Changes in Rate-Pressure Product Associated with Pregnancy.

BACKGROUND: In non-pregnant individuals, the rate-pressure product, the product of heart rate and systolic blood pressure, is used as a non-invasive surrogate of myocardial oxygen consumption during cardiac stress testing. Pregnancy is considered a physiologic cardiovascular stress test. Prior evidence describing the impact of pregnancy on myocardial oxygen demand, as assessed by the rate-pressure product, is limited.

OBJECTIVES: To describe changes in rate-pressure product by pregnancy trimester, during labor and delivery, and postpartum among low-risk pregnancies.

STUDY DESIGN: Retrospective cohort study assessing uncomplicated pregnancies delivered vaginally at term. We collected rate-pressure product (heart rate x systolic blood pressure) values pre-conception, during pregnancy by trimester (≤13 weeks 6/7 days, 14 weeks 0/7 days through 27 weeks 6/7 days, and ≥28 weeks 0/7 days), labor and delivery encounter (hospital admission until complete cervical dilation, complete cervical dilation until placental delivery, and after placental delivery until hospital discharge), and during outpatient postpartum visit 2-6 weeks following delivery. We calculated the percentage change at each time point from the preconception rate-pressure product (delta rate-pressure product). We used a mixed-linear model to analyze differences in mean delta rate-pressure product over time and the influence of pre-pregnancy age, pre-pregnancy body mass index, and neuraxial anesthesia status during labor and delivery on these estimates.

RESULTS: Our cohort was comprised of 316 patients. The mean rate-pressure product increased significantly from preconception starting in the third trimester of pregnancy and during labor and delivery (p = <0.05). Mean delta rate-pressure product peaked at 12% and 38% in the third trimester and during labor and delivery, respectively. Pre-pregnancy body mass index was inversely correlated with mean delta rate-pressure product changes (estimate -.308 95% p = 0.008). In contrast, neither pre-pregnancy age nor neuraxial anesthesia status during labor had a significant influence on this parameter.

CONCLUSION: This study validates the transient but significant increase in the rate-pressure product, a clinical estimate of myocardial oxygen demand, during uncomplicated pregnancies delivered vaginally at term. Pregnant individuals with lower pre-pregnancy body mass index experienced a sharper increase in this parameter. Patients who receive neuraxial anesthesia during labor and delivery experience similar changes in the rate-pressure product to those who do not.