Non-invasive Characterization of Human AV-Nodal Conduction Delay and Refractory Period During Atrial Fibrillation

During atrial fibrillation (AF), the heart relies heavily on the atrio-ventricular (AV) node to regulate the heart rate. Thus, characterization of AV-nodal properties may provide valuable information for patient monitoring and prediction of rate control drug effects. In this work we present a network model consisting of the AV node, the bundle of His, and the Purkinje fibers, together with an associated workflow, for robust estimation of the model parameters from ECG. The model consists of two pathways, referred to as the slow and the fast pathway, interconnected at one end. Both pathways are composed of interacting nodes, with separate refractory periods and conduction delays determined by the stimulation history of each node. Together with this model, a fitness function based on the Poincaré plot accounting for dynamics in RR interval series and a problem specific genetic algorithm, are also presented. The robustness of the parameter estimates is evaluated using simulated data, based on clinical measurements from five AF patients. Results show that the proposed model and workflow could estimate the slow pathway parameters for the refractory period, RminSP and ΔRSP, with an error (mean ± std) of 10.3 ± 22 and −12.6 ± 26 ms, respectively, and the parameters for the conduction delay, Dmin,totSP and ΔDtotSP, with an error of 7 ± 35 and 4 ± 36 ms. Corresponding results for the fast pathway were 31.7 ± 65, −0.3 ± 77, 17 ± 29, and 43 ± 109 ms. These results suggest that both conduction delay and refractory period can be robustly estimated from non-invasive data with the proposed methodology. Furthermore, as an application example, the methodology was used to analyze ECG data from one patient at baseline and during treatment with Diltiazem, illustrating its potential to assess the effect of rate control drugs.

Experimental use of stereotactic radiosurgery for non-invasive interventions in arrhythmology

Purpose. The experimental study aimed to study the effects of stereotaxic radioablation of various doses on the myocardium of the atria, ventricles and atrioventricular (AV) node in the long term (up to 6 months); as well as assessment of collateral damage during radioablation.Methods. The study comprised 4 domestic pigs. The animals were 10-12 weeks old, the average weight was 30±2.7 kg. A linear accelerator was used for the experiment. Each animal underwent radiation exposure in different areas: 1st animal - AV node (dose 35 Gy), 2nd animal - AV node and the apex of the left ventricle (LV) (dose 40/35 Gy, respectively), 3rd animal - pulmonary veins (PV) and left atrium (dose 30 Gy), 4th - AV node and LV free wall (dose 45/40 Gy). Under intravenous sedation with hemodynamic monitoring, contrast-based CT of the heart was performed to assess the degree of displacement of the heart chambers in one respiratory and cardiac cycle and to assess the anatomy of the chambers of the heart and adjacent organs. The allocation and the contouring of the target zones were carried out in three projections: axial, frontal and sagittal. For electrocardiographic control, a loop recorder was implanted in each animal. The average exposure time was 11±7 minutes. After a follow-up period, morphological examination of the autopsy material was performed.Results. The average follow-up period after ablation was 134.75±77.34 days. The electrophysiological effect of the ablation was achieved in cases of complete AV-block development. This effect was developed in 2 out of 3 animals, where AV-node was exposed: 2nd animal - 40 Gy on 108th day of observation and 4th animal - 45 Gy on 21st day of observation. No cardiac tachyarrhythmia was recorded in the animals. The results of myocardium macro- and microscopic examination showed significant changes in the target zones. These areas had precise but uneven damage boundaries, which were within the planned ones (conformal exposure with a high degree of precision). The transmural nature of the changes was noted as well. Massive fields of fibrous tissue of various degrees of maturity (with a predominance of subepicardial localization) with focal hemorrhages of various ages and granulations were detected, which were surrounded by cardiomyocytes with coagulated and vacuolated cytoplasm.Conclusion. The use of non-invasive stereotactic treatment of tachyarrhythmias has high prospects in modern electrophysiology as an alternative ablation method.

An Unusual Case of Dilated Coronary Sinus: Case Report and Clinical Implications

BACKGROUND The presence of a dilated coronary sinus (CS) assessed by echocardiography (TTE) is highly suggestive of inferior or superior vena cava anomalies, in the absence of a shunt. The most frequent finding is the persistence of a left superior vena cava (LSVC): well-known feature to electrophysiologists. Abnormal inferior vena cava (IVC) drainage is another cause of CS dilatation. CASE SUMMARY An 83-year-old woman presented with heart failure symptoms, atrial fibrillation with rapid ventricular rate and a dilated CS assessed by TTE. Atrioventricular (AV) node ablation was considered given the poor efficacy of a rate-control strategy. Cardiac computed tomography (CT) revealed a double superior vena cava with a LSVC draining directly into the dilated CS. Single-lead pacemaker implantation was performed using a right-side vascular access with no technical difficulties. An aborted AV node ablation procedure was due to the impossibility of getting to the right atrium. Fluoroscopy and CT imaging at second-look analysis confirmed the diagnosis of an abnormal IVC with an agenesia of its supra-hepatic segment directly drained into the CS. DISCUSSION Our clinical case illustrates an unusual and rare double venous abnormality: both LSVC and IVC directly drained into the CS and were responsible for its massive dilatation.

New Onset of AV- Nodal Reentrant Tachycardia (AVNRT) in the elderly – an uncommon diagnosis?

Background Arrhythmias in elderly patients (>70 years) are common in daily clinical practice. Most frequently, they are based on atrial fibrillation or other atrial tachycardia with an indication for oral anticoagulation and specific antiarrhythmic medications. The electrographic (ECG) documentation related to symptoms is essential before therapy initiation. In case of suspected AVNRT based on surface ECG, an electrophysiological study (EP) with ablation as curative strategy should be planned. Methods We analysed all patients >70 years with AVNRT diagnosed by electrophysiologic (EP) studies between May 2018 and December 2020. Results An EP study for suspected AVNRT was performed in 27 patients >70 years. The diagnosis of AVNRT was confirmed in 20 patients (75%). From all EP- studies with the diagnosis of AVNRT (n=93) in this period, 20 patients (22%) were older than 70 years (mean age 77 years with a range of 70–85 years), 12 were women. In most of the patients, the duration of symptoms was short (3 month). Only 4 patients had symptoms of paroxysmal tachycardia longer than 10 years. Except for 2 patients, all patients had at least one ECG- documentation (12- lead- ECG, Holter- ECG, telemetric ECG and/or in the loop recorder). In 12 patients, a 12- lead- ECG- documentation was available, in 5 patients the tachycardia has been registered in the Holter-ECG and in 1 in a loop recorder. In the 12- lead- ECG before ablation in sinus rhythm the PQ interval was with 196 (120- 300) ms in the upper range. In 16/ 20 patients was during the EP- study a sustained AVNRT (CL 410, 314- 538 ms) inducible. In the others, up to 3 typical AV- nodal- echo beats were induced in the EP- study. A slow pathway ablation/ modification was performed in all patients in typical position. In 2 patients, the implantation of a dual- chamber- pacemaker was necessary due to intermittent high- degree AV-nodal-block during the same hospital stay. In both patients, a first degree AV-block with PQ- interval of 250 and 300 ms was pre-existing. Discussion Especially for the elderly patients with new onset of clinical symptoms of arrhythmia, clinical anamnesis including an ECG- documentation is required for planning the therapeutic strategy. A borderline long PQ- interval as sign of an age- dependent fibrosis in the AV- node and, therefore, altered conduction properties in the AV node can be a cause of AVNRT in these older patients. In patients with pre-existing long PQ- interval (>250 ms), the risk of pacemaker implantation after successful ablation is higher. In this group of patients, medical therapeutic options are limited and often associated with the need of pacemaker implantation. FUNDunding Acknowledgement Type of funding sources: None.

Atypical twin atrioventricular nodal re-entrant tachycardia in a Congenitally Corrected Transposition of the Great Arteries patient with a surgical repair of a Ventricular Septal Defect: a Case report

Background Twin atrio ventricular (AV) nodal tachycardia is a rare mechanism of supra ventricular arrhythmia, only seen in some specific congenital heart defects (CHD). It consists of a reentrant circuit between two distinct AV nodes (anterior and inferior). Since both nodes have antegrade and retrograde conduction, there is usually two QRS morphologies in sinus rhythm. Case summary This case is about an atypical twin AV nodal tachycardia in a 15 years-old patient with congenitally corrected transposition of the great arteries (cc-TGA) and previous history of a ventricular septal defect (VSD) repair. The surgical closure was probably responsible of a poor antegrade conduction over the inferior AV node, that was responsible for a unique QRS morphology. He finally received a catheter ablation of the inferior AV node. He remained asymptomatic without anti-arrhythmic drugs at 8-months post-ablation. Discussion Twin atrioventricular nodal re-entrant tachycardia is a rare phenomenon. The presentation and electrophysiological study can be both atypical due to previous surgical repair. Operator should be aware of specific CHD where twin atrioventricular nodal re-entrant tachycardias are expected.