The effect of left bundle branch block on left ventricular remodeling, dyssynchrony and deformation of the mitral valve apparatus: an observational cardiovascular magnetic resonance imaging study

Assessment of myocardial strain patterns in patients with left bundle branch block using cardiac magnetic resonance

Recently, a classification with four types of septal longitudinal strain patterns was described using echocardiography, suggesting a pathophysiological continuum of left bundle branch block (LBBB)-induced left ventricle (LV) remodeling. The aim of this study was to assess the feasibility of classifying these strain patterns using cardiovascular magnetic resonance (CMR), and to evaluate their association with LV remodeling and myocardial scar. Single center registry included LBBB patients with septal flash (SF) referred to CMR to assess the cause of LV systolic dysfunction. Semi-automated feature-tracking cardiac resonance (FT-CMR) was used to quantify myocardial strain and detect the four strain patterns. A total of 115 patients were studied (age 66 ± 11 years, 57% men, 28% with ischemic heart disease). In longitudinal strain analysis, 23 patients (20%) were classified in stage LBBB-1, 37 (32.1%) in LBBB-2, 25 (21.7%) in LBBB-3, and 30 (26%) in LBBB-4. Patients at higher stages had more prominent septal flash, higher LV volumes, lower LV ejection fraction, and lower absolute strain values (p < 0.05 for all). Late gadolinium enhancement (LGE) was found in 55% of the patients (n = 63). No differences were found between the strain patterns regarding the presence, distribution or location of LGE. Among patients with LBBB, there was a good association between strain patterns assessed by FT-CMR analysis and the degree of LV remodeling and LV dysfunction. This association seems to be independent from the presence and distribution of LGE.

Regional Left Ventricular Fiber Stress Analysis for Cardiac Resynchronization Therapy Response

Cardiac resynchronization therapy (CRT) is an effective treatment for a subgroup of heart failure (HF) patients, but more than 30% of those selected do not improve after CRT implantation. Imperfect pre-procedural criteria for patient selection and optimization are the main causes of the high non-response rate. In this study, we evaluated a novel measure for assessing CRT response. We used a computational modeling framework to calculate the regional stress of the left ventricular wall of seven CRT patients and seven healthy controls. The standard deviation of regional wall stress at the time of mitral valve closure (SD_MVC) was used to quantify dyssynchrony and compared between patients and controls and among the patients. The results show that SD_MVC is significantly lower in controls than patients and correlates with long-term response in patients, based on end-diastolic volume reduction. In contrast to our initial hypothesis, patients with lower SD_MVC respond better to therapy. The patient with the highest SD_MVC was the only non-responder in the patient cohort. The distribution of fiber stress at the beginning of the isovolumetric phase seems to correlate with the degree of response and the use of this measurement could potentially improve selection criteria for CRT implantation. Further studies with a larger cohort of patients are needed to validate these results.

Cardiac magnetic resonance imaging in patients with left bundle branch block: Patterns of dyssynchrony and implications for late gadolinium enhancement imaging

Background

Left bundle branch block (LBBB) is a ventricular conduction delay with high prevalence. Aim of our study is to identify possible recurring patterns of artefacts in late gadolinium enhancement (LGE) imaging in patients with LBBB who undergo cardiac magnetic resonance imaging (MRI) and to define parameters of mechanical dyssynchrony associated with artefacts in LGE images.

Materials and methods

Fifty-five patients with LBBB and 62 controls were retrospectively included. Inversion time (TI) scout and LGE images were reviewed for artefacts. Dyssynchrony was identified using cardiac MRI by determining left ventricular systolic dyssynchrony indices (global, septal segments, and free wall segments) derived from strain analysis and features of mechanical dyssynchrony (apical rocking and septal flash).

Results

Thirty-seven patients (67%) with LBBB exhibited inhomogeneous myocardial nulling in TI scout images. Among them 25 (68%) patients also showed recurring artefact patterns in the septum or free wall on LGE images and artefacts also persisted in 18 (72%) of those cases when utilising phase sensitive inversion recovery. Only the systolic dyssynchrony index of septal segments allowed differentiation of patient subgroups (artefact/no artefact) and healthy controls (given as median, median ± interquartile range); LBBB with artefact: 10.44% (0.44–20.44%); LBBB without artefact: 6.82% (-2.18–15.83%); controls: 4.38% (1.38–7.38%); p < 0.05 with an area under the curve of 0.863 (81% sensitivity, 89% specificity). Septal flash and apical rocking were more frequent in the LBBB with artefact group than in the LBBB without artefact group (70 and 62% versus 33 and 17%; p < 0.05).

Conclusion

Patients with LBBB show recurring artefact patterns in LGE imaging. Use of strain analysis and evaluation of mechanical dyssynchrony may predict the occurrence of such artefacts already during the examination and counteract misinterpretation.

Validation and quantification of left ventricular function during exercise and free breathing from real-time cardiac magnetic resonance images

Exercise cardiovascular magnetic resonance (CMR) can unmask cardiac pathology not evident at rest. Real-time CMR in free breathing can be used, but respiratory motion may compromise quantification of left ventricular (LV) function. We aimed to develop and validate a post-processing algorithm that semi-automatically sorts real-time CMR images according to breathing to facilitate quantification of LV function in free breathing exercise. A semi-automatic algorithm utilizing manifold learning (Laplacian Eigenmaps) was developed for respiratory sorting. Feasibility was tested in eight healthy volunteers and eight patients who underwent ECG-gated and real-time CMR at rest. Additionally, volunteers performed exercise CMR at 60% of maximum heart rate. The algorithm was validated for exercise by comparing LV mass during exercise to rest. Respiratory sorting to end expiration and end inspiration (processing time 20 to 40 min) succeeded in all research participants. Bias ± SD for LV mass was 0 ± 5 g when comparing real-time CMR at rest, and 0 ± 7 g when comparing real-time CMR during exercise to ECG-gated at rest. This study presents a semi-automatic algorithm to retrospectively perform respiratory sorting in free breathing real-time CMR. This can facilitate implementation of exercise CMR with non-ECG-gated free breathing real-time imaging, without any additional physiological input.

The Effect of Accessory Pathway Location on Cardiac Function in Adult Patients with Wolff-Parkinson-White Syndrome

Introduction

The relationship between ventricular pre-excitation and left ventricular dysfunction has been described in the absence of sustained supraventricular tachycardia in a series of case reports. However, there have been no systematic studies about the effect of ventricular pre-excitation on cardiac function in adult patients with different accessory pathway locations.

Methods and Results

Patients were divided into four groups based on the type and location of their accessory pathway: septal, right free wall, left free wall, and concealed. N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels, electrocardiogram recordings, electrophysiological properties, and transthoracic echocardiographic data (septal-to-posterior wall motion delay (SPWMD) and interventricular mechanical delay (IVMD) indicating intraventricular and interventricular dyssynchrony) were compared before and after successful ablation. Before radiofrequency catheter ablation, left ventricular ejection fraction (LVEF) was significantly lower in patients with septal and right free wall accessory pathways. Within three months after radiofrequency catheter ablation, NT-proBNP levels decreased, left ventricular function improved, and intraventricular left ventricular dyssynchrony disappeared. There was a negative correlation between initial LVEF with initial QRS duration and initial SPWMD. Notably, SPWMD had a stronger correlation with LVEF than initial QRS duration.

Conclusions

Anterograde conduction with a septal or right free wall accessory pathway may cause left ventricular dyssynchrony and impair left ventricular function. Intraventricular left ventricular dyssynchrony seems to be responsible for the pathogenesis of left ventricular dysfunction. Radiofrequency catheter ablation results in decreased NT-proBNP levels, normalized QRS duration, mechanical resynchronization, and improved left ventricular function.

Increases in repolarization heterogeneity predict left ventricular systolic dysfunction and response to cardiac resynchronization therapy in patients with left bundle branch block

INTRODUCTION

This study aimed to investigate the association between T-wave morphology and impaired left ventricular ejection fraction (LVEF) in patients with complete left bundle branch block (cLBBB), and the predictive value of T-wave morphology for response to cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

We enrolled 189 patients with cLBBB on electrocardiogram performed between January 2007 and December 2011 who underwent standard echocardiography. Repolarization parameters, including the QRS-to-T angle (TCRT), T-wave morphology dispersion (TMD), T-wave loop area (PL), and T-wave residuum (TWR), were reconstructed from digital standard 12-lead electrocardiograms by T-wave morphology analysis. CRT response was defined as ≥15% reduction in left ventricular end-systolic volume at 12 months after CRT implantation. The clinical outcome endpoint was a composite of heart failure hospitalization, heart transplantation, or death during follow up (mean, 5.8 years). On logistic regression, a higher heart rate, longer QRS duration, increased TMD, and larger TWR were all independently associated with LVEF < 40%. Among 40 patients who underwent CRT, those with a larger TMD (P = .007), larger PL (P = .025), and more negative TCRT (P = .015) had better response to CRT. A large TMD (P = .018) and large PL (P = .003) were also independent predictors of the clinical outcome endpoint.

CONCLUSIONS

Increases in repolarization heterogeneity in patients with cLBBB are associated with impaired LVEF. A large TMD and large PL may be useful as additional predictors of response to CRT, improving patient selection for CRT.

The prevalence and association of patients with impaired left ventricular ejection fraction and complete left bundle-branch block in Taiwan

BACKGROUND/PURPOSE

A deleterious effect of complete left bundle-branch block (cLBBB) on left ventricular (LV) function has been established. The underutilization of cardiac resynchronization therapy has been noted in Taiwan and the Asian-Pacific area, but the reasons remain unclear. This study aimed to evaluate the prevalence and association of cLBBB and impaired LV ejection fraction (LVEF) in patients at the National Taiwan University Hospital (NTUH).

METHODS

We enrolled 164,049 patients who underwent standard 12-lead electrocardiography (ECG) between January 2010 and December 2013 at NTUH. Echocardiographic examinations within one year of the index ECG were analyzed. Baseline clinical characteristics, electrocardiography and ECG parameters, in patients with cLBBB were compared among those with three different LVEFs (EF <35%, 35%≤ EF<50%, and EF ≥50%). Multivariable logistic regression analysis were conducted to identify independent predictors of impaired LVEF in patient with cLBBB.

RESULTS

The prevalence of cLBBB was 0.4% (648 patients), and it increased with age. The estimated prevalence of cLBBB and LVEF <35% was about 0.1%. The effects of age on the distributions of patients with cLBBB by three different EF statuses were significantly disparate. In patients with cLBBB aged >80 years, 64% had a normal EF. However, in those aged between 40 and 60 years, the risk of EF <35% was as high as 45%, and the risk of EF <50% was even higher at 60%.

CONCLUSION

Patients in Taiwan had a low prevalence of LVEF<35% and cLBBB. About three-fourth of patients with cLBBB did not experience HF events, and 56% of them had a normal LVEF. The development of an effective triage strategy for these patients is warranted.

Successful Catheter Ablation as a Substitute for Cardiac Resynchronization Therapy in Patient with an Accessory Pathway-induced Cardiomyopathy

A 50-year-old man presented with exertional dyspnea and orthopnea. An electrocardiogram showed a delta wave and a wide QRS complex, similar to left bundle branch block. Cardiac echocardiography revealed diffuse severe hypokinesis and dyssynchrony. The patient was diagnosed with congestive heart failure. We considered that the patient's condition was caused by an accessory pathway-induced cardiomyopathy after heart failure compensation with guideline-oriented medical therapy. We therefore performed catheter ablation for right-sided pre-excitation syndrome as cardiac resynchronization therapy. The left ventricular dyssynchrony was resolved immediately after the procedure, and the patient's ventricular contraction improved, with a reduced cardiac volume at 6 months after the procedure-thus suggesting that the accessory pathway had affected the patient's cardiac function.

Cardiac resynchronization therapy restored ventricular septal myocardial perfusion and enhanced ventricular remodeling in patients with nonischemic cardiomyopathy presenting with left bundle branch block

BACKGROUND

Left bundle branch block (LBBB) causes intraventricular conductional delay, which results in left ventricle (LV) mechanical dyssynchrony. In the absence of coronary artery disease, patients with LBBB often have diminished accumulation of technetium-99m compounds at the myocardial septal area in electrocardiogram-gated single-photon emission computed tomography.

OBJECTIVE

To investigate whether cardiac resynchronization therapy (CRT) could improve septal myocardial perfusion, leading to favorable reverse remodeling.

METHODS

The study included all 26 patients with nonischemic cardiomyopathy eligible for CRT, who presented with LBBB, New York Heart Association class II-IV heart failure, and LV ejection fraction ≤35%. Single-photon emission computed tomography was performed at baseline and 6 months after CRT. Perfusion counts were measured at the ventricular septum and LV lateral free wall. Left ventricular end-systolic volume (LVESV) was measured by echocardiography to evaluate LV reverse remodeling by CRT.

RESULTS

At baseline, a perfusion defect at the LV septal myocardial area was confirmed in 19 of 26 (73%) patients. In these patients, septal perfusion significantly increased 6 months after CRT (56.1% ± 22.8% vs 82.9% ± 21.2%; P < .001). LVESV reduction and improved septal perfusion index were positively correlated (r = .561; P = .012), whereas no correlation was found between LVESV reduction and the difference of QRS duration before and 6 months after CRT (r = .218; P = .371). The improvement in LV septal perfusion was associated with LV reverse remodeling.

CONCLUSIONS

CRT could restore LV septal myocardial perfusion and ameliorate ventricular reverse remodeling in most patients with nonischemic cardiomyopathy and LBBB.

Cardiac magnetic resonance evaluation of the impact of interventricular and intraventricular dyssynchrony on cardiac ventricular systolic and diastolic function in patients with isolated left bundle branch block

Ventricular dyssynchrony significantly impairs cardiac performance. However, the independent role of interventricular dyssynchrony (interVD) and intraventricular dyssynchrony (intraVD) in the development of abnormalities of systolic and diastolic performance is unclear. Cardiac magnetic resonance imaging was performed in 39 patients with left bundle branch block and 13 healthy patients. Structural and functional parameters of the left ventricle and degrees of interVD and intraVD were measured. We found that interVD was inversely correlated with left ventricular (LV) ejection fraction (r = -0.8, p <0.0001) and positively correlated with LV end-diastolic volume (r = 0.4, p <0.01), LV end-systolic volume (r = 0.6, p <0.0001), and LV mass (r = 0.4, p <0.01), thus indicating that interVD significantly affects systolic function and favors ventricular remodeling. Multivariate analysis further confirmed that interVD was an independent predictor of systolic dysfunction. Interestingly, we found that interVD was not associated with abnormalities of diastolic performance. Conversely, we found that intraVD significantly impaired diastolic function, whereas it had no effect on systolic function. IntraVD was inversely correlated with peak filling rate (r = -0.7, p <0.0001) and 1/2 filling fraction (r = 0.4, p = 0.04) and positively correlated with time to peak filling rate (r = 0.6, p <0.0001), validated parameters of diastolic function. Multivariate analysis confirmed that intraVD was an independent predictor of diastolic dysfunction. In conclusion, our study suggests that the 2 components of ventricular dyssynchrony differently affect cardiac performance. If confirmed in prospective studies, our results may help to predict the prognosis of patients with left bundle branch block and different degrees of interVD and intraVD, particularly those subjects undergoing cardiac resynchronization therapy.

Echocardiographic prediction of outcome after cardiac resynchronization therapy: conventional methods and recent developments

Echocardiography plays an important role in patient assessment before cardiac resynchronization therapy (CRT) and can monitor many of its mechanical effects in heart failure patients. Encouraged by the highly variable individual response observed in the major CRT trials, echocardiography-based measurements of mechanical dyssynchrony have been extensively investigated with the aim of improving response prediction and CRT delivery. Despite recent setbacks, these techniques have continued to develop in order to overcome some of their initial flaws and limitations. This review discusses the concepts and rationale of the available echocardiographic techniques, highlighting newer quantification methods and discussing some of the unsolved issues that need to be addressed.

Ventricular pacing-induced loss of contractile function and development of epicardial inflammation

Perturbations in the normal sequence of ventricular activation can create regions of early and late activation, leading to dysynchronous contraction and areas of dyskinesis. Dyskinesis occurs across the left ventricular (LV) wall, and its presence may have important consequences on cardiac structure and function in normal and failing hearts. Acutely, dyskinesis can trigger inflammation and, in the long term (6 wk and above), leads to LV remodeling. The mechanisms that trigger these changes are unknown. To gain further insight, we used a canine model to evaluate transumural changes in myocardial function and inflammation induced by epicardial LV pacing. The results indicate that 4 h of LV suprathreshold pacing resulted in a 30% local loss of endocardial thickening. Assessment of neutrophil infiltration showed a significant approximately fivefold increase in myeloperoxidase activity in the epicardium versus the midwall/endocardium. Matrix metalloproteinase-9 activity increased ∼2 fold in the epicardium and ROS generation increased ∼2.5-fold compared with the midwall/endocardium. To determine the effects that electrical current alone has on these end points, a group of animals was subjected to subthreshold pacing. Significant increases were observed only in epicardial myeloperoxidase levels. Thus, the results indicate that transmural dyskinesis induced by suprathreshold epicardial LV activation triggers a localized epicardial inflammatory response, whereas subthreshold stimulation appears to solely induce the trapping of leucocytes. Suprathreshold pacing also induces a loss of endocardial function. These results may have important implications as to the nature of the mechanisms that trigger the inflammatory response and possibly long-term remodeling in the setting of dysynchrony.

Effect of bundle branch block on cardiac output: a whole heart simulation study

The heart is an electrically controlled fluid pump which operates by mechanical contraction. Whole heart modelling is a computationally daunting task which must incorporate several subsystems: mechanical, electrical, and fluidic. Numerous feedback mechanisms on many levels, and operating at different scales, exist to finely control behaviour. Understanding these interactions is necessary to understand heart operation, as well as pathologies and therapies. A review of the components in such a model is given. The authors then present a framework for their electro-mechano-fluidic whole heart model based on cable methods. The model incorporates atria and ventricles, and has functioning valves with papillary muscles. The effect of altered propagation due to left and right bundle branch block on cardiac output is examined using the cable-based model. Results are compared to clinically observed phenomena. Good agreement was obtained, but tighter coupling of mechanical and electrical events is needed to fully account for behaviour. Cable-based models offer an alternative to continuum models.