2D Echocardiography for Aortic Dissection
2D transthoracic echocardiography (TTE) is recommended as an initial imaging modality for suspected aortic dissection in the emergency setting, but a negative TTE cannot rule out dissection and requires confirmatory imaging with CT angiography, TEE, or MRI. 1
Role of TTE in Emergency Evaluation
When TTE is Appropriate as Initial Test
The European Association of Cardiovascular Imaging explicitly recommends TTE as an initial imaging modality for diagnosis of suspected aortic dissection in the emergency setting. 1
TTE can rapidly identify critical findings at the bedside including intimal flap in the proximal ascending aorta, pericardial effusion/tamponade, and left ventricular dysfunction. 2
In patients presenting with acute chest pain and hemodynamic instability, TTE provides immediate assessment while definitive imaging is being arranged. 1
TTE is particularly valuable when it can detect complications such as acute aortic regurgitation, which occurs in approximately 50% of proximal dissections. 1
Critical Limitations of TTE
A normal TTE examination cannot exclude aortic dissection—this is the most important caveat. 1, 2
The sensitivity and specificity of TTE for aortic dissection diagnosis are only 60-80%, which is inadequate for definitive diagnosis. 1
TTE has limited visualization of the distal ascending aorta, aortic arch, and descending thoracic aorta—areas commonly involved in dissection. 1, 2
Reverberation artifacts are a major pitfall that can lead to false-positive interpretations, requiring an experienced operator. 1
Diagnostic Performance Data
In a prospective study, TTE demonstrated 91% sensitivity and 100% positive predictive value for aortic dissection when diagnostic criteria were met. 3
Another study showed TTE correctly identified all 13 patients with ascending aortic dissection (100% sensitivity) with 88% specificity and 91% overall accuracy. 4
However, TTE failed to identify any of 5 patients with Type III (descending) dissection in one series, highlighting its blind spots. 4
Prognostic Information from TTE
The presence of pericardial effusion on TTE in confirmed ascending aortic dissection carries a 75% mortality within 24 hours. 4
Detection of cardiac tamponade by TTE is critical, as this represents a surgical emergency requiring immediate intervention. 1
If TTE demonstrates both dissection and pericardial collection, transesophageal echocardiography (TEE) is unnecessary and potentially dangerous before surgery, as it may provoke hemodynamic decompensation. 1
Recommended Diagnostic Algorithm
Step 1: Initial Assessment
Perform TTE immediately in hemodynamically unstable patients or when other imaging modalities are not rapidly available. 1
Use TTE to screen for cardiac tamponade and LV wall motion abnormalities before proceeding to TEE. 1
Step 2: Interpretation of TTE Results
If TTE is positive (intimal flap visualized):
Proceed directly to surgical consultation for Type A dissection without delay for additional imaging. 5
Document presence and severity of aortic regurgitation, pericardial effusion, and ventricular function. 2
If TTE is negative or non-diagnostic:
Immediately proceed to definitive imaging with CT angiography (preferred), TEE, or MRI—never rely on negative TTE alone. 1, 5, 2
CT angiography is preferred as first-line definitive imaging due to rapid availability and 93% sensitivity. 5
Step 3: Time-Sensitive Considerations
When clinical probability of dissection is high (ADD score ≥1), excessive delays in obtaining imaging affect survival at a rate of 1% per hour. 6
A CT scan obtained within 2 hours yields higher survival than a more accurate MRI obtained within 9 hours when dissection probability is 50%. 6
Never delay transfer to a surgical center for imaging at a non-surgical facility when probability is high. 5
Common Pitfalls to Avoid
Never use TTE alone to rule out aortic dissection—this is the most dangerous error, as negative TTE requires confirmatory imaging. 1, 2
Do not mistake reverberation artifacts for intimal flaps—requires experienced interpretation. 1
Avoid performing TEE before TTE screening in suspected dissection, as unrecognized tamponade could lead to hemodynamic collapse during TEE. 1
Do not delay definitive imaging in stable patients even with negative TTE—other imaging techniques must be considered. 2, 6
Never administer antithrombotic therapy if aortic dissection is suspected based on clinical presentation, regardless of TTE findings. 7, 5
Alternative Imaging When TTE is Non-Diagnostic
TEE has 98-100% sensitivity and 95-100% specificity for aortic dissection, making it superior to TTE. 1
CT angiography is the preferred first-line definitive test in the ED due to rapid availability and ability to detect alternative diagnoses in 13% of cases. 5
MRI has the highest accuracy but is rarely used in unstable patients due to time constraints and limited monitoring capability. 1, 6