Eπιπωματισμος Περικαρδιτιδα

Description
Cardiac Tamponade, Constrictive Pericarditis, and Restrictive Cardiomyopathy James A. Goldstein, M.D.* The pericardium envelopes the cardiac chambers and under physiological conditions exerts subtle functions, including mechanical effects that enhance normal ventricular interactions that contribute to balancing left and right cardiac outputs. Because the pericardium is non-compliant, conditions that cause intrapericardial crowding elevate intrapericardial pressure, which may be the mediator of a

Please download to get full document.

View again

of 65
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Information
Category:

Documents

Publish on:

Views: 4 | Pages: 65

Extension: PDF | Download: 0

Share
Tags
Transcript
  Cardiac Tamponade, ConstrictivePericarditis, and RestrictiveCardiomyopathy  James A. Goldstein, M.D.* The pericardium envelopes the cardiac chambersand under physiological conditions exerts subtlefunctions, including mechanical effects that enhancenormal ventricular interactions that contribute tobalancing left and right cardiac outputs. Because thepericardium is non-compliant, conditions that causeintrapericardial crowding elevate intrapericardialpressure, which may be the mediator of adversecardiac compressive effects. Elevated intrapericar-dial pressure may result from primary disease of thepericardium itself (tamponade or constriction) orfrom abrupt chamber dilatation (eg, right ventricu-lar infarction). Regardless of the mechanism leadingto increased intrapericardial pressure, the resultantpericardial constraint exerts adverse effects on car-diac filling and output. Constriction and restrictivecardiomyopathy share common pathophysiologicaland clinical features; their differentiation can bequite challenging. This review will consider thephysiology of the normal pericardium and its dy-namic interactions with the heart and review indetail the pathophysiology and clinical manifesta-tions of cardiac tamponade, constrictive pericarditis,and restrictive cardiomyopathy. (Curr Probl Cardiol2004;29:503-67.) No conflict of interest exists in this article.*Address for correspondence: James A. Goldstein, M.D., Director of Research and Education, WilliamBeaumont Hospital, Division of Cardiology, 3601 West Thirteen Mile Road, Royal Oak, Michigan 48073.E-mail: jgoldstein@beaumont.eduCurr Probl Cardiol 2004;29:503-67.0146-2806/$ – see front matterdoi:10.1016/j.cpcardiol.2004.03.002 Curr Probl Cardiol, September 2004 503  Pericardial Anatomy T he pericardium is a bilayered, flask-shaped sac structured of aninner visceral layer made up of a thin elastic membrane of mesothelial cells and a thick, stiff outer parietal layer consistingpredominantly of collagen and elastic fibers. 1-3 Between the two pericar-dial layers is a potential “space” that normally contains a small (approx-imately 20 ml) amount of pericardial fluid which physiologically resem-bles an ultrafiltrate of plasma. The pericardium envelops the cardiacchambers but does not directly attach to them at any point (Fig 1). 4 Instead, at the base of the heart, the serous pericardium reflects up andaround the great vessels, forming the pericardial sinuses and recesses. Thepericardium is in the shape of an inverted U and the cul-de-sac enclosedbetween the limbs of the U lies behind the left atrium and is known as theoblique sinus. The passage between the venous and arterial mesocardia,that is, that between the aorta and pulmonary trunk anteriorly and the atriaposteriorly, is the transverse sinus. The upper recess, the transverse sinus,is a small tubular recess reflecting the pericardial outpouchings necessaryto allow entrance of the superior vena cava and exit from the pericardiumof the pulmonary trunk and aorta. The oblique sinus is a larger pericardialoutpouching in which the pericardium splits to permit passage of the fourpulmonary veins and the vena cavae. It is noteworthy that the left atrium(LA) is not entirely an “intrapericardial” structure. The pericardium hasimportant ligamentous attachments to surrounding thoracic structures.The external fibrous layer of the pericardium is anchored to the dia-phragm by the pericardiophrenic ligament and to the sternum by thevariable sternopericardial ligaments. Posteriorly, the fibrous pericardiumis bound by loose connective tissue to the structures of the posteriormediastinum. These connections provide structural support for the heartwithin the thoracic cage and thereby limit excessive cardiac motion,particularly with changes in body position. The main arterial supply of thepericardium is the pericardiophrenic artery, a branch of the internalthoracic artery. Venous drainage occurs by way of pericardiophrenicveins which are tributaries of the brachiocephalic veins. Sensory enerva-tion is provided by the phrenic nerves with vasomotor enervation from thesympathetic trunks. Pericardial Functions Although an intact pericardium is not critical to maintenance of cardiovascular function (as evidenced by the innocent effects of incisionand subsequent lack of pericardial closure after surgery), potentially 504 Curr Probl Cardiol, September 2004  important subsidiary functions have been attributed to the pericardium. 1-4 These include (a) limitation of intrathoracic cardiac motion; (b) balancingright and left ventricular output through diastolic and systolic interac-tions; (c) buffering of positional changes in chamber fi lling and thereforeoutput; (d) suction fi lling; (e) limitation of acute dilatation; (f) lubricanteffects that minimize friction between cardiac chambers and surroundingstructures, and (g) lymphatic/immunological functions, mediated in partthrough anatomic barriers that help prevent spread of infection fromcontiguous structures, especially the lung. Compliance Properties of the Normal Pericardium The most important physiological role of the pericardium relates to itsmechanical interactions with the cardiac chambers it encompasses.Elevated intrapericardial pressure (IPP) is the mechanism by which the FIG 1. A diagram of the long axis of the heart at right angles to the outlets shows thearrangement of the pericardium. The outer fibrous sack is firmly attached to the great arteriesand veins at the base. The heart itself invaginates a second sack, the serous pericardium. Thetwo layers of this serous membrane, however, are densely adherent to other structures. Theinner layer (visceral) is attached to the surface of the myocardium as the epicardium. The outerlayer (parietal) is attached to the fibrous pericardium. Effectively the pericardial cavity is locatedbetween the tough fibrous layer and the surface of the heart. Within this cavity are two recesses:transverse and oblique sinuses. As shown in the diagram, the transverse sinus is in the innerheart curvature while the oblique sinus is behind the diaphragmatic aspect of the left atrium,limited by the attachments of the pulmonary veins. Hurst JW. Anatomy of the normal heart andits response to disease. In: Atlas of the Heart. Hagerstown, MD: Lippincott, 1998:Part I:1.2. Curr Probl Cardiol, September 2004 505  pericardium exerts adverse pathophysiological effects. Therefore, anappreciation of the normal physiologic effects of the pericardium oncardiac chamber compliance is essential to understanding its in fl uenceunder pathophysiologic conditions.The pericardium must accommodate the cardiac chambers and has asmall capacitance reserve volume that allows for a modest amount of chamber dilatation. Under physiologic conditions the pericardium be-haves as a relatively fi xed and inelastic sac exhibiting stiff non-compliantpressure – volume characteristics. 2,4-8 The normal pericardium has a smallcapacitance reserve (150-250 ml) whereby initial increments in intraperi-cardial volume results in trivial increases in IPP. However, owing to theinelastic nature of the fi brous parietal layer, acutely the pericardial sac isstiff and non-compliant and once this capacitance has been exceeded,further increases in intrapericardial volume result in steep increments inIPP. The compliance characteristics of the pericardium are an aggregatere fl ection of the intrinsic compliance of the pericardial layers (predomi-nantly the stiff parietal layer), the volume of the pericardial space itself,and the combined volume of the cardiac chambers contained within thepericardium. Therefore, IPP re fl ects the total intrapericardial volume(chamber volumes plus fl uid, clots, or masses in the intracardial space)relative to the compliance of the pericardial layers.Normally, IPP closely tracks intrapleural and right atrial (RA) pressure.The pericardium acts as a hydrostatic system, equally distributinghydrostatic forces over the surface of the cardiac chambers; this favorsequality of end diastolic transmural pressures throughout the ventriclesand therefore uniform stretch of muscle fi bers (thereby tending to balancepreload), which permits the Frank  – Starling mechanism to operate uni-formly at all intraventricular pressures. 5,6 The presence of the pericardiumalso constantly compensates for changes in inertial and gravitationalforces by distributing them evenly around the heart providing a mutuallyrestrictive interpericardial chamber which favors balanced output fromboth ventricles when this is integrated over several cardiac cycles.The parietal pericardium makes potentially important contributions toventricular interactions. It may be speculated that the presence of theparietal pericardium helps maintain a functionally optimal cardiac shape,since after pericardiectomy the heart tends to be more spherical.Even in the absence of the pericardium, pressure or volume overload of one ventricle in fl uences the compliance and fi lling of the contralateralchamber via septal mediated diastolic interactions. 1,6-8 The normal peri-cardium is less compliant than the myocardium and limits cardiacdistention, thereby more tightly coupling the ventricles and enhancing 506 Curr Probl Cardiol, September 2004
Similar documents
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks