Noninvasive/invasive correlates of exaggerated ventricular interdependence in cardiac tamponade

Ventricular interdependence is that property of the normal heart such that distension of one ventricle alters the distensibility and filling pressure of the other. This phenomenon coupled with reciprocal changes in right and left heart venous return during normal quiet respiration results in minor decreases in left ventricular stroke volume, systolic blood pressure, pulse pressure, total electromechanical systole (Q-A2), left ventricular ejection time and mitral e-wave velocity during inspiration and minor increases in these parameters during expiration. Opposite changes in these parameters occur in the right heart with increases occurring during inspiration and decreases during expiration. Exaggerated ventricular interdependence occurs in cardiac tamponade when the pericardial constraint limits the total contents in the pericardial sac. This, together with the decreased effective left ventricular filling pressure which occurs during inspiration, is responsible for the exaggerated decrease in stroke volume, blood pressure, pulse pressure, left ventricular ejection time and mitral e-wave velocity in this condition. These observations, together with the echocardiographic findings of right atrial collapse, right ventricular collapse, and inferior vena cava plethora constitute the noninvasive diagnosis of pericardial tamponade. The utility of these noninvasive tests in detecting both the presence and degree of increased pericardial pressure was evaluated in 33 invasively studied patients with pericardial effusion. In Group 1 (n = 13) intrapericardial pressure was elevated but less than both right atrial pressure and pulmonary wedge pressure, in Group 2 (n = 10) intrapericardial pressure equaled right atrial pressure but was less than pulmonary wedge pressure, and in Group 3 (n = 10) intrapericardial pressure equaled right atrial pressure and pulmonary wedge pressure. From these data it is concluded that right atrial and right ventricular collapse are highly sensitive techniques for predicting increased intrapericardial pressure in all three groups, but fail to predict the level of intrapericardial pressure and the severity of hemodynamic compromise. However, the absence of inferior vena cava plethora helped separate Group 1 patients from Groups 2 and 3 patients, thereby aiding in distinguishing a group of patients with severe hemodynamic derangement requiring urgent intervention. Exaggerated reciprocal changes in mitral and tricuspid e-wave velocity is a very sensitive finding for increased intrapericardial pressure. However, its presence correlates poorly with the severity of tamponade. Acute pericardial tamponade is a clinical diagnosis determined by the integration of the history, physical exam and appropriate noninvasive physiologic and imaging techniques.