[New frontiers in pacing: from myocardial pacing to conduction system pacing]. / Nuove frontiere dell'elettrostimolazione: dal pacing del miocardio comune al pacing del sistema di conduzione.

For many years, cardiac pacing has been based on the stimulation of right ventricular common myocardium to correct diseases of the conduction system. The birth and the development of cardiac resynchronization have led to growing interest in the correction and prevention of pacing-induced dyssynchrony. Many observational studies and some randomized clinical trials have shown that conduction system pacing (CSP) can not only prevent pacing-induced dyssynchrony but can also correct proximal conduction system blocks, with reduction of QRS duration and with equal or greater effectiveness than biventricular pacing. Based on these results, many Italian electrophysiologists have changed the stimulation target from the right ventricular common myocardium to CSP. The two techniques with greater clinical impact are the His bundle stimulation and the left bundle branch pacing. The latter, in particular, because of its easier implantation technique and better electric parameters, is spreading like wildfire and is representing a real revolution in the cardiac pacing field. However, despite the growing amount of data, until now, the European Society of Cardiology guidelines give a very limited role to CSP.

Transient 2:1 Atrioventricular Block with Peri-Conduction System Pacing After Leadless Pacemaker Implantation.

This report discusses a case of transient 2:1 atrioventricular block with conduction system pacing 4 hours after leadless right ventricular pacemaker implantation in a 19-year-old patient with a history of cardioinhibitory syncope and asystole cardiac arrest but without preexisting atrioventricular block. The atrioventricular block was resolved spontaneously. Pacing morphology was suggestive of right bundle branch pacing. Neither 2:1 atrioventricular block nor conduction system pacing has previously been a reported outcome of right ventricular leadless pacemaker implantation. The report demonstrates that conduction system pacing with leadless devices is achievable. Further study of techniques, limitations, and complications related to intentional right ventricular leadless conduction system pacing is warranted.

The cardiac conduction system: History, development, and disease.

The heart is the first organ to form during embryonic development, establishing the circulatory infrastructure necessary to sustain life and enable downstream organogenesis. Critical to the heart's function is its ability to initiate and propagate electrical impulses that allow for the coordinated contraction and relaxation of its chambers, and thus, the movement of blood and nutrients. Several specialized structures within the heart, collectively known as the cardiac conduction system (CCS), are responsible for this phenomenon. In this review, we discuss the discovery and scientific history of the mammalian cardiac conduction system as well as the key genes and transcription factors implicated in the formation of its major structures. We also describe known human diseases related to CCS development and explore existing challenges in the clinical context.

Comprehensive analysis of right fascicular and right bundle branch blocks: A multi-center study.

Electrocardiographic patterns of right bundle branch and fascicular blocks were comprehensively analyzed in a two-phase study. The research aimed to address the scarcity of literature and the absence of standardized diagnostic criteria for these conditions. It revealed a weak correlation between the cardiac axis and age and highlighted the high misdiagnosis rate of these blocks. Furthermore, it discussed the challenges in fulfilling existing diagnostic criteria. The study emphasizes the need for a more precise understanding of right ventricular conduction disorders and the importance of developing robust diagnostic criteria.

Redefining left bundle branch block from high-density electroanatomical mapping.

BACKGROUND: The existing ECG criteria for diagnosing left bundle branch block (LBBB) are insufficient to distinguish between true and false blocks accurately. METHODS: We hypothesized that the notch width of the QRS complex in the lateral leads (I, avL, V5, V6) on the LBBB-like ECG could further confirm the diagnosis of true complete left bundle branch block (t-LBBB). We conducted high-density, three-dimensional electroanatomical mapping in the cardiac chambers of 37 patients scheduled to undergo CRT. These patients' preoperative electrocardiograms met the ACC/AHA/HRS guidelines for the diagnosis of complete LBBB. If the left bundle branch potential could be mapped from the base of the heart to the apex on the left ventricular septum, it was defined as a false complete left bundle branch block (f-LBBB). Otherwise, it was categorized as a t-LBBB. We conducted a comparative analysis between the two groups, considering the clinical characteristics, real-time correspondence between the spread of ventricular electrical excitation and the QRS wave, QRS notch width of the lateral leads (I, avL, V5, V6), and the notch width/left ventricular end-diastolic diameter (Nw/LVd) ratio. We performed the ROC correlation analysis of Nw/LVd and t-LBBB to determine the sensitivity and specificity for diagnostic authenticity. RESULTS: Twenty-five patients were included in the t-LBBB group, while 12 patients were assigned to the f-LBBB group. Within the t-LBBB group, the first peak of the QRS notch correlated with the depolarization of the right ventricle and septum, the trough corresponded to the depolarization of the left ventricle across the left ventricle, and the second peak aligned with the depolarization of the left ventricular free wall. In contrast, within the f-LBBB group, the first peak coincided with the depolarization of the right ventricle and a majority of the left ventricle, the second peak occurred due to the depolarization of the latest, locally-activated myocardium in the left ventricle, and the trough was a result of delayed activation of the left ventricle that did not align with the usual peak timing. The QRS notch width (45.2 ± 12.3 ms vs. 52.5 ± 9.2 ms, P < 0.05) and the Nw/LVd ratio (0.65 ± 0.19 ms/mm vs. 0.81 ± 0.17 ms/mm, P < 0.05) were compared between the two groups. After conducting the ROC correlation analysis, a sensitivity of 56% and a specificity of 91.7% for diagnosing t-LBBB using Nw/LVd were obtained. CONCLUSION: By utilizing the current diagnostic criteria for LBBB, an increased Nw/LVd value can enhance the effectiveness of diagnosing LBBB.

[Historical development of diagnosis of bradyarrhythmias : The early years of clinical electrophysiology in Germany]. / Historische Entwicklung der Diagnostik der bradykarden Rhythmusstörungen : Die frühen Jahre der Klinischen Elektrophysiologie in Deutschland.

The introduction of His bundle electrography by Benjamin Scherlag (New York) in 1969, together with programmed stimulation of the heart by Philip Coumel (Paris) in 1967, and Hein Wellens (Amsterdam) in 1972, were decisive turning points on the way to invasive electrophysiology and the development of an independent, now distinctly interventional subspecialty of cardiology. The main topic of the 1970s was bradycardic arrhythmias, promoted by pacemaker therapy, which had been introduced just over 10 years earlier. The recording of the potentials of the bundle of His and other recording locations in the atria and ventricles allowed a differentiated assessment of the excitation process and the refractory periods. High-rate atrial stimulation to determine sinus node recovery time and premature stimulation to determine sinoatrial conduction time were developed to analyze sinoatrial node function. This article describes the introduction of His bundle electrography in a gradually increasing number of centers in Germany and their scientific contribution.

[History of cardiac pacemaker therapy in Germany]. / Geschichte der Herzschrittmacher-Therapie in Deutschland.

Cardiac pacemaker therapy began with successful stimulation of human hearts already in the first half of the 20th century. Complete implantation of a pacemaker by the cardiac surgeon Åke Senning on October 8, 1958 at the Karolinska Hospital in Stockholm is considered the actual birth of today's pacemaker therapy. The first pacemaker implantation in Germany was performed by Hans-Joachim Sykosch on October 6, 1961 at the Surgical Clinic of the University of Düsseldorf. Two years later, the first implantation in East Germany (GDR) was carried out by Friedrich Flemming on September 2, 1963 at the Charité in East Berlin. The first pacemaker manufactured in West Germany arrived on the market 1963; East Germany started device production in 1978. In 1974, pacemaker therapy in West Germany showed a 50% survival rate after 6.3 years compared to < 1 year with drug therapy. After initially using bare metal wires, pacemaker leads have significantly improved in both quality and reliability. Development culminated in the leadless pacemaker. Battery development led to a variety of inventions: rechargeable pacemakers, biogalvanic cells, bioenergy sources, nuclear generators and lithium batteries, the latter ultimately prevailed. In the beginning, only fixed-rate ventricular pacemakers were available. Subsequently, systems adapted to physiological requirements were developed: on-demand pacemakers, atrial-based pacing and rate-adaptive systems. However, it was not until the return to direct stimulation of the conduction system that truly physiological stimulation of the heart became possible.

The spiral wave frequency effect in atrial fibrillation.

A spiral wavefront (WF), generated by a cardiac rotor that drifts between surface electrodes during atrial fibrillation, exhibits frequency changes inconsistent with classical Doppler effect (CDE) phenomena. Recent clinical studies reveal three repeatedly observed events--1) side-dependent frequency changes across the path of the rotor, 2) one additional WF strike on the higher frequency side, and 3) a reversal of WF strike sequence--which constitute a diametrical property of spinning WF sources. A linear ray model is first used to reveal and develop the diametrical phenomena. Mathematical models of an Archimedean spiral and a spiral generated by the diffusion equation are developed and compared. Each formulation predicts the diametrical property that CDE does not capture and illuminates the occurrence of a strong side and weak side with respect to the rotor path. Whereas CDE exhibits higher and lower frequencies from approaching and receding sources of WFs, respectively, spiral rotors generate higher and lower frequencies on opposite sides of the migration path. This motivates the reconsideration of mapping and ablation strategies that have traditionally been based on identifying sites of the dominant frequency. While this research aims to characterize the path of a spiral rotor during atrial fibrillation accurately, the results are applicable in other fields of science and engineering in which rotating spiral waves occur.

Successful high-resolution three-dimensional electroanatomical mapping and radiofrequency catheter ablation of a posteroseptal accessory pathway in a dog using CARTO 3.

A one-year-and-seven-month-old, 28 kg, male castrated crossbreed dog was presented for supraventricular tachycardia causing recurrent episodes of anorexia and lethargy. Sotalol (2.2 mg/kg q12 h) reduced the frequency of symptomatic episodes but did not provide full relief. Three-dimensional electroanatomical mapping was performed at the Ghent University Small Animal Teaching hospital using the CARTO 3. Right atrial activation mapping identified the earliest atrial activation right posteroseptal, near the tricuspid annulus. Fast retrograde ventriculoatrial conduction during tachycardia and extrastimulus testing confirmed the presence of a concealed right posteroseptal accessory pathway. Six radiofrequency catheter ablation applications were delivered, and tachycardia remained uninducible. The dog recovered well from the procedure. Sotalol was stopped three weeks later, and no more clinical signs were noted by the owner. Repeated 24-hour electrocardiography monitoring on day one and at one, three, and 12 months after the procedure showed no recurrence of tachycardia.

Assessing Torque Transfer in Conduction System Pacing: Development and Evaluation of an Ex Vivo Model.

BACKGROUND: Conduction system pacing (CSP) faces challenges in achieving reliable and safe deployments. Complex interactions between tissue and lead tip can result in endocardial entanglement, a drill effect that prevents penetration. No verified ex vivo model exists to quantitatively assess this relationship. OBJECTIVES: The purpose of this study was to quantitatively characterize CSP lead tip to tissue responses for 4 commonly used leads. METHODS: CSP leads (from Medtronic, Biotronik, Boston Scientific, and Abbott) were examined for helix rotation efficiency in ex vivo ovine right ventricular septa. A custom jig was utilized for rotation measurements. Fifteen turns were executed, documenting tissue-interface changes every 90° using high-resolution photography. Response curves (input rotation vs helix rotation) were evaluated using piecewise linear regression, with a focus on output vs input response slopes and torque breakpoint events. RESULTS: We analyzed 3,840 quarter-turn CSP insertions with 4 different lead types. Helix rotations were consistently less than input: Abbott Tendril = 0.21:1, Medtronic 3830 = 0.21:1, Biotronik Solia = 0.47:1, and Boston Scientific Ingevity = 0.56:1. Torque breakpoint events were observed on average 7.22 times per insertion (95% CI: 6.08-8.35; P = NS) across all leads. In 57.8% of insertions (37 of 64), uncontrolled torque breakpoint events occurred, signaling unexpected excess helix rotations. CONCLUSIONS: Using a robust ex vivo model, we revealed a muted helix rotation response compared with input turns on the lead, and frequent torque change events during insertion. This is critical for CSP implanters, emphasizing the potential for unexpected torque breakpoint events, and suggesting the need for novel lead designs or deployment methods to enhance CSP efficiency and safety.