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PubMed2005

Reproducibility of methods for assessing baroreflex sensitivity and temporal QT variability in end-stage renal disease and healthy subjects.

Spontaneous baroreflex sensitivity (BRS), the reflex heart rate modulation in response to blood pressure changes (predominantly an index of cardiac vagal activity) and temporal QT variability (an index of myocardial repolarization) have been demonstrated to convey important prognostic information. The information about reproducibility of BRS and temporal QT variability is limited and there is lack of information regarding patients with cardiovascular diseases. We investigated reproducibility of spontaneous BRS using the sequence technique and temporal QT variability index (QTVI) in terms of intra-, interexaminer and within-subject variability in end-stage renal disease patients (ESRD, n=17, age 55+/-14 years) and healthy subjects (HS, n=29, age 32+/-12 years, P<0.01). ECG and blood pressure (Portapres) were recorded on two separate days and BRS and QTVI were evaluated by two independent examiners. The mean heart rate was similar in ESRD patients in comparison to healthy controls, whereas the mean arterial pressure was 13 % higher in ESRD patients (P<0.01). Spontaneous BRS was 62% lower (P<0.01) and QTVI was 41% higher in ESRD patients (P<0.01) compared to healthy subjects, respectively. Coefficient of variation (CV) of within-subject reproducibility of BRS and QTVI measurements was moderate (BRS: 33 % for ESRD, 27% for HS; QTVI: 40% for ESRD, 18% for HS). The 95% limit of within-subject reproducibility of BRS measurements was 3.8 ms/mm Hg for ESRD patients and 8.1 ms/mm Hg for healthy subjects; whereas the 95% limit of reproducibility of within-subject reproducibility of QTVI measurements was 0.73 for ESRD patients and 0.55 for healthy subjects. Concordance correlation coefficients of within-subject variability of BRS and QTVI were between 0.74 and 0.83 in both groups. CV of intra- and inter-examiner reproducibility of BRS and QTVI measurements in both groups ranged between 1 and 11%. In conclusion, the intra- and inter-examiner reproducibility/agreement of BRS and QTVI were high, whereas the within-subject reproducibility of these two methods was moderate, in both ESRD patients and healthy subjects. Thus, small differences in BRS and QTVI in longitudinal/interventional studies should be interpreted with caution.

Adult↗
PubMed1979

Effect of cardiotonic polypeptide anthopleurin-A on canine Purkinje and ventricular muscle fibers.

Effects of Anthopleurin-A (AP-A, polypeptide from sea anemone) were studied on electrophysiological properties of isolated canine Purkinje and ventricular muscle fibers. Ap-A (in concentrations above 20 micrograms/l) produced a dose-dependent increase in action potential duration (APD) and the refractory period (RFP) in electrically driven Purkinje fibers, but had no effect on other parameters. Similar but less prominent change in APD and RFP was observed in ventricular muscle fibers. AP-A in high concentrations (200 micrograms/l or higher) did alter the spontaneous firing rate of Purkinje fibers. Since AP-A in low concentrations will increase the refractory period of conducting fibers without affecting a conduction velocity, it may abolish some re-entrant arrhythmias.

Action Potentials↗
PubMed2006

Increased myocardial vulnerability and autonomic nervous system imbalance in obstructive sleep apnea syndrome.

BACKGROUND: Obstructive sleep apnea syndrome (OSAS) is characterized by the repeated episodes of upper airway obstruction during sleep, leading to significant hypoxia. Noninvasive evaluation of autonomic nervous system (ANS) and myocardial vulnerability may help determination of OSAS patients who are under high risk of malignant cardiac arrhythmias. The aim of this study was to show the effects of OSAS on predictors of arrhythmias by the evaluation of heart rate turbulence (HRT), heart rate variability (HRV) and QT dynamicity reflecting the ANS balance and myocardial vulnerability. METHODS: After polysomnographic study, 80 patients with OSAS and 55 age matched OSAS (-) subjects were included in the study. Twenty-four-hour Holter monitoring was performed in all subjects. HRT, HRV and QT dynamicity parameters were calculated. RESULTS: Turbulence slope was significantly decreased in OSAS patients whereas turbulence onset was increased (P<0.001). QT/RR slopes were significantly increased for QT end and QT apex (P<0.001). In HRV analysis, autonomic balance changed in favor of sympathetic system at night in OSAS patients. Furthermore, HRT and QT dynamicity parameters are found to be correlated with Apnea-Hypopnea Index (AHI). CONCLUSION: OSAS is associated with a significant worsening in HRV, HRT, and QT dynamicity parameters. Our results may indicate that HRV and QT dynamicity parameters can be useful noninvasive methods that may detect autonomic nervous system activity and ventricular vulnerability in OSAS.

Aged↗
PubMed1990

Cumulative effects of cycle length on ventricular refractoriness in man.

This study examined the time course of changes of ventricular effective refractory period (VERP) following an abrupt change of cycle length (CL) in man. Stimulation at the right ventricular apex consisted of 19 cycles of an initial CL, followed by a variable number of cycles (0 to 50 cycles) of a new CL, and an extrastimulus to test for VERP. Fifteen patients were enrolled in each part of the study. In part A, initial CLs were long (mean +/- standard error, 650 +/- 20 msec) and new CLs were short (325 +/- 10 msec). VERPs were 259 +/- 6 msec after the long cycles, 238 +/- 6 msec after one short cycle (p less than 0.05), 224 +/- 5 msec after 10 short cycles, and 210 +/- 6 msec after 50 short cycles (p less than 0.05 versus 1 or 10 short cycles). Thus 43% of total shortening of VERP occurred in the first short cycle and 57% occurred in subsequent short cycles. In part B, initial CLs were short and new CLs were long. VERPs were 212 +/- 7 msec after the short cycles, 237 +/- 7 msec after one long cycle (p less than 0.05), 239 +/- 7 msec after 10 long cycles, and 247 +/- 7 msec after 50 long cycles (p less than 0.05 versus 1 or 10 long cycles). Thus 71% of total lengthening of VERP occurred in the first long cycle and 29% occurred in subsequent long cycles. In conclusion, following an abrupt change of CL in man, VERP changes markedly in the first new cycle (immediate effect) and then undergoes further, more gradual change over a large number of subsequent cycles (cumulative effects). Cumulative effects appear to be greater following shortening of CL than following lengthening of CL.

Adult↗
PubMed2004

Modification to the Fontan procedure for the prophylaxis of intra-atrial reentrant tachycardia: short-term results of a prospective randomized blinded trial.

OBJECTIVES: We evaluated the feasibility, safety, and short-term efficacy of an interventional atrial incision placed at the time of the Fontan operation to reduce the development of intra-atrial reentrant tachycardia. METHODS: This prospective randomized blinded trial was conducted in patients with congenital heart disease undergoing an initial lateral tunnel Fontan. Intervention patients underwent a lateral tunnel Fontan with an interventional atrial incision/cryoablation from the atriotomy to the right atrioventricular annulus. Controls underwent a standard lateral tunnel Fontan. Safety of the intervention was monitored. Short-term efficacy was determined by comparisons of conduction block across the incision area and spontaneous or inducible atrial arrhythmias. RESULTS: There were no significant differences between intervention (n = 21, median 2.4 years, range 0.8-3.9) and controls (n = 21, median 2.7 years, range 1.5-13.9) in age, type of heart disease, surgical parameters, or postoperative outcomes. Safety parameters showed no difference between groups in number or severity of adverse events. Short-term efficacy included evidence of conduction block with a longer conduction time across the incision area in intervention patients (median 97 ms, range 35-160) compared with controls (median 40 ms, range 8-77, P =.0001). No intervention patients had spontaneous or inducible intra-atrial reentrant tachycardia versus 2 controls (0/21 versus 2/21, P = NS). CONCLUSIONS: An interventional atrial incision to reduce intra-atrial reentrant tachycardia in the Fontan operation was feasible and safe. The intervention changed the atrial substrate as shown by an increase in conduction time. Short-term results showed a low incidence of intra-atrial reentrant tachycardia in all patients. Longer follow-up is necessary to assess clinical efficacy.

Adolescent↗
PubMed1984

Clinical use and pharmacology of amiodarone.

Amiodarone, an investigational drug in the United States, has had considerable use in this country and worldwide in the treatment of cardiac arrhythmias. This article reviews the clinical pharmacology of this potentially useful antiarrhythmic agent.

Amiodarone↗
PubMed2000

Cardiac autonomic denervation in congestive heart failure: comparison of Chagas' heart disease with other dilated cardiomyopathy.

Congestive heart failure (CHF) is associated with activation of the cardiac sympathetic nerves. However, impairment of the sympathetic nerve terminals in patients with CHF has been indicated by studies showing reduction of cardiac norepinephrine uptake and stores. This investigation studies the histochemical evaluation of the sympathetic nerve terminals in CHF. The cardiac parasympathetic innervation was also studied to address the question of specificity of the presumed sympathetic denervation. Nineteen patients with CHF underwent cardiac transplantation or partial ventriculectomy, which provided the heart tissue. In 11 of them, the dilated cardiomyopathy was associated with Chagas' disease. Inflammatory process and fibrosis were studied histologically. The sympathetic and parasympathetic nerve fibers were visualized through histochemical techniques for, respectively, catecholamines and acetylcholinesterase activity. By using a computer-assisted morphometric program, the inflammation, fibrosis, and parasympathetic innervation were quantified. Moderate to severe fibrosing myocarditis characterized the hearts of the chagasic patients. In cardiomyopathies not associated with Chagas' disease, the inflammation was discrete, if present, but the amount of fibrosis was similar to that found in Chagas' cardiomyopathy. Reduction of both kinds of nerve terminals occurred in the heart of all patients. The parasympathetic denervation was proven to be more severe in chagasic cardiomyopathy. Our data on the heart innervation indicate a progressive autonomic denervation in heart failure. In Chagas' heart disease, the denervation seems to be more severe or rapid, probably because of the sustained inflammatory process.

Acetylcholinesterase↗
PubMed1997

Changes in arrhythmia profile and heart rate variability during abrupt withdrawal of antiepileptic drugs. Implications for sudden death.

Sudden unexpected death (SUD) has been associated with low or undetectable concentrations of antiepileptic drugs in patients with epilepsy suggesting that a sudden fall in plasma levels of these drugs might be a critical factor for the occurrence of SUD. We studied the changes in arrhythmia profile and heart-rate variability, during abrupt withdrawal of carbamazepine and phenytoin treatment in 10 patients with side effects on these drugs. Continuous ECG recording and daily measurements of drug plasma concentrations were performed from the last day of steady-state treatment and the following 4 days. Three patients had a 10-fold increase in ventricular premature beats. In addition, there was a significant reduction in heart-rate variability, assessed over 24 hours, in both the time (SDNN index, P = 0.03) and frequency domains from days 1-5. In the frequency domain analysis there was a significant reduction in total power (P = 0.01), very-low-frequency power (P = 0.004) and in low-frequency (LF) power (P = 0.01). Similar reductions in heart-rate variability and increases in ventricular automaticity have been associated with increased mortality in other patient groups. Two factors that might contribute to the increased rate of SUD in patients with epilepsy have thus been identified.

Adult↗
PubMed2000

QT interval lengthening in cardiac disease relates more to left ventricular systolic dysfunction than to autonomic function.

BACKGROUND: There are multiple influences on the QTc interval, including the autonomic nervous system. Which influence is the principal determinant of the variation in QTc interval between different cardiac diseases is not yet clear, though some studies have suggested that the QTc interval primarily reflects sympatho-vagal balance. This study investigated this claim further. AIM: To determine if autonomic tone was the prime determinant of variation in the QTc interval between subjects with different cardiac diseases. METHODS: Subjects with different cardiac diseases were studied, QTc interval determined and correlated with three different measures of the autonomic nervous system, that of baroreflex sensitivity, catecholamine levels (epinephrine and norepinephrine) and sympatho-vagal balance as determined by power spectrum analysis. RESULTS: 47 subjects were studied, comprising 17 subjects with heart failure, 14 subjects with left ventricular hypertrophy and 16 control subjects. For the group as a whole there was no relationship between QTc interval and any measure of the autonomic nervous system function, but there was a reasonable relationship between fractional shortening and QTc interval (r=0.47, P<0.003). For subjects with an echocardiographic fractional shortenings less than 0.35 (which correlates with an ejection fraction of <50%), a strong relationship between fractional shortening and QTc interval remained (r=0.57, P<0.002), but in addition a relationship between QTc interval and catecholamine levels developed (for epinephrine: r=0.67, P<0.002; and for norepinephrine: r=0.62, P<0.005). Multiple regression analysis showed that fractional shortening and epinephrine levels were independently related to QTc interval. CONCLUSION: In subjects with a variety of cardiac diseases, the prime determinant of QTc interval is left ventricular systolic performance rather than the autonomic nervous system, though in subjects with low normal and less fractional shortenings catecholamine levels are independently related to QTc interval.

Autonomic Nervous System↗
PubMed2006

Decrease in the heart rate complexity prior to the onset of atrial fibrillation.

AIMS: To assess heart rate complexity changes prior to the onset of atrial fibrillation (AF) using sample entropy. It has been proposed that the autonomic nervous system might have a role in the initiation of AF. METHODS AND RESULTS: The study included 25 patients with lone AF. Each record set contained two 30 min records from 25 subjects. Each patient had 30 min records containing the ECG immediately preceding an episode of AF (pre-AF) and 30 min of ECG during a period distant from any episode of AF (AFd). Sample entropy was used for complexity analysis. The sample entropy of R-R intervals was significantly reduced in the pre-AF period compared with the AFd period (0.45+/-0.25 vs. 0.78+/-0.46, P=0.003). The pre-AF periods were divided into three successive 10 min segments. There was a significant decreasing trend in entropy towards the onset of AF with linear mixed models (P=0.002). CONCLUSIONS: The heart rate complexity is reduced with a significant decreasing trend as assessed by R-R interval entropy prior to the onset of AF. There is a need for well-defined studies with larger patient groups in order to assess the entropy changes further and to look for possible changes, which might predict impending AF episodes.

Atrial Fibrillation↗