Transcranial direct current stimulation improves the QT variability index and autonomic cardiac control in healthy subjects older than 60 years

Background

Noninvasive brain stimulation technique is an interesting tool to investigate the causal relation between cortical functioning and autonomic nervous system (ANS) responses.

Objective

The objective of this report is to evaluate whether anodal transcranial direct current stimulation (tDCS) over the temporal cortex influences short-period temporal ventricular repolarization dispersion and cardiovascular ANS control in elderly subjects.

Subjects and methods

In 50 healthy subjects (29 subjects younger than 60 years and 21 subjects older than 60 years) matched for gender, short-period RR and systolic blood pressure spectral variability, QT variability index (QTVI), and noninvasive hemodynamic data were obtained during anodal tDCS or sham stimulation.

Results

In the older group, the QTVI, low-frequency (LF) power expressed in normalized units, the ratio between LF and high-frequency (HF) power, and systemic peripheral resistances decreased, whereas HF power expressed in normalized units and α HF power increased during the active compared to the sham condition (P<0.05).

Conclusion

In healthy subjects older than 60 years, tDCS elicits cardiovascular and autonomic changes. Particularly, it improves temporal ventricular repolarization dispersion, reduces sinus sympathetic activity and systemic peripheral resistance, and increases vagal sinus activity and baroreflex sensitivity.

Time- and frequency-domain analysis of beat to beat P-wave duration, PR interval and RR interval can predict asystole as form of syncope during head-up tilt

To seek possible differences in short-period temporal RR interval, P-wave and PR interval dispersion and spectral coherence in patients with a head-up tilt test positive for vasovagal syncope with or without prolonged asystole, severe symptoms and at high risk of trauma. We retrospectively reviewed 5 min ECG and blood pressure recordings obtained at baseline, at rest and during head-up tilt in 40 patients diagnosed as having recurrent vasovagal syncope confirmed at a head-up tilt test. We analysed autoregressive spectral power for all the ECG-derived variables, focusing on temporal P-wave and PR interval dispersion indexes as well as their spectral coherence calculated on the same 5 min recordings at rest and during tilt. ECG recordings obtained during tilt before syncope showed significantly lower P  →  PR spectral coherence and higher RR standard deviations in patients with tilt-induced asystole than in those without (0.567  ±  0.097 versus 0.670  ±  0.127, p: 0.010 and 84  ±  36 versus 46  ±  22 ms², p  <  0.0001). Differences in the RR standard deviations persisted also on the last hundred beats (_-100) (113  ±  54 versus 34  ±  17 ms², p  <  0.0001). Multiple regression analysis identified a significantly negative association between the maximum RR intervals and P  →  PR coherence at rest (β:  -0.3, p  <  0.05) and positive association with RR_-100 standard deviation during tilt-induced syncope (β: 0.621, p  <  0.001). P  →  PR spectral coherence could be used to assess the risk of prolonged asystole in patients with tilt-induced vasovagal syncope as well as as a possible surrogate for tilt-testing during these patients' follow-up.

P wave analysis and left ventricular systolic function in chronic heart failure. Possible insights form the P wave - PP interval spectral coherence

BACKGROUND

Chronic increase in left ventricular filling pressure represents one of the most important mechanism underlying the structural, as well as the electrical, atrial chamber remodeling leading to atrial fibrillation. The present pilot pathophysiological study sought to investigate possible relationship between short-period cross-spectral coherence of P-Q, R-R and P-P intervals and echocardiographic indices of left ventricular and atrial function.

METHODS

Electrocardiographic single lead short-term cross-spectral analysis on P-Q and P-P intervals was performed in 31 patients with chronic heart failure (CHF). Twenty age and therapy matched hypertensive patients acted as control group. The interval between the beginning of P wave and its peak (Ppeak) was also analyzed.

RESULTS

Patients with CHF showed a significant lower PQ → PP and Ppeak → PP coherence (P<0.001) than the counterpart. At multivariate analysis only Ppeak → PP was independently associated to LVEF (r2:0.312; b:60; β:0.559; P<0.0001) and atrial volume (r2:-0.160; b:-0.15; β:-0.400, P<0.05).

CONCLUSIONS

Ppeak → PP coherence might be a simple marker of left ventricular and atrial function. Whether this index could be a useful noninvasive marker of increased left ventricular filling pressure and, possibly, of atrial fibrillation risk or not, it needs to be tested in larger prospective studies.

QT interval variability in body surface ECG: measurement, physiological basis, and clinical value: position statement and consensus guidance endorsed by the European Heart Rhythm Association jointly with the ESC Working Group on Cardiac Cellular Electrophysiology

This consensus guideline discusses the electrocardiographic phenomenon of beat-to-beat QT interval variability (QTV) on surface electrocardiograms. The text covers measurement principles, physiological basis, and clinical value of QTV. Technical considerations include QT interval measurement and the relation between QTV and heart rate variability. Research frontiers of QTV include understanding of QTV physiology, systematic evaluation of the link between QTV and direct measures of neural activity, modelling of the QTV dependence on the variability of other physiological variables, distinction between QTV and general T wave shape variability, and assessing of the QTV utility for guiding therapy. Increased QTV appears to be a risk marker of arrhythmic and cardiovascular death. It remains to be established whether it can guide therapy alone or in combination with other risk factors. QT interval variability has a possible role in non-invasive assessment of tonic sympathetic activity.

[Syncope: physiopathology, diagnosis and therapy]

Nowadays, syncope still generates complicated challenges for clinicians for the alarm it arises in patients and, at the same time, for the multiple causes it has determined by. In almost one third of cases, syncope is neuromediated, in young subjects in vasovagal, whereas in elderly is often determinated by carotid sinus hypersensitivity. These two kinds of syncope have two completely different diagnostic approach. In some cases pace-maker implantation will be suggested to avoid new syncope episodes. In a 20% of cases, the underlying cause is arrhythmic, most of all bradiarrhythmia which is treated with pace-maker implantation. In a little number of cases, syncope is caused by ventricular arrhythmias, that require the implantation of a defibrillator device. In this review, we analyze in detail every cause of syncope with its diagnostic and therapeutic approach.

Spatial QT Dispersion Predicts Nonsustained Ventricular Tachycardia and Correlates with Confined Systodiastolic Dysfunction in Hypertrophic Cardiomyopathy

Objectives: An increased dispersion of myocardial repolarization represents one of the mechanisms underlying the arrhythmic risk in hypertrophic cardiomyopathy (HCM). We investigated spatial myocardial repolarization dispersion indices in HCM patients with nonsustained ventricular tachycardia (NSVT) and, contextually, their main clinical determinants. Methods: Fifty-two well-matched HCM outpatients were categorized into two groups according to the presence or the absence of NSVT at 24-hour Holter electrocardiogram (ECG) monitoring. Each patient underwent a clinical examination, including Doppler echocardiogram integrated with tissue Doppler imaging, cardiac magnetic resonance, and 12-lead surface ECG to calculate the dispersion for the following intervals: QRS, Q-Tend (QTe), Q-Tpeak, Tpeak-Tend (TpTe), J-Tpeak, and J-Tend. Results: The NSVT group showed only QTe dispersion and TpTe dispersion values to be significantly higher than their counterparts. NSVT occurrence was independently predicted by late gadolinium enhancement presence (p = 0.021) and QTe Bazett dispersion (p = 0.030), the latter strongly associated with the myocardial performance index (MPI) obtained at the basal segment of the interventricular septum (p = 0.0004). Conclusion: Our data support QTe dispersion as an easy and noninvasive tool for identifying HCM patients with NSVT propensity. The strong relationship between QTe dispersion and MPI allows us to hypothesize an intriguing link between electrical instability and confined myocardial areas of systodiastolic dysfunction.

Global and regional left ventricular strain indices in post-myocardial infarction patients with ventricular arrhythmias and moderately abnormal ejection fraction

The aim of the study described here was to compare myocardial strains in ischemic heart patients with and without sustained ventricular tachycardia (VT) and moderately abnormal left ventricular ejection fraction (LVEF) to investigate which index could better predict VT on the basis of the analysis of global and regional left ventricular (LV) dysfunction. We studied 467 patients with previous myocardial infarction and LVEF >35%. Fifty-one patients had documented VT, and 416 patients presented with no VT. LV volumes and score index were obtained by 2-D echocardiography. Longitudinal, radial and circumferential strains were determined. Strains of the infarct, border and remote zones were also obtained. There were no differences in standard LV 2-D parameters between patients with and those without VT. Receiver operating characteristic values were -12.7% for global longitudinal strain (area under the curve [AUC] = 0.72), -4.8% for posterior-inferior wall circumferential strain (AUC = 0.80), 61 ms for LV mechanical dispersion (AUC = 0.84), -10.1% for longitudinal strain of the border zone (AUC = 0.86) and -9.2% for circumferential strain of the border zone (AUC = 0.89). In patients with previous myocardial infarction and moderately abnormal LVEF, peri-infarct circumferential strain was the strongest predictor of documented ventricular arrhythmias among all strain quantitative indices. Additionally, strain values from posterior-inferior wall infarctions had a higher association with arrhythmic events compared with global strain.

[QT Variability Index as a tool for risk stratification of sudden cardiac death]

Sudden cardiac death is the leading cause of mortality in patients with chronic heart failure (CHF) and history of myocardial infarction. Selection of patients at risk of sudden cardiac death is dramatically important to choose the correct therapeutic approach. The QT Variability Index (QTVI) is a non-invasive measure of repolarization lability that has been applied to a wide variety of subjects with cardiovascular disease. It is a ratio of normalized QT variability to normalized heart rate variability, and therefore includes an assessment of the autonomic nervous system tone. As opposed to T wave alternans, QTVI assesses variance in repolarization at all frequencies. Recent studies suggest that QTVI may help clinicians choosing the appropriate implantable cardiovester defibrillator timing implantation, in patients with dilated or hypertrophic cardiomyopathy or CHF because of its efficacy in patient evaluation and follow-up.

Myocardial repolarization dispersion and autonomic nerve activity in a canine experimental acute myocardial infarction model

BACKGROUND

Evidence from a canine experimental acute myocardial infarction (MI) model shows that until the seventh week after MI, the relationship between stellate ganglion nerve activity (SGNA) and vagal nerve activity (VNA) progressively increases.

OBJECTIVE

The purpose of this study was to evaluate how autonomic nervous system activity influences temporal myocardial repolarization dispersion at this period.

METHODS

We analyzed autonomic nerve activity as well as QT and RR variability from recordings previously obtained in nine dogs. From a total of 48 short-term ECG segments, 24 recorded before and 24 recorded 7 weeks after experimentally-induced MI, we obtained three indices of temporal myocardial repolarization dispersion: QTe (from Q-wave to T-wave end), QTp (from Q-wave to T-wave peak), and Te (from T-wave peak to T-wave end) variability index (QTeVI, QTpVI, TeVI). We also performed heart rate variability power spectral analysis on the same segments.

RESULTS

After MI, all the QT variables increased QTeVI (median [interquartile range]) (from -1.76[0.82] to -1.32[0.68]), QTeVI (from -1.90[1.01] to -1.45[0.78]), and TeVI (from -0.72[0.67] to -0.22[1.00]), whereas all RR spectral indices decreased (P <.001 for all). Distinct circadian rhythms in QTeVI (P <.05,) QTpVI (P <.001) and TeVI (P <.05) appeared after MI with circadian variations resembling that of SGNA/VNA. The morning QTpVI and TeVI acrophases approached the SGNA/VNA acrophase. Conversely, the evening QTeVI acrophase coincided with another SGNA/VNA peak. After MI, regression analysis detected a positive relationship between SGNA/VNA and TeVI (R(2): 0.077; β: 0.278; p< 0.001).

CONCLUSION

Temporal myocardial repolarization dispersion shows a circadian variation after MI reaching its peak at a time when sympathetic is highest and vagal activity lowest.

Influence of aging and chronic heart failure on temporal dispersion of myocardial repolarization

Background and purpose:

QT and T_peak-T_end (Te) intervals are associated with sudden cardiac death in patients with chronic heart failure (CHF). We studied age-dependent influence on short-term temporal dispersion of these two variables in patients with postischemic CHF.

Method:

We grouped 75 CHF and 53 healthy control subjects into three age subsets: ≤50 years, >50 years and ≤65 years, and >65 years. We then calculated the following indices: QT and Te variability index (QTVI and TeVI), the ratio between the short-term variability (STV) of QT or Te, and the STV of resting rate (RR) (QT/RR STV and Te/RR STV).

Results:

In all different age subgroups, patients with CHF showed a higher level of QTVI than age-matched control subjects (≤50 years: P < 0.0001; >50 years and ≤65 years: P < 0.05; >65 years: P < 0.05). Patients with CHF < 50 years old also had all repolarization variability indices higher than normal age-matched controls (TeVI, P < 0.05; QT/RR STV, P < 0.05; Te/RR STV, P < 0.05), whereas we did not find any difference between the two older classes of subjects. Both QTVI (r²: 0.178, P < 0.05) and TeVI (r²: 0.433, P < 0.001) were positively related to age in normal subjects, even if the first correlation was weaker than the second one.

Conclusion:

Our data showed that QTVI could be used in all ages to evaluate repolarization temporal liability, whereas the other indices are deeply influenced by age. Probably, the age-dependent increase in QTVI was more influenced by a reduction of RR variability reported in older normal subjects.

Indexes of temporal myocardial repolarization dispersion and sudden cardiac death in heart failure: any difference?

BACKGROUND

The QT variability index, calculated between Q- and the T-wave end (QTend VI), is an index of temporal myocardial repolarization lability associated with sudden cardiac death (SCD) in chronic heart failure (CHF). Little is known about temporal variability in the other two temporal myocardial repolarization descriptors obtained from Q-Tpeak and Tpeak -Tend intervals. We therefore investigated differences between these indexes in patients with CHF who died suddenly and in those who survived with a left ventricular ejection fraction (LVEF) ≤35% or >35%.

METHODS AND RESULTS

We selected 127 ECG and systolic blood pressure (SPB) recordings from outpatients with CHF all of whom had been followed up for 30 months. We calculated RR and SPB variability by power spectral analysis and QTend VI, QTpeak VI, Tpeak Tend VI. We then subdivided data patients into three groups SCD, LVEF ≤ 35%, and LVEF > 35%. The LVEF was higher in the SCD than in the LVEF ≤ 35% group, whereas no difference was found between the SCD and LVEF > 35% groups. QTend VI, QTpeak VI, and Tpeak Tend VI were higher in the SCD and LVEF ≤ 35% groups than in the LVEF > 35% group. Multivariate analysis detected a negative relationship between all repolarization variability indexes, low frequency obtained from RR intervals and LVEF.

CONCLUSIONS

Our data show that variability in the first (QTpeak VI) and second halves of the QT interval (Tpeak -Tend VI) significantly contributes to the QTend VI in patients with CHF. Further studies should investigate whether these indexes might help stratify the risk of SCD in patients with a moderately depressed LVEF.

Autonomic nerve activity and the short-term variability of the Tpeak-Tend interval in dogs with pacing-induced heart failure

BACKGROUND

In congestive heart failure (CHF), autonomic nervous system (ANS) activity is known to modulate arrhythmic risk through its effects on myocardial repolarization. An increased interval between the peak and the end of the T wave (T(peak)-T(end)) has been reported to increase the incidence of sudden cardiac death. However, the ANS influence on the T(peak)-T(end) interval remains unclear.

OBJECTIVE

We directly measured ANS nerve activity in ambulatory dogs with pacing-induced CHF to test the hypothesis that ANS activity modulates the T(peak)-T(end) variability index (T(peak)-T(end)VI), the short-term variability of the T(peak)-T(end) interval obtained on 30 beats (T(peak)-T(end)STV(30)), and the short-term variability of the T(peak)-T(end) interval obtained on 5-minute ECG recording (T(peak)-T(end)STV(T)).

METHODS

By using data previously recorded in 6 ambulatory dogs before and after pacing-induced CHF, we assessed ANS activity recorded with an implanted radiotransmitter that monitored integrated left stellate ganglion nervous activity (iSGNA), integrated vagus nerve activity (iVNA), and electrocardiogram (ECG). We selected for analysis 36 segments recorded at baseline and 36 after pacing-induced CHF with similar iSGNA.

RESULTS

During CHF, T(peak)-T(end)STV(30) (P<.001) and T(peak)-T(end)STV(T) (P<.05) were significantly higher than those at baseline. The multiple linear mixed regression analysis disclosed a significant positive correlation between iSGNA and T(peak)-T(end)STV(T) (baseline: β 2.92, P<.001; CHF: β 1.13, P<.001) and a significant negative correlation between iVNA and T(peak)-T(end)STV(T) (baseline: β-6.74, P<.001; CHF: β-1.42, P< .001).

CONCLUSIONS

In a canine model of pacing-induced CHF, iSGNA correlates positively while iVNA correlates negatively with T(peak)-T(end)STV(T). These findings suggest that SGNA increases while VNA decreases the dispersion of ventricular repolarization in ambulatory dogs with CHF.

Effect of Acute Mental Stress on Heart Rate and QT Variability in Postmyocardial Infarction Patients

Emotionally charged events are associated with an increased risk of sudden cardiac death (SCD). In this study we assessed RR and QT variability index (QTVI) at baseline during anger recall test (AR). We calculated QTVI from a 5-min ECG recording and from a 10-beats segment around the presumed maximum sympathetic activation in thirty post-myocardial infarction patients under β-blocker therapy and 10 controls underwent. In all groups, the low-frequency component of RR and SBP increased during AR. In all recordings, the QTVI calculated on a 5-min ECG recording and the QTVI_{10 beats} were higher in patients than in controls (P < 0.05). The QTVI during AR remained unchanged from baseline within each group. Conversely, during AR, the QTVI_{10 beats} in controls diminished significantly (P < 0.05) from baseline whereas in patients remained unchanged. The inability to buffer an acute stress-induced increase in sympathetic activity could explain why events charged with acute stress are associated with an increased risk of ventricular arrhythmias in this setting of patients and support the role of cognitive behavior stress management strategies.

Widespread microstructural white matter involvement in amyotrophic lateral sclerosis: a whole-brain DTI study

BACKGROUND AND PURPOSE

The extensive application of advanced MR imaging techniques to the study of ALS has undoubtedly improved our knowledge of disease pathophysiology, even if the actual spread of the neurodegenerative process throughout the central nervous system is not fully understood. The present study aimed to detect WM patterns of microstructural abnormalities to better investigate the pathologic process in ALS, within but also beyond CSTs, in a whole-brain analysis.

MATERIALS AND METHODS

DTI was performed in 19 patients with ALS and 20 matched healthy controls, by using whole-brain TBSS and VOI analyses.

RESULTS

We observed a significant decrease of FA in the body of CC of the ALS group (P < .05). At the VOI level, both FA decrease and RD increase in the body of CC significantly correlated with the UMN score (P = .003 and P = .02). Additionally, significant voxelwise positive correlations between FA and the ALSFRS-R were detected in the WM tracts underneath the left premotor cortex (P < .05).

CONCLUSIONS

The correlations between reduction of FA and increase of RD in the body of CC with the UMN score indicate that the WM degeneration in the CC is strictly related to the ALS pyramidal impairment, while the correlation between FA and ALSFRS-R in the associative tracts underneath the left premotor cortex might reflect the progressive spread of the disease from the motor toward the extramotor areas.

Electroanatomic remodeling of the left stellate ganglion after myocardial infarction

OBJECTIVES

The purpose of this study was to evaluate the changes of left stellate ganglionic nerve activity (SGNA) and left thoracic vagal nerve activity (VNA) after acute myocardial infarction (MI).

BACKGROUND

Whether MI results in remodeling of extracardiac nerve activity remains unclear.

METHODS

We implanted radiotransmitters to record the SGNA, VNA, and electrocardiogram in 9 ambulatory dogs. After baseline monitoring, MI was created by 1-h balloon occlusion of the coronary arteries. The dogs were then continuously monitored for 2 months. Both stellate ganglia were stained for growth-associated protein 43 and synaptophysin. The stellate ganglia from 5 normal dogs were used as control.

RESULTS

MI increased 24-h integrated SGNA from 7.44 ± 7.19 Ln(Vs)/day at baseline to 8.09 ± 7.75 Ln(Vs)/day after the MI (p < 0.05). The 24-h integrated VNA before and after the MI was 5.29 ± 5.04 Ln(Vs)/day and 5.58 ± 5.15 Ln(Vs)/day, respectively (p < 0.05). A significant 24-h circadian variation was noted for the SGNA (p < 0.05) but not the VNA. The SGNA/VNA ratio also showed significant circadian variation. The nerve densities from the left SG were 63,218 ± 34,719 μm(2)/mm(2) and 20,623 ± 4,926 μm(2)/mm(2) for growth-associated protein 43 (p < 0.05) and were 32,116 ± 8,190 μm(2)/mm(2)and 16,326 ± 4,679 μm(2)/mm(2) for synaptophysin (p < 0.05) in MI and control groups, respectively. The right SG also showed increased nerve density after MI (p < 0.05).

CONCLUSIONS

MI results in persistent increase in the synaptic density of bilateral stellate ganglia and is associated with increased SGNA and VNA. There is a circadian variation of the SGNA/VNA ratio. These data indicate significant remodeling of the extracardiac autonomic nerve activity and structures after MI.

Intracellular calcium and the mechanism of anodal supernormal excitability in langendorff perfused rabbit ventricles

BACKGROUND

Anodal stimulation hyperpolarizes the cell membrane and increases the intracellular Ca(2+) (Ca(i)) transient. This study tested the hypothesis that the maximum slope of the Ca(i) decline (-(dCa(i)/dt)(max)) corresponds to the timing of anodal dip on the strength-interval curve and the initiation of repetitive responses and ventricular fibrillation (VF) after a premature stimulus (S(2)).

METHODS AND RESULTS

We simultaneously mapped the membrane potential (V(m)) and Ca(i) in 23 rabbit ventricles. A dip in the anodal strength-interval curve was observed. During the anodal dip, ventricles were captured by anodal break excitation directly under the S(2) electrode. The Ca(i) following anodal stimuli is larger than that following cathodal stimuli. The S(1)-S(2) intervals of the anodal dip (203±10 ms) coincided with the -(dCa(i)/dt)(max) (199±10 ms, P=NS). BAPTA-AM (n=3), inhibition of the electrogenic Na(+)-Ca(2+) exchanger current (I(NCX)) by low extracellular Na(+) (n=3), and combined ryanodine and thapsigargin infusion (n=2) eliminated the anodal supernormality. Strong S(2) during the relative refractory period (n=5) induced 29 repetitive responses and 10 VF episodes. The interval between S(2) and the first non-driven beat was coincidental with the time of -(dCa(i)/dt)(max).

CONCLUSIONS

Larger Ca(i) transient and I(NCX) activation induced by anodal stimulation produces anodal supernormality. The time of maximum I(NCX) activation is coincidental to the induction of non-driven beats from the Ca(i) sinkhole after a strong premature stimulation.

Increased temporal dispersion of myocardial repolarization in myotonic dystrophy type 1: beyond the cardiac conduction system

BACKGROUND AND OBJECTIVES

The most frequently mechanism underlying sudden cardiac death in myotonic dystrophy type 1 (DM1) is bradyarrhythmias due to cardiac conduction abnormalities. However the risk of ventricular tachyarrhythmias remains a concern in clinical management as well as in its determinant. We therefore assessed autonomic nervous system activity aiming to disclose differences in the QT variability index (QTVI)-a marker of temporal myocardial repolarization lability-between DM1 patients and healthy controls. We also investigated the possible differences within DM1 patients by subdividing them according either to the presence of first degree atrioventricular block (1st AVB) or to the cytosine-thymine-guanine (CTG) repeat expansion size.

METHODS

Sixty-two DM1 patients and 20 healthy subjects underwent neurological and cardiological examinations, the latter including ECG, echocardiography and 24-hour Holter monitoring. All underwent a 5-minute ECG recording to assess heart rate variability power spectral components, and the QTVI values.

RESULTS

Power spectral data, namely total power, low frequency power and high frequency power, were lower, whereas QTVI values were higher in DM1 patients than in controls (p<.0001). Higher QTVI values were found in DM1 subgroups with 1st AVB (p=.009) and more than 500 CTG repeat (p=.014) with respect to DM1 patients without 1st AVB and CTG<500. Spectral data did not significantly differ. At multivariable analysis, QTVI and age were independently associated with PR interval and CTG repeat.

CONCLUSIONS

The increased values of QTVI argue in favour of an important heart involvement extending beyond the conduction system. Whether QTVI could be useful in predicting clinical course of DM1 clearly requires larger prospective studies.