Right Axis Deviation: Common Causes
Right axis deviation (RAD) on a 12-lead ECG most commonly results from right ventricular hypertrophy/overload, chronic lung disease, left posterior fascicular block, and normal variants—particularly in young adults and athletes. 1
Definition and Technical Verification
- RAD is defined as a frontal plane QRS axis ≥90° to 180° 1
- Before pursuing any cardiac workup, repeat the ECG with meticulous attention to lead placement to exclude technical artifact, as electrode misplacement is a frequent cause of apparent axis deviation 1
- Compare with prior ECGs when available to determine whether RAD is new or longstanding 1
Primary Pathological Causes
Right Ventricular Hypertrophy and Overload
- RV hypertrophy is the most important pathological cause of RAD, characterized by tall R waves in V1, ST depression and T-wave inversion in right precordial leads, and persistent S waves across precordial leads 1, 2
- RAD occurs in 79% of patients with idiopathic pulmonary arterial hypertension 1
- The diagnostic accuracy of RAD for RV pathology is highest in congenital heart disease, intermediate in acquired heart disease and primary pulmonary hypertension, and lowest in chronic pulmonary disease 1
- Echocardiography should be obtained to assess RV size, function, and estimated pulmonary artery pressure 1
Chronic Lung Disease
- RAD is common in chronic obstructive pulmonary disease but has low diagnostic accuracy for RV overload 1
- Look for additional features including low voltage in limb leads, rightward P-wave axis, and persistent S waves in all precordial leads 1
- The terminal QRS (S wave) in lead I is particularly informative for detecting elevated right ventricular pressure 3
Conduction Abnormalities
- Left posterior fascicular block produces RAD but is a diagnosis of exclusion, as it is less common than left anterior fascicular block 4
- Incomplete right bundle branch block (RBBB) with RAD is frequently a normal variant, especially in young adults and athletes, requiring no intervention unless accompanied by symptoms, family history of sudden cardiac death, or other abnormalities 1
- Complete RBBB is defined by QRS duration ≥120 ms, while incomplete RBBB shows QRS 110-119 ms 1
Normal Variants and Physiological Causes
Athletes and Young Adults
- In asymptomatic athletes without family history of sudden cardiac death, isolated RAD without other abnormalities may not require extensive workup 1, 2
- RAD with incomplete RBBB is common and benign in athletes unless accompanied by pathological findings 1
- ECG evidence of right atrial enlargement and/or RV hypertrophy are uncommon in athletes (prevalence 0.08% for right atrial enlargement, 0.6% for right-axis deviation) 2
Pediatric Considerations
- Normal QRS axis varies by age in children, with neonates exhibiting a rightward axis (≈60°–190°) that gradually shifts leftward during childhood 4
Systematic Evaluation Algorithm
- Verify technical accuracy: Repeat ECG with proper lead placement 1
- Assess QRS duration: <110 ms (normal), 110-119 ms (incomplete RBBB), ≥120 ms (complete RBBB) 1
- Examine for RV hypertrophy features: Tall R in V1, ST-T changes in right precordial leads, persistent S waves 1
- Evaluate clinical context: Symptoms, lung disease, congenital heart disease history 1
- Order echocardiography if RAD is accompanied by other abnormalities or clinical suspicion of cardiac pathology 1
- Consider serial ECGs and troponins if symptoms persist or change 1
Critical Pitfalls to Avoid
- Do not dismiss RAD as benign without investigation when accompanied by other ECG abnormalities, as it has significant association with cardiac pathology 1
- Do not rely on ECG alone for diagnosis of pulmonary hypertension (sensitivity 73%, specificity 70%) 1
- In chronic lung disease, RAD alone has limited diagnostic value; look for constellation of findings 1
- If isolated RAD with normal echocardiography and no other abnormalities, no further cardiac testing is necessary 1