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

Abstract

Background Evidence from a canine experimental acute myocardial infarction (MI) model shows that until the seventh week after MI the relationship between stellate ganglionic nerve and vagal nerve activities (SGNA/VNA) progressively increases. Objective We evaluated 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 9 dogs. From a total 48 short-term electrocardiographic segments, 24 recorded before and 24 seven weeks after experimentally-induced MI, we obtained three indices of temporal myocardial repolarization dispersion: QTe (from q wave T to 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 a 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 indexes decreased (p<0.001 for all). Distinct circadian rhythms in QTeVI (p<0.05,) QTpVI (p<0.001) and TeVI (p<0.05) 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 (R2: 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.

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

“…24,26,27 Therefore, the mean and variance values for each of these intervals were calculated and then the original formula proposed by Berger et al34 was used to calculate three different QT variability indexes (QTVIs) (Figure 3). 24,26,27 $\begin{array}{c}{\text{QT}}_{\mathrm{normale}}\text{VI}={\log }_{10}\left\{\frac{\left[\left[{\text{QT}}_{\mathrm{normale}}\text{variance}\right]/{\left[{\text{QT}}_{\mathrm{normale}}\text{mean}\right]}^2\right]}{\left[\left[\text{RR}\text{variance}\right]/{\left[\text{RR}\text{mean}\right]}^2\right]}\right\}\\ {\text{QT}}_{\mathrm{normalp}}\text{VI}={\log }_{10}\left\{\frac{\left[\left[{\text{QT}}_{\mathrm{normalp}}\text{variance}\right]/{\left[{\text{QT}}_{\mathrm{normalp}}\text{mean}\right]}^2\right]}{\left[\left[\text{RR}\text{variance}\right]/{\left[\text{RR}\text{mean}\right]}^2\right]}\right\}\\ {\mathrm{normalT}}_{\mathrm{normale}}\text{VI}={\log }_{10}\left\{\frac{\left[\left[{\mathrm{normalT}}_{\mathrm{normale}}\text{variance}\right]/{\left[{\mathrm{normalT}}_{\mathrm{normale}}\text{mean}\right]}^2\right]}{\left[\left[\text{RR}\text{variance}\right]/{\left[\text{RR}\text{mean}\right]}^2\right]}\right\}\end{array}$…”

Heart Rate Variability in Shift Workers: Responses to Orthostatism and Relationships with Anthropometry, Body Composition, and Blood Pressure

“…Piccirillo et al [27] showed, in a canine experimental acute myocardial infarction model, that, during congestive heart failure, the reduction of LF power and LF/HF ratio probably reflect diminished sinus node responsiveness to autonomic modulation or an abnormal baroreflex function. In another study of the same authors, they showed that LF and HF power were significantly lower seven weeks after acute canine myocardial infarction than at baseline [29]. Other authors have proposed that LF is predominantly associated with parasympathetic activity based on the findings: increases in HF and LF occur after the use of drugs that specifically enhance the cardiac vagal tone; there is similarity of LF values between individuals with cardiac sympathetic denervation and normal baroreflex sensitivity; some validated measures of sympathetic control of the heart, such as plasma epinephrine levels and cardiac norepinephrine spillover, are not correlated with LF [17, 18].…”

A Time-Varying Nonparametric Methodology for Assessing Changes in QT Variability Unrelated to Heart Rate Variability

“…a) Sim1: The model in (12), represented in Fig. 1B, was utilized to simulate the case where TF coherence between output y(t) and input x(t), γ ref 2 xy (t) = a(t), changes quickly over time, therefore modulating the proportion of the output power related and unrelated to input x(t), denoted as P y,rx (t) and P y,ux (t), respectively.…”

“…Figure 3 shows the results of Sim1, which demonstrate that the method for correcting for the TF coherence bias provides accurate estimates. Mean trends of γ TOT xy (t), P TOT y,rx (t) and P TOT y,ux (t), calculated from mean TF representations obtained from 100 realizations of the model in (12), are shown along with their corresponding theoretical values. Before correcting for the bias (panels on the left), estimated trends correlated well with the theoretical patterns (correlation coefficients > 0.96), but the relative estimation error was high, being equal to 24% ± 25% for γ TOT xy (t), 103% ± 94% for P TOT y,rx (t) and −36%±10% for P TOT y,ux (t) (mean ± standard deviation).…”