The definition of left bundle branch block influences the response to cardiac resynchronization therapy

Cardiac resynchronization therapy in heart failure based on Strauss criteria for left bundle branch block

AIMS

The left bundle branch block (LBBB) is a strong predictor of response to cardiac resynchronization therapy (CRT). However, a significant number of patients do not respond to the treatment. The study sought to evaluate the impact of the stricter Strauss criteria for left bundle branch block (St-LBBB) on CRT response, hospitalizations, ventricular arrhythmia (VA) events and mortality.

METHODS

This study is a retrospective analysis of prospectively collected data on heart failure (HF) patients with LBBB admitted for CRT implantation. Patients were divided into two groups according to the fulfilment or not of St-LBBB criteria.

RESULTS

The study included 82 patients with ischaemic (ICM) and non-ischaemic (NICM) cardiomyopathy [46 (56%) with St-LBBB and 36 (44%) with non-St-LBBB]. Patients with St-LBBB showed higher CRT response rates compared with those with non-St-LBBB (P < 0.01), while the group with NICM exhibited the greatest benefit (P < 0.01). St-LBBB CRT responders displayed significantly lower rates of HF hospitalization (P < 0.0001) compared with the non-St-LBBB group. According to Kaplan-Meier time curves, this was primarily evident in patients with NICM (P < 0.0001). CRT responders displayed significantly fewer VA events (P < 0.001) and lower mortality rates (P < 0.0001) than non-responders. Kaplan-Meier estimates demonstrated a significantly lower incidence of VAs in NICM patients with St-LBBB (P = 0.049) compared with ICM patients with St-LBBB (P = 0.25). Lower mortality rates were observed in CRT responders than non-responders (P < 0.0001), with the group of NICM with St-LBBB criteria exhibiting the greatest benefit (P = 0.0238).

CONCLUSIONS

Patients with NICM and St-LBBB present the greatest benefit concerning CRT response, HF hospitalizations, VA events and mortality. Although St-LBBB criteria seem to improve patient selection for CRT, more data are needed to elucidate the role of St-LBBB criteria in this setting.

Cardiac resynchronization therapy guided by interventricular conduction delay: How to choose between biventricular pacing or conduction system pacing

BACKGROUND

Biventricular pacing (BIV) is the gold standard for cardiac resynchronization therapy (CRT). Thirty percent of patients do not respond to CRT. Conduction system pacing (CSP) represents a viable alternative. Interventricular conduction delay (IVCD), as electrical desynchrony marker, is a CRT response predictor. The aim of this study was to determine the incidence of CRT responders by selecting the best approach between BIV and CPS based on intraoperative IVCD measurement in patients with HFrEF and LBBB.

METHODS

Ninety-six patients were randomly assigned in a 1:1 ratio to either a standard BIV group(control group, CG) or a group where the CRT approach was determined based on IVCD evaluation(study group, SG). If the right ventricular sensed electrogram (RVs)-left ventricular sensed electrogram (LVs) interval was ≥100 ms, the lead was left in its original position; otherwise, the LV lead was removed, and CSP was performed instead. Clinical, EKG, and echocardiographic features have been assessed pre- and 6 months post-implant. Echocardiographic and clinical responder were evaluated.

RESULTS

Thirty-seven percent of patients in the SG underwent CSP, as the operative algorithm. The incidence of CRT responders was significantly higher in the SG (echocardiographic criterion: 92.5% vs. 69.8%, p:.009; clinical criterion 87.5% vs. 62.8%, p:.014). The SG showed a significantly greater difference in EF between pre- and post-implant as well as reduced end-diastolic and systolic volumes. Univariate and multivariate regression analysis indicated that enrollment in the SG was the only factor associated with CRT response.

CONCLUSION

Intraoperative assessment of IVCD could help determine the optimal CRT approach between BIV and CSP, leading to a significant improvement in the rate of CRT responders.

Is Conduction System Pacing a Valuable Alternative to Biventricular Pacing for Cardiac Resynchronization Therapy?

Cardiac resynchronization therapy (CRT) significantly improves clinical outcomes in patients with ventricular systolic dysfunction and dyssynchrony. Biventricular pacing (BVP) has a class IA recommendation for patients with symptomatic heart failure with reduced ejection fraction (HFrEF) and left bundle branch block (LBBB). However, approximately 30% of patients have a poor therapeutic response and do not achieve real clinical benefit. Pre-implant imaging, together with tailored programming and dedicated device algorithms, have been proposed as possible tools to improve success rate but have shown inconsistent results. Over the last few years, conduction system pacing (CSP) is becoming a real and attractive alternative to standard BVP as it can restore narrow QRS in patients with bundle branch block (BBB) by stimulating and recruiting the cardiac conduction system, thus ensuring true resynchronization. It includes His bundle pacing (HBP) and left bundle branch area pacing (LBBAP). Preliminary data coming from small single-center experiences are very promising and have laid the basis for currently ongoing randomized controlled trials comparing CSP with BVP. The purpose of this review is to delve into the emerging role of CSP as an alternative method of achieving CRT. After framing CSP in a historical perspective, the pathophysiological rationale and available clinical evidence will be examined, and crucial technical aspects will be discussed. Finally, evidence gaps and future perspectives on CSP as a technique of choice to deliver CRT will be summarized.

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.

Landmark Evolutions in Time and Indication for Cardiac Resynchronization Therapy: Results from a Multicenter Retrospective Registry

Background: Cardiac resynchronization therapy (CRT) has evolved into an established therapy for patients with chronic heart failure and a wide QRS complex. Data on long-term outcomes over time are scarce and the criteria for implantation remain a subject of investigation. Methods: An international, multicenter, retrospective registry includes 2275 patients who received CRT between 30 November 2000 and 31 December 2019, with a mean follow-up of 3.6 ± 2.7 years. Four time periods were defined, based on landmark trials and guidelines. The combined endpoint was a composite of all-cause mortality, heart transplantation, or left ventricular assist device implantation. Results: The composite endpoint occurred in 656 patients (29.2%). The mean annual implantation rate tripled from 31.5 ± 17.4/year in the first period to 107.4 ± 62.4/year in the last period. In the adjusted Cox regression analysis, the hazard ratio for the composite endpoint was not statistically different between time periods. When compared to sinus rhythm with left bundle branch block (LBBB), a non-LBBB conduction pattern (sinus rhythm: HR 1.51, 95% CI 1.12-2.03; atrial fibrillation: HR 2.08, 95% CI 1.30-3.33) and a QRS duration below 130 ms (HR 1.64, 95% CI 1.29-2.09) were associated with a higher hazard ratio. Conclusions: Despite innovations, an adjusted regression analysis revealed stable overall survival over time, which can at least partially be explained by a shift in patient characteristics.

Quest for the ideal assessment of electrical ventricular dyssynchrony in cardiac resynchronization therapy

This paper reviews the literature on assessing electrical dyssynchrony for patient selection in cardiac resynchronization therapy (CRT). The guideline-recommended electrocardiographic (ECG) criteria for CRT are QRS duration and morphology, established through inclusion criteria in large CRT trials. However, both QRS duration and LBBB morphology have their shortcomings. Over the past decade, various alternative measures of ventricular dyssynchrony have been proposed, ranging from simple options such as vectorcardiography (VCG), ultra-high frequency ECG, and electrical dyssynchrony mapping to more advanced techniques such as ECG imaging electro-anatomic mapping. Despite promising results, none of these methods have yet been widely adopted in daily clinical practice. The VCG is a relatively cost-effective option for potential clinical implementation, as it can be reconstructed from the standard 12‑lead ECG. With the emergence of conduction system pacing, in addition to predicting the outcome of conventional biventricular CRT, the assessment of electrical dyssynchrony holds promise for defining and optimizing the type of resynchronization strategy. Additionally, artificial intelligence has the potential to reveal unknown features for CRT outcomes, and computer models can provide deeper insights into the underlying mechanisms of these features.

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.

Echocardiographic mechanical dyssynchrony predicts long-term mortality in patients with cardiac resynchronisation therapy

Cardiac resynchronisation therapy (CRT) is an established treatment for patients with symptomatic heart failure with reduced left ventricular ejection fraction (LVEF ≤ 35%; HFrEF) and conduction disturbances (QRS duration ≥ 130 ms). The presence of mechanical dyssynchrony (MD) on echocardiography has been hypothesised to be of predictive value in determining indication for CRT. This study investigated the impact of MD (apical rocking [AR] and septal flash [SF]) on long-term survival in CRT recipients. HFrEF patients (n = 425; mean age 63.0 ± 10.6 years, 72.3% male, 60.7% non-ischaemic aetiology) with a guideline-derived indication for CRT underwent device implantation. MD markers were determined at baseline and after a mean follow-up of 11.5 ± 8.0 months; long-term survival was also determined. AR and/or SF were present in 307 (72.2%) participants at baseline. During post-CRT follow-up, AR and/or SF disappeared in 256 (83.4%) patients. Overall mean survival was 95.9 ± 52.9 months, longer in women than in men (109.1 ± 52.4 vs. 90.9 ± 52.4 months; p < 0.001) and in younger (< 60 years) versus older patients (110.6 ± 53.7 vs. 88.6 ± 51.1 months; p < 0.001). Patients with versus without MD markers at baseline generally survived for longer (106.2 ± 52.0 vs. 68.9 ± 45.4 months; p < 0.001), and survival was best in patients with resolved versus persisting MD (111.6 ± 51.2 vs. 79.7 ± 47.6 months p < 0.001). Age and MD at baseline were strong predictors of long-term survival in HFrEF patients undergoing CRT on multivariate analysis. Novel echocardiography MD parameters in HFrEF CRT recipients predicted long-term mediated better outcome, and survival improved further when AR and/or SF disappear after CRT implantation.

Biventricular or Conduction System Pacing for Cardiac Resynchronization Therapy: A Strategy for Cardiac Resynchronization Based on a Hybrid Approach

BACKGROUND

Cardiac resynchronization therapy (CRT) is usually performed with biventricular pacing (BiVP), but recently, conduction system pacing (CSP) has been proposed as an alternative in case of BiVP failure. The aim of this study is to define an algorithm to choose between BiVP and CSP resynchronization using the interventricular conduction delays (IVCD) as a guide.

METHODS

Consecutive patients from January 2018 to December 2020 with an indication for CRT were prospectively enrolled in the study group (delays-guided resynchronization group, DRG). A treatment algorithm based on IVCD was used to decide whether to leave the left ventricular (LV) lead to perform BiVP or pull it out and perform CSP. Outcomes from the DRG group were compared to a historical cohort of CRT patients who underwent CRT procedures between January 2016 and December 2017 (resynchronization standard guide group, SRG). The primary endpoint was a composite of cardiovascular mortality, heart failure (HF) hospitalization, or HF event at 1 year after the date of intervention.

RESULTS

The study population consisted of 292 patients, of which 160 (54.8%) were in the DRG and 132 (45.2%) in the SRG. In the DRG, 41 of 160 patients underwent CSP based on the treatment algorithm (25.6%). The primary endpoint was significantly higher in the SRG (48/132, 36.4%) compared to the DRG (35/160, 21.8%) (hazard ratio (HR): 1.72; 95% confidence interval (CI): 1.12-2.65; p = 0.013).

CONCLUSIONS

A treatment algorithm based on IVCD shifted one patient out of every four from BiVP to CSP, with consequent reduction in the primary endpoint after implantation. Therefore, its application could be useful to determine whether to perform BiVP or CSP.

Comparison of the relation of the ESC 2021 and ESC 2013 definitions of left bundle branch block with clinical and echocardiographic outcome in cardiac resynchronization therapy

INTRODUCTION

We aimed to investigate the impact of the 2021 European Society of Cardiology (ESC) guideline changes in left bundle branch block (LBBB) definition on cardiac resynchronization therapy (CRT) patient selection and outcomes.

METHODS

The MUG (Maastricht, Utrecht, Groningen) registry, consisting of consecutive patients implanted with a CRT device between 2001 and 2015 was studied. For this study, patients with baseline sinus rhythm and QRS duration ≥ 130ms were eligible. Patients were classified according to ESC 2013 and 2021 guideline LBBB definitions and QRS duration. Endpoints were heart transplantation, LVAD implantation or mortality (HTx/LVAD/mortality) and echocardiographic response (LVESV reduction ≥15%).

RESULTS

The analyses included 1.202, typical CRT patients. The ESC 2021 definition resulted in considerably less LBBB diagnoses compared to the 2013 definition (31.6% vs. 80.9%, respectively). Applying the 2013 definition resulted in significant separation of the Kaplan-Meier curves of HTx/LVAD/mortality (p < .0001). A significantly higher echocardiographic response rate was found in the LBBB compared to the non-LBBB group using the 2013 definition. These differences in HTx/LVAD/mortality and echocardiographic response were not found when applying the 2021 definition.

CONCLUSION

The ESC 2021 LBBB definition leads to a considerably lower percentage of patients with baseline LBBB then the ESC 2013 definition. This does not lead to better differentiation of CRT responders, nor does this lead to a stronger association with clinical outcomes after CRT. In fact, stratification according to the 2021 definition is not associated with a difference in clinical or echocardiographic outcome, implying that the guideline changes may negatively influence CRT implantation practice with a weakened recommendation in patients that will benefit from CRT.

Defining left bundle branch block according to the new 2021 European Society of Cardiology criteria

Correctly diagnosing left bundle branch block (LBBB) is fundamental, as LBBB occurs frequently in heart failure and may trigger a vicious cycle of progressive left ventricular dysfunction. Moreover, a correct diagnosis of LBBB is pivotal to guide cardiac resynchronisation therapy. Since the LBBB diagnostic criteria were recently updated by the European Society of Cardiology (ESC), we assessed their diagnostic accuracy compared with the previous ESC 2013 definition. We further discuss the complexity of defining LBBB within the context of recent insights into the electromechanical pathophysiology of LBBB.

Electrocardiographic predictors of echocardiographic response in cardiac resynchronization therapy: Update of an old story

BACKGROUND

A better selection of patients with left bundle branch block (LBBB) might increase the response to cardiac resynchronization therapy (CRT). The aim of the study was to investigate the association between the Strauss criteria, absence of S wave in V₅-V_6, the Selvester score and response to CRT.

METHODS AND RESULTS

The retrospective analysis included all consecutive patients having undergone implantation of biventricular defibrillators in primary prevention between 2018 and 2020. The final analysis included 236 patients (mean age 69.7 ± 9.9; 77.5% of males). The Strauss criteria were significantly associated with CRT response (p < 0.01) with a sensitivity of 71.3% and specificity of 64.1%. The Strauss criteria along with the absence of S wave in V₅ and V₆ showed a sensitivity of 56.7%, a specificity of 82.6% and a positive predictive value of 90.5%. The Selvester score was significantly and inversely associated with CRT response (OR 0.818, 95% CI 0.75-0.89; p < 0.001). The multivariable model showed that left ventricular ejection fraction (LVEF) and QRS duration (≥140 ms in males and ≥ 130 ms in females) were independently associated with CRT response (respectively OR 0.92, CI 95% 0.86-0.98, p = 0.01 and OR 3.70, CI 95% 1.12-12.21, p = 0.03).

CONCLUSIONS

Strauss criteria, especially in association with absence of S wave in V₅ and V₆, were able to increase specificity and positive predictive value for predicting CRT response. The Selvester score was inversely associated with CRT response. Finally, LVEF and QRS duration were independently associated with echocardiographic response to CRT.

Cardiac resynchronization considerations in left bundle branch block

Cardiac resynchronization therapy (CRT) via biventricular pacing (BiVP) is an established treatment for patients with left ventricular systolic heart failure and intraventricular conduction delay resulting in wide QRS. Seminal trials demonstrating mortality benefit from CRT were conducted in patients with wide left bundle branch block (LBBB) pattern on electrocardiogram (ECG) and evidence of clinical heart failure. The presence of conduction block was assumed to correlate with commonly applied criteria for LBBB. More recent data has challenged this assertion, revealing that LBBB pattern may include distinct underlying pathophysiology, including patients with complete conduction block, either at the left-sided His fibers or the proximal left bundle, intact Purkinje activation with wide LBBB-like QRS, and patients demonstrating both proximal block and distal delay. Currently, BiVP-CRT is indicated for all QRS duration ≥150 ms and may be considered for BBB patterns from 130 to 149 ms with robust clinical data to support its use. Despite this, however, there remains a significant number of non-responders to BVP. Conduction system pacing (CSP) has emerged as an alternative approach to deliver CRT and correct QRS in patients with conduction block. Newer hybrid approaches which combine CSP and traditional BiVP-CRT and may hold promise for patients with IP or mixed-level block. As various approaches to CRT continue to be studied, physiologic phenotyping of the LBBB pattern remains an important consideration.

Electrical dyssynchrony mapping and cardiac resynchronization therapy

PURPOSE

There is no clinical methodology for quantification or display of electrical dyssynchrony over a wide range of atrial-ventricular delays (AVD) and ventricular-ventricular delays (VVD) in patients with cardiac resynchronization therapy (CRT). This study aimed to develop a new methodology, based on wavefront fusion, for mapping electrical synchrony.

METHODS

A cardiac resynchronization index (CRI) was measured at multiple device settings in 90 patients. Electrical dyssynchrony maps (EDM) were constructed for each patient to display CRI at any combination of AVD and VVD. An optimal synchrony line (OSL) depicted the AVD/VVD combinations producing the highest CRIs. Fusion of right ventricular paced (RVp), left ventricular paced (LVp), and native wavefront offsets were calculated.

RESULTS

CRI significantly increased (p < 0.0001) from 58.0 ± 28.1% at baseline to 98.3 ± 1.7% at optimized settings. EDMs in patients with high-grade heart block (n = 20) had an OSL parallel to the simultaneous biventricular pacing (BiVP_VV-SIM) line with leftward shift across all AVDs (RVp-LVp^OFFSET = 50.5 ± 29.8 ms). EDMs in patients with intact AV node conduction (n = 64) had an OSL parallel to the BiVP_VV-SIM line with leftward shift at short AVDs (RVp-LVp^OFFSET = 33.4 ± 23.3 ms), curvilinear at intermediate AVDs (triple fusion), and vertical at long AVDs (native-LVp^OFFSET = 85.2 ± 22.8 ms) in all patients except those with poor LV lead position (n = 6).

CONCLUSION

A new methodology is described for quantifying and graphing electrical dyssynchrony over a physiologic range of AVDs/VVDs. This methodology offers a noninvasive, practical, clinical approach for measuring electrical synchrony that could be applied to optimization of CRT devices.

Status and Update on Cardiac Resynchronization Therapy Trials

After decades of clinical use, cardiac resynchronization therapy (CRT) can be considered an established therapy. However, there are multiple open questions to be addressed that shall further improve the proportion of patients responding to CRT. Progress in better understanding the relationship between electrical and mechanical disorder in patients with heart failure with ventricular conduction abnormalities is important. This article presents and discusses ongoing studies in different areas of CRT research, including patient selection by novel diagnostic tools, extension of clinical criteria, left ventricular lead positioning and pacing site selection, optimization of CRT delivery and programming, and selection of device type.

What Intracardiac Tracings Have Taught Us About Left Bundle Branch Block

Current electrocardiogram (ECG) criteria for left bundle branch block (LBBB) are largely based on early work in animal models or on mathematical models of cardiac activation. The resulting criteria have modest specificity, and up to one-third of patients who meet current ECG criteria for LBBB may have intact conduction through their His-Purkinje systems. Intracardiac tracings offer the ability to accurately discriminate between LBBB and other causes of delayed activation, which may facilitate the development of more accurate ECG criteria. Assessing these distinctions are particularly salient to applications for conduction system pacing.

Electrical management of heart failure: from pathophysiology to treatment

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

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.

Vectorcardiographic QRS area as a predictor of response to cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is a good treatment for heart failure accompanied by ventricular conduction abnormalities. Current ECG criteria in international guidelines seem to be suboptimal to select heart failure patients for CRT. The criteria QRS duration and left bundle branch block (LBBB) QRS morphology insufficiently detect left ventricular activation delay, which is required for benefit from CRT. Additionally, there are various definitions for LBBB, in which each one has a different association with CRT benefit and is prone to subjective interpretation. Recent studies have shown that the objectively measured vectorcardiographic QRS area identifies left ventricular activation delay with higher accuracy than any of the current ECG criteria. Indeed, various studies have consistently shown that a high QRS area prior to CRT predicts both echocardiographic and clinical improvement after CRT. The beneficial relation of QRS area with CRT-outcome was largely independent from QRS morphology, QRS duration, and patient characteristics known to affect CRT-outcome including ischemic etiology and sex. On top of QRS area prior to CRT, the reduction in QRS area after CRT further improves benefit. QRS area is easily obtainable from a standard 12-lead ECG though it currently requires off-line analysis. Clinical applicability will be significantly improved when QRS area is automatically determined by ECG equipment.

Fusion Pacing with Biventricular, Left Ventricular-only and Multipoint Pacing in Cardiac Resynchronisation Therapy: Latest Evidence and Strategies for Use

Despite advances in the field of cardiac resynchronisation therapy (CRT), response rates and durability of therapy remain relatively static. Optimising device timing intervals may be the most common modifiable factor influencing CRT efficacy after implantation. This review addresses the concept of fusion pacing as a method for improving patient outcomes with CRT. Fusion pacing describes the delivery of CRT pacing with a programming strategy to preserve intrinsic atrioventricular (AV) conduction and ventricular activation via the right bundle branch. Several methods have been assessed to achieve fusion pacing. QRS complex duration (QRSd) shortening with CRT is associated with improved clinical response. Dynamic algorithm-based optimisation targeting narrowest QRSd in patients with intact AV conduction has shown promise in people with heart failure with left bundle branch block. Individualised dynamic programming achieving fusion may achieve the greatest magnitude of electrical synchrony, measured by QRSd narrowing.

Current Role of Echocardiography in Cardiac Resynchronization Therapy: from Cardiac Mechanics to Flow Dynamics Analysis

PURPOSE OF REVIEW

The aim of this review is to summarily explain what LV synchrony, coordination, myocardial work, and flow dynamics are, trying to clarify their advantages and limitations in the treatment of heart failure patients undergoing or with implanted cardiac resynchronization therapy (CRT).

RECENT FINDINGS

CRT is an established treatment for patients with heart failure and left ventricular systolic dysfunction. In the current guidelines, CRT implant indications rely only on electrical dyssynchrony, but in the last years, many aspects of cardiac mechanics (including contractile synchrony, coordination, propagation, and myocardial work) and flow dynamics have been studied using echocardiographic techniques to better characterize patients undergoing or with implanted CRT. However, the concepts, limits, and potential applications of all these echocardiographic evaluations are unclear to most clinicians. The use of left ventricular dyssynchrony and discoordination indices may help to identify those significant mechanical alterations whose correction may increase the probability of a favorable CRT response. Assessment of myocardial work and intracardiac flow dynamics may overcome some limitations of the conventional evaluation of cardiac mechanics but more investigations are needed before extensive clinical application.

Aortic valve implantation-induced conduction block as a framework towards a uniform electrocardiographic definition of left bundle branch block

Introduction

New-onset left bundle branch block (LBBB) following transcatheter or surgical aortic valve replacement (LBBB_AVI) implies a proximal pathogenesis of LBBB. This study compares electrocardiographic characteristics and concordance with LBBB definitions between LBBB_AVI and non-procedure-induced LBBB controls (LBBB_control).

Methods

All LBBB_AVI patients at Ghent University Hospital between 2013 and 2019 were enrolled in the study. LBBB_AVI patients were matched for age, sex, ischaemic heart disease and ejection fraction to LBBB_control patients in a 1:2 ratio. For inclusion, a non-strict LBBB definition was used (QRS duration ≥ 120 ms, QS or rS in V1, absence of Q waves in V5-6). Electrocardiograms were digitally analysed and classified according to three LBBB definitions: European Society of Cardiology (ESC), Strauss and American Heart Association (AHA).

Results

A total of 177 patients (59 LBBB_AVI and 118 LBBB_control) were enrolled in the study. LBBB_AVI patients had more lateral QRS notching/slurring (100% vs 85%, p = 0.001), included a higher percentage with a QRS duration ≥ 130 ms (98% vs 86%, p = 0.007) and had a less leftward oriented QRS axis (−15° vs −30°, p = 0.013) compared to the LBBB_control group. ESC and Strauss criteria were fulfilled in 100% and 95% of LBBB_AVI patients, respectively, but only 18% met the AHA criteria. In LBBB_control patients, concordance with LBBB definitions was lower than in the LBBB_AVI group: ESC 85% (p = 0.001), Strauss 68% (p < 0.001) and AHA 7% (p = 0.035). No differences in electrocardiographic characterisation or concordance with LBBB definitions were observed between LBBB_AVI and LBBB_control patients with lateral QRS notching/slurring.

Conclusion

Non-uniformity exists among current LBBB definitions concerning the detection of proximal LBBB. LBBB_AVI may provide a framework for more consensus on defining proximal LBBB.

Supplementary Information

The online version of this article (10.1007/s12471-021-01565-8) contains supplementary material, which is available to authorized users.

Left bundle branch block without a typical contraction pattern is associated with increased risk of ventricular arrhythmias in cardiac resynchronization therapy patients

Cardiac resynchronization therapy (CRT) reduces the risk of ventricular arrhythmias (VA) in heart failure (HF) patients with left bundle branch block (LBBB) while the effect is less clear among non-LBBB patients. This study aimed to investigate if absence of LBBB features whether by echocardiography or strict ECG criteria would identify patients at risk of developing VA in a cohort with LBBB according to conventional ECG criteria. Two hundred six CRT candidates were prospectively included from 2 centers. Prior to CRT presence of a typical LBBB contraction pattern was identified using longitudinal strain in the apical 4-chamber view. All preimplantation ECGs were categorized as LBBB or non-LBBB according to Strauss´ strict criteria. Primary end-point was defined as any appropriate antitachycardia pacing (ATP) or shock therapy within 2 years after CRT implantation. A total of 129 (63%) patients had a typical LBBB contraction pattern, while 134 (66%) met the strict ECG criteria. Over 2 years, 45 patients (22%) experienced VA. Absence of a typical LBBB contraction pattern was independently associated with an increased risk of VA (hazard ratio ([HR] 1.89; 95% CI 1.04 to 3.44; p: 0.036). Strict LBBB was not independently associated with the occurrence of VA. Fulfilling neither strict ECG nor echocardiographic criteria for LBBB was associated with a 3.3-fold increase in risk of VA ([HR] 3.34; 95% CI 1.75 to 6.94; (p < 0.001). The risk of VA was almost 2-fold higher if a typical LBBB contraction pattern was absent prior to CRT.

Electrocardiographic predictors of successful resynchronization of left bundle branch block by His bundle pacing

BACKGROUND

His bundle pacing (HBP) is an alternative to biventricular pacing (BVP) for delivering cardiac resynchronization therapy (CRT) in patients with heart failure and left bundle branch block (LBBB). It is not known whether ventricular activation times and patterns achieved by HBP are equivalent to intact conduction systems and not all patients with LBBB are resynchronized by HBP.

OBJECTIVE

To compare activation times and patterns of His-CRT with BVP-CRT, LBBB and intact conduction systems.

METHODS

In patients with LBBB, noninvasive epicardial mapping (ECG imaging) was performed during BVP and temporary HBP. Intrinsic activation was mapped in all subjects. Left ventricular activation times (LVAT) were measured and epicardial propagation mapping (EPM) was performed, to visualize epicardial wavefronts. Normal activation pattern and a normal LVAT range were determined from normal subjects.

RESULTS

Forty-five patients were included, 24 with LBBB and LV impairment, and 21 with normal 12-lead ECG and LV function. In 87.5% of patients with LBBB, His-CRT successfully shortened LVAT by ≥10 ms. In 33.3%, His-CRT resulted in complete ventricular resynchronization, with activation times and patterns indistinguishable from normal subjects. EPM identified propagation discontinuity artifacts in 83% of patients with LBBB. This was the best predictor of whether successful resynchronization was achieved by HBP (logarithmic odds ratio, 2.19; 95% confidence interval, 0.07-4.31; p = .04).

CONCLUSION

Noninvasive electrocardiographic mapping appears to identify patients whose LBBB can be resynchronized by HBP. In contrast to BVP, His-CRT may deliver the maximum potential ventricular resynchronization, returning activation times, and patterns to those seen in normal hearts.

[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.

Defining Left Bundle Branch Block Patterns in Cardiac Resynchronisation Therapy: A Return to His Bundle Recordings

Left bundle branch block (LBBB) is associated with improved outcome after cardiac resynchronisation therapy (CRT). One historical presumption of LBBB has been that the underlying pathophysiology involved diffuse disease throughout the distal conduction system. The ability to normalize wide QRS patterns with His bundle pacing (HBP) has called this notion into question. The determination of LBBB pattern is conventionally made by assessment of surface 12-lead ECGs and can include patients with and without conduction block, as assessed by invasive electrophysiology study (EPS). During a novel extension of the classical EPS to involve left-sided recordings, we found that conduction block associated with the LBBB pattern is most often proximal, usually within the left-sided His fibres, and these patients are the most likely to demonstrate QRS correction with HBP for resynchronisation. Patients with intact Purkinje activation and intraventricular conduction delay are less likely to benefit from HBP. Future EPS are required to determine the impact of newer approaches to conduction system pacing, including intraseptal or left ventricular septal pacing. Left-sided EPS has the potential to refine patient selection in CRT trials and may be used to physiologically phenotype distinct conduction patterns beyond LBBB pattern.

Typical BBB morphology and implantation depth of 3830 electrode predict QRS correction by left bundle branch area pacing

AIM

Strict criteria of typical left bundle branch block (LBBB) can help with the prediction for cardiac resynchronization therapy response. The aim of this study is to determine whether the use of strict criteria for both LBBB and right bundle branch block (RBBB) predicts successful QRS correction (≤130 ms) by left bundle branch area pacing (LBBAP).

METHODS

Consecutive patients with pacemaker indications according to the present guideline who also underwent LBBAP implantation were retrospectively assessed. Inclusion criteria were patients with BBB and the baseline QRSd > 130 ms. Baseline characteristics and pacing parameters were compared between typical and atypical BBB groups. Multivariate logistic regression was used to adjust for covariates that were found in univariate analyses for successful QRS correction by LBBAP.

RESULTS

Seventy-three patients were enrolled. Among them, 10 (13.6%) had atypical BBB (5 LBBB and 5 RBBB) and 63 (86.4%) had typical BBB (30 LBBB and 33 RBBB). The rate of successful QRS correction was higher in typical-BBB patients (52/63; 82.5%) than that in atypical-BBB patients (3/10; 30%), P < .001. Paced QRSd was obviously narrower in patients with typical BBB than that in patients with atypical-BBB (118 ± 14 vs 133 ± 14 ms, P = .003). In multivariate logistic regression, only typical BBB morphology and the implantation depth of 3830 pacing electrode in the ventricular septum were independent predictors for successful QRS correction.

CONCLUSION

This study demonstrates that patients with typical-BBB morphology benefit more from LBBAP for QRS correction. Typical BBB morphology together with deep penetration of 3830 ventricular electrode in the interventricular septum predicts the success of QRS correction by LBBAP.

Changes in QRS Area and QRS Duration After Cardiac Resynchronization Therapy Predict Cardiac Mortality, Heart Failure Hospitalizations, and Ventricular Arrhythmias

Background

Predicting clinical outcomes after cardiac resynchronization therapy (CRT) and its optimization remain a challenge. We sought to determine whether pre‐ and postimplantation QRS area (QRS_area) predict clinical outcomes after CRT.

Methods and Results

In this retrospective study, QRS_area, derived from pre‐ and postimplantation vectorcardiography, were assessed in relation to the primary end point of cardiac mortality after CRT with or without defibrillation. Other end points included total mortality, total mortality or heart failure (HF) hospitalization, total mortality or major adverse cardiac events, and the arrhythmic end point of sudden cardiac death or ventricular arrhythmias with or without a shock. In patients (n=380, age 72.0±12.4 years, 68.7% male) undergoing CRT over 7.7 years (median follow‐up: 3.8 years [interquartile range 2.3–5.3]), preimplantation QRS_area ≥102 μVs predicted cardiac mortality (HR: 0.36; P<0.001), independent of QRS duration (QRSd) and morphology (P<0.001). A QRS_area reduction ≥45 μVs after CRT predicted cardiac mortality (HR: 0.19), total mortality (HR: 0.50), total mortality or heart failure hospitalization (HR: 0.44), total mortality or major adverse cardiac events (HR: 0.43) (all P<0.001) and the arrhythmic end point (HR: 0.26; P<0.001). A concomitant reduction in QRS_area and QRSd was associated with the lowest risk of cardiac mortality and the arrhythmic end point (both HR: 0.12, P<0.001).

Conclusions

Pre‐implantation QRS_area, derived from vectorcardiography, was superior to QRSd and QRS morphology in predicting cardiac mortality after CRT. A postimplant reduction in both QRS_area and QRSd was associated with the best outcomes, including the arrhythmic end point.

An S wave in ECG lead V6 predicts poor response to cardiac resynchronization therapy and long-term outcome

BACKGROUND

Cardiac resynchronization therapy (CRT) is a standard treatment for selected patients with chronic heart failure (HF). However, up to 30%-50% of patients still do not respond to CRT.

OBJECTIVE

Our aim was to identify the predictive value of an S wave in lead V₆ in CRT response in patients with complete left bundle branch block (CLBBB).

METHODS

The CLBBB definition included the Strauss left bundle branch block criteria and the absence of q waves in leads I, V₅, and V₆. According to the electrocardiogram at baseline, CLBBB patients were divided into 3 groups: T-CLBBB group (CLBBB without an S wave in lead V₅ or V₆), V₅S group (CLBBB with an S wave in lead V₅ and no S wave in lead V₆), and V₅&V₆S group (CLBBB with S waves in leads V₅ and V₆). CRT response was defined as left ventricular end-systolic volume reduction ≥ 15% at 6-month follow-up. The combined end point included HF rehospitalization or all-cause death.

RESULTS

Of 181 patients with left bundle branch block-like pattern, 112 patients with CLBBB were included into 3 groups: 54 in the T-CLBBB group, 32 in the V₅S group, and 26 in the V₅&V₆S group. The CRT response rate was 85.2% (46), 65.6% (21), and 38.5% (10), respectively (P < .001). Kaplan-Meier curves demonstrated that patients in the V₅&V₆S group had a higher incidence of HF rehospitalization or all-cause death than those in the other 2 groups (P < .001). In a multivariate logistic regression model analysis, an S wave in lead V₆ was significantly associated with CRT nonresponse (hazard ratio 0.33; 95% confidence interval 0.11-0.96; P = .042).

CONCLUSION

An S wave in lead V₆ can predict poor response to CRT and long-term outcome.

The relationship between ECG predictors of cardiac resynchronization therapy benefit

INTRODUCTION

Cardiac resynchronization therapy (CRT) is an effective treatment that reduces mortality and improves cardiac function in patients with left bundle branch block (LBBB). However, about 30% of patients passing the current criteria do not benefit or benefit only a little from CRT. Three predictors of benefit based on different ECG properties were compared: 1) "strict" left bundle branch block classification (SLBBB); 2) QRS area; 3) ventricular electrical delay (VED) which defines the septal-lateral conduction delay. These predictors have never been analyzed concurrently. We analyzed the relationship between them on a subset of 602 records from the MADIT-CRT trial.

METHODS & RESULTS

SLBBB classification was performed by two experts; QRS area and VED were computed fully automatically. High-frequency QRS (HFQRS) maps were used to inspect conduction abnormalities. The correlation between SLBBB and other predictors was R = 0.613, 0.523 and 0.390 for VED, QRS area in Z lead, and QRS duration, respectively. Scatter plots were used to pick up disagreement between the predictors. The majority of SLBBB subjects- 295 of 330 (89%)-are supposed to respond positively to CRT according to the VED and QRS area, though 93 of 272 (34%) non-SLBBB should also benefit from CRT according to the VED and QRS area.

CONCLUSION

SLBBB classification is limited by the proper setting of cut-off values. In addition, it is too "strict" and excludes patients that may benefit from CRT therapy. QRS area and VED are clearly defined parameters. They may be used to optimize biventricular stimulation. Detailed analysis of conduction irregularities with CRT optimization should be based on HFQRS maps.

[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.

Non-invasive cardiac mapping for non-response in cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is an effective intervention in selected patients with moderate-to-severe heart failure with reduced ejection fraction and abnormal left ventricular activation time. The non-response rate of approximately 30% has remained nearly unchanged since this therapy was introduced 25 years ago. While intracardiac mapping is widely used for diagnosis and guidance of therapy in patients with tachyarrhythmia, its application in characterization of the electrical substrate to elucidate the mechanisms involved in CRT response remain anecdotal. In the present review, we describe the traditional determinants of CRT response before presenting novel non-invasive techniques used for CRT optimization. We discuss efforts to identify the target electrical substrate to guide the deployment of pacing electrodes during the operative procedure. Non-invasive body surface mapping technologies such as ECG imaging or ECG belt enables prediction of acute and chronic CRT response. While electrical dyssynchrony parameters provide high predictive accuracy for CRT response when obtained during intrinsic conduction, their predictive value is less when acquired during CRT or LV-pacing. Key messages Classic predictors of CRT response are female gender, NYHA class ≤ III, left ventricular ejection fraction ≥25%, QRS duration ≥150 ms and estimated glomerular filtration rate ≥60 mL/min. ECG-imaging is a comprehensive non-invasive mapping system which allows to express the amount of electrical asynchrony of a CRT candidate. Non-invasive body surface mapping technologies enables excellent prediction of acute and chronic CRT response before implantation. When performed during CRT or LV-pacing, the added value of these mapping systems remains unclear.

Automatic diagnosis of strict left bundle branch block using a wavelet-based approach

Patients with left bundle branch block (LBBB) are known to have a good clinical response to cardiac resynchronization therapy. However, the high number of false positive diagnosis obtained with the conventional LBBB criteria limits the effectiveness of this therapy, which has yielded to the definition of new stricter criteria. They require prolonged QRS duration, a QS or rS pattern in the QRS complexes at leads V1 and V2 and the presence of mid-QRS notch/slurs in 2 leads within V1, V2, V5, V6, I and aVL. The aim of this work was to develop and assess a fully-automatic algorithm for strict LBBB diagnosis based on the wavelet transform. Twelve-lead, high-resolution, 10-second ECGs from 602 patients enrolled in the MADIT-CRT trial were available. Data were labelled for strict LBBB by 2 independent experts and divided into training (n = 300) and validation sets (n = 302) for assessing algorithm performance. After QRS detection, a wavelet-based delineator was used to detect individual QRS waves (Q, R, S), QRS onsets and ends, and to identify the morphological QRS pattern on each standard lead. Then, multilead QRS boundaries were defined in order to compute the global QRS duration. Finally, an automatic algorithm for notch/slur detection within the QRS complex was applied based on the same wavelet approach used for delineation. In the validation set, LBBB was diagnosed with a sensitivity and specificity of Se = 92.9% and Sp = 65.1% (Acc = 79.5%, PPV = 74% and NPV = 89.6%). The results confirmed that diagnosis of strict LBBB can be done based on a fully automatic extraction of temporal and morphological QRS features. However, it became evident that consensus in the definition of QRS duration as well as notch and slurs definitions is necessary in order to guarantee accurate and repeatable diagnosis of complete LBBB.

The 43rd International Society for Computerized Electrocardiology ECG initiative for the automated detection of strict left bundle branch block

The presence of left bundle branch block (LBBB) is an important predictor of benefit from cardiac resynchronization therapy (CRT). New "strict" electrocardiographic (ECG) criteria for LBBB have been shown to better predict benefit from CRT. The "strict" LBBB criteria include: QRS duration ≥140 ms (men) or ≥130 ms (women), QS- or rS-configurations of the QRS complex in leads V1 and V2, and mid-QRS notching or slurring in ≥2 of leads V1, V2, V5, V6, I and aVL. The "strict" LBBB criteria are not regularly used and most hospital automated ECG systems and physicians still use more conventional LBBB criteria. As part of the 43rd International Society for Computerized Electrocardiology (ISCE) meeting, we conducted an initiative on the automated detection of "strict" LBBB where industry and academic investigators could present their algorithm results on digital 12-lead ECGs with varying QRS morphologies from the MADIT-CRT trial (300 training and 302 test set ECGs that were manually adjudicated for "strict" LBBB presence). The results revealed a 64-82% accuracy, 48-76% sensitivity and 46-87% specificity for automated "strict" LBBB detection from 7 participants. Most mismatches were likely attributed to differences in detection and absence of specific definitions for notches and slurs while differences in QRS duration and S-waves in leads V1 and V2 were less problematic. The full unblinded training and test datasets including all ECG signals are being made available through the Telemetric and Holter ECG Warehouse (THEW) for further exploration.