Myocardial tissue

Glass IB Antiarrhythmic Agents. Class IB antiarrhythmic agents produce less inhibition of the inward sodium current than Class lA agents. In normal myocardial tissue, phase 0 may be unaffected or minimally depressed. However, in ischemic or infarcted tissue, phase 0 is depressed. Myocardial tissue exposed to Class IB agents exhibits decreased automaticity, shortened action potential duration, ie, shortened repolarization, and shortened refractory period. Excitability of the myocardium is not affected and conduction velocity is increased or not modified. The refractory period is shortened less than its action potential duration, thus the ratio of refractory period to action potential duration is increased by these agents. The net effect is increased refractoriness. The PR and QT intervals of the ECG are shortened and the QRS interval is unchanged (1,2). 

Some cardiac arrhythmias result from many stimuli present in the myocardium. Some of these are weak or of low intensity but are still able to excite myocardial tissue Lidocaine, by raising the threshold of myocardial fibers, reduces the number of stimuli that will pass along these fibers and therefore decreases the pulse rate and corrects the arrhythmia Mexiletine (Mexitil) and tocadnide (Tonocard) are also antiarrhythmic drag s with actions similar to those of lidocaine... 

Myocardial tissue pH measurement has been used in the studies of different approaches to myocardial protection in various cardiac operations. A needle type glass membrane miniature electrode has been used in studies for pH-guided myocardial management [127], As described in the previous section, this electrode was also adapted to measure brain pH [132], The electrode has a right-angled glass electrode... 

Online measurement of myocardial tissue pH. Ann. Thorac. Surg. 72, S2227-S2234 (2001). 

Which of the following is an anti arrhythmic agent that has relatively few electro physiologic effects on normal myocardial tissue hut suppresses the arrhythmogenic tendencies of ischemic myocardial tissues ... 

The answer is d. (Hardman, pp 865-867.) Lidocaine usually shortens the duration of the action potential and, thus, allows more time for recovery during diastole. It also blocks both activated and inactivated Na channels. This has the effect of minimizing the action of lidocaine on normal myocardial tissues as contrasted with depolarized ischemic tissues. Thus, lidocaine is particularly suitable for arrhythmias arising during ischemic episodes such as myocardial infarction (Ml). 

Complex 65 (Cardiolite), 99mTc(I)-sestamibi, is used for myocardial perfusion imaging. It was designed on the basis that lipophilic cationic complexes behave as potassium mimics and are taken up by the myocardium (281). The sequential metabolism of the six methoxy groups of 65 to hydroxyl groups in the liver leads to formation of 99mTc complexes with greater hydrophilicity which are not retained in myocardial tissues (282). 

Ischaemic heart disease diminished oxygen supply in the myocardial tissue cells... 

Myocardial infarction is caused by acute thrombotic occlusion of a coronary artery (A). Therapeutic interventions aim to restore blood flow in the occluded vessel in order to reduce infarct size or to rescue ischemic myocardial tissue. 

Rhodes CG, Camici PG, Taegtmeyer H, Doenst T. Variability of the lumped constant for [18F]2-deoxy-2-fluoroglucose and the experimental isolated rat heart model clinical perspectives for the measurement of myocardial tissue viability in humans. Circulation 1999 99 1275-1276... 

Leor J, Patterson M, Quinones MJ, Kedes LH, Kloner RA. Transplantation of fetal myocardial tissue into the infarcted myocardium of rat. A potential method for... 

The heart is innervated by both sympathetic and parasympathetic neurons however, their distribution in the heart is quite different. Postganglionic noradrenergic fibers from the stellate and inferior cervical ganglia innervate the sinoatrial (S-A) node and myocardial tissues of the atria and ventricles. Activation of the sympathetic outflow to the heart results in an increase in rate (positive chronotropic effect), in force of contraction (positive inotropic effect), conduction tissue (positive dro-motropic effect). 

It is difficult to suggest a mechanism for lidocaine s antiarrhythmic action on the basis of its effects on normal ventricular myocardial tissue and His-Purkinje tissue. 

Dofetilide blocks IKr in all myocardial tissues. It blocks open channels, and its binding and release from the channels is voltage dependent. The effects of dofetilide are exaggerated when the extracellular potassium concentration is reduced, which is important, as many patients may be receiving diuretics concurrently. Conversely, hyperkalemia decreases the effects of dofetilide, which may limit its efficacy when local hyperkalemia occurs, such as during myocardial ischemia. Dofetilide demonstrates reverse use dependence, that is, less influence on the action potential at faster heart... 

Two main subtypes of P adrenoreceptors, P and P2, have been identified in the periphery and in the CNS (Minneman et ak, 1979 Palacios and Kuhar, 1980). Both are located at postsynaptic terminals and have been cloned. In the periphery, P receptors are located in myocardial tissue, and P2 receptors are located in pulmonary bronchi and bronchioli, as well as in some blood vessels. P Adrenoceptors are the major subtype throughout the brain, except for the cerebellum, where P2 receptors are predominant. Areas that contain high concentrations of P adrenoceptors include the superfi-... 

In this chapter changes in the distribution of gap junctions within the myocardial tissue, alterations of the distribution of special isoforms in the course of heart disease are described. Thus, changes in gap junction pattern for Cx43 and for Cx40 in the border zone of a chronic infarction are pointed out. Changes with growing age and in the course of heart failure are discussed as well. 

Treatment of myocardial malfunction and tissue damage. It is desirable to induce a slower heartbeat (bradycardia) in order to reduce O2 consumption without causing a reduction in contractile force. Existing drugs (calcium channel blockers) could also reduce the contractile force of myocardial tissue which is undesirable. 

NA Shaikh. Assessment of various techniques for the quantitative extraction of lysophospholipids from myocardial tissues. Anal Biochem 216 313-321, 1994. 

S100A1 is the most abundant S100 protein found in striated muscle and predominates in myocardial tissue (Kato and Kimura, 1985). Besides its cytoplasmic occurrence, S100A1 was reported in these cells to associate with the sarcolemma, sarcoplasmatic reticulum (SR), contractile filaments, intercalated discs, outer mitochondrial membrane and other intracellular membrane stmctures (Arcuri et al., 2002 Donato et al., 1989 Haimoto and Kato, 1988 Sorci et al., 1999). However, the exact location of S100A1 on the contractile elements of the sarcomere is still controversial (Maco et al., 2001 Zimmer, 1991). 

Rat myocardial tissue Myocardial infarction MSI Phospholopase-A2 Arachidonic acid (27)... 

De Oliveira et al. explained the effects of hyaluronidase in terms of a reduction of the water content of the ischemic myocardium [107]. Hyaluronidase would reduce the edema during the acute phase following coronary occlusion and thereby reduce the injury. Intramyocardial edema occurs after the occlusion of coronary arteries, resulting in an increased water content of the myocardial tissues. Hyaluronidase produces a faster diffusion of fluids and thereby reduces edema in the damaged area. To examine the effects of hvaluronidase on in fere-... 

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