Repolarization Parameters Research Articles

Electrocardiographic Findings in Patients with Polycythemia Vera

The 12-lead surface electrocardiogram (ECG) is a useful tool to predict both atrial and ventricular arrhythmias via P-wave and QT measurements and its derivatives. Polycythemia vera (PV) is a chronic myeloproliferative disorder associated with cardiovascular events. The aim of this study was to assess ECG findings of patients with PV. Sixty patients with PV (34 male, mean age 58±11 years) and 60 age and gender-matched healthy volunteers were enrolled into the study. From the 12-lead surface ECG, P-wave and both conventional QT measurements and transmyocardial repolarization parameters (T(peak)-T(end) interval (T(p)-T(e)) and derivatives) were evaluated digitally by two experienced cardiologists. In addition, a novel parameter, Pi was calculated digitally as the standard deviation of the P-wave duration across the 12 ECG leads. QT duration and corrected QT interval were significantly longer in the PV group compared to healthy controls (p<0.01 and p<0.01, respectively). The T(p)-T(e) was longer and the T(p)-T(e)/QT ratio was significantly higher in the PV group compared to the controls. P-wave analyses showed that all P-wave parameters including Pmax, Pmin, P dispersion, and Pi were significantly prolonged in PV patients compared to the controls. The increase of both T(p)-T(e )and P max in the PV group was independent of age, BMI, diabetes and hypertension, gender, systolic blood pressure, hemoglobin, hematocrit, left atrial dimension, left ventricular end-diastolic diameter and early deceleration time in a univariate analysis of co-variance model (F=11.097, p=0.001 and F=31.537, p=0.0001, respectively). The present study demonstrated that PV may be associated with electrocardiographic abnormalities of both atrium and ventricle.

Abstract 17364: Abnormal Repolarizations in Electrocardiogram Correlate with Abnormal Diastolic Mechanics in Patients with Hypertrophic Cardiomyopathy

Introduction: HCM is often characterized by marked repolarization abnormalities. However the significance of repolarization changes in these patients has not been investigated. Aim: We investigated the prevalence and significance of ECG repolarization patterns on sensitive measures of systolic and diastolic function in a cohort of 110 patients (mean age 52± 17 yrs, male 65%, Caucasian 73%) with HCM. Method: We performed echocardiography and ECG evaluation in 110 HCM patients. ECG repolarization parameters including strain pattern, early repolarization pattern, ST elevation, ST depression and T wave inversion were measured. Conventional and longitudinal tissue Doppler- derived tissue velocity and strain were analyzed off-line. Result: The mean left ventricular mass index was 141± 48 g/m, 2 LVEF was 69± 10% and left ventricular outflow tract gradient was 27±29 mmHg. ECG analysis revealed mean QTc of 451± 34 ms; 45/110 had strain pattern, 17/110 had early repolarization pattern and 14/110 had deeply inverted T waves. Patients with strain pattern on ECG, demonstrated decreased early diastolic velocity (lateral: -3.7± 2.2 vs. -4.6± 2.3 cm/s, p= 0.044, anterior: -2.6± 1.5 vs. -3.4± 1.4 cm/s, p= 0.04 and inferior:-2.7± 1.4 vs. -3.9± 1.6 cm/s, p= 0.005 regions), and late diastolic velocity (lateral:-1.2+- 0.76 vs -2.3+- 1.6, p= 0.001, anterior: -1.6+- 0.7, -2.7+- 1.3, p= 0.0006 and inferior: -2.7+- 1.8 vs -4.1 +- 1.7, p= 0.0003) in the corresponding regional myocardium, when compared to HCM patients without strain pattern. Patients who exhibited deeply inverted T waves on ECG exhibited decrease in late diastolic strain rate in the corresponding regional myocardium (lateral: 0.44± 0.32 vs. 0.84±0.48 s -1 , p= 0.001 and anterior: 0.56±0.19 vs. 1.0± 0.56 s -1 , p= 0.005), when compared to HCM patients without this finding. In contrast, early diastolic strain rate was increased in the corresponding regional myocardium (lateral: 1.75± 0.6 vs. 1.1± 0.62 s -1 , p= 0.015 and anterior: 1.17± 0.3 vs. 0.87± 0.5 s -1 , p= 0.01) in patients with evidence of early repolarization on ECG, when compared to patients without this feature. Conclusion: Strain pattern and deeply inverted T waves are markers for abnormal diastolic mechanics in patients with hypertrophic cardiomyopathy.

Immediate ozone effects on heart rate and repolarisation parameters in potentially susceptible individuals

ObjectivesElevated ozone levels have been associated with cardiovascular morbidity and mortality. We investigated the effects of ozone on heart rate (HR) and repolarisation parameters in potentially susceptible populations.MethodsBetween March 2007...

QT Dispersion is Not Increased in Familial Mediterranean Fever

Familial Mediterranean fever (FMF) is an autoimmune disease inherited as an autosomal recessive trait and is characterized by recurrent attacks of fever and sterile polyserositis. This study examined electrocardiographic ventricular repolarization parameters (QT interval and QT dispersion) in 38 FMF patients and 35 healthy controls. The QT interval was measured manually from the onset of QRS to the end of the T wave (return to the TP baseline). QT dispersion was defined as the difference between the maximum and minimum QT values, and corrected QT was calculated according to the Bazett formula. There were no significant differences between FMF patients and healthy control subjects in any parameter of ventricular repolarization; hence QT dispersion was not affected by FMF. Electrocardiographic assessment of QT interval and QT dispersion are, therefore, of little value for the evaluation of cardiac impairment and risk of arrhythmia in FMF patients.

High-intensity interval training program improves body composition, exercise capacity and metabolic profile better than moderate-intensity continuous exercise in MetS patients with similar effects on ventricular repolarisation parameters

High-intensity interval training program improves body composition, exercise capacity and metabolic profile better than moderate-intensity continuous exercise in MetS patients with similar effects on ventricular repolarisation parameters

Transseptal Left Ventricular Endocardial Pacing Reduces Dispersion of Ventricular Repolarization

Cardiac resynchronization therapy (CRT) may be proarrhythmic in some patients. This may be due to the effect of left ventricular (LV) epicardial pacing on ventricular repolarization. The purpose of this study was to evaluate the effect of endocardial versus epicardial LV biventricular pacing on surface electrocardiogram (ECG) parameters that are known markers of arrhythmogenic repolarization. ECG markers of repolarization (QT dispersion, QTD; T peak to end, T(peak-end) ; T(peak-end) dispersion, T(peak-end) D; QTc) were retrospectively measured before and after CRT in seven patients with transseptal LV endocardial leads (TS group), 28 matched patients with coronary sinus (CS) LV leads (CS group), and eight patients with surgical LV epicardial leads (SUR group). All ECGs were scanned and analyzed using digital callipers. Compared to the CS group, the TS group CRT was associated with a significant postpacing reduction in QTD (-45.2 ± 35.6 vs -4.3 ± 43.6 ms, P = 0.03) and T(peak-end) (-24.2 ± 22.1 vs 3.4 ± 26.7 ms, P = 0.02). There was a nonsignificant post-CRT reduction in both T(peak-end) D (-11.3 ± 31.0 vs 2.4 ± 28.9 ms, P = 0.27) and QTc (-50.0 ± 46.4 vs 4.4 ± 70.2 ms, P = 0.06) in the TS versus the CS group. In contrast, there were no differences between the SUR and CS groups in terms of the effect of CRT on these repolarization parameters. CRT with (atrial transseptal) endocardial LV lead placement is associated with repolarization characteristics that are considered to be less arrhythmogenic than those generated by CS (epicardial) LV lead placement. Further work is needed to determine whether these changes translate to a reduction in proarrhythmia.

QT dispersion in amyloidosis due to familial Mediterranean fever

Cardiac amyloid deposition in FMF may cause increased QT dispersion (QTd), a marker for cardiac arrhythmias. The aim of this study was to further evaluate repolarization dispersion in familial Mediterranean fever (FMF) with amyloidosis. Findings on 12-lead electrocardiography were compared between 18 patients with FMF-amyloidosis and 18 age- and sex-matched control subjects. Repolarization and dispersion parameters were computed with designated computer software, and results of the 5 beats were subsequently averaged. There were no statistically significant differences between the groups as to average corrected QT interval length, average QTd interval, average QT corrected dispersion, or QT dispersion ratio. JT dispersion and JT corrected dispersion were also similar in both groups. In conclusion, patients with FMF-amyloidosis seem to have QT and JT dispersion parameters similar to those of healthy subjects. Future research and longer follow-ups should be conducted in order to evaluate the prognostic importance of repolarization dispersion parameters in amyloidosis of FMF.

Antiarrhythmic Effect of Cardiac Resynchronization Therapy with Triple-Site Biventricular Stimulation

The antiarrhythmic effect of triple-site biventricular stimulation (Tri-V) is poorly understood. This study aims to evaluate the effect of cardiac resynchronization therapy (CRT) on ventricular arrhythmia (VA) with Tri-V using a single right ven- tricular (RV) and double left ventricular (LV) lead. Methods and results Over a period of 3.5 years, 58 consecutive patients with New York Heart Association class II-IV heart failure, an LV ejection fraction of ≤0.35, and a QRS interval of ≥120 ms were enrolled. Acute haemodynamic responses to dual- site biventricular stimulation (Bi-V) and Tri-V were evaluated by assigning patients to a Bi-V or Tri-V group. Electrocar- diogram parameters (QT interval, JT interval, and transmural dispersion of repolarization (TDR)) were measured over time after CRT. Spontaneous VA detected by telemetry was reviewed and confirmed. During a mean follow-up of 481 days after implantation, VA occurred in 2 of 22 patients in the Tri-V group and 14 of 36 patients in Bi-V group. Triple-site biventricular stimulation was thus associated with a decreased VA risk (P ¼ 0.044). Multivariate Cox analysis showed that Tri-V pacing prevented arrhythmic events as compared with Bi-V pacing (hazard ratio, 0.13; 95% confidence interval, 0.029-0.610;P ¼ 0.009). Ventricular repolarization indices at 6 months were significantly shortened in Tri-V compared with Bi-V (QTc, 223.6 vs. 214.1%,P ¼ 0.008; JTc, 221.4 vs. 27.7%,P ¼ 0.005; TDRc, 239.9 vs. 217.0%,P , 0.001). Conclusion Compared with Bi-V, Tri-V reduced VA during long-term follow-up. Improvements in repolarization parameters may

The Effect of Air Pollution on Spatial Dispersion of Myocardial Repolarization in Healthy Human Volunteers

We tested the hypothesis that exposure to concentrated ambient particles (CAP) and/or ozone (O(3)) would increase dispersion of ventricular repolarization. Elevated levels of air pollution are associated with cardiac arrhythmias through mechanisms yet to be elucidated. Each of 25 volunteers (18 to 50 years of age) had four 2-h exposures to 150 μg/m(3) CAP; 120 parts per billion O(3); CAP + O(3); and filtered air (FA). Exposure-induced changes (Δ = 5-min epochs at end-start) in spatial dispersion of repolarization were determined from continuous 12-lead electrocardiographic recording. Spatial dispersion of repolarization assessed by corrected ΔT-wave peak to T-wave end interval increased significantly for CAP + O(3) (0.17 ± 0.03, p < 0.0001) exposure only, remaining significant when factoring FA (CAP + O(3) - FA) as control (0.11 ± 0.04, p = 0.013). The influence on repolarization was further verified by a significant increase in ΔQT dispersion (for CAP + O(3) compared with FA (5.7 ± 1.4, p = 0.0002). When the low-frequency to high-frequency ratio of heart rate variability (a conventional representation of sympathetic-parasympathetic balances) was included as a covariate, the effect estimate was positive for both corrected ΔT-wave peak to T-wave end interval (p = 0.002) and ΔQT dispersion (p = 0.038). When the high-frequency component (parasympathetic heart rate modulation) was included as a covariate with corrected ΔT-wave peak to T-wave end interval, the effect estimate for high frequency was inverse (p = 0.02). CAP + O(3) exposure alters dispersion of ventricular repolarization in part by increasing sympathetic and decreasing parasympathetic heart rate modulation. Detection of changes in repolarization parameters, even in this small cohort of healthy individuals, suggests an underappreciated role for air pollutants in urban arrhythmogenesis.

Using electrocardiographic morphology features to estimate action potential triangulation changes

The dissociation between a drug-induced increase of the QT interval prolongation and an increased risk for ventricular arrhythmias has been suggested by academic investigators and regulatory agencies. Yet, there are no alternative or complimentary electrocardiographic (ECG) techniques available for assessing the cardiotoxicity of novel compounds. In this study, we investigated a set of novel ECG parameters quantifying the morphology of the T-loop. In a group of healthy individuals exposed to sotalol, we compared their drug-induced changes to the drug-induced prolongations of the QTc, QTc apex and T-peak to T-end intervals.We implemented a set of parameters describing the morphology of the T loop in its preferential plane. These parameters measure the time interval needed for the heart vector amplitude to change from its maximum value to a time when its amplitude has been reduced by 30%, 50%, and 70%. These measurements are called early repolarization duration (ERD) when they are located before the T-wave apex and late repolarization duration (LRD) when measured after the apex. They depend on both the speed of the repolarization process and the morphology of the T loop. Thirty-nine healthy individuals were exposed to sotalol in a crossover-design study. Sixteen ECGs were recorded per day during 3 days. The first day (day 0) was baseline; a single dose of sotalol (160 mg) was given during day 1, and a double dose was given during day 2 (320 mg). The plasma concentration of the drug was measured just before the ECG recordings.The values of all investigated parameters revealed a dose-dependent effect of sotalol (in average between parameters, ρ = 0.9, P < .001). Our investigations described profound and statistically significant changes in the morphology of the vectorial T loop for day 1 (peak effect of sotalol: ΔERD50% = 23 ± 6 msec, P < .05; ΔLRD50% = 8 ± 3 msec, P = .05) and day 2 (peak effect of sotalol: ΔERD50% = 51 ± 14 msec, P < .05; ΔLRD50% = 20 ± 12 msec, P = .05). When investigating the timing of peak drug concentration and peak effect of the drug on the various repolarization parameters, we found asynchrony between ERDs/LRDs (≥3.5 hours after dosing) and QTc/QTc apex profiles (<3.5 hours after dosing), suggesting that the time of maximum prolongation on the repolarization process was not synchronized with the time of maximum drug-induced heterogeneity of repolarization.This study describes the sotalol-induced changes of the T-loop morphology in healthy individuals based on novel vectocardiographic parameters. These observations might help in improving the next generation of ECG markers for the evaluation of drug cardiotoxicity.

Electrocardiographic image of myocardial ischemia: Real measurements and biophysical models

The peculiarities of the genesis of electrocardiosignal under myocardial ischemia in connection with an increase of its electrical inhomogeneity, as well as the electrophysiological mechanisms of morphological changes of the T wave of the electrocardiogram, including its "symmetrization" have been considered. A systemic approach to the problem has been used, which combines the mathematical, computer, and physiological modeling of the cardiac electrical activity with studies of the electric field of the human heart in terms of biophysical models. A database for the repolarization parameters of experimental electrocardiosignals ("Norm" and "Ischemia" samples) has been formed. The parameters of the ST-T interval and T wave, which could characterize the symmetry of the latter, and some additional properties of the repolarization process have been obtained. The methods of mathematical modeling were used also. Computer experiments were carried out on a system for 3-D modeling of the cardiac electrical activity at different structural levels of the object. By the results of preliminary analysis, the betaT index, which is calculated as the ratio of two maximum absolute values of the derivative of the cardiosignal at the left and right of the T wave apex, has been chosen as one of the main diagnostic markers of ischemia. There is reason to believe that the use of the betaT index allows one to recognize those deviations from the norm that are usually hidden from a physician in traditional ECG analysis. The ratios of repolarization intervals inside of the generalized QT interval have also appeared potentially informative. With the purpose to test and correct the hypotheses for conducting further investigations, some preliminary experiments on a low-resolution model for several alternatives of the degree, localization, and extensiveness of ischemia have been carried out. The results obtained at the first stage of the team-work are essential to the understanding of mechanisms of the genesis of an electrocardiographic image for myocardial ischemia and of interest for the biophysically sound development of new algorithms for computer cardiodiagnostics.

Altered Cardiac Repolarization in Association with Air Pollution and Air Temperature among Myocardial Infarction Survivors

BackgroundEpidemiological studies have shown that ambient particulate matter (PM) and changes in air temperature are associated with increased cardiopulmonary events.ObjectiveWe hypothesized that patients with previous myocardial infarction (MI) experience changes in heart rate (HR) and repolarization parameters, such as Bazett-corrected QT interval (QTc), and T-wave amplitude (Tamp), in association with increases in air pollution and temperature changes.MethodsBetween May 2003 and February 2004, 67 MI survivors from the Augsburg KORA-MI registry repeatedly sent 16 sec electrocardiograms (ECGs) with a personal transmitter (Viapac) via telephone to the Philips Monitoring Center, where ECG parameters were immediately analyzed. Meteorological data and air pollutants were acquired from fixed monitoring sites on an hourly basis. Additive mixed models were used for analysis. Effect modification by patient characteristics was investigated.ResultsThe analysis of the 1,745 ECGs revealed an increased HR associated with interquartile range (IQR) increases in PM levels among participants not using beta-adrenergic receptor blockers and among those with body mass index ≥ 30 kg/m2. We observed a 24- to 47-hr lagged QTc prolongation [0.5% change (95% confidence interval, 0.0–1.0%)] in association with IQR increases in levels of PM ≤ 2.5 μm in aerodynamic diameter, especially in patients with one [0.6% (0.1–1.0%)] or two [1.2% (0.4–2.1%)] minor alleles of the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2) single-nucleotide polymorphism rs2364725. Positive immediate (0–23 hr) and inverse delayed (48–71 hr up to 96–119 hr) associations were evident between PM and Tamp. We detected an inverse U-shaped association between temperature and Tamp, with a maximum Tamp at 5°C.ConclusionsIncreased air pollution levels and temperature changes may lead to changes in HR and repolarization parameters that may be precursors of cardiac problems.

Fragmented QRS is associated with torsades de pointes in patients with acquired long QT syndrome

Acquired long QT syndrome (LQTS) is a disease due to a secondary repolarization abnormality induced by various predisposing factors. In contrast to congenital LQTS, risk factors that produce acquired LQTS include organic heart diseases that often exhibit depolarization abnormality. Although various repolarization parameters have been evaluated in acquired LQTS, the existence of depolarization abnormality in association with torsades de pointes (TdP) has not been reported. The purpose of this study was to evaluate both repolarization (QT components) and depolarization parameters (fragmented QRS [fQRS]) in acquired LQTS patients with markedly prolonged QT interval. Seventy patients with acquired severe QT prolongation (QTc ≥ 550 ms) were studied. Thirty-two patients had syncope or TdP (syncope group). Thirty-eight patients did not have any symptoms (asymptomatic group). The existence of fQRS and QT components (QT, QTc, Tpe [interval between peak and end of T wave] intervals, and U-wave voltage) was analyzed. The syncope group had more frequent fQRS (81%) than did the asymptomatic group (21%, P < .01) and the incidence of fQRS was not different before and after removal of predisposing factors. The incidence of organic heart disease was not different between the two groups. No differences in QTc interval were noted between the syncope and asymptomatic groups, although the syncope group had longer QT and Tpe intervals and higher U wave than the asymptomatic group (P < .01). Acquired predisposing factors promoted repolarization abnormality (especially prolongation of QT and Tpe intervals), and the existence of fQRS had an important role in the development of TdP in patients with acquired LQTS.

Prediction of cardiovascular death and myocardial infarction by the QRS-T angle and T vector loop morphology after angioplasty in stable angina pectoris: an 8-year follow-up

Reliable cardiovascular (CV) risk assessment by a noninvasive tool would be of great value for CV event prevention. The present study consists of 187 coronary artery disease patients with 8 years of follow-up. Eight vectorcardiographic parameters characterizing different aspects of ventricular repolarization were analyzed at baseline: (1) the ST-segment (ST-VM), (2) the T vector angles (QRS-T angle, Televation, and Tazimuth), (3) the T vector loop morphology (Tavplan and Teigenvalue), and (4) Tarea and Tpeak-end. Cardiovascular death, myocardial infarction (MI), and repeated revascularization were traced via national registries. There were 16 CV deaths and 19 MIs; 89 patients remained free from CV events and revascularization. Ventricular repolarization parameters independently predicted CV death (widened QRS-T angle) and new MI (increased Tavplan) during follow-up. CV mortality was associated with increased divergence between depolarization and repolarization waves (widened QRS-T angle). Increased Tavplan, presumably reflecting heterogeneous repolarization, predicted future MI, which is a novel finding.

Spontaneous variability and reactive postural beat-to-beat changes of integral ECG body surface potential maps.

There is virtually no information on spontaneous variability of ECG body surface potential maps (BSPMs) and on dynamics of their reactive changes in healthy subjects. This study evaluated quantitatively the depolarization (QRS) and repolarization (QRST) parameters derived from the respective integral BSPMs, constructed beat-to-beat, from continual body surface ECG records in 9 healthy men resting supine, during head-up tilting and sitting. Spontaneous variability of the BSPMs parameters, both at rest and during postural reactions, was characterized by significant respiratory and low frequency oscillations, more pronounced when related to repolarization. Head-up tilting and sitting-up evoked significant decrease in the QRST-BSPM amplitudes, widening of the angle alpha and reduction of nondipolarity indexes, compared to the respective supine values. All these changes were gradual, characterized by transition phenomena and prolonged after-effects. Tilting back to horizontal restored the resting supine values. The postural effects on depolarization were individually more variable and in the average showed a minimal QRS-BSPM amplitude increase. Beat-to-beat analysis of a train of ECG BSPMs provided the first evidence of spontaneous, non-random, respiratory and low frequency oscillations of the ventricular repolarization pattern, and the first insight into the dynamics of body posture associated changes in ventricular recovery.

QT dispersion in uncomplicated familial Mediterranean fever

The aim of the study was to further evaluate repolarization dispersion in familial Mediterranean fever (FMF). Findings on 12-lead electrocardiography were compared with 32 patients with uncomplicated FMF and age- and sex-matched control subjects. All procedures followed stringent standards. Repolarization and dispersion parameters were computed with designated computer software, and results of the five beats were subsequently averaged. There were no statistically significant differences between the groups in average QT and average corrected QT interval length, average QT interval dispersion, average QT corrected dispersion, or QT dispersion ratio. During 6 months of follow-up, no cases of sudden death or arrhythmia were documented in either group. Patients with FMF who are continuously treated with low-dose colchicine and have not developed amyloidosis seem to have QT dispersion parameters similar to those of healthy subjects and therefore apparently have no increased risk of adverse cardiac events associated with abnormal repolarization.

Evaluation of the sesquiterpene (−)-α-bisabolol as a novel peripheral nervous blocker

Essential oils are natural, complex and multi-component systems composed mainly of terpenes in addition to some other non-terpenes compounds that are widely used to prevent and treat human diseases. (−)-α-Bisabolol is an unsaturated monocyclic sesquiterpene alcohol found as the major constituent of many essential oils, like the German chamomile ( Chamomilla recutita (L.) Rauschert), a plant reported to reduce the perception of acute pain and used for centuries for their medicinal properties. Recently, our group demonstrated the antinociceptive-like effect promoted by other terpenes could be associated with the decreased peripheral nerve excitability. Therefore, this study investigated the pharmacological activities of (−)-α-bisabolol on mice peripheral nervous system observing the changes on the compound action potential (CAP) characteristics. Using modified single sucrose-gap method in mice sciatic nerves, we acquired CAP recordings in the absence and presence of (−)-α-bisabolol (0.5, 1, 5 and 10 mM). We observed that this sesquiterpene was able to reduce the neuronal excitability in a concentration-dependent manner, although, such effects were not reversed when the nerve was submitted to wash out. Assessing CAP parameters of depolarization and repolarization, we noticed similarities between (−)-α-bisabolol and lidocaine but not with 4-aminopyridine that are considered good blockers for sodium and potassium voltage-gated channels, respectively. Additionally, we also characterized the non-use-dependent profile of (−)-α-bisabolol action, in contrast to lidocaine. Thus, we suggested that decreased nervous excitability elicited by (−)-α-bisabolol might be caused by an irreversible blockade of voltage-dependent sodium channels.

Long-Term Exercise-Training Improves QT Dispersion in the Metabolic Syndrome

Increased QT dispersion (QTd) is a marker of myocardial electrical instability and predicts ventricular arrhythmias and sudden cardiac death. Exercise training (ET) has been shown to reduce both QTd and cardiovascular mortality in various populations. Patients with metabolic syndrome (MS) have been shown to have increased QTd. The effect of ET on QTd in MS patients however is unknown. We sought to assess the effect of a long-term (> or = 6 months) ET program on QTd parameters in MS patients with and without coronary heart disease (CHD). Fifteen CHD and 31 non-CHD patients with MS (mean age, 64 +/- 7 and 57 +/- 9 years, respectively) were identified at entry into identical ET programs. MS was defined using modified National Cholesterol Education Program criteria. A control group consisted of 8 MS patients with CHD (mean age, 65 +/- 6 years). Ventricular repolarization (QT dispersion = QTd, standard deviation of QT = SDQT, relative dispersion of QT = RDQT, QT corrected dispersion = QTcd), metabolic and exercise parameters were measured before and after ET. Program duration was over 9 months (312 +/- 100 versus 284 +/- 101 days in CHD and non-CHD cohorts, P = NS). QTd decreased in both ET groups (QTd pre versus post = 66 versus 56 ms in CHD group, P < 0.01; 58 versus 51 ms in non-CHD group, P < or = 0.01). Other ventricular repolarization parameters also improved significantly in both MS groups following ET, but remained unchanged in the control group. A long-term ET program improves QTd in patients with MS with and without CHD.

In Vitro Cardiac Repolarization Assays: Guinea Pig Papillary Muscles Vs. Canine Purkinje Fibers

Delayed or accelerated cardiac repolarization is potentially proarrhythmic. In this study, we compared a guinea pig papillary muscle APD (GPPM-APD) assay to a canine Purkinje fiber APD (CPF-APD) assay in assessing drug effects on cardiac repolarization. Papillary muscles (right ventricle) and Purkinje fibers were stimulated at 0.5 Hz, action potentials were recorded using microelectrode techniques, repolarization assessed using APD30, 50, 90 values, and the calculated triangulation parameter, APD30-90. Eight compounds (6 positives, 2 negatives) were tested in both preparations. Percent changes in APD90 values obtained with the GPPM-APD assay were less than those obtained in the CPF-APD assay (table). Repolarization parameters in the GPPM-APD assay exhibited a rank sensitivity order of APD30 < APD50 ≈ APD90 < APD30-90 in detecting effects of the five hERG blockers on repolarization. APD90 was the most sensitive parameter in detecting effects of the hERG activator (A-935142.0). These results suggest the GPPM-APD assay and the CPF-APD assay are valuable in assessing drug effects on cardiac repolarization with comparable effects in both assays.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Spontaneous variability and reactive postural beat-to-beat changes of integral ECG body surface potential maps

There is virtually no information on spontaneous variability of ECG body surface potential maps (BSPMs) and on dynamics of their reactive changes in healthy subjects. This study evaluated quantitatively the depolarization (QRS) and repolarization (QRST) parameters derived from the respective integral BSPMs, constructed beat-to-beat, from continual body surface ECG records in 9 healthy men resting supine, during head-up tilting and sitting. Spontaneous variability of the BSPMs parameters, both at rest and during postural reactions, was characterized by significant respiratory and low frequency oscillations, more pronounced when related to repolarization. Head-up tilting and sitting-up evoked significant decrease in the QRST-BSPM amplitudes, widening of the angle α and reduction of nondipolarity indexes, compared to the respective supine values. All these changes were gradual, characterized by transition phenomena and prolonged after-effects. Tilting back to horizontal restored the resting supine values. The postural effects on depolarization were individually more variable and in the average showed a minimal QRS-BSPM amplitude increase. Beat-to-beat analysis of a train of ECG BSPMs provided the first evidence of spontaneous, non-random, respiratory and low frequency oscillations of the ventricular repolarization pattern, and the first insight into the dynamics of body posture associated changes in ventricular recovery.