Transthoracic echocardiography to identify or exclude cardiac cause of shock

Transesophageal echocardiography (TEE) is often still considered the echocardiographic test of choice in the general ICU patient population to establish the presence or absence of cardiac cause of shock, and is often requested and performed as the initial and only echocardiographic test. This premise is based on older studies in which transthoracic echocardiography (TTE) commonly offered inadequate images in ICU patients.

We hypothesized that current TTE imaging alone is adequate to identify or exclude cardiac cause of shock in the great majority of cases.

One hundred consecutive shock cases in which an echocardiogram was requested were prospectively analyzed by two blinded echocardiographers for image adequacy, and the absence or presence of cardiac cause of shock (defined as one or more of the following: severe left ventricular (LV) or right ventricular systolic dysfunction, tamponade, severe left-sided valve disease, or a postinfarction mechanical complication), and compared to a clinical standard of presence/absence of cardiac cause of shock as determined by autopsy, surgery, or objective testing. Shock was defined as systolic BP < 100 mm Hg or fall in BP >/= 25%, and inotrope use or evidence of low output or venous congestion. Cardiac output was determined by the LV outflow tract (LVOT) Doppler method.

Sixty-three percent of cases had a cardiac cause of shock. TTE image quality was adequate in 99% cases. Among the 99% of cases in which the imaging was adequate, the sensitivity of TTE for cardiac cause of shock was 100%, the specificity was 95%, the positive predictive value was 97%, and the negative predictive value was 100%. There were relative contraindications to TEE in 15% of cases. Stroke volume index (15 +/- 6 mL/m(2) vs 31 +/- 7 mL/m(2) [mean +/- 1 SD]; p < 0.001) and cardiac index (1.6 +/- 0.5 mL/min/m(2) vs 2.9 +/- 0.9 mL/min/m(2); p < 0.001) were significantly less in the group with a cardiac cause of shock than in the group with a noncardiac cause of shock.

In the general critical care population, current TTE imaging identifies the great majority of cardiac causes of shock. TTE should be considered not only the initial, but also the principal echocardiographic test in the critical care environment.