Identification of the rate-dependent functional refractory period of the atrioventricular node in simulated atrial fibrillation

Multiscale Entropy of the Heart Rate Variability for the Prediction of an Ischemic Stroke in Patients with Permanent Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is a significant risk factor for ischemic strokes, and making a robust risk stratification scheme would be important. Few studies have examined whether nonlinear dynamics of the heart rate could predict ischemic strokes in AF. We examined whether a novel complexity measurement of the heart rate variability called multiscale entropy (MSE) was a useful risk stratification measure of ischemic strokes in patients with permanent AF.

METHODS AND RESULTS

We examined 173 consecutive patients (age 69 ± 11 years) with permanent AF who underwent 24-hour Holter electrocardiography from April 2005 to December 2006. We assessed several frequency ranges of the MSE and CHA2DS2-VASc score (1 point for congestive heart failure, hypertension, diabetes, vascular disease, an age 65 to 74 years, and a female sex and 2 points for an age ≥ 75 years and a stroke or transient ischemic attack). We found 22 (13%) incident ischemic strokes during a mean follow up of 3.8-years. The average value of the MSE in the very-low frequency subrange (90-300 s, MeanEnVLF2) was significantly higher in patients who developed ischemic strokes than in those who did not (0.68 ± 0.15 vs. 0.60±0.14, P<0.01). There was no significant difference in the C-statistic between the CHA2DS2-VASc score and MeanEnVLF2 (0.56; 95% confidence interval, 0.43-0.69 vs. 0.66; 95% confidence interval, 0.53-0.79). After an adjustment for the age, CHA2DS2-VASc score, and antithrombotic agent, a Cox hazard regression model revealed that the MeanEnVLF2 was an independent predictor of an ischemic stroke (hazard ratio per 1-SD increment, 1.80; 95% confidence interval, 1.17-2.07, P<0.01).

CONCLUSION

The MeanEnVLF2 in 24-hour Holter electrocardiography is a useful risk stratification measure of ischemic strokes during the long-term follow-up in patients with permanent AF.

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.

Influence of Cheyne-Stokes respiration on ventricular response to atrial fibrillation in heart failure

In subjects with sinus rhythm, respiration has a profound effect on heart rate variability (HRV) at high frequencies (HF). Because this HF respiratory arrhythmia is lost in atrial fibrillation (AF), it has been assumed that respiration does not influence the ventricular response. However, previous investigations have not considered the possibility that respiration might influence HRV at lower frequencies. We hypothesized that Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) would entrain HRV at very low frequency (VLF) in AF by modulating atrioventricular (AV) nodal refractory period and concealed conduction. Power spectral analysis of R-wave-to-R-wave (R-R) intervals and respiration during sleep were performed in 13 subjects with AF and CSR-CSA. As anticipated, no modulation of HRV was detected at HF during regular breathing. In contrast, VLF HRV was entrained by CSR-CSA [coherence between respiration and HRV of 0.69 (SD 0.22) at VLF during CSR-CSA vs. 0.20 (SD 0.19) at HF during regular breathing, P < 0.001]. Comparison of R-R intervals during CSR-CSA demonstrated a shorter AV node refractory period during hyperpnea than apnea [minimum R-R of 684 (SD 126) vs. 735 ms (SD 147), P < 0.001] and a lesser degree of concealed conduction [scatter of 178 (SD 56) vs. 246 ms (SD 72), P = 0.001]. We conclude that CSR-CSA entrains the ventricular response to AF, even in the absence of HF respiratory arrhythmia, by inducing rhythmic oscillations in AV node refractoriness and the degree of concealed conduction that may be a function of autonomic modulation of the AV node.

Different features of ventricular arrhythmias and the RR-interval dynamics in atrial fibrillation related to the patient's clinical characteristics: an analysis using RR-interval plotting

The clinical features of ventricular arrhythmia and RR-interval dynamics in AF-patients remain unresolved. We successively plotted points on an X-Y plain as (X, Y) = (RRn, RRn + 1) from the consecutive RR-intervals of Holter ECGs. Eighty of 175 AF-patients were thus diagnosed to have ventricular arrhythmia based on the different plotting patterns between ventricular premature contractions (VPCs) and aberrations. Different characteristics of the RR-interval dynamics before VPCs were observed such as fixed or variable coupling, and a regular or irregular RR-interval sequence. Malignant arrhythmias occurred more frequently in AF-patients with variable coupling VPCs and/or an irregular RR-interval sequence before VPCs than in those with the fixed coupling VPCs and/or the regular RR-interval sequence before VPCs. The RR-interval plotting method enabled us to distinguish different types of VPCs which were related to the clinical characteristics of the AF-patients.

Circadian rhythm of atrioventricular conduction predicts long-term survival in patients with chronic atrial fibrillation

The R-R interval of the electrocardiogram during atrial fibrillation (AF) appears absolutely irregular. However, the Poincaré plot of the R-R interval reveals a sector shape of distribution that is unique to AF. Furthermore, the height of lower envelope (LE1.0) of the distribution and the degree of scatter above the envelope (scattering index) may reflect the refractoriness and concealment of atrioventricular (AV) conduction, respectively. We previously observed that both the LE1.0 and scattering index show clear circadian rhythms in patients with chronic AF and that the rhythms are blunted in those with congestive heart failure and chronic AF. In the present study, we examined if the blunted circadian rhythm of the AV conduction has prognostic value in patients with chronic AF. We studied a retrospective cohort of 120 patients who underwent 24h Holter monitoring at baseline. During an observation period of 33 +/- 16 mon, there were 25 deaths (21%) including 13 cardiac and 8 stroke deaths. All patients showed significant circadian rhythms in both LE1.0 and scattering index with acrophases occurring at night; however, patients dying subsequently from cardiac causes, but not those from fatal stroke were blunted in the circadian rhythms (the amplitudes were < 55% of those in surviving patients). Furthermore, the reduced circadian amplitude of scattering index was an increased risk for cardiac death even after adjustment of coexisting cardiovascular risks [adjusted relative risk (95% confidence interval) per 1-SD decrement, 4.24 (1.54-11.6)]. When patients were divided by the circadian amplitude of the scattering index of 36.5 msec (mean minus 1-SD), the 5yr cardiac mortality below and above the cutoff was 57 and 6%, respectively (log-rank test, p < 0.001). We conclude that the blunted circadian rhythm of AV conduction is an independent risk for cardiac death in patients with chronic AF.

Temporal organization of atrial activity and irregular ventricular rhythm during spontaneous atrial fibrillation: an in vivo study in the horse

INTRODUCTION

Atrial fibrillation (AF) is common in healthy horses. We studied the temporal organization of AF to test the hypothesis that the arrhythmia is governed by a high degree of periodicity and therefore is not random in the horse. Further, we surmised that concealed conduction of AF impulses in the AV node results in an inverse relationship between AF frequency and ventricular frequency.

METHODS AND RESULTS

Fast Fourier transform (FFT) analysis of atrial activity was done on signal-averaged ECGs (n = 11) and atrial electrograms (n = 3) of horses with AF at control (C), after quinidine sulfate (22 mg/kg by mouth every 2 hours) at 50% time to conversion (T50), and immediately before conversion (T90) to sinus rhythm. FFT always revealed a single dominant frequency peak. The mean dominant frequency decreased until conversion (C = 6.84 +/- 0.85 Hz, T50 = 4.87 +/- 1.5 Hz, T90 = 3.41 +/- 1.18 Hz; P < 0.001). Mean AA intervals (n = 500) gradually increased after quinidine. Mean RR intervals (n = 500), standard deviation of the mean (SDM), Poincaré plots, and serial autocorrelograms (SACs) of 500 RR intervals were measured at C and T90 to determine the ventricular response to AF and quinidine-induced changes in the variability of the ventricular response. Mean RR interval and SDM were reduced after quinidine (C = 1431 +/- 266 msec and 695 +/- 23 msec; T90 = 974 +/- 116 msec and 273 +/- 158 msec, respectively; P < 0.01). Poincaré plots and SAC at C and at T90 revealed a significant correlation of consecutive RR intervals typical of a system with a deterministic behavior. At T90, the variability of RR intervals was reduced and the overall periodicity of RR intervals was increased after quinidine administration.

CONCLUSION

In the horse, AF is a complex arrhythmia characterized by a high degree of underlying periodicity. The inverse AA-to-RR interval relationship and reduced variability of RR intervals after quinidine suggest that the ventricular response during AF results from rate-dependent concealment of AF wavelets bombarding the AV node, which nevertheless results in a significant degree of short-term predictability of beat-to-beat changes in RR intervals.

Circadian rhythms of atrioventricular conduction properties in chronic atrial fibrillation with and without heart failure

OBJECTIVES

We examined the circadian variations in atrioventricular (AV) conduction properties during atrial fibrillation (AF) by a technique based on the Lorenz plot of successive ventricular response (VR) intervals and analyzed their relations with clinical features.

BACKGROUND

The VR interval in chronic AF shows circadian variation, which is attenuated in patients with an increased risk of death. Although the VR interval is determined by the dynamic processes in the AV node randomly stimulated by rapid atrial activity, the circadian variations of the AV conduction properties related to this mechanism are unknown.

METHODS

In 48 patients with chronic AF, Lorenz plots were generated on overlapping sequential segments of 512 VR intervals in 24-h ambulatory electrocardiograms. For each scatter plot, the 1.0-s intercept of the lower envelope (LE1.0) of the plot and the degree of scatter above the envelope (root mean square difference from the envelope [scattering index]) were measured for estimating AV node refractoriness and concealed AV conduction, respectively.

RESULTS

In all patients, a significant circadian rhythm was observed for the average VR interval, LE1.0 and scattering index, with an acrophase occurring at night. The mesor, amplitude and acrophase of LE1.0 and the scattering index closely and independently correlated with the corresponding rhythm variables of the average VR interval (partial r2 0.98, 0.86 and 0.68 for LE1.0 and 0.98, 0.92 and 0.92 for scattering index). The amplitudes of these measures were lower in patients with congestive heart failure (CHF) even after adjustment for the effects of age, duration of AF, medications, left atrial diameter and blood pressure (p < 0.01 for all).

CONCLUSIONS

These results suggest that 1) both AV node refractoriness and the degree of concealed AV conduction during AF may show a circadian rhythm; 2) the circadian rhythms of these properties may independently contribute to the circadian variation of the VR interval; and 3) these circadian rhythms may be attenuated in patients with CHF.

Impulse formation and conduction of excitation in the atrioventricular node

Meijler et al. have recently challenged the classical concept of AV nodal conduction (the conduction hypothesis) and suggest that the AV node might be controlling ventricular rhythmicity through its automaticity electrotonically modulated by atrial excitation (the modulated pacemaker hypothesis). This article critically evaluates the three major arguments of Meijler: (1) the absence of convincing evidence for conduction of excitation in the AV node; (2) the prevalence of disproportionately short AV intervals in larger animals; and (3) elimination of RR intervals shorter than the cycle length of ventricular pacing during atrial fibrillation, to judge which of these two hypotheses would more satisfactorily explain various experimental and clinical findings accumulated in the past. Previous observations including microelectrode mapping of the rabbit AV junction during regular sinus rhythm as well as second-degree AV block, clinical and experimental studies on concealed conduction, and studies on the ventricular response to atrial fibrillation appear to be compatible with the conduction hypothesis, whereas clearcut evidence for automatic impulse formation in the AV node has not been presented, except in a small number of hearts showing spontaneous AV junctional rhythms. In view of these observations and theoretical considerations based on comparative anatomy of the AV node-His-Purkinje system and on the latest experimental study on the equine AV node, the authors conclude that the conduction hypothesis appears to better explain all the available data, except perhaps in a few cases with second-degree intra-AV nodal block.

Differentiation between aberrant ventricular conduction and ventricular ectopy in atrial fibrillation using RR interval scattergram

BACKGROUND

Differentiation between aberrant ventricular conduction and ventricular ectopy during atrial fibrillation (AF) is of etiologic, prognostic, and therapeutic importance. We developed a noninvasive technique to diagnose aberrant ventricular conduction and ventricular ectopy in AF.

METHODS AND RESULTS

We studied the Holter ECGs of 34 patients with paroxysmal AF and 62 patients with chronic AF. In all the patients, frequent wide QRS complexes were observed, and 32 patients were shown by electrophysiological examination to have ventricular ectopies or aberrant ventricular conductions. We obtained the RR interval scattergrams by plotting sequential pairs of RR intervals. Each point has the (n)th RR interval as its x value and the (n + 1)th RR interval as its y value. The irregularity of the RR intervals in AF resulted in widely scattered points delineated by the envelope along the axes. The y value of the envelope along the x axis indicates the shortest coupling interval to the preceding RR interval. Therefore, this curve defines the functional refractory period of atrioventricular conduction. The scattergram of the RR interval pairs immediately preceding the aberrant conduction (coupling points of aberrant conduction) specifically distributed along the envelope. In contrast, the coupling points of ventricular ectopies showed different distributions that had no relation to the envelope. That is, it included three typical patterns, ie, linear distribution below the envelope, linear distribution partially overlapped in the area of normal AF conduction, and chaotic distribution in the AF area. None of the scattergrams of ventricular ectopies showed curvilinear distribution along the envelope as aberrant conduction did. The specific distribution of the aberrant conduction on the RR interval scattergram suggested that aberrant conduction in AF could result from the difference of refractory periods between the AV node and bundle branch block.

CONCLUSIONS

We conclude that the RR interval scattergram makes it possible to differentiate between aberrant ventricular conduction and ventricular ectopy in atrial fibrillation, and thus, it is a useful noninvasive clinical tool.