Does Left Ventricular Tissue Doppler Peak Systolic Velocity (Sm) Reflect Cardiac Output in the Critically Ill?

Cardiac output (CO) is dependent on a number of factors, in particular, the systolic function of the heart. Tissue Doppler (TD) is a modality in echocardiography that measures myocardial velocity and is related to contractility. TD can therefore be used to measure the systolic function of the heart. This study sought to establish whether the systolic component of TD can be used to estimate CO in critically ill patients. Retrospective data was obtained from a total of 80 patients: 29 patients with a normal echocardiogram, and 51 intensive care unit patients; 28 septic and 23 with heart failure. The mean TD peak systolic velocity (Sm) was significantly lower in the heart failure patients (P <0.05) compared to both normal and septic group. The mean CO was significantly higher in septic patients when compared to heart failure patients. A mild to moderate positive correlation was found between Sm and CO in the heart failure group and with all patients combined (r2=0.19, P <0.001). Subsequent analysis of Sm versus stroke volume again showed a mild positive correlation in the heart failure group and combined results (r2=0.18, P <0.001). Sm was weakly correlated to heart rate only in the normal group but not in the combined cohort. Our data confirms a weak to moderate correlation between Sm and CO, probably resulting from a positive correlation of Sm and stroke volume. This correlation is not strong enough to support the use of an individual's Sm to estimate CO in intensive care patients.