What are the diagnostic and treatment approaches for concerns related to the left sternal border?

Diagnostic and Treatment Approaches for Left Sternal Border Concerns

The left sternal border (LSB) is a critical anatomical landmark where various cardiac and non-cardiac conditions may manifest, requiring specific diagnostic and treatment approaches based on the underlying pathology.

Diagnostic Approach

Initial Assessment

• Perform a focused cardiac examination, listening specifically for systolic ejection murmurs at the LSB which may indicate subaortic stenosis or other valvular abnormalities 1
• Evaluate for pericardial friction rub which can be transient and mono-, bi-, or triphasic, suggesting pericarditis 1
• Check for delayed carotid upstroke with decreased volume which may indicate aortic stenosis 1
• Assess for a systolic thrill in the suprasternal notch or upper right sternal border, which may suggest aortic stenosis 1

Electrocardiographic Evaluation

• Obtain a 12-lead ECG to evaluate for QRS voltage of left ventricular hypertrophy, left atrial abnormality pattern, and/or ST-T repolarization changes that may indicate valvular disease 1
• When ST-segment elevation is present, measure at the J-point in two contiguous leads (≥0.25 mV in men below 40 years, ≥0.2 mV in men over 40 years, ≥0.15 mV in women in leads V2–V3, and ≥0.1 mV in other leads) to differentiate between myocardial infarction and benign early repolarization 2
• Consider additional posterior leads (V7-V9) if standard 12-lead ECG is inconclusive for posterior infarction 2

Imaging Studies

• Perform transthoracic echocardiography to visualize left ventricular outflow tract anatomy, associated aortic valve abnormality, amount of aortic regurgitation, left ventricular function, left ventricular hypertrophy, and associated lesions 1
• Use Doppler echocardiography to determine the severity of any subvalvular obstruction, noting that Doppler-derived gradients may overestimate obstruction and may require confirmation by cardiac catheterization 1
• Consider chest radiography to evaluate for prominent right-sided heart–border silhouette of the ascending aorta (if dilated), calcification in the aortic valve, and left-sided heart–border silhouette of left ventricular hypertrophy/enlargement 1
• Look for a straight left heart border (SLHB) on chest X-ray, which may indicate hemopericardium in patients with penetrating chest injury 3
• Utilize computed tomography (CT) to assess sternal and peri-sternal regions for abnormalities that may cause anterior chest wall pain 4

Advanced Diagnostic Testing

• Consider transesophageal echocardiography (TEE) to demonstrate membrane in subaortic stenosis cases 1
• Three-dimensional TEE can be helpful to characterize complex left ventricular outflow tract anatomy 1
• In cases of suspected aortic dissection, employ transoesophageal echocardiography as the sole diagnostic procedure in hemodynamically unstable patients 1

Treatment Approach

Management of Valvular and Subvalvular Disease

• For patients with subaortic stenosis who are symptomatic (exertional dyspnea, angina, syncope) with a mean Doppler gradient ≥50 mmHg or severe aortic regurgitation, surgical intervention is strongly recommended 1
• Consider surgery for asymptomatic patients with subaortic stenosis when:
  • Left ventricular ejection fraction is <50% (even if gradient <50mmHg due to low flow) 1
  • Aortic regurgitation is severe with left ventricular end-systolic diameter >50mm (or 25 mm/m² BSA) and/or ejection fraction <50% 1
  • Mean Doppler gradient is ≥50 mmHg with marked left ventricular hypertrophy 1
  • Mean Doppler gradient is ≥50 mmHg with abnormal blood pressure response on exercise testing 1

Management of Pericardial Disease

• For acute pericarditis, implement appropriate therapy based on the underlying cause, which may include anti-inflammatory medications 1
• In cases of cardiac tamponade with hemodynamic instability:
  • Perform intubation and ventilation for profound hemodynamic instability 1
  • Use transoesophageal echocardiography as the sole diagnostic procedure and call surgeon 1
  • Consider surgery based on findings of cardiac tamponade by transthoracic echocardiography 1
  • Pericardiocentesis may be performed to lower intrapericardial pressure, but be aware of the risk of recurrent bleeding 1

Management of Aortic Dissection

• For suspected aortic dissection with hypertension, administer beta-blockers (first-line: esmolol, metoprolol, atenolol) to reduce blood pressure and the force of left ventricular ejection 1
• If beta-blockade alone does not control hypertension, add vasodilators (such as sodium nitroprusside) but always in combination with beta-blockers 1
• Titrate systolic blood pressure to values between 100 and 120 mmHg, modifying if oliguria or neurological symptoms develop 1

Surgical Approaches When Indicated

• For median sternotomy approaches (when required for cardiac surgery):
  • Consider lower hemisternotomy for minimally invasive mitral valve repair/replacement, atrial septal defect closure, tricuspid valve repair/replacement, and atrial fibrillation ablation 1
  • Use appropriate sternal closure techniques based on patient risk factors:
    • Single wire fixation methods for routine patients 5
    • Figure-of-eight technique for patients with fragile sternum 5
    • Rigid plate fixation for high-risk patients (chronic pulmonary disease, obesity, bilateral internal mammary artery harvesting, diabetes, off-midline sternotomy) 5

Special Considerations

High-Risk Features

• Patients with right bundle branch block (RBBB) and myocardial infarction have poor prognosis, necessitating prompt intervention when clinical suspicion exists 2
• Border zone geometry changes after myocardial infarction can increase wall stress, potentially contributing to ventricular remodeling and heart failure 6
• The differential diagnosis of ST-segment elevation includes STEMI, early repolarization, pericarditis, and ST elevation secondary to QRS complex abnormalities (left bundle branch block, left ventricular hypertrophy, or preexcitation) 7

Common Pitfalls

• Doppler-derived gradients may overestimate the obstruction in subaortic stenosis and may need confirmation by left heart catheterization 1
• The click murmur of a bicuspid aortic valve may be misdiagnosed as mitral valve prolapse 1
• A systolic murmur may be incorrectly thought to be "benign" because an ejection click is not recognized 1
• Never delay reperfusion therapy while waiting for cardiac biomarker results when clinical suspicion for STEMI is high 2
• Pericardiocentesis in cardiac tamponade may cause recurrent bleeding by reducing intrapericardial pressure 1