Appropriate timing of nitroglycerin prior to intravascular ultrasound

Objectives: To determine the time to maximal coronary dilation following intracoronary (IC) nitroglycerin (NTG) and whether the decrease in aortic pressure (AoP) is a surrogate marker for coronary vasodilatation. Background: Intravascular ultrasound (IVUS) facilitates assessment of coronary plaque severity and morphology and aids in stent sizing. NTG is often administered prior to IVUS to prevent catheter-induced spasm and to facilitate standardized and accurate vessel size measurements. The impact of dose, timing, and route of delivering NTG on vessel size remains undefined. Methods: Twelve patients undergoing IVUS-guided stent placement were studied. An IVUS catheter was positioned proximal to the target lesion and the following measurements made at baseline and 30 second (sec) intervals for 180 sec following 200 mcg IC NTG: AoP, IVUS-derived lumen diameter (Ld), lumen cross-sectional area (La), external elastic membrane diameter (EEMd) and EEM area (EEMa). Lumen and EEM measurements were compared at different time intervals and the relationship between time to max Ld and nadir AoP was analyzed. Results: All patients had a vasodilatory response to IC NTG. Increase from baseline to max Ld following IC NTG was statistically significant (mean change 0.31 ± 0.18 mm, P=.0001). Mean time to max Ld following IC NTG was 117 sec (range, 60-180 sec). No correlation between time to max Ld and AoP nadir was observed (r = 0.19). Conclusions: Our study suggests that administration of 200 mcg IC NTG results in a significant change in lumen diameter and area with maximal vasodilation occurring on average approximately 2 minutes following IC NTG administration. There was no significant correlation between AoP change and maximal NTG-induced coronary vasodilation.