Cardiac Resynchronization Therapy Selection Research Articles

The electrical substrate of vectorcardiographic QRS area in cardiac resynchronization therapy: insights from ECG-imaging

Abstract Background The QRS area shows promise as a vectorcardiographic (VCG) marker for electrical dyssynchrony in patient selection for cardiac resynchronization therapy (CRT). Nevertheless, little information is known about the underlying cardiac electrical substrate it may reflect. Purpose The aim of this study was to compare the VCG QRS area with measures of cardiac electrical dyssynchrony derived from electrocardiographic imaging (ECG-imaging). Methods QRS area from the synthesized VCG (Kors transformation matrix from the 12-lead ECG) was computed for 27 patients who underwent ECG-imaging (11 patients with no history of structural heart disease and 16 consecutive CRT patients). ECG-imaging measures for electrical dyssynchrony analyzed were: ventricular electrical uncoupling (VEU) computed as the difference between the average LV and RV activation times from ECG-imaging, standard deviation of activation times from the left ventricle (LV SDAT, and the maximal activation (Max AT). Pearson correlation analyses between VCG QRS area and ECG-imaging measures of dyssynchrony were carried out for the entire cohort and for patients with a wide-QRS only. Results ECG-imaging measures of dyssynchrony compared with QRS area in 11 patients with no structural heart disease with narrow-QRS (blue) and 16 candidates for CRT with heart failure (HF) and predominantly wide-QRS (LBBB [n=6], IVCD [n=8], RVpaced [n=1], and nQRS-HF [n=1]) are provided in Figure 1. QRS area were associated with all ECG-imaging measures of dyssynchrony. However, sub-analysis in only the wide-QRS patients revealed that QRS area exhibited the strongest association with VEU. Conclusion Vectorcardiographic QRS area is associated with cardiac electrical dyssynchrony on ECG-imaging, exhibiting a particularly strong association with ventricular electrical uncoupling.

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.

LBBB and heart failure-Relationships among QRS amplitude, duration, height, LV mass, and sex.

Height, left ventricular (LV) size, and sex were proposed as additional criteria for patient selection for cardiac resynchronization therapy (CRT) but their connections with the QRS complex in left bundle branch block (LBBB) are little investigated. We evaluated these. Among patients with "true" LBBB, QRS duration (QRSd) and amplitude, and LV hypertrophy indices, were correlated with patient's height and LV mass, and compared between sexes. In this study cohort (n = 220; 60 ± 12 years; left ventricular ejection fraction [LVEF] 21 ± 7%; mostly New York Heart Association II-III, QRSd 165 ± 19 ms; 57% female; 70% responders [LVEF increased ≥5%]), LV mass was increased in all patients. QRS amplitude did not correlate with LV mass or height in any individual lead or with Sokolow-Lyon or Cornell-Lyon indices. QRSd did not correlate with height. In contrast, QRSd correlated strongly with LV mass (r = .51). CRT response rate was greater in women versus men (84% vs. 58%, p < .001) despite shorter QRSd [7% shorter (p < .0001)]. QRSd normalized for height resulted in a 2.7% and for LV mass 24% greater index in women. True LBBB criteria do not exclude HF patients with increased LV mass. QRS amplitudes do not correlate with height or LV mass. Height does not affect QRSd. However, QRSd correlates with LV size. QRSd normalized for LV mass results in 24% greater value in women in the direction of sex-specific responses. LV mass may be a significant nonelectrical modifier of QRSd for CRT.

Contractile asymmetry and survival in patients with left bundle branch abnormality treated with cardiac resynchronization therapy

Abstract Aims Currently, electrical rather than mechanical parameters of delayed left ventricular (LV) activation are used for patient selection for cardiac resynchronization therapy (CRT). However, despite adhering to current guideline-based criteria, about one-third of heart failure (HF) patients fail to derive benefit from CRT. This study sought to investigate the prognostic survival significance of a recently introduced index of contractile asymmetry (ICA) based on the deformation of entire opposing LV walls in the context of selecting patients with HF and left bundle branch abnormality (LBBB) for CRT. Methods and results We analysed 367 patients with HF and LBBB undergoing CRT (31.6% females, 69 ± 9 years, ischaemic aetiology in 50.7%, LV ejection fraction 27 ± 6%). ICA was calculated using LV strain rate values from curved anatomical M-mode plots of apical 2D echocardiography images. The predictive value of ICA was assessed using Kaplan–Meier analysis and Cox proportional hazards models. During a median follow-up time of 5.54 years, death or cardiac transplantation occurred in 105 (28.6%) cases. Higher baseline ICA values in all apical views, particularly in the two-chamber view (ICA-2ch), were associated with increased event-free survival, and the unadjusted hazard ratio was 0.28 (95% confidence interval 0.18–0.46). Higher ICA-2ch (&amp;gt;0.319 s−1) consistently predicted survival across clinical subgroups and remained significant after covariate adjustment, while the event rate sharply increased in low ICA-2ch cases. Additionally, including ICA-2ch improved the predictive value of the multivariate risk model containing the typical LBBB pattern. Conclusion Pre-implant ICA suggests a quantitative prognostic threshold for both long-term survival and adverse outcomes following CRT implantation.

Real-time three dimensional tte in quantification of left ventricular dyssynchrony

Background. The main problem in the patient selection for cardiac resynchronization therapy (CRT) is the lack of unified approaches to the definition of mechanical dyssynchrony (MD) and selection criteria.Objective. To reveal the dependence of the criteria of dyssynchrony in patients on the method and point of stimulation and to reveal the correlation of these data with the width of the QRS complex and the percentage of global two-dimensional longitudinal deformation.Design and methods. The study involved 12 patients with drug-compensated CHF of class II-IV, LVEF&lt; 35 % and a QRS duration &gt;130 ms, having CRT indications. All patients were intraoperatively injected with a retrograde transaortically guided electrode. During stimulation of each point (88 points), transesophageal Echo-KG (PE Echo-KG) was performed. TomTec and Philips Qlab 3DQ Advanced software was used for data analysis.Results. The segmental excursion and myocardial contractility differed significantly depending on the stimulation point. A moderate inverse correlation was found between ExcAvg, LVEF and QRS duration. There were a direct correlation of the SDI-16 and the QRS duration was shown, and an inverse correlation of SDI-16 with ExcAvg and LVEF. 2D longitudinal global strain was inversely correlated with the EF.Conclusion. The technique is useful for regional LV myocardial contractility assessment and patient selection and comparison of alternative approaches to LV pacing to improve response to CRT.

Modified Glasgow Prognostıc Score May Be Useful to Predict Major Adverse Cardiac Events in Heart Failure Patients Undergone Cardiac Resynchronization Treatment.

Whether modified Glasgow prognostic score predicts prognosis in patients with cardiac resynchronization therapy with defibrillation is unknown. Our aim was to investigate the association of modified Glasgow prognostic score with death and hospitalization in cardiac resynchronization therapy with defibrillation patients. A total of 306 heart failure with reduced ejection fraction patients who underwent cardiac resynchronization therapy with defibrillation implantation were categorized into 3 groups based on their modified Glasgow prognostic score categorical levels. C-reactive protein >10 mg/L or albumin <35 g/L was assigned 1 point each and the patients were classified into 0, 1, and 2 points, respectively. Remodeling was determined according to the clinical event and myocardial remodeling criteria. Major adverse cardiac events were defined as mortality and/or hospitalization for heart failure. Age, New York Heart Association functional class, modified Glasgow prognostic score prior to cardiac resynchronization therapy with defibrillation, sodium levels, and left atrial diameter were higher in the major adverse cardiac events(+) group. Age, left atrial diameter, and higher modified Glasgow prognostic score were found to be predictors of heart failure hospitalization/death in multivariable penalized Cox regression analysis. Besides, patients with lower modified Glasgow prognostic score showed better reverse left ventricular remodeling demonstrated by increase in left ventricle ejection fraction and decline in left ventricle end systolic volume. Modified Glasgow prognostic score prior to cardiac resynchronization therapy with defibrillation can be used as a predictor of long-term heart failure hospitalization and death in addition to age and left atrial diameter. These results can guide the patient selection for cardiac resynchronization therapy with defibrillation therapy and highlight the importance of nutritional status.

Novel electrocardiographic dyssynchrony criteria that may improve patient selection for cardiac resynchronization therapy.

Cardiac resynchronization therapy (CRT) is an evidence-based effective therapy of symptomatic heart failure with reduced ejection fraction refractory to optimal medical treatment associated with intraventricular conduction disturbance, that results in electrical dyssynchrony and further deterioration of systolic ventricular function. However, the non-response rate to CRT is still 20%−40%, which can be decreased by better patient selection. The main determinant of CRT outcome is the presence or absence of significant ventricular dyssynchrony and the ability of the applied CRT technique to eliminate it. The current guidelines recommend the determination of QRS morphology and QRS duration and the measurement of left ventricular ejection fraction for patient selection for CRT. However, QRS morphology and QRS duration are not perfect indicators of electrical dyssynchrony, which is the cause of the not negligible non-response rate to CRT and the missed CRT implantation in a significant number of patients who have the appropriate substrate for CRT. Using imaging modalities, many ventricular dyssynchrony criteria were devised for the detection of mechanical dyssynchrony, but their utility in patient selection for CRT is not yet proven, therefore their use is not recommended for this purpose. Moreover, CRT can eliminate only mechanical dyssynchrony due to underlying electrical dyssynchrony, for this reason ECG has a greater role in the detection of ventricular dyssynchrony than imaging modalities. To improve assessment of electrical dyssynchrony, we devised two novel ECG dyssynchrony criteria, which can estimate interventricular and left ventricular intraventricular dyssynchrony in order to improve patient selection for CRT. Here we discuss the results achieved by the application of these new ECG dyssynchrony criteria, which proved to be useful in predicting the CRT response in patients with nonspecific intraventricular conduction disturbance pattern (the second greatest group of CRT candidates), and the significance of other new ECG dyssynchrony criteria in the potential improvement of CRT outcome.

Does mechanical dyssynchrony in addition to QRS area ensure sustained response to cardiac resynchronization therapy?

Judicious patient selection for cardiac resynchronization therapy (CRT) may further enhance treatment response. Progress has been made by using improved markers of electrical dyssynchrony and mechanical discoordination, using QRSAREA, and systolic rebound stretch of the septum (SRSsept) or systolic stretch index (SSI), respectively. To date, the relation between these measurements has not yet been investigated. A total of 240 CRT patients were prospectively enrolled from six centres. Patients underwent standard 12-lead electrocardiography, and echocardiography, at baseline, 6-month, and 12-month follow-up. QRSAREA was derived using vectorcardiography, and SRSsept and SSI were measured using strain-analysis. Reverse remodelling was measured as the relative decrease in left ventricular end-systolic volume, indexed to body surface area (ΔLVESVi). Sustained response was defined as ≥15% decrease in LVESVi, at both 6- and 12-month follow-up. QRSAREA and SRSsept were both strong, multivariable adjusted, variables associated with reverse remodelling. SRSsept was associated with response, but only in patients with QRSAREA ≥ 120 μVs (AUC = 0.727 vs. 0.443). Combined presence of SRSsept ≥ 2.5% and QRSAREA ≥ 120 μVs significantly increased reverse remodelling compared with high QRSAREA alone (ΔLVESVi 38 ± 21% vs. 22 ± 21%). As a result, 92% of left bundle branch block (LBBB)-patients with combined electrical and mechanical dysfunction were 'sustained' volumetric responders, as opposed to 51% with high QRSAREA alone. Parameters of mechanical dyssynchrony are better associated with response in the presence of a clear underlying electrical substrate. Combined presence of high SRSsept and QRSAREA, but not high QRSAREA alone, ensures a sustained response after CRT in LBBB patients.

Mechanical dyssynchrony: How do we measure it, what it means, and what we can do about it

Left ventricular mechanical dyssynchrony (LVMD) is defined by a difference in the timing of mechanical contraction or relaxation between different segments of the left ventricle (LV). Mechanical dyssynchrony is distinct from electrical dyssynchrony as measured by QRS duration and has been of increasing interest due to its association with worse prognosis and potential role in patient selection for cardiac resynchronization therapy (CRT). Although echocardiography is the most used modality to assess LVMD, some limitations apply to this modality. Compared to echo-based modalities, nuclear imaging by gated single-photon emission computed tomography (GSPECT) myocardial perfusion imaging (MPI) has clear advantages in evaluating systolic and diastolic LVMD. GSPECT MPI can determine systolic and diastolic mechanical dyssynchrony by the variability in the timing in which different LV segments contract or relax, which has prognostic impact in patients with coronary artery disease and heart failure. As such, by targeting mechanical dyssynchrony instead of electrical dyssynchrony, GSPECT MPI can potentially improve patient selection for CRT. So far, few studies have investigated the role of diastolic dyssynchrony, but recent evidence seems to suggest high prevalence and more prognostic impact than previously recognized. In the present review, we provide an oversight of mechanical dyssynchrony.

Impact of left bundle branch block on myocardial perfusion and metabolism: A positron emission tomography study

BackgroundBetter understanding of pathophysiological changes, induced by left bundle branch block (LBBB), may improve patient selection for cardiac resynchronization therapy (CRT). Therefore, we assessed the effect of LBBB on regional glucose metabolism, 13N-NH3-derived absolute and semiquantitative myocardial blood flow (MBF), and their relation in non-ischemic CRT candidates. MethodsTwenty-five consecutive non-ischemic patients with LBBB underwent 18F-FDG and resting dynamic 13N-NH3 PET/CT prior to CRT implantation. Regional 18F-FDG uptake, absolute MBF, and late 13N-NH3 uptake were analyzed and corresponding septal-to-lateral wall ratios (SLR) were calculated. Segmental analysis was performed to evaluate “reverse mismatch,” “mismatch,” and “match” patterns, based on late 13N-NH3/18F-FDG uptake ratios. ResultsA significantly lower 18F-FDG uptake was observed in the septum compared to the lateral wall (SLR 0.53 ± 0.17). A similar pattern was observed for MBF (SLR 0.68 ± 0.18), whereas late 13N-NH3 uptake showed a homogeneous distribution (SLR 0.96 ± 0.13). 13N-NH3/18F-FDG “mismatch” and “reverse mismatch” segments were predominantly present in the lateral (52%) and septal wall (61%), respectively. ConclusionsNon-ischemic CRT candidates with LBBB demonstrate lower glucose uptake and absolute MBF in the septum compared to the lateral wall. However, late static 13N-NH3 uptake showed a homogenous distribution, reflecting a composite measure of altered regional MBF and metabolism, induced by LBBB.

The Evolving Role of Electrocardiography in Cardiac Resynchronization Therapy.

This study aims to summarize the literature on the role of electrocardiography (ECG) in (i) patient selection for cardiac resynchronization therapy (CRT), (ii) predicting clinical response after CRT system is implanted, and (iii) optimizing CRT programming. Progress has been made in interpreting ECG beyond QRS duration and left bundle branch (LBBB) morphology to select patients for CRT. We now understand a higher chance of response to CRT in patients with atypical right bundle branch block and lower response rates in subgroups with atypical LBBB. QRS area has emerged as a novel marker to quantify baseline electrical dyssynchrony to improve patient selection. After CRT, the resultant QRS narrowing remains the most validated predictor of long-term favorable outcome. There is increasing awareness of prolonged left ventricular pacing latency hindering the desired response to CRT. There is active interest in using ECG beyond minimizing QRS duration to optimize CRT programming for maximal resynchronization. Novel strategies include fusion of paced and/or conducted wavefronts and minimization of paced QRS area. ECG remains the ubiquitous method for ventricular electrical mapping in context of CRT. The role of ECG in elucidating baseline electrical dyssynchrony to aptly select patients for this treatment continues to evolve, and ECG is increasingly being evaluated as a reliable endpoint for optimal CRT programming.

Can machine learning improve patient selection for cardiac resynchronization therapy?

RationaleMultiple clinical trials support the effectiveness of cardiac resynchronization therapy (CRT); however, optimal patient selection remains challenging due to substantial treatment heterogeneity among patients who meet the clinical practice guidelines.ObjectiveTo apply machine learning to create an algorithm that predicts CRT outcome using electronic health record (EHR) data avaible before the procedure.Methods and resultsWe applied machine learning and natural language processing to the EHR of 990 patients who received CRT at two academic hospitals between 2004–2015. The primary outcome was reduced CRT benefit, defined as <0% improvement in left ventricular ejection fraction (LVEF) 6–18 months post-procedure or death by 18 months. Data regarding demographics, laboratory values, medications, clinical characteristics, and past health services utilization were extracted from the EHR available before the CRT procedure. Bigrams (i.e., two-word sequences) were also extracted from the clinical notes using natural language processing. Patients accrued on average 75 clinical notes (SD, 29) before the procedure including data not captured anywhere else in the EHR. A machine learning model was built using 80% of the patient sample (training and validation dataset), and tested on a held-out 20% patient sample (test dataset). Among 990 patients receiving CRT the mean age was 71.6 (SD, 11.8), 78.1% were male, 87.2% non-Hispanic white, and the mean baseline LVEF was 24.8% (SD, 7.69). Out of 990 patients, 403 (40.7%) were identified as having a reduced benefit from the CRT device (<0% LVEF improvement in 25.2%, death by 18 months in 15.6%). The final model identified 26% of these patients at a positive predictive value of 79% (model performance: Fβ (β = 0.1): 77%; recall 0.26; precision 0.79; accuracy 0.65).ConclusionsA machine learning model that leveraged readily available EHR data and clinical notes identified a subset of CRT patients who may not benefit from CRT before the procedure.

STRAIN IMAGING TECHNIQUES TO PREDICT CARDIAC RESYNCHRONIZATION THERAPY RESPONSE: A HEAD-TO-HEAD COMPARISON OF CARDIAC MAGNETIC RESONANCE MYOCARDIAL TAGGING, FEATURE TRACKING AND SPECKLE TRACKING ECHOCARDIOGRAPHY

Myocardial strain imaging could potentially improve patient selection for cardiac resynchronization therapy (CRT). Available techniques are CMR tagging (CMR-TAG), feature tracking (CMR-FT) and speckle tracking echocardiography (STE). Despite promising results per modality, a direct comparison is

Assessment of mechanical dyssynchrony can improve the prognostic value of guideline-based patient selection for cardiac resynchronization therapy.

To determine if incorporation of assessment of mechanical dyssynchrony could improve the prognostic value of patient selection based on current guidelines. Echocardiography was performed in 1060 patients before and 12 ± 6 months after cardiac resynchronization therapy (CRT) implantation. Mechanical dyssynchrony, defined as the presence of apical rocking or septal flash was visually assessed at the baseline examination. Response was defined as ≥15% reduction in left ventricular end-systolic volume at follow-up. Patients were followed for a median of 59 months (interquartile range 37-86 months) for the occurrence of death of any cause. Applying the latest European guidelines retrospectively, 63.4% of the patients had been implanted with a Class I recommendation, 18.2% with Class IIa, 9.4% with Class IIb, and in 9% no clear therapy recommendation was present. Response rates were 65% in Class I, 50% in IIa, 38% in IIb patients, and 40% in patients without a clear guideline-based recommendation. Assessment of mechanical dyssynchrony improved response rates to 77% in Class I, 75% in IIa, 62% in IIb, and 69% in patients without a guideline-based recommendation. Non-significant difference in survival among guideline recommendation classes was found (Log-rank P = 0.2). Presence of mechanical dyssynchrony predicted long-term outcome better than guideline Classes I, IIa, IIb (Log-rank P < 0.0001, 0.006, 0.004, respectively) and in patients with no guideline recommendation (P = 0.02). Comparable results were observed using the latest American Guidelines. Our data suggest that current guideline criteria for CRT candidate selection could be improved by incorporating assessment of mechanical asynchrony.

Strain analysis in CRT candidates using the novel segment length in cine (SLICE) post-processing technique on standard CMR cine images

ObjectivesAlthough myocardial strain analysis is a potential tool to improve patient selection for cardiac resynchronization therapy (CRT), there is currently no validated clinical approach to derive segmental strains. We evaluated the novel segment length in cine (SLICE) technique to derive segmental strains from standard cardiovascular MR (CMR) cine images in CRT candidates.MethodsTwenty-seven patients with left bundle branch block underwent CMR examination including cine imaging and myocardial tagging (CMR-TAG). SLICE was performed by measuring segment length between anatomical landmarks throughout all phases on short-axis cines. This measure of frame-to-frame segment length change was compared to CMR-TAG circumferential strain measurements. Subsequently, conventional markers of CRT response were calculated.ResultsSegmental strains showed good to excellent agreement between SLICE and CMR-TAG (septum strain, intraclass correlation coefficient (ICC) 0.76; lateral wall strain, ICC 0.66). Conventional markers of CRT response also showed close agreement between both methods (ICC 0.61–0.78). Reproducibility of SLICE was excellent for intra-observer testing (all ICC ≥0.76) and good for interobserver testing (all ICC ≥0.61).ConclusionsThe novel SLICE post-processing technique on standard CMR cine images offers both accurate and robust segmental strain measures compared to the ‘gold standard’ CMR-TAG technique, and has the advantage of being widely available.Key Points• Myocardial strain analysis could potentially improve patient selection for CRT.• Currently a well validated clinical approach to derive segmental strains is lacking.• The novel SLICE technique derives segmental strains from standard CMR cine images.• SLICE-derived strain markers of CRT response showed close agreement with CMR-TAG.• Future studies will focus on the prognostic value of SLICE in CRT candidates.

Pilot study using 3D\u2013longitudinal strain computation in a multi-parametric approach for best selecting responders to cardiac resynchronization therapy

BackgroundAlmost all attempts to improve patient selection for cardiac resynchronization therapy (CRT) using echo-derived indices have failed so far. We sought to assess: the performance of homemade software for the automatic quantification of integral 3D regional longitudinal strain curves exploring left ventricular (LV) mechanics and the potential value of this tool to predict CRT response.MethodsForty-eight heart failure patients in sinus rhythm, referred for CRT-implantation (mean age: 65 years; LV-ejection fraction: 26%; QRS-duration: 160 milliseconds) were prospectively explored. Thirty-four patients (71%) had positive responses, defined as an LV end-systolic volume decrease ≥15% at 6-months. 3D–longitudinal strain curves were exported for analysis using custom-made algorithms. The integrals of the longitudinal strain signals (IL,peak) were automatically measured and calculated for all 17 LV-segments.ResultsThe standard deviation of longitudinal strain peak (SDIL,peak) for all 17 LV-segments was greater in CRT responders than non-responders (1.18% s−1 [0.96; 1.35] versus 0.83% s−1 [0.55; 0.99], p = 0.007). The optimal cut-off value of SDIL,peak to predict response was 1.037%.s−1. In the 18-patients without septal flash, SDIL,peak was significantly higher in the CRT-responders.ConclusionsThis new automatic software for analyzing 3D longitudinal strain curves is avoiding previous limitations of imaging techniques for assessing dyssynchrony and then its value will have to be tested in a large group of patients.

Improved patient selection for cardiac resynchronization therapy by normalization of QRS duration to left ventricular dimension.

This study evaluates the relative importance of two components of QRS prolongation, myocardial conduction velocity and travel distance of the electrical wave front (i.e. path length), for the prediction of acute response to cardiac resynchronization therapy (CRT) in left bundle branch block (LBBB) patients. Thirty-two CRT candidates (ejection fraction <35%, LBBB) underwent cardiac magnetic resonance (CMR) imaging to provide detailed information on left ventricular (LV) dimensions. Left ventricular end-diastolic volume (LVEDV) was used as a primary measure for path length, subsequently QRSd was normalized to LV dimension (i.e. QRSd divided by LVEDV) to adjust for conduction path length. Invasive pressure-volume loop analysis at baseline and during CRT was used to assess acute pump function improvement, expressed as LV stroke work (SW) change. During CRT, SW improved by +38 ± 46% (P < 0.001). The baseline LVEDV was positively related to QRSd (R = 0.36, P = 0.044). Despite this association, a paradoxical inverse relation was found between LVEDV and SW improvement during CRT (R = -0.40; P = 0.025). Baseline unadjusted QRSd was found to be unrelated to SW changes during CRT (R = 0.16; P = 0.383), whereas normalized QRSd (QRSd/LVEDV) yielded a strong correlation with CRT response (R = 0.49; P = 0.005). Other measures of LV dimension, including LV length, LV diameter, and LV end-systolic volume, showed similar relations with normalized QRSd and SW improvement. Since normalized QRSd reflects myocardial conduction properties, these findings suggest that myocardial conduction velocity rather than increased path length mainly determines response to CRT. Normalizing QRSd to LV dimension might provide a relatively simple method to improve patient selection for CRT.

Left cardiac atrioventricular delay and inter-ventricular delay in cardiac resynchronization therapy responder and non-responder

Abstract Cardiac resynchronization therapy is an established therapy for heart failure patients. The aim of the study was to evaluate electrical left cardiac atrioventricular delay and interventricular desynchronization in sinus rhythm cardiac resynchronization therapy responder and non-responder. Cardiac electrical desynchronization were measured by surface ECG and focused transesophageal bipolar left atrial and left ventricular ECG before implantation of cardiac resynchronization therapy defibrillators. Preoperative electrical cardiac desynchronization was 195.7 ± 46.7 ms left cardiac atrioventricular delay and 74.8 ± 24.5 ms interventricular delay in cardiac resynchronization therapy responder. Cardiac resynchronization therapy responder New York Heart Association class improved during long term biventricular pacing. Transesophageal left cardiac atrioventricular delay and interventricular delay may be additional useful parameters to improve patient selection for cardiac resynchronization therapy.

Why QRS Duration Should Be Replaced by Better Measures of Electrical Activation to Improve Patient Selection for Cardiac Resynchronization Therapy.

Cardiac resynchronization therapy (CRT) is a well-known treatment modality for patients with a reduced left ventricular ejection fraction accompanied by a ventricular conduction delay. However, a large proportion of patients does not benefit from this therapy. Better patient selection may importantly reduce the number of non-responders. Here, we review the strengths and weaknesses of the electrocardiogram (ECG) markers currently being used in guidelines for patient selection, e.g., QRS duration and morphology. We shed light on the current knowledge on the underlying electrical substrate and the mechanism of action of CRT. Finally, we discuss potentially better ECG-based biomarkers for CRT candidate selection, of which the vectorcardiogram may have high potential.

Newer Echocardiographic Techniques in Cardiac Resynchronization Therapy.

Echocardiographic imaging plays a major role in patient selection for cardiac resynchronization therapy (CRT). One-third of patients do not respond; there is interest in advanced echocardiographic imaging to improve response. Current guidelines favor CRT for patients with electrocardiographic (ECG) QRS width of 150 milliseconds or greater and left bundle branch block. ECG criteria are imperfect; there is interest in advanced echocardiographic imaging to improve patient selection. This discussion focuses on newer echocardiographic methods to improve patient selection, improve delivery, and identify patients at risk for poor outcomes and serious ventricular arrhythmias.