Physiological basis of electrocardiography
The electrocardiogram is a key tool for reflecting the electrical activity of the heart muscle. It details two main physiological processes: depolarization (excitation) and repolarization (restoration of the electrical potential).
To understand pathology, one must clearly navigate the elements of the normal curve:
- P wave: represents the atrial component, demonstrating their electrical activity.
- PQ (PR) interval: shows the conduction of the impulse from the atria to the ventricular structures. This interval necessarily includes the physiological delay in the atrioventricular node, which is critical for the correct transition of excitation.
- QRS complex: a marker of general depolarization of the ventricular musculature. At the same time, the initial Q wave may be relatively subtle.
- S wave: associated with a delay in electrical impulse conduction. In standard leads (I and II), it should not be excessively deep, whereas a deep S wave is a normal characteristic for chest leads.
- T wave: directly responsible for displaying the process of ventricular repolarization, specifically its active stage.
Secondary repolarization abnormalities in hypertrophy
Repolarization abnormalities can be secondary in nature, which is prominently manifested in right ventricular hypertrophy (RVH). In this case, pathological changes are localized predominantly in the right chest leads ($V_1-V_2$), as well as in the inferior leads (III, aVF).
Characteristic manifestations of secondary ST-T abnormalities:
- The ST segment acquires an arched depression shape.
- A negative T wave is formed, which has a distinct asymmetric shape.
Additionally, RVH is accompanied by changes in the amplitude of ventricular complexes in the left chest leads ($V_5-V_6$). The main sign here is the predominance of the S wave over the R wave. The diagnostic criterion is the $R/S$ amplitude ratio < 1.0. Important condition: this criterion is considered reliable exclusively in the absence of concomitant left bundle branch block (anterior fascicular block) and in the absence of cicatricial post-infarction changes of the anterior wall.
Pathological patterns and risk stratification
Analysis of repolarization processes on a 12-lead resting ECG plays a crucial role in risk stratification, especially in patients with syncope or suspected bradyarrhythmias. Even if the arrhythmia is absent at the time of recording, the electrocardiogram can reveal signs of dangerous conditions with similar clinical symptoms.
Such prognostically significant ECG markers include:
- Specific ECG signs of Brugada syndrome.
- Pathological prolongation or, conversely, shortening of the QT interval (which reflects the duration of electrical systole and repolarization).
- The presence of an epsilon wave, characteristic of arrhythmogenic right ventricular cardiomyopathy.
- Abnormal atrioventricular conduction, for example, a shortened PQ interval, indicating premature ventricular excitation.
The role of ECG in the diagnostic algorithm
To assess repolarization processes, rhythm character, and conduction, a standard 12-lead ECG is indicated for absolutely all patients with existing or suspected bradyarrhythmias. This is a basic non-invasive procedure aimed at verifying structural and systemic heart diseases.
Resting ECG recording is a strict and mandatory prerequisite before proceeding to more complex diagnostic methods, such as:
- Ambulatory (long-term) ECG monitoring (used for intermittent arrhythmias to search for clinical-electrocardiographic correlations).
- Exercise ECG testing.
- Invasive cardiac electrophysiological study (EPS).
Class and exam questions
What is the pathophysiological basis of repolarization abnormalities?
The main cause is an inflammatory process affecting the subepicardial layers of the ventricular myocardium.
Which elements of a normal ECG reflect the repolarization process?
The T wave is responsible for the active stage of ventricular repolarization. Also, in repolarization pathologies, changes affect the ST segment.
What do secondary repolarization abnormalities look like in right ventricular hypertrophy?
They manifest as arched depression of the ST segment and the formation of a negative asymmetric T wave in leads $V_1-V_2$, III, and aVF.
Why is the S wave deep?
The S wave reflects impulse conduction delay. Normally, its significant depth is characteristic of chest leads, whereas in standard leads (I and II) it should not be too deep.
What else to study on this topic
- Additional ECG criteria for right ventricular hypertrophy (RVH)
- ECG signs of bundle branch blocks
- Atrial "overdrive" phenomenon (re-entry)
- Provocative tests in transient bradyarrhythmias
- Methods of long-term ambulatory ECG monitoring
Master the entire topic in the "Propaedeutics" course
This is a summary. The course covers everything tested in classes and exams.
- Full study guide on "Myocardial repolarization abnormalities on the ECG" and 3,152 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 113 video lessons on the subject
Other topics in the "Cardiovascular system" section
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.