Maternal cardiovascular disease (MCD) remains the leading cause of death in pregnant women, especially in the United States, where heart disease is on the rise. The worse outcomes disproportionately affect disadvantaged populations, including those with poor access to healthcare, and ethnic minorities. Reducing maternal mortality is a World Health Organization global health goal, and multiple efforts have been initiated to both study maternal cardiac disease as well as reduce morbidity and mortality. At least half of serious cardiac complications can be prevented with closer monitoring and adequate care. A multidisciplinary approach using the Cardio-obstetrics clinic model has been shown to improve outcomes in women with cardiovascular disease, but successful efforts have been limited to comprehensive care centers in larger cities. Over the past decades, there have also been advances in the risk assessment for pregnant women with cardiac disease, but all risk models have not been as accurate in validation models and further research is warranted.
Hemodynamic changes of pregnancy, during labor, and in the early postpartum period include a decrease in systemic vascular resistance (SVR) and increases in blood volume and heart rate, all resulting in increased cardiac output (CO). There is also an associated increase in ventricular muscle mass and end diastolic volumes with improved systolic function, but without a pathologic increase in end-diastolic pressures. Such hemodynamic and anatomic alterations can exacerbate underlying cardiac disease, as well as uncover previously unrecognized cardiovascular pathology, thereby increasing the risk of cardiac complications.12 Several cardiac complications during pregnancy and in the postpartum period are due to the inapt response to pregnancy with either an inability to augment CO or inability to tolerate the increased CO. Addressing maternal cardiac complications would require earlier detection and identification of those at risk.
Wearable derived biomarkers: Physiological health parameters derived from either non-invasive monitors or wearables allow continuous tracking of such parameters in an ambulatory state:
* Pulse Oximetry (SpO2) is used to detect peripheral cyanosis, normal being \>95%, and has been used to detect newborn cyanosis in children with congenital heart disease, albeit with reduced accuracy at saturations \<60%.
* Respiratory rate in breaths per minute (RRp) can increase in pregnancy from 8-12 breaths per minute to 15-17 breaths per minute, but it increases to a larger extent in states of distress, infection, and cardiovascular decompensation. In one study, increased RRp, and heart rate (HR) were detected early in women that were found to have an intraamniotic infection, demonstrating the benefit of such monitors in early detection of pathology.
* Heart rate variability (HRV) measures changes in the time intervals between consecutive heartbeats and is a surrogate for neural cardiac control and the balance between the sympathetic and parasympathetic drive. Higher variability (50-100 ms) is normal with an overall decline with age. Low HRV has been shown to be a predictor of poor outcomes in patients with cardiac disease in small studies, a wearable device was used to evaluate HRV during normal pregnancy, and it was found to be overall decreased (50-70 ms), but with a dynamic burst in autonomic activity in the transition from second to third trimester
* In addition, these monitors can provide dynamic indices that include the perfusion index (Pi), which depends on the blood flow in the peripheral circulation, the cardiac output, and the vascular tone, which is calculated from the amount of light constantly absorbed by skin from non-pulsatile blood, and the variable amount of light absorbed by pulsating arterial inflow, with values ranging from 0.2%-20%, with lower percentages indicating lower perfusion state. There have been unvalidated suggestions that Pi can be used as a surrogate for CO.
* The pleth variability index (PVi), is the maximal and minimal Pi over a respiratory cycle and is also expressed in %, with a range of 9-13%. In a randomized controlled trial of intraoperative and postoperative patients, elevated PVi was used to direct fluid management by administering crystalloid infusions in PVi \>13%, with appropriate fluid responsiveness. Such intervention reduced the overall fluid infused to patients, and reduced lactate levels. Elevated PVi has also been used to predict hypotension in pregnant women undergoing c-section.
Masimo® noninvasive monitors (Masimo Corp, Irvine, CA) are FDA approved for use in adults and newborns to provide real time pulse oximetry (SpO2) and heart rate. Masimo has CE mark for additional parameters which include PVR, atrial fibrillation respiratory rate per minute (RRp), heart rate variability (HRV), and PVi. Clinical studies demonstrated they are motion-tolerant, report functional oxygen saturation, and validation in low perfusion conditions. Smart wristbands are an unobtrusive, and promising novel method to monitor ambulatory health parameters throughout pregnancy. The Masimo W1® wristband is FDA approved and uses clinically tested technology in a wearable patient-friendly format. Compliance with wearable devices has been demonstrated in a small study of 20 pregnant women where it was worn approximately 6 out of 7 months, with a slight drop in adherence postpartum.
