摘要:

The cardiovascular reflexes, by regulating the traffic in the sympathetic nerves, govern the amount of norepinephrine released from the nerve endings. However, the final adjustments in the amount of neurotransmitter available to activate the β1receptors in the heart and the α receptors in the blood vessels take place at the sympathetic neuroeffector junction. Thus, a decrease in pH, hyperosmolarity, moderate increases in the concentration of K+ion, adenosine and adenine nucleotides depress the release of norepinephrine at any given level of sympathetic nerve activity. These metabolic changes, which occur In active tissues, and in particular in adenosine, have been proposed as mediators of the accompanying local hyperenlia. In addition, they apparently facilitate this local dilatation by disconnecting the blood vessels in the active tissues from sympathetic control. Acetylcholine, histamine and 5‐hydroxytryptamine are present in and around certain blood vessels and can activate specific receptors on the prejunctional fibers and cause vasodilatation by reducing the output of neurotransmitter. Some of the norepinephrine released into the synaptic cleft may depress its continued release by activating prejunctional a receptors. In contrast, angiotensin II, by a local action on the nerve endings, can augment the release of transmitter. Decreases in local temperature reduce transmitter release but augment the affinity of the postjunctional a receptors for norepinephrine. The role of these local events at the neuroeffector junction, their physiologic significance and potential clinical importance are discussed in this review.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Randomized clinical trials constitute the formal experiments in therapeutics. Many such trials in coronary heart disease have terminated inconclusively or in controversy. In this editorial, we analyze some of the methodologic issues that may lead to controversy; the main reason for the low success rate may lie in insufficient understanding of the complex biology of the disease and in failure to select the appropriate models for therapy. We argue that these difficulties only strengthen the need for the rigorous experimental approach to the evaluation of therapies for coronary heart disease.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

The realization that bias in patient selection may influence the results of clinical studies has helped to establish the randomized controlled clinical trial in medical research. However, bias can be equally important at other stages of a trial, especially at the time of analysis. Withdrawing patients from consideration in the analysis because of ineligibility on account of study entry criteria, lack of compliance to the protocol, or data of poor quality may be a source of systematic error. Examples to illustrate the possible consequences are taken from trials in the cardiovascular field. We recommend that reported study results should include outcome data from all subjects randomized in the group to which they were originally assigned.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We evaluated 193 consecutive unstable angina patients by clinical features, hospital course and electrocardiography. All patients were managed medically. Of the 193 patients, 150 (78%) had a technetium‐99m pyrophosphate (Tc‐PYP) myocardial scintigram after hospitalization. Of these, 49 (33%) had positive scintigrams. At a follow‐up of 24.9 ± 10.8 months after hospitalization, 16 of 49 patients (33%) with positive scintigrams died from cardiac causes, compared with six of 101 patients (6%) with negative scintigrams (p< 0.001). Of 49 patients with positive scintigrams, 11 (22%) had had nonfatal myocardial infarction at follow‐up, compared with seven of 101 patients (7%) with negative scintigrams (p< 0.01). Age, duration of clinical coronary artery disease, continuing angina during hospitalization, ischemic ECG, cardiomegaly and a history of heart failure also correlated with cardiac death at follow‐up. Ischemic ECG and a history of angina with a crescendo pattern also correlated with nonfatal infarction at follow‐up. Patients with continuing angina, an ischemic ECG and a positive scintigram constituted a high‐risk unstable angina subgroup with a survival rate of 58% at 6 months, 47% at 12 months and 42% at 24 and 36 months. We conclude that the assessment of clinical features, hospital course, ECG and Tc‐PYP scintigraphy may be useful in identifying high‐risk unstable angina patients.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

One hundred fourteen patients with variant angina performed bicycle exercise stress tests, and were divided into three groups. Group 1 included 37 patients with a normal exercise test. Coronary arteriography revealed absence of significant coronary stenoses in 18 patients, one‐vessel disease in 17 and involvement of two or more vessels in two. Group 2 consisted of 40 patients who had ST‐segment elevation during or just after exercise. Coronary arteriography in these cases revealed absence of significant coronary stenoses in nine patients, one‐vessel disease in 18 and disease of two or more vessels in 13. Group 3 included 37 patients who had ST‐segment depression during exercise. Absence of coronary artery disease was found in only two patients, one‐vessel disease was found in 19 and disease of two or more vessels was found in 16.Sixty‐one patients repeated the exercise test after a mean of 18 months after hospital discharge. Exerciseinduced ST‐segment elevation was no longer present in surgically or medically treated patients; ST‐segment depression was still evident in all the medically treated patients, but was absent in eight of 13 patients who underwent aortocoronary bypass surgery.Exercise testing can be useful in the follow‐up of patients with variant angina and in selecting patients most likely to be helped by bypass surgery.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Regional metabolism of exogenous fatty acid extracted by myocardium depends primarily on oxidation. Positron‐emission tomography (PET) delineates necrotic myocardium by virtue of its failure to extract labeled fatty acid. In ischemic myocardium, fatty acid is extracted, but metabolized slowly. This study was performed to determine whether viable, but ischemic, tissue could be detected and localized in vivo based on external detection of impaired fatty acid metabolism. Accordingly, regional clearance of11C‐palmitate was assessed by sequential PET in 15 anesthetized dogs. Clearance was consistently monoexponential from 5–15 minutes after administration of the tracer. In the absence of coronary stenosis (n= 7), clearance was homogeneous throughout the heart, with an average rate constant (K) of −0.060 ± 0.005 min-1(± SEM) and a coefficient of variation (CV) of 11.1 ± 2.1% in each heart. Homogeneity persisted when the heart rate was increased from 84.4 ± 6.0 to 202.7 ± 11.5 beats/min with atropine (CV 13.2 ± 3.5%). With left circumflex coronary stenosis (≤ 70% reduction in vessel diameter), homogeneity of11C‐clearance under control conditions and with tachycardia did not differ from clearance in hearts without coronary stenosis. However, with stenosis > 70% sufficient to induce ischemia without gross infarction, regional clearance of11C became markedly heterogeneous under control conditions (CV 28.1 ± 5.5%,p< 0.01 compared with normal hearts) and with tachycardia (CV 34.8 ± 5.4%,p< 0.01). The heterogeneity resulted from reduced clearance of11C in regions supplied by the stenotic vessel (K = −0.044 ± 0.011 min−1) compared with clearance in well perfused regions (K = −0.064 ± 0.011 min-1,p< 0.025), a difference accentuated by tachycardia.Thus, sequential PET after i.v. injection of11C‐palmitate delineates zones of viable, ischemic myocardium that characteristically exhibit impaired oxidation of extracted fatty acid.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Regional myocardial function and blood flow were determined for 48 hours after permanent occlusion of the left circumflex coronary artery in conscious swine. Systolic wall thickening and end‐diastolic wall thickness (EDWTh) were correlated with regional myocardial flow (RMBF) at 15 minutes, 24 and 48 hours after occlusion. Both regional function and blood flow were compared with the extent of myocardial necrosis (determined histologically) after 48 hours in functionally distinct zones. Group 1 (control zones) was characterized by increased systolic wall thickening, EDWTh, RMBF and had no necrosis. Group 2 (marginal zones) had depressed systolic wall thickening (35 ± 3% [mean ± SEM] of preocclusion level at 48 hours) and RMBF (64 ± 6% of preocclusion values), transiently decreased EDWTh and 46 ± 5% necrosis. In Group 3 (ischemic zones), all values were greatly reduced: systolic wall thickening was 3.6 ± 1.2%, EDWTh 76 ± 8% and RMBF 25 ± 9% of preocclusion values; necrosis was 90 ± 5%. Groups 2 and 3 had increased RMBF at 24 and 48 hours from that at 15 minutes after occlusion; however, in neither case was systolic wall thickening greater than that at 15 minutes after occlusion. We conclude that there is close correlation between RMBF, systolic wall thickening and the extent of necrosis present after 48 hours of coronary artery occlusion in the conscious swine; subsequent increases in RMBF to the marginal zone after occlusion are not accompanied by improved regional function.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

The effects of equipotent β1‐receptor‐blocking doses of propranolol, metoprolol and sotalol on distal coronary pressure, stenosis resistance and regional myocardial blood flow (endo/epi) were studied in anesthetized dogs with a severe noncircumferential stenosis of the left circumflex coronary artery. No significant differences between the three β blockers were observed for overall hemodynamics and regional myocardial blood flow. After drug treatment, subendocardial blood flow (0.47 ± 0.05 to 0.78 ± 0.05 ml/min/g) and endo/epi (0.67 ± 0.04 to 1.18 ± 0.04) increased significantly (p< 0.05) in the ischemic region. These changes were associated with a marked increase in distal coronary perfusion pressure and a decrease in heart rate. Resistance across the stenosis decreased significantly (p< 0.05) after, β‐receptor blockade (3.2 ± 0.3 to 1.4 ± 0.2 units). Atrial pacing to control heart rate only partially attenuated these changes. These results suggest that a favorable redistribution of ischemic blood flow after β blockade is the result of an increase in distal diastolic pressure‐time index and an autoregulation‐induced increase in distal bed vascular resistance due to a decrease in myocardial oxygen demand associated with β blockade. The latter effect also resulted in a decrease in the dynamic severity of a proximal coronary stenosis.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

The percentage of cross‐sectional area narrowing by atherosclerotic plaques in each 5‐mmlong segment of the right, left main, left anterior descending and left circumflex coronary arteries was determined at necropsy in 50 patients who died of a first acute transmural myocardial infarction (AMI). The amount and extent of the coronary narrowing were compared in the 22 patients with anterior wall AMI and in the 28 patients with posterior wall AMI. Although the percentage of coronary arteries narrowed 76–100% was similar in the anterior and posterior wall AMI patients (74% vs 75%; average 3.0 of 4 coronary arteries per patient), the patients with anterior wall AMI had less severe narrowing of each of the 5‐mm segments of the four major coronary arteries than did the patients with posterior wall AMI. Of the 1166 5‐mm coronary segments examined in the 22 anterior wall AMI patients, 23% were narrowed 76–100% in cross‐sectional area by atherosclerotic plaque, and of the 28 patients with posterior wall AMI, 39% of the segments were 76–100% narrowed (p< 0.001). Among the anterior AMI patients, a higher percentage of the 5‐mm segments of the left anterior descending coronary artery was severely (> 75%) narrowed than either posterior perfusing coronary artery. The percentage of segments narrowed 76–100% for each of the major coronary arteries in the posterior AMI patients, however, was similar. Thus, our necropsy patients with posterior wall AMI had more extensive and severe coronary artery narrowing than did our patients with anterior wall AMI. If the coronary arteries had not been examined quantitatively, this difference in severity would not have been apparent.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

A deficiency or an excessive intake of metals with cardiovascular effects is suspected to be involved in the pathogenesis of coronary heart disease (CHD) and sudden death. Therefore, In 106 patients undergoing coronary arteriography, serum levels of six essential metals (magnesium, chromium, copper, manganese, selenium and zinc) and whole blood concentrations of two elements without known esetial function (cadmium and lead) were measured using atomic absorption spectrophotometry, including the flameless technique, or neutron activation analysis.The patients were clasifed into three groups according to severity of CHD as assessed by coronary angiography: those without coronary lesions (n= 31) and those with moderate (n= 34) or severe CHD (n= 41). Patients with severe CHD had lower mean serum magnesium and higher serum copper and manganese levels than those without CHD (magnesium, 1.63 ± 0.16 [SD] VS 1.78 ± 0.16 mEq/l,p< 0.005; copper, 1.39 ± 0.22 vs 1.24 ± 0.24 mg/l,p< 0.05; manganese, 1.30 ± 0.43 vs 1.05 ± 0.40 μg/l,p< 0.05). In contrast, metal concentrations in patients with moderate CHD did not differ significantly from control values. There was no significant association between prevalence and severity of CHD and the other elements investigated. Analysis of associations between metal concentrations and clinical characteristics revealed markedly elevated blood cadmium levels in cigarette smokers compared with nonsmokers (2.49 ± 1.72 [n= 28] vs 0.43 ± 0.22 Mg/1 [n= 181,p< 0.001). A correlation was noted between cadmium levels and the number of cigarettes smoked per day (r= 0.725,p< 0.001).Our results suggest that a deficiency of magnesium but not of the other metals studied may be present in patients with severe CHD; elevated serum copper and manganese levels do not play a role in the development of CHD in the sample of patients studied; and cigarette smoking may be associated with increased serum cadmium levels, which may explain in part the contribution of smoking to the risk of sudden death in patients with CHD.

ISSN:0009-7322    

出版商:OVID    

年代:1981

数据来源: OVID