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.
