The value of the 12-lead ECG for evaluation and optimization of cardiac resynchronization therapy in daily clinical practice

Concepts of Cardiac Dyssynchrony and Dynamic Approach

Cardiac conduction involves electrical activity from one myocyte to another, creating coordinated contractions in each. Disruptions in the conducting system, such as left bundle branch block (LBBB), can result in premature activation of specific regions of the heart, leading to heart failure and increased morbidity and mortality. Structural alterations in T-tubules and the sarcoplasmic reticulum can lead to dyssynchrony, a condition that can be treated by cardiac resynchronization therapy (CRT), which stands as a cornerstone in this pathology. The heterogeneity in patient responses underscored the necessity of improving the diagnostic approach. Vectocardiography, ultra-high-frequency ECG, 3D echocardiography, and electrocardiographic imaging seem to offer advanced precision in identifying optimal candidates for CRT in addition to the classic diagnostic methods. The advent of His bundle pacing and left bundle branch pacing further refined the approach in the treatment of dyssynchrony, offering more physiological pacing modalities that promise enhanced outcomes by maintaining or restoring the natural sequence of ventricular activation. HOT-CRT emerges as a pivotal innovation combining the benefits of CRT with the precision of His bundle or left bundle branch area pacing to optimize cardiac function in a subset of patients where traditional CRT might fall short.

R-R' interval in the left bundle branch block predicts long-term outcomes after cardiac resynchronization therapy by estimating greater mechanical dyssynchrony and viable myocardium

BACKGROUND

Typical left bundle branch block (LBBB) shows 2 peaks of the R wave, which reflect activation reaching the interventricular septum (R) and posterolateral wall (R') sequentially.

OBJECTIVE

The purpose of this study was to investigate the relationship among R-R' interval (RR'), mechanical dyssynchrony, extent of viable myocardium, and long-term outcomes in cardiac resynchronization therapy (CRT) candidates.

METHODS

The study enrolled 49 patients (34 men; mean age: 69 ± 11 years) with LBBB who received CRT. The LBBB definition used requires the presence of mid-QRS notching in leads V1, V2, V5, V6, I, and aVL. Baseline evaluations were QRS duration (QRSd) and RR' measured from the 12-lead electrocardiogram; eyeball dyssynchrony (apical rocking and septal flash) and opposing-wall delay by speckle tracking from echocardiography, and extent of viable myocardium assessed by thallium-201 single-photon emission computed tomography. Primary outcomes included the combination of all-cause death and heart failure-related hospitalization.

RESULTS

RR' predicted volumetric response better than QRSd (area under the curve 0.73 vs 0.67, respectively). The long RR' group (≥48 ms) revealed more frequent eyeball dyssynchrony and significantly greater radial (SL) and circumferential dyssynchrony (AP and SL) and %viable segment than the short RR' group. In multivariate regression analysis, only RR' ≥48 ms was independently associated with higher event-free survival rates following CRT (hazard ratio 0.21; P = .014).

CONCLUSION

These findings suggest that RR' in complete LBBB was associated with mechanical dyssynchrony, extent of viable myocardium, and long-term outcomes following CRT.

Ultra-high-frequency ECG volumetric and negative derivative epicardial ventricular electrical activation pattern

From precordial ECG leads, the conventional determination of the negative derivative of the QRS complex (ND-ECG) assesses epicardial activation. Recently we showed that ultra-high-frequency electrocardiography (UHF-ECG) determines the activation of a larger volume of the ventricular wall. We aimed to combine these two methods to investigate the potential of volumetric and epicardial ventricular activation assessment and thereby determine the transmural activation sequence. We retrospectively analyzed 390 ECG records divided into three groups-healthy subjects with normal ECG, left bundle branch block (LBBB), and right bundle branch block (RBBB) patients. Then we created UHF-ECG and ND-ECG-derived depolarization maps and computed interventricular electrical dyssynchrony. Characteristic spatio-temporal differences were found between the volumetric UHF-ECG activation patterns and epicardial ND-ECG in the Normal, LBBB, and RBBB groups, despite the overall high correlations between both methods. Interventricular electrical dyssynchrony values assessed by the ND-ECG were consistently larger than values computed by the UHF-ECG method. Noninvasively obtained UHF-ECG and ND-ECG analyses describe different ventricular dyssynchrony and the general course of ventricular depolarization. Combining both methods based on standard 12-lead ECG electrode positions allows for a more detailed analysis of volumetric and epicardial ventricular electrical activation, including the assessment of the depolarization wave direction propagation in ventricles.

[Left bundle branch block - dilated cardiomyopathy - heart failure: common links in the closed pathogenetic chain]

This review summarizes the available information on the epidemiology and prognosis of patients with left bundle branch block (LBBB), morphological alterations of the myocardium both resulting in and ensuing LBBB, cardiac biomechanics in LBBB, and possibilities of its correction.

Ventricular Dyssynchrony and Pacing-induced Cardiomyopathy in Patients with Pacemakers, the Utility of Ultra-high-frequency ECG and Other Dyssynchrony Assessment Tools

The majority of patients tolerate right ventricular pacing well; however, some patients manifest signs of heart failure after pacemaker implantation and develop pacing-induced cardiomyopathy. This is a consequence of non-physiological ventricular activation bypassing the conduction system. Ventricular dyssynchrony was identified as one of the main factors responsible for pacing-induced cardiomyopathy development. Currently, methods that would allow rapid and reliable ventricular dyssynchrony assessment, ideally during the implant procedure, are lacking. Paced QRS duration is an imperfect marker of dyssynchrony, and methods based on body surface mapping, electrocardiographic imaging or echocardiography are laborious and time-consuming, and can be difficult to use during the implantation procedure. However, the ventricular activation sequence can be readily displayed from the chest leads using an ultra-high-frequency ECG. It can be performed during the implantation procedure to visualise ventricular depolarisation and resultant ventricular dyssynchrony during pacing. This information can assist the electrophysiologist in selecting a pacing location that avoids dyssynchronous ventricular activation.

RT-RCG: Neural Network and Accelerator Search Towards Effective and Real-time ECG Reconstruction from Intracardiac Electrograms

There exists a gap in terms of the signals provided by pacemakers (i.e., intracardiac electrogram (EGM)) and the signals doctors use (i.e., 12-lead electrocardiogram (ECG)) to diagnose abnormal rhythms. Therefore, the former, even if remotely transmitted, are not sufficient for doctors to provide a precise diagnosis, let alone make a timely intervention. To close this gap and make a heuristic step towards real-time critical intervention in instant response to irregular and infrequent ventricular rhythms, we propose a new framework dubbed RT-RCG to automatically search for (1) efficient Deep Neural Network (DNN) structures and then (2) corresponding accelerators, to enable Real-Time and high-quality Reconstruction of ECG signals from EGM signals. Specifically, RT-RCG proposes a new DNN search space tailored for ECG reconstruction from EGM signals, and incorporates a differentiable acceleration search (DAS) engine to efficiently navigate over the large and discrete accelerator design space to generate optimized accelerators. Extensive experiments and ablation studies under various settings consistently validate the effectiveness of our RT-RCG. To the best of our knowledge, RT-RCG is the first to leverage neural architecture search (NAS) to simultaneously tackle both reconstruction efficacy and efficiency.

Improvement of LV Reverse Remodeling Using Dynamic Programming of Fusion-Optimized Atrioventricular Intervals in Cardiac Resynchronization Therapy

Background: The patient-tailored SyncAV algorithm shortens the QRS duration (QRSd) beyond what conventional biventricular (BiV) pacing can. However, evidence of the ability of SyncAV to improve the cardiac resynchronization therapy (CRT) response is lacking. The aim of this study was to evaluate the impact of CRT enhanced by SyncAV on echocardiographic and clinical responses.

Methods and Results: Consecutive heart failure (HF) patients from three centers treated with a quadripolar CRT system (Abbott) were enrolled. The total of 122 patients were divided into BiV+SyncAV (n = 68) and BiV groups (n = 54) according to whether they underwent CRT with or without SyncAV. Electrocardiographic, echocardiographic, and clinical data were assessed at baseline and during follow-up. Echocardiographic response to CRT was defined as a ≥15% decrease in left ventricular end-systolic volume (LVESV), and clinical response was defined as a NYHA class reduction of ≥1. At the 6-month follow-up, the baseline QRSd and LVESV decreased more significantly in the BiV+SyncAV than in the BiV group (QRSd −36.25 ± 16.33 vs. −22.72 ± 18.75 ms, P < 0.001; LVESV −54.19 ± 38.87 vs. −25.37 ± 36.48 ml, P < 0.001). Compared to the BiV group, more patients in the BiV+SyncAV group were classified as echocardiographic (82.35 vs. 64.81%; P = 0.036) and clinical responders (83.82 vs. 66.67%; P = 0.033). During follow-up, no deaths due to HF deterioration or severe procedure related complications occurred.

Conclusion: Compared to BiV pacing, BiV combined with SyncAV leads to a more significant reduction in QRSd and improves LV remodeling and long-term outcomes in HF patients treated with CRT.

[Association of left bundle branch block definitions with response to cardiac resynchronisation therapy in patients with congestive heart failure]

Aim To compare diagnostic significance of different criteria for complete left bundle branch block (cLBBB) in prediction of reverse left ventricular (LV) remodeling associated with cardiac resynchronization therapy (CRT).Materials and methods This study included 93 patients (men, 81.7 %; mean age at the time of implantation, 56.6±9.3 years). Achievement of a maximum decrease in LV end-systolic volume (ESV) was recorded during the entire follow-up period for evaluation of LV reversibility by CRT. Based on the dynamics of LV ESV, patients were divided into two groups, non-responders (n=27) and responders (n=66). cLBBB was determined by 9 criteria (ESC 2006 and 2013, AHA 2009, Strauss, and MIRACLE, CARE-HF, MADIT-CRT, REVERSE, and RAFT used in large multicenter studies).Results Incidence of cLBBB was significantly higher in the group of responders as demonstrated by the AHA (p=0.001), ESC 2013 (p=0.014), Strauss (p=0.002), MADIT-CRT (p=0.014), REVERSE (p=0.013), and RAFT (p&lt;0.001) criteria. The highest specificity was shown for the AHA and RAFT (92.6 %) criteria, and the highest sensitivity and overall accuracy were shown for the Strauss (80.3 % and 72.04 %, respectively) criterium. The criteria proposed in actual clinical guidelines (AHA and ESC 2013) demonstrated a strong consistency in detecting cLBBB (κ=0.818, 95 % CI, 0.7-0.936; p&lt;0.001). However, the Strauss and ESC 2006 / AHA / ESC 2013 showed the least consistency in identifying cLBBB. For the criteria described in large multicenter studies, consistency in detecting cLBBB was minimal in most cases. However, criteria with moderate or strong consistency were used in the studies, which results have substantiated the use of cLBBB as a selection criterium (MADIT-CRT, REVERSE, and RAFT).Conclusion The reversibility of LV remodeling associated with CRT was different in patients with cLBBB determined by different criteria. All actual cLBBB criteria (AHA, ESC 2013, and Strauss) were significantly more frequently observed in the responder group. Nevertheless, these criteria differed in their sensitivity and specificity. A number of large multicenter studies have used criteria with minimal consistency in detecting cLBBB, which should be taken into account in interpreting results of these studies.

Patient-tailored SyncAV algorithm: A novel strategy to improve synchrony and acute hemodynamic response in heart failure patients treated by cardiac resynchronization therapy

INTRODUCTION

Several automatic algorithms have developed to optimize the timing cycle setting in cardiac resynchronization therapy (CRT). The present study aims to investigate whether the novel device-based SyncAV algorithm could elicit better synchrony and acute hemodynamic response.

METHODS AND RESULTS

Thirty five patients undergoing CRT implantation were prospectively studied. The device was programmed to three biventricular (BiV) pacing modes sequentially after the procedure: QuickOpt algorithm (mode I), SyncAV algorithm with default 50 ms offset (mode II), and SyncAV algorithm with optimized offset minimizing QRS duration (QRSd) (mode III). After each setting, electrocardiographic and echocardiographic data were collected. As a result, QRSd was reduced from 172.8 ± 17.9 ms during intrinsic conduction to 153.1 ± 15.9 ms in mode I, further narrowed to 140.5 ± 16.7 ms in mode II, and reached shortest (134.8 ± 16.1 ms) in mode III (P < .01 for all). Besides, significantly shorter QT intervals were observed in mode I (453.2 ± 45.5 ms), mode II (443.9 ± 34.2 ms) and mode III (444.1 ± 28.7 ms), compared with native condition (472.5 ± 51.2 ms) (P < .01). All three BiV modes exhibited comparable T_p T_e interval and T_p T_e /QT ratio (P > .05). Mode I presented significantly higher aortic velocity time integral than intrinsic conduction (21.0 ± 6.4 cm vs 18.4 ± 5.5 cm; P < .01), which was even higher in mode II (22.0 ± 6.5 cm) and mode III (23.7 ± 6.5 cm). All three BiV modes significantly reduced standard deviation of time to peak contraction of 12-LV segments (Ts-SD) (Mode I: 55.2 ± 16.5 ms, Mode II: 50.2 ± 14.7 ms, Mode III: 45.4 ± 14.4 ms) compared with intrinsic conduction (66.3 ± 18.4 ms) (P < .01), with Mode III demonstrating the smallest (P < .01).

CONCLUSION

SyncAV CRT ameliorated electrical and mechanical synchrony as well as acute hemodynamic response beyond conventional QuickOpt optimization. An additional individualized adjustment to the SyncAV offset added to its advantage.

Role of electrocardiographic and echocardiographic types of left bundle branch block in prediction of response to cardiac resynchronization therapy

AIM

To assess the value of the complex analysis of electrocardiographic (ECG) variants and echocardiographic (echo) manifestation of left bundle branch block (LBBB) in predicting the success of cardiac resynchronization therapy (CRT).

MATERIALS AND METHODS

The study included 39 patients (mean age 61.49±9.0 years) on sinus rhythm with LBBB, QRS duration ≥130 ms, left ventricular ejection fraction (LVEF) ≤35%, heart failure (HF) NYHA II-IV despite optimal pharmacological therapy during 3 month. All patients had undergone CRT-D implantation. Depending on presence or absence of ECG-criteria, proposed by D.G. Strauss et al., patients were divided into 2 groups: 1 group - strict LBBB, proposed by D.G. Strauss et al. (n=29) and 2 group - other patients (n=10). In addition to standard echocardiography, global longitudinal 2-dimensional strain (GLS) and LBBB contraction pattern have been performed initially and in 6 months after implantation. Response to CRT was defined as decrease in LV end-systolic volume by &gt;15% after 6 months of follow-up.

RESULTS

Typical LBBB echo contraction pattern was detected in 25 patients (64% of all included). These patients had more pronounced longitudinal dissynchrony and a more expressed global longitudinal strain before CPT-D implantation (p&lt;0.05). 27 patients (69% of all included) were included in the &quot;response&quot; group, the remaining 12 patients (31% of all included) - the &quot;non-response&quot; group. In the &quot;response&quot; group the morphology of the QRS complex was significantly more likely to meet the criteria, proposed by D.G. Strauss et al., than other variants (23 vs. 6, respectively, p=0.02), and the echo contraction pattern of this patients more often corresponded to &quot;typical&quot; LBBB (24 vs. 1, p=0.001). All patients, who had the ECG criteria, proposed by D.G. Strauss et al., and echo &quot;typical&quot; LBBB contraction pattern, responded on CPT. Moreover, the proportion of these patients in the &quot;response&quot; group was rather high - 81.5% (22 of 27 patients).

CONCLUSION

ECG criteria LBBB, proposed by D.G. Strauss et al., identify patients with delayed transseptal interventricular conduction due to complete LBBB, what is a good target for CPT. Evaluation of the echo contraction pattern based on the definition of longitudinal myocardial deformation by means of a two-dimensional strand technology allows predicting the success of CPT in patients with LBBB. Patients with «typical» LBBB contraction pattern show more pronounced global longitudinal strain and larger longitudinal dissynchrony compared with other patients, and it explains their better response to CPT. Complex analysis of strict LBBB ECG criteria and echo contraction pattern are promising parameters in predicting beneficial response to CRT in patients with HF.

[Assessment of myocardial electrical dissynchrony by noninvasive activation mapping and its role in achieving the success of cardiac resynchronization]

PURPOSE

To assess and to compare the ventricular myocardium activation patern obtained by non-invasive epi- and endocardial mapping (NIEEM), as well as electrocardiographic (ECG) variants of lef bundle branch block (LBBB) and to estimate the value of these data for the success of cardiac resynchronization therapy (CRT).

MATERIALS AND METHODS

Te study included 23 patients (mean age 59,6±9,9 years) with LBBB, QRS duration ≥ 130 ms, lef ventricular ejection fraction (LVEF) ≤ 35%, heart failure (HF) NYHA II-IV despite optimal pharmacological therapy during 3 month. All patients had undergone CRT-D implantation. Depending on presence or absence of LBBB ECG-criteria, proposed by Strauss D.G. et. al, patients were divided into 2 groups: 1group - strict LBBB, proposed by Strauss D.G. et. al. (n=14) and 2 group - other ECG morphologies of LBBB (n=9). NIEEM by the Amycard 01C system with an analysis of epi- and endocardial ventricular electrical activation was performed in all patients and 5 healthy volunteers (mean age 29±1,0years). Response to CRT was estimated by echo and was defned as decrease in lef ventricular (LV) end-systolic volume by &gt; 15% afer 6 months of follow-up.

RESULTS

LBBB ECG-criteria, proposed by Strauss D.G. et. al, was detected in 14 patients (61% of all included). According to the results of NIEEM, these patients had more pronounced ventricular electrical uncoupling (VEU) (р=0,002). Most ofen the line of block was detected in the anteroseptal or posterolateral region of the LV. Te zone of late LV activation, which is the most optimal position for the LV pacing electrode, was located in the basal and middle segments of the lateral and posterior walls. Afer 6 months of CRT 15 patients (65%) were included in the "response" group, the remaining 8 patients (35%) formed the "non-response" group according to echo criteria. In the "response" group the morphology of the QRS complex more frequently met the criteria, proposed by Strauss D.G. et al, than other ECG variants of LBBB (12 vs. 3 respectively, p = 0.023). Initially, VEU was more pronounced in the "response" group (VEU 55 [51, 64] ms in the "response" group vs 22 [8, 38] ms in the "non-response" group).Сonclusions. LBBB ECG criteria, proposed by Strauss D.G., identify patients with delayed transseptal interventricular conduction due to complete LBBB, what is a good target for CPT. Identifcation of individual ventricular activation properties may help to reveal responders to CRT in patients with LBBB.

Electrocardiographic optimization techniques in resynchronization therapy

Cardiac resynchronization therapy (CRT) is a cornerstone of therapy for patients with heart failure, reduced left ventricular (LV) ejection fraction, and a wide QRS complex. However, not all patients respond to CRT: 30% of CRT implanted patients are currently considered clinical non-responders and up to 40% do not achieve LV reverse remodelling. In order to achieve the best CRT response, appropriate patient selection, device implantation, and programming are important factors. Optimization of CRT pacing intervals may improve results, increasing the number of responders, and the magnitude of the response. Echocardiography is considered the reference method for atrioventricular and interventricular (VV) intervals optimization but it is time-consuming, complex and it has a large interobserver and intraobserver variability. Previous studies have linked QRS shortening to clinical response, echocardiographic improvement and favourable prognosis. In this review, we describe the electrocardiographic optimization methods available: 12-lead electrocardiogram; fusion-optimized intervals (FOI); intracardiac electrogram-based algorithms; and electrocardiographic imaging. Fusion-optimized intervals is an electrocardiographic method of optimizing CRT based on QRS duration that combines fusion with intrinsic conduction. The FOI method is feasible and fast, further reduces QRS duration, can be performed during implant, improves acute haemodynamic response, and achieves greater LV remodelling compared with nominal programming of CRT.

QRS Complex Detection and Measurement Algorithms for Multichannel ECGs in Cardiac Resynchronization Therapy Patients

We developed an automated approach for QRS complex detection and QRS duration (QRSd) measurement that can effectively analyze multichannel electrocardiograms (MECGs) acquired during abnormal conduction and pacing in heart failure and cardiac resynchronization therapy (CRT) patients to enable the use of MECGs to characterize cardiac activation in such patients. The algorithms use MECGs acquired with a custom 53-electrode investigational body surface mapping system and were validated using previously collected data from 58 CRT patients. An expert cohort analyzed the same data to determine algorithm accuracy and error. The algorithms: 1) detect QRS complexes; 2) identify complexes of the most prevalent morphology and morphologic outliers; and 3) determine the array-specific (i.e., anterior and posterior) and global QRS complex onsets, offsets, and durations for the detected complexes. The QRS complex detection algorithm had a positive predictivity and sensitivity of ≥96% for complex detection and classification. The absolute QRSd error was 17 ± 14 ms, or 12%, for array-specific QRSd and 12 ± 10 ms, or 8%, for global QRSd. The absolute global QRSd error (12 ms) was less than the interobserver variation in that measurement (15 ± 10 ms). The sensitivity, positive predictivity, and error of the algorithms were similar to the values reported for current state-of-the-art algorithms designed for and limited to simpler data sets and conduction patterns and within the variation found in clinical 12-lead ECG QRSd measurement techniques. These new algorithms permit accurate, real-time analysis of QRS complex features in MECGs in patients with conduction disorders and/or pacing.

Refining success of cardiac resynchronization therapy using a simple score predicting the amount of reverse ventricular remodelling: results from the Markers and Response to CRT (MARC) study

Aims

Cardiac resynchronization therapy (CRT) reduces morbidity and mortality in systolic heart failure patients with ventricular conduction delay. Variability of individual response to CRT warrants improved patient selection. The Markers and Response to CRT (MARC) study was designed to investigate markers related to response to CRT.

Methods and results

We prospectively studied the ability of 11 clinical, 11 electrocardiographic, 4 echocardiographic, and 16 blood biomarkers to predict CRT response in 240 patients. Response was measured by the reduction of indexed left ventricular end-systolic volume (LVESVi) at 6 months follow-up. Biomarkers were related to LVESVi change using log-linear regression on continuous scale. Covariates that were significant univariately were included in a multivariable model. The final model was utilized to compose a response score. Age was 67 ± 10 years, 63% were male, 46% had ischaemic aetiology, LV ejection fraction was 26 ± 8%, LVESVi was 75 ± 31 mL/m2, and QRS was 178 ± 23 ms. At 6 months LVESVi was reduced to 58 ± 31 mL/m2 (relative reduction of 22 ± 24%), 130 patients (61%) showed ≥ 15% LVESVi reduction. In univariate analysis 17 parameters were significantly associated with LVESVi change. In the final model age, QRSAREA (using vectorcardiography) and two echocardiographic markers (interventricular mechanical delay and apical rocking) remained significantly associated with the amount of reverse ventricular remodelling. This CAVIAR (CRT-Age-Vectorcardiographic QRSAREA -Interventricular Mechanical delay-Apical Rocking) response score also predicted clinical outcome assessed by heart failure hospitalizations and all-cause mortality.

Conclusions

The CAVIAR response score predicts the amount of reverse remodelling after CRT and may be used to improve patient selection. Clinical Trials: NCT01519908.

Three-Dimensional Visualization of Myocardial Ischemia Based on the Standard Twelve-Lead Electrocardiogram

A novel method was proposed for transforming the ischemic information in the 12-lead electrocardiogram (ECG) into the pseudo-color pattern displayed on a 3D heart model based on the projection of a ST injury vector in this study. The projection of the ST injury vector at a point on the heart surface was used for identifying the presence of myocardial ischemia by the difference between the projection value and the detection threshold. Supposing that myocardial ischemia was uniform and continuous, the location and range of myocardial ischemia could be accurately calculated and visually displayed in a color-encoding way. The diagnoses of the same patient were highly consistent (kappa coefficient k = 0.9030) between the proposed method used by ordinary people lacking medical knowledge and the standard 12-lead ECG used by experienced cardiologists. In addition, the diagnostic accuracy of the proposed method was further confirmed by the coronary angiography. The results of this study provide a new way to promote the development of the 3D visualization of the standard 12-lead ECG, which has a great help for inexperienced doctors or ordinary family members in their diagnosis of patients with myocardial ischemia.

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.

The electrocardiographic characteristics of septal flash in patients with left bundle branch block

AIMS

In patients with systolic heart failure and left bundle branch block (LBBB), septal flash (SF) movement has been described by echocardiography. We evaluated the prevalence of SF in LBBB and non-LBBB patients and evaluated whether specific electrocardiographic (ECG) characteristics within LBBB are associated with the presence of SF on echocardiography.

METHODS AND RESULTS

One hundred and four patients with probable LBBB on standard 12-lead ECG were selected, 40 patients with non-LBBB served as controls. Left bundle branch block and non-LBBB were defined, according to the most recent guidelines. The presence of SF was assessed by echocardiography. Strict LBBB criteria were met in 93.3% of the patients. Septal flash was present in 45.2% of LBBB patients and was not present in non-LBBB patients. This was more prevalent in patients without anterior ischaemic cardiomyopathy (ICMP) compared with those with anterior ICMP (P = 0.008). The duration of QRS was longer in SF patients compared with that of non-SF patients (P < 0.05). The presence of a mid-QRS notching in more than two consecutive leads was a good predictor for the presence of SF (P = 0.01), and when combined with an absent R-wave in lead V1, the presence of SF is very likely (P = 0.001).

CONCLUSION

Our data show that SF is present in 45.2% of LBBB patients, whereas it was absent in patients with non-LBBB. Patients with SF fulfilled more LBBB criteria compared with LBBB patients without SF. Our findings raise the provocative question of whether the presence of SF identifies patients with 'true LBBB' and whether this echocardiographic finding might be considered as a selection parameter in cardiac resynchronization therapy.

Can we hear ventricle dyssynchrony? Yes, we can

This study introduces a method for detection of ventricular depolarization activity and the transfer of this activity into an audible stereo audio signal. Heart potentials are measured by an ultra-high-frequency high-dynamic-range electrocardiograph (UHF-ECG) with a 25-kHz sampling rate. Averaged and prolonged UHF amplitude envelopes of V1-3 and V4-6 leads at a frequency range of 500-1000 Hz are used as a modulating function for two carrier audio frequencies. The right speaker makes it possible to listen to the depolarization of the septum and right ventricle (V1-3) and the left speaker the left ventricle lateral wall (V4-6). In the healthy heart, both speakers can be heard simultaneously. A delayed L or R speaker represents the dyssynchronous electrical activation of the ventricles. Examples of the normal heart, right bundle branch block and left bundle branch block can be heard at www.medisig.com/uhfecg.

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.

ECG Patterns In Cardiac Resynchronization Therapy

Cardiac resynchronization therapy is an established treatment modality in heart failure. Though non-response is a serious issue. To address this issue, a good understanding of the electrical activation during underlying intrinsic ventricular activation, biventricular as well as right- and left ventricular pacing is needed. By interpreting the 12-lead electrocardiogram, possible reasons for suboptimal treatment can be identified and addressed. This article reviews the literature on QRS morphology in cardiac resynchronization therapy and its role in optimization of therapy.

A U-shaped type II contraction pattern in patients with strict left bundle branch block predicts super-response to cardiac resynchronization therapy

BACKGROUND

New criteria to define strict left bundle branch block (LBBB) on the basis of pathophysiological principles predict response to cardiac resynchronization therapy (CRT). Heterogeneous activation and contraction patterns have been identified in patients with classical LBBB. Cardiac magnetic resonance (CMR) imaging has demonstrated that a U-shaped (type II) contraction predicts reverse remodeling post-CRT. A homogeneous spread of (type I) contraction is less predictive.

OBJECTIVES

The purpose of this study was to investigate contraction patterns among patients with strict LBBB and to test whether a type II contraction pattern better predicts CRT response and super-response.

METHODS

Thirty-seven patients with strict LBBB (QRS duration ≥140 ms for men and ≥130 ms for women with mid-QRS notching or slurring in ≥2 contiguous leads) underwent cine CMR imaging pre-CRT with an analysis of their contraction patterns by using endocardial contour tracking software. Patients were evaluated for reverse remodeling 6 months postimplantation.

RESULTS

Nineteen patients (51%) had a type II contraction pattern. A total of 25 patients (68%) of the cohort reverse remodeled. In the type II contraction group, all 19 patients (100%) reverse remodeled as compared with 6 patients (33%) in the type I contraction group (P < .01). Super-response was achieved in 21 patients (57%) of the total cohort: 5 patients with a type I contraction pattern (28%) and 16 patients with a type II contraction pattern (84%) (P < .01).

CONCLUSION

Patients with strict LBBB who are guideline indicated for CRT have heterogeneous contraction patterns derived from cine CMR. A type II contraction pattern is strongly predictive for reverse remodeling and super-response. This questions whether strict LBBB criteria alone are sufficient to reliably predict a positive response to CRT.

Strategies to improve cardiac resynchronization therapy

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

Comparison of the relation between left ventricular anatomy and QRS duration in patients with cardiomyopathy with versus without left bundle branch block

QRS duration (QRSd) is used to diagnose left bundle branch block (LBBB) and is important to determine cardiac resynchronization therapy eligibility. The same QRSd thresholds established decades ago are used for all patients. However, significant interpatient variability of normal QRSd exists, and individualized QRSd thresholds might improve diagnosis and intervention strategies. Previous work reported left ventricular (LV) mass and papillary muscle location predicted QRSd in healthy subjects, but the relation in diseased ventricles is unknown. The aim of the present study was to determine the association between LV anatomy and QRSd in patients with cardiomyopathy. Patients referred for primary prevention implantable defibrillators (n = 166) received cardiac magnetic resonance imaging, and those with normal conduction (without bundle branch or fascicular block) and LBBB were studied. The LV mass, length, internal diameter, LV end-diastolic volume, septal and lateral wall thicknesses, and papillary muscle location were measured. In patients with normal conduction, LV length (r = 0.35, p <0.001), mass (r = 0.32, p <0.001), diameter (r = 0.20, p = 0.03), and septal wall thickness (r = 0.20, p = 0.03) had positive correlations with QRSd. In patients with LBBB, LV length (r = 0.32, p = 0.03), mass (r = 0.39, p = 0.01), diameter (r = 0.34, p = 0.02), and LV end-diastolic volume (r = 0.32, p = 0.04) had positive correlations with QRSd. Contrary to previous studies in healthy subjects, papillary muscle angle (location) was not associated with QRSd in cardiomyopathy patients with normal conduction or LBBB. In conclusion, increasing LV anatomical measurements were associated with increasing QRSd in patients with cardiomyopathy. Future work should investigate the use of LV anatomical measurements in developing individualized QRSd thresholds for diagnosing conduction abnormalities such as LBBB and identifying candidates for cardiac resynchronization therapy.