ECG criteria
- Evaluate QRS in lead I: total amplitude is predominantly negative (S is deeper than or equal to R) — criterion for RAD
- Evaluate QRS in aVF: total amplitude is predominantly positive (R is taller than S) — confirms RAD
- Lead III: as a rule, QRS is positive; when the axis deviates rightward of approximately +105–120°, R in III may be taller than in aVF
- Calculated electrical axis angle (using tables or the Bayley hexaxial system) is greater than +90°
- Differentiate from extreme axis deviation ("northwest axis"): in that case, QRS is negative in both lead I and lead aVF
- Check QRS width and morphology: in RBBB (QRS ≥120 ms, rsR' in V1), RAD requires a separate search for the cause; left posterior fascicular block requires QRS ≥120 ms, marked RAD (often ≥+120°), rS in I and aVL, qR in III and aVF while excluding other causes of rightward shift
- Correlate with clinical findings: age, body habitus, pulmonary history, signs of right ventricular hypertrophy
What it looks like on ECG
The electrical axis is assessed using six limb leads (Bayley hexaxial system): I (0°), II (+60°), III (+120°), aVR (-150°), aVL (-30°), aVF (+90°).
In RAD, the QRS complex in lead I becomes predominantly negative (total S amplitude exceeds R), and in aVF — predominantly positive (R exceeds S). The prominence of these changes depends on the angle: with an axis slightly exceeding +90°, the negative part in I and positive part in aVF may be small, whereas a deep S and tall R are typical closer to +120...+150°.
| Lead | Typical morphology in RAD |
|---|---|
| I | QRS predominantly negative (rS) |
| II | R dominates |
| III | QRS positive; with an axis to the right of approximately +105–120°, R may be taller than in aVF |
| aVF | R dominates |
QRS morphology in aVR in RAD is variable and is not used as an independent criterion: lead aVR points to approximately −150° (or +210°), so with an axis around +120°, the complex in aVR may be close to isoelectric, and with an axis approaching +180°, it becomes predominantly negative. For RAD diagnosis, focus primarily on the net QRS polarity in I and aVF and precise axis calculation rather than the appearance of the complex in aVR.
The threshold axis angle for RAD is cited in various guidelines as "greater than +90°" (Goldberger, Hampton) or "greater than +100°" in adults, taking into account the age-related normal rightward axis shift in children and adolescents. At an angle of exactly +90°, the axis is considered borderline (vertical) rather than definitive RAD. This discrepancy should be kept in mind with borderline values.
Precise calculation uses an isoelectric lead: if QRS is isoelectric in any lead, the axis is perpendicular to it; the direction is clarified by the sign of QRS in adjacent leads.
Mechanism
The electrical QRS axis reflects the net ventricular depolarization vector. Normally, the left ventricle is more massive than the right, so the vector is directed leftward and inferiorly (normal axis from -30° to +90°).
RAD occurs when the depolarization vector shifts rightward — either due to increased right ventricular mass or overload (the RV vector begins to compete with or predominate over the LV vector), or due to slowed conduction through the left half of the His-Purkinje system (e.g., left posterior fascicular block, which activates later and pulls the axis rightward and inferiorly), or due to anatomical causes — specific rotation or vertical position of the heart (e.g., in asthenic body habitus, vertical heart position, dextrocardia with normal electrode placement).
Causes
- Normal variant: in newborns, infants, and some younger children, a rightward axis direction can be normal due to the relatively greater right ventricular mass at this age; in adolescents and tall, thin adults, a moderate axis shift to the right is also possible due to a vertical heart position
- Right ventricular hypertrophy (valvular heart disease, pulmonary hypertension)
- Right ventricular overload (acute — PE, chronic — COPD, cor pulmonale)
- Left posterior fascicular block
- Dextrocardia
- Lateral myocardial infarction — a reduction in leftward depolarization forces can produce a rightward axis shift, but the axis shift itself is not a diagnostic sign of infarction
- WPW syndrome with a left-sided accessory pathway (mimicking RAD due to the delta wave)
- Pneumothorax, marked pulmonary emphysema (verticalization and rotation of the heart)
- Hyperkalemia and certain toxic effects on conduction
Differential diagnosis
- Extreme axis deviation ("northwest", indeterminate axis): QRS is negative in both I and aVF simultaneously — differing from RAD, where the complex in aVF is positive
- Lateral myocardial infarction: lateral infarction can reduce leftward depolarization vectors and cause rightward axis shift, but pathological Q waves are evaluated in aggregate in I, aVL, V5–V6 taking into account infarction criteria (duration, depth, adjacent leads) and clinical picture — the axis shift itself does not confirm the diagnosis of infarction
- Swapped limb leads (e.g., arm-leg): can mimic extreme axis deviation — check P wave morphology and clinical correlation
- Dextrocardia: RAD combined with a negative P wave and QRS in lead I and progressively decreasing R wave amplitude from V1 to V6 (reversed transition zone)
- Right bundle branch block: isolated RBBB does not usually cause significant RAD, although terminal right ventricular forces may produce a slight rightward axis shift; marked RAD in RBBB prompts a search for left posterior fascicular block, RV hypertrophy/overload, or another cause
Clinical significance and management
Isolated RAD in a young, thin patient without other pathology is a normal variant and requires no intervention. In adults, especially newly detected RAD, a cause should be sought: compare with previous ECGs, assess signs of right ventricular hypertrophy/overload (e.g., tall R or R/S ratio >1 in V1, ST-T changes in right chest leads, as well as possible P pulmonale as a sign of right atrial involvement), take a history (COPD, pulmonary hypertension, heart defects, acute dyspnea and suspected PE).
In acute onset of RAD with tachycardia and symptoms of acute dyspnea or chest pain, the ECG is evaluated in the workup for PE: signs of RV overload and the possible SI-QIII-TIII pattern are considered, but these changes are non-specific and occur in only a fraction of patients, and their absence does not rule out PE. Diagnosis is based on clinical probability, D-dimer testing in low/intermediate probability, and imaging (CT pulmonary angiography and other methods) as indicated. For chronic RAD with signs of RV hypertrophy — referral for echocardiography to assess structure and pulmonary artery pressure. RAD itself is not treated — the cause is treated.
Common interpretation errors
- Assessing the axis purely "by eye" from a single lead without correlating leads I, II, III, and aVF
- Mistaking RAD in a newborn or infant for pathology without considering the age-related norm
- Failing to distinguish RAD from extreme axis deviation (an error that alters the diagnostic workup)
- Forgetting to check if limb leads are swapped in the presence of sudden "new" RAD without symptoms
- Ignoring concomitant signs (P pulmonale, ST-T changes in right chest leads) when searching for the cause of RAD
"White, white — left" (I positive, II positive → normal axis); in RAD — I is predominantly negative, aVF is predominantly positive
1. What QRS morphology in lead I is typical for right axis deviation?
In RAD, the depolarization vector is directed rightward, so lead I (0°) records a predominantly negative QRS complex.
2. How does extreme (northwest) axis deviation differ from typical RAD?
In extreme axis deviation, QRS is negative in both I and aVF, whereas in standard RAD, the complex in aVF is positive.
3. Which of the listed causes of RAD is not associated with right ventricular hypertrophy or overload?
Left posterior fascicular block shifts the axis to the right due to delayed conduction rather than increased right ventricular mass.
Frequently asked questions
What electrical axis angle is considered right deviation?
Most guidelines indicate a range from greater than +90° to ±180°. Some sources use a threshold of +100° in adults, considering that a moderate rightward shift up to +100° occurs as a normal variant in lean individuals and adolescents. At an angle of exactly +90°, the axis is considered borderline.
Is right axis deviation dangerous?
The axis deviation itself is not dangerous — it is an ECG finding, not a diagnosis. The danger depends on the underlying cause: in young lean individuals it is a normal variant, while in adults with signs of right ventricular hypertrophy or acute overload, it requires investigation for an underlying disease, including PE.
How to distinguish RAD from extreme axis deviation?
In RAD, lead aVF is positive (R wave dominant), while lead I is predominantly negative. In extreme (northwest) axis deviation, the QRS complex is negative in both I and aVF simultaneously.
Can bundle branch block cause RAD?
Isolated right bundle branch block does not usually cause significant RAD. Left posterior fascicular block is a recognized but rare cause of RAD without ventricular hypertrophy; the diagnosis requires characteristic morphology (QRS ≥120 ms, marked RAD, rS in I/aVL, qR in III/aVF) and exclusion of other causes, especially right ventricular hypertrophy and overload.
Should RAD in a child be considered pathological?
In newborns and infants, a rightward axis direction is often normal due to the relatively greater right ventricular mass at this age. In older children and adolescents, age-specific normative values are evaluated, which are usually already close to adult values; marked or new-onset RAD requires correlation with clinical presentation and other ECG findings.
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Related terms
More in the section «Basics: waves, intervals, axes»
Sources
- Goldberger A. Clinical Electrocardiography: A Simplified Approach
- Hampton J. The ECG Made Easy
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice
- AHA/ACCF/HRS Recommendations for the Standardization of the ECG, 2009
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.