Electrocardiography as a research method

Specialized ECG diagnostic methods

In addition to standard ECG, where it is important to consider the recording speed (25 or 50 mm/s) for accurate heart rate calculation, a number of supplementary techniques are used in clinical practice:

• Holter monitoring: long-term rhythm recording. It allows for quantitative assessment of arrhythmias and correlation of ECG changes (especially the ST-T segment in ischemia) with patient complaints and physical activity.
• Transesophageal ECG (TEEG): the electrode is lowered into the esophagus to a depth of 35–40 cm from the front teeth. This ensures maximum proximity to the left atrium for detailed study of the P wave and therapeutic electrical stimulation.
• Signal-averaged ECG: detects low-amplitude "late potentials" immediately after the QRS complex. Their prolongation is a marker of conduction delay and high risk of ventricular arrhythmias.
• Intracardiac EPS: multi-channel catheters are inserted directly into the heart chambers. The method identifies hidden conduction pathways and re-entry circuits (re-entry). It is often concluded with radical treatment: radiofrequency or laser ablation.

Assessment of fetal cardiac activity

Auscultation, ECG, and cardiotocography (CTG) are used to monitor the condition of the fetus.

Auscultation is performed using an obstetric stethoscope. The topography of auscultation depends on the fetal presentation: in cephalic presentation, heart tones are heard below the umbilicus; in breech presentation, at or above the umbilicus. An exception is face presentation, where due to maximal head extension, the heartbeat is heard better from the side of the fetal chest rather than the back. It is important to distinguish fetal heart tones from maternal sounds (pulsation of uterine vessels, bowel sounds).

Fetal ECG comes in two types:

1. Indirect (external): electrodes are attached to the mother's abdomen (after 32 weeks). The fetal ventricular QRS complex is clearly visible on the strip.
2. Direct (internal): used strictly during labor (with cervical dilation from 3 cm and amniotic rupture). A spiral electrode is fixed directly to the scalp skin. Rhythm, heart rate (norm 120–160 bpm), voltage (9–65 µV), and QRS width (0.03–0.07 s) are assessed.

Cardiotocography (CTG) evaluates the basal rhythm (average heart rate over 10 minutes excluding accelerations and decelerations) and its variability (frequency and amplitude of instantaneous oscillations). External CTG is recorded for 40–60 minutes with the woman lying on her left side.

ECG criteria for atrial fibrillation and flutter

Complete disappearance of the normal sinus P wave is a marker sign of atrial rhythm disturbances.

Atrial fibrillation (AF) is confirmed by three signs:

• Absence of the P wave.
• Presence of fibrillation f waves (small, variable in shape and amplitude, best seen in leads V1, V2, II, III, aVF).
• Absolutely irregular R-R intervals with normal, unchanged morphology of QRS complexes.

Important: for diagnosis on a standard ECG, the episode must last ≥ 10 seconds, and during continuous monitoring ≥ 30 seconds.

Atrial flutter (AFl) is characterized by the presence of regular saw-tooth F (Flutter) waves at a rate of 250–350 per minute (without an isoelectric line between them). The ventricular rhythm may be regular, which clinically masks the arrhythmia as sinus rhythm. For better visualization of F waves, a diagnostic test is used: carotid sinus massage, which temporarily slows down the ventricular rate.

Differential diagnosis of atrial activity

To reliably identify pathology, one must remember the parameters of the normal P wave: it reflects the physiological sequential activation of the right and then the left atrium. Normally, its width is less than 0.12 s, height less than 3 mm; it is always negative in aVR.

Conditions for differential diagnosis of atrial fibrillation:

• Atrial premature complex: premature cycle, P wave is present but deformed, followed by an unchanged QRS and an incomplete compensatory pause.
• Retrograde conduction: the impulse travels from the AV junction or ventricles to the atria, causing the P wave to become negative.
• Sinus tachycardia: heart rate increases to 90–180 bpm, but the association of each P wave with the subsequent QRS complex is strictly preserved. At high rates, the T wave may merge with the P wave of the next cycle, mimicking an arrhythmia, but the P wave itself does not disappear.

Class and exam questions

What else to study on this topic

• Topography of fetal heartbeat auscultation in various presentations and positions.
• Methodology for performing intracardiac electrophysiological study (EPS).
• Analysis of basal rhythm variability during cardiotocography (CTG).
• Multidisciplinary approach to finding extracardiac causes of arrhythmias.
• Radiofrequency ablation as a method of radical treatment for rhythm disorders.

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.