What is transmural injury and its signs
Depending on the depth of the lesion, myocardial infarctions are classified as subendocardial, intramural, subepicardial, and transmural. Transmural infarction is the most severe variant, in which the entire thickness of the muscular wall dies. As a rule, it is extensive and develops due to the occlusion of a major vessel (e.g., the main trunk of the left coronary artery).
In clinical practice, it is categorized among acute coronary syndromes with ST-segment elevation (STEMI) and classified as a Q-wave myocardial infarction. The classic ECG picture consists of two types of changes:
- Direct signs: recorded in leads located directly over the necrosis zone. A pronounced ST-segment elevation is observed. In severe cases, it merges with the T wave, forming a monophasic curve. The ventricular complex takes the form of QS — the R wave completely disappears, leaving only a deep pathological Q wave indicating transmural necrosis.
- Reciprocal (mirror) changes: recorded on the opposite wall. For example, with massive ST elevation on the anterior wall, ST-segment depression is recorded in the inferior leads (II, III, aVF).
ECG evolution by stages
The electrocardiogram during an infarction is not static — it reflects the dynamics of tissue death and the subsequent replacement of muscle tissue with a scar. Chronology of changes:
- Hyperacute stage (1 hour after the onset of pain). Early markers of ischemia and acute injury are recorded. The main sign is massive ST-segment elevation.
- Acute and subacute stages (24 hours). Necrosis is definitively established in the zone of pronounced ischemia. On the ECG, this manifests as the appearance of a pathological Q wave or QS complex.
- Scarring stage (10 days and later). The changes consolidate. The ST segment gradually returns to the isoelectric line, but the pathological Q wave persists — this is a lifelong electrocardiographic "scar".
Topical diagnosis: localization of the infarction
By identifying the leads where direct signs (ST elevation and Q wave) are recorded, one can precisely determine the localization of necrosis and the basin of the affected artery. Detailed analysis of chest leads allows for the identification of specific structures: a pathological Q wave in V2 indicates involvement of the interventricular septum, in V4 — the apex, and in V6 — the lateral wall of the left ventricle.
Correspondence of leads to the affected zone:
| Infarction localization | ECG leads with direct signs |
|---|---|
| Anteroseptal | I, aVL, V1–V4 |
| Anterolateral (extensive) | I, II, aVL, V1–V6 |
| Isolated lateral | I, aVL, V4–V6 |
| Inferior (diaphragmatic) | II, III, aVF |
| Inferolateral | II, III, aVF and aVL, V5–V6 |
| Posterior | Occlusion of the circumflex branch (posterior wall and septum) |
Note: If the clinical picture suggests an infarction, but changes are absent in the standard 12 leads ("silent" ECG), ECG mapping is used — recording biopotentials at 35 precordial points.
Reciprocal (mirror) changes on the ECG operate on a "seesaw principle". If the ST segment rises massively (elevation) on the anterior wall, it predictably drops (depression) on the opposite, inferior wall (leads II, III, aVF).
Class and exam questions
What does a QS-type ventricular complex mean?
This is a curve shape in which the R wave is entirely absent and only a deep Q wave is recorded. It indicates the death of muscle tissue across the entire thickness of the wall (transmural necrosis), leaving no viable myocardium to generate an R wave.
Does myocardial infarction always present with typical substernal pain?
Not always. In the abdominal form (2–3% of cases), the posterior wall or apex is affected, causing abdominal pain, vomiting, and stool disorders, which is often mistaken for poisoning. In the painless form, complications such as pulmonary edema or severe arrhythmia may be the very first manifestations.
Does a normal ECG rule out the presence of a myocardial infarction?
No. The absence of changes at the moment of recording does not rule out a non-Q-wave infarction (intramural or small-focal). In such cases, the diagnosis relies heavily on tracking the dynamics of cardiospecific enzymes.
What else to study on this topic
- Non-Q-wave myocardial infarction: ECG features and enzymatic diagnostics
- ECG mapping technique: rules for placing 35 precordial leads
- Atypical forms of myocardial infarction: asthmatic, arrhythmic, cerebral, and peripheral
- Right ventricular infarction: why it rarely develops and how it is detected
- ACS classification by ECG in the first 24 hours: differential diagnosis of unstable angina and MI
Master the entire topic in the "Propaedeutics" course
This is a summary. The course covers everything tested in classes and exams.
- Complete guideline on "Transmural Myocardial Infarction on 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 "Additional Topics" section
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.