What does marked right axis deviation in an electrocardiogram (ECG) mean?

Marked Right Axis Deviation in ECG: Clinical Significance and Implications

Marked right axis deviation (RAD) in an electrocardiogram (ECG) indicates a QRS axis of greater than +120° in adults and suggests underlying cardiovascular or pulmonary pathology that requires further evaluation. 1

Definition and Classification

• Right axis deviation is defined as:
  • Adults: QRS axis >+90° (moderate: +90° to +120°; marked: >+120°) 1
  • Children: Age-specific normal ranges differ significantly:
    • 8-16 years: up to +120°
    • 5-8 years: up to +140°
    • 1-5 years: up to +110°
    • Neonates: up to +190° 1

Clinical Significance and Associated Conditions

Marked RAD is often associated with:

Primary Cardiac Causes

• Right ventricular hypertrophy (RVH) 2
• Left posterior fascicular block 2, 1
• Congenital heart disease 1
• Lateral myocardial infarction 1, 3
• Right bundle branch block (RBBB) 1

Pulmonary Causes

• Pulmonary hypertension 2
• Pulmonary embolism 1
• Chronic lung disease 2, 1

Diagnostic Approach

When marked RAD is identified on ECG, consider the following approach:

1. Look for associated ECG findings:

   • Right ventricular hypertrophy patterns:
     • Tall R wave and small S wave with R/S ratio ≥1 in lead V1
     • qR complex in lead V1
     • rSR' pattern in lead V1
     • Large S wave and small R wave with R/S ratio ≤1 in leads V5 or V6
     • S1, S2, S3 pattern 2

2. Consider echocardiography:

   • Essential for evaluating right ventricular size and function
   • Assess for pulmonary hypertension
   • Rule out congenital heart disease 2, 1

3. Additional testing based on clinical suspicion:

   • Pulmonary function tests if lung disease suspected
   • CT pulmonary angiography if pulmonary embolism suspected
   • Right heart catheterization if pulmonary hypertension suspected 2

Prognostic Implications

Marked RAD can have significant prognostic implications:

• In pulmonary arterial hypertension, RAD is seen in 79% of patients and may indicate significant disease 2
• In acute myocardial infarction, new-onset extreme RAD may signal poor prognosis 4
• The presence of RAD in combination with other ECG abnormalities (such as RBBB) may indicate more severe disease 4

Important Caveats

• ECG has limited sensitivity (73%) for detecting pulmonary hypertension, so normal ECG does not rule out significant disease 2, 1
• RAD may be a normal variant in some individuals, particularly in children and young adults 2, 5
• Body position, lead placement, and body habitus can influence QRS axis determination 1
• In athletes, RAD is considered a borderline ECG finding that may warrant further investigation if accompanied by other abnormal findings 2

Management Recommendations

Management should focus on identifying and treating the underlying cause:

• For pulmonary hypertension: pulmonary vasodilators and management of right heart failure 2, 1
• For congenital heart disease: referral to a specialist for appropriate management 1
• For chronic lung disease: optimization of pulmonary therapy 1
• For acute coronary syndromes with RAD: consider early revascularization 4, 3

Remember that marked RAD is an ECG finding requiring clinical correlation and should prompt a search for underlying cardiovascular or pulmonary pathology, especially when it represents a change from previous ECGs.