ECG criteria
- Negative T wave in V1–V3 (sometimes V1–V4) — a key yet nonspecific sign of RV strain
- Negative T in III and/or aVF with simultaneous inversion in V1–V3 — often described as an acute cor pulmonale pattern, but nonspecific on its own
- S1Q3T3 pattern: S in I, Q in III, negative T in III
- Rightward axis deviation or a sharp axis shift compared to a previous ECG
- Incomplete (QRS 110–119 ms) or complete (QRS ≥120 ms) right bundle branch block with rsR'/rSR' in V1–V2 and a wide terminal S in I, aVL, V5–V6; new onset is established only by comparison with a prior ECG
- ST elevation in aVR and/or V1 with widespread ST depression is sometimes described in severe PE, but it is nonspecific and not a criterion for massive PE; diagnosis and risk are determined by clinical presentation, hemodynamics, imaging, and echocardiography
- P pulmonale (tall peaked P ≥ 2.5 mm in II) — a possible but nonspecific sign of right atrial enlargement; its absence does not rule out RV strain or PE
- Sinus tachycardia as a background, nonspecific, but frequent companion
What it looks like on ECG
The basis of the pattern is secondary ST-T changes in leads reflecting the right ventricle: V1–V3, sometimes V4. The T wave here becomes negative, often symmetrical, and variable in depth. The ST segment may be slightly depressed or, with marked overload, minimally elevated in V1.
T-wave inversion in III and aVF may accompany RV strain, but it is nonspecific and cannot be explained simply by these leads corresponding to the RV outflow tract — the changes depend on the net depolarization and repolarization vector, heart position, and the degree of overload. The classic combination is the S1Q3T3 pattern: S wave in I, Q wave in III, and negative T in III. This is not mandatory, but a frequently mentioned companion of acute RV overload in PE.
The electrical axis of the heart (EAX) may shift acutely to the right compared to the previous tracing — dynamics matter more than the absolute angle. Incomplete or complete right bundle branch block may appear: complete — QRS ≥120 ms, rsR'/rSR' in V1–V2, and wide terminal S in I, aVL, V5–V6; incomplete — the same morphology with QRS 110–119 ms in adults. A "new" block can only be claimed when compared with a previous ECG.
| Leads | Typical change |
|---|---|
| V1–V3 | negative T, possible minor ST depression/elevation |
| III, aVF | negative T, Q in III |
| I | S (as part of S1Q3T3) |
| aVR | ST elevation possible with marked overload |
Background often includes sinus tachycardia and possible signs of right atrial enlargement (P pulmonale in II).
Mechanism
When pressure or volume increases in the right ventricle (dilatation, RV wall ischemia, increased afterload), the sequence and velocity of myocardial depolarization and repolarization change. This shifts the repolarization vector, causing the T wave in leads facing the anterior RV wall (V1–V3) to become negative — secondary ST-T changes. The same mechanism underlies the pattern in hypertrophy, but in acute overload it develops rapidly without time for structural myocardial remodeling; in chronic overload (pulmonary hypertension, chronic cor pulmonale), strain may coexist with pre-existing RV hypertrophy. Acute PE adds acute RV dilatation and interventricular septum shifting, which increases electrical instability of the right heart and may be accompanied by axis shifts and bundle branch block.
Causes
- Acute pulmonary embolism (the most frequent acute cause)
- Decompensation of chronic cor pulmonale (COPD, pulmonary hypertension)
- Acute right ventricular infarction
- Severe bronchial asthma attack, pneumothorax (acute pulmonary circulation load)
- Acute respiratory distress syndrome
- Chronic pulmonary hypertension of any etiology
- Decompensation of right-sided valvular lesions, congenital heart disease with RV overload
Differential diagnosis
- Right ventricular hypertrophy — signs of increased myocardial mass (tall R in V1, persistent rightward axis deviation) and often a chronic cause of strain; hypertrophy and overload can coexist, one does not exclude the other
- Wellens' syndrome — deep symmetrical or biphasic T-wave inversion in V2–V3 (may extend), occurring in the pain-free phase after an anginal episode, most commonly with critical proximal LAD stenosis; pathological Q waves and marked R-wave reduction are absent, ST changes are minimal; requires urgent evaluation as ACS
- Normal juvenile T wave — negative T in V1–V3 in young people and children as a normal variant, without acute clinical symptoms or dynamics
- Right bundle branch block per se — secondary T-wave inversion in V1–V2 without signs of right heart overload (no S1Q3T3, no acute clinical presentation)
- Anterior wall ischemia — T-wave inversion in V1–V4 can also occur in NSTEMI; differentiate based on clinical presentation, troponin dynamics, and concomitant changes
Clinical significance and management
The ECG pattern of RV strain is nonspecific on its own, but in an acute clinical setting (sudden dyspnea, chest pain, hypotension, venous thromboembolism risk factors), it increases suspicion of PE and warrants urgent workup. In low/intermediate clinical probability, a validated D-dimer algorithm is used; in high probability, proceed directly to imaging. In a hemodynamically unstable patient, resuscitation assessment and bedside echocardiography take priority; CT pulmonary angiography is performed only if the patient is stable and can be safely transported. The ECG does not replace imaging, and a normal ECG does not rule out PE. Dynamic ECG changes (appearance of new RV strain signs) raise alertness, but severity and hemodynamic risk are determined by blood pressure, lactate, biomarkers, and imaging data, not by the ECG alone. In chronic cor pulmonale, the pattern is used as one of the markers of right heart load requiring adjustment of underlying lung disease therapy.
Common interpretation errors
- Mistaking isolated T-wave inversion in V1 (a common normal variant) for pathology without clinical context
- Failing to compare serial ECGs — the appearance of new changes is more important than absolute values
- Automatically interpreting S1Q3T3 as an inferior myocardial infarction: the Q wave in III can be small and physiological; evaluate other inferior leads, ST-T dynamics, clinical picture, and troponin
- Ignoring concurrent sinus tachycardia and P pulmonale as part of the overall picture
- Interpreting right bundle branch block as an independent diagnosis without assessing acuteness and comparing with a prior ECG
S1Q3T3 is a simple, but not mandatory, clue in acute cor pulmonale
1. Which ECG sign is most characteristic (though nonspecific) of right ventricular overload?
T-wave inversion in the right precordial leads is the most characteristic, yet nonspecific, secondary sign of right ventricular load.
2. Which condition most frequently produces an acute right ventricular strain pattern on the ECG?
Acute PE sharply increases pulmonary circulation pressure and produces the classic acute RV strain pattern.
3. What does the S1Q3T3 pattern consist of?
The classic combination is an S wave in lead I, a Q wave and a negative T wave in lead III.
Frequently asked questions
Does S1Q3T3 always indicate PE?
No, this pattern occurs in less than half of patients with PE and can be a normal variant or the result of other causes of right heart overload. Diagnosis is based on a combination of clinical presentation and imaging, not on a single ECG finding.
How to distinguish right ventricular strain from Wellens' syndrome?
Both show negative T waves in the right-to-mid precordial leads, but Wellens' sign typically appears in the pain-free phase following an anginal episode, is associated with critical proximal LAD stenosis, and is not accompanied by signs of right ventricular overload (S1Q3T3, right axis deviation). When in doubt, evaluation for a possible ACS is required.
Is right ventricular strain on ECG dangerous?
The finding itself is non-specific and not dangerous per se, but in an acute situation, it signals a potential significant load on the right heart chambers—most commonly due to PE—and requires prompt further investigation and hemodynamic assessment.
Is echocardiography necessary when right ventricular strain is suspected on ECG?
Yes, bedside echocardiography allows for a rapid assessment of right ventricular dilation and function and helps determine severity, especially in unstable hemodynamics.
How does RV strain differ from right ventricular hypertrophy?
Strain refers to secondary ST-T changes that can be acute, subacute, or chronic and do not rule out structural myocardial remodeling. Right ventricular hypertrophy refers to signs of increased myocardial mass and is often a chronic cause of strain; the two phenomena frequently coexist.
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Related terms
More in the section «Hypertrophy and Chamber Enlargement»
Sources
- Goldberger A. Clinical Electrocardiography, latest edition
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice
- ESC Guidelines on acute pulmonary embolism
- Orlov V.N. Guide to Electrocardiography
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.