摘要:

Background Small-scale clinical investigations have demonstrated that single doses of beta -blocking agents can improve left ventricular function in heart failure from idiopathic dilated cardiomyopathy (IDC). The purpose of this multicenter clinical trial was to determine the dose-effect characteristics of beta -blockade in a heart failure population that includes ischemic dilated cardiomyopathy (ISCD).=5 units.Conclusions In heart failure from systolic dysfunction, beta -blockade with bucindolol produces a dose-related improvement in and prevents deterioration of left ventricular function. (Circulation. 1994;89:1632-1642.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background During static exercise in normal subjects, the mean arterial pressure increases as a result of an increase in heart rate and thereby cardiac output with no significant change in stroke volume or systemic vascular resistance. We hypothesized that if one component of the blood pressure response to static exercise, ie, heart rate, were fixed, plasticity of the neural control mechanisms during exercise would allow for preservation of the blood pressure response by alternative mechanisms.Methods and Results Thirteen patients 20 to 68 years old with structurally normal hearts, complete heart block, and dual chamber pacemakers performed static exercise during three conditions: (1) normal dual chamber sensing and pacing mode, (2) heart rate fixed at the resting value obtained in the DDD mode of 78+-4 beats per minute, and (3) heart rate fixed at the peak value obtained during exercise in the DDD mode of 94+-4 beats per minute. Heart rate, blood pressure, and cardiac output were measured and stroke volume and systemic vascular resistance were calculated at rest and at 1 and 5 minutes during static one-leg extension at 20% of maximal voluntary contraction. The mean arterial pressures at rest and at 5 minutes were higher when the heart rate was fixed at the faster peak exercise heart rate. In the DDD mode, heart rate increased by 16 beats per minute and cardiac output by 1.1 L/min, with a resultant 25 mm Hg increase in mean arterial pressure at 5 minutes with no change in the stroke volume or systemic vascular resistance. In both fixed heart rate pacing modes, mean arterial pressure increased by 24 mm Hg when the heart rate was fixed at the resting heart rate and by 25 mm Hg when the heart rate was fixed at the faster peak exercise heart rate pacing modes associated with an increase in stroke volume, with similar increases in cardiac output. During static exercise there was no change in systemic vascular resistance from the resting value in any pacing mode.Conclusions When heart rate is fixed in the presence of normal left ventricular function, the mean arterial pressure increases normally during static exercise because of an increase in stroke volume with no change in the systemic vascular resistance. (Circulation. 1994;89:1643-1647.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Cardiac aging alters many of the acute responses to exercise stress, but the extent to which chronic exercise (ie, training) can alter or improve the effects of aging in humans is largely unknown.Methods and Results Cardiovascular responses to graded supine exercise stress (beginning at 200 kpm and increasing by 200 kpm every 3 minutes till exhaustion) were assessed using radionuclide ventriculography in 13 older (age, 60 to 82 years) and 11 young (age, 24 to 32 years) rigorously screened healthy men before and after 6 months of endurance training. Repeated-measures ANOVA was used to test significance. During exercise, the old group had a lesser increase in heart rate (+105% old versus +166% young), a greater increase in mean blood pressure (+35% old versus +22% young), lesser increases in ejection fraction (+3 ejection fraction units old versus +11 units young) and peak ejection rate (+62% old versus +119% young), a greater increase in end-diastolic volume index (+8% old versus -10% young), a lesser fall in end-systolic volume index (-0% old versus -32% young), and a lesser increase in cardiac index (+135% old versus +189% young) (all P<.01 young/old versus exercise stage). Stroke volume index response to exercise was not different with aging (+14% old versus +6% young, P=NS). Exercise training increased maximal oxygen intake by 21% in the older group (28.9+-4.6 to 35.1+-3.8 mL x kg sup -1 x min sup -1, P<.001) and by 17% in the young (44.5+-5.1 to 52.1+-6.3 mL x kg sup -1 x min sup -1, P<.001) and increased peak workload by 24% in the old and 28% in the young. Exercise training had no differential effects on old versus young men. Among all subjects, training significantly reduced the resting heart rate by 12% (-8 beats per minute) and increased resting end-diastolic volume index by 13% (+9 mL/M2) and resting stroke volume index by 18% (+7 mL/M[2]) (all P<.01). At peak exercise, cardiac index increased by 16% (+1.07 L x M sup -2 x min sup -1) compared with before training, which was the result of an increase in stroke volume of 18% (+7 mL/M2) (P<.001); peak heart rate was unchanged. The increase in stroke volume index at peak exercise was the result of both a 12% increase in end-diastolic volume index (+8 mL/M2) (P<.01) and an increase in ejection fraction (+3 ejection fraction units) (P<.05) at peak exercise. The increased ejection fraction at peak exercise occurred despite a 9% increase in systolic blood pressure (+18 mm Hg) (P<.01), suggesting an increase in contractility. Thus, both the young and old increased peak exercise cardiac output by use of the Frank-Starling mechanism (ie, cardiac dilatation) as well as an increase in ejection fraction.Conclusions We conclude that there is an age-associated decline in heart rate, ejection fraction, and cardiac output responses to supine exercise in healthy men. Although the stroke volume responses of the young and old are similar, the old tend to augment stroke volume during exercise more through cardiac dilatation, with an increase in end-diastolic volume (+8%) but without much change in ejection fraction (+3 ejection fraction units), whereas the young rely more on an increase in the ejection fraction (+11 ejection fraction units) with no cardiac dilatation (-10%). Despite the significant cardiovascular changes that occur in the response to a single bout of exercise with aging, adaptations to chronic exercise training were not different with aging and included improvements in maximal workload and increases in ejection fraction, stroke volume index, and cardiac index at peak exercise. (Circulation. 1994;89:1648-1655.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Signal-averaged ECG is a noninvasive test designed to detect "late potentials." The effects of alterations in autonomic tone on the signal-averaged ECG have not been evaluated systematically.Methods and Results The effects of autonomic stimulation and blockade on the signal-averaged ECG were evaluated in 14 healthy subjects (8 men and 6 women; age, 28.5+-4.8 years) on 2 separate days. The signal-averaged ECG was recorded at baseline and after physiological and pharmacologic beta -adrenergic stimulation (tilt, exercise, and epinephrine and isoproterenol infusions), sequential and combined beta -adrenergic and parasympathetic blockade, and alpha -adrenergic stimulation before and after parasympathetic blockade. Analysis was performed with a bidirectional filter (40-Hz high-pass). Significant changes in the signal-averaged QRS duration from baseline (105.1+-12.0 milliseconds) were noted with tilt (96.8+-8.8 milliseconds), tilt after double blockade (97.5+-9.0 milliseconds), epinephrine (110.5+-11.8 milliseconds), and isoproterenol (99.6+-12.6 milliseconds). Changes in the root-mean-square voltage of the terminal 40 milliseconds and the low-amplitude (<40 microvolts) signal duration paralleled the changes in the QRS duration.Conclusions The signal-averaged ECG does not measure only "fixed" parameters but rather is altered under a variety of physiological and pharmacologic conditions. Upright tilt leads to shortening of the QRS duration before and after autonomic blockade; thus, the decrease in QRS duration with tilt may be related to factors other than changes in autonomic tone. These findings have implications for interpretation of the results of signal-averaged ECG. (Circulation. 1994;89:1656-1664.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Mapping studies in animals have suggested that atrial fibrillation (AF) is based on multiple reentering wavelets. Little information is available about the patterns of activation during AF in humans. The objective of the present study was to reconstruct and classify the patterns of human right atrial (RA) activation during electrically induced AF.Methods and Results AF was induced by rapid atrial pacing in 25 patients with Wolff-Parkinson-White syndrome undergoing surgery for interruption of their accessory pathway(s). The free wall of the RA was mapped using a spoon-shaped electrode containing 244 unipolar electrodes. The activation of the RA during AF showed large interindividual differences. Based on the complexity of atrial activation, three types of AF were defined. In type I (40% of patients), single broad wave fronts propagated uniformly across the RA. Type II (32%) was characterized by one or two nonuniformly conducting wavelets, whereas in type III (28%), activation of the RA was highly fragmented and showed three or more different wavelets that frequently changed their direction of propagation as a result of numerous arcs of functional conduction block. There were significant differences (P<.05) among the three types of AF in median intervals (174+-28, 150+-14, and 136+-16 milliseconds), variation in AF intervals (P sub 5-95) (54+-25, 94+-21, and 104+-22 milliseconds), incidence of electrical inactivity (42+-11%, 21+-4%, and 8+-4%) and reentry (3+-7%, 36+-28%, and 99+-36%), and average conduction velocity during AF (61+-6, 54+-4, and 38+-10 cm/s).Conclusions During pacing-induced AF in humans, the RA is activated by one or multiple wavelets propagating in different directions. Three types of RA activation during AF were identified. From type I to type III, the frequency and irregularity of AF increased, and the incidence of continuous electrical activity and reentry became higher. These various types of AF in humans appear to be characterized by different numbers and dimensions of the intra-atrial reentrant circuits. (Circulation. 1994;89:1665-1680.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background QT interval dispersion, measured as interlead variability of QT, is a marker of dispersion of ventricular repolarization and, hence, of cardiac electrical instability. We tested the hypothesis that dispersion of ventricular repolarization may be differently affected by interventions destined to provide complete or incomplete protection against malignant arrhythmias in patients with long QT syndrome (LQTS). Twenty-eight patients affected by the Romano Ward form of LQTS entered the study and were divided into three groups: LQTS patients before institution of therapy, patients who did respond to beta -blocker therapy, and patients who continued to have syncope and cardiac arrest despite beta -blockade and who underwent left cardiac sympathetic denervation. A group of 15 healthy volunteers served as control subjects.Methods and Results Dispersion of QT and QT sub c were calculated using two indexes: the difference between the longest and the shortest value measured in each of the 12 ECG leads (QTmax-QTmin, QTcmax-QTcmin) and the relative dispersion of QT and QTc(standard deviation of QT/QT average x 100, standard deviation of QTc/QTcaverage x 100). Both indexes of dispersion of repolarization were higher in the LQTS patients than in control subjects; also, patients not responding to beta -blockers had a significantly higher dispersion of repolarization than responders. A cutoff value of 100 milliseconds for QTmax-QTminhad an 80% sensitivity and 82% specificity in discriminating between responders and nonresponders. A cutoff value of 6 for QT relative dispersion yielded similar results. The LQTS patients who did not respond to beta -blockade underwent left cardiac sympathetic denervation and thereafter remained asymptomatic (mean follow-up, 5+-4 years). In this group, dispersion of repolarization was significantly reduced by the surgical denervation to values similar to that of the responders to beta -blockade.Conclusions These data indicate that QT dispersion is a useful clinical tool to predict efficacy of antiadrenergic therapy in LQTS patients. (Circulation. 1994;89:1681-1689.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background The feasibility and efficacy of radiofrequency ablation therapy in idiopathic left ventricular tachycardia has not been assessed in a large group of patients.Methods and Results Twenty consecutive patients with idiopathic left ventricular tachycardia and without structural heart disease underwent electrophysiological study, pharmacological interventions with administration of verapamil and adenosine, and radiofrequency ablation therapy. There were 17 men and 3 women with a mean age of 28+-8 years. The QRS configuration during tachycardia was of right bundle branch block and superior axis in 13 patients, indeterminate axis in 6 patients, and right axis in 1 patient. The tachycardia was electrically inducible and responsive to verapamil but not to adenosine. Thirteen patients demonstrated entrainment. Activation and pace-mapping studies disclosed that the tachycardia originated from the inferior apical septum in 15 patients, the midseptum in 4 patients, and the anterior lateral wall of the left ventricle in 1 patient. Radiofrequency ablation was successful in 17 of the 20 patients (85%). The successful ablation sites were characterized by an endocardial activation time 30 milliseconds earlier than the onset of QRS during tachycardia and by a pace-mapping QRS similar to or closely resembling the tachycardia. All patients displayed sharp spikes preceding the local ventricular electrogram at the ablation site. However, these sharp spikes also were noted in 15 control patients and were not specific for this tachycardia; they persisted after ablation. There were no complications. A follow-up of 7+-8 months in the 17 successfully ablated patients showed no symptomatic tachyarrhythmias without medications. Six patients underwent repeat electrophysiological study, and no induction of tachycardia was revealed.Conclusions Radiofrequency ablation therapy is effective and safe in patients with idiopathic left ventricular tachycardia. It should be considered as the primary therapeutic modality in these patients. (Circulation. 1994;89:1690-1696.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Cardiac conduction is influenced by peptidergic mechanisms as well as classic neurotransmitters. The distribution of peptide-containing nerves has not been well defined.Methods and Results Immunofluorescence and histochemical techniques were used to visualize the innervation of the human conduction system and to distinguish nerve subpopulations according to their peptide and enzyme content. Nerve fibers and fascicles displaying immunoreactivity for protein gene product 9.5 (PGP 9.5) were more numerous in the sinus and atrioventricular nodes than in the penetrating bundle, bundle branches, and adjacent myocardium. The relative density of innervation was greater in the central region of the sinus node than in the peripheral regions. Nerve densities were also higher in the transitional region of the atrioventricular node compared with its compact region. Acetylcholinesterase (AChE)-positive nerves were the main subtype identified in the sinus and atrioventricular nodes, representing half to two thirds of the stained area occupied by PGP 9.5-immunoreactive nerves. Neuropeptide Y-immunoreactive nerves represented the main peptide-containing subpopulation and occurred throughout the conduction system, displaying a similar pattern of distribution and relative density to those demonstrating tyrosine hydroxylase immunoreactivity. Nerve fibers showing immunoreactivity for vasoactive intestinal polypeptide, somatostatin, substance P, or calcitonin gene-related peptide exhibited distinct patterns of distribution and comprised a relatively minor component of the innervation, the percentage of stained area being 10- to 40-fold lower than that occupied by neuropeptide Y- and PGP 9.5-immunoreactive nerves, respectively.Conclusions The innervation of human conduction tissues exhibits significant regional variation and comprises putative parasympathetic nerves and intrinsic neurons (AChE positive), sympathetic efferent nerves (neuropeptide Y- and tyrosine hydroxylase-immunoreactive nerves), and other peptide- containing nerves, some of which (substance P and calcitonin gene-related peptide containing) are considered to represent afferent nerves. Locally released peptides may be involved in the neural modulation of the human conduction system. (Circulation. 1994;89:1697-1708.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background The metabolic changes of myocardial ischemia in patients with coronary artery disease assessed by Phosphorus-31 magnetic resonance spectroscopy (MRS) have been reported previously. A significant decrease in the ratio of phosphocreatine (PCr) to ATP during handgrip exercise in a group of patients with severe coronary artery disease has been demonstrated. However, there are no reports at present that directly compare cardiac Phosphorus-31 MRS data with exercise Thallium-201 myocardial scintigraphy, now established as one of the most important clinical methods to assess myocardial ischemia. The purpose of this study was to investigate whether Phosphorus-31 MRS with handgrip exercise testing is able to detect myocardial ischemia, demonstrated by exercise Thallium-201 scintigraphy.RD(-), 1.24+-0.30; P<.05). The PCr/ATP ratio decreased significantly from 1.60+-0.19 at rest to 0.96+-0.28 during exercise (P<.001) in the RD(+) group (n=15). However, in the RD(-) group (n=12), the ratio did not change significantly during handgrip exercise (1.24+-0.30 at rest versus 1.19+-0.28 during exercise). Similarly, the ratio did not change in the control group (n=11) (1.85+-0.28 at rest versus 1.90+-0.23 during exercise).Conclusions Contrary to normal subjects or patients with fixed thallium defects, the PCr/ATP ratio was significantly altered by exercise in patients with reversible thallium defects. These results suggest that Phosphorus-31 MRS with handgrip exercise testing is a sensitive method for detecting myocardial ischemia. (Circulation. 1994;89:1709-1716.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background It has been suggested that echocardiographically determined left ventricular mass (LVM) is useful in the prediction of hypertension. To examine the relation between LVM and subsequent blood pressure (BP) change, a 6- to 8-year follow-up was conducted in adult Japanese men.Methods and Results LVM was determined by M-mode echocardiography using the American Society of Echocardiography formula among 354 normotensive men aged 30 to 59 years from a rural community (n=193) and from urban companies (n=161) in Japan between 1979 and 1983. BP was remeasured 6 to 8 years after baseline in 148 rural men (77%) and 127 urban men (79%). For men whose BP was remeasured, the mean+-SD LVM index (LVM/body surface area (g/m2)) at baseline was 117+-22 in rural men and 99+-15 in urban men (the difference, P<.001). For both populations, LVM index was positively associated with age and physical activity but not with body mass index. Associations of LVM index with usual alcohol intake and initial BPs were generally weak. According to linear regression analyses after controlling for these covariates at baseline, a 20-g/m2greater LVM index at baseline was associated with a 5 mm Hg increase in systolic and a 4 mm Hg increase in diastolic BP during the subsequent 6 to 8 years for urban men. A 1-mm greater average ventricular wall thickness was associated with a similar BP increase. For rural men, positive associations of LVM index with BP increase existed but were weak. The weaker association between LVM index and BP increase in rural compared with urban men was probably the result of effects of higher physical activity, leading to a larger left ventricular internal dimension. The increase in systolic and diastolic BPs over the 6 to 8 years of observation was significantly related to baseline LVM index in rural and urban men with a smaller internal dimension (rural men, <=49 mm; urban men, <=47 mm) but not in those with larger dimensions.Conclusions An increased LVM index predicts subsequent BP increase in middle-aged normotensive men in the presence of a normal or small internal dimension. (Circulation. 1994; 89:1717-1724.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID