What does “cardiac tamponade” mean to you? The formal definition is “a clinical syndrome caused by the accumulation of fluid in the pericardial space, resulting in reduced ventricular filling and subsequent hemodynamic compromise.” (eMedicine Nov. 20, 2016; http://bit.ly/2sjcHZf.) But what constitutes hemodynamic compromise? When the patient becomes hypotensive? When the echo shows mass effect on the right heart?
The exact point at which a subacute effusion becomes tamponade is a bit vague, making it difficult to assess when intervention is necessary. At some point in the natural history of a gradually accumulating pericardial effusion, it may enlarge to a point that ventricular filling is compromised, which will lead to obstructive shock and death if not addressed. But what is that point? At what point should we get the drainage kit to the bedside or push our colleagues to the OR when an effusion is present? Is there a specific finding that's sufficiently sensitive and specific? Maybe it is like Supreme Court Justice Potter Stewart famously declared in his classification of pornography, “I know it when I see it.”
A review by Argulian and Messerli revealed several of the common tenets of the evaluation of pericardial effusions, putting some long-held beliefs under scrutiny. (Am J Med 2013;10:858.) They found that many tamponade patients are hypertensive and that depending on clinical or physical exam findings is unreliable.
Most people, when they think of cardiac tamponade, think of echo findings, specifically mass effect from the effusion on the right side of the heart and subsequent impairment of ventricular filling. The authors' literature review found that right ventricular collapse is a specific but not terribly sensitive finding. Similarly, right atrial collapse can occur in the absence of tamponade.
A finding of prolonged right atrial collapse, however, for at least one third of the cardiac cycle, adds more specificity for ruling in tamponade. Evaluating mass effect on the cardiac chambers carries more weight when other findings are added. These other findings include evaluating the respiratory variation in the inflow across the mitral and tricuspid valves. This is the echocardiographic equivalent of pulsus paradoxus and also adds specificity, as do dilation and lack of respiratory phasicity of the inferior vena cava. All of these findings together make the diagnosis of tamponade much more likely in the face of a normotensive or even hypertensive patient.
Patients with acute pericardial effusions (penetrating trauma patients specifically) are in their own class, but the point at which tamponade occurs appears to be a moving target in patients with slower accumulating effusions. Looking at the big picture will help to identify which patients need urgent drainage.
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