**6. Invasive hemodynamic assessment**

Simultaneous right- and left-heart catheterization is currently the gold standard for the diagnosis of CP. Evidence of equalization of end-diastolic pressures (≤ 5 mmHg difference between right- and left-ventricle-end-diastolic pressures secondary to fixed pericardial volume and consequent ventricular interdependence) and the visualization

#### **Figure 5.**

*Invasive pressure measurement characteristics of constrictive pericarditis. Constrictive physiology is characterized by sharp ventricular pressure increase after early diastolic inflow that, in comparison with normal hearts, is highlighted by a peculiar diastolic pressure curve morphology known as "square root" or "dip and plateau" (panel A). Moreover, ventricular interdependence (panel B) is another crucial marker of constriction and is demonstrated by equalization of end-diastolic pressures (≤ 5 mmHg difference between RV and LV end-diastolic pressures) secondary to fixed pericardial volume in which both ventricles are moving (\*). The same mechanism, added to the dissociation between intra-cardiac and intrathoracic pressures, explains the evidence of RV and LV opposite respiratory variations (panel B). This is also a useful marker to distinguish pericardial constriction from myocardial restriction (in this case, LV pressure variates in the same manner whereas RV pressure remains stable as its preload is not influenced by intrathoracic pressure and both ventricles are independent from each other).*

of "square root" or "dip and plateau" sign (secondary to sharp ventricular-pressure increase when pericardial constraining volume is reached immediately after early diastolic inflow) are considered the most important features for the diagnosis [20]. Another important marker of constriction is the presence of significant respiratory variations of LV and RV systolic and diastolic pressures as a consequence of dissociation between intracardiac and intrathoracic pressures (**Figure 5**). This has been quantified using the *systolic area index* (ratio of RV to LV systolic pressures × time area during inspiration). If >1.1 (RV pressure increasing while LV pressure decreasing during inspiration), it is highly suggestive of CP. Moreover, *Kussmaul's sign*, quantified as <5 mm Hg decrease in right atrial pressure during inspiration, is often encountered. It is worth mentioning that hypovolemia secondary to previous aggressive diuretic therapy can mask hemodynamic features described above. An important tip in these cases is to perform a fluid challenge with rapid infusion of saline (500–1000 ml over 5–10 min) before assessment [21]. Finally, not specific but important findings at invasive assessment are also the reduction of stroke volume (as per Frank-Starling effect secondary to reduced diastolic filling) and the maintenance of pulmonary artery pressures within or mildly above upper normal limit, explaining the higher prevalence of right instead of left heart-failure symptoms.
