ≥1 follow-up between August 2012 and September 2013 in our hospital were investigated. Intrinsic electrocardiogram was recorded and fQRS in any lead was calculated. Response to CRT was defined as absolute improvement in left ventricular ejection fraction by ≥10% or by improvement >1 New York Heart Association class and without heart failure hospitalization.

RESULTS

A total of 75 patients (48 male, mean ages, 61 ± 9 years) were included in this study. At a median follow-up of 13 months, 57 patients had response to CRT. Responders had narrowed QRS (from 167 ± 23 ms to 158 ± 19 ms, P = 0.003) and reduced fQRS post-CRT. Nonresponders had QRS prolonging (from 151 ± 26 ms to 168 ± 16 ms, P = 0.033) and increase in fQRS. Eleven of 12 patients with reduced fQRS were responders and 8 of 12 with increased fQRS were nonresponders. Both changes in QRS and fQRS correlated strongly with CRT response (r = 0.389, P = 0.001 and r = 0.403, P = 0.000, respectively). Reduction of fQRS in ≥1 leads had high specificity (95%) in association to responders, though in low sensitivity (19%).

CONCLUSIONS

The changes in fQRS associated with therapeutic response to CRT. Regression of fQRS could be a maker of electrical reverse remodeling following CRT.

Probability and magnitude of response to cardiac resynchronization therapy according to QRS duration and gender in nonischemic cardiomyopathy and LBBB

BACKGROUND

QRS morphology and QRS duration (QRSd) determine cardiac resynchronization therapy (CRT) candidate selection but criteria require refinement.

OBJECTIVE

To assess CRT effect according to QRSd, treated by dichotomization vs a continuous function, and modulation by gender.

METHODS

Patients selected were those with New York Heart Association class III/IV heart failure and with left bundle branch block and nonischemic cardiomyopathy (to test "pure" CRT effect) with pre- and postimplant echocardiographic evaluations. Positive response was defined as increased left ventricular ejection fraction (LVEF) post-CRT.

RESULTS

In 212 patients (LVEF 19% ± 7.1%; QRSd 160 ± 23 ms; 105 (49.5%) women), CRT increased LVEF to 30% ± 15% (P < .001) during a median follow-up of 2 years. Positive response occurred in 150 of 212 (71%) patients. Genders did not differ for QRSd, pharmacotherapy, and comorbidities, but response to CRT among women was greater: incidence 84% (88 of 105) in women vs 58% (62 of 107) in men (P < .001); increase in LVEF 15% ± 14% vs 7.2% ± 13%, respectively (P < .001). Overall, the response rate was 58% when QRSd <150 ms and 76% when QRSd ≥150 ms (P = .009). This probability differed between genders: 86% in women vs 36% in men (P < .001) when QRSd <150 ms and 83% vs 69%, respectively, when QRSd ≥150 ms (P = .05). Thus, female response rates remained high whether QRSd was <150 ms or ≥150 ms (86% vs 83%; P = .77) but differed in men (36% vs 69%; P < .001). With QRSd as a continuum, the CRT-response relationship was nonlinear and significantly different between genders. Female superiority at shorter QRSd inverted with prolongation >180 ms.

CONCLUSION

The QRSd-CRT response relationship in patients with heart failure and with left bundle branch block and nonischemic cardiomyopathy is better described by a sex-specific continuous function and not by dichotomization by 150 ms, which excludes a large proportion of women with potentially favorable outcome.