The utility of microvascular perfusion assessment in heart failure: a pilot study

BACKGROUND: The evaluation of heart failure is routinely based on subjective patient symptoms and physician examination. We propose the noninvasive evaluation of microvascular and global perfusion can objectify heart failure severity and provide additional prognostic information. METHODS: A prospective, observational pilot study of patients previously stratified into New York Heart Association (NYHA) heart failure classes and who after a routine cardiology clinic evaluation were felt to be at their stable baseline state. Measurements included: thoracic impedance (Zo), hypothenar tissue hemoglobin oxygen saturation (StO2), and Zo-derived cardiac index (CI). To determine if adverse outcomes (hospitalization or death) occurred, patients or their families were contacted 6 months after enrollment and their charts reviewed. Monitor values between the NYHA classes were compared using analysis of variance. Values of those who later developed adverse outcomes were compared to patients who remained stable using a Student t-test (P < .05 considered significant). A Kaplan-Meier survival curve was used to describe the adverse outcome rate over time, and a Cox's proportional hazards model was used to relate perfusion values to adverse outcomes. RESULTS: There were no differences in CI (P = .08), Zo (P = .38), or StO2 (P = .14) found between NYHA classes (n = 46). After 6 months, 6 patients required hospitalization for heart failure and 1 died. This group had lower StO2 values compared with the stable group (P = .015). The time course of the adverse events was found not to be due to chance alone when evaluated using a Kaplan-Meier curve and the StO2 was significantly associated with time to adverse outcome (P < .05).CONCLUSIONS: Outpatient heart failure patients who later develop adverse outcomes have significantly lower StO2 values than those who remain stable. This suggests cardiac performance in stable heart failure patients may be better reflected at the microvascular level using measures such as StO2 as opposed to a global level using the physical exam or impedance cardiography. StO2 may serve as a predictor for future adverse events and as an adjunct to current evaluation techniques.