Atrioventricular Conduction System Research Articles

Effect of Maternal Ursodeoxycholic Acid Treatment on Fetal Atrioventricular Conduction in Patients with Intrahepatic Cholestasis of Pregnancy.

The aim of this study was, first, to investigate the difference in fetal atrioventricular conduction in patients with and without intrahepatic cholestasis of pregnancy (ICP) by measuring the fetal PR interval; second, to evaluate the altering effect of ursodeoxycholic acid (UDCA) treatment on the fetal PR interval in ICP patients. The study consisted of 42 ICP patients and 48 healthy pregnant women. Fetal echocardiography was performed to measure the mechanical PR interval. The fetal PR interval and the clinical characteristics were compared between the two groups. The effect of UDCA treatment on the fetal PR interval in ICP patients was evaluated. In ICP patients, significantly longer fetal PR intervals were observed than in the control group (123.21 ± 8.54 vs. 115.13 ± 5.95 ms, p < 0.001). In the ICP group, there was a positive correlation between the fetal PR interval and maternal fasting total bile acid (TBA) levels (r = 0.514, p = 0.001). After 1 week of treatment with UDCA in patients with ICP, the PR interval was shorter than before, although the reduction was not statistically significant (120.98 ± 6.70 vs. 123.21 ± 8.54 ms, p = 0.095). In patients with severe ICP (TBA >40 mmol/L, n = 10), a significant reduction in the fetal PR interval was observed after treatment with UDCA (127.5 ms [IQR, 118.0-134.75] before vs. 122 ms [IQR, 109.5-126.5] after, p = 0.037). Fetal PR interval increased in ICP patients in correlation with maternal serum TBA concentration. Treatment with UDCA may have limited positive effects on the fetal AV conduction system. The beneficial effects of UDCA on the fetal PR interval may be more pronounced in patients with higher bile acid levels.

Fasciculoventricular accessory pathway masked extensive atrioventricular conduction system disease in a patient with PRKAG2 syndrome

Fasciculoventricular accessory pathway masked extensive atrioventricular conduction system disease in a patient with PRKAG2 syndrome

Left bundle branch area pacing in the setting of cardiac amyloidosis: a case series

Abstract Background Cardiac amyloidosis (CA) is a highly prevalent cause of congestive heart failure. It often requires cardiac pacing due atrioventricular conduction (AV) system disorders, often with cardiac resynchronization (CRT) to prevent development/deterioration of left ventricular (LV) dysfunction. Left bundle branch area pacing (LBBAP) is an emerging alternative to CRT, offering a strict physiological LV activation and very limited use of iodinated contrast. The feasibility of LBBAP in CA is considered limited due to the presence of septal pseudohypertrophy which theoretically limits left-sided conduction system engagement. Purpose To evaluate the feasibility and effectiveness of LBBAP in cardiac amyloidosis. Methods Consecutive patients with CA (both light-chain -AL- or wild-type transtiretin -wtATTr) with a pacing indication for AV conduction disorders were enrolled. Patients underwent baseline echocardiographic examination. LBBAP was achieved by means of stylet-driven leads advanced transeptally (right ventricle (RV) to LV) via dedicated delivery systems, with continuous monitoring of 12-lead electrocardiographic morphology and impedance until a typical QRS morphology in V1 was obtained (usually rSr’ or Sr’). Standard measures for left bundle (LB) capture were used (stimulus to peak R in V6 – S-RV6, V6-V1 interpeak interval, presence of transition in these measures during threshold testing, presence of fascicular signal during spontaneous QRS). Results Between January 2022 and June 2023, among 63 patients undergoing LBBAP, 7 patients (11%) had CA, 2 AL (28%) and 5 (72%) wtATTR. Patients were prevalently old (78±7 y) males (6, 85%); LV mean septal thickness was 17±2 mm (min 16, max 20 mm) and mean LV ejection fraction (LVEF) was 45±6%. Indications were PR prolongation in 3, bradycardic atrial fibrillation and LB branch block (LBBB) in 2, primary LBBB in 1 and chronic RV pacing in 1. Baseline QRS duration was 145±47 ms (QRS<120 ms: 97±15 ms, QRS>120 ms: 182±13 ms). LBBAP success was 100%. Fascicular electrograms were observed in ¾ of patients without LBBB; S-RV6 interval was 74 ±11 ms (³70 ms in 3), RV6-RV1 interpeak interval was 47±9 ms (³ 30 ms in 6 patients). DQRS in baseline broad QRS was -52 ms and +32 ms in narrow. No complications were observed. Over a short follow up of 6 months, an increase in average LVEF was observed (LVEF at 6 months: 51±3%, p<0.05). Conclusions In patients with CA, LBBAP is easily achievable with stylet-driven systems with frequent selective engagement of conduction system. QRS narrowing in baseline broad QRS is significant while QRS broadening in baseline narrow QRS is limited. Early results regarding follow-up of surrogate endpoint such as LVEF are promising.

The Safety and Feasibility of Pulsed-Field Ablation in Atrioventricular Nodal Re-Entrant Tachycardia: First-in-Human Pilot Trial

BackgroundThe incidence of atrioventricular conduction system damage during the catheter ablation procedure has long been a safety concern in patients with atrioventricular nodal re-entrant tachycardia (AVNRT). Pulsed-field ablation (PFA) with high tissue selectivity is a promising technique to address this problem in patients with AVNRT. ObjectivesThis study aimed to evaluate the safety and feasibility of PFA in patients with AVNRT. MethodsThis was an investigator-initiated, single-center, single-arm, prospective study performed in West China Hospital, Sichuan University. Patients diagnosed with AVNRT by electrophysiological examination were included and treated using PFA. The primary outcome was the ability to achieve acute ablation success. The secondary outcomes were ablation success after 6 months and safety incidents reported. ResultsA total of 30 patients with AVNRT with a mean age of 47.9 ± 13.9 years were included and underwent PFA. Acute ablation success was achieved in all patients. The skin-to-skin procedure time was 109.1 ± 32.1 minutes, and fluoroscopy time was 4.1 ± 0.9 minutes. A median of 8 (range: 6.5 to 11.0) PFA applications were delivered. The average distance of the closest ablation site to the His bundle was 6.5 ± 2.5 mm, with a minimum distance of 2.0 mm. All patients maintained sinus rhythm after 6 months. No adverse events occurred in any patient during the ablation or the 6-month follow-up. ConclusionsPFA showed favorable feasibility and safety in patients with AVNRT in this pilot study. Further study with larger population and longer follow-up time is warranted to verify the results.

Iatrogenic Atrioventricular Block.

Iatrogenic atrioventricular (AV) block can occur in the context of cardiac surgery, percutaneous transcatheter, or electrophysiologic procedures. In cardiac surgery, patients undergoing aortic and/or mitral valve surgery are at the highest risk for developing perioperative AV block requiring permanent pacemaker implantation. Similarly, patients undergoing transcatheter aortic valve replacement are also at increased risk for developing AV block. Electrophysiologic procedures, including catheter ablation of AV nodal re-entrant tachycardia, septal accessory pathways, para-Hisian atrial tachycardia, or premature ventricular complexes, are also associated with risk of AV conduction system injury. In this article, we summarize the common causes for iatrogenic AV block, predictors for AV block, and general management considerations.

Pseudo-pacemaker syndrome with prolonged PR interval: A narrative review.

Pseudo-pacemaker syndrome (PPMS) is a rare complication of first-degree atrio-ventricular (AV) block in which a very prolonged PR interval causes AV dyssynchrony and subsequent symptoms of hemodynamic instability in the absence of an implanted pacemaker. The aim of this manuscript was to describe a unique case of PPMS and to provide a comprehensive review of the topic to help clinicians in the diagnosis and management of this condition. Through systematic research on PubMed, Google Scholar, EBSCO, and Ovid MEDLINE and using the search strings "pseudo-pacemaker syndrome" and "symptomatic first-degree AV block," we identified 14 articles accounting for 17 cases of PPMS, including our case report. The most common age group for PPMS was middle-aged and young adults, with an average age of 47 years. Palpitations were the most common presenting symptom and four main etiologies of PPMS were identified, as follows: (1) Idiopathic PPMS with evidence of impaired conduction over the AV node (20% of cases), (2) PPMS associated with reversable inflammatory causes (13%) or (3) associated with iatrogenic surgical or interventional procedures leading to the permanent damage of the normal AV conduction system (20%), and, finally, (4) PPM related to dual AV nodal physiology (DAVNP) as a primary finding (27%) or occurring after fast or slow pathway ablation for treatment of AV nodal re-entrant tachycardia (AVNRT) (20%). Treatment should be patient-tailored and based on the specific etiology once identified. However, the treatment of PPMS due to DAVNP without AVNRT presentation is yet to be clarified.

Comprehensive pathological and genetic investigation of three young adult myotonic dystrophy type 1 patients with sudden unexpected death.

The mechanism and pathological substrate of arrhythmogenic events in dystrophic myopathy type 1 (DM1) have not been fully established, especially for patients without progression of motor and/or cardiac disability. Therefore, we aimed to clarify the pathological appearance and genetic factors, other than CTG repeats in DMPK, associated with sudden cardiac death in patients with DM1. A pathological investigation including the cardiac conduction system in the heart and whole-exome sequencing was conducted for three young adults (Patient 1; 25-year-old female, Patient 2; 35-year-old female, Patient 3; 18-year-old male) with DM1 who suffered sudden death. Only Patient 1 showed abnormal electrocardiogram findings before death. The pathological investigation showed severe fibrosis of the atrioventricular conduction system in Patient 1 and severe fatty infiltration in the right ventricle in Patient 2. Several minimal necrotic/inflammatory foci were found in both patients. Patient 3 showed no significant pathological findings. A genetic investigation showed CORIN_p.W813* and MYH2_p. R793* in Patient 1, KCNH2_p. V794D and PLEC_p. A4147T in Patient 2, and SCN5A_p.E428K and SCN3B_ p.V145L in Patient 3 as highly possible pathogenic variants. The present study showed varied heart morphology in young adults with DM1 and sudden death. Synergistic effects of various genetic factors other than CTG repeats may increase the risk of sudden cardiac death in DM1 patients, even if signs of cardiac and skeletal muscle involvement are mild. Comprehensive genetic investigations, other than CTG repeat assessment, may be useful to estimate the risk of sudden cardiac death in DM1 patients.

Efficient generation of TBX3+ atrioventricular conduction-like cardiomyocytes from human pluripotent stem cells

Atrioventricular conduction cardiomyocytes (AVCCs) regulate the rate and rhythm of heart contractions. Dysfunction due to aging or disease can cause atrioventricular (AV) block, interrupting electrical impulses from the atria to the ventricles. Generation of functional atrioventricular conduction like cardiomyocytes (AVCLCs) from human pluripotent stem cells (hPSCs) provides a promising approach to repair damaged atrioventricular conduction tissue by cell transplantation. In this study, we put forward the generation of AVCLCs from hPSCs by stage-specific manipulation of the retinoic acid (RA), WNT, and bone morphogenetic protein (BMP) signaling pathways. These cells express AVCC-specific markers, including the transcription factors TBX3, MSX2 and NKX2.5, display functional electrophysiological characteristics and present low conduction velocity (0.07 ± 0.02 m/s). Our findings provide new insights into the understanding of the development of the atrioventricular conduction system and propose a strategy for the treatment of severe atrioventricular conduction block by cell transplantation in future.

Mid-term follow-up of atrioventricular node ablation and conduction system pacing without a ventricular backup lead in atrial fibrillation-induced tachycardiomyopathy - a single-center experience

Abstract Funding Acknowledgements Type of funding sources: None. In the permanent form of atrial fibrillation (AF), ablation is not recommended or has failed and the only option is rate control. The most effective rate control strategy is atrioventricular node (AVN) ablation, but this renders the patient pacing-dependent. Several observational studies have shown that both His bundle pacing (HBP) and left bundle branch area pacing (LBBAP), provide a narrower QRS complex and a more synchronous ventricular activation compared to right ventricular pacing. Current guidelines recommend placing a ventricular backup lead as a safety measure. We present our mid-term follow-up data on the feasibility of AVN ablation and physiological pacing without a ventricular backup lead in patients with tachycardiomyopathy due to rapidly conducted permanent AF. MATERIAL AND METHODS A total of 25 patients with permanent AF and HF and rate control failure with AVN-blocking drugs, that underwent physiological pacing and AVN ablation at our institution, were included in this retrospective review. During the procedure, HBP was the first option, followed by LBBAP if the His bundle was not captured at a threshold below 2.5V at 1 ms. The lead was connected to a single chamber pacemaker, without a backup pacing lead. In the same setting, using a femoral vein approach, a 4-mm tip ablation catheter was used to perform AVN ablation. Patient and procedural characteristics were recorded as well as the electrical parameters and complications at the follow-up visits. Results The mean age of the patients was 69 ± 12.4 years and 64% were males. The heart rate was 133±20.43 bpm and the ejection fraction was 28.84±9.02 %. 17 patients had normal QRS complex, 3 had right bundle branch block and 5 had left bundle branch block patterns. HBP was successful in 9 patients (36%) and LBBAP in 16 patients (64%). In patients with a baseline-wide QRS, physiological pacing significantly reduced the QRS duration (135.25±17.58 vs. 159±32.38 ms, p=0.04). The paced QRS complex was significantly narrower in HBP than LBBAP (95.67±14.37 vs. 129.88±17.46 ms, p<0.001). There was a significantly lower pacing threshold for LBBAP (0.77±0.3 V at 1 ms vs. 0.87±0.72 V at 0.4 ms, p<0.05) and better sensitivity for LBBAP (6.23±4.56 mV vs. 10.2±5.19 mV, p=0.66). The fluoroscopy time was non-statistically different between HBP and LBBAP (13.21±15.47 min vs. 18.72±12.95 min, p=0.35). AV node ablation was successful in all patients. The mean follow-up period was 524±110.2 days. 11 patients became pacemaker-dependent. There was no significant difference in pacing thresholds for both LBBAP (0.67±0.27 V at 0.4 ms, p=0.24) and HBP (0.87±0.56 V at 1 ms, p=0.485) patients and there was no recurrence in AV node conduction. No lead dislodgements were recorded. Conclusions AVN ablation and physiological pacing is feasible and safe without the need for a backup ventricular pacing lead, thus minimizing the risks and costs associated with a higher lead burden.

PO-05-018 GIANT INTRASEPTAL HEMATOMA COMPLICATING LEFT BUNDLE BRANCH PACING: AN UNUSUAL CLINICAL CHALLENGE

Left bundle branch pacing (LBBP) is an excellent alternative to His bundle pacing (HBP). Due to its non-traditional intraseptal lead placement, rare but unusual complications have been described. We present the case of a unique complication of a very large septal hematoma following LBBP. n/a An 88-year-old female with Coronary disease, renal insufficiency, and uncontrolled atrial fibrillation was referred for AV node ablation and conduction system pacing. Due to high HBP thresholds, a LBBP lead was implanted in proximal location (Stim-V6 peak=70ms, QRSd=135ms) with a backup second LBBP lead at a slightly distal location (Stim-V6 peak=61ms, QRSd=121ms) with low capture thresholds. She was discharged home the same day. She was readmitted a-day later with nausea, weakness, and significant dyspnea. Echocardiogram revealed a very large septal hematoma (61mm x 40mm) with complete obliteration of right ventricle cavity and no pericardial effusion (Figure 1A). IV fluid bolus was given, and Apixaban/Clopidogrel/ASA were held. Angiography and possible embolization of bleeding septal perforator was considered but not performed due to her CKD and hemodynamic stability. Serial echo revealed improved RV filling, stable hematoma and absent effusion. She was discharged on day 7 in stable condition. Anticoagulation was resumed after 2 weeks. Repeat echo at 6 weeks showed complete resolution of interventricular septal hematoma and lead parameters were stable (Figure 1B). This is a unique and rare case of a giant interventricular septal hematoma post LBBP, successfully managed with conservative management. Given rarity of complication, maintaining a broad differential for early recognition and treatment remains paramount. Avoiding a very proximal and anterior left bundle area, if possible, can be considered to avoid a major septal perforator. Repeat imaging and close hemodynamic monitoring is recommended in such patients. Angiography to localize the bleeding septal perforator and possible embolization may be considered for hemodynamic instability. This was deferred in our patient due to severe renal insufficiency, as well as lack of pericardial effusion and improving hemodynamics not requiring inotropic support. However, we recommend a multidisciplinary heart team and critical care approach, as was used in this case, to help personalize management.

The anatomical basis of third-degree atrioventricular block in dogs with atrioventricular valve endocardiosis

The cardiac conduction system was examined histologically in 13 canine cases of atrioventricular (AV) valve endocardiosis with third-degree AV block. In all cases, gross examination revealed marked thickening and distortion of the base of the central fibrous body (CFB) and varying degrees of endocardial thickening of the upper portion of the ventricular septum (VS) as well as marked thickening of the mitral and tricuspid valve leaflets due to myxomatous degeneration. Microscopically, the thickened and distorted CFB had encased or trapped, either partly or totally, the underlying penetrating and branching portions of the AV bundle. The myxomatous and/or fibrofatty tissue, which had proliferated at the base of the extensive CFB, protruded into or encroached on the AV bundle, causing severe (51–75%) to very severe (76% or more) reduction of the conduction fibres. The upper portions of the left and right bundle branches were involved in the endocardial thickening due to degenerative and fibrotic changes at the uppermost VS; however, both bundle branches were much less severely affected than the AV bundle, the degree of reduction of the conduction fibres ranging from mild (25% or less) to moderate (26–50%). These observations suggest that the sites most vulnerable to lesions in the AV conduction system are the penetrating and branching portions of the AV bundle, which would represent the anatomical basis for third-degree AV block in canine cases of AV valve endocardiosis.

Pathological and Comprehensive Genetic Investigation of Autopsy Cases of Idiopathic Bradyarrhythmia.

Idiopathic bradyarrhythmia is considered to be due to pathological degeneration of the cardiac conduction system (CCS) during aging. There appears to have been no comprehensive genetic investigations in patients with idiopathic bradyarrhythmia. Ten autopsy cases with advanced bradyarrhythmia (6 men and 4 women; age: 70-94 years, 81.5±6.9 years; 5 cases each of sinus node dysfunction [SND] and complete atrioventricular block [CAVB]) were genetically investigated by using whole-exome sequencing. Morphometric analysis of the CCS was performed with sex-, age- and comorbidity-matched control cases. As a result, severe loss of nodal cells and distal atrioventricular conduction system were found in SND and CAVB, respectively. However, the conduction tissue loss was not significant in either the atrioventricular node or the proximal bundle of His in CAVB cases. A total of 13 heterozygous potential variants were found in 3 CAVB and 2 SND cases. Of these 13 variants, 4 were missense in the known progressive cardiac conduction disease-related genes: GATA4 and RYR2. In the remaining 9 variants, 5 were loss-of-function mutation with highly possible pathogenicity. In addition to degenerative changes of selectively vulnerable areas in the heart during advancing age, the vulnerability of the CCS, which may be associated with "rare variants of small effect," may also be a contributing factor to the degeneration of CCS, leading to "idiopathic" bradyarrhythmia.

S2000 Colonoscopy-Induced Transient Mobitz Type 1 Block

Introduction: Propofol is a commonly used anesthetic in endoscopic procedures. It can prolong the atrioventricular (AV) conduction through vagal stimulation leading to AV block. We report a unique case of a previously healthy patient undergoing a routine screening colonoscopy who developed a Mobitz type 1 block during the procedure, in which propofol was the sole agent used for sedation. Case Description/Methods: A 74-year-old female with a medical history of diverticulosis and a family history of colon cancer in her first-degree relative presented for a routine colonoscopy performed under monitored supervised propofol sedation. During the final phase of the colonoscopy which was performed with minimal air insufflation, she was observed to have a transient 2:1 heart block mixed with periods of 3:2 heart block on the monitor. After the procedure was completed, she reported no cardiac or neurological symptoms. Review of an electrocardiogram strip showed lengthening of the PR interval consistent with Wenckebach (Mobitz type 1 block; Figure. This resolved post procedure. All labs were within normal limits. Prior to this procedure, she had no cardiac history nor was she on any medications. She was referred for a formal cardiology evaluation which included a 14-day Holter monitor showing 22 asymptomatic episodes of supraventricular tachycardia with longest being 26. No treatment was initiated. She also underwent an echocardiogram showing an ejection fraction of 75%, with a normal left ventricle. The incident was deemed to be a vagal affect due to the probe being in the colon/rectum and the effects of propofol. She has not had any recurrences of the Wenckebach phenomenon on subsequent electrocardiograms and continues to remain asymptomatic. Discussion: Propofol can prolong the AV conduction system leading to a heart block even in patients without any cardiac history. The suggested mechanism is hypervagal stimulation causing slow sinus rate, prolongation of stimulus to the bundle of His interval, lengthening of the Wenckebach cycle and the effective refractory period. While air distention in the stomach or colon can also result in a vasovagal reaction and bradycardia, cases of nodal block in this situation are extremely rare. This case demonstrates that in addition to expected vasovagal bradycardia, nodal block is a rare possibility and hence the need for close continuous cardiac monitoring during endoscopy.Figure 1.: Lengthening of the PR interval consistent with Wenckebach (Mobitz type 1 block).

Abstract P3092: Transcriptomic Landscape Of The Postnatal Atrioventricular Conduction System

The atrioventricular conduction system (AVCS) is a network of specialized cardiomyocytes responsible for coordinated spreading of electrical impulses throughout the heart to allow synchronized contractions. Specifically, it is composed of the AV node (AVN), which delays the electrical signal, and the ventricular conduction system (VCS) (i.e. His bundle, bundle branches and Purkinje fibers), which rapidly propagates the signal throughout the ventricles. Although these AVCS structures were discovered >100 years ago, its molecular constituents are not fully known. In this study, AVCS cells, making up ~0.05% of myocytes (~500 cells/heart), were isolated from early postnatal hearts (Postnatal day 1 to 4) of fluorescent reporter mice (Cntn2- Cre;Rosa26TdTomato), purified using fluorescence-activated cell sorting, and were subjected to single-cell RNA-sequencing. Unbiased cluster analysis on ~7000 AVCS cells demonstrated distinct transcriptomic profiles in the AVN, proximal-VCS (i.e. His bundle and bundle branches) and distal-VCS (i.e. Purkinje fibers). Conforming to previous studies, global conduction markers, such as Etv1 and Kcne1, were present throughout the entire AVCS, whereas a VCS-specific TF, Irx3 , was expressed only in the VCS. Additionally, Tbx3, Pcp4, Nppa and Lyz2 were enriched in the proximal, not distal, VCS. Sub-clustering analysis of AVN and proximal-VCS further identified unique molecular profiles, such as Shox2 (in compact AVN) and Rspo3 (likely in lower nodal region connecting AVN and proximal-VCS). Moreover, we uncovered a potential regulatory relationship between Irx3 and Tbx3 in the AVCS, mediating their downstream targets, Gja5 and Gja1 . In Irx3 and Tbx3 -positive proximal-VCS, Gja5 and Gja1 expressions were lower compared to only Irx3 -positive distal-VCS, whereas in only Tbx3 -positive AVN, both Gja5 and Gja1 expressions were undetected. Importantly, this regional difference was recapitulated in cultured neonatal mouse atrial and ventricular myocytes overexpressing Irx3 and/or Tbx3 . Overall, our study provides a comprehensive view of the cellular and molecular heterogeneity within the postnatal AVCS at a high-resolution and reveals novel gene regulatory mechanisms that may govern the development of the AVCS.

Simultaneous conduction system pacing and atrioventricular node ablation via axillary vs femoral access.

Atrioventricular node ablation (AVNA) and conduction system pacing (CSP) using His bundle pacing (HBP) and/or left bundle branch area pacing (LBBAP) are excellent options for patients with atrial fibrillation and rapid ventricular rates refractory to medical therapy.1,2 While many operators perform AVNA several weeks after the device implantation to allow lead stabilization, most physicians perform simultaneously.3 Femoral venous access is the most commonly used approach to perform AVNA but can be associated with groin-related bleeding complications.

Left bundle branch area pacing: predictors of success

Abstract Funding Acknowledgements Type of funding sources: None. Background Frequent conventional pacing of the right ventricle can be deleterious. In the last three years, left bundle branch area pacing (LBBAP) has experienced a great development as a tool for the specific conduction system stimulation. Methods Single-center prospective study of consecutive patients with attempted LBBAP for bradycardia or heart failure indications (bailed-out strategy). A 3830-69 lead was implanted using a C-315-His sheath, and we aimed for left bundle branch pacing (LBBP) in all patients. Current criteria to define LBAPP, LBBP (selective or non-selective), and left ventricle septal pacing (LVSP) were used. The goal of our study was to analyze clinical, electrical, and echocardiographic variables that may predict the achievement of LBBP. Results We included 149 patients between Feb/20 and Jan/22. Baseline characteristics and pacing indications are shown in table 1. We had success in 145 patients (97.3%): 78.9% were considered LBBP (44.4% SLBBP), and 21.1% LVSP. Paced QRS was significantly higher in patients with wide basal QRS (120.9 ± 15.2 ms vs 110.7 ± 12.6 ms, p<0.001). Likewise, left ventricular activation time (LVAT) in V5/V6 and aVL was shorter in the group with narrow basal QRS (77.2 ± 10.5 vs 83.3 ± 11.4, p<0.001, and 80.0 ± 14.1 vs 87.6 ± 14.4, p <0.001, respectively), being much more frequent to achieve an LVAT <80 ms in the group with narrow QRS (64.9% vs 42.2%, OR 2.6, p = 0.004). Logically, the variation of the paced QRS compared to baseline was also different in both groups (-25.4 ± 12.5 ms in the wide QRS group and + 16.2 ± 13.8 ms in the narrow QRS group). LBBP was achieved to a greater extent in the narrow QRS group (89.2% vs 67.6%, OR 3.9, p=0.002); the difference between selective and non-selective LBBP based on baseline QRS was not significant. Regarding the clinical variables, the presence of hypertension, diabetes mellitus, heart failure or COPD did not show a significant difference in the achievement of LBBP. In contrast, it was significantly less frequent to achieve LBBP in patients with LV systolic dysfunction of any degree (62.0% vs 83.2%, p=0.02), or chronic ischemic heart disease (61.1% vs 82.1%, p=0.04), with a trend in patients with CKD (67.7% vs 82.6%, p=0.06). Also, the bradycardia pacing indication had a significant influence, with the percentage of LBBP being lower in patients with atrioventricular conduction system disease compared to sick sinus syndrome (72.0% vs 85.1%, p=0.04). On the other hand, there was no significant association between the achievement of LBBP and echocardiographic parameters such as interventricular septum thickness, and left atrial volumen. Conclusions LBBAP as elective ventricular pacing is feasible, with a high success rate, and in most cases, it is possible to capture the conduction system. However, there appear to be factors that a priori may pose a greater challenge in its achievement, highlighting the electrical conduction system and myocardial disease.

Mahaim Revisited.

The name Ivan Mahaim is well-known to electrophysiologists. However, alternative anatomical substrates can produce the abnormal rhythms initially interpreted on the basis of the pathways he first described. These facts have prompted suggestions that Mahaim should be deprived of his eponym. It is agreed that specificity is required when describing the pathways that produce the disordered cardiac conduction, and that the identified pathways should now be described in an attitudinally appropriate fashion. The authors remain to be convinced that understanding will be enhanced simply by discarding the term ‘Mahaim physiology’ from the lexicon. It is fascinating to look back at the history of accessory atrioventricular junctional conduction pathways outside the normal accessory atrioventricular conduction system, and their possible role in rhythm disturbances. It took both the anatomist and the clinical arrhythmologist quite some time to understand the complex anatomical architecture and the ensuing electrophysiological properties. Over the years, the name Mahaim was often mentioned in those discussions, although these pathways were not the ones that produced the eponym. The reason for this review, therefore, is to present relevant information about the person and what followed thereafter.

Predictors of Early and Late Atrioventricular Block Requiring Permanent Pacemaker Implantation After Transcatheter Aortic Valve Replacement: A Single-Center Experience

PurposeComplete heart block requiring permanent pacemaker can occur early following transcatheter aortic valve replacement (TAVR) due to mechanical compression of the aortic valve annulus and associated atrio-ventricular (AV) conduction system. Data are limited regarding late PM implantation after TAVR. The purpose of this study was to determine predictors of early vs. late PM implantation post-TAVR procedure. MethodsBaseline characteristics of patients who required PM <7 days following TAVR were compared with patients who required a PM >7 days to 1 year following TAVR using Chi-Square and multivariate regression analysis. ResultsThere were 362 TAVR patients, of which 39 (10.4%) received a PM after TAVR. Of these 18 (4.6%) patients required PM within 7 days after TAVR, and 21 (5.8%) required PM after 7 days and up to 1 year later. Right bundle branch block (RBBB) (OR 6.721, CI 2.3–36.9, p < 0.005) was a positive predictor of early PM placement. Left bundle branch block (LBBB) (OR = 3.5, CI 1.19–10.80, p-value < 0.05) and atrial fibrillation (AF) (OR = 3.5, 1.36–9.4 p < 0.05) were predictors for late PM. Early and late PM were associated with a longer median hospital stay compared to no PM (4.9 ± 4.86 days vs. 10.1 ± 10.04 days vs. 6.10 ± 6.02 days). The incidence of heart failure was higher in the late PM group. The overall motility was not increased in early and late PM compared to no PM. ConclusionPatients requiring PM implant after TAVR was 10.4%, of which 5.8% need PM >7 days post-TAVR. RBBB is a predictor for early PM. AF and LBBB were predictors for late PM.

Histological Features of the Atrioventricular Conduction System in Cats with High-Grade Atrioventricular Block

The histopathological features of the atrioventricular (AV) conduction system of nine cats with high-grade atrioventricular block (H-AVB) were compared with those of 22 cases of third-degree atrioventricular block (3-AVB). All nine H-AVB cats had experienced syncopal attacks of variable severity and had been diagnosed electrocardiographically. The AVB, which was permanent in all cases, had been observed for 15-1,981 days (average 663 days) before death. Histological examination of the AV conduction system revealed moderate (25-50%) or severe (>50%) loss of conduction fibres associated with fibrous replacement in the regions of the branching portion of the AV bundle and the upper portion of the left bundle branch in almost all of the H-AVB cases and in all the 3-AVB cases. Comparison of lesion severity in each region in the H-AVB and 3-AVB cases revealed that the branching portion of the AV bundle was less severely affected in the H-AVB cases. This finding might explain why the H-AVB cases had intermittent block of AV conduction while the 3-AVB cats had permanent block.

Underlying Heart Diseases and Lesions of the Atrioventricular Conduction System in Dogs with Third-degree Atrioventricular Block

Underlying Heart Diseases and Lesions of the Atrioventricular Conduction System in Dogs with Third-degree Atrioventricular Block