TRIPLE RULE OUT CT ANGIOGRAPHY

Overview

This guide discusses Triple Rule Out CT Angiography, focusing on its protocol for patients with acute chest pain in emergency settings. We will cover indications, patient selection, contraindications, necessary CT hardware, radiation considerations, preparation steps, and image interpretation.

Understanding Acute Chest Pain

Acute chest pain can arise from various conditions, with acute coronary syndrome (ACS) accounting for only 25% of cases. Other possible causes include:

• Pulmonary Embolism
• Aortic Dissection
• Other conditions like pneumonia, pneumothorax, rib fractures, or pericardial effusion.

Use of Triple Rule Out CT Angiography

When all three conditions (ACS, pulmonary embolism, aortic dissection) are suspected, Triple Rule Out CT Angiography serves as a comprehensive diagnostic tool.

Protocol for Acute Chest Pain

Initial Assessment

1. Serial ECGs: Monitor heart activity.
2. Troponin Levels: Check for myocardial injury.
3. Stress Test: May or may not be performed.

Indications for Triple Rule Out

• Patients presenting with complex symptoms of acute chest pain, shortness of breath, or pain radiating to the neck or left arm.
• Negative troponin tests and no ECG changes.

Patient Selection Criteria

• Ideal Candidates: Young adults with low risk of ACS, negative biomarkers, and no ECG changes.
• Other Requirements: Acceptable cardiac rhythm, adequate renal function, ability to hold breath during the scan.

Contraindications

• Renal Insufficiency: Risk of contrast-induced nephropathy.
• Contrast Allergy: Previous adverse reactions to contrast agents.
• Beta Blockers: Can interfere with heart rate control.

CT Hardware Requirements

• Minimum: 64-slice CT scanner capable of scanning 20 cm in 15 seconds.
• Settings: 120 kVp, 60 mAs (modulated to 8.75 mAs during the scan).
• Radiation Reduction: Use of tube current modulation and ECG gating can significantly reduce patient radiation exposure.

Patient Preparation

1. Caffeine and Stimulants: Patients should avoid these before the study.
2. IV Access: Place an 18-gauge IV catheter.
3. ECG Leads: Attach to monitor heart activity.
4. Beta Blockers: Administer as needed (2.5 to 30 mg) to achieve bradycardia.
5. Nitroglycerin: Give sublingually just before the scan.

CT Protocol

• Contrast Administration: Use a biphasic injection method:
  • Phase 1: 70 mL of 350 mg iodine/mL contrast.
  • Phase 2: 25 mL of contrast mixed with 25 mL of saline.
• Injection Speed: 5 mL/sec to opacify the left and right heart.

Scanning Technique

• Scan from 1 to 2 cm above the aortic arch to the lower chest, ensuring coverage of the heart's base.
• Initiate acquisition 5 seconds after achieving a threshold of 100 HU in the left atrium.

Image Interpretation

• Use axial slices of 3 to 5 mm for the aorta and pulmonary arteries.
• Thin sections (6 to 8 mm) are ideal for assessing coronary arteries.
• Key Findings:
• Stenosis: Indicates coronary artery disease.
• Aortic Dissection: Visualized with thrombus.
• Pulmonary Embolism: Confirmed through typical scan patterns.

Conclusion

Triple Rule Out CT Angiography is an effective triage method in emergency settings for patients with acute chest pain. Proper patient selection, preparation, and adherence to CT protocols are critical for accurate diagnosis. For more educational content, follow our channels on Instagram and YouTube!