Impact of sublingual nitroglycerin dosage on FFR assessment and coronary luminal volume-to-myocardial mass ratio.

Objectives: Fractional flow reserve computed tomography (FFR) depends upon nitroglycerin (NTG) inducing maximal hyperemia. However, the impact of NTG dosages on FFR analysis including coronary volume-to-mass ratio (V/M) is unknown.

Methods: Eighty patients with repeat coronary CT angiograms (CCTAs) with different sublingual spray NTG doses (0.4 mg and 0.8 mg) were retrospectively analyzed with 45 patients excluded. Patient and scan demographics, post-stenosis and nadir FFR values, coronary volume, and coronary volume-to-mass ratio (V/M) were compared at initial CCTA (0.4 mg NTG) and follow-up CCTA (0.8 mg NTG). Differences were compared by Wilcoxon signed-rank test.

Results: Thirty-five patients were included (time between CCTAs, 3.9 ± 1.6 years). Segment involvement score was 2.4 ± 3.3 and 2.8 ± 3.4 at initial and repeat CCTA (0.4 and 0.8 mg NTG), respectively (p = 0.004). There was similar image quality (4.1 ± 0.7 vs 4.1 ± 0.8; p = 0.51). Nadir FFR values did not differ in the left (0.4 mg, 0.80 ± 0.08 vs 0.8 mg, 0.80 ± 0.03; p = 0.66), right (0.4 mg, 0.90 ± 0.04 vs 0.8 mg, 0.90 ± 0.06; p = 0.25), or circumflex coronaries (0.4 mg, 0.87 ± 0.06 vs 0.8 mg, 0.88 ± 0.06; p = 0.34). Post-stenosis FFR values did not differ (p = 0.65). Coronary volume increased with 0.8 mg of NTG (2639 ± 753 mm vs 2844.8 ± 827 mm; p = 0.009) but V/M ratio did not (p = 0.20).

Conclusions: Use of 0.8 mg versus 0.4 mg of NTG in routine clinical CCTAs significantly increased coronary volume determined from FFR analysis but did not alter FFR or V/M. Further evaluation of repeat CCTAs in a more contemporaneous fashion using varied nitrate doses and disease severity is needed.

Key Points: • Fractional flow reserve from computed tomography (FFR) is a noninvasive method for evaluating the coronary arteries and relies on nitroglycerin (NTG) to induce coronary vasodilation, but the impact of different NTG dosages is unknown. • Retrospective analysis evaluated use of different NTG doses on FFR. • Increased NTG dose increased coronary luminal volume on FFRanalysis, but did not change FFRvalues.