Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0151744 (myocardial ischemia)
 31,282 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Alterations of autonomic tone appear to have important effects on the electrical stability of the heart. Since altered electrical stability, ventricular fibrillation, is the cause of death in the majority of patients who die from ischemic heart disease, the effects of the autonomic nervous system on ventricular electrical stability have been examined. Increased vagal tone increases the electrical stability of the heart and reduces the incidence of spontaneous ventricular fibrillation after coronary occlusion. These salutary effects of increased cholinergic tone appear to be mediated by cholinergic innervation of the ventricular conducting system. Conversely, increased adrenergic tone decreases the electrical stability of the heart and increases the propensity of the heart to develop ventricular arrhythmias during coronary occlusion. The interaction of the adrenergic and cholinergic system during myocardial ischemia may be one of the important determinants of survival in patients with coronary artery disease and acute myocardial infarction.
 ...
PMID:Neural basis for the genesis and control of arrhythmias associated with myocardial infarction. 78 2

Nitroglycerin (TNG) reduces ischemic injury during acute coronary occlusion in dogs with otherwise normal coronary arteries, but its effect in the presence of pre-existing multivessel coronary disease is unknown. We therefore examined the influence of TNG on acute ischemia in dogs with chronic multivessel coronary occlusions. The left anterior descending (LAD) coronary artery was acutely occluded by a balloon cuff in conscious dogs two weeks after placement of ameroid constrictors to produce gradual occlusion of the obtuse marginal and posterior descending coronary arteries. Adequacy of balloon and ameroid coronary occlusion and degree of collateralization were assessed by coronary angiography. Nitroglycerin decreased arterial pressure and increased heart rate. Myocardial ischemia, determined after LAD occlusion by summing ST-segment elevation (sigmaST) from eight intramyocardial electrodes, lessened with TNG in those six dogs whose heart rate increased less than 50 per cent, but increased in those four whose heart rate increased greater than 50 per cent. When TNG-induced change in either heart rate or arterial pressure was prevented by adding methoxamine, sigma ST was diminished even more (avg decrease 25 per cent; P smaller than 0.05). We conclude that, in the presence of pre-existing multivessel coronary occlusions, 1) TNG reduces ischemic injury during experimental acute coronary occlusion provided arterial pressure and heart rate responses are not excessive and 2) uniform improvement occurs when pressure and rate responses are abolished by an alpha-adrenergic agonist. Although results in animal studies must be extrapolated to the clinical situation with caution, these findings suggest that a similar pharmacologic approach might be applicable to the treatment of acute myocardial infarction in man, even in the presence of multivessel disease.
 ...
PMID:Effects of nitroglycerin and nitroglycerin-methoxamine during acute myocardial ischemia in dogs with pre-existing multivessel coronary occlusive disease. 80 82

Previous studies have shown that nitroglycerin (TNG) exerts beneficial electrophysiological effects in the setting of acute myocardial ischemia. To investigate the basis for these actions, the effects of TNG during coronary occlusion were studied in 19 anesthetized mongrel dogs. Refractory periods (obtained by extrastimulus method) and conduction times measured from local electrograms were determined in potentially ischemic and nonischemic areas prior to and after varying periods of occlusion of the left anterior descending coronary artery and following administration of TNG (300-400 mug intravenous bolus followed by an infusion titrated to reduce systolic blood pressure by 20 mm Hg). Following 15 minutes of occlusion, refractory periods in the ischemic zones shortened to 83% of control (P less than 0.001) resulting in a difference between refractory periods in the nonischemic and ischemic zones of 17.7%. After TNG administration this difference was decreased to 10.0% (P less than 0.001). However, with periods of occlusion of 60-90 min TNG did not significantly affect the difference of refractory periods. TNG had no significant effects on conduction times in nonischemic or ischemic areas. In six dogs, the effects of coronary occlusion and TNG on ventricular automaticity were examined by induction of complete heart block. The idioventricular rate and ventricular escape intervals after cessation of ventricular overdrive were used as indices of automaticity. Control idioventricular rates (62.5 +/- 3.7 beats/min) remained unchanged following both coronary occlusion (62.0 +/- 3.9) and TNG administration (60.7 +/- 3.2). Similarly, mean control escape intervals (1.84 +/- 0.2 sec) did not change after occlusion (1.78 +/- 0.3 sec) or TNG administration (1.86 +/- 0.2 sec). In conclusion, these observations suggest that 1) TNG enhances the electrical stability of the acutely ischemic myocardium by decreasing the difference of refractory periods between nonischemic and ischemic areas in the immediate period following occlusion, 2) since TNG has no significant effects on ventricular automaticity, its beneficial effects might be limited in suppression of arrhythmias of re-entrant origin.
 ...
PMID:Electrophysiologic effects of nitroglycerin during experimental coronary occlusion. 81 Feb 64

Nitroglycerin (NTG) traditionally has bben avoided in the treatment of pain caused by acute myocardial infarction because of the belief that NTG-induced decrease in arterial pressure and concomitant reflex increase in heart rate might extend the ischemic process. However, recent experimental and clinical investigations cast doubt on this concept. For example, when the left anterior descending coronary artery is acutely occluded in normal dogs or in dogs when chronic coronary occlusions and extensive collaterals, NTG reduces ST-segment evevation (and presumably myocardial ischemia). This salutary effect occurs despite lowering of systemic arterial pressure, as long as excessive reflex tachycardia does not result; the magnitude of ischemia reduction is potentiated when methoxamine or phenylephrine are administered simultaneously to abolish the NTG -induced hypotension and reflex tachycardia. NTG and methoxamine treatment also results in 1) reduction of infarct size as (as assessed by gross morphologic examinations and myocardial CPK levels) in dogs subjected to 5 hours of coronary occlusion, and 2) increase in ventricular fibrillation (VF) threshold and reduction of the incidence of spontaneously occurring VF in dogs with acute coronary occlusion. Finally, the effectiveness of NTG during acute myocardial iinfarction (AMI) in man has been studied. Multiple precordial electrodes were used to measure changes in the degree of ST-segment elevation; these changes were used as an index of alterations in myocardial ischemic injury. Patients with normal pulmonary capillary wedge pressures ( less than 15 mm Hg) did not benefit consistently from NTG alone; however, when phenylephrine was administered with NTG (to abolish NTG-induced arterial pressure reduction and reflex increase in heart rate), ST-segment elevation diminished consistently. In patients with elevated wedge pressures ( greater than 15 mm Hg), NTG alone consistently reduced ischemia; addition of phenylephrine often partially reversed this benefit. Thus, administration of NTG, alone or with phenylephrine, appears to reduce myocardial ischemic injury during AMI in man; however, the response to phenylephrine depends upon the presence or absence of LV failure prior to treatment. These experimental and clinical results suggest this form of therapy may be use in reducing infarct size in man, although additional studies are necessary to determine the functional significance of these acute electrophysiologic alterations.
 ...
PMID:Protection of ischemic myocardium by nitroglycerin: experimental and clinical results. 81 59

Brain stimulation can provoke a variety of arrhythmias and lower the ventricular vulnerable threshold. In the animal with acute myocardial ischemia such stimuli suffice to provoke ventricular fibrillation. Vagal neural traffic or adrenal catecholamines are not the conduits for this brain-heart linkage. Accompanying increases in heart rate or blood pressure are not prerequisites for the changes in cardiac excitability. Increased sympathetic activity, whether induced by neural or neurohumoral action, predisposes the heart to ventricular fibrillation. Protection can be achieved with surgical and pharmacologic denervation or reflex reduction in sympathetic tone. With acute myocardial ischemia, augmented sympathetic activity accounts for the early surge of ectopic activity frequently precipitating ventricular fibrillation. Asymmetries in sympathetic neural discharge may also contribute to the genesis of serious arrhythmias. The vagus nerve, through its muscarinic action, exerts an indirect effect on cardiac vulnerability, the consequence of annulment of concomitant adrenergic influence, rather than of any direct cholinergic action on the ventricles. There exist anatomic, physiologic as well as molecular bases for such interactions. Available experimental evidence indicates that environmental stresses of diverse types can injure the heart, lower the threshold of cardiac vulnerability to ventricular fibrillation and, in the animal with coronary occlusion, provoke potentially malignant ventricular arrhythmias. Available evidence indicates that in man, as in the experimental animal, administration of catecholamines can induce ventricular arrhythmia, whereas vagal activity exerts an opposite effect. Furthermore, in certain subjects diverse stresses and various psychologic states provoke ventricular ectopic activity.
 ...
PMID:Neural and psychologic mechanisms and the problem of sudden cardiac death. 86 Jun 97

The capacity of computerized tomography to assess myocardial edema resulting from acute coronary occlusion was investigated in 19 arrested and 2 beating canine hearts. Edematous myocardium was consistently detected as areas of decreased attenuation values. The magnitude of the decrease in attenuation value was linearly related to the severity of the edema. The anatomic definition and tomographic information in the arrested hearts provided the capability for localization and quantitation of the extent of the lesion. The results of these in vitro investigations indicate that CT scanning is a technique which will contribute important pathophysiologic information about the evolution of myocardial ischemia.
 ...
PMID:Computerized tomography of ischemic myocardium: quantitation of extent and severity of edema in an in vitro canine model. 86 25

The effects of coronary occlusion and of subsequent propranolol administration were examined in 18 conscious dogs. Overall left ventricular (LV) function was assessed by measurements of LV pressure and dP/dt, and regional myocardial function was assessed by measurements of segment length (SL), velocity of SL shortening and regional myocardial "work", i.e., pressure-length loops in normal, moderately, and severely ischemic zones. Regional intra-myocardial electrograms were measured from the same sites along with regional myocardial blood flow as determined by the radioactive microsphere technique. Coronary occlusion resulted in graded loss of function from the normal to severely ischemic zones with graded flow reduction and graded elevation of the ST segment. Propranolol depressed overall LV function, function in the normal zone (work fell by 17+/-4%), and in the majority of moderately ischemic segments (work fell by 7+/-3%). In severely ischemic segments the extent of paradoxical motion and post-systolic shortening was reduced by propranolol. After propranolol regional myocardial blood flow fell in the normal zone (11+/-2%) and rose in the moderately (15+/-4%) and severely (63+/-10%) ischemic zones. Thus, in the conscious dog with regional myocardial ischemia, propranolol induces a redistribution of myocardial blood flow, with flow falling in normal zones and rising in moderately and severely ischemic zones. The improvement in perfusion of ischemic tissue was associated with slight but significant depression of shortening, velocity, and work in the moderately ischemic zones and of paradoxical bulging and post-systolic shortening in the severely ischemic zone.
 ...
PMID:Effects of propranolol on regional myocardial function, electrograms, and blood flow in conscious dogs with myocardial ischemia. 87 96

Using an experimental canine model, we have employed echocardiography to study segmental dyskinesis produced by acute coronary occlusion. Characteristic alterations in posterior wall and septal motion occur after acute coronary ligation; these resemble clinical abnormalities described in acute and old myocardial infarction. The degree of dyskinesis produced is directly related to the severity of the perfusion deficit. Coronary reperfusion had variable effects on dyskinesis; most animals showed improvement but in some the myocardial contraction abnormalities became more severe. A vaviety of interventions were undertaken during ischemia. The elevated level of arterial pressure induced by the administration of methoxamine increased ventricular diameter and presumably oxygen requirements, and was deleterious to ischemic wall motion whereas the administration of norpinephrine reduced ventricular diameter and improved function. Intra-aortic balloon counterpulsation had little effect on either ischemic motion or perfusion. These experimental studies generally support conclusions drawn from clinical echocardiograms about the relationship of abnormalities of wall motion to coronary artery lesions and myocardial ischemia, and suggest further clinical uses for echocardiography in coronary disease.
 ...
PMID:Echocardiography in experimentally-induced myocardial ischemia. 87 94

We investigated whether prolonged infusion of hypertonic mannitol results in a sustained increase in coronary flow and reduces myocardial necrosis after ventriculotomy or two hours of circumflex coronary artery occlusion. Cardiac outputs, intracardiac pressures, and heart rates did not differ between mannitol and control animals. Those receiving mannitol after ventriculotomy had coronary flows to myocardium near the incision which did not differ from controls. During coronary occlusion, mannitol did increase flow to ischemic and peri-ischemic regions by one hour, but this increase was not sustained at two hours. On histologic examination, myocardial necrosis involving the right ventricular free wall in the ventriculotomy animals and the posterior papillary muscle and subadjacent free wall in the coronary occlusion animals, did not differ between the mannitol treated and control groups. The data obtained in the present study, combined with those from earlier evaluations of the influence of mannitol during ventriculotomy and myocardial ischemia, suggest that mannitol's ability to increase coronary flow to injured areas of myocardium is relatively short-lived.
 ...
PMID:Influence of mannitol on maintaining coronary flows and salvaging myocardium during ventriculotomy and during prolonged coronary artery ligation. 88 88

Thallium-201 was found to be a reliable agent for detecting decreased myocardial perfusion in domestic pigs 1-4 hours after acute coronary occlusion. Substantial variation in myocardial-to-liver count ratios and diagnostic quality was observed in serial images performed in 3 normal pigs, although areas of 1-4 hours-old myocardial ischemia produced by acute circumflex coronary artery ligation in 6 pigs could be reliably detected by in vivo 201Ti imaging. After intravenous 201Ti administration, the animals were sacrificed and sections of normal and ischemic myocardium were counted in a scintillation well counter. The activity in the ischemic area in pigs averaged 12% of the activity in the normal area, and varied over a narrow range; in dogs the activity averaged 62% of normal, and varied over a wide range. The pig was a more consistent model than the dog.
 ...
PMID:Evaluation of early myocardial ischemia with thallium-201 in the pig. 91 53


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>