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PubMed1990

Electrocardiographic abnormalities and left ventricular systolic function in Chagas' heart disease.

In chagasic patients, the electrocardiogram becomes abnormal very late in the course of the disease. Most clinical studies concerning cardiac autonomic function of chagasic patients have been carried out in this very late stage of the disease. The purpose of this study was to assess accurately the left ventricular systolic function of chagasic patients with abnormal electrocardiograms. We performed left ventricular contrast cineangiography in 44 patients with positive complement fixation test for Chagas' disease and abnormal electrocardiograms. On the basis of the electrocardiographic abnormalities found in the electrocardiogram taken the night before the hemodynamic procedure, we divided our patients into three subgroups; those with rhythm disturbances, those with ventricular conduction abnormalities, and those with rhythm disturbances plus ventricular conduction abnormalities. The chagasic patients with only cardiac rhythm disturbances, had left ventricular volumes and ejection fractions which were similar to those of controls. On the other hand, the left ventricular volumes of the chagasic patients with ventricular conduction defects, although slightly larger, were still not different from those of controls. Finally, the chagasic patients, with cardiac rhythm disturbances and left ventricular conduction defects, had the largest left ventricular volumes (P less than 0.05), and the lowest ejection fractions (P less than 0.001) of all three subgroups. These findings clearly indicate that chagasic patients, in this very late stage of the disease, have a very variable degree of left ventricular systolic dysfunction. Furthermore, our results show a distinct tendency for the left ventricular volumes to increase, and for the ejection fraction to decrease; when the electrocardiogram becomes progressively more abnormal, and "mixed" electrocardiographic abnormalities appear.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2005

Evaluation of autonomic activity in patients with subclinical hypothyroidism.

It has been shown that impaired cardiac autonomic activity is closely related with lethal arhythmias. Heart rate variability (HRV), analysis of beat-to-beat variations, is an important and widely used non-invasive method to assess autonomic function. Impaired cardiac autonomic activity and altered sympathovagal balance were previously documented in patients with hypothyroidism. However, the effect of subclinical hypothyroidism (SH) on autonomic function has not been studied yet. We aimed to investigate the effect of SH on sympathovagal balance using the HRV method. The study included 31 patients with SH and 28 healthy volunteer controls. Patients with cardiac, metabolic, neurological disease or any other systemic disease that could affect autonomic activity were excluded from the study. HRV time domain and frequency domain parameters were determined over a period of 24 h. All time and frequency domain measures of HRV in patients with SH were not significantly different compared to those of healthy control group (p > 0.05). Additionally, we compared SH subgroups (TSH level > or =10 and TSH level <10 mU/l) with each other and the controls. A statistically significant difference was observed only in time domain parameters of SD of normal-to-normal intervals (SDNN) and SD of all 5-min mean normal NN intervals (SDANN) between subgroup with TSH level > or =10 and controls (p < 0.05, p < 0.05, respectively). In correlation analysis with TSH, there was positive relationship between TSH and the root mean square of successive differences between adjacent R-R intervals (rMSSD). These findings indicate that SH may affect cardiac autonomic activity in correlation with TSH levels.

Adult↗
PubMed2002

Effects on heart rate variability of metoprolol supplementary to ongoing ACE-inhibitor treatment in Type I diabetic patients with abnormal albuminuria.

AIMS/HYPOTHESIS: Diabetic nephropathy is associated with a high risk of cardiac mortality including sudden death. This is presumably related to an imbalance between sympathetic and parasympathetic tone resulting in a decreased heart rate variability (HRV). In non-diabetic patients a decreased HRV is known to be a strong predictor of cardiovascular death. Studies in non-diabetic patients have shown that beta-blockers improve HRV parameters known to reflect parasympathetic function. The aim of our study was to investigate effects of additional beta-blocker treatment on: cardiac autonomic function, blood pressure, and urine albumin excretion in ACE-inhibitor treated Type I (insulin-dependent) diabetes mellitus patients with abnormal albuminuria. METHODS: We studied the effects of 6 weeks treatment with metoprolol (100 mg once daily, zero order kinetics formulation) in 20 patients participating in a randomised, placebo controlled, double blind, crossover trial. Patients were simultaneously monitored under ambulatory conditions with 24-h Holter-monitoring, 24-h ambulatory blood pressure recording, and 24-h fractionated urine collections. Heart rate variability was assessed by four different methods; ambulatory HRV analysis was carried out by spectral and time domain analysis, and on days of investigation short-term spectral analysis and bed-side tests were carried out. RESULTS: Metoprolol treatment improved in vagal tone assessed by short-term spectral analysis. The 24-h ambulatory HRV analysis showed improvement in some parameters reflecting vagal function. A minor decrease in daytime diastolic blood pressure was shown, no alterations in diurnal variation of blood pressure or urine albumin excretion were observed. CONCLUSION/INTERPRETATION: These preliminary findings indicate that beta-blocker treatment could improve autonomic function in Type I diabetic patients with abnormal albuminuria and an associated high risk of cardiovascular disease.

Adolescent↗
PubMed2006

Relation of heart rate variability to serum levels of C-reactive protein in patients with unstable angina pectoris.

Heart rate variability (HRV) and systemic markers of inflammation have prognostic value in patients with unstable angina pectoris (UAP). However, it is unknown whether any relation exists between HRV parameters and indexes of inflammation in this clinical context. We assessed HRV on 24-hour electrocardiographic Holter recordings, performed within 24 hours of admission, and measured C-reactive protein (CRP) serum levels by a high-sensitivity assay on admission, in 531 patients with UAP (65+/-10 years of age; 347 men) who were enrolled in the prospective multicenter study Stratificazione Prognostica dell'Angina Instabile (SPAI). A significant inverse correlation was found between CRP levels and all HRV parameters, with the highest r coefficient shown with SD of all RR intervals (r= -0.23; p<0.001) in the time domain and with very low-frequency amplitude (r= -0.22; p<0.001) in the frequency domain. When patients were categorized into 4 groups according to CRP quartile levels, statistically significant lower HRV values were observed in the upper CRP quartile. On separate multiple regression analyses, including the most important clinical and laboratory variables, SD of all RR intervals and very low-frequency amplitude were the most significant predictors of increasing CRP levels (p<0.001 for the 2 comparisons). In contrast, in models with SD of all RR intervals and very low-frequency amplitude as dependent variables, CRP was a strong predictor of impaired cardiac autonomic function (p<0.001 for the 2 comparisons). Thus, our data show that, in patients with UAP, high levels of serum CRP levels are significantly associated with decreased HRV, suggesting a possible pathophysiologic link between cardiac autonomic dysfunction and inflammatory activity.

Adult↗
PubMed2006

Heart rate variability and QT dispersion in patients with subclinical hypothyroidism.

UNLABELLED: The effect of subclinical hypothyroidism (SH) on cardiovascular autonomic function and ventricular repolarization has not been yet elucidated. The aim of the present study was to evaluate the dispersion of QT interval, i.e. an index of inhomogeneity of repolarization, and heart rate variability (HRV), i.e. a measure of cardiac autonomic modulation, in SH patients. METHODS: The study included 42 patients (29 women and 13 men; mean age 53.2+/-14.2 years; body surface area 1.76+/-0.14 m2) with SH, as judged by elevated serum TSH levels (>3.6 mIU/l; range, 3.8-12.0) and normal free thyroid hormones (FT4 and FT3) and 30 euthyroid volunteer. Subjects with cardiac, metabolic, neurological disease or any other systemic disease that could affect autonomic activity were excluded from the study. Patients with SH and control subjects underwent a full history, physical examination, standard 12-lead ECG, and 24-h ambulatory ECG monitoring. To evaluate the effect of treatment with L-thyroxine on QT dispersion and HRV, 15 patients with SH were randomly assigned to receive therapy with L-thyroxine. All the subjects were evaluated at enrolment and after 6 months. RESULTS: Patients with SH showed higher QT dispersion and lower HRV measures than healthy controls (P<0.01 for all). In SH patients, the standard deviation of N-Ns (SDNN) was negatively related to TSH (r=-0.42, P=0.006), while low frequency (LF)/high frequency (HF) ratio was positively related to TSH (r=0.42, P=0.006). Moreover, in SH patients both QT dispersion and QTc dispersion were positively related to TSH (r=0.64 and r=0.63, P<0.001 for both). After 6 months, the patients treated with L-tiroxine exhibited a reduction of QT dispersion and an increase of HRV parameters. CONCLUSION: The results of the present study demonstrated that SH can alter autonomic modulation of heart rate and cause increased inhomogeneity of ventricular recovery times. Accordingly, early L-thyroxine treatment may be advised not only to prevent progression to overt hypothyroidism but also to improve abnormal cardiac autonomic function and ventricular repolarization inhomogeneity.

Electrocardiography↗
PubMed1981

Heart rate variability in healthy subjects measured with a bedside computer-based technique.

1. A computer-based technique is described for measuring and analysing cardiac beat-to-beat intervals. 2. The R-R intervals were recorded at rest, during forced deep breathing and during the Valsalva manoeuvre in 174 healthy subjects aged between 16 and 89 years. 3. The mean resting R-R interval was independent of sex, age and smoking habit. The normal range was 654.6-1141.4 ms with a mean value of 864.7 ms. 4. Variation in interval length at rest and during deep breathing depended on age and the mean interval length, whereas the Valsalva ratio depended on age alone. Normal ranges were calculated from regression analysis of these relationships. 5. It is concluded that the technique described can be used to test cardiac autonomic function at the bedside.

Adolescent↗
PubMed2002

Major depression with ischemic heart disease: effects of paroxetine and nortriptyline on long-term heart rate variability measures.

BACKGROUND: Studies have linked depression to sudden death and serious cardiovascular events in patients with preexisting cardiac illness. Recent studies have shown decreased vagal function in cardiac patients with depression and depressed patients without cardiac illness. METHODS: We compared 20-hour, sleeping, and awake heart period variability measures using spectral analysis, fractal dimension, and symbolic dynamics in two patient groups with major depression and ischemic heart disease (mean age 59-60 years) before and after 6 weeks of paroxetine or nortriptyline treatment. RESULTS: Spectral measures showed decreases in awake and sleeping total power (TP: 0.0-0.5 Hz), ultra low frequency power (ULF: 0-0.0033 Hz), very low frequency power (VLF: 0.0033-0.04 Hz), and low-frequency power (LF: 0.04-0.15 Hz) for nortriptyline condition and a decrease in high-frequency power (HF: 0.15-0.5 Hz) for the awake condition in patients who received nortriptyline. A measure of nonlinear complexity, WC-100, significantly increased after paroxetine during the awake condition. CONCLUSIONS: These findings suggest that nortriptyline has stronger vagolytic effects on cardiac autonomic function compared with paroxetine, which is in agreement with previous clinical and preclinical reports. Paroxetine may have some cardio-protective effects, especially in cardiac patients.

Adrenergic Uptake Inhibitors↗
PubMed2003

Outcome of epilepsy surgery correlates with sympathetic modulation and neuroimaging of the heart.

Temporal lobe epilepsy (TLE) is frequently associated with sympathetic over-activity. Single photon emission computed tomography (SPECT) with 123iodine-meta-iodobenzylguanidine (MIBG), a norepinephrine analogue, showed reduced tracer uptake in cardiac sympathetic nerve endings, indicating myocardial catecholamine disturbance. We investigated whether outcome of epilepsy surgery correlates with cardiac autonomic function in TLE patients. We studied 16 TLE patients before and after epilepsy surgery. We recorded heart rate (HR) and determined sympathetic and parasympathetic cardiac modulation as powers of low (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.5 Hz) heart rate oscillations. The LF/HF-ratio was calculated as index of sympathovagal balance. Cardiac MIBG uptake was assessed with MIBG-SPECT and compared to control data. After surgery, eight patients were seizure-free and eight had persistent seizures. Sympathetic LF-power and LF/HF-ratio were higher in patients who had persistent seizures than in patients who became seizure-free. After surgery, both parameters decreased in seizure-free patients but increased in patients with persistent seizures. MIBG uptake was lower in patients than controls and even lower in the patient subgroup who had persistent seizures. In this subgroup, MIBG uptake further decreased after surgery (P<0.05). Sympathetic cardiac modulation decreased in TLE patients after successful surgery, but further increased if seizures persisted. Reduction of cardiac MIBG uptake progressed after surgery in patients with persistent seizures. Interference of epileptogenic discharges with autonomic neuronal transmission might account for sympathetic cardiac over-stimulation and reduced MIBG uptake. Both findings are possible risk factors for sudden unexplained death and might be relevant for risk stratification in epilepsy patients.

3-Iodobenzylguanidine↗
PubMed2006

No apparent effect of surgery for temporal lobe epilepsy on heart rate variability.

BACKGROUND: Impaired cardiac autonomic function may contribute to the risk of sudden unexpected death in epilepsy (SUDEP). Clinical observations indicate that successful epilepsy surgery is associated with a reduced risk of SUDEP. However, in a previous study we found impaired cardiac control pre-surgically in patients with poor outcome of surgery, indicating an a priori lower risk in responders to epilepsy surgery. We have now examined the effect of surgery on cardiac autonomic control in the same patients. METHODS: We used 24 h EKG recordings to assess heart rate variability (HRV) by spectral analysis in 21 consecutive patients after temporal lobe epilepsy surgery. The HRV was compared with healthy controls, with pre-surgical HRV in the same patients, and analyzed in relation to seizure control 1 year after surgery. RESULTS: The patients with poor outcome after surgery had significantly lower SD of RR-intervals, total power, very low frequency power and low frequency power than matched healthy controls. The patients with favorable outcome did not differ from the controls, and the postoperative HRV was not different from HRV before surgery in any of the patient groups. CONCLUSION: We could not demonstrate any effect on HRV of temporal lobe epilepsy surgery in these patients. The observed lower HRV in the poor outcome group was present already before epilepsy surgery as previously reported. Although our results need confirmation in a larger study, the observations suggest that the increased risk of SUDEP in patients failing epilepsy surgery may be due to a common factor predisposing to surgical failure, impaired HRV as well as to an increased risk of SUDEP.

Autonomic Nervous System↗
PubMed2005

Parasympathetic dysfunction in hypertrophic cardiomyopathy assessed by heart rate variability: comparison between short-term and 24-h measurements.

In this study, we evaluate cardiac autonomic function in hypertrophic cardiomyopathy (HCM) by assessing heart rate variability (HRV), comparing a short-term laboratory method with an ambulatory (24-h) method, in patients with and without beta-blockade. Reduced HRV is a risk factor for adverse events in some cardiac diseases, but is not a proven risk indicator in HCM. Analysis of HRV has been based on either short- or long-term electrocardiographic recordings and previous studies in HCM have shown conflicting results. There is no consensus on which method to prefer, and we evaluate, for the first time, both short- and long-term analyses in patients with HCM. Long- and short-term HRV analyses were performed in 43 patients with HCM. They were divided in two groups, 22 patients on beta-blockade and 21 non-treated patients. As controls, 121 healthy subjects were used. Young patients without beta-blockade showed a reduction in HRV parameters reflecting parasympathetic function, both in the short- and long-term registrations, which was attenuated by beta-blockade. Parasympathetic autonomic regulation was found to be impaired in young patients with HCM. This may be of clinical relevance as abnormal autonomic function might be a substrate for malignant dysrhythmias. The impairment was attenuated by beta-blockade, which might indicate a clinically useful effect. We also show that short- and long-term methods yield similar results, suggesting that a short-term registration might be sufficient to assess HRV in patients with HCM.

Adult↗
PubMed2000

Effects of nortriptyline and paroxetine on QT variability in patients with panic disorder.

This study investigated beat-to-beat QT variability in patients with panic disorder before and after treatment with nortriptyline (n = 13) and paroxetine (n = 16), using an automated algorithm to compute QT intervals. An increase in QT variability appears to be associated with symptomatic patients with dilated cardiomyopathy and also with an increased risk for sudden cardiac death. QTvi (QT variability index: a log ratio of QT variance normalized for mean QT over heart rate variability normalized for mean heart rate) was significantly higher in supine posture in patients with panic disorder treated with nortriptyline (P = 0.006) but not paroxetine. Thus paroxetine may be a better drug of choice especially in patients with coexisting cardiac disease. These findings are important especially in view of the recent reports of increased risk for cardiovascular mortality and sudden death in patients with anxiety and depression. QTvi can be a valuable noninvasive measure of temporal repolarization lability, especially to study the side effects of medications which affect cardiac autonomic function.

Adult↗
PubMed1995

Identification of patients with hypertrophic cardiomyopathy at high risk for sudden death.

Patients with hypertrophic cardiomyopathy are at increased risk for sudden death. Recent studies have improved our ability to risk-stratify such patients and have elucidated several potential mechanisms of sudden death and syncope. Certain noninvasive tests, such as signal-averaged electrocardiography and measurements of cardiac autonomic function and QT/QT dispersion, are often abnormal in hypertrophic cardiomyopathy, but are not useful for risk stratification. Myocardial ischemia determined by exercise thallium scintigraphy, however, identifies young patients with hypertrophic cardiomyopathy who are at high risk for cardiac arrest and syncope. Nonsustained ventricular tachycardia on ambulatory Holter monitoring in the absence of symptoms of impaired consciousness is associated with a benign prognosis and is not predictive of sudden death. Conversely, ventricular tachycardia induced at electrophysiologic study identifies adult patients with hypertrophic cardiomyopathy who subsequently experience sudden death. Finally, characterization of the natural history of the genetic defects will increasingly become an integral part of risk evaluation in hypertrophic cardiomyopathy.

Adult↗
PubMedDate not supplied

Cardiovascular autonomic function in healthy adolescents.

OBJECTIVE: The purpose of this study was to determine effects of age, sex, race, body mass index, and Tanner's stage on short-term evoked cardiovascular autonomic tests (ie, Valsalva ratio and change in heart rate with deep breathing) and 24-hour heart rate variability (HRV) in a sample of healthy adolescents, as well as to identify normative indices of both short-term evoked and 24-hour HRV in this age group. DESIGN: A descriptive, correlational design was used. SETTING: Study took place in a university hospital in a health science center located in the mid-South. SUBJECTS: Participants included 75 healthy adolescents: mean age was 15.0 +/- 1.6 years, 14 were African American, 61 were white, 49 were girls, and 26 were boys. OUTCOME MEASURES: Study measures included the Valsalva ratio, change in heart rate with deep breathing, and 24-hour HRV with power spectral analysis with Holter monitoring. RESULTS: Major significant findings included lower values of 24-hour HRV measures for girls and African American adolescents (P <.05). Indices for normal ranges of both the short-term evoked and 24-hour HRV measures were computed with 95% confidence intervals. CONCLUSIONS: Few published studies address cardiac autonomic function, including 24-hour HRV, in adolescents. Most studies reporting actual normative control values of HRV for youth typically have not addressed sex or racial differences. Our study included the largest number of adolescents to date in the reported literature and demonstrated the importance of considering sex and race variation in interpreting test results. The availability of state-of-the-art technology for obtaining HRV data allows for the early identification of subclinical cardiac autonomic changes in youth who have predispositions for cardiac complications, such as those with diabetes, congenital heart disease, or obesity.

Adolescent↗
PubMedDate not supplied

Relationship between retinal ischemia and cardiovascular autonomic damage in diabetes.

In order to investigate the relationship between ischemic diabetic retinopathy and cardiac autonomic dysfunction we studied 40 diabetic patients (mean age +/- SEM: 48 +/- 2 years). Retinopathy was evaluated by fluorescein angiography and patients were divided into three groups: a) with ischemic retinopathy (15 patients), b) with edematous retinopathy (13 patients) and c) without retinopathy (12 patients). Cardiac autonomic function was assessed by 4 tests based on cardiovascular reflexes (heart rate response to Valsalva maneuver and to deep breathing; systolic blood pressure fall after standing and diastolic blood pressure rise during handgrip) and by the cross-correlation test, a computerized technique for the analysis of respiratory sinus arrhythmia based on spectral analysis of electrocardiographic and respiratory signals. Abnormalities of cardiac autonomic tests were present in 26/40 patients (65%); considering the retinal angiographic classification, autonomic test abnormalities were found in 13/15 (86.6%) patients with ischemic retinopathy, in 7/13 (53.9%) patients with edematous retinopathy and in 6/12 (50%) patients without retinopathy. The prevalence of cardiac autonomic dysfunction was significantly higher (p less than 0.005) in the ischemic retinopathy group compared to the other groups. These results show a strong association between ischemic retinopathy and cardiac autonomic dysfunction.

Autonomic Nervous System↗
PubMed2004

Complex demodulation of cardiac interbeat intervals: increased cardiac sympathovagal interaction during human sexual activity.

In this study, we analyzed heart rate variability during sexual activity using complex demodulation, which is a useful technique to study continuous changes in different frequency bands over short periods of time. Complex demodulation has the advantage of having higher time resolution compared to spectral analysis. We quantified the low frequency (LF: 0.04-0.15 Hz) and high frequency (HF: 0.15-0.5 Hz) amplitudes, and the LF/HF ratio before, during, and after the occurrence of orgasm. LF power is dually mediated by cardiac sympathetic and parasympathetic systems while HF power is mainly influenced by cardiac vagal function. We found a significant increase of cardiac sympathovagal interaction (LF/HF ratios) during the phase of orgasm. These findings are discussed in light of normal sexual physiology and the effect of sex on cardiac autonomic function in patients with heart disease, such as myocardial infarction.

Adult↗
PubMed2004

Incremental prognostic implications of brain natriuretic peptide, cardiac sympathetic nerve innervation, and noncardiac disorders in patients with heart failure.

UNLABELLED: Plasma brain natriuretic peptide (BNP) level and cardiac autonomic function are closely related to prognosis in patients with heart failure. However, their correlation and incremental prognostic values in human heart failure are unclear. We sought to evaluate the correlation between BNP level and cardiac sympathetic innervation assessed by (123)I-metaiodobenzylguanidine ((123)I-MIBG) and the prognostic value of combined assessment of risk factors for mortality in patients with heart failure. METHODS: After conventional examinations and measurements of plasma BNP level and heart-to-mediastinum ratio (HMR) of cardiac (123)I-MIBG activity, 158 patients with heart failure were prospectively followed with an endpoint of cardiac death for 16 mo. RESULTS: Fifteen deaths due to pump failure and 2 sudden cardiac deaths were documented. Plasma BNP level correlated with HMR significantly but not so tightly (r = 0.330, P < 0.0001). Univariate analysis identified plasma BNP level, HMR, chronic renal dysfunction, diabetes mellitus, age, and use of nitrates as significant predictors of fatal pump failure, and multivariate Cox analysis showed that plasma BNP level was the most powerful predictor of cardiac death. Patients with both plasma BNP level of > or = 172 pg/mL and late HMR of < or =1.74 had a greater annual rate of fatal pump failure than did those without (17.5%/y vs. 0%-3.9%/y, respectively). The hazard ratio of plasma BNP level (7.2) or cardiac (123)I-MIBG activity (10.1) increased to 34.4 when both variables were used, and prevalence of fatal pump failure significantly increased from 22% to 62.5% when diabetes mellitus and chronic renal dysfunction were present with a higher plasma BNP level and low cardiac (123)I-MIBG activity. CONCLUSION: Plasma BNP level is a stronger predictor than other risk factors for mortality in heart failure patients and is statistically significantly, but roughly, related to cardiac sympathetic nerve innervation. Impaired cardiac sympathetic nerve innervation and the presence of diabetes mellitus and chronic renal dysfunction, however, improve risk stratification of patients with heart failure and increased plasma BNP concentration.

3-Iodobenzylguanidine↗
PubMed1988

Clinical utility of exercise, pacing, and pharmacologic stress testing for the noninvasive determination of myocardial contractility and reserve.

The ability of the left ventricle to modulate its performance is an important and integral component in the cardiovascular system's adaptive response to increased workload. Abnormalities in ventricular contractility can blunt this response and thus significantly limit the patient's functional capacity. The accurate determination and quantitation of cardiac contractility and reserve is a difficult task in the symmetrically contracting ventricle and more so when regional contraction abnormalities are present. Moreover, derangements in other physiologic variables, such as ventricular loading conditions, heart rate, systemic vascular tone, cardiac autonomic function, and pulmonary gas exchange, can diminish cardiopulmonary reserve. This report relates the determinants of myocardial oxygen demand and efficiency to the currently available forms of exercise, pacing, and pharmacologic stress testing. Within this framework, commonly used as well as newer approaches to the noninvasive assessment of stress-induced changes in left ventricular performance and contractility are addressed. In addition, several examples are presented in which noninvasive techniques for assessing intracardiac structures, pressures, and flows (eg, echo/Doppler, radionuclide angiography, rapid acquisition computed tomography, and magnetic resonance imaging) are combined with various cardiovascular stress tests to achieve more reliable measures of myocardial contractility and reserve.

Cardiac Pacing, Artificial↗
PubMed2001

[Present and future of cardiac function tests: electrophysiologic tests].

Various electrocardiographic and physiologic tests have been developing for almost 100 years since Einthoven established the standard 12 lead electrocardiogram(ECG) system. Recently, interest has focused on the new developing parameters associated with cardiac ventricular repolarization, such as transmural dispersion of repolarization, T wave alternans and QT dispersion. QT dispersion, measured as interlead difference of QT interval, has been suggested to reflect regional variation of ventricular repolarization. However, still unsolved basic problems give difficulties for clinical acceptance of this parameter. On the other hand, it is generally accepted that heart rate variability obtained from Holter ECG is useful tool to assess the autonomic tone. Head-up tilt test is a valuable diagnostic tool to identify patients with neurally mediated syncope and also useful for assessment of reflex cardiac autonomic function, such as baroreflex sensitivity. The number of electrophysiologic study(EPS) dramatically increased together with increase of radiofrequency catheter ablation. A new three-dimensional nonfluoroscopic electroanatomical mapping system(CARTO) is an exciting development in catheter ablation treatment. Transtelephonic ECG and its computer-assisted answering system are also useful for diagnose and treatment in the patients of paroxysmal cardiac symptoms.

Action Potentials↗