Exercise-induced left bundle branch block and subsequent mechanical left ventricular dyssynchrony--resolved with pharmacological therapy

A 53-year-old man with depressed ejection fraction (EF) of 35% and QRS width of 88 ms at rest was admitted to our institution with a complaint of exertional chest discomfort and dyspnea. During treadmill exercise, left bundle-branch block (LBBB) with a QRS width of 152 ms occurred at a heart rate of 100 bpm. During LBBB, the patient showed significant mechanical dyssynchrony as evidenced by a two-dimensional speckle tracking radial strain of 260 ms (≥ 130 ms), defined as the time difference between anterior-septum and posterior wall. Five-month after carvedilol and candesartan administration, EF had improved to 49% and LBBB did not occur until a heart rate of 126 bpm was attained during treadmill exercise. It appears that pharmacological therapy may be useful for patients with heart failure and exercise-induced LBBB.     

Tailoring cardiac resynchronisation therapy to non-left bundle branch block: Successful cardiac resynchronisation for right bundle branch block with left posterior fascicular block without implantation of a left ventricular lead

Despite advances, cardiac resynchronisation therapy (CRT) remains fundamentally orientated to the dyssynchrony of left bundle branch block (LBBB), in which septo-lateral electrical and mechanical delays predominate. For non-LBBB patients response rates to conventional CRT are lower and mortality and rehospitalisation rates are not reduced. Despite this, alternative approaches which tailor CRT to the differing dyssynchrony patterns of non-LBBB have yet to be developed. In the specific non-LBBB subgroup of right bundle branch block (RBBB) with left posterior fascicular block (LPFB), ventricular conduction via the left anterior fascicle results in a unique early lateral, and late septal depolarisation, or lateral to septal left ventricular (LV) delay, an electrical sequence which is followed mechanically. This latero-septal delay is somewhat the reverse of LBBB and was overcome by fusing right ventricular (RV) septal pacing with intrinsic conduction via the left anterior fascicle, achieving successful resynchronisation without implantation of a left ventricular lead. A stable fusion pattern was achieved via the ‘Negative AV Hysteresis with Search’ algorithm (Abbott, St Paul, Minnesota). Improvement in all standard CRT response indices was achieved at 3 months: QRS duration was reduced from 153 to 106 ms, ejection fraction increased from 14 to 32%, and LV end-systolic and end-diastolic diameters reduced by 19% and 12.5% respectively. NYHA class improved from III-IV to class II. Cardiac resynchronisation for RBBB with LPFB can be successfully achieved with a standard pacemaker or defibrillator without left ventricular lead implantation by fusing RV septal-only pacing with intrinsic conduction.     

Cardiac resynchronisation therapy in patients with left bundle branch block with residual conduction

AimTo evaluate whether left bundle branch block with residual conduction (rLBBB) is associated with worse outcomes after cardiac resynchronisation therapy (CRT).MethodsAll consecutive CRT implants at our institution between 2006 and 2013 were identified from our local device registry. Pre- and post-implant patient specific data were extracted from clinical records.ResultsA total of 690 CRT implants were identified during the study period. Prior to CRT, 52.2% of patients had true left bundle branch block (LBBB), 19.1% a pacing-induced LBBB (pLBBB), 11.2% a rLBBB, 0.8% a right bundle branch block (RBBB), and 16.5% had a nonspecific intraventricular conduction delay (IVCD) electrocardiogram pattern. Mean age at implant was 67.5 years (standard deviation [SD] = 10.6), mean left ventricular ejection fraction (LV EF) was 25.7% (SD = 7.9%), and mean QRS duration was 158.4 ms (SD = 32 ms). After CRT, QRS duration was significantly reduced in the LBBB (p < 0.001), pLBBB (p < 0.001), rLBBB (p < 0.001), RBBB (p = 0.04), and IVCD groups (p = 0.03). LV EF significantly improved in the LBBB (p < 0.001), rLBBB (p = 0.002), and pLBBB (p < 0.001) groups, but the RBBB and IVCD groups showed no improvement. There was no significant difference in mortality between the LBBB and rLBBB groups. LV EF post-CRT, chronic kidney disease, hyperkalaemia, hypernatremia, and age at implant were significant predictors of mortality.ConclusionCRT in patients with rLBBB results in improved LV EF and similar mortality rates to CRT patients with complete LBBB. Predictors of mortality post-CRT include post-CRT LV EF, presence of CKD, hyperkalaemia, hypernatremia, and older age at implant.     

Persistent ventricular preexcitation despite right bundle branch block

A 44-year-old man with a history of ventricular preexcitation and supraventricular tachycardia was evaluated. The baseline electrocardiogram exhibited ventricular preexcitation with a normal PR interval and a minimally negative delta wave in lead V1 and positive delta waves in the inferior leads. The administration of adenosine resulted in a progressive prolongation of the PR interval with a fixed preexcitation degree, suggesting the presence of antegrade conduction over the fasciculo-ventricular pathway. When complete right bundle branch block occurred, the degree of preexcitation never changed. These findings suggested that the fasciculo-ventricular pathway was likely to be connected to the left-sided His-Purkinje system.     

Left ventricular endocardial or triventricular pacing to optimize cardiac resynchronization therapy in a chronic canine model of ischemic heart failure

Cardiac resynchronization therapy (CRT) is a proven treatment for heart failure but ~30% of patients appear to not benefit from the therapy. Left ventricular (LV) endocardial and multisite epicardial [triventricular (TriV)] pacing have been proposed as alternatives to traditional LV transvenous epicardial pacing, but no study has directly compared the hemodynamic effects of these approaches. Left bundle branch block ablation and repeated microembolizations were performed in dogs to induce electrical dysynchrony and to reduce LV ejection fraction to <35%. LVdP/dt(max) and other hemodynamic indexes were measured with a conductance catheter during LV epicardial, LV endocardial, biventricular (BiV) epicardial, BiV endocardial, and TriV pacing performed at three atrioventricular delays. LV endocardial pacing was obtained with a clinically available pacing system. The optimal site was defined as the site that increased dP/dt(max) by the largest percentage. Implantation of the endocardial lead was feasible in all canines (n = 8) without increased mitral regurgitation seen with transesophageal echocardiography and with full access to the different LV endocardial pacing sites. BiV endocardial pacing increased dP/dt(max) more than BiV epicardial and TriV pacing on average (P < 0.01) and at the optimal site (P < 0.01). There were no significant differences between BiV epicardial and TriV pacing. BiV endocardial pacing was superior to BiV epicardial and to TriV pacing in terms of acute hemodynamic response. Further investigation is needed to confirm the chronic benefit of this approach in humans.     

Influence of left bundle branch block on left ventricular volumes, ejection fraction and regional wall motion

Background. Left ventricular volumes, ejection fraction and regional wall motion are cardiac parameters which provide valuable information for patient management in a large variety of cardiac conditions. Differences in regional wall motion are of relevance in the field of cardiac resynchronisation therapy. We quantified three-dimensional echocardiographic measurements of left ventricular volumes, ejection and regional wall motion (e.g. expressed as systolic dyssynchrony index (SDI)) in two patient cohorts: patients with normal conduction and patients with complete left bundle branch block. Methods. Thirty-five patients scheduled for routine cardiac examination underwent three-dimensional echocardiography: 23 patients with normal conduction and 12 patients with a complete left bundle branch block. Full-volume datasets were analysed and end-systolic volume (ESV), end-diastolic volume (EDV) and ejection fraction (EF) were obtained. SDI was derived from the standard deviation of the measured times to reach minimal regional volume for each of the 16 segments of the left ventricle. Results. A significant difference was observed in left ventricular volumes, ejection fraction and SDI between the two groups. Patients with complete left bundle branch block showed higher EDV (p=0.025) and ESV (p<0.01) and a lower EF (p<0.01) than patients with normal conduction. SDI is significantly higher in patients with complete left bundle branch block (p=0.004) expressing a higher amount of ventricular dyssynchrony. Intraobserver variability showed excellent correlation coefficients: r=0.99 for EDV, ESV and SDI and r=0.98 for EF. Conclusion. Three-dimensional echocardiography is a feasible and reproducible method for the quantification of left ventricular volumes, left ventricular ejection fraction and regional wall motion. Differences can be assessed between normal patients and patients with left bundle branch block. (Neth Heart J 2007;15:89-94.)     

The left bundle branch block revised with novel imaging modalities

Left bundle branch block (LBBB) is related to abnormal cardiac conduction and mechanical asynchrony and is associated with hypertension and coronary artery disease. Improved evaluation of left ventricular (LV) mechanical asynchrony is needed, because of the increasing number of patients with LBBB and heart failure. In this paper, we describe tissue Doppler imaging (TDI), strain (rate) imaging and tissue tracking in LBBB patients. A variety of patterns of mechanical activation can be observed in LBBB patients. A recent development, referred to as tissue synchronisation imaging, colour codes TDI time-to-peak systolic velocities of segments and displays mechanical asynchrony. Furthermore, real-time 3D echocardiography provides new regional information about mechanical asynchrony. Contained in an LV model and projected on a bull''s eye plot, this modality helps to display the spatial distribution of mechanical asynchrony. Finally, segmental time-to-peak circumferential strain curves, produced by cardiac magnetic resonance imaging, provide additional quantification of LV mechanical asynchrony. Effects of LBBB on regional and global cardiac function are impressive, myocardial involvement seems to play a role and with the help of these novel imaging modalities, new insights continue to develop.     

Selective left bundle branch pacing for pediatric complete heart block

Traditionally Right Ventricle has been the preferred site of pacing for the management of symptomatic brady-arrhythmias. The deleterious effect of chronic RV pacing has been shown by several studies. This has generated interest into a novel pacing strategy called physiological pacing wherein the His bundle or the left bundle is paced directly with 4.1 F pacing lead. Herewith we are reporting a case of congenital complete heart block in a 13-year-old child for whom selective left bundle branch pacing was done. This physiological pacing will ensure a synchronized contraction of the ventricles thereby avoiding the deleterious effect of RV pacing.     

Mechanism of prolonged electromechanical delay in late activated myocardium during left bundle branch block

During left bundle branch block (LBBB), electromechanical delay (EMD), defined as time from regional electrical activation (REA) to onset shortening, is prolonged in the late-activated left ventricular lateral wall compared with the septum. This leads to greater mechanical relative to electrical dyssynchrony. The aim of this study was to determine the mechanism of the prolonged EMD. We investigated this phenomenon in an experimental LBBB dog model (n = 7), in patients (n = 9) with biventricular pacing devices, in an in vitro papillary muscle study (n = 6), and a mathematical simulation model. Pressures, myocardial deformation, and REA were assessed. In the dogs, there was a greater mechanical than electrical delay (82 ± 12 vs. 54 ± 8 ms, P = 0.002) due to prolonged EMD in the lateral wall vs. septum (39 ± 8 vs.11 ± 9 ms, P = 0.002). The prolonged EMD in later activated myocardium could not be explained by increased excitation-contraction coupling time or increased pressure at the time of REA but was strongly related to dP/dt at the time of REA (r = 0.88). Results in humans were consistent with experimental findings. The papillary muscle study and mathematical model showed that EMD was prolonged at higher dP/dt because it took longer for the segment to generate active force at a rate superior to the load rise, which is a requirement for shortening. We conclude that, during LBBB, prolonged EMD in late-activated myocardium is caused by a higher dP/dt at the time of activation, resulting in aggravated mechanical relative to electrical dyssynchrony. These findings suggest that LV contractility may modify mechanical dyssynchrony.     

Coexistence of a bradycardia- and tachycardia-dependent bundle branch block

Aberrant ventricular conduction is a rare phenomenon as compared with the more frequently occurring antrioventricular conduction disturbances. It leads to widening of the QRS complex, which is either due to a complete or functional block in one of the bundle branches or a block within the intramyocardial conduction system itself. Mechanisms that are potentially involved in the genesis of aberrant ventricular conduction are sudden shortening of cycle length (tachycardia-dependent phase III), antegrade block with retrograde concealed conduction, or bradycardia-dependent block (enhanced phase IV). In this paper, we present a patient with aberrant ventricular conduction with the occurrence of a tachycardia-dependent, as well as a bradycardia-dependent bundle branch block, which is an even rarer phenomenon.