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

EKG Findings in Secundum Atrial Septal Defect

The most common EKG findings in secundum atrial septal defect (ASD) include right-axis deviation, right atrial enlargement, and incomplete right bundle branch block (RBBB). 1

Classic EKG Findings

• Incomplete right bundle branch block (RBBB): Characterized by an rSR' pattern in lead V1

  • Present in approximately 26-56% of patients with secundum ASD 2, 3
  • More commonly seen in patients with moderate-to-large defects (>5 mm) 2

• Right-axis deviation: Typically seen in secundum ASD 1

  • Helps differentiate from primum ASD, which shows superior left-axis deviation

• Right atrial enlargement: Manifested as tall, peaked P waves (≥2.5 mm) in leads II, III, or aVF 4

• Crochetage sign (notched R wave): A notch in the R wave in inferior leads (II, III, aVF)

  • Present in up to 57% of ASD patients 3
  • High specificity (92%) for ASD diagnosis 3
  • May disappear after ASD closure 5

Clinical Correlation

The presence and severity of EKG findings correlate with:

1. Defect size: Larger defects (>5 mm) are more likely to show characteristic EKG changes 2

   • 78% of patients with rSR' pattern had moderate-to-large ASDs 2
   • The presence of rSR' pattern predicts lower likelihood of spontaneous closure (7% vs 36%) 2

2. Hemodynamic significance: EKG findings reflect right heart volume overload 1

   • Right ventricular volume overload is the key finding that characterizes hemodynamic relevance 1

3. Need for intervention: The presence of rSR' pattern has predictive value for eventual need for device or surgical closure (71% vs 38%) 2

Important Caveats

1. Absence of classic findings does not exclude diagnosis:

   • 18% of patients with hemodynamically significant ASDs have normal ECGs 6
   • 7% have neither physical nor ECG findings 6
   • Echocardiography remains essential for diagnosis 4

2. Changes after closure:

   • Mean QRS axis typically reduces from around 108° to 70° 5
   • QRS duration often decreases 5
   • The rSR' pattern may revert to normal in most patients 5
   • Persistence of EKG abnormalities after closure may indicate residual shunt 5

3. Post-closure arrhythmias:

   • Increased supraventricular ectopy may occur immediately after transcatheter closure 7
   • Small risk of AV conduction abnormalities including complete heart block 7

Diagnostic Approach

When EKG findings suggest ASD:

1. Echocardiography is the key diagnostic technique 1, 4

   • Transthoracic echocardiography (TTE) is first-line
   • Transesophageal echocardiography (TEE) may be necessary for sinus venosus defects or before device closure

2. Evaluate for associated findings:

   • Right ventricular enlargement
   • Right atrial enlargement
   • Pulmonary artery pressure estimation
   • Associated lesions (anomalous pulmonary venous connection, persistent left SVC)

3. Consider exercise testing in patients with symptoms that are discrepant with clinical findings 1

Remember that while EKG findings are valuable diagnostic clues, they should not be used in isolation, as dependence on classical EKG findings alone may result in underdiagnosis of a significant number of patients with ASD 6.