What are the implications and treatment options for an abnormal lower 2/3rds of the septum found on an echocardiogram (echo)?

Echocardiographic Findings of Lower 2/3rds Septum Abnormalities

Primary Diagnostic Considerations

When an abnormality is identified in the lower 2/3rds of the interventricular septum on echocardiography, the most critical initial step is to determine whether this represents a ventricular septal defect (VSD), septal hypertrophy with outflow obstruction, post-traumatic injury, or ischemic wall motion abnormality. 1, 2

Ventricular Septal Defects in the Lower Septum

The lower 2/3rds of the septum—specifically the muscular portion near the ventricular apex—is the most common location for traumatic ventricular septal ruptures due to rapid anterior-posterior compression of the heart between the spine and sternum 1. However, congenital VSDs in this region are also common:

• Muscular VSDs affecting the lower septum can present with variable hemodynamic significance depending on size and associated complications 1, 2
• Perimembranous VSDs with anteriorly malaligned outlet septum frequently involve the lower 2/3rds and carry specific risks for progressive complications 3
• Color Doppler echocardiography with agitated saline contrast should be performed to confirm the presence and direction of shunting 1

Critical Associated Complications to Assess

Patients with lower septal abnormalities require systematic evaluation for four key complications that significantly impact management:

1. Right ventricular outflow tract obstruction develops in 51% of patients with anteriorly malaligned VSDs, more commonly in those without aneurysmal transformation 3

2. Aortic valve prolapse occurs in 23-33% of cases with anteriorly malaligned septal defects due to the location and geometry of the defect 3

3. Aneurysmal transformation of the septum occurs in 52% of patients and may decrease VSD size but is associated with development of subaortic ridge 3

4. Subaortic ridge formation develops more frequently when aneurysmal transformation is present 3

Hemodynamic Assessment Requirements

Transthoracic echocardiography must evaluate:

• Biventricular systolic function and chamber dimensions to assess for volume overload 1, 2
• Left-to-right shunt magnitude (Qp:Qs ratio should be calculated if possible) 4, 2
• Pulmonary artery systolic pressure estimation via tricuspid regurgitation velocity 1, 2
• Right ventricular size and function, as RV enlargement indicates hemodynamically significant shunting 5
• All four cardiac valves for regurgitation, particularly aortic and tricuspid 1

When Transthoracic Echo is Insufficient

Transesophageal echocardiography should be performed when: 1

• Transthoracic images are suboptimal for defining septal anatomy
• Multiple VSDs are suspected
• Precise localization and sizing are needed for intervention planning
• Associated anomalies of the atrioventricular valves require detailed assessment

Indications for Surgical or Catheter-Based Intervention

The European Society of Cardiology recommends closure when: 2

• Symptoms are attributable to left-to-right shunting without severe pulmonary vascular disease
• Evidence of left ventricular volume overload exists even in asymptomatic patients
• History of infective endocarditis is present
• VSD-associated aortic valve prolapse causes progressive aortic regurgitation
• Pulmonary hypertension exists with net left-to-right shunt (Qp:Qs >1.5) and pulmonary artery pressure or pulmonary vascular resistance <2/3 of systemic values

Surgery is typically performed at median age 50 months for isolated VSD, but timing depends on: 3

• Significant left-to-right shunt magnitude
• Development of right ventricular obstruction
• Presence of aortic valve prolapse
• Combinations of the above complications

Absolute Contraindications to Closure

Closure must NOT be performed when: 4

• Pulmonary artery systolic pressure exceeds 2/3 of systemic pressure
• Pulmonary vascular resistance exceeds 2/3 of systemic resistance
• Net right-to-left shunt is present (Eisenmenger physiology)

Alternative Diagnoses in the Lower Septum

If VSD is excluded, consider:

• Septal hypertrophy with sigmoid configuration causing left ventricular outflow tract obstruction, which responds to negative ionotropic agents (beta-blockers followed by disopyramide if needed) 6
• Post-infarction septal dysfunction in the setting of anteroseptal myocardial infarction, which correlates with higher rates of congestive heart failure, bundle branch block, and mortality 7
• Septal bowing from chronic pulmonary hypertension, where elevated pulmonary artery systolic pressure is the primary determinant of leftward ventricular septal displacement 8

Common Pitfalls to Avoid

• Failing to perform serial echocardiographic follow-up, as progressive complications (aortic regurgitation, right ventricular obstruction, subaortic stenosis) develop over time and require annual assessment at specialized centers 2, 3
• Missing muscular VSDs in the apical septum due to inadequate imaging windows; multiple apical views with contrast enhancement may be necessary 1
• Underestimating the complexity of anteriorly malaligned VSDs, which can evolve into a pathology complex comprising right ventricular outflow obstruction, subaortic ridge, aortic valve prolapse, and the VSD itself 3
• Proceeding with closure in patients with elevated pulmonary vascular resistance without proper hemodynamic catheterization assessment 4, 2