User:Dankod/Draft/Fetal ST Analysis

In obstetrics, fetal ST analysis is a method for interpretation of the ECG of the fetal heart. It is used during labour as an adjunct to cardiotocography (CTG).

The aim of fetal monitoring during labour is to identify fetuses at risk of an adverse outcome based on our ability to understand what is happening, and how the fetus reacts to stress before it becomes a risk situation. Despite developments within labor management, the need remains to improve fetal outcome. Standard Cardiotocography (CTG) has high specificity for classification of normality and severe pathological traces. ST Analysis of the Fetal ECG grades the deviation. The combination of ST Analysis and standard CTG parameters provides more accurate information about the fetus during labor than CTG alone.

During hypoxia, the ST interval of the fetal ECG waveform is affected indicating the fetus is suffering from oxygen deficiency. ST Analysis consists of highlighting theses changes. In adults, the ECG is commonly used to diagnose cardio-vascular diseases using a treadmill to induce physical stress. For a fetus, the birth is the treadmill. Changes in ST interval of the fetal ECG shows how the fetus handles the stress of labor and helps clinicians detect signs of hypoxia.

Changes in the ST interval of the Fetal ECG
The ST segment and T wave relate to the repolarisation of myocardial (heart muscle) cells in preparation for the next contraction. This repolarisation process is energy consuming. An increase in T wave height occurs when the energy balance within the myocardial cells is threatened. During hypoxia this balance becomes negative and the cells produce energy using glycogen reserves. This process produces lactic acid and potassium ions (K+) which cause a rise of the ST waveform.

When energy balance cannot be maintained and ischemia occurs in the heart muscle, the sequence of repolarisation will alter. This result in a change of myocardial cell potentials and a depression of the ST segment with or without negative T wave will occur. The maintenance of fetal myocardial function and survival of the fetus during hypoxia depends on myocardial glycogenolysis. With increasing glycogenolysis, there is a further increase in T-wave amplitude and the correlation between the rates of glycogenolysis and increase in T/QRS has been described as linear.

ST depression and negative T waves indicate an imbalance between endo- and epicardium: Unless the myocardium is generally activated (ability of the myocardium to respond to volume load), a decrease in performance for whatever reason, may cause ST depression. Thus, not only hypoxia per se may cause ST depression as a sign of mal-adaptation, but also factors substantially altering the balance and the performance characteristics within the myocardial wall. A number of clinical situations have been associated with ST depression/negative T waves such as prematurity, infections, maternal fever, myocardial dystrophy and cardiac malformations.

ST Analysis of the fetal ECG
The condition of the fetal heart indicates the condition of the brain and the ST waveform reflects the energy balance in the myocardium. A normal ST waveform shows that the fetus has a sufficient oxygen supply with aerobic myocardial metabolism and a positive energy balance

When fetal ECG is recorded with a scalp and a skin electrode, changes in the T wave and the ST segment of the ECG can be automatically identified and analysed using the STAN technology software. In addition to recording the standard CTG parameters, the STAN technology calculates the ratio between the T wave amplitude and the QRS complex amplitude. The T/QRS ratio is displayed as data points (x’es) in the lower section of the STAN screen. If there is a significant change calculated over time, a ST Event will be displayed on the tracing.

CTG + ST Analysis – the STAN method
The ST Analysis is used as an adjunct to standard CTG interpretation to indicate when intervention is required. The user interprets the CTG parameters together with the ST Analysis results, and the STAN Clinical Guidelines helps to decide what clinical action should be taken. The STAN Guidelines provide detailed information on the definition of parameters of the fetal heart rate patterns, and recommends intervention depending on both the CTG interpretation and the ST indicated ST Events.