Focused Cardiac Ultrasound Identification of Dynamic Left Ventricular Outflow Tract Obstruction

Focused cardiac ultrasound can narrow the differential diagnosis of shock between four categories: hypovolemic, cardiogenic, vasoplegic, and obstructive. Among subcategories of obstructive shock, dynamic left ventricular outflow tract obstruction is of special relevance to anesthesiologists because it (1) can arise in structurally normal hearts under common perioperative conditions (i.e., hypovolemia, vasoplegia, tachycardia, and/or inotropic excess)¹ ; (2) masquerades as cardiogenic shock by causing a constellation of hypotension, low cardiac output, and high filling pressures² ; (3) requires ultrasound for diagnosis^1–3 ; and (4) requires unique treatments to dilate or distend the left ventricular outflow tract that are diametrically opposite the treatments of cardiogenic shock.^1–3 

The focused cardiac ultrasound image in figure 1 (left) shows a normal parasternal long-axis view (Supplemental Digital Content 1, https://links.lww.com/ALN/D239): the open state of the aortic valve identifies systole during which the left ventricular outflow tract is also open (proposed mnemonic: “open-open”). In contrast figure 1 (right) shows the analogous view obtained in a patient who had been started on dopamine empirically for hypotension due to a history of left ventricular systolic dysfunction. While the aortic valve is open (identifying systole), the left ventricular outflow tract is partly obstructed by the anterior mitral leaflet (“open-closed”). The focused cardiac ultrasound evidence of systolic anterior motion of the mitral valve causing left ventricular outflow tract obstruction prompted a drastic change in management that resolved the patient’s hypotension: immediate cessation of dopamine and at the same time fluid loading.

Dynamic left ventricular outflow tract obstruction can be suspected using two-dimensional ultrasound (assisted by proposed mnemonic “open-closed”) and supported by color Doppler (Supplemental Digital Content 2, https://links.lww.com/ALN/D240). Treatment consists of the following: cessation of inotropes, fluid loading, vasoconstrictors, and (occasionally) β-blockade.^1–3