Intra- and interatrial conduction abnormalities: hemodynamic and arrhythmic significance

The Influence of Interatrial Conduction Disorders on Atrial Mechanical Function - Atrial Strain and Pulmonary Veins Reversal Flow in Patients with COVID-19

Background

The physiological activation of the left atrium (LA) happens through the Bachmann bundle, which is crucial for the heart's proper functioning. Bayes de Luna first described interatrial blocks (IABs) in 1979, noting their disruption of atrioventricular (AV) synchrony. This study aims to evaluate LA mechanics by analyzing LA strain in cases of normal and impaired interatrial conduction, focusing on retrograde flow in the pulmonary veins (PV).

Methods

The study included 51 patients who tested positive for SARS-CoV-2 and exhibited related symptoms. Six patients with persistent atrial fibrillation (AF) were excluded from the study (45 patients qualified in total: 23 males, 22 females; mean age 69.0 ± 12.9 years).

Results

IABs were more frequently observed in COVID-19 patients. Thus, they were included despite SARS-CoV-2 being a potential limitation of the study. All participants underwent clinical evaluation, electrocardiography (ECG) (200 mm/s ×256), and echocardiography to assess left ventricular ejection fraction (LVEF), mitral regurgitation (MR), LA volume, global and regional strain, and retrograde flow in the PV. A statistical dependency was found between LA global strain and P-wave morphology, MR, heart failure (HF), and paroxysmal atrial fibrillation (PAF). However, no clear correlation was found between retrograde flow in the PV and LA strain. The mean P-wave duration correlated with its morphology. Additionally, correlations were observed between P-wave morphology and hypertension, being overweight, and PAF.

Conclusions

LA mechanics are negatively influenced by IABs. LA global strain correlates with P-wave duration, ejection fraction (EF), and MR independently. Regional LA strain examination is potentially effective for assessing LA mechanics and complements precise ECG.

Atypical Atrial Flutter: Electrophysiological Characterization and Effective Catheter Ablation

Atrial flutter (AFL), defined as macro-re-entrant atrial tachycardia, is associated with debilitating symptoms, stroke, heart failure, and increased mortality. AFL is classified into typical, or cavotricuspid isthmus (CTI)-dependent, and atypical, or non-CTI-dependent. Atypical AFL is a heterogenous group of re-entrant atrial tachycardias that most commonly occur in patients with prior heart surgery or catheter ablation. The ECG pattern is poorly predictive of circuit anatomy but may still provide mechanistic insight. AFL is difficult to manage medically and catheter ablation is the preferred treatment for most patients. Recent progress in technology and clinical electrophysiology has led to detailed characterization of re-entry circuits and effective ablation strategies. Combined activation and entrainment mapping are key to identifying the re-entry circuit. The presence of a slow-conducting isthmus, localized re-entry, dual-loop re-entry or bystander loops may lead to misleading activation maps but can be identified by electrogram examination and entrainment mapping. In the occasional patient without inducible AFL, substrate mapping in sinus rhythm may be a viable strategy. Long-term ablation success requires the creation of a transmural continuous lesion across a critical component of the re-entry circuit. Procedural endpoints include bidirectional conduction block across linear lesions and non-inducibility of atrial tachycardia. The present review discusses the epidemiology, mechanisms, ECG characteristics, electrophysiological characterization, and catheter ablation of atypical AFL.

Advanced Interatrial Block across the Spectrum of Renal Function

Background and Objective: Interatrial block (IAB) is defined as a conduction delay between the right and left atria. No data are available about the prevalence of both partial IAB and advanced IAB among the different stages of chronic kidney disease. The aim of this study was to describe the prevalence and type of advanced IAB across the spectrum of renal function, including patients on dialysis and the clinical characteristics associated with advanced IAB. Materials and Methods: Retrospective, single-center study of 151 patients consecutively admitted to the Nephrology and Ophthalmology Unit for 3 months. The study population was divided into three groups according to stages of chronic kidney disease. We evaluated the prevalence and pattern of IAB among the groups and the clinical characteristics associated with advanced IAB. Results: The prevalence of partial IAB was significantly lower in end-stage kidney disease (ESKD) group compared to control group (36.7% vs. 59.6%; p = 0.02); in contrast the prevalence of advanced IAB was significantly higher in both chronic kidney disease (CKD) (17.8% vs. 5.3%, p = 0.04) and ESKD group (24.5% vs. 5.3%, p = 0.005) compared to control group. The atypical pattern of advanced IAB was more frequent in both the ESKD and CKD group than in the control group (100% and 75% vs. 33.3%; p = 0.02). Overall, among patients that showed advanced IAB, 17 (73.9%) showed an atypical pattern by morphology and 2 (8.7%) showed an atypical pattern by duration of advanced IAB. The ESKD group was younger than the control group (65.7 ± 12.3 years vs. 71.3 ± 9.9 years; p = 0.01) and showed a higher prevalence of beta blockers (42.9% vs. 19.3%; p = 0.009), as in the CKD group (37.8% vs. 19.3%; p= 0.04). Conclusions: The progressive worsening of renal function was associated with an increasing prevalence of advanced IAB. Advanced IAB may be a sign of uremic cardiomyopathy and may suggest further evaluation with long-term follow-up to investigate its prognostic significance in chronic kidney disease.

Exercise-Induced Electrocardiographic Changes in Healthy Young Males with Early Repolarization Pattern

Background: Exercise-induced modifications in ECG parameters among individuals with an early repolarization pattern (ERP) have not been evaluated in detail. We aimed to assess this phenomenon, with potential associations with arrhythmogenesis. Methods: Twenty-three young, healthy males with ERP (ERP+) participated in this study, alongside a control group, which consisted of nineteen healthy males without ERP (ERP-). ECGs at baseline, at peak exercise (Bruce protocol), and during the recovery phase were analyzed and compared between the two groups. Results: The treadmill test demonstrated strong cardiovascular fitness, with similar chronotropic and pressor responses in both groups. In the baseline ECGs, the QRS complex and the QT interval were shorter in the ERP+ group. During exercise, the P-wave duration was significantly longer and the QRS was narrower in the ERP+ group. In the recovery phase, there was a longer P wave and a narrower QRS in the ERP+ group. During the treadmill test, the J wave disappeared or did not meet the criteria required for ERP diagnosis. Conclusions: The slowed intra-atrial conduction found during exercise could be predictive of atrial arrhythmogenesis in the setting of ERP. The disappearing of J waves during exercise, due to increased sympathetic activity, has potential clinical significance.

P-wave durations from automated electrocardiogram analysis to predict atrial fibrillation and mortality in heart failure

BACKGROUND

P-wave indices have been used to predict incident atrial fibrillation (AF), stroke, and mortality. However, such indices derived from automated ECG measurements have not been explored for their predictive values in heart failure (HF). We investigated whether automated P-wave indices can predict adverse outcomes in HF.

METHODS

This study included consecutive Chinese patients admitted to a single tertiary centre, presenting with HF but without prior AF, and with at least one baseline ECG, between 1 January 2010 and 31 December 2016, with last follow-up of 31 December 2019.

RESULTS

A total of 2718 patients were included [median age: 77.4, interquartile range (IQR): (66.9-84.3) years; 47.9 males]. After a median follow-up of 4.8 years (IQR: 1.9-9.0 years), 1150 patients developed AF (8.8/year), 339 developed stroke (2.6/year), 563 developed cardiovascular mortality (4.3/year), and 1972 had all-cause mortality (15.1/year). Compared with 101-120 ms as a reference, maximum P-wave durations predicted new-onset AF at ≤90 ms [HR: 1.17(1.11, 1.50), P < 0.01], 131-140 ms [HR: 1.29(1.09, 1.54), P < 0.001], and ≥141 ms [HR: 1.52(1.32, 1.75), P < 0.001]. Similarly, they predicted cardiovascular mortality at ≤90 ms [HR: 1.50(1.08, 2.06), P < 0.001] or ≥141 ms [HR: 1.18(1.15, 1.45), P < 0.001], and all-cause mortality at ≤90 ms [HR: 1.26(1.04, 1.51), P < 0.001], 131-140 ms [HR: 1.15(1.01, 1.32), P < 0.01], and ≥141 ms [HR: 1.31(1.18, 1.46), P < 0.001]. These remained significant after adjusting for significant demographics, past co-morbidities, P-wave dispersion, and maximum P-wave amplitude.

CONCLUSIONS

Extreme values of maximum P-wave durations (≤90 ms and ≥141 ms) were significant predictors of new-onset AF, cardiovascular mortality, and all-cause mortality.

Electro-Mechanical Alterations in Atrial Fibrillation: Structural, Electrical, and Functional Correlates

Atrial fibrillation is the most common arrhythmia encountered in clinical practice affecting both patients’ survival and well-being. Apart from aging, many cardiovascular risk factors may cause structural remodeling of the atrial myocardium leading to atrial fibrillation development. Structural remodelling refers to the development of atrial fibrosis, as well as to alterations in atrial size and cellular ultrastructure. The latter includes myolysis, the development of glycogen accumulation, altered Connexin expression, subcellular changes, and sinus rhythm alterations. The structural remodeling of the atrial myocardium is commonly associated with the presence of interatrial block. On the other hand, prolongation of the interatrial conduction time is encountered when atrial pressure is acutely increased. Electrical correlates of conduction disturbances include alterations in P wave parameters, such as partial or advanced interatrial block, alterations in P wave axis, voltage, area, morphology, or abnormal electrophysiological characteristics, such as alterations in bipolar or unipolar voltage mapping, electrogram fractionation, endo-epicardial asynchrony of the atrial wall, or slower cardiac conduction velocity. Functional correlates of conduction disturbances may incorporate alterations in left atrial diameter, volume, or strain. Echocardiography or cardiac magnetic resonance imaging (MRI) is commonly used to assess these parameters. Finally, the echocardiography-derived total atrial conduction time (PA-TDI duration) may reflect both atrial electrical and structural alterations.

P-wave parameters and their association with thrombi and spontaneous echo contrast in the left atrial appendage

BACKGROUND

The aim of this study was to examine the prevalence of abnormal P-wave parameters in patients with thrombus and/or spontaneous echo contrast (SEC) in the left atrial appendage (LAA), and to identify P-wave parameters particularly associated with thrombus and SEC formation.

HYPOTHESIS

We presume a significant relationship of P-wave parameters with thrombi and SEC.

METHODS

All patients in whom a thrombus or SEC was detected in the LAA on transoesophageal echocardiography were included in this study. Patients at risk (CHA2DS2-VASc Score ≥3) and routine transoesophageal echocardiography to exclude thrombi served as the control group. A detailed ECG analysis was performed.

RESULTS

Of a total of 4062 transoesophageal echocardiographies, thrombi and SEC were detected in 302 patients (7.4%). Of these patients, 27 (8.9%) presented with sinus rhythm. The control group included 79 patients. There was no difference in mean CHA2DS2-VASc score in the two groups (p = .182). A high prevalence of abnormal P-wave parameters was detected in patients with thrombus/SEC. Indicators for the presence of thrombi or SEC in the LAA were P-wave duration >118 ms (Odds ratio (OR) 3.418, Confidence interval (CI) 1.522-7.674, p < .001), P-wave dispersion >40 ms (OR 2.521, CI 1.390-4.571, p < .001) and advanced interatrial block (OR 1.431, CI 1.033-1.984, p = .005).

CONCLUSION

Our study revealed that several P-wave parameters are associated with thrombi and SEC in the LAA. The results may help identify patients who are at particularly high risk for thromboembolic events (e.g., in patients with embolic stroke of undetermined source).

Safety, Efficacy and Prognostic Benefit of Atrial Fibrillation Ablation in Heart Failure with Preserved Ejection Fraction

Up to 65% of patients with heart failure with preserved ejection fraction (HFpEF) develop AF during the course of the disease. This occurrence is associated with adverse outcomes, including pump failure death. Because AF and HFpEF are mutually reinforcing risk factors, sinus rhythm restoration may represent a disease-modifying intervention. While catheter ablation exhibits acceptable safety and efficacy profiles, no randomised trials have compared AF ablation with medical management in HFpEF. However, catheter ablation has been reported to result in lower natriuretic peptides, lower filling pressures, greater peak cardiac output and improved functional capacity in HFpEF. There is growing evidence that catheter ablation may reduce HFpEF severity, hospitalisation and mortality compared to medical management. Based on indirect evidence, early catheter ablation and minimally extensive atrial injury should be favoured. Hence, individualised ablation strategies stratified by stepwise substrate inducibility provide a logical basis for catheter-based rhythm control in this heterogenous population. Randomised trials are needed for definitive evidence-based guidelines.

Electrocardiographic Changes Associated with Early Repolarization Pattern in Healthy Young Males

Background and Objectives: Early repolarization pattern (ERP) has recently been shown to be related with an increased risk of ventricular arrhythmias in susceptible individuals. Materials and Methods: We studied the ERP-associated ECG changes, with potential clinical relevance, in 220 young (age 22.1 ± 1.6 years), healthy, male subjects using 12-lead ECG recordings. A total of 38 subjects (17.3%) fulfilled the diagnostic criteria for ERP, and a total of 90 ECG characteristics were compared between the groups of subjects with and without ERP. Results: None of the ECGs were pathological, and 22 ECG parameters differed significantly (p < 0.05) between the subjects with and without ERP. Among them, the P wave-related parameters (e.g., average P wave duration: 101.5 ± 9.2 ms vs. 106.8 ± 9.9 ms, p = 0.004) and the presence of fragmented QRS complexes (67.6% vs. 92.1%, p = 0.002) revealed a potential propensity for atrial and ventricular arrhythmogenesis. The time-domain parameters of repolarization, those not corrected for QRS duration, showed shorter values (e.g., Tpeak-Tend interval: 70.9 ± 8.1 ms vs. 67.8 ± 8.0 ms, p = 0.036), reflecting the accelerated repolarization. Conclusions: Certain ECG characteristics seem to be more associated with ERP. The clinical significance of this finding at the individual level needs further prospective investigations.

Cardiovascular Complications of Interatrial Conduction Block: JACC State-of-the-Art Review

Interatrial block (IAB) is an electrocardiographic pattern describing the conduction delay between the right and left atria. IAB is classified into 3 degrees of block that correspond to decreasing conduction in the region of Bachmann's bundle. Although initially considered benign in nature, specific subsets of IAB have been associated with atrial arrhythmias, elevated thromboembolic stroke risk, cognitive impairment, and mortality. As the pathophysiologic relationships between IAB and stroke are reinforced, investigation has now turned to the potential benefit of early detection, atrial imaging, cardiovascular risk factor modification, antiarrhythmic pharmacotherapy, and stroke prevention with oral anticoagulation. This review provides a contemporary overview of the epidemiology, pathophysiology, diagnosis, and management of IAB, with a focus on future directions.

Notched P-wave on digital electrocardiogram predicts cardiovascular events in patients with cardiovascular risks: The Japan Morning Surge Home Blood Pressure (J-HOP) Study

Background: The relationship between notched P-wave characteristics on digital electrocardiogram (ECG) and long-term cardiovascular events remains unclear. Methods: We enrolled 810 subjects from the J-HOP Study who had one or more of cardiovascular risk factors. Twelve-lead electrocardiography was conducted, and the peak-to-peak distance in the M-shape was calculated automatically using a 12-lead ECG analysis system. We compared two definitions: P waves were defined as "notched" if the peak-to-peak distance in the M-shape was ≥20 ms or ≥40 ms in lead II. We assessed the left atrial diameter and left ventricular mass index (LVMI) by echocardiography. The primary endpoint was defined as a composite endpoint that combines fatal events (stroke, heart failure, coronary artery disease, and sudden death) and non-fatal events (acute myocardial infarction, angina, congestive heart failure, stroke, and aortic dissection). Results: The mean follow-up period was 101±34 months, and 85 cardiovascular events occurred. When we defined a notched P-wave as ≥20 ms in the M shape (n=92), a notched P-wave was a significant predictor of cardiovascular events after adjustment for age, gender, and comorbidity (hazard ratio: 1.83; 95% confidence interval: 1.01–3.31, p=0.045). When we defined a notched P-wave as ≥40 ms in the M shape (n=25), the hazard ratio of cardiovascular events in the notched P-wave group was not significant after adjustment for covariates (hazard ratio: 1.52; 95% confidence interval: 0.51–4.53, p=0.455). The left atrial diameter and LVMI in the patients in the notched P-wave group (peak-to-peak distance of ≥20 ms in the M shape) were significantly higher than those in the control group (left atrial diameter: 38.8±5.9 vs. 36.8±5.0 mm, p=0.001; LVMI: 103.9±27.7 vs. 96.3±25.7 g/m2, p=0.010). Conclusions: The notched P-wave by digital electrocardiogram analysis was associated with cardiovascular events and left atrial enlargement.

Vectorial theory surpasses the local theory in explaining the origin of P-wave dispersion

BACKGROUND

Local theory and the vectorial theory are used to explain the origin of P-wave dispersion (PWD). There are no previous studies that analyze both at the same time.

OBJECTIVES

We set out to determine the implication of local and vectorial theories in the origin of PWD.

METHODS

Cross-sectional study in 153 randomly selected patients aged 18-70 years, undergoing electrophysiological study. Inhomogeneous atrial conduction was evaluated by atrial electrogram dispersion in terms of duration (EGM_durdis) and morphology (EGM_morph dis). P-distal coronary sinus interval (P-DCS) was also measured. P-wave was measured twice, firstly at a calibration of 20 mm/mV and a sweep speed of 50 mm/s, enhancement 10× (basic measurement [BM]), and second time at sweep speed of 150 mm/s, enhancement 80-160× (high precision measurement [HPM]).

RESULTS

PWD with BM was 48 ms [36-54 ms] while with HPM it was 4 ms [0-10 ms], p < 0.001. With BM, maximum and minimum P- wave duration presented a moderate correlation (r = 0.342; p < 0.001), using HPM it becomes strong (r = 0.750; p < 0.001). In cases with P-DCS < 80 ms (r = 0.965; p < 0.001), but not with P-DCS ≥ 80 ms (r = 0.649; p < 0.001), the previous correlation became almost perfect with HPM. EGM_durdis and EGM_morphdis were weak but significantly correlated with PWD. This correlation became moderate in patients with P-DCS ≥ 80 ms and disappeared in those with P-DCS, using BM and HPM.

CONCLUSION

Vectorial theory explains almost entirely the PWD phenomenon. Inhomogeneous conduction could be an additional mechanism to explain PWD, but its contribution is small.

Cardiac Stimulation in the Third Millennium: Where Do We Head from Here?

Over the years, pacemakers have evolved from a life-saving tool to prevent asystole to a device to treat heart rhythm disorders and heart failure, aiming at improving both cardiac function and clinical outcomes. Cardiac stimulation nowadays aims to correct the electrophysiologic roots of mechanical inefficiency in different structural heart diseases. This has led to awareness of the concealed risks of customary cardiac pacing that can inadvertently cause atrioventricular and inter-/intra-ventricular dyssynchrony, and has promoted the development of new pacing modalities and the use of stimulation sites different from the right atrial appendage and the right ventricular apex. The perspective of truly physiologic pacing is the leading concept of the continued research in the past 30 years, which has made cardiac stimulation procedure more sophisticated and challenging. In this article, we analyze the emerging evidence in favor of the available strategies to achieve an individualized physiologic setting in bradycardia pacing.

Pacing devices to treat bradycardia: current status and future perspectives

Introduction: Cardiac stimulation evolved from life-saving devices to prevent asystole to the treatment of heart rhythm disorders and heart failure, capable of remote patient and disease-progression monitoring. Cardiac stimulation nowadays aims to correct the electrophysiologic roots of mechanical inefficiency in different structural heart diseases.Areas covered: Clinical experience, as per available literature, has led to awareness of the concealed risks of customary cardiac pacing, that can inadvertently cause atrio-ventricular and inter/intra-ventricular dyssynchrony. New pacing modalities have emerged, leading to a new concept of what truly represents 'physiologic pacing' beyond maintenance of atrio-ventricular coupling. In this article we will analyze the emerging evidence in favor of the available strategies to achieve an individualized physiologic setting in bradycardia pacing, and the hints of future developments.Expert opinion: 'physiologic stimulation' technologies should evolve to enable an effective and widespread adoption. In one way new guiding catheters and the adoption of electrophysiologic guidance and non-fluoroscopic lead implantation are needed to make His-Purkinje pacing successful and effective at long term in a shorter procedure time; in the other way leadless stimulation needs to upgrade to a superior physiologic setting to mimic customary DDD pacing and possibly His-Purkinje pacing.

Acute Effects of Red Bull Energy Drinks on Atrial Electromechanical Function in Healthy Young Adults

Energy drinks (EDs) are widely consumed by adolescents and young adults. Almost all kinds of arrhythmias have been reported following EDs consumption, most of which is atrial fibrillation (AF). Atrial conduction time prolongation and heterogeneous sinusal impulses propagation to the atriums are the key electrophysiological mechanisms leading AF. We aimed to evaluate the acute effects of Red Bull ED ingestion on atrial electromechanical conduction times in healthy young adults. After a 12-hour fasting, 54 healthy young adults consumed 330 mL of Red Bull ED. Atrial electromechanical coupling (PA), intra-atrial electromechanical delay (intra-AEMD), and interatrial electromechanical delay (inter-AEMD) were measured at baseline and 2-hour after Red Bull ED ingestion by echocardiographic tissue-Doppler imaging (TDI) method. PA-lateral (49.7 ± 11.2 vs 54.1 ± 11.0 msn, p = 0.001) and PA-septal (40.8 ± 9.1 vs 43.7 ± 10.5 msn, p = 0.032) times were statistically significantly prolonged after Red Bull ED ingestion. There was also a statistically significant increase in the duration of inter-AEMD (14.4 ± 10.6 vs 18.1 ± 8.5 msn, p = 0.010) after ED ingestion. It was showed that even a single can of ED can acutely increase atrial electromechanical conduction times in young adults. These findings may be the cause of ED-associated AF.

Intra-Atrial Block: Definition and Relationship to Atrial Fibrillation and Other Adverse Outcomes

In 1916, Bachmann first reported on the inter-auricular time interval. However relatively little attention was paid to this ECG measurement for decades. Then, in 1956, Samuel Bradley and Henry JJ Marriott reported on intra-atrial block (IAB) in 4,500 ECGs.As defined by them, IAB was a P wave duration of 0.12 sec or longer. Since that time, others have defined IAB as 0.11 sec or longer or 0.12 sec or longer. Several authors have suggested subcategories, such as first-, second-, and third-degree patterns and some have defined specific intra-atrial and inter-atrial pathways. These are of electrocardiographic interest but have not been substantiated as related to different clinical outcomes. Many disorders have been associated with IAB. More importantly, however, IAB has been associated with several adverse outcomes, including sinus node dysfunction, atrial tachyarrhythmias - especially atrial fibrillation, thromboembolic events, and increased mortality. This brief review will detail the above to emphasize to ECG readers the importance of not overlooking IAB in their interpretations.

Individualised Approaches for Catheter Ablation of AF: Patient Selection and Procedural Endpoints

Pulmonary vein isolation (PVI) is the cornerstone of AF ablation, but studies have reported improved efficacy with high rates of repeat procedures. Because of the large interindividual variability in the underlying electrical and anatomical substrate, achieving optimal outcomes requires an individualised approach. This includes optimal candidate selection as well as defined ablation strategies with objective procedure endpoints beyond PVI. Candidate selection is traditionally based on coarse and sometimes arbitrary clinical stratification such as AF type, but finer predictors of treatment efficacy including biomarkers, advanced imaging and electrocardiographic parameters have shown promise. Numerous ancillary ablation strategies beyond PVI have been investigated, but the absence of a clear mechanistic and evidence-based endpoint, unlike in other arrhythmias, has remained a universal limitation. Potential endpoints include functional ones such as AF termination or non-inducibility and substrate-based endpoints such as isolation of low-voltage areas. This review summarises the relevant literature and proposes guidance for clinical practice and future research.

The Value of Baseline and Arrhythmic ECG in the Interpretation of Arrhythmic Mechanisms

Owing to the rapid development of new electrophysiologic techniques, our understanding of arrhythmias and their underlying mechanisms has reached unprecedented levels. In some cases, baseline ECG alterations can be identified before arrhythmia development; early recognition of these alterations is of utmost importance to start appropriate preventive therapies and stratify the risk according to patients' outcomes. Hereby, we report a systematic revision of main baseline ECG abnormalities and their implications on clinical outcomes.