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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 V 6 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, V 5 , and V 6 . According to the electrocardiogram at baseline, CLBBB patients were divided into 3 groups: T-CLBBB group (CLBBB without an S wave in lead V 5 or V 6 ), V 5 S group (CLBBB with an S wave in lead V 5 and no S wave in lead V 6 ), and V 5 &V 6 S group (CLBBB with S waves in leads V 5 and V 6 ). 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 V 5 S group, and 26 in the V 5 &V 6 S 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 V 5 &V 6 S 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 V 6 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 V 6 can predict poor response to CRT and long-term outcome., (Copyright © 2019 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Left bundle branch block (LBBB) morphology is associated with improved outcome of cardiac resynchronisation therapy (CRT) and is an important criterion for patient selection. There are, however, multiple definitions for LBBB. Moreover, applying these definitions seems subjective. We investigated the inter- and intraobserver agreement in the determination of LBBB using available definitions, and clinicians' judgement of LBBB., Methods: Observers were provided with 12‑lead ECGs of 100 randomly selected CRT patients. Four observers judged the ECGs based on different LBBB-definitions (ESC, AHA/ACC/HRS, MADIT, and Strauss). Additionally, four implanting cardiologists scored the same 100 ECGs based on their clinical judgement. Observer agreement was summarized through the proportion of agreement (P) and kappa coefficient (k)., Results: Relative intra-observer agreement using different LBBB definitions, and within clinical judgement was moderate (range k 0.47-0.74 and k = 0.76 (0.14), respectively). The inter-observer agreement between observers using LBBB definitions as well as between clinical observers was minimal to weak (range k 0.19-0.44 and k = 0.35 (0.20), respectively). The probability of classifying an ECG as LBBB by available definitions varied considerably (range 0.20-0.76). The agreement between different definitions of LBBB ranged from good (P = 0.95 (0.07)) to weak (P = 0.40 (0.22)). Furthermore, correlation between the different LBBB definitions and clinical judgement was poor (range phi 0.30-0.55)., Conclusion: Significant variation in the probability of classifying LBBB is present in using different definitions and clinical judgement. Considerable intra- and inter-observer variability adds to this variation. Interdefinition agreement varies significantly and correlation of clinical judgement with LBBB classification by definitions is modest at best., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: QRS morphology on postprocedural ECG indicating posterolateral left ventricular pacing may be predictive of response to cardiac resynchronization therapy (CRT)., Objective: The purpose of this study was to assess whether a positive vector in V1 and/or negative vector in lead I on the first postprocedural ECG, suggesting posterolateral capture from CRT, correlates with improvement in left ventricular ejection fraction (LVEF)., Methods: A retrospective chart review was conducted on all patients who underwent CRT implantation at our institution between April 2008 and December 2011. Biventricular (BiV) paced QRS morphology was defined as R/S ≥1 in V1 and/or R/S ≤ 1 in lead I. The primary outcome was improvement of LVEF ≥7.5%. The χ(2) and t tests were used for analysis., Results: Of 68 patients, 49 (72%) met our BiV paced QRS morphology criteria. Thirty-four of these 49 patients (69%) had improvement in LVEF. Of the 19 patients who did not meet our criteria, 17 (89%) did not have an improvement in LVEF (sensitivity 94%, specificity 53%, χ(2) = 19.04, P < .0001). The average LVEF improvement in patients who met our BiV paced QRS morphology criteria was significantly greater than in those who did not (14.27% vs 2.63%, P = .0001). Preprocedural left bundle branch block was not a predictor of echocardiographic response., Conclusion: Our results highlight the importance of periprocedural ECG analysis to optimize response to CRT. Moreover, patients without left bundle branch block still benefited from CRT if they met our BiV paced morphology criteria. This suggests that postprocedural left ventricular activation as reflected on the ECG may supersede the baseline conduction delay., (Copyright © 2015 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Cardiac resynchronization therapy (CRT) is an electrical treatment of heart failure with reduced ejection fraction and wide QRS. It aims to correct the electrical dyssynchrony present in 30% to 50% of patients in this population. Dyssynchrony results in widening of the QRS complex on the electrocardiogram (ECG). CRT was initially developed to treat patients who had left bundle branch block (LBBB) and delayed activation of the lateral left ventricular wall. However, a large proportion of heart failure patients present with a widened QRS that is neither an LBBB nor a right bundle branch block (RBBB): nonspecific intraventricular conduction delay (NICD). Less studied than RBBB or LBBB, its pathophysiology is both complex and varied yet still reflects intramyocardial conduction delay. NICD is most often associated with cardiomyopathy (eg, ischemic or hypertensive). Conduction pathways can be either healthy or affected. Results from CRT are contradictory in this patient group, despite a seemingly neutral trend. Unfortunately, prospective studies are lacking. Guidelines recommending implantation of CRT devices in this group are based solely on analyses of subgroups with small sample sizes. A dedicated prospective study is therefore warranted for this question to be answered properly. A detailed study of the ECG and noninvasive study of ventricular electrical activation may enable clinicians to better identify patients with NICD who will respond to CRT., (Copyright © 2015 Heart Rhythm Society. All rights reserved.)

Objectives: This study examined the time course of clinical events in cardiac resynchronization therapy (CRT) trials., Background: Recent randomized controlled trial results suggest that in heart failure with narrow QRS, biventricular pacing (CRT) may increase mortality. The authors proposed implant complications as the cause, rather than a progressive adverse physiological effect., Methods: The study identified all trials comparing CRT with no CRT, which reported Kaplan-Meier curves in groups defined by QRS: narrow, non-left bundle branch block (LBBB) broad, and LBBB broad. For each trial, the change in life span every 3 months up to 3.5 years (the longest time for which data are available) was calculated and a power law was fitted, that is, ∝ time(n)., Results: Four trials (MADIT-CRT [Multicenter Automatic Defibrillator Implantation Trial-Cardiac Resynchronization Therapy], RAFT [Resynchronization-Defibrillation for Ambulatory Heart Failure Trial], REVERSE [REsynchronization reVErses Remodeling in Systolic left vEntricular dysfunction], and EchoCRT [Echocardiography Guided Cardiac Resynchronization Therapy]), totaling 4,717 patients, reported curves for mortality or heart failure-related hospitalization, or for mortality. In patients with LBBB broad QRS (within MADIT-CRT), life span gain increased in proportion to time(1.94). In contrast, in patients with non-LBBB broad QRS (within MADIT-CRT) and patients with narrow QRS (EchoCRT), life span was lost in proportion to time(1.92) and time,(1.96) respectively. Hospitalization-free survival showed similar patterns., Conclusions: The nonlinear growth of life span gained when a CRT device is implanted in patients with LBBB broad QRS is unfortunately mirrored by a similarly progressive loss in life span in narrow QRS heart failure. This suggests the culprit is a progressive physiological effect of pacing rather than implant complications. If these data are not sufficient, a randomized controlled trial of deactivating CRT in patients with narrow QRS may now be needed, with a primary endpoint of increasing survival., (Copyright © 2015 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Twelve-lead electrocardiogram (ECG) criteria for epicardial ventricular tachycardia (VT) origins have been described. In patients with structural heart disease, the ability to predict an epicardial origin based on QRS morphology is limited and has been investigated only for limited regions in the heart., Objective: The purpose of this study was to determine whether a computerized algorithm is able to accurately differentiate epicardial vs endocardial origins of ventricular arrhythmias., Methods: Endocardial and epicardial pace-mapping were performed in 43 patients at 3277 sites. The 12-lead ECGs were digitized and analyzed using a mixture of gaussian model (MoG) to assess whether the algorithm was able to identify an epicardial vs endocardial origin of the paced rhythm. The MoG computerized algorithm was compared to algorithms published in prior reports., Results: The computerized algorithm correctly differentiated epicardial vs endocardial pacing sites for 80% of the sites compared to an accuracy of 42% to 66% of other described criteria. The accuracy was higher in patients without structural heart disease than in those with structural heart disease (94% vs 80%, P = .0004) and for right bundle branch block (82%) compared to left bundle branch block morphologies (79%, P = .001). Validation studies showed the accuracy for VT exit sites to be 84%., Conclusion: A computerized algorithm was able to accurately differentiate the majority of epicardial vs endocardial pace-mapping sites. The algorithm is not region specific and performed best in patients without structural heart disease and with VTs having a right bundle branch block morphology., (Copyright © 2014 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)