Right Atrial Effects on Right Ventricular Ejection Fraction Derived From Thermodilution Measurements

Objective: The thermodilution technique provides a convenient means to monitor cardiac output, right ventricular (RV) ejection fraction (EF), and volumes at the bedside. To calculate RVEF from the pulmonary artery temperature curve, the bolus thermodilution technique assumes that right atrial (RA) temperature returns to baseline value within 1 beat following the cold saline injection. The authors hypothesized that this assumption is the reason why the thermodilution technique consistently underestimates RVEF.Design: A theoretical analysis and animal study.Setting: Laboratory, university, multi-institutional.Participants: Animals.Interventions: Cold saline injections.Measurements and Main Results: In 2 porcine experiments, after a rapid injection of cold saline into right atrium, RA temperature took several heartbeats to return to baseline. In a theoretical analysis, if after the cold saline injection RA temperature returned to baseline in 1 beat (RAEF = 1), then thermodilution-derived RVEFT = actual RVEFA. In contrast, if RA temperature took several beats to return to baseline (RAEF = RVEF), then RVEFT consistently underestimated RVEFA. A least square fit of RVEFA versus RVEFT resulted in RVEFA = 1.0 × RVEFT + 0.11. Applying this correction (adding 0.11 to RVEFT) to the data gave relatively small errors in estimating RVEF over a wide EF range.Conclusions: After injecting cold saline into the right atrium, RA temperature takes several heart beats to return to baseline temperature, leading to underestimating RVEF and overestimating RV volumes. The pulsed thermal energy approach by injecting heat into the RV avoids these problems, but the impact of its small temperature signal on RVEF measurements needs to be determined.