What is the significance and appropriate management of a trapezoid cardiac border on a chest X-ray?

Trapezoid Cardiac Border on Chest X-Ray

A trapezoid cardiac border on chest X-ray most commonly indicates congenitally corrected transposition of the great arteries (ccTGA), characterized by an abnormally straight left heart border due to the leftward and anterior position of the ascending aorta. 1

Primary Diagnostic Consideration

The trapezoid or abnormally straight left cardiac border is a classic radiographic finding in ccTGA (also called L-TGA), where:

• The ascending aorta is positioned leftward and anteriorly, creating the characteristic straight left heart border instead of the normal curved contour 1
• This geometric abnormality results from the double discordance (atrioventricular and ventriculoarterial) that defines this congenital heart disease 1
• The finding may be accompanied by dextrocardia (20% of cases) or mesocardia (relatively common) 1

Immediate Diagnostic Workup

Proceed directly to transthoracic echocardiography (TTE) as the key diagnostic test to confirm the diagnosis and assess associated abnormalities 1

Essential Echocardiographic Assessment

TTE must document:

• Double discordance: The inverted position of ventricles with usual atrial arrangement 1
• Morphological ventricular identification: The anatomic right ventricle (systemic ventricle) shows increased trabeculation, moderator band, and more apically inserted tricuspid valve 1
• Associated lesions that occur frequently:
  • Ventricular septal defect (VSD) 1
  • Left ventricular outflow tract obstruction (LVOTO) or pulmonary stenosis 1
  • Ebstein-like malformation of the systemic atrioventricular (tricuspid) valve with regurgitation 1
• Systolic function of the systemic (subaortic) right ventricle 1

Complementary Imaging

Cardiac MRI is indicated for:

• Quantification of ventricular volumes, mass, and ejection fraction 1
• Detailed intracardiac and great vessel anatomy when echocardiography is inadequate 1

Critical ECG Findings to Recognize

The ECG in ccTGA shows characteristic patterns that can be misinterpreted:

• Deep Q waves in leads II, III, aVF, and V1-V3 due to inverted bundle branches causing early septal activation from right to left—this mimics myocardial infarction but is a normal finding in ccTGA 1
• Reversal of normal precordial progression (QR pattern in V1, rS in V6) 1
• Prolonged PR interval or complete heart block 1
• WPW syndrome present in 2-4% of patients 1

Management Priorities

Immediate Referral

All patients with ccTGA must be referred to a specialized grown-up congenital heart disease (GUCH) center for annual follow-up, regardless of symptoms 1

Key Clinical Concerns

Monitor for:

• Systemic right ventricular failure: The morphologic right ventricle functions as the systemic ventricle and commonly fails in the fourth or fifth decade 1
• Severe systemic AV valve regurgitation: Especially with Ebstein-like tricuspid valve 1
• Progressive AV block and arrhythmias: Require Holter monitoring, event recorders, and potentially electrophysiology testing 1
• Sudden cardiac death risk: Particularly in high-risk patients 1

Catheter Interventions

Consider for:

• Pulmonary artery stenosis or conduit stenosis: Can be dilated or stented 1
• Note: Residual LVOTO may actually benefit the dilated systemic right ventricle by improving septal position and reducing tricuspid regurgitation 1

Activity Restrictions

Patients with ccTGA should avoid competitive and static sports 1

• Those with significant associated lesions or decreased systemic RV function: Restrict to low-intensity sports only 1
• Patients with symptoms or arrhythmia history: Individual counseling required due to elevated risk of exercise-provoked arrhythmias (exercise testing recommended) 1
• Those with excellent hemodynamics: Encourage regular exercise but avoid extreme exertion 1

Pregnancy Considerations

Patients with hemodynamic compromise or atrial arrhythmias have elevated pregnancy risks and require specialized counseling 1

Common Pitfalls to Avoid

• Do not misdiagnose as dilated cardiomyopathy: Patients presenting with dyspnea and exercise intolerance in their 40s-50s may be incorrectly labeled as having acquired cardiomyopathy rather than ccTGA with systemic RV failure 1
• Do not interpret Q waves as myocardial infarction: The characteristic ECG pattern is due to inverted conduction pathways, not ischemia 1
• Do not overlook associated lesions: VSD, LVOTO, and Ebstein-like tricuspid valve are common and significantly impact prognosis 1