Low prognostic value of novel nocturnal metrics in patients with OSA and high cardiovascular event risk: post hoc analyses of the SAVE Study

Abstract

Background: Traditional methods for the quantification of OSA severity may not encapsulate potential relationships between hypoxemia in OSA and cardiovascular risk. Research Question: Do novel nocturnal oxygen saturation (Spo2) metrics have prognostic value in patients with OSA and high cardiovascular event risk? Study Design and Methods: We conducted post hoc analyses of the Sleep Apnea Cardiovascular Endpoints (SAVE) trial. In 2687 individuals, Cox proportional hazards models that were stratified for treatment allocation were used to determine the associations between clinical characteristics, pulse oximetry-derived metrics that were designed to quantify sustained and episodic features of hypoxemia, and cardiovascular outcomes. Metrics included oxygen desaturation index, time <90% Spo2, average Spo2 for the entire recording (mean Spo2), average Spo2 during desaturation events (desaturation Spo2), average baseline Spo2 interpolated across episodic desaturation events (baseline Spo2), episodic desaturation event duration and desaturation/resaturation-time ratio, and mean and SD of pulse rate. Results: Neither apnea-hypopnea index, oxygen desaturation index, nor any of the novel Spo2 metrics were associated with the primary SAVE composite cardiovascular outcome. Mean and baseline Spo2 were associated with heart failure (hazard ratio [HR], 0.81; 95% CI, 0.69-0.95; P = .009; and HR, 0.78; 95% CI, 0.67-0.90; P = .001, respectively) and myocardial infarction (HR, 0.86; 95% CI, 0.77-0.95; P = .003; and HR, 0.81; 95% CI, 0.73-0.90; P < .001, respectively). Desaturation duration and desaturation/resaturation time ratio, with established risk factors, predicted future heart failure (area under the curve, 0.86; 95% CI, 0.79-0.93). Interpretation: Apnea-hypopnea index and oxygen desaturation index were not associated with cardiovascular outcomes. In contrast, the pattern of oxygen desaturation was associated with heart failure and myocardial infarction. However, concomitant risk factors remained the predominant determinants for secondary cardiovascular events and thus deserve the most intensive management.