Pulsus paradoxus: an underused tool

Point-of-Care Diagnosis of Cardiac Tamponade Identified by the Flow Velocity Paradoxus

The presentation of cardiac tamponade is a spectrum from occult to extreme. The clinical history, physical exam, electrocardiogram, and radiographic findings of tamponade have poor sensitivities and even worse specificities. We use a clinical scenario to demonstrate how point-of-care cardiac ultrasound can diagnose impending cardiac tamponade in a clinically stable patient. The ultrasound finding we recommend is the flow velocity paradoxus, in which respiratory variation causes significant changes in transvalvular inflow velocities, which are exaggerated when tamponade is present. The management of a pericardial effusion depends on its physiologic effect, and point-of-care ultrasound directly measures that effect and expedites patient care.

Unrecognized tamponade diagnosed pre-induction by focused echocardiography

PURPOSE

We report a case of unrecognized cardiac tamponade diagnosed pre-induction by focused transthoracic echocardiography (TTE). The value of focused perioperative TTE, the anesthetic implications of Churg-Strauss syndrome, and the diagnosis of cardiac tamponade are discussed.

CLINICAL FEATURES

A 58-yr-old man with a history of severe asymptomatic aortic stenosis presented for elective endoscopic sinus surgery for intractable nasal polyps with recurrent sinusitis. His cardiologist and cardiac surgeon had recommended proceeding with surgery, as aortic valve replacement was not indicated because he was asymptomatic. Prior to induction, a focused TTE was performed by anesthesia in order to document the degree of aortic stenosis, baseline ventricular function, and baseline volume status. This provided a baseline for comparison in case the patient's hemodynamic status should deteriorate intraoperatively. Unexpectedly, the TTE examination revealed cardiac tamponade. After confirmation of the diagnosis by cardiology, urgent pericardiocentesis was performed. A diagnosis of Churg-Strauss syndrome was ultimately made, and the patient was treated with high-dose prednisone therapy.

CONCLUSION

Focused TTE has significant clinical utility for the diagnosis and assessment of hemodynamically significant cardiac conditions, particularly in the complex patient where clinical examination is challenging and echocardiographic findings can have immediate management implications.

Mechanism study of pulsus paradoxus using mechanical models

Pulsus paradoxus is an exaggeration of the normal inspiratory decrease in systolic blood pressure. Despite a century of attempts to explain this sign consensus is still lacking. To solve the controversy and reveal the exact mechanism, we reexamined the characteristic anatomic arrangement of the circulation system in the chest and designed these mechanical models based on related hydromechanic principles. Model 1 was designed to observe the primary influence of respiratory intrathoracic pressure change (RIPC) on systemic and pulmonary venous return systems (SVR and PVR) respectively. Model 2, as an equivalent mechanical model of septal swing, was to study the secondary influence of RIPC on the motion of the interventriclar septum (IVS), which might be the direct cause for pulsus paradoxus. Model 1 demonstrated that the simulated RIPC had different influence on the simulated SVR and PVR. It increased the volume of the simulated right ventricle (SRV) when the internal pressure was kept constant (8.16 cmH₂O), while it had the opposite effect on PVR. Model 2 revealed the three major factors determining the respiratory displacement of IVS in normal and different pathophysiological conditions: the magnitude of RIPC, the pressure difference between the two ventricles and the intrapericardial pressure. Our models demonstrate that the different anatomical arrangement of the two venous return systems leads to a different effect of RIPC on right and left ventricles, and thus a pressure gradient across IVS that tends to shift IVS left- and rightwards. When the leftward displacement of IVS reaches a considerable amplitude in some pathologic condition such as cardiac tamponade, the pulsus paradoxus occurs.