The Kussmaul sign is seen in constrictive pericarditis, some cases of endomyocardial restrictive disease (such as endocardial fibroelastosis), myocardial restrictive disease (such as amyloidosis), tricuspid stenosis, congestive failure (especially that called right sided), superior vena cava syndrome, and right ventricular infarction. But, contrary to what was formerly taught, it is never seen in uncomplicated pericardial tamponade. In fact, its apperance in the latter setting suggests the development of a constrictive or restrictive pericardial component and/or epimyocardial fibrosis. In pure tamponade, pericardial pressure and right atrial pressure are elevated but equal to each other. The inspiratory fall in intrathoracic pressure is transmitted to the pericardial space, and the normal inspriatory increase in systemic venous return is preserved so that Kussmaul sign does not occur. The pericardial space is obliterated in constrictive pericarditis so that during inspiration the decrease in intrathoracic pressure is not transmitted to the heart, venous return does not fall, and systemic venous return does not increase.
