Electro-energetics of Biventricular, Septal and Conduction System Pacing

Abnormal electrical activation of the ventricles creates abnormalities in cardiac mechanics. Local contraction patterns, as reflected by strain, are not only out of phase, but also show opposing length changes in early and late activated regions. Consequently, the efficiency of cardiac pump function (the amount of stroke work generated by a unit of oxygen consumed), is approximately 30% lower in dyssynchronous than in synchronous hearts. Maintaining good cardiac efficiency appears important for long-term outcomes. Biventricular, left ventricular septal, His bundle and left bundle branch pacing may minimise the amount of pacing-induced dyssynchrony and efficiency loss when compared to conventional right ventricular pacing. An extensive animal study indicates maintenance of mechanical synchrony and efficiency during left ventricular septal pacing and data from a few clinical studies support the idea that this is also the case for left bundle branch pacing and His bundle pacing. This review discusses electro-mechanics and mechano-energetics under the various paced conditions and provides suggestions for future research.

Comparison of the Acute Effects of Different Pacing Sites on Cardiac Synchrony and Contraction Using Speckle-Tracking Echocardiography

Background: Cardiac pacing in patients with bradyarrhythmia may employ variable pacing sites, which may have different effects on cardiac function. Left bundle branch pacing (LBBP) is a new physiological pacing modality, and the acute outcomes on cardiac mechanical synchrony during LBBP remain uncertain. We evaluated the acute effects of four pacing sites on cardiac synchrony and contraction using speckle-tracking echocardiography, and comparisons among four different pacing sites were rare.Methods: We enrolled 21 patients with atrioventricular block or sick sinus syndrome who each sequentially underwent acute pacing protocols, including right ventricular apical pacing (RVAP), right ventricular outflow tract pacing (RVOP), His bundle pacing (HBP), and left bundle branch pacing (LBBP). Electrocardiograms and echocardiograms were recorded at baseline and during pacing. The interventricular mechanical delay (IVMD), the standard deviation of the times to longitudinal peak strain during 17 segments (PSD), and the Yu index were used to evaluate ventricular mechanical synchrony. Layer-specific strain was computed using two-dimensional speckle tracking technique to provide in-depth details about ventricular synchrony and function.Results: Left ventricular ejection fraction (LVEF) and tricuspid annulus plane systolic excursion (TAPSE) were significantly decreased during RVAP and RVOP but were not significantly different during HBP and LBBP compared with baseline. RVAP and RVOP significantly prolonged QRS duration, whereas HBP and LBBP showed non-significant effects. IVMD and PSD were significantly increased during RVAP but were not significantly different during RVOP, HBP, or LBBP. LBBP resulted in a significant improvement in the IVMD and Yu index compared with RVAP. No significant differences in mechanical synchrony were found between HBP and LBBP.Conclusion: Among these pacing modalities, RVAP has a negative acute impact on cardiac synchrony and contraction. HBP and LBBP best preserve physiological cardiac synchrony and function.

Importance of frame rate for the measurement of strain and synchrony in fetuses using speckle tracking echocardiography

Objectives To assess the influence of frame rate settings on longitudinal strain (LS) and mechanical synchrony (SYN) values in Speckle Tracking Echocardiography (STE) of healthy fetuses. Methods In this prospective study, we collected transversal or apical four-chamber-views of 121 healthy fetuses between 20 and 38 weeks of gestation using three different frame rate (FR) settings (≥ 110, 100 ± 10, 60 ± 10 frames per second). We assessed the segmental and the global LS of both ventricles (2C) and of the left ventricle (LV) offline with QLab 10.8 (Philips Medical Systems, Andover, MA, USA). Inter- and intraventricular SYN were calculated as time difference in peak myocardial strain between the mid-segments of left and right ventricle (interventricular, 2C_Syn) and lateral wall and septum of the left ventricle (intraventricular, LV_Syn), respectively. Results In 84.3% STE was feasible at all three FR settings. The LS increased in both views at higher FRs to a statistically noticeable extent. SYN measurements and the absolute differences at patient level between the FR settings showed no statistically noticeable alterations. Conclusions STE is feasible at low and high FR settings. SYN emerges to be a robust parameter for fetal STE as it is less affected by the FR. High FRs enable high temporal resolutions and thus an accurate examination of fetal hearts. Future research for the technical implementation of tailored fetal STE software is necessary for reliable clinical application.

A Comparative Study of Systolic and Diastolic Mechanical Synchrony in Canine, Primate, and Healthy and Failing Human Hearts

Aim: Mechanical dyssynchrony (MD) is associated with heart failure (HF) and may be prognostically important in cardiac resynchronization therapy (CRT). Yet, little is known about its patterns in healthy or diseased hearts. We here investigate and compare systolic and diastolic MD in both right (RV) and left ventricles (LV) of canine, primate and healthy and failing human hearts.Methods and Results: RV and LV mechanical function were examined by pulse-wave Doppler in 15 beagle dogs, 59 rhesus monkeys, 100 healthy human subjects and 39 heart failure (HF) patients. This measured RV and LV pre-ejection periods (RVPEP and LVPEP) and diastolic opening times (Q-TVE and Q-MVE). The occurrence of right (RVMDs) and left ventricular systolic mechanical delay (LVMDs) was assessed by comparing RVPEP and LVPEP values. That of right (RVMDd) and left ventricular diastolic mechanical delay (LVMDd) was assessed from the corresponding diastolic opening times (Q-TVE and Q-MVE). These situations were quantified by values of interventricular systolic (IVMDs) and diastolic mechanical delays (IVMDd), represented as positive if the relevant RV mechanical events preceded those in the LV. Healthy hearts in all species examined showed greater LV than RV delay times and therefore positive IVMDs and IVMDd. In contrast a greater proportion of the HF patients showed both markedly increased IVMDs and negative IVMDd, with diastolic mechanical asynchrony negatively correlated with LVEF.Conclusion: The present IVMDs and IVMDd findings have potential clinical implications particularly for personalized setting of parameter values in CRT in individual patients to achieve effective treatment of HF.

Prospective evaluation of clinical safety and efficacy of left bundle branch area pacing in comparison with right ventricular sepal pacing

BackgroundLeft bundle branch area pacing (LBBaP) has recently emerged as alternative a new physiologic strategy of pacing to His-bundle pacing (HBP) associated with difficulty of lead implantation, His bundle damage, high and unstable thresholds.ObjectiveThe purpose of this study is to compare clinical safety and efficacy of LBBaP with right ventricular sepal pacing (RVSP).MethodsFrom February 2019 to May 2020, consecutive pacing-indicated patients were prospectively enrolled and divided into two groups. Ventricular synchrony index such as QRS duration (QRSd), interventricular mechanical delay (IVMD) and septal-posterior wall motion delay (SPWMD), left ventricular function such as left ventricular end-diastolic diameter (LVEDD) and left ventricular ejection fraction (LVEF), pacing parameters, and complications were evaluated in perioperative period and during follow-up.ResultsLBBaP was successful in 45 patients (88.2%), and finally 46 patients underwent RVSP. With LBBaP, the ventricular electrical- mechanical synchrony were similar with the native-conduction system (P = .784). However, the ventricular electrical synchrony (QRSd, 108.47 ± 7.64 vs 130.63 ± 13.63 ms, P < .0001) and mechanical synchrony (IVMD, 27.68 ± 4.33 vs 39.88 ± 5.83, P < .0001; SPWMD, 40.39 ± 23.21 vs 96.36 ± 11.55, P < .0001) in the LBBaP group were significantly superior to the RVSP group. No significant differences in LVEDD (46 [44-48.5] vs 47 [44–52] mm, P = .488) and LVEF% (66 [62.5–70] vs 64 [61–68], P = .759) were noted in both two groups at last follow-up. But, in the subgroup analysis, LVEDD was shorter (46 [44–49] vs 50 [47–58] mm, P = .032) and the LVEF% was higher (65 [62–68] vs 63 [58–65], P = .022) in the LBBaP-H (high ventricular pacing ratio > 40%) group compared with RVSP-H group at last follow-up. There was lower capture thresholds (0.59 ± 0.18V vs. 0.71 ± 0.26V, P = 0.011) at implantation in the LBBaP group than RVSP group, and R-wave amplitudes and pacing impedances did not differ between the two groups. No serious complications were found in both two groups at implantation and follow-ups.ConclusionThis study confirms the clinical safety and efficacy of LBBaP, and that produces better ventricular electrical-mechanical synchrony than RVSP. The event of pacing-induced left ventricular dysfunction is lower in the LBBaP-H group than RVSP-H group.Trial registrationTrial registration Chinese Clinical Trial Registry, ChiCTR2100046901, Registered 30 May 2021—Retrospectively registered, http://www.chictr.org.cn/searchproj.aspx?regstatus=1008001.

Improving Cardiac Resynchronisation Therapy

CRT is a cornerstone of therapy for patients with heart failure and reduced ejection fraction. By restoring left ventricular (LV) electrical and mechanical synchrony, CRT can reduce mortality, improve LV function and reduce heart failure symptoms. Since its introduction, many advances have been made that have improved the delivery of and enhanced the response to CRT. Improving CRT outcomes begins with proper patient selection so CRT is delivered to all populations that could benefit from it, and limiting the implantation of CRT in those with a small chance of response. In addition, advancements in LV leads and delivery technologies coupled with multimodality imaging and electrical mapping have enabled operators to place coronary sinus leads in locations that will optimise electrical and mechanical synchrony. Finally, new pacing strategies using LV endocardial pacing or His bundle pacing have allowed for CRT delivery and improved response in patients with poor coronary sinus anatomy or lack of response to traditional CRT.

Feasibility and cardiac synchrony of permanent left bundle branch pacing through the interventricular septum

Aims Left bundle branch pacing (LBBP) recently emerges as a novel pacing modality. We aimed to evaluate the feasibility and cardiac synchrony of permanent LBBP in bradycardia patients. Methods and results Left bundle branch pacing was successfully performed in 56 pacemaker-indicated patients with normal cardiac function. Left bundle branch pacing was achieved by penetrating the interventricular septum (IVS) into the left side sub-endocardium with the pacing lead. His-bundle pacing (HBP) was successfully performed in another 29 patients, 19 of whom had right ventricular septal pacing (RVSP) for backup pacing. The QRS duration, left ventricular (LV) activation time (LVAT), and mechanical synchrony using phase analysis of gated SPECT myocardial perfusion imaging were evaluated. Paced QRS duration in LBBP group was significantly shorter than that in RVSP group (117.8 ± 11.0 ms vs. 158.1 ± 11.1 ms, P < 0.0001) and wider than that in HBP group (99.7 ± 15.6 ms, P < 0.0001). Left bundle branch potential was recorded during procedure in 37 patients (67.3%). Left bundle branch pacing patients with potential had shorter LVAT than those without potential (73.1 ± 11.3 ms vs. 83.2 ± 16.8 ms, P = 0.03). Left bundle branch pacing patients with potential had similar LV mechanical synchrony to those in HBP group. R-wave amplitude and capture threshold of LBBP were 17.0 ± 6.7 mV and 0.5 ± 0.1 V, respectively at implant and remained stable during a mean follow-up of 4.5 months without lead-related complications. Conclusion Permanent LBBP through IVS is safe and feasible in bradycardia patients. Left bundle branch pacing could achieve favourable cardiac electrical and LV mechanical synchrony.

Ventricular synchrony is not significantly determined by absolute myocardial perfusion in patients with chronic heart failure: A 13N-ammonia PET study

Background It is thought that heart failure (HF) patients may benefit from the evaluation of mechanical (dys)synchrony, and an independent inverse relationship between myocardial perfusion and ventricular synchrony has been suggested. We explore the relationship between quantitative myocardial perfusion and synchrony parameters when accounting for the presence and extent of fixed perfusion defects in patients with chronic HF. Methods We studied 98 patients with chronic HF who underwent rest and stress Nitrogen-13 ammonia PET. Multivariate analyses of covariance were performed to determine relevant predictors of synchrony (measured as bandwidth, standard deviation, and entropy). Results In our population, there were 43 (44%) women and 55 men with a mean age of 71 ± 9.6 years. The SRS was the strongest independent predictor of mechanical synchrony variables (p < .01), among other considered predictors including: age, sex, body mass index, smoking, diabetes mellitus, dyslipidemia, hypertension, rest myocardial blood flow (MBF), and myocardial perfusion reserve (MPR). Results were similar when considering stress MBF instead of MPR. Conclusions The existence and extent of fixed perfusion defects, but not the quantitative PET myocardial perfusion parameters (sMBF and MPR), constitute a significant independent predictor of ventricular mechanical synchrony in patients with chronic HF.