摘要:

BackgroundAlthough neurostimulation has been shown to be of benefit in angina pectoris, the exact mechanism of its action is not clear. This study was performed to examine the effect of transcutaneous electrical nerve stimulation on coronary blood flow.Methods and ResultsThe effect of transcutaneous electrical nerve stimulation was studied in 34 syndrome X patients (group 1), 15 coronary artery disease patients (group 2), and 16 heart transplant patients (group 3). Coronary blood flow velocity (CBFV) in the left coronary system was measured at rest and after a 5-minute stimulation period with a Judkins Doppler. There was a significant increase in the resting CBFV in group 1 (from 6.8±4.1 to 10.5±5.7 cm/s,P< .001) and group 2 (from 6.8±4.1 to 10.5±5.7 cm/s,P< .001). However, there was no significant change in the resting CBFV in group 3. There were no significant changes in the coronary arterial diameters as a result of neurostimulation. There was a significant decrease in the epinephrine levels in group 1 (from 79.6±17.8 to 58.5±17.5 ng/L,P= .01) and group 2 (from 102.2±27.2 to 64.1 ± 19.1 ng/L,P= .01).ConclusionsTranscutaneous electrical nerve stimulation can increase resting coronary blood flow velocity. The findings suggest that the site of action is at the microcirculatory level and that the effects may be mediated by neural mechanisms.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundA cohort of 2181 men and women, aged 40 to 79 years, without evidence of coronary heart disease or cancer at entry to the Tecumseh Study was evaluated.Methods and ResultsSubjects were defined as lean if their Metropolitan Life Insurance table relative weight was <110 (n=584) and as obese if their relative weight was ≥120 (n= 1024). There were 688 subjects with hypertension at study entry (systolic blood pressure >160, diastolic blood pressure >95, or treated). The 29-year relative risk (RR) of mortality from ischemic heart disease (IHD) or cardiovascular disease (CVD) associated with systolic blood pressure level was significant for both lean and obese subjects. Among hypertensive subjects, the RR of fatal IHD for lean versus obese hypertensive subjects was 1.87 (95% confidence interval, 1.21 to 2.88) and the RR of fatal CVD was 1.56 (95% confidence interval, 1.10 to 2.20) using a Cox proportional-hazards model to adjust for the independent effects of age and traditional CVD risk factors. The findings are consistent with other studies in men showing lean hypertensive subjects to be at greater risk of IHD or CVD mortality than obese hypertensive subjects. A similar finding is now observed in women.ConclusionsAssociations do not prove causality or dictate management. Nevertheless, the unexplained higher mortality in lean versus obese hypertensive subjects has now been reported with sufficient frequency to suggest that the association is real (if unexplained). Determining the reasons for this association may improve targeted prevention and treatment strategies.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundIntravascular ultrasound (IVUS) of arteries is limited by the inability of current instruments to visualize beyond the catheter tip. We have developed a prototype 4-mm-diameter forward-viewing IVUS catheter (Cardiovascular Imaging Systems, Sunnyvale, Calif) that has the ability to provide B-mode cross-sectional ultrasound data for a distance of up to 2 cm distal to the catheter tip.Methods and ResultsTo study the utility of this device, a 20-MHz forward-viewing IVUS catheter was used to examine 13 arterial segments (5 human femoral arteries, 1 human carotid artery, 7 canine arteries) in vitro and 1 phantom. After imaging, all data were compared with histology (Histo). In all cases, the IVUS catheter provided forward-viewing images corresponding to the arterial geometry and demonstrated vascular landmarks and atherosclerotic lesions. There was a good correlation between Histo-determined luminal diameters (LD) and IVUS-determined diameters for a distance of 14 mm ahead of the catheter tip: IVUS LD= 1.0 Histo LD+ 1.3 (r= .87).ConclusionsThese preliminary data suggest that a forward- viewing IVUS catheter is feasible, accurate, and useful for evaluation of arterial geometry distal to the catheter tip.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundCurrent intravascular ultrasound (IVUS) catheters provide transverse imaging at the level of the ultrasound transducer. This limits imaging to large-diameter segments without critical atherosclerotic narrowings. We have developed a prototype 20-MHz forward-viewing IVUS catheter that provides two-dimensional sector imaging distal to the catheter tip. A present limitation of this technique is that the catheter must be manually rotated to obtain multiple longitudinal views required to integrate the segment into a three-dimensional matrix. To overcome this, we have developed an algorithm that reconstructs these multiple two-dimensional forward-viewing IVUS images into a three-dimensional matrix for more complete depiction of the segment distal to the ultrasound catheter. This algorithm allows display and multidimensional slicing of the three-dimensional reconstruction.Methods and ResultsTo test our algorithms, five arterial segments (three canine aortas, two human femoral arteries) were evaluated in vitro. In each segment, 36 forward-viewing longitudinal slices were collected, digitized, processed, and reoriented to produce a three-dimensional reconstruction (3DR) matrix. The matrix data were sliced into parallel transverse sections and compared with morphometric interpretation of histological sections (Histo). As a result, image data could be reconstructed for a distance of 2.0 cm ahead of the catheter. 3DR easily demonstrated wall and luminal morphology and provided transverse IVUS images comparable to the histological specimens. A good correlation was noted between Histo- and 3DR-determined luminal diameters (LD) and luminal areas: 3DR LD=1.4 Histo LD−0.4,r= .86; 3DR LD=0.7±0.20 cm (mean±SD); and Histo LD=0.7±0.13 cm.ConclusionsThese preliminary data demonstrate the feasibility of 3DR of forward-viewing IVUS data. This method allows rapid, detailed analysis of diseased arterial segments previously unavailable with standard IVUS and may permit better targeting of interventional techniques.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundAlthough structural heart disease is often present in patients with nonrheumatic atrial fibrillation, the echocardiographic precursors of atrial fibrillation have not been reported previously. In this elderly, population-based cohort, our objective was to examine prospectively the echocardiographic predictors of nonrheumatic atrial fibrillation.Methods and ResultsSubjects in the Framingham Heart Study were routinely evaluated with M-mode echocardiography; 1924 subjects, ranging in age from 59 to 90 years, comprised the population at risk. Cox proportional hazards modeling was used to analyze the association of selected echocardiographic features with atrial fibrillation risk after adjustment for age, sex, hypertension, coronary heart disease, congestive heart failure, diabetes, and valvular heart disease. During a mean follow-up interval of 7.2 years, 154 subjects (8.0%) developed atrial fibrillation. Multivariable stepwise analysis identified left atrial size (hazard ratio [HR] per 5-mm increment, 1.39; 95% confidence interval [CI], 1.14 to 1.68), left ventricular fractional shortening (HR per 5% decrement, 1.34; 95% CI, 1.08 to 1.66), and sum of septal and left ventricular posterior wall thicknesses (HR per 4-mm increment, 1.28; 95% CI, 1.03 to 1.60) as independent echocardiographic predictors of atrial fibrillation. For each of the echocardiographic predictors, risk increased progressively over successive quartiles. Moreover, risk increased markedly when highest-risk-quartile measurements for these features were present in combination; the cumulative 8-year age-adjusted atrial fibrillation rates were 7.3% and 17.0%, respectively, when one and two or more highest-risk-quartile features were present, compared with 3.7% when none was present.ConclusionsIn this elderly, population-based sample, left atrial enlargement, increased left ventricular wall thickness, and reduced left ventricular fractional shortening were predictive of risk for nonrheumatic atrial fibrillation. These echocardiographic precursors offer prognostic information beyond that provided by traditional clinical atrial fibrillation risk factors.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundIntraoperative epicardial coronary Doppler ultrasound has the potential to provide anatomic and functional information. This technique has been hindered by the large size of standard transducers, but a miniature transducer is available that may fulfill the potential of coronary ultrasound.Methods and ResultsTwenty consecutive patients who were undergoing coronary artery bypass grafting were studied and compared with 9 control patients with normal coronary arteries who were undergoing routine mitral valve surgery. A miniature 6.5-MHz transducer was used to image coronary arteries and measure coronary blood flow velocities. Seventeen proximal left anterior descending and 3 right coronary artery stenoses were studied. As defined by coronary angiography (1 to 34 days before surgery), there were 13 severe stenoses (>70%), 4 moderate stenoses (40% to 70%), 2 minor stenoses (<40%), and 1 subtotal occlusion. Stenoses were readily identified by ultrasound. Color flow mapping demonstrated laminar flow in normal arteries and nonlaminar flow across moderate and severe stenoses. In the control patients with unobstructed arteries, peak and mean diastolic velocities were 35±2.1 and 26±1.9 cm/s with peak and mean systolic velocities of 16± 1.4 and 11±0.8 cm/s, respectively. Prestenotic flow velocities were not significantly different from normal control values, but a wide range of poststenotic flow disturbances were detected. Analysis of the 20 study patients did not reveal significant differences in poststenotic compared with prestenotic flow. A subgroup analysis of 12 patients with severe left anterior descending coronary artery stenoses was performed, and reversed poststenotic systolic flow was seen in 9. Prestenotic peak and mean systolic velocities were 16.5 ± 1.7 and 11.9±1.1 cm/s, respectively, and were significantly altered downstream of the stenoses at −22.7±17.2 and −15.9±10.9 cm/s (P< .05 andP< .01, respectively). Reversed systolic flow was seen only distal to severe left anterior descending coronary artery stenoses and did not correlate with retrograde collateral filling as determined by preoperative coronary angiography. Moderate stenoses appeared to increase both systolic and diastolic components of poststenotic flow.ConclusionsEpicardial Doppler ultrasound with a miniature transducer identifies coronary stenoses and associated blood flow disturbances. Compared with moderate lesions, severe stenoses demonstrated different poststenotic flow patterns. Intraoperative use of this technique may determine the hemodynamic significance of coronary stenoses.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundMyocardial tissue tagging with the use of magnetic resonance imaging allows noninvasive regional analysis of heart wall motion and deformation. However, any evaluation of the effect of disease or treatment requires a baseline reference of normal values and variation. We studied the two-dimensional motion of material points imaged within the left ventricular wall using spatial modulation of magnetization (SPAMM) in 12 normal human volunteers.Methods and ResultsFive parallel short-axis and five parallel long-axis slices were acquired at five times during systole. SPAMM tags were generated at end diastole using a 7-mm grid. Intersection point data were analyzed for displacement, rotation, and torsion, and triangles of points were analyzed for local rotation and principal strains. Short-axis displacement was the least in the septum for all longitudinal levels (P< .001). Torsion about the long axis was uniform circumferentially because of the motion of the centroids used to reference the rotation. In the long-axis images, the base displaced longitudinally toward the apex, with the posterior wall moving farther than the anterior wall (13.4±2.2 versus 9.7±1.8 mm,P< .001) in this direction. The largest principal strain (maximum lengthening) was approximately radially oriented in both views. In the short-axis images, the minimum principal strain (maximum shortening) increased in magnitude toward the apex (P< .001) with little circumferential variation, except at midventricle, where the anterior wall showed greater contraction than the posterior wall (−0.21±0.03 versus −0.19±0.02,P< .02).ConclusionsConsistent regional variations in deformation are seen in the normal human heart. Displacement and maximum shortening strains are well characterized with twodimensional magnetic resonance tagging; however, higherresolution images will be required to study transmural variations.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundThe aim of this study was to compare the results of dipyridamole-echocardiography test (DET: twodimensional echo monitoring during dipyridamole infusion up to 0.84 mg/kg over a period of 10 minutes) with both anatomic and physiological parameters of coronary artery disease severity, assessed by computer-assisted quantitative coronary arteriography, and regional coronary flow reserve, measured by [13N]ammonia (13NH3) and dynamic positron emission tomography (PET), respectively.Methods and ResultsWe studied 31 patients with a history of chest pain and neither previous myocardial infarction nor resting wall motion abnormalities. Eighteen patients had single- vessel disease (>50% stenosis of one major coronary vessel), and 13 had normal coronary arteries. The criterion for DET positivity was the appearance of a new transient regional wall motion abnormality. In patients with a positive DET, two parameters were evaluated: the dipyridamole time (ie, the time from the beginning of drug infusion to the development of obvious dyssynergy) and the wall motion score index WMSI, a semiquantitative integrated estimation of extent and severity of the stress-induced dyssynergy). WMSI was derived by summation of individual segment scores divided by the number of segments interpreted. Quantification of regional myocardial blood flow was obtained by PET measurements of13NTH3arterial input function and left ventricular myocardial tissue concentration both at control and after dipyridamole 0.56 mg/kg over 4 minutes). Maximal regional blood flow after dipyridamole in the region supplied by the stenotic vessel was significantly lower in the 11 patients with coronary artery disease and positive DET than in the 7 patients with coronary artery disease and negative DET (1.08±0.33 versus 1.98±0.37 mL ·min−1· g−1,P< .01). In patients with a positive DET, regional coronary flow reserve correlated well with dipyridamole time (r= .87,P< .01) but not with peak WMSI (r= .25,P= NS). Patients with dipyridamole-induced akinesia or dyskinesia (n=6) had a greater reduction in regional coronary flow reserve than did those showing hypokinesia (n=5): 1.38±0.51 versus 2.17±0.42,P< .05. Percent area reduction was more severe in patients with DET positivity than in those with DET negativity (93.7±8.7% versus 77±10.3%,P< .01), and it correlated with regional coronary flow reserve (r= .64,P< .01) and dipyridamole time (r= − .59,P< .01).ConclusionsIn patients with single-vessel disease, DET shows an excellent specificity but a limited sensitivity; in these patients, DET positivity is associated with a physiologically important coronary stenosis. Severity of the anatomic stenosis and impairment in regional flow reserve are greater when the dipyridamole-induced dyssynergy appears earlier during the test. Therefore, a stratification of the anatomophysiological severity of coronary artery disease can be obtained with DET, based mainly on the temporal allocation of the transient dyssynergy.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundAcute mental stress evokes responses in the cardiovascular and the immune systems. In particular, the subset of natural killer (NK) cells is found to be responsive to mental stress. The role of β-adrenergic mechanisms in these processes is the subject of this investigation.Methods and ResultsHealthy male volunteers (n=31) were subjected to two consecutive mental tasks. Subjects were randomly assigned to a β-blocker (propranolol 40 mg) or a placebo group. The capsules were ingested 1 hour before the tasks. The tasks evoked sympathetic responses, as indicated by an increase in heart rate and a decrease in the preejection period. These effects were abolished under β-blockade, indicating that effective β-blockade was achieved. In the immune system, significant increases were found for the number of NK cells and NK cell activity in the placebo group; these increases were absent in the propranolol group. In addition, an increase in all lymphocyte subsets was observed in subjects who had ingested propranolol. This increase, however, was also observed in subjects who had received propranolol but had not performed the tasks, indicating that these non-subset-specific increases in lymphocytes were a side effect of the βblocker.ConclusionsMental stress induces activation of the sympathetic nervous system, with concomitant increases in the number of NK cells in the circulation. These changes were inhibited by propranolol, indicating that stress-induced increases in the number and activity of NK cells in the circulation are controlled by a β-adrenergic mechanism.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundHeparin inhibits proliferation of smooth muscle cells in culture and intimal hyperplasia in experimental animals but paradoxically exacerbates vascular injury in clinical trials. To determine whether the difference in the means by which heparin was administered explained the benefit in animals and aggravation in humans, we examined the vascular effects of a range of heparin treatments.Methods and ResultsWhen laboratory rats were injected subcutaneously with heparin (55.5 IU, ≈1.0 mg/kg) per clinical trial protocols, intimal hyperplasia after arterial injury was exacerbated rather than alleviated. The intima to media area ratio was increased 22.5% with every-other-day injections and was increased 16.8% with daily injections. When the daily dose of heparin was increased to 7.2 mg/kg or when injections were initiated a week before injury, intimal hyperplasia was made even worse (52.2% and 59.9% above control). Twice-daily heparin, 7 and 17 hours apart, had no demonstrable effect one way or the other, and it was not until the heparin was administered at 12-hour intervals that intimal hyperplasia and cell proliferation were lessened (44.6% decrease). The greatest reduction in intimal hyperplasia was obtained when the heparin was administered continuously. The continuous osmotic pump intravenous infusion of heparin inhibited 62.5% of the expected proliferation, and perivascular polymeric device release of heparin blocked the response by 74.2%. While subcutaneous injections transiently increased activated partial thromboplastin time, neither mode of continuous delivery altered coagulation.ConclusionsWe might reconsider the use of heparin in vascular diseases and not neglect this promising compound because of inappropriate extrapolation from the laboratory to clinical use.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID