Bimodal RR interval distribution in chronic atrial fibrillation: impact of dual atrioventricular nodal physiology on long-term rate control after catheter ablation of the posterior atrionodal input

Atrio-ventricular junction: Can precision electrocardiology bridge cell and electrocardiogram?

The Atrio Ventricular Junction (AVJ) is a well-defined anatomical region of the heart the physiology of which, despite extensive and numerous observations, it is not fully understood. The aim of this review is to present an up to date summary of old and more recent findings on histology, cellular electrophysiology and intracellular connectivity of this region. We have also attempted to relate our increasing understanding of nodal pathophysiology to the interpretation of the electrocardiographic (ECG) manifestations of AVN behavior. Bridging cellular observations with ECG analysis in a process we call "Precision Electrocardiology" renders this tool far more sensitive and clinically useful than the pattern analysis too often employed in the ECG interpretation.

Computational Simulation of Cardiac Function and Blood Flow in the Circulatory System under Continuous Flow Left Ventricular Assist Device Support during Atrial Fibrillation

Prevalence of atrial fibrillation (AF) is high in heart failure patients supported by a continuous flow left ventricular assist device (CF-LVAD); however, the long term effects remain unclear. In this study, a computational model simulating effects of AF on cardiac function and blood flow for heart failure and CF-LVAD support is presented. The computational model describes left and right heart, systemic and pulmonary circulations and cerebral circulation, and utilises patient-derived RR interval series for normal sinus rhythm (SR). Moreover, AF was simulated using patient-derived unimodal and bimodal distributed RR interval series and patient specific left ventricular systolic functions. The cardiovascular system model simulated clinically-observed haemodynamic outcomes under CF-LVAD support during AF, such as reduced right ventricular ejection fraction and elevated systolic pulmonary arterial pressure. Moreover, relatively high aortic peak pressures and middle arterial peak flow rates during AF with bimodal RR interval distribution, reduced to similar levels as during normal SR and AF with unimodal RR interval distribution under CF-LVAD support. The simulation results suggest that factors such as distribution of RR intervals and systolic left ventricular function may influence haemodynamic outcome of CF-LVAD support during AF.

Dual atrioventricular nodal pathways physiology: a review of relevant anatomy, electrophysiology, and electrocardiographic manifestations

More than half a century has passed since the concept of dual atrioventricular (AV) nodal pathways physiology was conceived. Dual AV nodal pathways have been shown to be responsible for many clinical arrhythmia syndromes, most notably AV nodal reentrant tachycardia. Although there has been a considerable amount of research on this topic, the subject of dual AV nodal pathways physiology remains heavily debated and discussed. Despite advances in understanding arrhythmia mechanisms and the widespread use of invasive electrophysiologic studies, there is still disagreement on the anatomy and physiology of the AV node that is the basis of discontinuous antegrade AV conduction. The purpose of this paper is to review the concept of dual AV nodal pathways physiology and its varied electrocardiographic manifestations.

Ablate and Pace: Is There Still a Role?

Despite the development of newer drugs and procedures to improve rhythm control, there is still a place for ablation of the atrioventricular junction (AVJ) in the management of selected patients with AF who are refractory to medical therapy, to improve quality of life, prevent ventricular dysfunction, and to optimize cardiac resynchronization therapy. We review all aspects of the "ablate and pace" strategy, from its history to patient selection, technique, outcomes and applications, and identify the need for randomized clinical trials to address some of the remaining questions regarding its application in some groups of patients.

Cardiac arrhythmias imprint specific signatures on Lorenz plots

BACKGROUND

Despite the growing number of studies using Lorenz (Poincaré) plots (LPs) for the analysis of heart rate variability (HRV), a possible correlation between the underlying ECG waveforms and the RR scatter plots has never been systematically studied. We report a comprehensive investigation of distinct Lorenz plot patterns (LPPs) encountered in the context of major cardiac tachyarrhythmias as assessed by 24-hour Holter monitoring and detail the mechanisms underlying the specific LPPs.

METHODS

The 24-hour ambulatory electrocardiograms (AECGs) of 2700 patients with atrial and/or ventricular tachyarrhythmias and the AECGs of 200 controls with pure sinus rhythm were analyzed using an Elatec arrhythmia analyzing system (Elamedical, Paris 1996). This system allows for the generation of two-dimensional LPs and the exploration of the underlying ECG waveforms. Each LPP obtained was categorized according to its shape and basic geometric parameters. In accordance with the most characteristic LPP feature, the LPPs were grouped into the following distinct classes: 1) comet shape; 2) torpedo shape; 3) H-Fan shape; 4) SZ-Fan shape; 5) double side lobe pattern type A (DSLP-A); 6) double side lobe pattern type B (DSL-B); 7) triple side lobe pattern type A (TSLP-A); 8) triple side lobe pattern type B (TSLP-B);9 island pattern type A (IP-A); 10) island pattern type B (IP-B).

RESULTS

While a comet or a torpedo shape was associated with sinus rhythms, the other LPPs were specifically linked to the presence of cardiac tachyarrhythmias. Thus, a Fan shape was associated with atrial fibrillation or multifocal atrial tachycardia, whereas a DSLP indicated the presence of atrial premature beats, and a TSLP was highly specifically linked to frequent ventricular premature beats. An island pattern was exclusively associated with the presence of an atrial tachycardia or atrial flutter (sensitivity: 100%, specificity: 100%).

CONCLUSION

Major tachyarrhythmias imprint specific patterns on two-dimensional Lorenz plots generated from 24-hour Holter recordings. Thus, the Lorenz plot method has the potential to significantly improve the accuracy of arrhythmia detection and differentiation, particularly with respect to supraventricular tachyarrhythmias.

Analysis of surface electrocardiograms in atrial fibrillation: techniques, research, and clinical applications

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Neither the natural history of AF nor its response to therapy is sufficiently predictable by clinical and echocardiographic parameters. The purpose of this article is to describe technical aspects of novel electrocardiogram (ECG) analysis techniques and to present research and clinical applications of these methods for characterization of both the fibrillatory process and the ventricular response during AF. Atrial fibrillatory frequency (or rate) can reliably be assessed from the surface ECG using digital signal processing (extraction of atrial signals and spectral analysis). This measurement shows large inter-individual variability and correlates well with intra-atrial cycle length, a parameter which appears to have primary importance in AF maintenance and response to therapy. AF with a low fibrillatory rate is more likely to terminate spontaneously and responds better to antiarrhythmic drugs or cardioversion, whereas high-rate AF is more often persistent and refractory to therapy. Ventricular responses during AF can be characterized by a variety of methods, which include analysis of heart rate variability, RR-interval histograms, Lorenz plots, and non-linear dynamics. These methods have all shown a certain degree of usefulness, either in scientific explorations of atrioventricular (AV) nodal function or in selected clinical questions such as predicting response to drugs, cardioversion, or AV nodal modification. The role of the autonomic nervous system for AF sustenance and termination, as well as for ventricular rate responses, can be explored by different ECG analysis methods. In conclusion, non-invasive characterization of atrial fibrillatory activity and ventricular response can be performed from the surface ECG in AF patients. Different signal processing techniques have been suggested for identification of underlying AF pathomechanisms and prediction of therapy efficacy.

Effects of Ablation, Digitalis, and Beta‐Blocker on Dual Atrioventricular Nodal Pathways and Conduction During Atrial Fibrillation

INTRODUCTION

Modification of AV nodal conduction by radiofrequency ablation (RFA) results in a variable reduction in heart rate during atrial fibrillation (AF). Using AF induced in patients with dual AV nodal pathways as a model, we tested the effect of additional treatment with digitalis (ouabain) and beta-blocker (esmolol).

METHODS AND RESULTS

Ten patients were randomized to control (group I) and studied only before ablation. AF was induced in 30 patients before and after slow pathway ablation (group II). Mean ventricular cycle lengths (AF CLmean) were recorded. Slow pathway conduction was eliminated after ablation in 10 patients (group IIA), whereas slow pathway conduction was still present in 20 patients (group IIB). Compared to pre-RFA there was a 10% increase in AF CLmean post-RFA (P < 0.01). During isoproterenol infusion the increase was 8% (P = NS). Adding digitalis and beta-blocker during isoproterenol infusion increased AF CLmean by 75% (95% in group IIA) compared to 36% in group I (P < 0.001 II vs I).

CONCLUSION

Slow pathway ablation reduces ventricular rate during AF. Addition of digitalis and beta-blocker during isoproterenol infusion significantly decreases ventricular rate after ablation compared to the control group. The finding suggests that beta-blocker has significant effects on fast AV nodal pathway conduction during induced AF with isoproterenol infusion.

Concealed conduction and dual pathway physiology of the atrioventricular node

INTRODUCTION

Both concealed conduction and dual pathway physiology are important electrophysiologic characteristics of the AV node. The interaction of AV nodal concealment and duality, however, is not clearly understood.

METHODS AND RESULTS

The properties of AV conduction curves in the presence and absence of a conditioning blocked impulse were prospectively studied during premature atrial stimulation in 20 patients with AV nodal reentrant tachycardia before and after slow pathway ablation and in 14 control patients. AV nodal duality in the control conduction curve in the absence of a conditioning impulse was observed in 19 (95%) of 20 patients with AV nodal reentrant tachycardia. However, AV nodal duality in the modulated conduction curve in the presence of a blocked impulse was only identified in 2 (10%) of 20 patients (2/20 vs 19/20, P < 0.0001). The modulated curve was characterized by a significantly longer AV nodal effective and functional refractory periods compared to the control curve (P < 0.0001) in both patients with and without AV nodal reentry and in AV nodal reentry patients after successful slow pathway ablation. The maximum AH interval (AH(max)) of the modulated curve was significantly shorter than the control curve in both patients with (217 +/- 74 ms vs 347 +/- 55 ms, P < 0.0001) and without AV nodal reentry (178 +/- 50 ms vs 214 +/- 54 ms, P = 0.02). AH(max) of the control curve was significantly longer in AV nodal reentry patients than in controls (P < 0.0001). AH(max) of the modulated curve, however, was not significantly different between the two groups. After slow pathway ablation, AH(max) of the control curve was significantly reduced (347 +/- 55 ms vs 191 +/- 40 ms, P < 0.0001). Significant reduction in AH(max) of the modulated curve was not observed.

CONCLUSION

An interaction of AV nodal concealed conduction and dual pathway physiology was demonstrated by our data. Slow pathway conduction of the AV node was prevented by the concealed beat in both patients with and without AV nodal reentry.

Ventricular rate control during atrial fibrillation and AV node modifications: past, present, and future

Atrial fibrillation (AF) is the most common arrhythmia. Currently there are two broad strategic treatment options for AF: rhythm control and rate control. For rhythm control, the treatment is directed toward restoring and maintaining the sinus rhythm. For rate control, the intention is to slow ventricular rate while allowing AF to continue. In both cases anticoagulation therapy is recommended. The results of currently available clinical trials demonstrated clearly that rate control is not inferior to rhythm control. Thus, rate control is an acceptable primary therapy for many AF patients. The rate control can be achieved essentially by depressing or modifying the filtering properties of the atrioventricular (AV) node. This can be attained by medications that depress the impulse transmission within the AV node, by anatomic modification of the AV communications, as well as by autonomic manipulations that produce AV node negative dromotropic effect. We are reviewing current clinical and newer experimental modalities aimed at enhancing the lifesaving function of this remarkable nodal structure.

Multiple AV nodal pathways with multiple peaks in the RR interval histogram of the Holter monitoring ECG during atrial fibrillation

Two or more peaks on the 24-hour electrocardiogram (ECG) RR interval histogram of patients with atrial fibrillation suggests the presence multiple AV nodal pathways. The prevalence of multiple AV nodal pathways in this population is unknown. The study included 250 patients with permanent atrial fibrillation during 24-hour ECG. The number of peaks on the RR interval histogram was measured in each patient. A single peak was present in 153 patients (61%), 80 patients (32%) had two peaks, 13 patients (5%) had three, and 4 patients (2%) had four peaks. Among the 97 patients (39%) with > 1 AV nodal pathway, the estimated mean heart rate reduction by hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods was 16 beats/min, from 82 to 65 beats/min. Among the overall population, 16 patients (6%) with > 1 AV nodal pathway had a mean heart rate > 100 beats/min. In this subgroup, modulation of AV node conduction by hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods yielded an estimated reduction in mean heart rate of 26 +/- 15 beats/min, from 110 +/- 9 beats/min to 84 +/- 14 beats/min (P < 0.01), a 23% decrease. The presence of > 1 AV nodal pathway was suspected in 39% of all patients with permanent atrial fibrillation. The hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods resulted in a clinically significant reduction in heart rate in 6% of patients in this population.