Rate-Control Drugs Affect Variability and Irregularity Measures of RR Intervals in Patients with Permanent Atrial Fibrillation

Heart rate characteristic based modelling of atrial fibrillatory rate using implanted cardiac monitor data

Objective. The objective of the present study is to investigate the feasibility of using heart rate characteristics to estimate atrial fibrillatory rate (AFR) in a cohort of atrial fibrillation (AF) patients continuously monitored with an implantable cardiac monitor. We will use a mixed model approach to investigate population effect and patient specific effects of heart rate characteristics on AFR, and will correct for the effect of previous ablations, episode duration, and onset date and time.Approach. The f-wave signals, from which AFR is estimated, were extracted using a QRST cancellation process of the AF episodes in a cohort of 99 patients (67% male; 57 ± 12 years) monitored for 9.2(0.2-24.3) months as median(min-max). The AFR from 2453 f-wave signals included in the analysis was estimated using a model-based approach. The association between AFR and heart rate characteristics, prior ablations, and episode-related features were modelled using fixed-effect and mixed-effect modelling approaches.Main results. The mixed-effect models had a better fit to the data than fixed-effect models showing h.c. of determination (R2 = 0.49 versusR2 = 0.04) when relating the variations of AFR to the heart rate features. However, when correcting for the other factors, the mixed-effect model showed the best fit (R2 = 0.04). AFR was found to be significantly affected by previous catheter ablations (p< 0.05), episode duration (p< 0.05), and irregularity of theRRinterval series (p< 0.05).Significance. Mixed-effect models are more suitable for AFR modelling. AFR was shown to be faster in episodes with longer duration, less organizedRRintervals and after several ablation procedures.

ECG based assessment of circadian variation in AV-nodal conduction during AF—Influence of rate control drugs

The heart rate during atrial fibrillation (AF) is highly dependent on the conduction properties of the atrioventricular (AV) node. These properties can be affected using β-blockers or calcium channel blockers, mainly chosen empirically. Characterization of individual AV-nodal conduction could assist in personalized treatment selection during AF. Individual AV nodal refractory periods and conduction delays were characterized based on 24-hour ambulatory ECGs from 60 patients with permanent AF. This was done by estimating model parameters from a previously created mathematical network model of the AV node using a problem-specific genetic algorithm. Based on the estimated model parameters, the circadian variation and its drug-dependent difference between treatment with two β-blockers and two calcium channel blockers were quantified on a population level by means of cosinor analysis using a linear mixed-effect approach. The mixed-effects analysis indicated increased refractoriness relative to baseline for all drugs. An additional decrease in circadian variation for parameters representing conduction delay was observed for the β-blockers. This indicates that the two drug types have quantifiable differences in their effects on AV-nodal conduction properties. These differences could be important in treatment outcome, and thus quantifying them could assist in treatment selection.

An atrioventricular node model incorporating autonomic tone

The response to atrial fibrillation (AF) treatment is differing widely among patients, and a better understanding of the factors that contribute to these differences is needed. One important factor may be differences in the autonomic nervous system (ANS) activity. The atrioventricular (AV) node plays an important role during AF in modulating heart rate. To study the effect of the ANS-induced activity on the AV nodal function in AF, mathematical modelling is a valuable tool. In this study, we present an extended AV node model that incorporates changes in autonomic tone. The extension was guided by a distribution-based sensitivity analysis and incorporates the ANS-induced changes in the refractoriness and conduction delay. Simulated RR series from the extended model driven by atrial impulse series obtained from clinical tilt test data were qualitatively evaluated against clinical RR series in terms of heart rate, RR series variability and RR series irregularity. The changes to the RR series characteristics during head-down tilt were replicated by a 10% decrease in conduction delay, while the changes during head-up tilt were replicated by a 5% decrease in the refractory period and a 10% decrease in the conduction delay. We demonstrate that the model extension is needed to replicate ANS-induced changes during tilt, indicating that the changes in RR series characteristics could not be explained by changes in atrial activity alone.

Role of Metoprolol Succinate in the Treatment of Heart Failure and Atrial Fibrillation: A Systematic Review

BACKGROUND

Beta-blockers are one of the most important classes of cardiovascular agents and have been considered a cornerstone therapy in heart diseases, such as heart failure (HF) and atrial fibrillation (AF). Among different beta-blockers, metoprolol is a selective beta1-adrenergic antagonist, which has been extensively used since the 1970s.

AREAS OF UNCERTAINTY

Although current guidelines include recommendations for the use of controlled-release metoprolol succinate in specific HF and AF indications, and despite extensive clinical experience with metoprolol, comparative evidence on the use of metoprolol succinate compared with other beta-blockers in these indications is limited.

DATA SOURCES

We systematically reviewed the data from head-to-head studies directly comparing this compound with other beta-blockers in the treatment of HF or AF. Only clinical trials and observational studies were considered; no other limits were applied. The quality and relevance of retrieved articles were reviewed.

RESULTS

A total of 18 articles of the 353 articles identified were selected for inclusion; 12 HF articles and 6 for AF. Additional references were identified from the bibliographies of retrieved articles. The studies show that oral prophylaxis with an appropriate dose of metoprolol may reduce new incidents of AF in high-risk patients. Furthermore, metoprolol succinate is associated with significant mortality and morbidity benefits in the treatment of HF.

CONCLUSIONS

Despite the introduction of newer beta-blockers with differing clinical characteristics since its introduction, metoprolol succinate remains a useful drug in both HF and AF.

The effect of head-up tilt upon markers of heart rate variability in patients with atrial fibrillation

BACKGROUND

Heart rate variability (HRV) analysis is uncommonly undertaken in patients with atrial fibrillation (AF) due to an assumption that ventricular response is random. We sought to determine the effects of head-up tilt (HUT), a stimulus known to elicit an autonomic response, on HRV in patients with AF; we contrasted the findings with those of patients in sinus rhythm (SR).

METHODS

Consecutive, clinically indicated tilt tests were examined for 207 patients: 176 in SR, 31 in AF. Patients in AF were compared to an age-matched SR cohort (n = 69). Five minute windows immediately before and after tilting were analyzed using time-domain, frequency-domain and nonlinear HRV parameters. Continuous, noninvasive assessment of blood pressure, heart rate and stroke volume were available in the majority of patients.

RESULTS

There were significant differences at baseline in all HRV parameters between AF and age matched SR. HUT produced significant hemodynamic changes, regardless of cardiac rhythm. Coincident with these hemodynamic changes, patients in AF had a significant increase in median [quartile 1, 2] DFA-α2 (+0.14 [-0.03, 0.32], p < .005) and a decrease in sample entropy (-0.17 [-0.50, -0.01], p < .005).

CONCLUSION

In the SR cohort, increasing age was associated with fewer HRV changes on tilting. Patients with AF had blunted HRV responses to tilting, mirroring those seen in an age matched SR group. It is feasible to measure HRV in patients with AF and the changes observed on HUT are comparable to those seen in patients in sinus rhythm.

Relationship between HRV measurements and demographic and clinical variables in a population of patients with atrial fibrillation

Little is known about the role of HRV in atrial fibrillation (AF) patients. Aim of our study was to assess the relationship between HRV measurements and demographic and clinical variables in a population of 274 AF patients. We selected all consecutive patients with persistent/permanent AF among whom had performed a Holter ECG in our Department from April 2010 to April 2015. Time-domain analysis of HRV was evaluated. Demographic and clinical variables were collected for each patient. At multivariable logistic regression, a higher pNN50 was associated with ACE inhibitors/ARBs (p = 0.016) and a lower pNN50 with obesity (p = 0.037) and higher heart rate (HR) (p < 0.0005). A higher RMSSD was associated with ACE inhibitors/ARBs (p = 0.001), digitalis (p < 0.0005) and beta-blockers (p = 0.002) and a lower RMSSD with a higher HR (p < 0.0005). A higher SDNNi was associated with ACE inhibitors/ARBs (p < 0.0005), digitalis (p < 0.0005) and beta-blockers (p = 0.002) and a lower SDNNi with dysthyroidism (p = 0.048) and higher HR (p < 0.0005). A higher SDANN was associated with non-dihydropyiridine calcium-channel-blockers (p = 0.002) and ACE inhibitors/ARBs (p = 0.002) and a lower SDANN with hypertension (p = 0.034), obesity (p = 0.011), stroke (p = 0.031), pneumonia (p = 0.005) and higher HR (p < 0.0005). A higher SDNN was associated with ACE inhibitors/ARBs (p < 0.0005), digitalis (p < 0.0005) and beta-blockers (p = 0.022) and a lower SDNN with obesity (p = 0.012), pneumonia (p = 0.049) and higher HR (p < 0.0005). Our study showed that, in AF patients, there is a direct relationship between some clinical variables and HRV measurements; as for patients with sinus rhythm, even in AF patients this relationship seemed to reflect the autonomic nervous system activity.

Is 10-second electrocardiogram recording enough for accurately estimating heart rate in atrial fibrillation

BACKGROUND

At present, the estimation of rest heart rate (HR) in atrial fibrillation (AF) is obtained by apical auscultation for 1min or on the surface electrocardiogram (ECG) by multiplying the number of RR intervals on the 10second recording by six. But the reasonability of 10second ECG recording is controversial.

METHODS

ECG was continuously recorded at rest for 60s to calculate the real rest HR (HR60s). Meanwhile, the first 10s and 30s ECG recordings were used for calculating HR10s (sixfold) and HR30s (twofold). The differences of HR10s or HR30s with the HR60s were compared. The patients were divided into three sub-groups on the HR60s <80, 80-100 and >100bpm.

RESULTS

No significant difference among the mean HR10s, HR30s and HR60s was found. A positive correlation existed between HR10s and HR60s or HR30s and HR60s. Bland-Altman plot showed that the 95% reference limits were high as -11.0 to 16.0bpm for HR10s, but for HR30s these values were only -4.5 to 5.2bpm. Among the three subgroups with HR60s <80, 80-100 and >100bpm, the 95% reference limits with HR60s were -8.9 to 10.6, -10.5 to 14.0 and -11.3 to 21.7bpm for HR10s, but these values were -3.9 to 4.3, -4.1 to 4.6 and -5.3 to 6.7bpm for HR30s.

CONCLUSION

As 10s ECG recording could not provide clinically accepted estimation HR, ECG should be recorded at least for 30s in the patients with AF. It is better to record ECG for 60s when the HR is rapid.

Circadian variation of variability and irregularity of heart rate in patients with permanent atrial fibrillation: relation to symptoms and rate control drugs

The aim of the present study was to evaluate diurnal variations of the variability and irregularity of heart rate (HR) in patients with permanent atrial fibrillation (AF) with and without rate control drugs. Thirty-eight patients with permanent AF were part of an investigator-blind crossover study comparing diltiazem, verapamil, metoprolol, and carvedilol. We analyzed five Holter recordings per patient: at baseline (no rate control drug) and with each of the four drug regimens. HR, variability (SD; percentages of interval differences of successive RR intervals of >20, 50, and 80 ms; and root of the mean squared differences of successive RR intervals), and irregularity (approximate and sample entropy) parameters were computed in 20-min long nonoverlapping segments. Circadian rhythmicity was evaluated using cosinor analysis to each parameter series, which is characterized by the 24-h mean [midline statistic of rhythm (MESOR)] and excursion over the mean (amplitude). Arrhythmia-related symptoms were assessed by a questionnaire measuring symptom severity and frequency. HR and variability parameters showed a significant circadian variation in most patients, whereas only a small minority of the patients had circadian variations of irregularity parameters. Patients with circadian approximate entropy n at baseline had more severe symptoms (symptom severity: 9 ± 4 vs. 6 ± 5, P < 0.05, circadian vs. noncircadian variations). All drugs decreased the MESOR of HR and increased the MESOR of variability parameters. Only carvedilol and metoprolol decreased the normalized amplitude over 24 h of all parameters and HR. In conclusion, HR and RR variability parameters present a circadian variation in patients with permanent AF, whereas few patients demonstrated circadian fluctuations in irregularity parameters, suggesting different physiological mechanisms.