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Hemodynamic Changes in a Parturient with Severe Left Ventricular Outflow Obstruction
Abstract Number: T-60
Abstract Type: Case Report/Case Series
A 21 year-old G4P1021 underwent induction of labor at 37 weeks gestation for cardiac decompensation in the setting of a bicuspid aortic valve and subaortic membrane. Cardiac evaluation revealed an aortic valve area of 1.4cm2 with subvalvular narrowing and a peak left ventricular outflow tract gradient of 80mmHg. Prior to induction of labor, epidural analgesia was initiated with 0.1% ropivacaine/0.0002% fentanyl at 8mL/hour. During labor, the patient’s systolic blood pressure (SBP) gradually decreased from 120 to 90mmHg. A phenylephrine infusion was titrated to maintain SBPs >100mmHg. About 8 hours into labor, the patient was noted to be tachycardic with cyclic variations of her heart rate(arrow B) correlating with uterine contractions(arrow C). Fetal heart rate(arrow A) was unaffected. Further evaluation revealed an afebrile, normotensive (with a phenylephrine infusion) patient resting comfortably in the supine position.
Tachycardia in the parturient is commonly associated with pain, fever, hypotension, and/or administration of β-adrenergic agents. In this patient, the sinusoidal pattern of the maternal heart rate (HR) suggests the tachycardia was associated with dynamic hemodynamic changes. Given that the patient was in the supine position, aortocaval compression was undoubtably a contributing factor. Maintenance of adequate preload is fundamental in the management of aortic stenosis. As venous return is impaired, stroke volume (SV) decreases, and the HR must increase to maintain adequate cardiac output (box 1). In a laboring patient, ~400mL of blood is displaced from the intervillous space into the central circulation with each uterine contraction.1 This transient fluid influx leads to an increase in preload, with a concomitant increase in SV and a reflexive decrease in HR (box 2), hence the decrease in maternal HR seen with each contraction.
The sinusoidal maternal heart rate pattern resolved following a 400mL fluid bolus and repositioning into left uterine displacement. The remainder of parturition progressed uneventfully with a vaginal delivery via a planned vacuum-assisted 2nd stage. Stenotic heart lesions and pregnancy is a precarious combination and is associated with higher maternal and neonatal morbidity and mortality.2 Management of the parturient with cardiac disease requires meticulous attention to positioning and fluid administration throughout labor and delivery.
1. Am J Obstet Gynecol 1989; 161:974-7. 2. Obstet Gynecol 1988; 72:113-118.