What is the correct way to write an order for CT coronary angiography with Fractional Flow Reserve (FFR) in an elderly patient with suspected coronary artery disease, impaired renal function, and a history of hypertension and hyperlipidemia?

How to Order CT Coronary Angiography with FFR

For an elderly patient with impaired renal function, order functional imaging (stress SPECT or PET) instead of CT coronary angiography, as CCTA is contraindicated or high-risk in this population due to nephrotoxicity concerns. 1, 2

Critical Renal Function Assessment

Before considering any contrast-based imaging, assess kidney function within 7 days of the planned procedure: 2

• GFR ≥60 mL/min: CCTA is safe with standard protocol (contrast-induced nephropathy risk <3%) 2
• GFR 30-60 mL/min: CCTA carries 10-20% nephropathy risk; implement full prophylactic measures or strongly consider alternative imaging 2
• GFR <30 mL/min: Do not order CCTA—this is a Class III recommendation (contraindicated) 1, 2

In your elderly patient with "impaired renal function," functional imaging is the guideline-recommended first-line test. 1, 3

Why Functional Imaging is Preferred in This Case

The 2024 ESC guidelines explicitly state that functional imaging (stress echo, SPECT, PET, or CMR) should be selected when: 1

• Patient has moderate-to-high pre-test likelihood of obstructive CAD 1
• CCTA limitations exist in certain groups: older patients with extensive coronary calcifications, renal insufficiency 1
• Information on myocardial ischemia is desired (which is more clinically relevant than anatomic stenosis alone) 3

Nuclear stress testing (SPECT or PET) is equally effective—and safer—for risk stratification in patients with impaired renal function compared to CCTA. 3

If CCTA is Still Considered (GFR 30-60 Range)

Only proceed if GFR is 30-60 mL/min AND full prophylactic protocol is implemented: 2

Proper Order Format

"CT coronary angiography with ECG gating using iso-osmolar contrast (iodixanol 320 mg iodine/mL)" 2, 4

Contrast Selection

• Use iso-osmolar contrast media (iodixanol) or low-osmolar agents (avoid ioxaglate and iohexol specifically) 1, 4
• Iodixanol is FDA-approved for coronary CTA at 320 mg iodine/mL concentration 4
• In patients with chronic kidney disease, iso-osmolar contrast is preferred over ionic low-osmolar agents 1

Nephropathy Prevention Protocol

• Ensure adequate hydration before and after contrast administration 1, 2, 5
• Consider N-acetylcysteine (offers potential benefit without known harm) 3
• Minimize total contrast dose 2

Regarding FFR from CT (FFRCT)

FFRCT is a post-processing computational analysis applied to standard CCTA images—it is not a separate order. 6, 7, 8, 9

• FFRCT is derived from the anatomic CCTA dataset using computational fluid dynamics 6, 8
• You order standard "CT coronary angiography with ECG gating" and then the images can be sent for FFRCT analysis if intermediate stenoses are found 7, 9
• FFRCT improves diagnostic accuracy by reducing false positives from anatomic assessment alone 6, 7
• However, FFRCT correlation with invasive FFR is imperfect (approximately 47-54% discordance rate in some studies) 7

Clinical Decision Algorithm

Step 1: Check GFR within 7 days 2

Step 2: Apply decision tree:

• GFR <30: Order stress SPECT or PET (not CCTA) 1, 2, 3
• GFR 30-60: Strongly prefer stress imaging; only proceed with CCTA if prophylaxis implemented and clinical benefit clearly outweighs risk 1, 2
• GFR ≥60: CCTA is appropriate if low-to-moderate pre-test probability 1, 2

Step 3: If CCTA is performed and shows intermediate stenosis (30-70%), images can be sent for FFRCT analysis to determine hemodynamic significance 6, 7, 9

Step 4: If FFRCT shows values <0.80, consider invasive coronary angiography with invasive FFR for definitive assessment before revascularization decisions 1

Common Pitfalls to Avoid

• Do not order CCTA in elderly patients with impaired renal function without first considering safer alternatives 1, 2, 3
• Do not assume FFRCT is a separate imaging test—it requires a diagnostic-quality CCTA first 6, 8
• Do not use high-osmolar or ionic low-osmolar contrast (ioxaglate, iohexol) in patients with renal impairment 1
• Do not proceed with contrast imaging without recent (within 7 days) renal function assessment 2
• Do not forget that age >70 years is an independent predictor of contrast-induced nephropathy 1, 5

When Invasive Angiography with FFR is Preferred

The 2024 ESC guidelines recommend invasive coronary angiography with FFR/iFR when: 1

• Very high pre-test likelihood of obstructive CAD 1
• Severe symptoms refractory to medical treatment 1
• High-risk clinical profile (severe LV dysfunction, ventricular arrhythmia, hypotension during exercise) 1
• Stenoses with diameter reduction <90% require FFR guidance for revascularization decisions 1

In symptomatic elderly patients with high-risk features, proceeding directly to invasive angiography with FFR may be more appropriate than non-invasive imaging. 1