Left Bundle Branch Block Activation Research Articles

Decoding electrocardiographic predictors of left ventricular mechanical remodeling in patients with left bundle branch block

Introduction – Left bundle branch block (LBBB) occurrence is uncommon in the general population (~1-3%), but is more prevalent among patients with congestive heart failure (~30%), and portends worse prognosis1-3. The impact of LBBB on left ventricular (LV) systolic function can range from minimal to dramatic reduction of ejection fraction. The delay in electrical activation subsequently triggers dyssynchronous contraction of the LV opposing walls, leading to ventricular remodeling and elevated LV filling pressures. This is turn results in electrical and mechanical left atrium (LA) remodeling. The left ventricular activation time (LVAT) and P-wave terminal force in lead V1 (PTFV1) have been correlated with cardiac resynchronization response. However, the relationship between these electrocardiographic markers and LV mechanical remodeling has not been evaluated. Aims – The aim of this study is to investigate the relationship between LVAT and PTFV1 recorded on ECG and the LV mechanical remodeling evaluated by the left ventricular end-diastolic diameter (LVEDd) in patients with LBBB. Methods – We have conducted a retrospective, observational study on 155 consecutive patients diagnosed with LBBB admitted in our clinic between January 2017 and December 2019 with NYHA class I-IV, regardless of the left ventricle ejection fraction (LVEF). Biventricular electrical activation in LBBB was performed by measuring the right and left ventricular activation times (RVAT, LVAT) and electrical activation of the LA was analyzed by measuring P-wave terminal force in lead V1 (PTFV1). Results – In our cohort, LVEDd is statistically significantly correlated with LVAT and PTFV1, with a higher Pearson correlation coefficient for LVAT compared to PTFV1. In multivariate analysis LVAT and PTFV1 are independent predictors of LVEDd. Conclusion – This study suggests that LV mechanical remodeling in patients with LBBB can be predicted by the delayed electrical activation of the LV and the magnitude of P-wave negative terminal forces in V1.

A left bundle branch block activation sequence and ventricular pacing influence voltage amplitudes: an in vivo and in silico study.

The aim of this study was to investigate the influence of the activation sequence on voltage amplitudes by evaluating regional voltage differences during a left bundle branch block (LBBB) activation sequence vs. a normal synchronous activation sequence and by evaluating pacing-induced voltage differences. Twenty-one patients and three computer models without scar were studied. Regional voltage amplitudes were evaluated in nine LBBB patients who underwent endocardial electro-anatomic mapping (EAM). Pacing-induced voltage differences were evaluated in 12 patients who underwent epicardial EAM during intrinsic rhythm and right ventricular (RV) pacing. Three computer models customized for LBBB patients were created. Changes in voltage amplitudes after an LBBB (intrinsic), a normal synchronous, an RV pacing, and a left ventricular pacing activation sequence were assessed in the computer models. Unipolar voltage amplitudes in patients were approximately 4.5 mV (4.4-4.7 mV, ∼33%) lower in the septum when compared with other segments. A normal synchronous activation sequence in the computer models normalized voltage amplitudes in the septum. Pacing-induced differences were larger in electrograms with higher voltage amplitudes during intrinsic rhythm and furthermore larger and more variable at the epicardium [mean absolute difference: 3.6-6.2 mV, 40-53% of intrinsic value; interquartile range (IQR) differences: 53-63% of intrinsic value] compared to the endocardium (mean absolute difference: 3.3-3.8 mV, 28-30% of intrinsic value; IQR differences: 37-40% of intrinsic value). In patients and computer models without scar, lower septal unipolar voltage amplitudes are exclusively associated with an LBBB activation sequence. Pacing substantially affects voltage amplitudes, particularly at the epicardium.

Identification of Typical Left Bundle Branch Block Contraction by Strain Echocardiography Is Additive to Electrocardiography in Prediction of Long-Term Outcome After Cardiac Resynchronization Therapy

Current guidelines suggest that patients with left bundle branch block (LBBB) be treated with cardiac resynchronization therapy (CRT); however, one-third do not have a significant activation delay, which can result in nonresponse. By identifying characteristic opposing wall contraction, 2-dimensional strain echocardiography (2DSE) may detect true LBBB activation. This study sought to investigate whether the absence of a typical LBBB mechanical activation pattern by 2DSE was associated with unfavorable long-term outcome and if this is additive to electrocardiographic (ECG) morphology and duration. From 2 centers, 208 CRT candidates (New York Heart Association classes II to IV, ejection fraction ≤35%, QRS duration ≥120 ms) with LBBB by ECG were prospectively included. Before CRT implantation, longitudinal strain in the apical 4-chamber view determined whether typical LBBB contraction was present. The pre-defined outcome was freedom from death, left ventricular assist device, or heart transplantation over 4 years. Two-thirds of patients (63%) had a typical LBBB contraction pattern. During 4 years, 48 patients (23%) reached the primary endpoint. Absence of a typical LBBB contraction was independently associated with increased risk of adverse outcome after adjustment for ischemic heart disease and QRS width (hazard ratio [HR]: 3.1; 95% CI: 1.64 to 5.88; p < 0.005). Adding pattern assessment to a risk prediction model including QRS duration and ischemic heart disease significantly improved the net reclassification index to 0.14 (p = 0.04) and improved the C-statistics (0.63 [95% CI: 0.54 to 0.72] vs. 0.71 [95% CI: 0.63 to 0.80]; p = 0.02). Use of strict LBBB ECG criteria was not independently associated with outcome in the multivariate model (HR: 1.72; 95% CI: 0.89 to 3.33; p = 0.11. Assessment of LBBB contraction pattern was superior to time-to-peak indexes of dyssynchrony (p < 0.01 for all). Contraction pattern assessment to identify true LBBB activation provided important prognostic information in CRT candidates.

Detailed analysis of ventricular activation sequences during right ventricular apical pacing and left bundle branch block and the potential implications for cardiac resynchronization therapy.

Left bundle branch block (LBBB) leads to prolonged left ventricular (LV) total activation time (TAT) and ventricular electrical uncoupling (VEU; mean LV activation time minus mean right ventricular [RV] activation time); both have been shown to be preferential targets for cardiac resynchronization therapy (CRT). Whether right ventricular apical pacing (RVAP) produces similar ventricular activation patterns has not been well studied. The purpose of this study was to compare electrical ventricular activation patterns during RVAP and LBBB. We performed ECG mapping during sinus rhythm, RVAP, and CRT in 24 patients with LBBB. We observed differences in the electrical activation pattern with RVAP compared to LBBB. During LBBB, RV activation occurred rapidly; in contrast, RV activation was prolonged during RVAP (46 ± 21 ms vs 69 ± 17 ms, P <.001). There was no significant difference in LVTAT; however, differences in conduction pattern were observed. During LBBB, LV activation was circumferential, whereas with RVAP, LV activation proceeded from apex to base. Differences in the number, size, and orientation of lines of slow conduction also were observed. With LBBB, VEU was nearly twice as long as during RVAP (73 ± 12 ms vs 38 ± 21 ms, P <.001). CRT resulted in a greater reduction in VEU relative to LBBB activation (P <.001). RVAP produces significant differences in ventricular activation characteristics compared to LBBB. Significantly less VEU occurs with RVAP, and as a result CRT produces a smaller relative reduction in VEU. This may explain the finding that CRT appears to be more effective in patients with LBBB than in those who were upgraded because of high percentages of RV pacing.

Noninvasive Assessment of LV Contraction Patterns Using CMR to Identify Responders to CRT

Type II activation describes the U-shaped electrical activation of the left ventricle (LV) with a line of block in patients with left bundle branch block (LBBB). We sought to determine if a corresponding pattern of contraction could be identified using cardiac magnetic resonance (CMR) cine imaging and whether this predicted response to cardiac resynchronization therapy (CRT). U-shaped LV electrical activation in LBBB has been shown to predict favorable response to CRT. It is not known if the degree of electromechanical coupling is such that the same is true for LV contraction patterns. A total of 52 patients (48% ischemic) scheduled for CRT implantation prospectively underwent pre-implantation CMR cine analysis using endocardial contour tracking software to generate time-volume curves and contraction propagation maps. These were analyzed to assess the contraction sequence of the LV. The effect of contraction pattern on CRT response in terms of reverse remodeling (RR) and clinical parameters (New York Heart Association functional class, 6-min walk distance and Heart Failure Questionnaire score) was assessed at 6 months. Two types of contraction pattern were identified; homogenous spread from septum to lateral wall (type I, n = 27) and presence of block with a subsequent U-shaped contraction pattern (type II, n = 25). Rates of RR in those with a type 2 pattern were significantly greater at 6 months (80% vs. 26%, p < 0.001) as was mean increase in 6-min walk distance (126 ± 106 m vs. 55 ± 60 m; p = 0.004). Cine CMR can identify a U-shaped pattern of contraction which predicts increased echocardiographic and clinical response rates to CRT in patients with LBBB.

Vectorcardiography as a Tool for Easy Optimization of Cardiac Resynchronization Therapy in Canine Left Bundle Branch Block Hearts

Background— In cardiac resynchronization therapy (CRT), optimization of left ventricular (LV) stimulation timing is often time consuming. We hypothesized that the QRS vector in the vectorcardiogram (VCG) reflects electric interventricular dyssynchrony, and that the QRS vector amplitude (VA QRS ), halfway between that during left bundle branch block (LBBB) and LV pacing, reflects optimal resynchronization, and can be used for easy optimization of CRT. Methods and Results— In 24 canine hearts with LBBB (12 acute, 6 with heart failure, and 6 with myocardial infarction), the LV was paced over a wide range of atrioventricular (AV) delays. Surface ECGs were recorded from the limb leads, and VA QRS was calculated in the frontal plane. Mechanical interventricular dyssynchrony (MIVD) was determined as the time delay between upslopes of LV and right ventricular pressure curves, and systolic function was assessed as LV dP/dt max . VA QRS and MIVD were highly correlated ( r =0.94). The VA QRS halfway between that during LV pacing with short AV delay and intrinsic LBBB activation accurately predicted the optimal AV delay for LV pacing (1 ms; 95% CI, –5 to 8ms). Increase in LV dP/dt max at the VCG predicted AV delay was only slightly lower than the highest observed ∆LV dP/dt max (–2.7%; 95% CI, –3.6 to –1.8%). Inability to reach the halfway value of VA QRS during simultaneous biventricular pacing (53% of cases) was associated with suboptimal hemodynamic response, which could be corrected by sequential pacing. Conclusions— The VA QRS reflects electric interventricular dyssynchrony and accurately predicts optimal timing of LV stimulation in canine LBBB hearts. Therefore, VCG may be useful as a reliable and easy tool for individual optimization of CRT.

Electrical and mechanical ventricular activation during left bundle branch block and resynchronization.

Cardiac resynchronization therapy (CRT) aims to treat selected heart failure patients suffering from conduction abnormalities with left bundle branch block (LBBB) as the culprit disease. LBBB remained largely underinvestigated until it became apparent that the amount of response to CRT was heterogeneous and that the therapy and underlying pathology were thus incompletely understood. In this review, current knowledge concerning activation in LBBB and during biventricular pacing will be explored and applied to current CRT practice, highlighting novel ways to better measure and treat the electrical substrate.

A Study of Arrival of Excitation at Selected Ventricular Sites during Human Bundle Branch Block Using Close Bipolar Catheter Electrodes

<h2> </h2> One mm apart bipolar catheter electrodes were used to study the arrival of excitation at the right ventricular apex (RVA), right ventricular outflow tract (RVOT) and posterosuperior wall of the left ventricle (PSLV) during high right atrial, as well as during ventricular, pacing. In absence of bundle branch block the RVA appeared to have been activated by the impulse descending through the right branch (V-RVA intervals ranging between 15 and 30 msec). The short interval elapsing between inscription of RVA and RVOT electrograms (range 10 to 20 msec) suggested that propagation from apex to outflow tract did not occur in a linear fashion, as when these sites were stimulated directly (60 to 80 msec). Arrival of excitation at the explored right ventricular endocardial sites was delayed when "complete" right bundle branch block was present (V-RVA intervals between 50 and 60 msec). The corresponding endocardial electrograms were inscribed significantly before depolarization of the free right ventricular wall was completed. During "complete" left bundle branch block activation of the posterosuperior wall of the left ventricle was significantly prolonged (120 to 130 msec as compared with the normal range of 50 to 60 msec). The delay in activation of the blocked ventricle (50 to 70 msec) after homolateral "complete" bundle branch block was twice as long as in canine hearts.

Left ventricular activation time in left ventricular hypertrophy and in left bundle-branch block.

Simultaneous tracings of right and left ventricular leads were taken in 6 dogs with experimentally produced left bundle-branch block, and in 30 clinical cases of left ventricular hypertrophy. In the experimental study it was found that the initial phase of the QRS complex in the right epicardial lead did not change its configuration or its duration after the production of left bundle-branch block. This observation offers a new concept of the septal and left ventricular activation in left bundle-branch block. It was concluded that a considerable portion of the left ventricle is activated normally in some cases of left bundle-branch block.