Abnormal Nocturnal Heart Rate Variability and QT Dynamics in Patients with Brugada Syndrome

Autonomic cardiac innervation: impact on the evolution of arrhythmias in inherited cardiac arrhythmia syndromes

The autonomic nervous system (ANS) is an essential component of arrhythmogenicity, especially in the absence of structural heart disease and channelopathy. In this article, the authors review the role and characteristics of ANS in various channelopathies. Some of these, such as most long QT syndromes and catecholaminergic polymorphic ventricular tachycardia, are highly dependent on sympathetic activation, while parasympathetic tone is an important factor for arrhythmias in other channelopathies such as Brugada syndrome or early repolarisation syndrome. Recent advances highlighting the subtle role of ANS in channelopathies are presented here, demonstrating that all is far from being so simple and straightforward and revealing some paradoxical behaviours of channelopathies in relation to discrete ANS imbalance.

Recursive model identification for the analysis of the autonomic response to exercise testing in Brugada syndrome

This paper proposes the integration and analysis of a closed-loop model of the baroreflex and cardiovascular systems, focused on a time-varying estimation of the autonomic modulation of heart rate in Brugada syndrome (BS), during exercise and subsequent recovery. Patient-specific models of 44 BS patients at different levels of risk (symptomatic and asymptomatic) were identified through a recursive evolutionary algorithm. After parameter identification, a close match between experimental and simulated signals (mean error = 0.81%) was observed. The model-based estimation of vagal and sympathetic contributions were consistent with physiological knowledge, enabling to observe the expected autonomic changes induced by exercise testing. In particular, symptomatic patients presented a significantly higher parasympathetic activity during exercise, and an autonomic imbalance was observed in these patients at peak effort and during post-exercise recovery. A higher vagal modulation during exercise, as well as an increasing parasympathetic activity at peak effort and a decreasing vagal contribution during post-exercise recovery could be related with symptoms and, thus, with a worse prognosis in BS. This work proposes the first evaluation of the sympathetic and parasympathetic responses to exercise testing in patients suffering from BS, through the recursive identification of computational models; highlighting important trends of clinical relevance that provide new insights into the underlying autonomic mechanisms regulating the cardiovascular system in BS. The joint analysis of the extracted autonomic parameters and classic electrophysiological markers could improve BS risk stratification.

Model-based analysis of the autonomic response to head-up tilt testing in Brugada syndrome

The etiology of Brugada syndrome (BS) is complex and multifactorial, making risk stratification in this population a major challenge. Since changes in the autonomic modulation of these patients are commonly related to arrhythmic events, we analyze in this work whether the response to head-up tilt (HUT) testing on this population may provide useful, complementary information for risk stratification. In order to perform this analysis, a coupled physiological model integrating the cardiac electrical activity, the cardiovascular system and the baroreceptors reflex control of the autonomic function, in response to HUT is proposed. A sensitivity analysis was performed, based on a screening method, evidencing the influence of cardiovascular parameters on blood pressure and of baroreflex regulation on heart rate. The most sensitive parameters have been identified on a set of 20 subjects (8 controls and 12 BS patients), so as to assess subject-specific model parameters. According to the results, controls showed an increased sympathetic modulation after tilting, as well as a reduced left ventricular contractility was observed in symptomatic, with respect to asymptomatic BS patients. These results provide new insights regarding the autonomic mechanisms regulating the cardiovascular system in BS which might be used as a complementary source of information, along with classical electrophysiological parameters, for BS risk stratification.

Multivariate classification of Brugada syndrome patients based on autonomic response to exercise testing

Ventricular arrhythmias in Brugada syndrome (BS) typically occur at rest and especially during sleep, suggesting that changes in the autonomic modulation may play an important role in arrhythmogenesis. The autonomic response to exercise and subsequent recovery was evaluated on 105 patients diagnosed with BS (twenty-four were symptomatic), by means of a time-frequency heart rate variability (HRV) analysis, so as to propose a novel predictive model capable of distinguishing symptomatic and asymptomatic BS populations. During incremental exercise, symptomatic patients showed higher HF_nu values, probably related to an increased parasympathetic modulation, with respect to asymptomatic subjects. In addition, those extracted HRV features best distinguishing between populations were selected using a two-step feature selection approach, so as to build a linear discriminant analysis (LDA) classifier. The final features subset included one third of the total amount of extracted autonomic markers, mostly acquired during incremental exercise and active recovery, thus evidencing the relevance of these test segments in BS patients classification. The derived predictive model showed an improved performance with respect to previous works in the field (AUC = 0.92 ± 0.01; Se = 0.91 ± 0.06; Sp = 0.90 ± 0.05). Therefore, based on these findings, some of the analyzed HRV markers and the proposed model could be useful for risk stratification in Brugada syndrome.

The utility of T-wave alternans during the morning in the summer for the risk stratification of patients with Brugada syndrome

The prognostic value of the seasonal variations of T-wave alternans (TWA) and heart rate variability (HRV), and the seasonal distribution of ventricular fibrillation (VF) in Brugada syndrome (Br-S) is unknown. We assessed the utility of seasonal variations in TWA and HRV for risk stratification in Br-S using a 24-h multichannel Holter electrocardiogram (24-M-ECG). We enrolled 81 patients with Br-S (grouped according to their history of VF, n = 12; syncope, n = 8; no symptoms, n = 61) who underwent 24-M-ECG in all four seasons. Precordial electrodes were attached to the third (3L-V2) and fourth (4L-V2, 4L-V5) intercostal spaces. We determined the maximum TWA (max-TWA) values and calculated HRV during night and morning time periods for all seasons. During a follow-up period of 5.8 ± 2.8 years, 11 patients experienced new VF episodes and there was a peak in new VF episodes in the summer. The VF group had the greatest 3L-V2 max-TWA value during morning time in the summer among the three groups and showed higher 3L-V2 max-TWA value than in the other seasons. The cutoff value for the 3L-V2 max-TWA during morning time in the summer was determined to be 42 µV using ROC analysis (82 % sensitivity, 74 % specificity; p = 0.0006). Multivariate analysis revealed that a 3L-V2 max-TWA value ≥42 µV during morning time in the summer and previous VF episodes were predictors of future VF episodes. The 3L-V2 max-TWA value during morning time in the summer may be a useful predictor of future VF episodes in Br-S.

Autonomic and cardio-respiratory responses to exercise in Brugada Syndrome patients

Background

Imbalances of the autonomic nervous (ANS), the cardiovascular system, and ionics might contribute to the manifestation of The Brugada Syndrome (BrS). Thus, this study has aimed to investigate the cardio-respiratory fitness and the responses of the ANS both at rest and during a sub-maximal exercise stress test, in BrS patients and in gender-matched and age-matched healthy sedentary controls.

Methods

Eleven BrS patients and 23 healthy controls were recruited in Khon Kaen, Thailand. They performed an exercise test on a cycle ergometer, and during the exercise, expired gas samples and electrocardiograms were collected. Blood glucose and electrolyte concentrations were analyzed before and after exercise. Then the heart rate variability (HRV) and the heart rate recovery (HRR) were analyzed from the electrocardiograms.

Results

The BrS patients showed a higher parasympathetic activation during exercise recovery than baseline. They had a smaller level of sympathetic activation during the period of exercise recovery than the controls did. They also showed a significantly lower peak HR, HRR, and peak oxygen consumption than the controls (p<0.05). All subjects had a significantly lower percentage of peak oxygen consumption and respiratory exchange ratio during low-intensity (p<0.01) and moderate-intensity (p<0.05) exercise than during high-intensity exercise. The BrS patients had mild hyperkalemia which is reduced according to the exercise.

Conclusion

Thai BrS patients had a more rapid rate of restoration of the parasympathetic and smaller level of sympathetic activation after exercise. They had mild hyperkalemia which is reduced according to the exercise. Furthermore, they exhibited impaired cardio-respiratory fitness.

Late Gadolinium Enhancement on Cardiac MRI Correlates with QT Dynamicity Represented by QT/RR Relationship in Patients with Ventricular Arrhythmias

BACKGROUND

The distribution of late gadolinium enhancement (LGE) on the cardiac MRI (CMR) indicates myocardial fibrosis and provides information of possible reentry substrates. QT dynamicity reflecting repolarization abnormalities has gained attention as a potential prognostic predictive factor.

OBJECTIVE

To clarify the correlation between the LGE distribution on CMR and QT dynamicity represented by the QT/RR relationship.

METHODS

CMR and QT/RR analyses using Holter monitoring were performed in 34 patients (24 males, 60 ± 11 years) with ventricular tachycardia (VT) and/or ventricular fibrillation (VF). The LGE on CMR was scored using a 4-point score in 17 left ventricular segments. The sum of the LGE scores was calculated for each patient. The QT/RR slope and daytime/nighttime QT/RR ratio (day/night ratio) were calculated. The correlation between the slope or the day/night QT/RR ratio and late enhancement findings was analyzed.

RESULTS

All patients were divided into 23 LGE positive (LGE(+)) and 11 LGE negative (LGE(-)) patients. The slopes of the QTe/RR and QTa /RR were significantly steeper in the LGE(+) than in LGE(-) patients (0.21 ± 0.03 vs 0.13 ± 0.02; P < 0.001, 0.19 ± 0.03 vs 0.13 ± 0.02; P < 0.001, respectively), and both slopes were significantly correlated with the total LGE scores (r = 0.83, P < 0.001; r = 0.71, P < 0.001, respectively). In the LGE(+) patients, the QTe day/night (1.37 ± 0.38 vs 0.91 ± 0.33; P = 0.002) and QTa day/night ratios (1.33 ± 0.26 vs 1.06 ± 0.30; P = 0.011) were significantly greater than those in the LGE(-) patients.

CONCLUSION

The LGE distribution was closely related to the QT dynamicity, suggesting that a combination of these markers can be a powerful tool for understanding the background pathophysiology.

Deterioration of the circadian variation of heart rate variability in Brugada syndrome may contribute to the pathogenesis of ventricular fibrillation

AIMS

Abnormal sympathetic innervation triggers ventricular fibrillation (VF). We examined the circadian variation of autonomic nervous system and its relevance to risk stratification of VF in patients with Brugada syndrome (Brs).

METHODS

We enrolled 12 male Brs patients with documented VF (Brs-S; mean age, 42±4 years), 17 without documented VF (Brs-N; mean age 48±4 years), and 16 age- and gender-matched controls. The clinical data, 12-lead electrocardiography (ECG), signal-averaged ECG, electrophysiological study (EPS), and heart rate variability from 24h Holter ECG were compared between the groups.

RESULTS

The low frequency components (LF) in Brs-S and Brs-N and high frequency components (HF) in Brs-S patients were significantly lower than in the controls (409.8±128.6ms(2), 329.5±108ms(2) vs. 945.3±111.3ms(2); 135.1±73.8ms(2) vs. 391.8±63.9ms(2), respectively). The circadian variation of the LF and LF/HF decreased in the Brs patients, the standard deviation (SD) of LF/HF (<2.5) and SD of LF (<400ms(2)) had sufficiently high sensitivity (96.6%) and specificity (92.9%) for the diagnosis of Brs. Most of the Brs-S patients (83.3%) were located under the line formed by the SD/mean of HF=SD/mean of LF in the scatter plots.

CONCLUSION

Lack of the circadian variation of autonomic function occurs in Brs, and this may contribute to the pathogenesis of VF.

Impaired signaling intrinsic to sinoatrial node pacemaker cells affects heart rate variability during cardiac disease

The normal heart beat intervals are neither strictly stationary nor completely random, and continuously shift from one period to another. Decoding the ECG identifies this "hidden" information that imparts inherent complexity to the heart-beating interval time series. Loss of this complexity in cardiovascular disease is manifested as a reduction in heart rate variability (HRV) and this reduction correlates with an increase in both morbidity and mortality. Because HRV measurements are noninvasive and easy to perform, they have emerged as an important tool in cardiology. However, the identities of specific mechanisms that underline the changes in HRV that occur in cardiovascular diseases remain largely unknown. Changes in HRV have mainly been interpreted on a neural basis, ie due to changes in autonomic impulses to the heart: sympathetic activity decreases both the average heart beat interval and HRV, and parasympathetic activity increases both. It has now become clear, however, that the heart rate and HRV are also determined by intrinsic properties of the pacemaker cells that comprise the sinoatrial node, and the responses of these properties to autonomic receptor stimulation. Here we review how changes in the properties of coupled-clock mechanisms intrinsic to pacemaker cells that comprise the sinoatrial node and their impaired response to autonomic receptor stimulation are implicated in the changes of HRV observed in heart diseases.

Cardiac autonomic control in Brugada syndrome patients during sleep: the effects of sleep disordered breathing

AIMS

Brugada syndrome is characterized by typical ECG features, ventricular arrhythmias and sudden cardiac death (SCD), more frequent during nighttime. Autonomic cardiovascular control has been implicated in triggering the ventricular arrhythmias. Sleep-disordered breathing (SDB) elicits marked autonomic changes during sleep and is also associated with an increased risk of nighttime SCD. Brugada patients may have a higher likelihood of SDB compared to controls. However, no data are available on cardiac autonomic control in Brugada patients, particularly with regard to the comorbidity of SDB.

METHODS

We evaluated autonomic cardiovascular control in Brugada patients with SDB (BRU-SDB, n=9), without SDB (BRU, n=9), in controls (CON, n=8) and in non-Brugada patients with SDB (n=6), during wakefulness and sleep (N2, N3 and REM). Linear spectral and entropy-derived measures of heart rate variability (HRV) were performed during apnea-free stable breathing epochs.

RESULTS

Total HRV was attenuated in BRU-SDB compared to CON and BRU. During N2 and REM, in BRU-SDB patients sympathetic modulation decreased compared to BRU and CON, while during REM, they showed an increased parasympathetic modulation, compared to the other two groups. BRU-SDB and SDB were similar in terms of spectral components. Entropy-derived indices showed preserved dynamic changes in Brugada patients compared to controls through the different sleep stages.

CONCLUSION

Brugada syndrome per se does not appear associated with an altered autonomic cardiovascular control during wakefulness and sleep. The comorbidity with SDB may contribute to disrupted autonomic cardiovascular regulation during sleep, possibly predisposing to the increased likelihood of sleep-related ventricular tachyarrhythmias and SCD.