A Network Meta-analysis and Systematic Review of Left Bundle Branch Pacing, His Bundle Pacing, Biventricular Pacing or RV Pacing in Patients Requiring Permanent Pacemaker

Background: Cardiac dyssynchronization is the proposed mechanism for pacemaker-induced cardiomyopathy. The standard of treatment is biventricular pacing. Left bundle branch pacing and His bundle pacing are novel interventions that imitate the natural conductionof the heart with, theoretically, less interventricular dysynchrony. One of the surrogate markers of interventricular synchrony is QRS duration. Our study aimed to compare the change of QRS duration before and after implantation between types of cardiac implantable electronic device (CIED): left bundle branch pacing versus His bundle pacing versus biventricular pacing and conventional right ventricular pacing. Methods: A literature search for studies that reported an interval change of QRS duration after CIED implantation was conducted utilizing the MEDLINE, EMBASE, and Cochrane databases. All relevant work through September 2020 from these databases was included in this analysis. A random-effects model network meta-analysis was used to analyze QRS duration changes (i.e., electrical cardiac synchronization) across different CIED implantations. Results: The mean study sample size, from 16 included studies, was 185 subjects. According to SUCRA analysis for the studies analyzed, the His bundle pacing intervention resulted in the most dramatic decline in QRS duration (mean difference -53 ms, 95% CI -67, -39), followed by left bundle branch pacing (mean difference -46 ms, 95% CI -60, -33) and biventricular pacing (mean difference -19 ms, 95% CI -37, -1.8), when compared to conventional right ventricle apical lead placement. Conclusion: Our network meta-analysis found that His bundle branch pacing devices have the greatest effect on QRS duration reduction after implantation, followed by left bundle branch pacing. Physiologic pacing interventions result in improved electrocardiography markers of cardiac synchronicity, narrower QRS duration, and might lower electromechanical dyssynchrony.

Morphometric Characterization of Human Coronary Veins and Subvenous Epicardial Adipose Tissue—Implications for Cardiac Resynchronization Therapy Leads

Subvenous epicardial fat tissue (SEAT), which acts as an electrical insulation, and the venous diameter (VD) both constitute histomorphological challenges for optimal application and lead design in cardiac synchronization therapy (CRT). In this study, we characterized the morphology of human coronary veins to improve the technical design of future CRT systems and to optimize the application of CRT leads. We retrospectively analyzed data from cardiac computed tomography (CT) of 53 patients and did studies of 14 human hearts using the postmortem freeze section technique and micro CT. Morphometric parameters (tributary distances, offspring angles, luminal VD, and SEAT thickness) were assessed. The left posterior ventricular vein (VVSP) had a mean proximal VD of 4.0 ± 1.4 mm, the left marginal vein (VMS) of 3.2 ± 1.5 mm and the anterior interventricular vein (VIA) of 3.9 ± 1.3 mm. More distally (5 cm), VDs decreased to 2.4 ± 0.6 mm, 2.3 ± 0.7 mm, and 2.4 ± 0.6 mm, respectively. In their proximal portions (15 mm), veins possessed mean SEAT thicknesses of 3.2 ± 2.4 (VVSP), 3.4 ± 2.4 mm (VMS), and 4.2 ± 2.8 mm (VIA), respectively. More distally (20–70 mm), mean SEAT thicknesses decreased to alternating low levels of 1.3 ± 1.1 mm (VVSP), 1.7 ± 1.1 mm (VMS), and 4.3 ± 2.6 mm (VIA), respectively. In contrast to the VD, SEAT thicknesses alternated along the further distal vein course and did not display a continuous decrease. Besides the CRT responsiveness of different areas of the LV myocardium, SEAT is a relevant electrophysiological factor in CRT, potentially interfering with sensing and pacing. A sufficient VD is crucial for successful CRT lead placement. Measurements revealed a trend toward greater SEAT thickness for the VIA compared to VVSP and VMS, suggesting a superior signal-to-noise-ratio in VVSP and VMS.

Doppler ultrasound cardiac gating of intracranial flow at 7T

Background Ultra-high field magnetic resonance imaging (MR) may be used to improve intracranial blood flow measurements. However, standard cardiac synchronization methods tend to fail at ultra-high field MR. Therefore, this study aims to investigate an alternative synchronization technique using Doppler ultrasound. Methods Healthy subjects (n = 9) were examined with 7T MR. Flow was measured in the M1-branch of the middle cerebral artery (MCA) and in the cerebral aqueduct (CA) using through-plane phase contrast (2D flow). Flow in the circle of Willis was measured with three-dimensional, three-directional phase contrast (4D flow). Scans were gated with Doppler ultrasound (DUS) and electrocardiogram (ECG), and pulse oximetry data (POX) was collected simultaneously. False negative and false positive trigger events were counted for ECG, DUS and POX, and quantitative flow measures were compared. Results There were fewer false positive triggers for DUS compared to ECG (5.3 ± 11 vs. 25 ± 31, p = 0.031), while no other measured parameters differed significantly. Net blood flow in M1 was similar between DUS and ECG for 2D flow (1.5 ± 0.39 vs. 1.6 ± 0.41, bias ± 1.96SD: − 0.021 ± 0.36) and 4D flow (1.8 ± 0.48 vs. 9 ± 0.59, bias ± 1.96SD: − 0.086 ± 0.57 ml). Net CSF flow per heart beat in the CA was also similar for DUS and ECG (3.6 ± 2.1 vs. 3.0 ± 5.8, bias ± 1.96SD: 0.61 ± 13.6 μl). Conclusion Gating with DUS produced fewer false trigger events than using ECG, with similar quantitative flow values. DUS gating is a promising technique for cardiac synchronization at 7T.

Novel left ventricular cardiac synchronization: left ventricular septal pacing or left bundle branch pacing?

It is well recognized that a high burden of right ventricular pacing results in deleterious clinical outcomes over the long term. His bundle pacing can achieve optimal ventricular synchronization; however, relatively high pacing thresholds, low R-wave amplitudes, and the long-term performance have been concerns. Recently, left ventricular (LV) septal endocardium pacing (LVSP) has demonstrated improved acute haemodynamics. Another novel technique of intraseptal left bundle branch pacing (LBBP) via transvenous approach has been adopted rapidly and has demonstrated its feasibility and effectiveness. This article reviews the clinical application and differences between LVSP and LBBP. Compared with LVSP, LBBP has strict criteria for left conduction system capture and lead location. In addition to LV septal capture it also stimulates the proximal left bundle branch, resulting in rapid and physiological LV activation. With a uniformity and standardization of the implant procedure and definitions, it may be possible to achieve widespread application of this form of physiological pacing.

P603Cardiac Magnetic Resonance evaluation and risk stratification of patients with unexplained or suspected arrhythmias

Introduction The etiological diagnosis of cardiac arrhythmias is often difficult. Cardiac Magnetic Resonance (CMR) is the gold standard exam for anatomical and functional cardiac evaluation and it may be indicated in patients with ventricular arrhythmias when echocardiography does not provide an accurate assessment of left and right ventricles (LV, RV). Purpose The aim of this study was to determine the impact of CMR in the diagnosis and stratification of arrhythmic risk in patients with confirmed or suspected arrhythmias, as well as to describe the changes observed. Methods We performed a prospective registry over a 5-year period of all the patients with arrhythmias who underwent CMR for diagnostic and risk stratification purposes. We followed a protocol to evaluate both anatomically and functionally the ventricles and to look for the presence of late gadolinium enhancement (LGE). Results A total of 78 patients were included, of which 65% were male and a mean age of 46±17 years-old was observed. The indications for CMR evaluation of patients with confirmed or suspected arrhythmias were as follows: 33% (n=26) of the patients had very frequent premature ventricular complexes (PVC), 23% (n=18) had sustained ventricular tachycardia (VT), 17% (n=13) suspected structural heart disease with high arrhythmic potential, 12% (n=9) unexplained recurrent syncope, 6% (n=5) supraventricular tachycardia, 5% (n=4) non-sustained VT and 4% (n=3) aborted sudden cardiac death. Depressed ventricular ejection fraction (<50%) was present in 9% (n=7) for the LV and in 14% (n=11)for the RV. Dilation of the LV was found in 24% of the patients (n=19, mean LV volume: 115±4ml/m2) and RV dilation was present in only 1 patient who had right ventricle arrhythmogenic dysplasia (RVAD) (RV volume: 152ml/m2). Cardiac synchronization artifacts due to the presence of very frequent PVC compromised the calculation of v volumes in only 4% (n=3) of the patients. In total, 6% (n=5) had interventricular septum hypertrophy (mean 15±6g/m2), 10% (n=8) had a slight prolapse of the anterior leaflet of the mitral valve and 19% (n=15) had a dilated left auricle. LGE was present in 13% (n=10) and slight pericardium effusion was detected in 12% (n=9). CMR was considered normal in 65% (n=51), in 15% (n=12) we found nonspecific changes deserving follow-up and in 20% (n=15) it was possible to establish a diagnosis which was previously unknown: 5% (n=4) had hypertrophic cardiomyopathy, 4% (n=3) LV non-compaction, 4% (n=3) a myocarditis sequelae, 3% (n=2) RVAD, 3% (n=2) a myocardial infarction scar and 1 had non-ischemic dilated cardiomyopathy. Conclusions CMR is a technique with high spatial resolution, feasible and safe, which allowed an increase in diagnosis in 20% of the patients, thus contributing to the risk stratification of our study population with suspected high arrhythmic potential when the first-line complementary exams were inconclusive.

Sinoatrial node pacemaker cell pool dynamics upon synchronization with vagus nerve rhythm

Aim: To reveal the dynamics of sinoatrial node pacemaker cell pools upon synchronization with vagus nerve rhythm through the model of vagal-cardiac synchronization. Materials and methods: Observations were carried out on 10 narcotized cats. The animals were tracheostomized and pump-ventilated, and the pericardium accessed via an open-chest transsternal incision. A device (KELSY scanner manufactured by Elsys, St. Petersburg, Russia) accompanied by a microscope and a video-camera, to visualize the luminescence of excitation processes in the sinoatrial node in a high-frequency electromagnetic field (1024 Hz) was placed in the sinoatrial area of a working heart. Luminescent focus in the sinoatrial node was registered as a peripherally cut end of the vagus nerve was stimulated with bursts of electrical impulses (5 impulses, 2 ms, 20 Hz) from an electrostimulator. Results: Luminescence localized at the entrance of the cranial vena cava was visualized in a high-frequency electrical field in narcotized cats. The luminescent focal area was not homogenous and looked like a number of luminescent pools. Upon vagal-cardiac synchronization caused by the stimulation of a peripherally cut end of the vagus nerve with bursts of electrical impulses, the focus was wide and solid. Conclusion: Here, pacemaker cell dynamics were studied in the feline heart. When vagal- cardiac synchronization was activated, synchronization of the heart with vagus nerve rhythm was accompanied by an increase in the early depolarization area in the sinoatrial area of the feline heart. The mechanisms underlying heart rate synchronization are not clearly defined. Rhythm is achieved through actions of the SA node and the vagus nerve. Our data confirm the vagal- cardiac synchronization model.