Direct fetal electrocardiography

Equipment and methods. It is recommended to use the fetal monitor BMT 9141 in combination with a recording and recording device. Screw electrodes are used as electrodes. The electrodes are placed on the protruding part of the fetus (head, buttocks) taking into account contraindications: placenta previa (partial or complete), presentation of the umbilical cord loops, rupture of the fetal bladder with a high-standing head. A connector plate is placed on the mother's thigh, which is practically the closing link in the chain between the electrode and the monitor. To record a direct ECG of the fetus, the recommended tape speed is 50 mm/s, and to distinguish a greater number of components in a number of obstetric situations, it is advisable to increase the tape speed to 100 mm/s. Among the complications with a direct ECG, in rare cases (0.6-0.8%), the fetus may experience: scalp abscesses, bleeding, necrosis, sepsis. During rotational movement of the fetal head, the screw electrodes may become skewed, so that sometimes their partial displacement (tearing off) occurs, which can damage the soft tissues of the mother's birth canal. Therefore, it is necessary to observe the rules of asepsis both during pregnancy and childbirth:

• vaginal sanitation during pregnancy;
• strict adherence to the rules of asepsis and antisepsis when applying electrodes;
• After childbirth, immediately treat the site of application of the electrodes with an alcohol solution.

The fetal ECG consists of two parts - atrial and ventricular. As an empirical rule, it can be considered that the time norms in the fetal ECG are % of the time norms of the adult ECG.

It is important to determine the electrical axis of the heart according to Larks:

• if the vector of the electrical axis of the heart lies in the zone between 180" and 330", it is in the critical zone;
• if there is no pathology of the umbilical cord, a heart defect can be assumed;
• This information is made available to the neonatologist;
• It is advisable to perform a heart axis calculation curve so that the position of the heart axis can be immediately determined from it.

It is advisable to compare (methods of determining) the position of the intranatal and postnatal cardiac axis. For example, with a tight umbilical cord around the fetus's neck, admixture of meconium, when the fetus's cardiac axis was found in the critical zone during labor, it is possible to assume the persistence of this pathological cardiac axis in the first 2 days after labor. Therefore, with an intranatal pathological cardiac axis, a postnatal ECG is necessary.

Possibility of erroneous conclusions (deviations from the norm):

• technical malfunctions of equipment;
• superposition of maternal impulses in the ECG in case of intrauterine fetal death;
• maternal impulses in normal fetal ECG;
• incorrect connection (polarization) of electrodes from the skin of the fetal head;
• superposition of alternating currents on the fetal ECG curve.

Recommended:

• Before each decoding of the fetal ECG, it is necessary to additionally check whether a free from disturbing effects, cleanly recorded and technically correlative ECG has been obtained;
• In unclear, doubtful cases, other data should have priority (CTG, analysis of acid-base and gas composition of blood, ECG of the mother). ECG of the fetus is always an additional diagnostic method.

Abnormalities in fetal ECG:

• reversible or persistent negative P waves may be a sign of umbilical cord pathology. Differential diagnosis: migrating pacemaker;
• rhythm disturbances in the intranatal ECG of the fetus are mainly caused by hypoxia and congenital defects;
• in case of persistent sinus tachycardia there is a risk of fetal heart failure, therefore an attempt at transplacental cardioversion is indicated with certain precautions;
• the upper AV node rhythm may be a symptom of hypoxia and/or umbilical cord pathology;
• In some cases, ventricular extrasystoles that appear are usually harmless and safe. Regularly alternating extrasystoles (bi-, tri- and quadrigeminy) are warning signals. Postnatal monitoring with ECG is necessary.
• supraventricular tachycardia is a serious rhythm disorder and perinatal pharmacology of the fetal heart is indicated (adrenergic agents, calcium antagonists, etc.). Intensive therapy is mandatory in the postnatal period. If no congenital malformations are detected, the prognosis for supraventricular tachycardia is good;
• in case of AV block of I-III degree, heart defect should be excluded postnatally. Newborns with AV block require intensive observation by a neonatologist;
• jaggedness and splitting of the P wave in the sense of delay of the upper transition point or blockade of the legs of the bundle of His is almost always a symptom of umbilical cord pathology. It is also necessary to exclude a heart defect and take an ECG in the postnatal period.

Intranatal therapy of rhythm disorders. In case of persistent fetal tachycardia it is recommended:

• establishing the supraventricular origin of tachycardia by analyzing the ECG;
• recording the mother's ECG to exclude contraindications to the prescribed therapy;
• monitoring the mother's blood pressure and pulse;
• 1 tablet of anaprilin (obzidan, propranolol) - 25 mg orally to the mother (or 1 tablet - 0.25 mg of digoxin);
• continuous monitoring of fetal ECG;
• postnatal ECG and intensive neonatal monitoring, postnatal digoxin therapy is possible.

ST segment elevation and depression.ST segment depression may indicate the following pathology:

• violation of regulation (dysregulation) of cerebro-vagotropic effects of blood circulation due to compression of the head during passage through the birth canal;
• umbilical cord pathology (entanglement, knots, vascular anomalies);
• shift in electrolyte balance (hyperkalemia);
• Bland-White-Garland syndrome;
• myocarditis.

There are three forms of ST segment depression in the fetal ECG:

• trough-shaped depression of the ST segment,
• horizontal depression of the ST segment,
• oblique upward depression of the ST segment.

Thus, a sharp and prolonged decrease in the ST segment is mostly a symptom of hypoxia and/or umbilical cord pathology. Therefore, it is necessary to try to use other methods to determine the state of the fetus - acid-base balance and blood gases.

The T wave during the excitation process in the fetal ECG, in particular the decrease or increase of the T wave, should never be performed in isolation and there should be careful interpretation of these changes.

ECG of a dying fetus. The most characteristic signs:

• tall, sharp, biphasic inverted P wave;
• jagged, mostly unusually shaped QRS complex;
• ST segment depression,
• shortening of the PR interval;
• T wave inversion.

It is important to take into account the ECG results and medications that the mother received during pregnancy and childbirth.

A program has been developed for computer analysis of fetal ECG during labor in various obstetric situations. With the increase in technical equipment of maternity hospitals and the simplification of automation of fetal ECG, the volume of information of which is far from exhausted, the obstetrician will receive important information about the condition of the fetus during labor.

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