When should a triple rule out (computed tomography angiography of the chest to rule out acute coronary syndrome, pulmonary embolism, or aortic dissection) be considered in patients presenting with chest pain?

Triple Rule Out CT: Indications and Appropriate Use

Triple rule out CT angiography should be considered in patients with acute chest pain who have low to intermediate risk for acute coronary syndrome (ACS) but also have clinical features suggesting possible pulmonary embolism (PE) or acute aortic syndrome as alternative diagnoses.

What is Triple Rule Out CT?

Triple rule out (TRO) CT is a specialized protocol of coronary CT angiography that uses a specific contrast acquisition scanning protocol to enable simultaneous assessment of:

• Coronary arteries
• Pulmonary arteries
• Aorta

This allows for evaluation of the three most life-threatening causes of acute chest pain in a single examination 1.

Appropriate Clinical Scenarios for Triple Rule Out CT

Recommended Use:

• Patients presenting with acute chest pain with low to intermediate risk for ACS 1, 2
• Cases where clinical presentation suggests possible alternative diagnoses of PE or aortic dissection 1
• Patients with atypical chest pain, especially older individuals with risk factors for multiple vascular conditions 3
• Situations where rapid diagnosis is needed but the clinical presentation is ambiguous between cardiac, pulmonary, and aortic etiologies 4

Not Recommended For:

• Patients with high pretest probability of ACS (should proceed directly to invasive coronary angiography) 1
• Patients with clear clinical indications of a single etiology (dedicated protocol preferred) 1, 3
• Young patients where radiation exposure is a significant concern 3
• Routine screening of all chest pain patients 4

Decision Algorithm for Triple Rule Out vs. Dedicated Imaging

1. High probability of ACS: Proceed with standard ACS protocol including ECG, cardiac troponins, and possible invasive coronary angiography 1

2. High probability of PE: Order dedicated CTPA using PE protocol 1

3. High probability of aortic dissection: Order dedicated CTA of chest, abdomen, and pelvis 1

4. Low to intermediate risk with unclear etiology:

   • If multiple etiologies are clinically suspected (ACS, PE, aortic pathology)
   • If initial workup (ECG, troponins) is non-diagnostic
   • If patient has risk factors for multiple vascular conditions → Consider Triple Rule Out CT 1, 2, 5

Clinical Benefits and Limitations

Benefits:

• Single examination can diagnose or exclude three life-threatening conditions 2
• May reduce ED length of stay and costs in appropriate patients 4
• Can reveal alternative diagnoses in approximately 35% of patients without PE 6
• Improves clinical evaluation and outcomes in patients with acute chest pain of uncertain etiology 2

Limitations:

• Increased radiation exposure compared to dedicated protocols 3
• Higher contrast volume requirements 5
• Limited utility in patients with known CAD, high calcium scores, or irregular heart rates 1
• Not widely available as a 24-hour service in many centers 1
• Not validated in patients with stents or previous CABG 1

Technical Considerations

• Requires meticulous attention to contrast timing and technique 6
• Thin-section acquisition is necessary for optimal imaging 6
• Should be performed on modern multidetector CT scanners capable of cardiac gating 4
• Viewing at dedicated workstations is recommended for proper interpretation 6

Important Caveats

• Triple rule out should not be used as a routine screening procedure for all chest pain patients 4
• The increased radiation dose from extended coverage must be carefully considered, especially in younger patients 3
• When ordering, specify "triple rule out CT" rather than standard CT chest with contrast to ensure proper protocol 6
• Clinical risk stratification should always precede imaging decisions 6

By appropriately selecting patients for triple rule out CT based on their clinical presentation and risk factors, clinicians can optimize diagnostic efficiency while minimizing unnecessary radiation exposure and contrast administration.