What are the typical electrocardiogram (ECG) findings in a patient with an atrial septal defect (ASD)?

ECG Findings in Atrial Septal Defect

The ECG in atrial septal defect typically shows incomplete right bundle branch block (rSR' pattern in V1), right axis deviation, and right atrial enlargement, with specific patterns varying by ASD subtype. 1

Type-Specific ECG Patterns

Secundum ASD (Most Common)

• Incomplete right bundle branch block (rSR' pattern in V1) is the hallmark finding, present in 54-57% of patients with moderate-to-large defects 1, 2, 3
• Right axis deviation (mean QRS axis ~108 degrees) reflects right ventricular volume overload 1, 2
• Right atrial enlargement manifested by tall, peaked P waves in leads II, III, and aVF 1
• Crochetage sign (notching of the R wave in inferior leads II, III, aVF) occurs in approximately 57% of patients and correlates with larger defect size 4

Primum ASD (Partial AVSD)

• Superior left-axis deviation (leftward QRS axis) is the distinguishing feature, caused by the anatomic position of conduction bundles 1
• Incomplete right bundle branch block with RV conduction delay 1
• First-degree AV block may be present 1
• This superior left axis with RV conduction delay should not be confused with bifascicular block 1

Sinus Venosus ASD

• Abnormal P-wave axis (superiorly directed, often negative in inferior leads) due to the superior location of the defect near the SVC 1
• Right axis deviation and incomplete RBBB similar to secundum defects 1

Additional ECG Features

Common Findings

• Prolonged PR interval (mean ~188 ms pre-closure) may indicate atrial conduction delay 2
• Increased QRS duration (mean ~123 ms) reflects right ventricular conduction delay 2
• Defective T waves (inverted or flattened) in right precordial leads occur in 48% of patients 4

Age-Related Considerations

• ECG sensitivity for detecting RVE increases to 70% in younger patients and 80% for the largest defects 5
• However, ECG criteria for RVE are present in only 57% of young patients with large ASDs, making it an unreliable sole screening tool 5
• Atrial arrhythmias (atrial flutter, atrial fibrillation) become more common with increasing age and duration of unrepaired defect 1

Clinical Pitfalls and Diagnostic Limitations

Important Caveats

• Absence of typical ECG findings does not exclude ASD: Only 57% of patients with hemodynamically significant ASDs show ECG criteria for RVE 2, 5
• Sinus venosus defects are frequently missed on routine evaluation due to their superior location and subtle ECG changes 1
• The specificity of incomplete RBBB (95%), defective T waves (97%), and crochetage sign (92%) is high when present, but sensitivity is limited 4

Post-Closure ECG Changes

• Following successful ASD closure, ECG changes reverse over time: QRS axis normalizes (108° to 70°), QRS duration decreases (123 ms to 80 ms), and the rSR' pattern amplitude reduces 2
• Failure of ECG normalization post-closure should prompt investigation for residual shunt or pulmonary complications 2
• Acute post-closure arrhythmias include increased supraventricular ectopy (63% of patients) and rare AV conduction abnormalities including complete heart block (7%) 6

Diagnostic Algorithm

When evaluating suspected ASD:

1. Look for the triad: incomplete RBBB + right axis deviation + right atrial enlargement in secundum ASD 1
2. Check for subtype-specific patterns: superior left axis (primum) or abnormal P-wave axis (sinus venosus) 1
3. Assess for crochetage sign in inferior leads, which correlates with larger defects requiring intervention 4, 3
4. Remember ECG alone is insufficient: Echocardiography remains the primary diagnostic modality, as ECG has only 57% sensitivity even with significant defects 1, 5