Effect of chronic administration of perhexiline on pacing-induced S-T segment depression in the atherosclerotic rabbit

The effect of chronically administered perhexiline gluconate (a parenteral formulation of Pexid^®) on pacing-induced electrocardiographic S-T segment depression in atherosclerotic rabbits was studied. This model has been shown to be useful in demonstrating antianginal drug activity in the experimental animal. In this single-blind study the effects of intraperitoneal injections of perhexiline gluconate were compared with injections of equal volumes of normal saline solution. Either the active preparation or saline was injected daily for 8 days. The perhexiline-treated animals had significantly less S-T segment depression at each of three pacing rates when compared to the saline-treated animals. These results indicate that non-nitrate antianginal agents can prevent S-T segment depression in this model.     

Significance of Electrocardiographic Changes in Hypertension

Studies in 17 hypertensive patients showed that the electrocardiographic features of T-wave inversion and S–T segment depression distinguish those patients with higher systolic blood pressures. They do not indicate impaired cardiac function.     

Effects of intense exercise training on plasma catecholamines in coronary patients

This paper reports the effect of 12 mo of intense endurance exercise training on the plasma catecholamine response to exercise in 11 male patients [aged 50 +/- 8 yr (mean +/- SD)] with coronary artery disease. A substantial adaptation to training was attained as evidenced by a 42% increase in maximum O2 uptake capacity. At rest, heart rate was lower after training, but resting blood pressure and plasma catecholamines were unchanged. At the same absolute work rate, plasma norepinephrine and epinephrine levels, rate pressure product, and ischemic S-T segment depression were all significantly lower after training. A higher plasma norepinephrine level was attained at maximal exercise after training (2,049 +/- 654 before vs. 3,408 +/- 1,454 pg/ml after, P less than 0.025); this was associated with a higher systolic blood pressure (175 +/- 25 before vs. 188 +/- 22 mmHg after, P less than 0.025) and a higher rate-pressure product (25.3 X 10(3) +/- 4.5 X 10(3) before vs. 27.6 X 10(3) +/- 5.2 X 10(3) after, P less than 0.025). Despite the higher plasma norepinephrine level and rate pressure product, S-T segment depression at maximal exercise was unchanged. These findings suggest that some patients with coronary arterial disease can attain a higher myocardial O2 requirement, without electrocardiographic evidence of increased ischemia, after prolonged strenuous exercise training.     

Increasing step width reduces the requirements for subtalar joint moments and powers

The subtalar joint (STJ) contributes to the absorption and generation of mechanical energy (and power) during walking to maintain frontal plane stability. Previous observational studies have suggested that there may be a relationship between step width and STJ supination moment. This study directly tests the hypothesis that walking with a step width greater than preferred would reduce STJ moments, energy absorption, and power generation requirements, while increasing energy absorption at the hip during initial contact. Participants (n = 12, 7 females) were asked to walk on an instrumented treadmill at a constant velocity and cadence at a range of fixed step widths ranging from 0.1 to 0.4 times leg length (L). Walking at step widths greater than preferred (0.149 ± 0.04 L) reduced peak STJ moments at initial contact and propulsion which subsequently reduced the negative and positive work performed at the STJ. There was a 43% reduction in energy absorption (negative work) and approximately 30% decrease in positive work at the STJ as step width increased from 0.1 L to 0.4 L. An increase in energy absorption at the knee and hip was evident with an increase in step width during initial contact, although minimal mechanical changes were observed at the proximal joints during propulsion. These results suggest an increase in step width reduces the forces generated by muscles at the STJ across stance and is therefore likely to be beneficial in the prevention and treatment of their injuries. In terms of rehabilitation, the increase in mechanical costs occurring due to an increase in energy absorption by the hip and knee is of minimal concern.     

Cardiac electric field on the epicardial and body surfaces during the period of depolarization and repolarization of ventricular myocardium in pikes

Body surface and ventricular epicardial potential distributions during the electrocardiographic QRST interval were studied in pikes with the aid of potential mapping. The earliest epicardial activation was observed at the posterior base near the atrioventricular orifice. The areas of the earliest repolarization were found at the apex and the posterior base, whereas the area of the latest repolarization was detected at the anterior base. In the initial period of the QRS, the minimum was developed in the middle third of the right lateral body surface, and the maximum in the middle third of the ventral body surface. The body surface potential distribution during the ST-Twas characterized by the clear-cut negative potential zone in the cranial ventral area with the rest of the body surface having positive potentials, a pattern being largely unchanged throughout the period of the T-wave. The ventricular epicardial repolarization sequence differed from the activation sequence. The ventricular epicardial depolarization and repolarization sequences as well as epicardial potential distributions are expressed in the cardiac electric field on the body surface during the QRS and ST-T complexes.     

The University of Manitoba Follow-up Study. A Prospective Investigation of Cardiovascular Disease: Part II. Build,Blood Pressure and Electrocardiographic Factors Possibly Associated with the Development of Coronary Heart Disease

The relationship of selected physical and electrocardiographic factors to the occurrence of coronary heart disease was examined in a cohort of 3983 healthy North American males followed up for 15 years. Variations in build or mean heart rate were not found to be related to the occurrence of coronary heart disease. The risk of coronary heart disease rose progressively as blood pressure increased. With readings of 160/95 mm. Hg or higher the risk was 1.77 times that of the population as a whole. Non-specific S-T and/or T wave changes in the electrocardiogram were associated with three times the risk of developing coronary heart disease. Individuals with the combination of a blood pressure of 160/95 mm. Hg and nonspecific T wave changes exhibited an augmented susceptibility to coronary heart disease, the risk being four times that of the whole population.     

Cardiac Abnormalities in Poisoning with Tricyclic Antidepressants

Of 80 consecutive admissions to a general hospital for drug overdose, 10 had taken one or other of the tricyclic antidepressants. All 10 had abnormalities of cardiac conduction as shown by prolonged Q–T_e intervals, and eight had S–T segment and T-wave changes. Five of the 10 patients had arrhythmias and two of these died. Continuous electrocardiographic monitoring is recommended in patients with overdosage of tricyclic antidepressants.     

Effect of acute exercise stress in cardiac hypertrophy: I. correlation of regional blood flow and qualitative ultrastructural changes.

Ultrastructural myocardial cell changes were determined in eight miniswine after the development of pressure-overload hypertrophy induced by supra-valvular aortic constriction. Four miniswine served as control animals. Regional myocardial blood flows were measured at rest and during exercise stress with radioactive microspheres after two days and one month of aortic constriction. Exercise stress, causing the heart rate to increase to 85 percent of its maximum, was imposed twice weekly for 7 minutes on four pressure-overloaded animals and the four control animals to elicit differences between the control and experimental groups that might not occur at rest. After one month of pressure overload the swine were killed and myocardial samples were processed for electron microscopy. Ultrastructural changes similar to those in hypertrophied hearts were present throughout the left ventricular walls of the pressure-overloaded animals. Other changes consistent with ischemic injury were present in the subendocardial regions of pressure-overloaded animals subjected to exercise stress. These changes included disorganization of myofibrils, disintegration and broadening of Z-bands, swelling and aggregation of mitochondria, electron-dense deposits in mitochondria, decreased cristal density and vacuolization of mitochondria, intracellular edema, margination and clumping of nuclear chromatin, and a decrease of glycogen granules. Regional ischemia in the subendocardium of these animals was confirmed by functional studies which showed decreased regional myocardial blood flow to the subendocardium during exercise and S-T segment elevation for the first 2-10 days after inducing pressure overload. The ischemia, as shown by flow studies, during exercise stress persisted in the compensatory stage of hypertrophy although S-T segments returned to normal. Thus, the combined effect of pressure overload and exercise stress can produce focal subendocardial ischemia in the compensated, hypertrophied heart.     

Alterations in the rat electrocardiogram induced by stationary magnetic fields

A field strength dependent increase in the amplitude of the T-wave signal in the rat electrocardiogram (ECG) was observed during exposure to homogeneous, stationary magnetic fields. For 24 adult Sprague-Dawley and Buffalo rats of both sexes, the T-wave amplitude was found to increase by an average of 408% in a 2.0 Tesla (1 Tesla = 10⁴ Gauss) field. No significant magnetically induced changes were observed in other components of the ECG record, including the P wave and the QRS complex. The minimum field level at which augmentation of the T wave could be detected was 0.3 Tesla. The magnetically induced increase in T-wave amplitude occurred instantaneously, and was immediately reversible after exposure to fields as high as 2.0 Tesla. No abnormalities in any component of the ECG record, including the T wave, were noted during a period of 3 weeks following cessation of a continuous 5-h exposure of rats to a 1.5-Tesla field. The heart rate and breathing rate of adult rats were not altered during, or subsequent to, application of fields up to 2.0 Tesla. The effect of animal orientation within the field was tested using juvenile rats 3–14 days old. The maximum increase in T-wave amplitude was observed when subjects were placed with the long axis of the body perpendicular to the lines of magnetic induction. These experimental observations, as well as theoretical considerations, suggest that augmentation of the signal amplitude in the T-wave segment of the ECG may result from a superimposed electrical potential generated by aortic blood flow in the presence of a stationary magnetic field.     

Changes in the T-wave vector loop of the three-dimensional vectorcardiogram during exposure to cold pressor stress

Three-dimensional vectorcardiography was used to characterize changes in the T-wave vector loop during exposure to cold pressor stress. Data were collected from 8 subjects during baseline, cold pressor, and recovery periods. Maximum vector length, polar angle of the longest vector, azimuth angle of the longest vector, sum of all vectors, polar angle of the vector sum, azimuth angle of the vector sum, surface area of the loop, and maximum distance between adjacent vectors were computed from the T-wave vector loop. The amplitude of the one-dimensional T-wave (TWA) was also computed. Interbeat interval and TWA decreased during hand immersion and increased during recovery. Of the vectorcardiographic measures, only maximum vector length and vector sum showed statistically significant change; both decreased during the task and returned to baseline during recovery. TWA accounted for 46% of the task related variance compared to 53% and 47% respectively, for vector sum and maximum vector length. Changes in TWA probably reflect a true change in cardiac electrical potential rather than a change in T-wave vector loop shape or orientation.     

多态T 波区间检测技术的研究

目的:利用小波变换进行T波区间的检测。方法:在23尺度上通过模极大值法定位R波。在24尺度上首先根据R峰以及T波起点和终点的经验值确定起始T波区间。然后对每个心拍在此区间上找到T波的模极大值,根据模极值的个数和正负顺序确定T波波形的形态。由于不同形态的T波对应不同的T波起点和终点的检测方法,实现T波区间的分类检测,提高T波检测的精确度。由于本文算法是作为T波交替检测的前期工作,为了验证算法的准确率,采用了QT数据库中的部分记录进行了仿真,评价实验结果。结果:仿真实验证明了本文算法能正确地分辨出每个T波的形态,并在此基础上得到较为准确的T波区间。结论:本文采用模极大值算法根据T波的不同形态进行T波区间的分类检测,检测结果比较理想,且计算简单,较易实现。     

A training whole-heart model for simulating propagation and ECG patterns

The forward problem of electrocardiography describes the spatio-temporal source–field relationship generating the body surface potential (BSP) and, thus, the electrocardiogram (ECG). The paper presents a ventricular and atrial model for simulating cardiac de- and repolarization and the P-, QRS- and T-wave. The atria and the ventricles are coupled, so that electroanatomical function can be simulated at ones. Movement and contraction are not taken into account while an individual geometry, fibre architecture and ECG sensor arrangement including the Wilson central terminal (WCT) as common reference were considered. This in silico whole-heart model can be used for detailed investigations of the nature of the ECG for the normal beat, arrhythmias, ischemia and infarction. In addition, this model was used as a reference tool for developing and testing different electrocardiographic inverse approaches.     

Multiscale Complexity Analysis of the Cardiac Control Identifies Asymptomatic and Symptomatic Patients in Long QT Syndrome Type 1

The study assesses complexity of the cardiac control directed to the sinus node and to ventricles in long QT syndrome type 1 (LQT1) patients with KCNQ1-A341V mutation. Complexity was assessed via refined multiscale entropy (RMSE) computed over the beat-to-beat variability series of heart period (HP) and QT interval. HP and QT interval were approximated respectively as the temporal distance between two consecutive R-wave peaks and between the R-wave apex and T-wave end. Both measures were automatically taken from 24-hour electrocardiographic Holter traces recorded during daily activities in non mutation carriers (NMCs, n = 14) and mutation carriers (MCs, n = 34) belonging to a South African LQT1 founder population. The MC group was divided into asymptomatic (ASYMP, n = 11) and symptomatic (SYMP, n = 23) patients according to the symptom severity. Analyses were carried out during daytime (DAY, from 2PM to 6PM) and nighttime (NIGHT, from 12PM to 4AM) off and on beta-adrenergic blockade (BBoff and BBon). We found that the complexity of the HP variability at short time scale was under vagal control, being significantly increased during NIGHT and BBon both in ASYMP and SYMP groups, while the complexity of both HP and QT variability at long time scales was under sympathetic control, being smaller during NIGHT and BBon in SYMP subjects. Complexity indexes at long time scales in ASYMP individuals were smaller than those in SYMP ones regardless of therapy (i.e. BBoff or BBon), thus suggesting that a reduced complexity of the sympathetic regulation is protective in ASYMP individuals. RMSE analysis of HP and QT interval variability derived from routine 24-hour electrocardiographic Holter recordings might provide additional insights into the physiology of the cardiac control and might be fruitfully exploited to improve risk stratification in LQT1 population.     

Tracking cardiac electrical instability by computing interlead heterogeneity of T-wave morphology.

Oscillations in T-wave morphology, particularly T-wave alternans (TWA), have been fundamentally linked to increased susceptibility to ventricular fibrillation (VF). We investigated whether the escalation in complexity of T-wave oscillations before VF is attributable to increased spatial heterogeneity of repolarization. Peak interlead T-wave heterogeneity (TWH) was measured by second central moment analysis of T-wave morphology in epicardial electrograms in dogs during left anterior descending coronary artery occlusion. TWH differentiated cases in which myocardial ischemia provoked VF from those without VF (563 +/- 56 vs. 139 +/- 36 microV, P < 0.01). In the former group, progressive, significant increases in TWH above preocclusion baseline (70 +/- 8 microV) began at 2.25 min after the start of occlusion and were associated successively with TWA (at 155 +/- 19 microV), T-wave multupling (at 386 +/- 100 microV), complex oscillatory T-wave forms (at 560 +/- 76 microV), discordant TWA (at 572 +/- 98 microV), and VF at 4.36 +/- 0.14 min. TWH in precordial ECGs in 12 pigs during angioplasty-balloon-induced myocardial ischemia also discriminated animals that experienced VF (from 90 +/- 14 at baseline to 382 +/- 39 microV, P < 0.05) from those without VF (from 96 +/- 17 at baseline to 199 +/- 61 microV, NS). Ischemia-induced changes in ST segment and T-wave amplitude did not predict VF. Heightened spatial heterogeneity of repolarization, as assessed by second central moment analysis of TWH, underlies TWA and increased risk for ischemia-induced VF. Monitoring spatial TWH from precordial leads could prove useful in stratifying risk for life-threatening arrhythmias.     

T-wave Oversensing with Inappropriate Therapy in Remote Monitoring

T-wave oversensing can cause inappropriate implantable cardioverter-defibrillator (ICD) therapies that are difficult to correct. Remote monitoring allows follow-up of ICD patients without visiting the hospital and can help in early detection of any malfunctions. We describe the case of a patient who experienced inappropriate antitachycardia pacing therapy due to T-wave oversensing; the problem was promptly detected by remote monitoring and corrected by device reprogramming.     

Standard deviations and correlations of GC levels in DNA sequences

In a DNA sequence that exhibits long-range correlations, standard deviations among the GC levels of its segments can be up to an order of magnitude higher than in a sequence consisting of independent, identically distributed nucleotides. Conversely, plots of inter-segment standard deviations vs. segment length reveal quantitative information about the correlations present in a sequence. We present and discuss formulae that relate long-range (power-law) correlations between the nucleotides of a sequence to the expected standard deviations of the GC levels of its segments, and to the correlations between them.     

Changes in theT-wave vector loop of the three-dimensional vectorcardiogram during exposure to cold pressor stress

Three-dimensional vectorcardiography was used to characterize changes in the T-wave vector loop during exposure to cold pressor stress. Data were collected from 8 subjects during baseline, cold pressor, and recovery periods. Maximum vector length, polar angle of the longest vector, azimuth angle of the longest vector, sum of all vectors, polar angle of the vector sum, azimuth angle of the vector sum, surface area of the loop, and maximum distance between adjacent vectors were computed from the T-wave vector loop. The amplitude of the one-dimensional T-wave (TWA) was also computed. Interbeat interval and TWA decreased during hand immersion and increased during recovery. Of the vectorcardiographic measures, only maximum vector length and vector sum showed statistically significant change; both decreased during the task and returned to baseline during recovery. TWA accounted for 46% of the task related variance compared to 53% and 47% respectively, for vector sum and maximum vector length. Changes in TWA probably reflect a true change in cardiac electrical potential rather than a change in T-wave vector loop shape or orientation.This material was presented in part at the annual meeting of the Association for Applied Psychophysiology and Biofeedback, Washington, D.C., March 1990.We are indebted to Lawrence E. Widman, M.D., Ph.D. for his invaluable advice throughout this study.     

Evidence for the Partial Dominance of Viability Genes Contributing to Inbreeding Depression in Mimulus Guttatus

The relative importance of different modes of gene expression of viability genes contributing to inbreeding depression was investigated in the wild plant, Mimulus guttatus. Viability genes were identified by self-fertilizing 31 outbred plants, each heterozygous for three to nine unlinked allozyme markers, and analyzing segregation ratios of selfed progeny at maturity for deviations from 1:2:1 ratios. In this study, 24 linkages of viability genes to marker loci were detected. To infer the nature of gene action for these viability genes, a ``model-free' graphical method was developed that examines the ``space' of segregation ratios allowed by each of seven selection models (i.e., overdominance, complete recessivity, partial recessivity, additivity, partial dominance, complete dominance and underdominance). Using this method, we found that, of 24 linkages detected, 18 were consistent with either partial dominance, complete dominance or underdominance. Six were consistent with either partial recessivity, complete recessivity or overdominance. This finding indicates that, in these chromosomal segments identified by allozyme markers, partial dominance plays the predominant role in inbreeding depression. This is inconsistent with either the dominance or overdominance hypotheses proposed to account for inbreeding depression.     

Interaction between cigarettes and propranolol in treatment of angina pectoris.

To determine whether cigarette smoking interferes with the medical management of angina pectoris, 10 patients with angina pectoris who smoked at least 10 cigarettes a day were studied before, during, and after a standardised maximal exercise test. This was done at the end of four randomly allocated one-week treatment periods during which the patients took glyceryl trinitrate while not smoking, took glyceryl trinitrate while smoking, took glycerly trinitrate and propranolol (380 mg/day) while not smoking, and took glyceryl trinitrate and propranolol while smoking. Carboxyhaemoglobin was measured to ensure compliance. Smoking was associated with a significantly higher heart rate, blood pressure, number of positions with ST-segment depression, and total ST-segment depression after exercise than non-smoking (p < 0.01) whether or not the patients were taking propranolol. These results suggest that smoking aggravates the simple haemodynamic variables used to assess myocardial oxygen requirements and the exercise-induced precordial electrocardiographic signs of myocardial ischaemia. These effects were still evident after treatment with propranolol and represent a hindrance to the effective medical treatment of angina pectoris.     

Effect of sulfamethoxazole-trimethoprim and sulfadoxine-primethamine against fatal pneumocystosis in SCID mice.

The effect of sulfamethoxazole-trimethoprim (S-T) and sulfadoxine-primethamine (S-P) against Pneumocystis carinii (Pc) were examined in severe combined immunodeficiency (SCID) mice which are known to be susceptible to Pc. These animals develop fatal pneumocystosis without treatment with any immunosuppressant. The results suggested that S-T and S-P were effective against both trophic and cystic forms of Pc in SCID mice.