[Electrocardiographic changes during at term labor]

Electrocardiographic ST-changes are known to occur during pregnancy, puerperium and cesarean section or spontaneous labor under oxytocic, tocolytic and anesthetic treatment. The aim of the study was to detect ST-changes during spontaneous labor in healthy women, without anesthetic or oxytocic therapy, and to verify their relation to plasmatic electrolyte variations and other pathophysiologic factors.

Electrocardiograms were performed in 46 healthy women (age 30.4 +/- 6) at term pregnancy, during labor, 12-24 hours after delivery and then again three months after delivery. Hemochrome and sideremia were tested before labor and electrolytes (Na, K, Cl, Mg, Ca) were tested during each electrocardiogram. The patients were divided in two groups, patients with (group A) and without (group B) ST-changes.

Before labor, three patients (7%) were in group A with nonspecific ST-changes (flat ST and/or fluctuating T wave) in precordial leads V2-V3-V4; group B had 43 patients (93%). During labor, group A included 27 patients (59%): 16 (59%) showed T inversion, 23 (85%) nonspecific changes, and eight (30%) had ST shift < or = 0.5 mm, in precordial and inferior leads. The three patients in group A before labor showed increased changes during labor. Group B had 19 patients (41%). Heart rate and blood pressure were within normal range in all patients. Early after delivery, seven patients out of 27 in labor were still in group A (15% of total) with nonspecific ST-changes; group B had 39 patients (85%). Three months after delivery, all patients were in group B. A drop in plasmatic K, detected during labor in all patients and returning to normal soon after delivery, was higher in group A than in group B (p < 0.01).

ST-changes detectable during labor, similar to the ones described during pregnancy and puerperium but greater and more frequent, are independent of anesthetic and/or oxytocic treatment; they are not ischemic and disappear after delivery. They are related to the drop in plasmatic K, hyperventilation, hormonal changes, uterine contractions, O2-consumption and pain.